Electrophotographic plate having a charge generating layer containing an organic pigment for charge generation

Abstract

An electrophotographic plate comprising an electroconductive layer, a charge generating layer and a charge transport layer and containing a silane coupling agent at least in the charge generating layer or in the charge transport layer, or at the interface of the charge generating layer and the charge transport layer shows small dark decay, little light fatigue and high sensitivity.

Description

This invention relates to an electrophotographic plate having a charge generating layer and a charge transport layer with small dark decay and little light fatigue.

Heretofore, as electrophotographic materials applying photoconductive substances as light sensitive materials, there have mainly been used inorganic photoconductive substances such as selenium, zinc oxide, titanium oxide, cadmium sulfide, etc. But most of these substances are generally highly toxic and there is a problem in dumping them.

On the other hand, organic photoconductive compounds have recently widely been studied, since they generally have weak toxicity compared with the inorganic photoconductive substances and are advantageous in transparency, flexibility, light-weight, surface smoothness, price, etc. Under such circumstances, complex type electrophotographic plates, which separate functions of charge generation and charge transport, have recently developed rapidly, since they can greatly improve sensitivity which has been a great defect of electrophotographic plates using organic photoconductive compounds.

But when these complex type electrophotographic plates are used, for example, in an electrophotographic copying devices according to the Carlson process, the initial potential is lowered by repeated use and the dark decay increases, which results in causing blushing in copied images obtained and often remarkably damaging contrast of the images. Further, when these complex type electrophotographic plates are used in an electrophotographic copying device wherein a plurality of copied images are obtained by repeating development and transfer without damaging an electrostatic latent image formed by one exposure to light, the copied image density is gradually lowered due to large dark decay.

As mentioned above, alghough the complex type electrophotographic plates have high sensitivity, they also have defects in that the dark decay is large and there appears a phenomenon of light fatigue wherein the initial potential is lowered and at the same time the dark decay increases when exposed to light for a long period of time. Particularly when the charge generating layer is thick, a lowering of properties due to light fatigue is remarkable.

An object of this invention is to solve the problems mentioned heretofore and to provide a complex type electrophotographic plate characterized in that

(1) the dark decay is small,

(2) lowering of the charge potential is small and the dark decay is not increased even if repeating charge/exposure (that is, light fatigue is little), and

(3) high sensitivity is shown.

In accordance with this invention, there is provided an electrophotographic plate comprising an electroconductive layer, a charge generating layer containing one or more organic pigments for charge generation and a charge transport layer having functions of charge maintenance and charge transport, characterized in that a silane coupling agent is present at least in the charge generating layer or in the charge transport layer, or at the interface of these two layers.

Materials used in the electrophotographic plate of this invention are explained below.

As the silane coupling agent which is present at least in the charge generating layer or in the charge transport layer, or at the interface of these layers, there can be used vinylsilanes such as vinyltrichlorosilane, vinyltriethoxysilane, vinyltris(.beta.-methoxyethoxy)silane, .gamma.-methacryloxypropyltrimethoxysilane, etc., epoxysilanes such as .gamma.-glycidoxypropyltrimethoxysilane, etc., aminosilanes such as N-.beta.-(aminoethyl)-.gamma.-aminopropyltrimethoxysilane, .gamma.-aminopropyltriethoxysilane, N-.beta.-(aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane, N-.beta.-(N-vinylbenzylaminoethyl)-.gamma.-aminopropyltrimethoxysilane, etc., and their hydrochlorides, mercaptosilanes such as .gamma.-mercaptopropyltrimethoxysilane, etc., alone or as a mixture thereof. Among them, the aminosilanes are particularly effective for improving the dark decay and the light fatigue.

When the silane coupling agent is included in the charge generating layer (CGL), it is included preferably in an amount of 0.5 to 40% by weight, more preferably 1 to 20% by weight, based on the weight of the charge generating layer. When the amount is less than 0.5% by weight, there is a tendency to exhibit less effects for reducing the dark decay and lessening the light fatigue, while if the amount is more than 40% by weight, although there show good effects on improving the initial potential, dark decay and light fatigue, there is a tendency to lower the sensitivity.

When the silane coupling agent is included in the charge transport layer (CTL), it is included preferably in an amount of 0.05 to 30% by weight, more preferably 0.1 to 10% by weight, based on the weight of the charge transport layer. When the amount is less than 0.05% by weight, there shows less effect for reducing the dark decay and lessening the light fatigue, while if the amount is more than 30% by weight, although there show good effects on improving the initial potential, dark decay and light fatigue, there is a tendency to lower the sensitivity and to increase residual potential.

When the silane coupling agent is present at the interface of the charge generating layer and the charge transport layer, it is used in terms of an amount in a unit area of preferably 10.sup.-4 mg/cm.sup.2 to 10.sup.2 mg/cm.sup.2, more preferably 10.sup.-3 mg/cm.sup.2 to 10 mg/cm.sup.2. When the amount is less than 10.sup.-4 mg/cm.sup.2, there is less effect for improving the light fatigue and the dark decay, while if the amount is more than 10.sup.2 mg/cm.sup.2, there is a tendency to lower the sensitivity and to increase the residual potential.

The silane coupling agent can be present both in the CGL and CTL, in the CGL or CTL and at the interface of CGL and CTL, or both in the CGL and CTL and at the interface of CGL and CTL at the same time.

As the organic pigment which is included in the charge generating layer for charge generation, there can be used azoxybenzenes, disazos, trisazos, benzimidazoles, multi-ring quinones, indigoids, quinacridones, metallic or non-metallic phthalocyanines having various crystal structures, perylenes, methines, etc., these pigments being known for charge generation. These pigments can be used alone or as a mixture thereof. These pigments are, for example, disclosed in British Pat. Nos. 1,370,197, 1,337,222, 1,337,224 and 1,402,967, U.S. Pat. Nos. 3,887,366, 3,898,084, 3,824,099 and 4,028,102, Canadian Pat. No. 1,007,095, German Offenlegungsschrift No. 2,260,540, etc. It is also possible to use all organic pigments which can generate charge carriers by illumination with light other than those mentioned above.

A part of typical examples of the organic pigments are illustrated below, but needless to say, the organic pigments are not limited thereto.

Examples of the phthalocyanine series pigments are copper phthalocyanine, metal free phthalocyanine, magnesium phthalocyanine, aluminum phthalocyanine, copper chromium phthalocyanine, copper-sulfated phthalocyanine, etc. As to their crystal forms, .alpha.-form, .beta.-form, .gamma.-form, .epsilon.-form, .chi.-form, etc., may be used.

Examples of the disazo series pigments are as follows: ##STR1##

As the charge transport material which is a major component included in the charge transport layer, there can be used high molecular weight compounds such as poly-N-vinylcarbazole, halogenated poly-N-vinylcarbazole, polyvinylpyrene, polyvinylindoloquinoxaline, polyvinylbenzothiophene, polyvinylanthracene, polyvinylacridine, polyvinylpyrazoline, etc., low molecular weight compounds such as fluorene, fluorenone, 2,7-dinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenone, 4H-indeno-(1,2,6)thiophene-4-one, 3,7-dinitro-dibenzothiophene-5-oxide, 1-bromopyrene, 2-phenylpyrene, carbazole, 3-phenylcarbazole, 2-phenylindole, 2-phenylnaphthalene, oxadiazole, triazole, 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 2-phenyl-4-(p-diethylaminophenyl)-5-phenyloxazole, triphenylamine, imidazole, chrysene, tetraphene, acridine, and their derivatives.

In order to further improve the dark decay and light fatigue, the charge generating layer may further containing a cyanine dye base of the formula: ##STR2## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently a hydrogen atom, a halogen atom, an alkyl group preferably having 1 to 4 carbon atoms, an aralkyl group preferably having 1 to 4 carbon atoms at the portion except for the aryl group such as a phenyl group, an acyl group, a hydroxyl group, a phenyl group or a substituted phenyl group, and/or a styryl dye base of the formula: ##STR3## wherein R.sub.7, R.sub.8, R.sub.9 and R.sub.10 are independently a hydrogen atom, a halogen atom, an alkyl group preferably having 1 to 4 carbon atoms, an aralkyl group preferably having 1 to 4 carbon atoms at the portion except for the aryl group such as a phenyl group, an acyl group, a hydroxyl group, a phenyl group or a substituted phenyl group; and R.sub.11 and R.sub.12 are independently a hydrogen atom or an alkyl group preferably having 1 to 4 carbon atoms.

Examples of the cyanine dye base of the formula (1) are ##STR4## and the like.

Examples of the styryl dye base of the formula (II) are: ##STR5## and the like.

The cyanine dye base of the formula (I) and/or the styryl dye base of the formula (II) are used in an amount of 40% by weight or less, if no silane coupling agent is added. When the cyanine dye base of the formula (I) and/or the styryl dye base of the formula (II) are used together with the silane coupling agent in the charge generating layer, these dye bases and the silane couplng agent are used in an amount of 40% by weight or less as a total. If the total amount is more than 40% by weight, the sensitivity of the electrophotographic plate is lowered. The charge generating layer may contain one or more conventional binders, plasticizers, additives other than the above-mentioned organic pigment and if necessary, the silane coupling agent, the cyanine dye base and/or the styryl dye base. The binder is used in an amount of 300% by weight or less based on the weight of the organic pigment. If the amount is more than 300% by weight, electrophotographic properties are lowered. The plasticizer is preferably used in an amount of 5% by weight or less based on the weight of the organic pigment. Other additives may be used in an amount of 3% by weight or less based on the organic pigment.

The charge transport layer may contain other than the above-mentioned charge transport material the above-mentioned cyanine dye base of the formula (I) and/or styryl dye base of the formula (II) in order to improve the dark decay and light fatigue. The cyanine dye base of the formula (I) and/or the styryl dye base of the formula (II) are used in an amount of 30% by weight or less, if no silane coupling agent is added. When the cyanine dye base and/or the styryl dye base are used together with the silane coupling agent in the charge transport layer, these dye bases and the silane coupling agent are used in an amount of 30% by weight or less as a total. If the total amount is more than 30% by weight, electrophotographic properties are lowered. The charge transport layer may contain one or more conventional binders, plasticizers, additives other than the charge transport material, and if necessary, the silane coupling agent, the cyanine dye base and/or the styryl dye base. When the high molecular compound is used as the charge transport material, the use of binder is not necessary, but the binder may be used in an amount of 300% by weight or less based on the weight of the high molecular compound. If the amount is more than 300% by weight, electrophotographic properties are lowered. When the low molecular weight compound is used as the charge transport material, the binder is used in an amount of 30 to 300% by weight based on the weight of the low molecular weight compound. If the amount is less than 30% by weight, the formation of the charge transport layer becomes difficult, while if the amount is more than 300% by weight, electrophotographic properties are lowered. The plasticizer and other additives may optionally be used in an amount of 5% by weight or less based on the weight of the charge transport material.

As the electroconductive layer, there can be used paper or plastic film treated for electroconductivity, metal (e.g. aluminum) foil-clad plastic film, and the like. The electroconductive material can take any shapes such as sheet, plate, etc. When a metal is used, a drum-like shape may be employed.

An electrophotographic plate produced by forming a charge generating layer on an electroconductive layer and forming a charge transport layer on the charge generating layer in this invention is preferable from the viewpoint of electrophotographic properties, but the charge generating layer may be formed on the charge transport layer which has been formed on the electroconductive layer. The thickness of the charge generating layer is preferably 0.01 to 10 .mu.m, more preferably 0.2 to 5 .mu.m. If the thickness is less than 0.01 .mu.m, there is a tendency to make the formation of uniform charge generating layer difficult, while if the thickness is more than 10 .mu.m, there is a tendency to lower electrophotographic properties. The thickness of the charge transport layer is preferably 5 to 50 .mu.m, more preferably 8 to 20 .mu.m. If the thickness is less than 5 .mu.m, the initial potential is lowered, while if the thickness is more than 50 .mu.m, there is a tendency to lower the sensitivity.

The charge generating layer can be formed by a conventional process, for example, by vapor deposition of the components of the charge generating layer, or by coating a uniform solution or dispersion of the components of the charge generating layer, followed by drying. In the latter case, there can be used as solvent ketones such as acetone, methyl ethyl ketone, etc., ethers such as tetrahydrofuran, dioxane, etc., aromatic solvents such as toluene, xylenes, etc.

The charge transport layer can be formed by a conventional process, for example, by coating a solution or dispersion obtained by dissolving the components of the charge transport layer in a solvent such as those mentioned above, followed by drying.

In any cases wherein the charge generating layer and the charge transport layer are formed on the electroconductive layer in this order or in reverse order, it is necessary to make the silane coupling agent present at least in the charge generating layer or in the charge transport layer or at the interface of these layers.

The silane coupling agent can be included in at least in the charge generating layer or in the charge transport layer by employing the methods mentioned above. When the silane coupling agent is made present at the interface of the charge generating layer and the charge transport layer, there may be used the following methods. First, the charge generating layer (or the charge transport layer) is formed on the electroconductive layer, then on the surface of the charge generating layer (or the charge transport layer) formed,

(1) a liquid silane coupling agent is coated, or

(2) a solution obtained by diluting the silane coupling agent with an organic solvent such as acetone, methyl ethyl ketone, ethyl ether, tetrahydrofuran, dioxane, chloroform, dichloromethane, carbon tetrachloride, ethyl acetate, benzene, toluene, xylenes, n-hexane, methanol, ethanol, isopropyl alcohol, n-butanol, or the like is coated, followed by drying. After such a treatment, the charge transport layer (or the charge generating layer) is formed thereon.

When the silane coupling agent is made present at the interface of the charge generating layer and the charge transport layer by a method as mentioned above, there may be used other than the silane coupling agent one or more conventional binders, plasticizers, additives such as flowability imparting agents, pin hole controller, etc. But these agents or additives should be used in an amount of 30% by weight or less as a whole based on the weight of the silane coupling agent. If the total amount is more than 30% by weight, the sensitivity is lowered and the residual potential is easily increased.

The electrophotographic plate of this invention may further contain a thin binding layer or barrier layer just over the electroconductive layer, or a protective layer such as a silicon layer on the surface of the electrophotographic plate.

The copying method using the electrophotographic plate of this invention can be conducted in the same manner as in a conventional process, i.e., after conducting the charge and exposure on the surface, development is conducted and images are transferred to a usual paper and fixed.

The electrophotographic plate of this invention has advantages in that the sensitivity is high, the dark decay is small and the light fatigue is little, and the like.

This invention is illustrated by way of the following Examples and Comparative Examples.

In the following Examples, the following materials are used. In the parentheses, abbreviations of individual materials are indicated.

______________________________________(1) Organic Pigments for Charge GenerationDisazo series: Symular East Blue 4135 (SFB) (a trade name, mfd. by Dainippon Ink and Chemicals, Inc., Japan)Phthalocyanine series: Fastogen Blue FGF (FGF) (a trade name, mfd. by Dainippon Ink and Chemicals, Inc., Japan)Monoazo series: Resino Red BX (BX) (a trade name, mfd. by Konishiroku Photo Industry Co., Ltd., Japan)(2) Charge Transport Material 2-(p-Diethylamino)phenyl-4-(p- dimethylamino)phenyl-6-(o-chloro)- phenyl-1,3-oxazole (OXZ) 1-Phenyl-3-(p-diethylaminostyryl-5-(p- diethylaminophenyl)pyrazoline (PYZ)(3) Silane Coupling AgentAminosilane: N.beta.-(Aminoethyl)-.gamma.-aminopropyltri- methoxysilane (KBM 603, a trade name, mfd. by Shin-etsu Chemical Industry Co., Ltd.)Mercaptosilane: .gamma.-Mercaptopropyltrimethoxysilane (KBM 803, a trade name, mfd. by Shin-etsu Chemical Industry Co., Ltd.)(4) BinderPolystyrene: Hammer ST (a trade name, mfd. by Mitsui Toatsu Chemical's Inc., Japan)Silicone Varnish: KR-255 (non-volatile content 50%) (a trade name, mfd. by Shin-etsu Chemical Industry Co., Ltd.)Polyester: Vylon 200 (a trade name, mfd. by Toyobo Co., Ltd., Japan)(5) Dye BaseCyanine Dye Base: ##STR6## (NK-2321, a trade name, mfd. by Japanese Research Institute for Photosensitizing Dyes, Ltd., Japan)Styryl Dye Base: ##STR7## (NK-2020, a trade name, mfd. by Japanese Research Institute for photosensitizing Dyes, Ltd., Japan)______________________________________

COMPARATIVE EXAMPLES 1 TO 3

An organic pigment and a binder as shown in Table 1 were mixed in prescribed amounts. To this, methyl ethyl ketone was added so as to make the solid content 3% by weight. The resulting mixed liquid in an amount of 80 g was kneaded in a ball mill (a 3-inch pot, mfd. by Nippon Kagaku Togyo Co., Ltd., Japan) for 8 hours. The thus obtained pigment dispersion was coated on an aluminum plate (the electroconductive layer having a size of 10 cm.times.8 cm.times.0.1 mm, the same size being used hereinafter) by using an applicator and dried at 90.degree. C. for 15 minutes to give a charge generating layer of 1 .mu.m thick.

Then, a charge transport material and a binder as shown in Table 1 were mixed in prescribed amounts. To this, methyl ethyl ketone was added so as to make the solid content 30% by weight to dissolve the solids completely. The resulting solution was coated on the above-mentioned charge generating layer by using an applicator and dried at 90.degree. C. for 20 minutes to form a charge transport layer of 15 .mu.m thick.

Electrophotographic properties of the resulting electrophotographic plates were measured by using an electrostatic recording paper analyzer (SP-428 made by Kawaguchi Electric Works Co., Ltd., Japan). The results are as shown in Table 1.

In Table 1, the initial potential (V.sub.o) means a charge potential obtained by conducting negative corona discharge at 5 kV for a moment, the dark decay (V.sub.k) means potential decay after placing the corona discharged plate in the dark for 10 seconds, and the half decay exposure sensitivity (E.sub.50) means the light amount necessary for decreasing the surface potential to a half after the illumination with white light of 10 lux.

Further, in order to study the effect of light fatigue, electrophotographic properties immediately after the exposure to white light of 1250 lux for 10 minutes (V.sub.o ', V.sub.k ' and E.sub.50 ' being measured in the same manner as described in the cases of V.sub.o, V.sub.k and E.sub.50) and the ratio of initial potentials after and before the exposure (V.sub.o '/V.sub.o), which is a measure of the light fatigue, are also listed in Table 1.

EXAMPLES 1 TO 3

To a pigment dispersion obtained by kneading an organic pigment and a binder in prescribed amounts as shown in Table 1 in the same manner as described in Comparative Examples 1 to 3, a silane coupling agent as shown in Table 1 in a prescribed amount was added and dissolved. The resulting coating liquid was coated on an aluminum plate by using an applicator and dried at 90.degree. C. for 15 minutes to form a charge generating layer of 1 .mu.m thick. A charge transport layer was formed by the formation as shown in Table 1 in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 1.

EXAMPLES 4 TO 6

Using an organic pigment and a binder as shown in Table 1, a charge generating layer was formed in the same manner as described in Comparative Examples 1 to 3. Using a charge transport material, a binder and a silane coupling agent as shown in Table 1, a charge transport layer was formed in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 1.

EXAMPLES 7 TO 9

To a pigment dispersion obtained by kneading an organic pigment and a binder in prescribed amounts as shown in Table 1 in the same manner as described in Comparative Examples 1 to 3, a silane coupling agent as shown in Table 1 in a prescribed amount was added and dissolved. The resulting coating liquid was coated on an aluminum plate by using an applicator and dried at 90.degree. C. for 15 minutes to form a charge generating layer of 1 .mu.m thick. Using a charge transport material, a binder and a silane coupling agent as shown in Table 1, a charge transport layer was formed in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 1.

TABLE 1__________________________________________________________________________(Effects of Silane Coupling Agent)__________________________________________________________________________ Charge generating layer Charge transport layer Organic pigment Binder Silane coupling Charge transport Binder Silane couplingExample No. (wt %) (wt %) agent (wt %) material (wt %) (wt %) agent (wt__________________________________________________________________________ %)ComparativeExample1 SFB 50 Silicone 50 -- -- OXZ 50 Polyester 50 -- -- varnish2 SFB 50 Silicone 50 -- -- PYZ 30 Silicone 70 -- -- varnish varnish3 FGF/BX 25/25 Polyester 50 -- -- OXZ 50 Silicone 50 -- -- varnishExample1 SFB 47.5 Polystyrene 47.5 Aminosilane 5 OXZ 50 Polyester 50 -- --2 SFB 45 Silicone 45 " 10 OXZ 50 " 50 -- -- varnish3 FGF/BX 31.5/31.5 Polyester 27 Mercapto- 10 OXZ 70 Silicone 30 -- -- silane varnish4 SFB 50 Silicone 50 -- -- OXZ 50 Polyester 49 Aminosilane 1 varnish5 SFB 70 Polyester 30 -- -- PYZ 30 Silicone 65 " 5 varnish6 FGF/BX 25/25 " 50 -- -- OXZ 55 Silicone 35 Mercapto- 10 varnish silane7 SFB 45 Silicone 45 Aminosilane 10 OXZ 50 Polyester 48 Aminosilane 2 varnish8 SFB 50 Silicone 40 Mercapto- 10 PYZ 35 Silicone 62 " 3 varnish silane varnish9 SFB 40 Polyester 40 Mercapto- 20 OXZ 50 Polyester 49.5 Mercapto- 0.5 silane silane__________________________________________________________________________ Electrophotographic properties (after exposure) Light fatigue Example No. V.sub.o (V) V.sub.k (%) E.sub.50 (lux-sec) V.sub.o ' (V) V.sub.k ' (%) E.sub.50 ' (lux-sec) V.sub.o '/V.sub.o__________________________________________________________________________ (%) 1 Comparative Example 1 870 44 5 200 22 * 23 2 820 35 2 150 18 * 18 3 860 43 11 190 27 * 22 Example 1 900 73 5 620 65 5 69 2 910 87 5 710 78 5 78 3 880 83 11 640 76 11 73 4 890 71 5 630 63 5 71 5 840 66 3 590 59 3 70 6 880 79 11 670 68 11 78 7 920 97 6 850 88 5 92 8 850 81 5 660 72 5 78 9 930 93 5 810 84 5 87__________________________________________________________________________ (Note) *: Impossible to measure

COMPARATIVE EXAMPLES 4 TO 6

Electrophotographic plates were produced in the same manner as described in Comparative Examples 1 to 3 except for thickening the thickness of each charge generating layer as shown in Table 2 using the materials as listed in Table 2.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 2.

EXAMPLES 10 TO 12

Electrophotographic plates were produced in the same manner as described in Examples 1 to 3 and 7 to 9 except for thickening the thickness of each charge generating layer as shown in Table 2 using the materials as listed in Table 2.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 2.

TABLE 2__________________________________________________________________________ Charge generating layer Charge transport layer (thickness 15 .mu.m) Organic Binder Silane coupling Thickness Charge transport Binder Silane couplingExample No. pigment (wt %) (wt %) agent (wt %) (.mu.m) material (wt %) (wt %) agent (wt__________________________________________________________________________ %)ComparativeExample 4 SFB 50 Silicone 50 -- -- 1 OXZ 50 Polystyrene 50 -- -- varnish 5 SFB 50 Silicone 50 -- -- 3 OXZ 50 " 50 -- -- varnish 6 SFB 50 Silicone 50 -- -- 5 OXZ 50 " 50 -- -- varnishExample10 SFB 45 Silicone 45 Aminosilane 10 3 OXZ 50 " 50 -- -- varnish11 SFB 45 Silicone 45 " 10 5 OXZ 50 " 49 Mercapto- 1 varnish silane12 SFB 45 Silicone 45 " 10 5 OXZ 50 Polyester 48 Aminosilane 2 varnish__________________________________________________________________________ Electrophotographic properties (after exposure) Light fatigue Example No. V.sub.o (V) V.sub.k (%) E.sub.50 (lux-sec) V.sub.o ' (V) V.sub.k ' (%) E.sub.50 ' (lux-sec) V.sub.o '/V.sub.o__________________________________________________________________________ (%) Comparative Example 4 860 66 5 550 54 5 64 5 920 59 6 320 51 -- 35 6 1010 54 8 220 48 -- 22 Example 10 920 84 5 790 78 5 86 11 1020 81 6 850 73 6 83 12 1060 83 6 860 72 6 81__________________________________________________________________________

EXAMPLE 13

In a ball mill (a 3-inch pot, mfd. by Nippon Kagaku Togyo Co., Ltd., Japan), 1.08 g of SFB, 0.24 g of aminosilane (KBM 603) and 20 g of tetrahydrofuran were placed and kneaded for 1 hour. Subsequently, 1.2 g of silicone varnish (KR-255) and 28 g of tetrahydrofuran were added to the ball mill and kneaded for 3 hours. Then, 0.96 g of KR-255 and 29 g of tetrahydrofuran were added to the ball mill and kneaded for 4 hours. The resulting pigment dispersion was coated on an aluminum plate using an applicator and dried at 90.degree. C. for 15 minutes to form a charge generating layer of 1 .mu.m thick.

A charge transport layer was formed by using a charge transport material and a binder in prescribed amounts as listed in Table 3 in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 3.

EXAMPLE 14

In a ball mill (a 3-inch pot, mfd. by Nippon Kagaku Togyo Co., Ltd., Japan), 0.96 g of SFB, 0.48 g of mercaptosilane (KBM 803), 0.36 g of polyester (Vylon 200), and 20 g of methyl ethyl ketone were placed and kneaded for 2 hours. Then, 0.3 g of polyester (Vylon 200) and 35 g of methyl ethyl ketone were added to the ball mill and kneaded for 4 hours. Subsequently, 0.3 g of polyester (Vylon 200) and 22 g of methyl ethyl ketone were added to the ball mill and kneaded for 3 hours. The resulting pigment dispersion was coated on an aluminum plate using an applicator and dried at 90.degree. C. for 15 minutes to form a charge generating layer of 1 .mu.m thick.

A charge transport layer was formed by using a charge transport material and a binder in prescribed amounts as listed in Table 3 in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 3.

TABLE 3__________________________________________________________________________ Charge generating layer Charge transport layer Organic pigment Binder Silane coupling Charge transport Binder Silane couplingExample No. (wt %) (wt %) agent (wt %) material (wt %) (wt %) agent (wt__________________________________________________________________________ %)Example 13 SFB 45 Silicone 45 Aminosilane 10 OXZ 50 Polyester 50 -- -- varnishExample 14 SFB 40 Polyester 40 Mercaptosilane 20 OXZ 50 " 49.5 Mercaptosilane 0.5__________________________________________________________________________ Electrophotographic properties (after exposure) Light fatigue Example No. V.sub.o (V) V.sub.k (%) E.sub.50 (lux-sec) V.sub.o ' (V) V.sub.k ' (%) E.sub.50 V.sub.o '/V.sub.o__________________________________________________________________________ (%) Example 13 930 90 5 750 80 5 81 Example 14 940 94 5 850 86 5 90__________________________________________________________________________

EXAMPLES 15 TO 22

To a pigment dispersion obtained by kneading an organic pigment and a binder in prescribed amounts as listed in Table 4 in the same manner as described in Comparative Examples 1 to 3, a silane coupling agent, and if required a cyanine dye base and/or a styryl dye base in prescribed amounts as listed in Table 4 (Examples 15, 16 and 19 to 22) were added and dissolved. The resulting coating liquid was coated on an aluminum plate using an applicator and dried at 90.degree. C. for 15 minutes to form a charge generating layer of 1 .mu.m thick.

In the next place, a charge transport material, a binder and a silane coupling agent, and if required a cyanine dye base and/or a styryl dye base in prescribed amounts, as listed in Table 4 (Examples 17 to 22) were mixed and a charge transport layer of 15 .mu.m thick was formed in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 4.

TABLE 4__________________________________________________________________________Charge generating layer (wt %)Example Organic pigment Binder Silane coupling agent Cyanine dye base Styryl dye baseNo. SFB Silicone varnish [Aminosilane, KBM603] (NK-2321) (NK-2020)__________________________________________________________________________Example15 45 45 7 3 --16 45 43 7 -- 517 45 45 10 -- --18 45 45 10 -- --19 43 42 8 7 --20 45 47 5 -- 321 45 45 6 4 --22 45 45 6 2 2__________________________________________________________________________Charge transport layer (wt %)Charge Electrophotographic Lightrtiestransport Silane coupling Cyanine Styryl (after exposure) fatigueExample material Binder agent [Amino- dye base dye base V.sub.o V.sub.k E.sub.50 V.sub.o ' V.sub.k ' E.sub.50 ' V.sub.o '/V.sub.oNo. OXZ Polyester silane, KBM603] (NK-2321) (NK-2020) (V) (%) (lux-sec) (V) (%) (lux-sec) (%)__________________________________________________________________________Example15 50 49 1 -- -- 900 94 6 810 84 6 9016 50 49 1 -- -- 910 95 6 830 87 6 9117 50 48 1 1 -- 920 94 6 850 86 6 9218 50 49 0.7 -- 0.3 880 92 6 770 81 6 8719 50 49 0.5 0.5 -- 920 93 6 830 82 6 9020 49 48 1.8 -- 1.2 900 92 6 820 82 6 9121 49 49 1.2 -- 0.8 920 95 6 860 86 6 9322 50 48 0.8 0.6 0.6 930 94 6 860 87 6 93__________________________________________________________________________

As is clear from Table 1, in Comparative Examples 1 to 3, the dark decay (V.sub.k) is as low as about 40%, the light fatigue is great, and the values of (V.sub.o ') are lowered to about 20% of (V.sub.o).

In contrast, when the silane coupling agent is added to at least one of the charge generating layer and the charge transport layer as shown in Examples 1 to 9, both the dark decay and the light fatigue are greatly improved. Particularly, as shown in Examples 7 to 9, when the silane coupling agent is added to both of the charge generating layer and the charge transport layer, the dark decay before and after the exposure to white light of 1250 lux is improved by about 50 to 60% and the light fatigue is also improved by about 60 to 70%. In addition, when the silane coupling agent is added, lowering in the half decay exposure sensitivity is hardly observed.

Further, the degree of light fatigue is also influenced by the kind of the binder in the charge transport layer and the thickness of the charge generating layer. As shown in Comparative Example 4 in Table 2, when polystyrene is used as the binder in the charge transport layer, lowering of (V.sub.o ') due to the light fatigue is relatively small in the case of the thickness of the charge generating layer being 1 .mu.m compared with Comparative Example 1 wherein polyester is used as the binder in the transporting layer. But, with an increase of the thickness of the charge generating layer, the lowering of (V.sub.o ') due to the light fatigue becomes remarkably worse even if polystyrene is used as the binder in the charge transport layer (Comparative Examples 5 and 6). In contrast, when the silane coupling agent is added according to this invention, the lowering of (V.sub.o ') due to the light fatigue is remarkably small and the dark decay becomes good, even if the thickness of the charge generating layer becomes thicker (Examples 10 to 12).

The pigment dispersion which is a coating liquid for forming the charge generating layer can be produced by either mixing whole amounts of an organic pigment, a binder, a solvent, and if required, a silane coupling agent at one time, followed by kneading as shown in Examples 1 to 12, or dispersing the pigment and the like in several times one after another as shown in Examples 13 and 14. Considering the dispersion of pigment, the latter process is preferable. Further, electrophotographic properties of the resulting electrophotographic plates obtained in Examples 13 and 14 in Table 3 are by far excellent compared with those obtained in Examples 2 and 9.

On the other hand, as shown in Table 4, when the cyanine dye base and/or styryl dye base are used together with the silane coupling agent in the charge generating layer and/or the charge transport layer, there are obtained excellent values in electrophotographic properties and the light fatigue.

COMPARATIVE EXAMPLES 7 TO 10

Electrophotographic plates were produced by using materials in prescribed amounts as listed in Table 5 in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 5.

EXAMPLE 23 TO 31

A pigment dispersion obtained by kneading an organic pigment and a binder in prescribed amounts as shown in Table 5 in the same manner as described in Comparative Examples 1 to 3 was coated on an aluminum plate by using an applicator and dried at 90.degree. C. for 15 minutes to form a charge generating layer of 1 .mu.m thick.

Then, a silane coupling agent and a binder were mixed in prescribed amounts as shown in Table 5 and isopropyl alcohol was added thereto so as to make the solid content 1% by weight. The resulting solution was coated on the surface of the charge generating layer by using an applicator and dried at 90.degree. C. for 15 minutes (the amount of silane coupling agent coated being shown in Table 5).

A charge transport layer was formed on the charge generating layer coated with the silane coupling agent by using the formulation as shown in Table 5 in the same manner as described in Comparative Examples 1 to 3.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 5.

As is clear from Table 5, in Comparative Examples 7 to 10, the initial potential after exposure (V.sub.o ') to white light of 1250 lux for 10 minutes are all remarkably lowered compared with (V.sub.o) and the phenomenon of light fatigue is also observed. Further, the dark decay (V.sub.k) is as poor as about 30 to 50%.

In contrast, when the surface of the charge generating layer is treated with the silane coupling agent as in Examples 23 to 31, the light fatigue is greatly lessened and the values (V.sub.o '/V.sub.o) are improved to 70% or more in all the cases. Further, the dark decay (V.sub.k) is improved to 80% or more and the initial potential (V.sub.o) is increased by 100 V or more. The half decay exposure (E.sub.k) sensitivity is not lowered greatly, although there is a tendency to be lowered slightly.

TABLE 5__________________________________________________________________________ Charge generating layer Treating liquid Organic Silane Coating amount of silaneExample No. pigment wt % Binder wt % coupling agent wt % Binder wt % coupling agent (mg/cm.sup.2)__________________________________________________________________________ComparativeExample 7 SFB 60 Silicone varnish 40 -- -- -- -- -- 8 " 50 " 50 -- -- -- -- -- 9 " 50 " 50 -- -- -- -- --10 FGF 60 " 40 -- -- -- -- --Example23 SFB 60 " 40 Aminosilane 100 -- -- 0.2024 " 60 " 40 Mercaptosilane 100 -- -- 0.7025 " 60 " 40 Aminosilane 80 Silicone 20 0.20 varnish26 " 50 " 50 " 100 -- -- 1.2027 " 50 " 50 " 75 Silicone 25 0.40 varnish28 " 50 " 50 " 100 -- -- 5.0029 " 50 " 50 Mercaptosilane 90 Silicone 10 0.10 varnish30 FGF 60 " 40 Aminosilane 100 -- -- 0.0531 " 60 " 40 Mercaptosilane 100 -- -- 0.01__________________________________________________________________________ Electrophotographic properties Charge transport layer (after exposure) Charge E.sub.50 E.sub.50 ' Light fatigueExample No. transport material wt % Binder wt % V.sub.o (V) V.sub.k (%) (lux-sec) V.sub.o ' (V) V.sub.k ' (%) (lux-sec) V.sub.o '/V.sub.o__________________________________________________________________________ (%)ComparativeExample 7 OXZ 50 Silicone 50 850 51 5 250 27 * 29 varnish 8 OXZ 50 Polyester 50 870 44 5 200 22 * 23 9 PYZ 40 Silicone 60 820 33 2 160 21 * 19 varnish10 OXZ 60 Silicone 40 860 49 7 230 30 * 27 varnishExample23 OXZ 50 Silicone 50 980 83 5 860 76 5 88 varnish24 OXZ 50 Silicone 50 1060 88 5 950 79 5 90 varnish25 OXZ 50 Silicone 50 1090 89 5 970 78 5 89 varnish26 OXZ 50 Polyester 50 1120 86 5 800 75 5 7127 OXZ 50 " 50 1220 88 6 960 76 6 7928 PYZ 40 Silicone 60 1060 82 4 820 72 4 77 varnish29 PYZ 40 Silicone 60 1020 83 3 780 71 3 76 varnish30 OXZ 60 Polyester 40 980 87 7 810 74 7 8331 OXZ 60 Silicone 40 960 86 7 810 75 7 84 varnish__________________________________________________________________________ (Note) *impossible to measure

COMPARATIVE EXAMPLES 11 TO 13

The surface of electrophotographic plate obtained in Comparative Example 8 was treated with a silane coupling agent as shown in Table 6 in the same manner as described in Example 23. Subsequently, a 5% by weight solution of tris(2-acyloyloxyethyl)isocyanurate (the solvent being a mixture of toluene and isorpopanol (1:1 by weight)) was coated thereon by using an applicator having a gap of 50 .mu.m and dried at 90.degree. C. for 2 minutes. Then, the resulting surface was exposed to ultraviolet light by using a high-pressure mercury lamp (an ultraviolet irradiation apparatus mfd. by Toshiba Denzai K.K., using one high-pressure mercury lamp H 5600L/2, 5.6 kW) at a distance of 10 cm for 30 seconds to form a protective layer thereon.

Electrophotographic properties of the resulting electrophotographic plates are shown in Table 6.

In Table 6, the residual potential V.sub.R means a residual potential obtained by charging an electrophotographic plate by conducting negative corona discharge at 5 kV at a moment, and then illuminating it with white light of 10 lux for 10 seconds and standing for 25 seconds, and the residual potential V.sub.R ' means a residual potential obtained in the same manner as mentioned above immediately after the illumination with white light of 1250 lux for 10 minutes, the unit being V (volt).

V.sub.R and V.sub.R ' of the electrophotographic plates obtained in Examples 1 to 31 were also measured in the same manner as mentioned above with the results that all the values were zero volt.

TABLE 6__________________________________________________________________________ Charge generating layer Charge transport layer Organic Charge Coating amount of silaneExample No. pigment (wt %) Binder (wt %) transport material (wt %) Binder (wt %) coupling agent (mg/cm.sup.2)__________________________________________________________________________ComparativeExample11 SFB 50 Silicone varnish 50 OXZ 50 Polystyrene 50 1.2012 SFB 50 " 50 OXZ 50 " 50 0.4013 SFB 50 " 50 OXZ 50 " 50 0.05__________________________________________________________________________ Electrophotographic properties (after exposure) Light fatigueExample No. V.sub.o (V) V.sub.k (%) E.sub.50 (lux-sec) V.sub.R (V) V.sub.o ' (V) V.sub.k ' (%) E.sub.50 ' (lux-sec) V.sub.R ' (V) V.sub.o '/V.sub.o (%)__________________________________________________________________________ComparativeExample11 1020 46 7 100 260 32 7 75 2512 940 47 6 60 220 27 6 40 2313 930 47 5 40 250 28 5 30 27__________________________________________________________________________

As mentioned above, the electrophotographic plates obtained in Examples 1 to 31 show excellent properties in the initial potential after the exposure, the dark decay before and after the exposure and the residual potential after and before the exposure.

As is clear from the above descriptions, the electrophotographic plate of this invention is characterized in that

(1) the dark decay is small,

(2) lowering in charge potential is small and the dark decay is not increased even if repeating charge/exposure (that is, light fatigue is little), and

(3) high sensitivity is shown.

Claims

1. In an electrophotographic plate comprising an electroconductive layer, a charge generating layer containfing one or more organic pigments for charge generation and a charge transport layer containing one or more charge transport materials, the improvement wherein a silane coupling agent is present in the charge transport layer in an amount of 0.05% to 30% by weight based on the weight of the charge transport layer.

2. An electrophotographic plate according to claim 1, wherein the silane coupling agent is at least one compound selected from the group consisting of aminosilanes and hydrochlorides thereof, mercaptosilanes, vinylsilanes and epoxysilanes.

3. An electrophotographic plate according to claim 1, wherein the silane coupling agent is an aminosilane.

4. An electrophotographic plate according to claim 1, wherein the silane coupling agent is a mercaptosilane.

5. An electrophotographic plate according to claim 3, wherein the aminosilane is N-.beta.-(aminoethyl)-.gamma.-aminopropyl-trimethoxysilane.

6. An electrophotographic place according to claim 4, wherein the mercaptosilane is .gamma.-mercaptopropyltrimethoxysilane.

7. An electrophotographic plate according to claim 1, wherein the charge generating layer and/or the charge transport layer contains a cyanine dye base of the formula: ##STR8## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an acyl group, a hydroxyl group, a phenyl group or a substituted phenyl group, and/or a styryl dye base of the formula: ##STR9## wherein R.sub.7, R.sub.8, R.sub.9 and R.sub.10 are independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an acyl group, a hydroxyl group, a phenyl group, or a substituted phenyl group; and R.sub.11 and R.sub.12 are independently a hydrogen atom or an alkyl group.

8. An electrophotographic plate according to claim 7, wherein the charge transport layer contains a silane coupling agent in an amount of 0.05% by weight, and the silane coupling agent and the cyanine dye base of the formula (I) and/or the styryl dye base of the formula (II) in a total amount of 30% by weight or less.

9. An electrophotographic plate according to claim 1, wherein the charge generating layer has a thickness of 0.1 to 10 .mu.m and the charge transport layer has a thickness of 5 to 50 .mu.m.

10. An electrophotographic plate comprising an electroconductive layer, a charge generating layer consisting essentially of organic material including at least one organic pigment for charge generation and a polymeric binder and a charge transport layer having functions of charge transport and consisting essentially of organic material including high or low molecular weight charge transporting compounds and a polymeric binder; a silane coupling agent being present in the charge transport layer and said coupling agent being in an amount of 0.05 to 30% by weight based on the weight of the charge transport layer.

11. In an electrophotographic plate comprising an electroconductive layer, a charge generating layer containing one or more organic pigments for charge generation and a charge transport layer containing one or more charge transport materials, the improvement wherein a silane coupling agent is present at the interface of the charge generating layer and the charge transport layer in an amount of 10.sup.-4 mg/cm.sup.2 to 10.sup.2 mg/cm.sup.2.

12. An electrophotographic plate according to claim 11, wherein the silane coupling agent is at least one compound selected from the group consisting of aminosilanes and hydrochlorides thereof, mercaptosilanes, vinylsilanes and epoxysilanes.

13. An electrophotographic plate according to claim 11, wherein the silane coupling agent is an aminosilane.

14. An electrophotographic plate according to claim 11, wherein the silane coupling agent is a mercaptosilane.

15. An electrophotographic plate according to claim 13, wherein the aminosilane is N-.beta.-(aminoethyl)-.gamma.-aminopropyl-trimethoxysilane.

16. An electrophotographic place according to claim 14, wherein the mercaptosilane is .gamma.-mercaptopropyltrimethoxysilane.

17. An electrophotographic plate according to claim 11, wherein the charge generating layer and/or the charge transport layer contains a cyanine dye base of the formula: ##STR10## wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5 and R.sub.6 are independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an acyl group, a hydroxyl group, a phenyl group or a substituted phenyl group, and/or a styryl dye base of the formula: ##STR11## wherein R.sub.7, R.sub.8, R.sub.9 and R.sub.10 are independently a hydrogen atom, a halogen atom, an alkyl group, an aralkyl group, an acyl group, a hydroxyl group, a phenyl group, or a substituted phenyl group; and R.sub.11 and R.sub.12 are independently a hydrogen atom or an alkyl group.

18. An electrophotographic plate according to claim 11, wherein the charge generating layer has a thickness of 0.1 to 10 .mu.m and the charge transport layer has a thickness of 5 to 50 .mu.m.

19. An electrophotographic plate comprising an electroconductive layer, a charge generating layer consisting essentially of organic material including at least one organic pigment for charge generation and a polymeric binder and a charge transport layer having functions of charge transport and consisting essentially of organic material including high or low molecular weight charge transporting compounds and a polymeric binder; a silane coupling agent being present at the interface between the charge generating layer and the charge transport layer, said coupling agent being in an amount of 10.sup.-4 mg/cm.sup.2 to 10.sup.2 mg/cm.sup.2.