GB2235985A - Electrophotographic photoreceptor - Google Patents

Abstract

An electrophotographic photoreceptor comprising an electrically conductive support 1 having thereon a subbing layer 2, a charge-generating layer 3 and optionally a charge-transporting layer 4, wherein said subbing layer is a layer having a degree of cure of 3.0 or more which is obtained by coating a mixed solution of a zirconium chelate compound or a zirconium alkoxide and a silane coupling agent, followed by curing. The photoreceptor exhibits excellent electrophotographic characteristics, particularly reduced dark decay and reduced residual potential, and durability and provides defect-free images irrespective of environmental changes. <IMAGE>

Description

ELECTROPHOTOGRAPHIC PHOTORECEPTOR

FIELD OF THE INVENTION

This invention relates to an electrophotographic photoreceptor comprising an electrically conductive support, a subbing layer, and a photosensitive layer. More particularly, it relates to an electrophotographic photoreceptor having an improved subbing layer.

BACKGROUND OF THE INVENTION

With the recent developments of electrophotographic copying machines which can produce copies of various sizes at an increasing speed, photoreceptors to be used in these electrophotographic copying machines have been accordingly demanded to have higher photosensitivity and longer working life.

Many proposals of separate function type electrophotographic photoreceptors in which a plurality of elements respectively perform functions as a photoreceptor have been made in an attempt to improve various electrophotographic characteristics, such as charge retention, stability on repeated use, light response, spectral characteristics, and mechanical strength.

These electrophotographic photoreceptors are known to have disadvantages, such as (1) poor stability of developed Image contrast against repeated use or environmental change, (2) liability to cause image defects called white.spot, black spot, roughness, pinhole, etc., and (3) insufficient durability due to low adhesive strength between a support and a photosensitive layer, causing separation of the photosensitive layer during use.

In order to eliminate these disadvantages, it has been proposed to provide a resin layer between a support and a photosensitive layer. As the resins to be used for the resin layer, poly-p-xylene, casein, polyvinyl alcohol, phenolic resins, polyvinyl acetal - resins, melamine resins, nitrocellulose, ethylene-acrylic acid copolymers, polyamide (e.g., nylon 6, nylon 66, nylon 610, copolymer nylon, alkoxymethylated nylon), polyurethane, gelatin, polyvinyl pyrrolidone, polyvinylpyridine, and polyvinyl methyl ether are known.

It has also been proposed to form an intermediate layer using organozirconium compounds, e.g., zirconium chelate compounds and zirconium alkoxides, or silane coupling agents as disclosed in JP-A-59- 223439, JP-A-61-94057, and JP-A-62-273549 (the term WP-A as used herein means an llunexamined published Japanese patent application,').

What is aimed at by providing a resin layer as a subbing layer is to control volume resistance at such a low level that does not deteriorate electrophotographic characteristics by chiefly using a resin having a relatively 2 large content of a polar group. Since volume resistance of a resin has character of being dependent on ion conduction, it is considerably influenced by temperature and humidity. That is, when a photoreceptor is exposed to a low temperature and low humidity condition or a high temperature and high humidity condition, the resin layer has markedly increased resistance, resulting in deterioration of electrophotographic characteristics of the photosensitive layer, or markedly decreased resistance, resulting in loss of expected functions, respectively.

Thus, the conventionally known resin layers achieved an improvement in only part of the above-described disadvantages associated with a photoreceptor. Susceptibility to environmental influences being taken into consideration, the effects of the resin layer are reduced by half. Therefore, the conventional resin layers have been extremely insufficient from the technical consideration.

Where organozirconium compounds, e.g., zirconium chelate compounds and zirconium alkoxides, or silane coupling agents are employed, the abovedescribed problem is considerably settled, but these compounds are still unsatisfactory because they cause reduction in developed image contrast with an increase in residual potential and are liable to cause image defects,, such as white spot.. black spot, roughness, ind pinhole.

3 Hence, the conventionally proposed subbing layers do not produce sufficient effects to eliminate various disadvantages associated with electrophotographic photoreceptors and, therefore, the state-of-the-art photoreceptors have unsatisfactory characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrophotographic photoreceptor which has excellent electrostatic characteristics with a small dark decay, hardly causes reduction in developed image contrast, and particularly has a low residual potential.

Another object of the present invention is to provide an electrophotographic photoreceptor which hardly causes image defects, such as white spot, black spot, roughness, and pinhole.

A further object of the present invention is to provide an electrophotographic photoreceptor which is hardly affected by environmental changes and excellent in durability.

As a result of investigations, the inventors have found that the above objects of the present invention are accomplished by a subbing layer prepared by coating an organozirconium compound and a silane coupling agent and curing the coating to a specific degree of cure.

That is, the present invention relates to an electrophotographic photoreceptor comprising an electrically 4 conductive support having thereon a subbing layer and a photosensitive layer, wherein the subbing layer is a layer having a degree of cure of 3. 0 or more which is obtained by coating a mixed solution of a zirconium chelate compound or a zirconium alkoxide compound (hereinafter sometimes inclusively referred to as an organozirconium compound) and a silane coupling agent, followed by curing.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 s a schematic section of an example of the electrophotographic photoreceptor according to the present invention. Numerals 1 to 4 indicate an electrically conductive support, a subbing layer, a charge generating layer, and a charge transporting layer, respectively.

Figure 2 is a graph of drying time vs. degree of cure of the subbing layers of Examples 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

The terminology "degree of cure,, as used herein means a ratio of (A) an intensity of a peak of an infrared absorption spectrum of SI-0-Zr in the vicinity of 940 cm-1 of the subbing layer af ter coating the abovedescribed mixed solution and curing to (B) an intensity of a peak of an infrared absorption spectrum of a silane coupling agent -Siro-R (in which R is an alkyl group) In the vicinity of 1090 m-1 before coating,, i.e., A/B. The Infrared absorption spectrum can be measured by an ordinary potassium bromide tablet method.

The degree of cure of the subbing layer is preferably 3. 0 to 6. 0, and more preferably 3. 0 to 4. 0 f rom the standpoints of curing time and production efficiency such as energy necessary for curing.

The conventionally known electrically conductive supports can be used in the present invention. Examples of suitable materials of supports are aluminum and stainless steel.

On the conductive support is coated a subbing layer. The subbing layer according to the present invention is a coating layer f ormed by coating a mixed solution of a zirconium chelate compound or a zirconium alkoxide and a silane coupling agent, followed by curing to a degree of cure of 3. 0 or more. If the reached degree of cure is less than 3.0, the resulting photoreceptor is liable to variation in electrophotographic characteristics due to environmental changes and variation in copying cycle and also easily causes image def ects such as white spot, black spot, and roughness.

An organozirconium compound and a silane coupling agent are preferably mixed at a Zr/Si molar ratio ranging from 1 / 1 to 811, particularly 211 to 411.

Since a subbing layer containing no silane coupling agent, though possible to be formed, is very inferior in filmforming properties and adhesion properties, a combined use of a silane coupling agent is essential in the present invention.

6 The organozirconium compound which can be.used in the present invention is represented by formula:

(R 0),Zr - R', wherein R represents an alkyl group having 1 to 5 carbon atoms; R' represents a residue of acetylacetone, keto ester, glycol or hydroxy acid; and n and m each represents 0 or an integer of from 1 to 4, provided that the sum of n and m is 4.

Typical examples of the organozirconium compound are tetrakisacetylacetonatozirconium, zirconium tetrabutoxide, and acetylacetonatotributoxyzirconium.

The silane coupling agent which can be used in the present invention includes vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyl-tris(2methoxyethoxy)silane, vinyltriacetoxysilane, Y_ glycidoxypropyltrimethoxysilane, ymethacryloxypropyl trimethoxy silane, y-aminopropyl triethoxy silane, ychloropropyl trimethoxy silane, y-2-aminoethyl-aminopropyl trimethoxy silane, y-mercaptopropyl trimethoxy silane, yureidopropyl triethoxy silane, and J3- (3,4-epoxycyclohexyl) ethyl trimethoxy silane.

The subbing layer of the present invention has a thickness usually of from 0.01 to 5 gm, and preferably from 0.2 to 2 gm.

The mixed solution for coating the subbing layer is prepared by, dissolving the organozirconium compound and silane 7 coupling agent in a solvent such as an alcohol, e.g., ethanol, methanol, propanol, and butanol; an aromatic hydrocarbon, e.g.

toluene; and esters, e.g., ethyl acetate and cellosolve acetate; or a mixture thereof.

The mixed solution is coated by, f or example, dip coating, spray coating, blade coating, spinning coating, bead coating, curtain coating, etc. Drying of the coating is carried out in an air f low or in still air at a temperature ranging from 110 to 2500C, and preferably from 1701 to 200C, for a period of from 5 minutes,to 6 hours, and preferably from 10 minutes to 2 hours. The drying temperature and time should be so selected as to obtain the above-recited degree of cure.

Heat curing of the coating layer may be effected immediately after coating or through heating for forming a photosensitive layer thereon.

A photosensitive layer is then formed on the thus formed subbing layer. The photosensitive layer may have either a single-layer structure or a laminate structure. A photosensitive layer of single-layer structure includes a dyesensitized Zno photosensitive layer or CdS photosensitive layer and a photosensitive layer comprising a charge transporting substance having dispersed therein a charge generating substance.

A photosensitive layer of laminate structure includes a combination of a charge generating layer and a charge 8 transporting layer each of which performs the. respective function. The order of laminating these layers is arbitrary.

The charge generating layer is formed from a charge generating substance which is, if desired, dispersed in an appropriate binder. Examples of suitable charge generating substances include selenium and selenium alloys; inorganic photoconductive substances, e.g., Cds, CdSe, CdSSe, ZnO, and ZnS; metallized or metal-free phthalocyanine pigments; azo pigments, e.g., bisazo pigments and trisazo pigments; squarylium compounds; azulenium compounds; perylene pigments; indigo pigments; quinacridone pigments, polycyclic quinone pigments; cyanine dyes; xanthene dyes; charge transfer complexes composed of poly-N-vinylcarbazole and trinitrofluorenone, etc.; and eutectic complexes composed of a pyrylium salt dye and a polycarbonate resin, etc.

Binder resins which can be used in the charge generating layer are conventional and include polycarbonate, polystyrene, polyester, polyvinyl butyral, methacrylic ester homo- or copolymers, vinyl acetate homo- or copolymers, cellulose esters or ethers, polybutadiene, polyurethane, and epoxy resins.

The charge transporting layer is formed mainly from a charge transporting substance. The charge transporting substance to be used is not particularly limited as long as it is transpa'rent against visible light and is capable of 9 transporting electric charge. Specific examples are imidazole, pyrazoline, thiazole, oxadiazole, oxazole, hydrazone, ketazine, azine, carbazole, polyvinylcarbazole, etc. and derivatives thereof; triphenylamine derivatives, stilbene derivatives, and benzidine derivatives. If desired, a binder resin is used in combination. Examples of suitable binder resins are polycarbonate, polyarylate, polyester, polystyrene, styreneacrylonitrile copolymers, polysulfone, polymethacrylic esters, and styrene-methacrylic ester copolymers.

The present invention is now illustrated in greater detail with reference to Examples, but it should be understood that the present invention is not construed as being limited thereto. All the parts, percents, and ratios are by weight unless otherwise indicated.

EXAMPLE 1

Tetrakisacetylacetonatozirconium (11W 15011 10 parts produced by Matsumoto Kosho K.K.) y-Methacryloxypropyl trimethoxy silane 20 parts (11KBM SOY' produced by Shin-etsu Chemical Industry Co., Ltd.) Methyl alcohol 400 parts n-Butyl alcohol 100 parts n-Amyl alcohol 200 parts The above components were stirred in a stirrer to prepare a coating composition for a subbing layer. The composition-was coated on the surface of an aluminum cylinder having a diameter of about 85 mm by dip coating to a dry thickness of about 0.2 gm, air-dried for about 5 minutes, and then heatdried at a drying temperature varying from 1350 to 1700C for a drying time varying from 7.5 to 360 minutes to form a subbing layer having a varied degree of cure. The resulting samples were designated Nos. 1 to 8. The relationship between drying conditions and degree of cure reached is shown in Fig. 2.

A solution of 87 parts of granular trigonal selenium and 13 parts of a vinyl chloride-vinyl acetate copolymer ("Solution Vinyl VMCH" produced by Union Carbide Inc.) in 200 parts of n-butyl acetate was dispersed in an attritor for 24 hours. To 30 parts of the resulting dispersion was added 57 parts of n-butyl acetate for dilution to prepare a dip coating composition.

The subbing layer on the aluminum cylinder was then dip-coated with the coating composition and dried at 1000C for 5 minutes to form an about 0.1 gm thick charge generating layer.

Ten parts of N,NI-diphenyl-N,NI-bis(3-methylphenyl)[1,11-biphenyl]-4,41diamine and 10 parts of polycarbonate Z resin were dissolved in 80 parts of monochlorobenzene to prepare a coating composition for a charge transporting layer. The composition was coated on the charge generating layer and dried in hot air at 100C for 60 minutes to form a 25 gm thick charge trafisporting layer.

The thus obtained electrophotographic photoreceptor was mounted on a dry electrostatic type copying machine (I1FX 2700 Modified Model" produced by Fuji Xerox Co., Ltd.). After adjusting a dark potential VD to -800 V, the photoreceptor was exposed to light at an exposure amount of 2 erg ICM2, and the light potential VL was measured. Thereafter, running test was conducted to obtain 10,000 copies, and changes in VD and VL were determined. Also, image quality of the copies after the running test was evaluated by using test chart copies of white paper, and solid images having optical densities of 0.2 and 1.0.

An electrophotographic photoreceptor produced in the same manner as described above was preserved at 400C and 85% RH for 1 month, and test for image quality was conducted.

The results of these evaluations are shown in Table 1 below.

EXAMPLE 2

Acetylacetonatotributoxyzirconium (IIZC 54011 100 parts produced by Matsumoto Kosho K.K.) y-Aminopropyl trimethoxy silane (,'A 111011 11 parts produced by Nippon Unicar Company LTD.) Ethyl alcohol 600 parts n-Butyl alcohol 150 parts The above components were stirred in a stirrer to prepare a coating composition for a subbing layer. The composition was coated on an aluminum support in the same - 12 manner as in Example 1 and air-dried for about 8.minutes and then heat- dried at a varied temperature for a varied time in the same manner as in Example 1 to form a subbing layer having a varied degree of cure. The resulting samples were designated Nos. 9 to 15. The relationship between drying conditions and degree of cure reached is shown in Fig. 2.

A charge transporting layer and a charge generating layer were laminated thereon in the same manner as in Example 1 to obtain an electrophotographic photoreceptor, and each photoreceptor was tested in the same manner as in Example 1. The results obtained are shown in Table 1.

- 13 TABLE 1

Image Quality Subbing Degree After Obtaining After Preserv Layer Drying of 10,000 Copies ation (40% -No. Condition Cure AVE, AVD AVRP Image Quality 95% RH, 1 Mth.1 Remark (V) (V) (V) 1 1350C x 10 min 1.1 -40 -15 20 White spot White spot Comparison 2 1500C x 20 min 1.6 -30 -5 20 el to 3 1350C x 180 min 2.0 -35 -10 15 No deterioration 4 1700C x 10 min 2.2 -25 -5 20 1500C x 60 min 2.4 -30 0 10 6 1700C x 20 min 2.7 -25 -5 5 7 1350C x 360 min 4.2 -20 0 10 No deterioration Invention 8 1700C x 60 min 4.8 -20 0 5 It 9 1350C x 9 min 1.2 -50 0 5 White spot White spot Comparison 1700C x 7.5 min 2.1 -35 -10 0 90 No deterioration to 11 1350C x 15 min 2.2 -40 -10 5 12 1500C x 15 min 2.5 -30 -5 10 13 135C x 60 min 3.3 -25 -10 0 No deterioration Invention 14 1700C x 15 min 3.4 -20 0 -5 is 1700C x 60 min 3.6 -20 0 -5 The electrophotographic photoreceptor according to the present invention having a subbing layer of the above-described construction has excellent electrostatic characteristics with a small dark decay and a low residual potential and hardly causes reduction in developed image contrast. Further, the photoreceptor of the present invention is less susceptible to environmental influences and has excellent durability. Therefore, when the photoreceptor of the present invention is used for continuously obtaining a large number of copies, it exhibits stable electrophotographic characteristics to steadily provide excellent images free from defects, such as white spot, black spot, roughness and pinhole.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the scope thereof.

Claims (6)

1. An electrophotographic photoreceptor comprising an electrically conductive support having thereon a subbing layer and a photosensitive layer, wherein said subbing layer is a layer having a degree of cure of 3. 0 or more which is obtained by coating a mixed solution of a zirconium chelate compound or a zirconium alkoxide and a silane coupling agent, followed by curing.

2. An electrophotographic photoreceptor as in Claim 1, wherein the degree of cure of said subbing layer is 3. 0 to 6 - 0.

3. An electrophotographic photoreceptor as in Claim 2, wherein the degree of cure of said subbing layer is 3. 0 to 4. 0.

4. An electrophotographic photoreceptor as in Claim 1, wherein said zirconium chelate compound or zirconium alkoxide and said silane coupling agent are used at a Zr/Si molar ratio of from 111 to 8/1.

5. An electrophotographic photoreceptor as in Claim 4, wherein said zirconium chelate compound or zirconium alkoxide and said silane coupling agent are used at a Zr/S1 molar ratio of from 2/1 to 411.

6. An electrophotographic receptor as in Claim 1. substantially as hereinbefore described in any one of Examples 1 and 2.

16 Published 1991 atIle Patent Office. State House. 66171 High Holbom. London WC1R4TP. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.