JP2002049165A - Electrophotographic photoreceptor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide such an electrophotographic photoreceptor that injection of positive charges from defects of an aluminum substrate can be prevented by incorporating titanium oxide fine particles subjected to the surface treatment to impart hydrophobicity into a charge generating layer, that the photoreceptor does not generate image defects in black speckles but has high sensitivity and low residual potential and that the photoreceptor is suitable for a digital copying machine and printer. SOLUTION: In the electrophotographic photoreceptor, the charge generating layer contains titanium oxide fine particles subjected to the surface treatment to impart hydrophobicity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photosensitive member such as a digital copying machine and a printer.

[0002]

2. Description of the Related Art With the development of electronic equipment, the demand for printers has increased, and copiers have also been digitized. In such digital copiers and printers, images are written using laser light as a light source. Therefore, the developing method is different from that of a conventional analog copier, and a reversal development method in which a portion irradiated with light becomes a toner image is preferable. However, in the reversal development method, there has been a problem that a black spot-like image defect (black spot) occurs due to the injection of positive charges from the aluminum base defect.

Conventionally, the injection of positive charges from defects in the aluminum base was prevented by alumite processing the aluminum base or by providing a thick intermediate layer on the aluminum base, but this was costly. Further, when trying to prevent black-spotted image defects, the sensitivity is reduced, the residual potential is increased, and other problems occur. In particular, other problems occur under high temperature and high humidity (30 ° C., 80% RH). Without this, it was not possible to prevent the injection of positive charges from defects in the aluminum base, and there was a problem.

[0004]

DISCLOSURE OF THE INVENTION The present invention has been proposed in view of the above problems.
The inclusion of hydrophobic titanium oxide particles in the charge generation layer prevents the injection of positive charges from defects in the aluminum base, prevents black spot-like image defects from occurring, and provides high sensitivity and residual potential. It is an object of the present invention to provide an electrophotographic photoreceptor suitable for digital copiers and printers having a small size.

[0005]

The object of the present invention is achieved by adopting the following constitution.

(1) An electrophotographic photoreceptor characterized in that fine particles of titanium oxide having been subjected to hydrophobic surface treatment are contained in a charge generation layer.

(2) The electrophotographic photoreceptor as described in (1) above, wherein the titanium oxide fine particles are surface-treated with a compound containing silicon.

(3) The electrophotographic photoreceptor as described in (1) or (2) above, wherein the charge generating substance is a phthalocyanine pigment.

(4) The electrophotographic photoreceptor as described in any one of the above items 1 to 3, wherein the titanium oxide fine particles are of an anatase type.

That is, the present inventor has found that when an electrophotographic photosensitive member in which hydrophobic surface-treated fine particles of titanium oxide are added to a layer containing a charge generating substance is applied to a digital copying machine and a printer, black spots are formed. No image defects occurred. It is presumed that the reason for this is that the titanium oxide fine particles whose surface is made hydrophobic prevent injection of positive charges from defects in the aluminum base.

Hereinafter, the present invention will be described in more detail. The surface of the titanium oxide fine particles of the present invention is hydrophobically treated with a hydrophobizing agent.

Examples of the hydrophobizing agent include a titanium coupling agent, a silane coupling agent, an aliphatic and metal salt thereof, and a silicone oil. A siloxane resin or a silane coupling agent containing silicon is preferable.

As the hydrophobizing agent, a portion imparting hydrophobicity such as an alkyl group or a siloxane group and a -Si-H group,
Those having a part which reacts with the surface of the titanium oxide fine particles, such as those which are converted into -Si-OH by hydrolysis and -Si-OH groups, are preferably used. Specific examples include propyltrimethoxysilane, decyltrimethoxysilane,
Examples thereof include isobutyltrimethoxysilane, dimethyldiethoxysilane, and methyl hydrogen polysiloxane.

It is preferable that the hydrophobic treatment agent is added by 1 to 10% by mass based on the titanium oxide fine particles for coating, and more preferably 3 to 7% by mass. Further, the hydrophobizing agents can be used in combination.

The titanium oxide fine particles to be surface-treated to be hydrophobic are not necessarily titanium oxide fine particles alone, and a small amount of silicon oxide may be mixed in for stabilizing the crystal, or the surface may be coated with aluminum oxide or silicon oxide. Includes what is covered. As the crystal forms of the titanium oxide fine particles, two types of rutile type and anatase type are known, but anatase type, which easily transports electrons (has a strong property as an N-type semiconductor), is preferable.

The titanium oxide fine particles subjected to the hydrophobic treatment of the present invention preferably have a primary particle diameter of 100 nm or less. If the primary particle diameter of the titanium oxide fine particles exceeds 100 nm, it is difficult to form a uniform layer, and the actual image quality is poor, and the effect of preventing black-spotted image defects is unfavorable.

Further, the photoreceptor containing the titanium oxide fine particles subjected to hydrophobic surface treatment according to the present invention is intended to improve black spot-like image defects generated during reversal development as described above. However, it is characterized by high sensitivity and low residual potential as compared with those not containing hydrophobic surface-treated titanium oxide fine particles, or those containing an inert binder resin or silica sol.

The binder resin used in the charge generation layer is not particularly limited, and is usually a binder resin used in the charge generation layer, for example, a polycarbonate resin, a polyester resin, a polystyrene resin, an acrylic resin, a polyvinyl chloride resin, Polyvinyl butyral resin,
It can be arbitrarily selected from a silicone resin, a cellulose resin, a polyamide resin and the like. There is no particular limitation on the coating solvent, for example, ethers such as tetrahydrofuran and dioxolan, ketones such as methyl ethyl ketone and cyclohexanone, aromatic compounds such as toluene and xylene, esters such as ethyl acetate and butyl acetate, isopropanol and Alcohols such as butanol can be arbitrarily selected.

The charge generation substance (CGM) contained in the layer containing the titanium oxide fine particles surface-treated to be hydrophobic includes phthalocyanine pigments, azo pigments, perylene pigments, and azurenium pigments. As described above, since it is necessary to particularly exert an effect in the laser exposure-reversal development process, a phthalocyanine pigment having sensitivity in the near infrared region which is the oscillation wavelength of the semiconductor laser used for exposure is preferable.

The phthalocyanine pigments include A-type, B-type and Y-type titanyl phthalocyanines, X-type and τ-type metal-free phthalocyanines, metal phthalocyanines represented by copper phthalocyanines, naphthalocyanines, and mixtures of these two types of phthalocyanines. And the like.

The mixing ratio of the charge generating substance and the titanium oxide fine particles in the charge generating layer of the present invention is preferably from 1: 5 to 5: 1 by mass ratio, and the mixing of the binder resin and the solid content (charge generating substance + titanium oxide). The ratio is preferably from 1: 7 to 5: 1 by mass.

The thickness of the layer containing the charge generating substance is preferably 5 μm for a function-separated type photosensitive member applied to negative charging and a laminated structure photosensitive member applied to positive charging, and 5 to 5 μm for a single-layered photosensitive member.
40 μm is preferred.

When the above-described hydrophobic surface-treated titanium oxide fine particles of the present invention are contained in the charge generation layer of the positively charged photoreceptor, the sensitivity can be improved and the residual potential can be reduced.

The coating solution for the charge generation layer of the present invention may be prepared by separately dispersing the charge generation substance and the titanium oxide fine particles in a binder resin solution by using a sand grinder or an ultrasonic disperser, and then mixing them. Alternatively, all the materials may be mixed and then dispersed. Depending on the type of the surface-treated titanium oxide fine particles, a phenomenon such as peeling of the surface treatment agent may be observed in the sand grinder dispersion,
In this case, the charge generating substance is dispersed in advance by a sand grinder, and then the titanium oxide fine particles are added and dispersed by an ultrasonic disperser, or the dispersion of the titanium oxide fine particles dispersed by the ultrasonic disperser is completed. It is mixed with the dispersion liquid of the charge generation substance thus prepared to prepare a coating liquid.

The layer constitution of the photoreceptor of the present invention is not particularly limited. When the present invention is applied to a negatively charged photoreceptor, a normal function-separated type photoreceptor, that is, a layer in which an undercoat layer (UCL), a charge generation layer (CGL), and a charge transport layer (CTL) are provided on an aluminum substrate in this order. Configuration can be taken.
In addition, when the present invention is applied to a positively charged photoreceptor, a laminated structure,
That is, a layer configuration in which an undercoat layer (UCL), a charge transport layer (CTL), and a charge generation layer (CGL) are provided in this order on an aluminum substrate can be employed. Further, it may have a single-layer structure, that is, a layer structure of an undercoat layer (UCL) and a photosensitive layer (containing a charge generating material and a charge transporting material). The containing layer, one of which may be a layer containing only ordinary pigments, may be used. Further, these photoconductors may be provided with a protective layer.

Known techniques can be used for the substrate, the undercoat layer (UCL), the charge transport layer (CTL), and the protective layer.

The substrate may be a metal plate such as aluminum or nickel, a metal drum, a plastic film on which aluminum, tin oxide, indium oxide, or the like is deposited, a plastic drum or paper coated with a conductive substance, a plastic film, a plastic drum, or the like. Although it can be used, an aluminum drum is preferable.

Examples of the binder resin used for the undercoat layer (UCL) include polycarbonate resin, polyester resin, polystyrene resin, acrylic resin, polyvinyl chloride resin, polyvinyl butyral resin, and polyamide resin. Can be. Further, a so-called ceramic obtained by condensing a hydroxide of a metal such as zirconia, titanium, or silane may be used. The thickness of the undercoat layer is preferably 0.1 to 5 μm, and 0.2 to 3 μm.
m is more preferred.

Examples of the charge transporting material used for the charge transporting layer (CTL) include triphenylamine derivatives, hydrazone compounds, styryl compounds, benzidine compounds and butadiene compounds, and any one can be selected. Representative charge transport materials are listed below.

1. Triarylamine compounds

[0031]

Embedded image

2. Hydrazone compounds

[0033]

Embedded image

3. Stilbene compounds

[0035]

Embedded image

4. Benzidine compounds

[0037]

Embedded image

5. Butadiene compounds

[0039]

Embedded image

6. Other compounds

[0041]

Embedded image

Examples of the binder resin used for the charge transport layer (CTL) include a polycarbonate resin, a polyester resin, a polystyrene resin, an acrylic resin, a polyvinyl chloride resin, a polybutyral resin, and a polyamide resin.

The mixing ratio of the charge transporting material and the binder resin in the charge transporting layer is preferably from 3: 1 to 1: 3 by mass.
The charge transport layer preferably has a thickness of 5 to 50 μm.
-40 μm is more preferred.

As the protective layer, ordinary organic polymers such as polycarbonate and polyester, and inorganic polymers having a polysiloxane bond can be used. Further, the protective layer may contain fine particles as necessary. The thickness of the protective layer is preferably from 0.1 to 10 μm, more preferably from 0.2 to 7 μm.

[0045]

EXAMPLES The present invention will be described below in more detail with reference to examples, but embodiments of the present invention are not limited thereto.

<Preparation of Coating Solution 1 for CGL> 2 parts of Y-type titanyl phthalocyanine, 1 part of polyvinyl butyral resin (Eslec BMS, manufactured by Sekisui Chemical Co., Ltd.), 70 parts of t-butyl acetate, 4-methoxy-4-methylpentane Non 30
Part was mixed and dispersed by a sand grinder, and the titanium oxide fine particles (anatase type,
TAF1500-S33, manufactured by Fuji Titanium Co., Ltd., particle size is 20 to 30 nm, propyltrimethoxysilane treatment 2
0% by mass) and dispersed by an ultrasonic dispersing machine.
Application liquid 1 "was prepared.

<Preparation of Coating Solution 2 for CGL> Instead of titanium oxide fine particles (anatase type, TAF1500-S33), hydrophobic surface-treated titanium oxide fine particles (anatase type, TAF1500-S32, manufactured by Fuji Titanium Co., Ltd.) A “CGL coating liquid 2” was prepared in the same manner as the CGL coating liquid 1 except that 2 parts of a particle diameter of 20 to 30 nm and isobutyltrimethoxysilane treatment (20% by mass) were used.

<Preparation of CGL coating liquid 3>"CGL coating liquid 3" was prepared in the same manner as CGL coating liquid 1 except that titanium oxide fine particles (anatase type, TAF1500-S33) were changed from 2 parts to 4 parts. Was prepared.

<Preparation of Coating Solution 4 for CGL> Fine particles of titanium oxide (anatase type, TAF15
"CGL coating liquid 4" was prepared in the same manner as CGL coating liquid 1 except that 00-S33) was excluded.

<Preparation of Coating Solution 5 for CGL> Titanium oxide fine particles (TAF1500-S33) were mixed with silica sol (IPA).
-ST, manufactured by Nissan Chemical Industries, Ltd., particle size 10 to 20 nm, isopropanol solvent, solid content concentration 30% by mass) Except that it was changed to 6.7 parts (solid content conversion 2 parts), in the same manner as coating liquid 1 for CGL. "Coating solution 5 for CGL" was prepared.

<Preparation of CGL Coating Solution 6> [CGL] was prepared in the same manner as the CGL coating solution 1 except that polyvinyl butyral resin (S-lec BMS) was further increased by 2 parts in place of the titanium oxide fine particles (TAF1500-S33). Application liquid 6 "was prepared.

Example 1 A polyamide resin (CM80) was placed on an aluminum drum substrate.
00, manufactured by Toray Industries, Inc.) was applied by dip coating to form an undercoat layer (UCL) having a dry film thickness of 0.4 μm. Next, the “coating liquid 1 for CGL” was dip-coated on the undercoat layer to form a charge generation layer having a dry film thickness of 0.8 μm. Next, a charge transport coating solution obtained by dissolving 0.65 part of the charge transport material (S-1) and 1 part of a polycarbonate resin (Iupilon Z-200, manufactured by Mitsubishi Gas Chemical Co., Ltd.) in 7.5 parts of dichloroethane was used. Dip coating on
The resultant was dried at 100 ° C. for 70 minutes to form a charge transport layer having a dry film thickness of 24 μm, thereby producing “Photoconductor 1”.

Example 2 Instead of the CGL coating liquid 1, the above-mentioned "CGL coating liquid 2" was used.
"Photoconductor 2" was prepared in the same manner as in Example 1 except that was used.

Example 3 Instead of the CGL coating liquid 1, the above-mentioned "CGL coating liquid 3" was used.
"Photoreceptor 3" was prepared in the same manner as in Example 1 except that was used.

Example 4 Instead of the CGL coating liquid 1, the above-mentioned "CGL coating liquid 4" was used.
"Photoreceptor 4" was prepared in the same manner as in Example 1 except that was used.

Example 5 Instead of the CGL coating liquid 1, the above-mentioned "CGL coating liquid 5" was used.
"Photoconductor 5" was prepared in the same manner as in Example 1 except that the photoreceptor was used.

Example 6 Instead of the CGL coating liquid 1, the above-mentioned "CGL coating liquid 6" was used.
"Photoconductor 6" was prepared in the same manner as in Example 1 except that was used.

<Evaluation 1> The above “Photoconductors 1 to 6” were Kon.
ika7150 (manufactured by Konica Corporation) was mounted on a remodeled digital copier, and charged, exposed, and neutralized in a high-temperature, high-humidity (30 ° C., 80% RH) environment in which an increase in the potential of the exposed portion is expected to be large. And the difference (ΔVL) in the exposed portion potential at the start and immediately before the end of 30,000 repetitions was measured. The measurement results are shown in Table 1 below.

<Evaluation 2> The above “Photoconductors 1 to 6” were replaced with Kon.
ica7150 (manufactured by Konica Corporation) modified digital copier, and in a high-temperature and high-humidity (30 ° C., 80% RH) environment where black spot-like image defects are expected to occur most severely, a grid voltage of −1000 V and -800V for developing bias
Of black spot-like image defects when printing was set to, and the solid black density after continuous printing of 1,000 sheets were measured with a Macbeth reflection densitometer RD-918 (manufactured by Macbeth Corporation). did. The results are shown in Table 1 below.

Evaluation criteria ○ No black-spotted image defects occurred △ Little black-spotted image defects occurred Practical problem × Many black-spotted image defects Practical problem

[0061]

[Table 1]

As shown in Table 1 above, the photoreceptors 1 to 3 of the embodiment of the present invention have a small potential increase (ΔVL) due to repetition, and have no black-spotted image defects. It was effective in preventing defects. On the other hand, the photoreceptor 4 containing no titanium oxide fine particles had remarkable occurrence of black spot-like image defects. The photoreceptor 5 using silica sol instead of titanium oxide slightly improved black spot-like image defects, but showed an increase in ΔVL, and the solid black density gradually decreased in continuous printing, which was a practical problem. In the photoreceptor 6 containing no titanium oxide fine particles and increasing the amount of binder resin, black spot-like image defects were somewhat improved, but a large increase in ΔVL was observed, and the solid black density was remarkably lowered in continuous printing. there were.

Example 7 1.0 g of polyvinyl butyral resin (Eslec BMS, manufactured by Sekisui Chemical Co., Ltd.) and charge transport material (S-3)
A coating solution for an undercoat layer in which 0 g was dissolved in a mixture of 85 mL of methyl ethyl ketone and 15 mL of cyclohexanone was applied to a PET base on which aluminum was vapor-deposited by a wire bar to form an undercoat layer having a dry film thickness of 0.2 μm.

Next, a coating solution for a charge transport layer obtained by dissolving 15 g of a polycarbonate resin (Bisphenol Z200, manufactured by Mitsubishi Gas Chemical Co., Ltd.) and 10 g of a charge transport material (S-3) in 100 mL of 1,2-dichloroethane was used with a doctor blade. Coated on the undercoat layer, dry film thickness 12μ
m of the charge transport layer was formed.

Next, 2 g of B-type titanyl phthalocyanine was added to a solution obtained by dissolving 5 g of a polycarbonate resin (bisphenol Z300, manufactured by Mitsubishi Gas Chemical Co., Ltd.) and 8 g of the charge transport material (S-3) in 150 mL of dioxolane, and dispersed by a sand grinder. . 10 g of a polycarbonate resin (bisphenol Z300) was further added and dissolved in this dispersion, and then titanium oxide fine particles (anatase type, T
AF1500-S22, 4 g of isobutyltrimethoxysilane treated 4 g), and a coating liquid for a charge transport layer dispersed by an ultrasonic disperser was applied on the charge transport layer by a doctor blade, and the charge having a dry film thickness of 6 μm was applied. Example 8 A Photosensitive Body 7 was Prepared by Forming a Generating Layer Example 8 Titanium Oxide Fine Particles Treated Hydrophobicly Instead of Titanium Oxide Fine Particles (Anatase Type, TAF1500-S22) in the Charge Generating Layer Solution of Example 7 (Rutile type, TTO-51,
"Photoreceptor 8" was prepared in the same manner as in Example 7, except that a particle diameter of 20 to 30 nm, manufactured by Ishihara Sangyo Co., Ltd., and 10% by mass of isobutyltrimethoxysilane treatment were used.

Example 9 A "photoreceptor 9" was prepared in the same manner as in Example 7, except that the titanium oxide fine particles (anatase type, TAF1500-S22) in the charge generation layer solution were removed.

<Evaluation 3> The above “Photoconductors 7 to 9” were analyzed using a paper analyzer EPA8100 (manufactured by Kawaguchi Electric Co., Ltd.).
The following tests were performed using

Under the condition of +80 μA, corona charging was performed for 5 seconds, and the received potential Va (V) immediately after charging and the initial potential Vi (V) after standing for 5 seconds were obtained.
Exposure is performed for 10 seconds at x, the exposure amount E1 / 2 (Lux) at which the initial potential is 1/2 Vi, and the initial potential is 600 V to 1
Exposure amount E600 / 100 required to lower to 00V
(Lux) and the residual potential Vr (V) after exposure were determined.
The dark decay rate DD is a measure of the decrease in surface charge in a dark place.
= (Va-Vi) Va% was determined. The measurement results are shown in Table 2 below.

[0069]

[Table 2]

The positively charged photoreceptor containing the titanium oxide fine particles having a hydrophobic surface treatment according to the present invention has a higher sensitivity (E600 / 10) than the photoreceptor containing no titanium oxide fine particles.
0) and the residual potential (Vr) is also small. As a result, it was found that the titanium oxide fine particles functioned as an N-type semiconductor.

[0071]

As has been demonstrated in the examples, the present invention can prevent the injection of positive charges from defects in an aluminum base by containing hydrophobic oxide-treated titanium oxide fine particles in the charge generation layer. As a result, an electrophotographic photoreceptor suitable for digital copying machines and printers having no black spot-like image defects, high sensitivity and low residual potential could be provided.

Claims (4)

[Claims] 1. An electrophotographic photoreceptor, wherein the charge generation layer contains titanium oxide fine particles having a hydrophobic surface treatment. 2. The electrophotographic photoreceptor according to claim 1, wherein the titanium oxide fine particles are surface-treated with a compound containing silicon. 3. The electrophotographic photoreceptor according to claim 1, wherein the charge generating substance is a phthalocyanine pigment. 4. The electrophotographic photoreceptor according to claim 1, wherein the titanium oxide fine particles are of an anatase type.