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Description  |
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BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to a photosensitive material for use in
electrophotography, in particular a photosensitive material comprising a
photoconductive layer on which there is a protective layer consisting
essentially of a substance resulting from partial hydrolysis of a
composition (mixture) of (a) a silane coupling agent, (b) an acryl resin
having a silane radical copolymerized with styrene, acrylic acid, maleic
acid, etc., and (c) a diorganopolysiloxane with terminal hydroxyl radicals
at both ends of the molecular chain.
(b) Description of the Prior Art
Electrophotographic photosensitive materials comprising a conductive
substrate on which there is a photoconductive layer of an inorganic or
organic semi-conductor are well known. And, the so-called Carlson process
is employed therein for the purpose of forming an electrostatic latent
image thereon, said process comprising electrifying the surface of the
photoconductive layer and then subjecting the thus electrified material to
an imagewise exposure. However, these photosensitive materials have been
defective in that the photoconductive layer, being exposed, is
deteriorated in mechanical strength and consequently is very often
destroyed by repeated use.
For this reason, various photosensitive materials have been proposed to
improve the durability of conventional materials by further providing a
transparent protective layer on the photoconductive layer. And the
materials used for the formation of said protective layer such as
polyethylene, poly-n-butylmethacrylate, polyamide, polyester,
polyurethane, polycarbonate, polyvinyl formal, polyvinyl acetal, polyvinyl
butyral, ethyl cellulose, cellulose acetate, polyethylene terephthalate,
polyethylene terephthalate-polyethylene isophthalate copolymer, etc. are
well known. These materials surely have some merit in protecting the
photoconductive layer, but are defective in that they are not always
sufficient in their durability and are liable to hamper the formation of
stable images under the influence of humidity and changes in humidity.
In addition, Japanese Laid-open Patent Applications No. 96229/1975 and No.
23636/1978 disclose photosensitive materials wherein a certain kind of
silicon compound has been incorporated in the protective layer in a fixed
quantity to improve its durability. These photosensitive materials are
surely superior in the properties such as hardness, abrasion resistance,
etc., but are somewhat inferior in their adhesive property. The fact is
that in particular when the photoconductive layer comprises a metal such
as Se, Se-Te or the like or a metal sulfide such as CdS, the adhesion
between the protective layer and the photoconductive layer is liable to
become so insufficient that a photosensitive material of a desired degree
of durability is not obtainable.
SUMMARY OF THE INVENTION
One object of the present invention is to overcome the foregoing defects
and to provide an electrophotographic photosensitive material having a
protective layer on its surface which is superior especially in durability
and moisture resistance and so capable of constantly forming stable
images.
Another object of the present invention is to provide an
electrophotographic photosensitive material which may be manufactured
without resort to complicated processes and operated in a known manner.
The present inventors have discovered that a substance resulting from
partial hydrolysis of a mixture of some specific substances can be applied
with extreme effectiveness for the purpose of forming a transparent
protective layer of the photosensitive material. The present invention has
been completed on the basis of this discovery.
In other words, the photosensitive material according to the present
invention is characterized by comprising a photoconductive layer on which
there is a transparent protective layer consisting essentially of a
substance resulting from partial hydrolysis of a mixture of (a) a compound
having the following general formula I, (b) a copolymer of a compound
having the following general formula II with a compound having the general
formula III or maleic anhydride and (c) a compound having the following
general formula IV,
(1) General formula I
(R.sup.1).sub.l Si(OR.sup.2).sub.m
[wherein R.sup.1 is a C.sub.1-4 alkyl radical, vinyl radical,
.gamma.-methacryloxypropyl radical, phenyl radical,
.gamma.-glycidoxypropyl radical, .gamma.-chloropropyl radical,
.gamma.-mercaptopropyl radical,
.gamma.-.beta.(aminoethyl).gamma.-aminopropyl radical or
.gamma.-aminopropyl radical; R.sup.2 is a hydroxyethylalkyl ether radical
or C.sub.1-4 alkyl radical; l is 0-2; and m is 2-4.]
(2) General formula II
##STR5##
[wherein R.sup.3 is hydrogen or a methyl radical; R.sup.4 is hydrogen or a
C.sub.1-4 alkyl radical; n is 1-4; and q is 1-3.]
(3) General formula III
##STR6##
[wherein R.sup.5 is hydrogen or a methyl radical; R.sup.6 is --COOR.sup.7
(R.sup.7 is hydrogen or a C.sub.1-12 alkyl radical, hydroxyalkyl radical,
glycidyl radical or dimethylaminoalkyl radical), --CN, --OCOCH.sub.3,
--CONH.sub.2,
##STR7##
(4) General formula IV
##STR8##
[wherein R.sup.8 is a C.sub.1-4 alkyl radical or phenyl radical; z is
2-25.]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The protective layer of the photosensitive material according to the
present invention, as described above, incorporates therein a substance
resulting from partial hydrolysis of a mixture of (a) a silane coupling
agent having the general formula I, (b) a copolymer of a compound having
the general formula II with a compound having the general formula III or
maleic anhydride, for instance, such as an acryl resin having a silane
radical copolymerized with styrene, acrylic acid, maleic acid, etc., and
(c) a diorganopolysiloxane with terminal hydroxyl radicals at both ends of
the molecular chain having the general formula IV.
In this instance, the compound having the general formula I (Component A)
includes, for instance, methyltrimethoxy silane, vinyltriethoxy silane,
dimethyldimethoxy silane, diphenyldimethoxy silane, phenylmethyldiethoxy
silane, phenyltrimethoxy silane, vinyltris (.beta.-methoxyethoxy) silane,
.gamma.-glycidoxypropyltrimethoxy silane,
.gamma.-methacryloxypropyltrimethoxy silane, N-.beta.(aminoethyl)
.gamma.-aminopropyltrimethoxy silane,
N-.beta.(aminoethyl).gamma.-aminopropylmethyldimethoxy silane,
.gamma.-chloropropyltrimethoxy silane, .gamma.-aminopropyltriethoxy
silane, .gamma.-mercaptopropyltrimethoxy silane, tetraethoxy silane,
tetrabutoxy silane, etc. In particular, methyltrimethoxy silane,
vinyltriethoxy silane, .gamma.-methacryloxypropyltrimethoxy silane,
tetraethoxy silane, vinyltrihydroxyethylmethylether silane are used
effectively. And these compounds may be used singly or in a suitable
combination of two kinds or more of them.
The copolymer of a compound having the general formula II with a compound
having the general formula III (inclusive of maleic anhydride) (Component
B) includes, for instance, copolymers of styrene, maleic anhydride,
acrylate such as methyl methacrylate, butylmethacrylate, ethylacrylate or
butylacrylate, acryl amide, glycidyl methacrylate,
hydroxyethylmethacrylate, acrylonitrile, isoprene, vinyl acetate, vinyl
pyrrolidone, vinyl pyridine, vinyl carbazole, etc. with
.gamma.-methacryloxypropyltrimethoxy silane. In particular, the copolymer
of methyl methacrylate, acrylate such as methyl acrylate or butyl
acrylate, glycidyl methacrylate or acrylic acid with
.gamma.-methacryloxpropyltrimethoxy silane and the copolymer of styrene or
maleic anhydride with .gamma.-methacryloxypropyltrimethoxy silane can be
used with effective results.
These copolymers may be used in a suitable combination of two kinds or more
of them, wherein the copolymerization ratio, inclusive of the monomer
specified in the general formula II, is not limited.
And, the compound having the general formula IV (Component C) includes, for
instance, a dimethylpolysiloxane with terminal hydroxyl radicals at both
ends of the molecular chain, a methylphenylpolysiloxane with terminal
hydroxyl radicals at both ends of the molecular chain, etc. The
polymerization degree z of these substances suitably should be in the
range of from 2 to 25, preferably 2 to 10 (integer), and they may be used
singly or in a suitable combination of two kinds or more of them.
In the present invention, as aforesaid, a substance is utilized for the
transparent protective layer which is obtained from partial hydrolysis of
the mixture of substances of three kinds (Component A: Component B:
Component C=70-98.9:1-20:0.1-10, % by weight). In this instance, if these
three kinds of components are utilized separately, it will result in a
number of drawbacks, whereby the objects of the present invention shall
never be achieved.
In more detail, for instance, a substance resulting from partial hydrolysis
of the silane coupling agent alone is superior in hardness and abrasion
resistance, but is so inferior in adhesive property that especially when
the photoconductive layer comprises Se, Se-Te, CdS or the like, it
scarcely adheres and consequently peels off. Additionally, since this
substance is devoid of a film property when the electrophotographic
photosensitive material uses it there occurs cracking so that the
durability is deteriorated even after production of several hundreds of
copies. Furthermore, the electrophotographic photosensitive material using
the acryl resin having a silane radical and its copolymer alone is liable
to cracks and is inferior in durability because the aforegoing substances
are extremely superior in adhesive property but inferior in hardness.
Still further, the single use of the diorganopolysiloxane with terminal
hydroxyl radicals at both ends of the molecular chain is impossible
because it possesses no film property.
The practical preparation of the photosensitive material according to the
present invention is completed by providing a photoconductive layer onto a
conductive substrate and applying a protective layer-forming solution
thereon and drying.
As the conductive substrate there can be used a metal plate or cylinder of
aluminum, copper, stainless steel or the like, a paper, plastic film,
glass plate, cloth or the like subjected to electroconductive treatment
such as metal evaporation or the like.
Further, as the photoconductor for use in the photoconductive layer there
can be enumerated inorganic semi-conductors such as selenium, zinc oxide,
titanium oxide, cadmium sulfide, etc., and film-forming organic
semi-conductors such as poly-N-vinyl carbazole,
poly-N-vinyl-3,6-dibromocarbazole, pyrene-formaldehyde resin,
polyvinyldibenzothiophene, polyvinylanthracene, etc. In the use of said
inorganic semi-conductors it is to be noted that therein are included
those such as Se which can be used solely as well as such as CdS and ZnO
which are to be used together with a resin binder. As such resins are
applicable, for instance, acryl resin, silicone resin, alkyd resin, epoxy
resin, styrene-butadiene resin and melamine resin.
Still further, sensitizers may be incorporated in the photosensitive layer.
For instance, when the photosensitive layer is made of ZnO there may be
added Rose bengal, fluorescein and so forth, when it is made of an organic
semi-conductor there may added coloring matters such as methylene blue,
benzopyrylium and so forth or electron acceptor such as
2,4,-7-trinitrofluorenone or the like and when the photosensitive layer is
made of Se it may be doped with Te.
Onto this photoconductive layer is formed the transparent protective layer
comprising the substance resulting from partial hydrolysis of the mixture
(composition) of three kinds of components as aforesaid. At this time,
hydrochloric acid, sulfuric acid, acetic acid, etc. may be added in order
to accelerate said hydrolysis reaction. This reaction product is also
preferred to be used dissolved in a solvent such as alcohol, toluene or
the like, and further a catalyst may be added thereto in order to
accelerate the hardness. The catalysts suitably used for that purpose
include alkali metal salts of inorganic acid or organic acid, for
instance, such as sodium nitrite, sodium sulfate, sodium acetate,
manganese naphthenate, cobalt naphthenate, etc.
The layer-forming operation using this composition can be achieved by spray
coating, roll coating, immersion coating, wire bar coating and the like.
This coating can be cured at a temperature ranging from room temperature
to 50.degree. C. within 1 hour with no necessity of drying at a
temperature more than 100.degree. C. for curing as in other silane
coupling agents. This feature is extremely serviceable for the purpose of
preventing the crystallization required in the cases of non-crystalline
selenium and the like.
In order to improve the sensitivity of the photosensitive material,
furthermore, this protective layer may be admixed, in suitable quantities,
with spectrum sensitizers, for instance, such as Rhodamine B, Rhodamine B
Extra, Rhodamine 6G, Crystal Violet, Methylene Blue, Fuchsine, Brilliant
Green, Victoria blue, Eosine S, Erythrosine, Rose bengale, fluorescein,
pinocyanol, etc., chemical sensitizers, for instance, such as
anthraquinone, 1-nitroanthraquinone, tetracyanoethylene,
tetracyanoquinodimethane, phthalic anhydride, maleic anhydride, picric
acid, Lewis acid, etc.
The aforesaid protective layer may be formed, directly or through a layer
of adhesives, for instance, such as G-103 (produced by Konishi K. K.), on
the photoconductive layer, or may be formed, in admixture with adhesives,
thereon so as to have a thickness of 0.1-20 .mu.m. When the thickness of
the protective layer is less than 0.1 .mu.m, it is inferior in durability,
and contrarily when said thickness is more than 20 .mu.m, it is
excessively electrified to thereby cause stains throughout the image area.
Therefore, it may be undesirable that the thickness of the protective
layer deviates from aforesaid range.
As the electrophotographic processes applicable to the thus prepared
photosensitive material there can be enumerated, in addition to Carlson
method, polarity inversion method comprising the processes of
electrification simultaneous with overall exposure--inverse polarity
electrification--imagewise exposure--development (which see Japanese
published examined patent application No. 2965/1973), KIP method
comprising the processes of electrification--imagewise exposure
simultaneous with inverse polarity electrification or imagewise exposure
simultaneous with AC electrification--overall exposure--development (which
see Japanese published examined patent application No. 2627/1968), NP
method comprising the processes of electrification--AC corona discharge
simultaneous with imagewise exposure--overall exposure--development (which
see English Pat. No. 1165405) and so forth. However, when the
photosensitive material of the present invention is applied to these
electrophotographic processes except the Carlson method, it is preferable
that the protective layer should have a thickness of from 5 to 20 .mu.m
because the transparent protective layer desirably should be electrified
as much as possible.
The transparent protective layer of the photosensitive material according
to the present invention is thus superior especially in durability and so
is not attacked by solvents such as acetone and kerosine, thereby being
capable of producing copies of the stable image independently of changes
in humidity and temperature. As a matter of course, there is no fear of
the electrophotographic characteristics of the photoconductive layer being
deteriorated by the provision of the protective layer.
Some synthesis examples of Component B (copolymer of a compound having the
general formula II with a compound having the general formula III
(inclusive of maleic anhydride)) will be given below. The term "part" used
herein is by weight.
SYNTHESIS EXAMPLE 1
Two parts of benzoyl peroxide was dissolved in a mixture of 200 parts of
methyl methacrylate, 50 parts of butyl acrylate, 45 parts of glycidyl
methacrylate, 5 parts of acrylic acid and 200 parts of
.gamma.-methacryloxypropyltrimethoxy silane. The same was added to 1500
parts of toluene heated to a temperature of 80.degree. to 85.degree. C.
with stirring for two hours. The viscosity was raised gradually, showing
the progress of the reaction. This reaction was completed by effecting
additional five hours' stirring at the same temperature.
SYNTHESIS EXAMPLE 2
Two parts of benzoyl peroxide was dissolved in a mixture of 300 parts of
styrene, 150 parts of maleic anhydride and 50 parts of
.gamma.-methacryloxypropyltrimethoxy silane. The same was added to 1500
parts of toluene heated to a temperature of 80.degree. to 85.degree. C.
with stirring for three hours. This reaction was completed by effecting
additional five hours' stirring at the same temperature. The resulting
white deposit was taken out by filtration and dried.
SYNTHESIS EXAMPLE 3
Three parts of benzoyl peroxide was dissolved in a mixture of 250 parts of
vinyl acetate, 150 parts of butyl acrylate and 100 parts of
.gamma.-methacryloxypropyltrimethoxy silane. The same was added to a
mixture of 1000 parts of toluene and 500 parts of isopropyl alcohol heated
to about 80.degree. C. with stirring for three hours. This reaction was
completed by effecting additional eight hours' stirring at the same
temperature.
EXAMPLES
The term "part" described hereinafter is by weight.
EXAMPLE 1
Hydrolysis was effected by adding 250 parts of 1% sulfuric acid to a
mixture of 2500 parts of methyltrimethoxy silane, 250 parts of ethyl
silicate, 750 parts of the copolymer of Synthetic Example 1 (toluene
solution, solid content: 25%) and 50 parts of the dimethylpolysiloxane
with terminal hydroxyl radicals at both ends of the molecular chain (a
mixture wherein z is 2-5). The resulting coating liquid, after eight
hours' ageing, was applied, by dipping method, onto a photoconductive
layer formed by evaporation-depositing selenium on an aluminum substrate
to a thickness of about 50 .mu.m, and the same was dried at 50.degree. C.
for one hour to thereby form a transparent protective layer having a
thickness of 1.5 .mu.m. The surface of this protective layer was
recognized to be glossy and exceedingly superior in smoothness.
The cycle of electrification-exposure-development-transfer was repeated
with the thus obtained photosensitive material by means of a conventional
image transfer type copying machine, whereby there were obtained copies of
clear-cut images likewise in both cases of 20.degree. C., 20% RH and
30.degree. C., 90% RH. And, even after repeated reproduction of 50,000
copies there were observed no changes in the clearness of image, and
scarcely occurred wear of the protective layer.
COMPARATIVE EXAMPLE 1
Hydrolysis was effected by adding 250 parts of 1% sulfuric acid to a
mixture of 2500 parts of methyltrimethoxy silane and 250 parts of ethyl
silicate. The resulting coating liquid, after eight hours' ageing, was
applied onto the same photoconductive layer as in Example 1, and the same
was dried at 50.degree. C. for one hour to thereby form a protective layer
having a thickness of about 1.5 .mu.m. The surface of this protective
layer was lusterless, and several cracks were observed thereon.
The cycle of electrification-exposure-development-transfer was repeated
with the thus obtained photosensitive material by means of a conventional
image transfer type copying machine. As a result, exfoliation of the
protective layer began to occur on obtaining the 500th copy, and 90% or
more of the protective layer exfoliated on obtaining the 800th copy.
COMPARATIVE EXAMPLE 2
Hydrolysis was effected by adding 300 parts of 1% sulfuric acid to a
mixture of 2000 parts of methyltrimethoxy silane, 500 parts of
.gamma.-glycidoxypropyltrimethoxy silane, and 250 parts of ethyl silicate.
The resulting coating liquid, after eight hours' ageing, was applied onto
the same photoconductive layer as in Example 1, and the same was dried at
40.degree. C. for three hours to thereby form a protective layer having a
thickness of about 20 .mu.m. The surface of this protective layer was
lusterless, and numeral air bubbles were observed therein.
The thus obtained photosensitive material was subjected to the same test
procedure as in Example 1, whereby exfoliation of the protective layer
began to occur on obtaining the 1200th copy, and 90% or more of the
protective layer exfoliated on obtaining the 2300th copy.
EXAMPLE 2
Hydrolysis was effected by adding 300 parts of 1% sulfuric acid to a
mixture having the following composition.
______________________________________
methyltrimethoxy silane 1700 parts
vinyltriethoxy silane 800 parts
ethyl silicate 250 parts
copolymer of Synthetic Example-2
210 parts
methylethyl ketone 500 parts
dimethylpolysiloxane with terminal
hydroxyl radicals at both ends of the
molecular chain 20 parts
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After eight hours' ageing of the resulting coating liquid, 500 parts of
polyurethane resin (TAKENATE M-402, manufactured by Takeda Yakuhin Kogyo
K. K.) and 10 parts of Rhodamine B were dissolved therein. Then, it was
applied onto the same photoconductive layer as in Example 1 by means of
dipping method, and was dried at 40.degree. C. for three hours to thereby
form a protective layer having a thickness of about 2 .mu.m. The surface
of this protective layer was recognized to be glossy and exceeding
superior in smoothness.
The thus obtained photosensitive layer was subjected to the same test
procedure as in Example 1, whereby there were obtained copies of clear-cut
image even after repeated reproduction of 60000 copies and there scarcely
occurred wear of the protective layer.
EXAMPLE 3
A coating liquid was prepared by dissolving 200 parts of nitrile rubber
(Bond G-103, manufactured by Konishi K. K.) in 4000 parts of methylethyl
ketone. This coating liquid was applied onto the same photoconductive
layer as in Example 1 by means of dipping method, and was dried at room
temperature to thereby form an about 0.3 .mu.m-thick film so as to be used
as an adhesive layer.
On the other hand, hydrolysis was effected by adding 250 parts of 2%
sulfuric acid to a mixture of 2000 parts of methyltrimethoxy silane, 500
parts of phenyltriethoxy silane, 300 parts of ethyl silicate, 50 parts of
dimethylpolysiloxane with terminal hydroxyl radicals at both ends of the
molecular chain (a mixture wherein z=2-10) and 500 parts of the copolymer
of Synthetic Example 3, and the same was subjected to eight hours' ageing
to form a protective layer-forming liquid.
Subsequently, this protective layer-forming liquid was applied onto said
adhesive layer by means of dipping method, and dried at 40.degree. C. for
three hours to thereby form an about 2 .mu.m-thick protective layer. The
surface of this protective layer was recognized to be glossy and
exceedingly superior in smoothness.
The thus obtained photosensitive material was subjected to the same test
procedure as in Example 1, whereby there were obtained copies of clear-cut
image even after repeated reproduction of 80,000 copies and there scarcely
occurred wear of the protective layer.
EXAMPLE 4
A photosensitive material was prepared by applying a solution having the
following composition onto an aluminum foil-laminated polyester film, and
drying.
______________________________________
poly-N-vinylcarbazole 5 parts
2,4,7-trinitrofluorenone
7 parts
polycarbonate 1 part
epoxy resin 2 parts
tetrahydrofuran 120 parts
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On the other hand, hydrolysis was effected by adding 5 parts of 1% sulfuric
acid to a mixture of 41 parts of methyltrimethoxy silane, 22 parts of
.gamma.-.beta.(aminoethyl).gamma.-aminopropyltrimethoxy silane, 5 parts of
ethyl silicate, 1 part of dimethylpolysiloxane with terminal hydroxyl
radicals at both ends of the molecular chain (a mixture wherein z is
2-10), 10 parts of the copolymer of Synthetic Example 1 and 50 parts of
isopropyl alcohol, and the same was subjected to eight hours' ageing to
form a protective layer-forming liquid.
Subsequently, the protective layer-forming liquid was applied onto said
photosensitive material by means of spray method, and dried at 50.degree.
C. for three hours to thereby form a protective layer having a thickness
of about 1.5 .mu.m.
The sensitivity of the thus obtained photosensitive material according to
the present invention was 4.5 lux.multidot.sec. Even after repeated
reproduction of 45,000 copies there occurred neither deterioration in
sensitivity nor disorder in image. In contrast, in the photosensitive
material lacking a protective layer there occurred stains and disorder in
image on the 3000th copy.
TABLE 1
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Adhesive*.sup.1
Lead pencil hardness*.sup.2
property (Scratch resistance)
______________________________________
Example 1 0 5H
Example 2 .DELTA. 5H
Example 3 .DELTA. 5H
Example 4 0 4H
Comparative
Example 1 x 3H
Comparative
Example 2 x 4H
Polyester*.sup.3
.DELTA. B
Nitro
cellulose*.sup.4
0 HB
Poly-
urethane*.sup.5
0 B
Acryl
resin*.sup.6 0 B
Poly-
carbonate*.sup.7
0 HB
______________________________________
*.sup.1 This property was decided according to the degree of exfoliation
of a coated film occurring when rapidly peeling a Scotch tape adhered to
the coated film in the direction of 180.degree.: 0 no exfoliation of
coated film, .DELTA. partial exfoliation of coated film and x complete
exfoliation of coated film.
*.sup.2 This property was decided according to JIS K5400 "Lead Pencil
Scratch Test" and under the load of 150 g.
*.sup.3 is VYLON200 (manufactured by TOYOBOSEKI K.K.),
*.sup.4 is JADLAC MT (manufactured by JARD K.K.),
*.sup.5 is Paraplene Pellet 27SM (manufactured by Nihon Polyurethane
Company),
*.sup.6 is DIANAL BR88 (manufactured by MITSUBISHI RAYON K.K.) and
*.sup.7 is PANLITE (manufactured by TEIJIN K.K.). These resins are all
available commercially.
* * * * *
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