JPS6033261B2 - electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic photoreceptor, and particularly to an electrophotographic photoreceptor having a photosensitive layer comprising a photoconductive material made of photoconductive zinc oxide dispersed in a binder resin.

Generally, the photosensitive layer of an electrophotographic photoreceptor used in electrophotography is composed of various photoconductive materials.

These photoconductive materials include zinc oxide, cadmium sulfide,
Although selenium and other materials are known, a photoconductive material made of zinc oxide is preferred because it is easy to manufacture, low cost, and is a light element substance that is harmful to living organisms including humans. The powder of this photoconductive zinc oxide is dispersed in a binder resin to constitute a photosensitive layer of an electrophotographic photoreceptor. However, since the sensitivity of photoconductive zinc oxide alone is in the ultraviolet region, in practice it is necessary to bring rose bengal or other sensitizer into contact with the surface of the zinc oxide powder particles to perform so-called spectral sensitization. .
For this reason, the photosensitive layer of an electrophotographic photoreceptor is usually constructed by dispersing zinc oxide powder and a sensitizer together in a binder resin. However, the photoconductivity of zinc oxide is 0.
3,0;,0 It is caused by the action of active species composed of oxygen atoms such as summer, and at the 8th point, the active species are adsorbed to zinc oxide particles, which causes electrons in the conduction band of zinc oxide to Because the zinc oxide is trapped, it has a high resistance, and when it is irradiated with light, the active species are desorbed and the electrical conductivity increases.In the actual electrophotographic process, the active species are absorbed into the photosensitive layer This is caused by the discharge of the charger during the charging process.

Therefore, in a photosensitive layer constructed by directly dispersing zinc oxide powder and a sensitizer in a binder resin, the active species involved in the photoconductivity of the zinc oxide particles cause the zinc oxide particles to exhibit the photoconductivity. It not only acts on the sensitizer and binder resin directly, but also acts directly on the sensitizer and binder resin, and since this active species has a very large oxidizing power, the sensitizer and binder resin are rapidly oxidized and deteriorated. As a result, when an electrophotographic photoreceptor having such a photosensitive layer is used to form a copy image in an electronic copying machine, its service life is short, and the maximum number of copies that can be made is about 1000 at most. In addition, a photosensitive layer made of a photoconductive material made of zinc oxide has the disadvantage that the recovery of fat resistance is slow when the light irradiation is stopped and the food is returned to the platter.

Although the electrophotographic photoreceptor having such a photosensitive layer is used in an atmosphere rich in active species in a copying machine as described above, it has a large memory effect, and once exposed to light, the entire photosensitive layer disappears. It takes a long time for the surface to recover to a state where it exhibits sufficient clear resistance. Therefore, it is necessary to wait a certain amount of time before a photoreceptor that has undergone one electrophotographic process is subjected to the next process, making it impossible to perform continuous copying at high speed, and making it difficult to increase the image density of copied images. I can't. Furthermore, since the zinc oxide powder itself is hydrophilic, its dispersibility in the binder resin, which is usually made of lipophilic resin, is generally poor, and the properties of the photosensitive layer tend to be non-uniform, and there are also various restrictions in the production of photoreceptors. receive.

In order to eliminate or reduce the inherent or practical disadvantages of zinc oxide photoconductive materials as described above, it may be effective to coat the surfaces of photoconductive zinc oxide powder particles with a coating substance. , in fact, special public service No. 43-759
4, Special Publication No. 43-22910, Tsubaki-batsu 1394-1983
Publication No. 28 and the like describes coating zinc oxide powder particles to improve their properties.

However, although these conventional coatings may have the effect of alleviating some of the above-mentioned drawbacks, they are far from eliminating the above-mentioned drawbacks, and even if they can be put to practical use, they are limited. It is only possible within a certain range, and the effects are not particularly noteworthy. In view of the above circumstances, the inventors have
The present invention was completed as a result of extensive research into coated zinc oxide, as well as investigation into the causes of failure to obtain good results in conventional techniques.

An object of the present invention is to have a photosensitive layer in which a photoconductive material made of zinc oxide powder is dispersed in a binder resin, and furthermore, the deterioration of the sensitizer used in the photoconductive material is small, and therefore, the photoconductive material can be used for a very long time. An object of the present invention is to provide an electrophotographic photoreceptor that has a long service life and can be copied an extremely large number of times.

Another object of the present invention is to provide an electrophotographic photoreceptor that has almost no memory effect and is therefore capable of high-speed continuous copying and is capable of forming high-quality copied images.

Still another object of the present invention is to provide an electrophotographic photoreceptor in which a photoconductive material is stable and has excellent dispersibility with respect to a binder resin constituting a photosensitive layer, and therefore has uniform characteristics.

In order to achieve the above objects, in the present invention,
A photoconductive material is a product in which a capsule wall film made of silicone resin with a three-dimensional network structure is formed on the surface of photoconductive zinc oxide powder particles, and a sensitizer for zinc oxide is encapsulated in this capsule wall film. An electrophotographic photoreceptor is constructed by dispersing it in a binder resin and forming a photosensitive layer on a conductive support.

By "capsule wall membrane" is meant here a grown coating consisting of a polymer.

It is desirable that the capsule wall film covers substantially the entire surface of the zinc oxide unit particle, but if it covers the exposed surface of an aggregate of multiple unit particles, or It is also effective when covering a part or a part of the exposed surface of the aggregate. Further, the sensitizer may be encapsulated between the inner surface of the capsule wall and the surface of the zinc oxide particles, or may be encapsulated by being contained within the membrane of the capsule wall. The thickness of the capsule wall membrane is 5 angstroms to 1 micron, preferably 10 to 1000 angstroms, more preferably 20 to 100 angstroms. The photoconductive material used in the present invention can be manufactured as follows.

That is, by preparing a solution of a sensitizer, adding photoconductive zinc oxide powder to the solution, and evaporating the solvent, or drying it after furnace separation, the sensitizer is dissolved into zinc oxide particles. Make sensitized zinc oxide by depositing it on the surface. On the other hand, a solution of the material for the capsule wall membrane is prepared, and the sensitized zinc oxide powder is added thereto and dispersed. A capsule wall membrane consisting of a polymer with a similar structure is formed. The capsule wall membrane materials used here include silicone resins and substances that are polymerized to produce silicone resins. The film forming means is as follows.

{1} When the material is silicone resin, in a state where sensitized zinc oxide is dispersed in the solution of the material,
A non-solvent that is freely miscible with the solvent of the solution but does not dissolve the material is substantially added to the dispersion to reduce the solubility of the material in the liquid phase of the dispersion. A method in which a certain silicone resin is deposited on the surface of zinc oxide particles to form a film.

This method is called the coacervation method, and the film formed here is the capsule wall film as it is. "Substantially adding a non-solvent" means not only actually adding a non-solvent, but also adding a non-solvent. This refers to a concept that includes increasing the concentration of non-solvent by excluding only the solvent contained in the liquid phase from the system. ■ When the material substance is a substance that undergoes a polymerization reaction to produce a silicone resin [a' In a state where sensitized zinc oxide is dispersed in a solution of the material substance, the material substance is deposited by the coacervation method to form a film. How to form.

The coating produced by this method is then transformed into a capsule wall membrane by polymerization.

Examples of this polymerization method include a method in which a dispersion is heated with or without the addition of a polymerization catalyst or initiator, or a method in which zinc oxide powder on which a film has been formed is taken out and heated.
'A method in which sensitized zinc oxide is dispersed in a solution of a material, and a monomer or prepolymer, which is the material, is polymerized and deposited on the surface of zinc oxide particles to form a film made of the polymer. .

This method is called the in-situ method, in which the zinc oxide particles serve as a core and the concentration of the polymerizable material on the surface increases, causing polymerization.

To promote film formation in this method, a non-solvent that is freely miscible with the solvent of the solution but does not dissolve the solute is substantially added to the dispersion, and the dispersion is heated to reflux to drive the polymerization reaction. Alternatively, it is preferable to vigorously weigh the dispersion using a homogenizer or the like to promote the growth of the film. A polymerization catalyst and an initiator may be added to the dispersion as necessary. The coating formed by this method is a capsule wall membrane as it is. The photoconductive material used in the present invention produced as described above has a sensitizer encapsulated between the surface of the zinc oxide particles and the inner surface of the formed capsule wall film.

However, in the present invention, a sensitizer may be contained in the membrane of the capsule wall, and such a photoconductive material is prepared by dissolving the sensitizer in a solution of the material of the capsule wall, It can be manufactured by dispersing photoconductive zinc oxide powder therein and forming a film by the above-mentioned method. That is, the sensitizer is brought into the film at this point as the film-forming substance is deposited. However, if the sensitizer has a large depositing property in the solution due to a large affinity for the surface of the zinc oxide particles, or if the non-solvent is used in a process in which substantial addition of the non-solvent is carried out, the sensitizer is If it is insoluble, the sensitizer may be deposited simultaneously with or prior to the deposition of the film-forming substance. In this way, the photoconductive material used in the present invention having a capsule wall made of silicone resin is manufactured. Since this capsule wall has a three-dimensional structure, it has excellent mechanical strength and high solvent resistance. Therefore, in the process of forming a photosensitive layer, even when the capsule wall film is added to and dispersed in a binder resin solution, the capsule wall film does not elute and is stable, resulting in uniform characteristics without uneven sensitivity.

If the polymerization in the above-mentioned manufacturing method involves a crosslinking reaction, the capsule wall membrane will of course become such a three-dimensional silk-like structure. However, if this is not the case, it is sufficient to crosslink the polymer constituting the capsule wall membrane. For this purpose, if the polymer undergoes a condensation reaction, it may be condensed by heating, or by using a crosslinking agent. It is sufficient if it is cross-linked. As the photoconductive material used in the present invention, photoconductive zinc oxide powder produced by any method can be used, but those having a particle size of 0.1 to 1 micron are practically suitable.

In addition, in the photoconductive material used in the present invention, as the silicone resin constituting the capsule wall film, in addition to three-dimensional polymers, linear polymers such as silicone oil and silicone rubber, and tertiary silicone resins modified with other resin components are used. Any material having an original network structure can be used.

Therefore, in addition to these resins, the materials used include methylated silanols, when polymerization reactions occur.
monomers such as methylated siloxanes, reactive atoms or atomic groups such as 1, -OH, -X bonded to silicon atoms;
(X represents a halogen atom), -OCQCH3, -O
Prepolymers and polymers having R (R represents an alkyl group), one CH=CH2, etc. are used. When using a prepolymer or polymer having a reactive atom or atomic group, it is necessary to carry out crosslinking and crosslinking by the presence of a catalyst or an initiator or by heating, but the operation is easy; In particular, when using prepolymers or polymers having hydroxyl groups bonded to silicon atoms, that is, silanol groups, other resin components such as phenol resins, acrylic resins, alkyd resins, polyester resins, and melamine resins or their monomers are added to the polymerization system. A capsule wall film made of a modified silicone resin can be formed by coexisting with the silicone resin. In addition, when the material has a polysiloxane structure, it is possible to form a three-dimensional silk-like structure using a catalyst and a compound having a silanol group or a hydroxyl group bonded to a carbon atom, or a crosslinking agent such as an alkyl titanate. be. In the present invention, any sensitizer for zinc oxide can be used, and examples include xanthene dyes such as fluorescein, erythrosine, phloxine, rose bengal, and rhodamine blue, promocresol green, and crystal violet. , triphenylmethane pigments such as malachite green, acridine pigments such as acridine orange, cyanine pigments such as merocyanine, indoaniline pigments, anthraquinone pigments such as anthraquinone violet, indigo pigments, azo pigments, and others. be able to.

Among these, xanthene dyes or triphenylmethane dyes, such as acid or lactone dyes, are particularly preferred because they have high solubility and are strongly adsorbed on the surface of zinc oxide particles. The photoconductive material used in the present invention is as described above, and since the capsule wall film formed on the surface of the zinc oxide powder particles is made of silicone resin, the capsule wall film is very strongly bonded to zinc oxide. It becomes fixed to the particle.

In other words, active sites due to hydroxyl groups of adsorbed water exist on the surface of zinc oxide particles, but oxygen atoms in the primary mirror of silicone resin, or reactive atoms or atomic groups contained in silicone resin, especially hydroxyl groups and halogens, exist on the surface of zinc oxide particles. Atoms, methoxy groups, etc. have a strong chemical affinity for the active sites, or a physical affinity acts to firmly fix the silicone resin. According to the above-mentioned film forming method, the affinity of the active points is fully and effectively utilized, and the film becomes uniform without any missing parts. However, even if there is a missing portion, the effects of the present invention can be obtained to a certain extent. Furthermore, the capsule wall made of silicone resin is strong and has excellent heat resistance and moisture resistance. According to the above-mentioned photoconductor having such an excellent capsule wall film, the following additional benefits can be obtained. tl) Since the sensitizer is encapsulated and retained by the capsule wall membrane, it is possible to protect the sensitizer, which is vulnerable to the effects of oxidation, moisture, light, and heat, and prevent its deterioration.
Therefore, by constructing a photosensitive layer using the photoconductive material, it is possible to provide an electrophotographic photoreceptor that has an extremely long service life and can be copied a large number of times. Further, since the sensitizer is held in close contact with the surface of the zinc oxide particles, a large sensitizing effect is exhibited. {2) The photosensitive layer made of the above-mentioned photoconductive material takes an extremely short time to recover its 8-tone resistance, so there is almost no memory effect, and the image density is always sufficiently high and gradation reproducibility is maintained. An electrophotographic photoreceptor capable of forming excellent copied images can be provided.

The reason for this is not clear, but it may be that the sensitizer encapsulated in the capsule wall has the same function as the active species consisting of oxygen atoms that are involved in the photoconductivity of zinc oxide, or that it One of the reasons for this is that a sufficient amount of active species are trapped within the capsule wall membrane to give a positive effect, and even when they are desorbed by light irradiation, these active species are retained very close to the surface of the zinc oxide particles. It is thought that it is a department. fact,
Active species generated by corona discharge inside the copying machine are
The fact that the photoconductive material does not contribute to recovery of the greasy resistance of the photosensitive layer is also confirmed from the fact that no memory effect appears even when these active species are actively eliminated by creating artificial air around the corona discharger. be done. Therefore, by eliminating oxidizing active species in this way, it is possible to prevent oxidative deterioration of the sensitizer and binder resin, and from this point of view as well, the life of the photosensitive layer can be extended. Furthermore, since there is no memory effect, high-speed continuous copying is of course possible.
'3l Zinc oxide particles are hydrophilic, but the silicone resin constituting the capsule wall film, which is the outer layer of the photoconductive material used in the present invention, is lipophilic, so usually acrylic resin, alkyd resin, melamine resin, eboxy resin The photoconductive material has high dispersibility with respect to the binder resin made of lipophilic resin such as, and can be easily dispersed in the binder resin solution. Moreover, since the silicone resin has a three-dimensional silk-like structure, it can be uniformly dispersed. A stable coating solution for forming a photosensitive layer can be obtained, and therefore a photosensitive layer with uniform characteristics can be formed.

In particular, in a silicone resin primary mirror, the oxygen atoms located on one side of the zigzag structure are deposited on the zinc oxide particles so that they face inward, so the lipophilic groups on the other side across the silicon atoms, e.g. The methyl groups and the like are oriented outward, and as a result, this effect is fully obtained. [4}
Silicone resin has excellent heat resistance and moisture resistance, so
It does not deteriorate due to heat or moisture, and is electrically insulating, so even if the photoconductive materials are brought into contact with each other in the photosensitive layer, no current-carrying path is formed, and no current-carrying phenomenon occurs when the photosensitive layer is charged. It is possible to prevent deterioration of the photosensitive layer due to the formation of a photosensitive layer.

[5] A photoconductive material having a capsule wall film made of a modified silicone resin can further provide properties depending on the type of the modifying substance, such as improving solvent resistance, and improving electrophotographic photoreceptor properties. Extremely preferred in terms of manufacturing.

Examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these.

Example 1 0.59% of the free acid Rose Bengal obtained by acid decomposition of ordinary Rose Bengal disodium salt was dissolved in 100% of methyl ethyl ketone, and 100% of photoconductive zinc oxide powder was added to this solution. After dispersing in a ball mill for 1 hour, methyl ethyl ketone was evaporated to obtain a sensitized zinc oxide powder coated with rose bengal.

After dispersing 100% of this sensitized zinc oxide in a mixed solvent of 100% of ethyl acetate, which is a solvent for the resin described below, and 100% of ``Aisopa Hichichi'' (manufactured by Esso Chemical Co., Ltd.), which is also a non-solvent. , and silicone resin "KR214" (
(manufactured by Shin-Etsu Chemical Co., Ltd.) was added thereto, and dispersion was carried out for 1 hour to obtain a dispersion in which the resin was completely dissolved.

By putting this dispersion in a rotary evaporator and gradually evaporating the ethyl acetate, the resin is deposited on the surface of the dust-sensitized zinc oxide powder particles to form a capsule wall film, and a crosslinking catalyst is added to the dispersion. Zinc octylate 0.
The mixture was heat-treated at 150° C. for 3 hours to form a capsule wall film consisting of a three-dimensional silk-like structure, and the mold was separated in an oven and dried to produce a photoconductive material.

The photoconductive material thus obtained was 100% of a 50% solution of acrylic resin "Dianal HR-112" (manufactured by Mitsubishi Rayon Co., Ltd.) and 40% of a butylated melamine resin "Super Beckamine J-820" (manufactured by Dainippon Ink Co., Ltd.) of 50%. %solution
8'Toluene
100 [(However, the solvent for the acrylic resin solution and the butylated melamine resin solution is n-
It is a mixed solvent of butanol and xylene.

) The above substances were mixed and dispersed in a ball mill for 1 hour to prepare a coating solution for forming a photosensitive layer.

This coating solution was applied onto a support consisting of a polyester film laminated with an aluminum film and a barrier layer formed thereon, and dried to form a coating film with a strength of 30 min/strength. An electrophotographic photoreceptor was produced by heat treatment at ℃ for 1 hour. This electrophotographic photoreceptor was used in an electronic copying machine "UBIX 2000R" (manufactured by Konishiroku Photo Industry Co., Ltd.).
When a high-speed continuous copying test was carried out by attaching the printer to a computer, even after over 10,000 copies, a copied image was obtained that was clear, had high resolution, and had high gradation reproducibility.

Comparative Example 1 A coating solution for forming a photosensitive layer was prepared using 100% of the same sensitized zinc oxide powder as in Example 1 in place of the photoconductive material of Example 1, and the other conditions were the same as in Example 1. When a photoreceptor was manufactured and a similar copying test was conducted, a memory effect was observed from the beginning of copying, and by the time the number of copies exceeded 1,000, the copied image became unclear and the blind image power decreased. The gradation reproducibility was poor, and the image density was insufficient and uneven.

Comparative Example 2 A photoconductive material of the present invention was produced in the same manner as in Example 1 except that no crosslinking treatment was performed, and an electrophotographic photoreceptor was produced in the same manner as in Example 1 and a copying test was conducted. A decrease in image density began to be seen after 8,000 times.

Example 2 100 g of the same sensitized zinc oxide powder as in Example 1 was mixed with alkyd-modified silicone resin "KR-206" (manufactured by Shin-Etsu Chemical Co., Ltd.) 2.2 g and its curing agent "D-14" (
Shin-Etsu Chemical Co., Ltd.) xylene 200' with 0.6 m
In addition, the resin and curing agent were dispersed in a ball mill for 2 hours to obtain a dispersion in which the resin and curing agent were dissolved. 400 (manufactured by Esso Petrochemicals) dropwise over a period of 2 hours to deposit the resin and curing agent on the zinc oxide powder particles;
This dispersion was heated as it was at a temperature of 120°C for 3 hours to harden the resin, and then the solid material was washed in an 8U oven with toluene 5 times, and further dried at a temperature of 120°C for 3 hours under vacuum, A photoconductive material was produced.

Photoconductive material thus obtained 100% silicone resin “KR-214” (70% solution)
15th evening acrylic resin “ST-10”
(Manufactured by Soken Chemical Co., Ltd.) (50% solution)
20 Taethyl Cellulose "STD-45" (manufactured by Dow Chemical Company) (7.5% solution) 60 Tatoluene 100 or more substances were mixed and dispersed in a ball mill for 1 hour to prepare a coating solution for forming a photosensitive layer.

The above coating solution was applied onto a support consisting of a polyester film laminated with an aluminum film and a 2 micron thick casein subbing layer formed thereon, and dried to form a coating film with a strength of 30 min/strength. An electrophotographic photoreceptor was produced. Example 3 A photoconductive zinc oxide powder was added to a solution of 0.5 ml of the sensitizer erythrosine dissolved in 300 ml of methyl ethyl ketone.
After adding 0.00 min and dispersing in a ball mill for 1 hour, alkyd modified silicone resin "KR206" 2.2
In addition to evening and non-solvent "Isopa one day" 200 shouts, 2 more
The dispersion thus obtained was transferred to a rotary evaporator and flooded under reduced pressure to evaporate the methyl ethyl ketone and deposit the resin.

Cobalt octylate (0.1 kg) was added to this dispersion, heat-treated at a temperature of 130 q○ for 1 hour, and after furnace separation, it was washed 5 times with toluene, and further dried under vacuum at a temperature of 100 oo for 3 hours, and then sensitized. A photoconductive material having a capsule wall film containing the agent was prepared. Using this photoconductive material, an electrophotographic photoreceptor was produced in the same manner as in Example 2.

Example 4 Monomethylsilanol 0 at 300 points of “Iso/゜One Day”
．． In this solution, the same sensitized zinc oxide powder 1 as in Example 1 was dissolved.
The mixture was dispersed in a ball mill for 1 hour and heated at 150° C. for 5 hours while shaking, and the solid material was dried in an oven to produce a photoconductive material.

An electrophotographic photoreceptor was produced in the same manner as in Example 2 using this light-guiding silkworm material.

The electrophotographic photoreceptors of Examples 2 to 4 were subjected to the same copying test as in Example 1, and as a result, all of them showed clear and excellent copied images even after being copied over 10,000 times. was gotten.

Claims (1)

[Claims] 1. A photoconductive material having a capsule wall film made of a silicone resin with a three-dimensional network structure in which a sensitizer for the zinc oxide is encapsulated on the surface of photoconductive zinc oxide powder particles is contained in a binder resin. An electrophotographic photoreceptor comprising a dispersed photosensitive layer. 2. The electrophotographic photoreceptor according to claim 1, wherein the silicone resin is a modified silicone resin. 3. The electrophotographic photoreceptor according to claim 1 or 2, wherein a sensitizer is encapsulated between the inner surface of the capsule wall film and the surface of the zinc oxide powder particles. 4. The electrophotographic photoreceptor according to claim 1 or 2, wherein the sensitizer is contained in the membrane of the capsule wall. 5. The electrophotographic photoreceptor according to claim 1, 2, 3, or 4, wherein the sensitizer is an acid or a compound having a lactone structure.