JPS6348053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a photoconductive composition, and more particularly to a method for producing a photoconductive composition comprising photoconductive zinc oxide powder.

In general, an electrophotographic photoreceptor using photoconductive zinc oxide powder has a photosensitive layer formed by dispersing the zinc oxide powder in a binder resin on a support made of metal, paper, or other material. obtained by
Specifically, the photosensitive layer is formed by adding a sensitizing dye such as rose bengal to the zinc oxide powder and dispersing it in a binder resin solution, and coating this dispersion on the support and drying it. be done.

An electrophotographic photoreceptor having a photosensitive layer containing such zinc oxide powder has the advantage that photoconductive zinc oxide is relatively cheap and easily available, and is less toxic, but has the major disadvantage of short printing durability. have Furthermore, this electrophotographic photoreceptor has the disadvantage of a large memory effect, and for this reason, conventionally, the electrophotographic photoreceptor is subjected to an electrophotographic process in an ozone-containing atmosphere in order to suppress the memory effect. Use in such an atmosphere accelerates oxidative deterioration of the sensitizing dye and binder resin forming the photosensitive layer, leading to a decrease in printing durability.

Under these circumstances, attempts have been made to make various improvements to photoconductive compositions made of zinc oxide powder in order to provide electrophotographic photoreceptors with high printing durability. For example, Special Publication No. 43-7594,
No. 43-22910, JP-A No. 52-139428, etc. propose a method of sensitizing photoconductive zinc oxide with a sensitizing dye and coating it with a resin. However, according to these methods, although it is possible to expect an improvement in the printing durability of the electrophotographic photoreceptor formed from the resulting photoconductive composition, the intended purpose cannot be fully achieved due to insufficient coating. cannot be achieved. In addition, sufficient dispersibility in the binder resin solution may not be obtained, or the viscosity of the dispersion may become high, and as a result, the coating properties of the dispersion are poor and the resulting electrophotographic photoreceptor has poor gradation. This results in poor reproducibility and resolution.

An object of the present invention is to provide a method for producing a photoconductive composition capable of forming an electrophotographic photoreceptor having excellent printing durability.

Another object of the present invention is to provide a method for producing a photoconductive composition capable of forming an electrophotographic photoreceptor with excellent gradation reproducibility and resolution.

Still another object of the present invention is to provide a method for producing a photoconductive composition having excellent dispersibility in a binder resin solution for forming a photosensitive layer.

Yet another object of the present invention is to provide a method for producing a photoconductive composition capable of forming an electrophotographic photoreceptor without memory effects.

As a result of research, the present inventor has found that the above-mentioned objectives are achieved by applying epoxy resin or urethane resin capsules made of a polymeric substance to the surface of photoconductive zinc oxide powder particles by either a coacervation method or an in-situ polymerization method. By producing a photoconductive composition by a method of forming a wall film and adsorbing a sensitizing dye on the surface of the zinc oxide powder particles before or simultaneously with the formation of the capsule wall film. The present invention has been completed by discovering that this can be achieved.

In the present invention, the photoconductive zinc oxide powder produced by any method can be used, but when forming an electrophotographic photoreceptor, a high charging potential and a sufficient amount of charging can be obtained. , Zinc oxide powder with low dark decay, high sensitivity, and small memory effect is preferable, such as "SAZEX-
4000'' [manufactured by Sakai Chemical Co., Ltd.] is known as a good photoconductive zinc oxide powder. In addition, the particle size is 0.1~
A size of 1 micron is preferred, and a size that is too small or too large is likely to cause problems.

Any sensitizing dye can be used as the sensitizing dye to be adsorbed onto the surface of the zinc oxide powder particles, examples of which include xanthene dyes such as fluorescein, erythrosine, phloxine, rose bengal, and rhodamine blue, and promocresol. Examples include triphenylmethane dyes such as green, crystal violet, and malachite green, acridine dyes such as acridine orange, cyanine dyes such as merocyanine, indigo dyes, azo dyes, and others.

Any method can be used to adsorb such a sensitizing dye onto the surface of the zinc oxide powder particles described above prior to the formation of the capsule wall film, such as by dissolving the sensitizing dye in a solvent. A method of adding zinc oxide powder to the resulting solution, dispersing it with a ball mill, etc., and then filtering off the solid matter and drying it.
Alternatively, a method can be used in which a solution of a sensitizing dye in which zinc oxide powder is added and dispersed is directly dried. The solvent for the solution of the sensitizing dye may be any solvent as long as it can dissolve the sensitizing dye used, and examples thereof include lower alcohols such as methanol, ethanol, and propanol, and ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone. , esters, etc. are preferred, and among these, ketones are particularly preferred.

Here, the adsorption amount of sensitizing dye is 100% of zinc oxide powder.
Practically, it is 0.01 g or more, preferably 0.1 to 1.0 g.

The sensitizing dye may be adsorbed onto the zinc oxide powder particles in advance as described above, but it may also be adsorbed at the same time as the capsule wall is formed, as will be described later.

In the present invention, a capsule wall film of epoxy resin or urethane resin made of a polymeric substance is formed on the surface of zinc oxide powder particles by a coacervation method or an in-situ polymerization method.
The material of the capsule wall may already be a polymeric substance when the capsule wall is formed, or it may be polymerized at the same time as the capsule wall is formed.

A method for forming a capsule wall film using a coacervation method and an in-situ polymerization method will be specifically described below.

Coacelvation method (1) Zinc oxide powder is added to the solution obtained by dissolving the material in a suitable solvent and dispersed using a colloid mill, ultrasonic dispersion, etc., and then the dispersion system is mixed with the solvent. However, a non-solvent that does not dissolve the material is added, and the material is deposited on the surface of the zinc oxide powder particles, thereby forming a capsule wall film. The zinc oxide powder on which the capsule wall film has been formed can be taken out by filtration.

(2) Zinc oxide powder is added to a solution obtained by dissolving the material in a mixed solvent with a non-solvent, similar to the solvent used for the material, and dispersed using a colloid mill, ultrasonic dispersion, etc., and then from this dispersion system. , by gradually removing the solvent, for example by distillation, and reducing the concentration of the solvent relative to the non-solvent in the liquid phase, the material is deposited on the surface of the zinc oxide powder particles, thereby forming the capsule wall. Forms a film.

(3) Zinc oxide powder is added to the solution obtained by dissolving the material substance in a suitable solution and dispersed using a colloid mill, ultrasonic dispersion, etc., and the resulting dispersion is vigorously stirred. The capsule wall film is formed by depositing the material on the surface of the zinc oxide powder particles by dropping it into a non-solvent.

In the above, the capsule wall membrane is made of a polymeric substance as mentioned above, but the material is already a polymeric substance when it is dissolved in a solvent to create a solution into which zinc oxide powder is added. However, when dissolved, it may be a monomer that polymerizes in the solution to become a polymeric substance.

Regarding the coacelvation method used in the method of the present invention, in addition to the above, for example, "Granulation Handbook" (edited by Japan Powder Industry Association, published by Ohmsha, 1975)
Published on May 30, 2013), pp. 372-383, U.S. Patent No.
No. 2800457, No. 3201353, No. 3336155, No. 3415758, No. 3510435, No. 3533958,
It is also described in the specifications of the same No. 3551346, the same No. 3578605, and the same No. 3607775.

In-situ polymerization method (1) Zinc oxide powder is added to a monomer solution whose solution polymerization conditions are set so that the polymer layer generated on the surface of the zinc oxide powder particles uniformly covers the surface, and as needed. The monomer is polymerized and deposited on the surface of the zinc oxide powder particles by the presence of a polymerization catalyst,
This forms a capsule wall membrane. Here, as the monomer, only one monomer that is polymerizable itself may be used, but two or more monomers that are mutually polymerizable may also be used.

Regarding the in-situ polymerization method used in the method of the present invention, in addition to the above, for example, "Granulation Handbook" (edited by Japan Powder Industry Association, published by Ohmsha, Showa
Published on May 30, 1950) pp. 367-370, U.S. Patent No.
No. 2969330, No. 3516846, “Journal of Colloid and Interface Science”
Interface Science) Volume 42, No. 3 No. 589-596
It is also written on the page.

Any epoxy resin or urethane can be used as the polymer material constituting the capsule wall film formed as described above, and examples include silicone-modified urethane resin, silicone-modified epoxy resin,
Typical examples include phenol-modified epoxy resins, urethane resins, and others. These polymeric substances may also contain additives, if necessary.

In the present invention, instead of adsorbing the sensitizing dye on the surface of the zinc oxide powder particles prior to the formation of the capsule wall film as described above, the sensitizing dye is adsorbed simultaneously with the formation of the capsule wall film. In this case, when using the coacervation method, the sensitizing dye is also dissolved in the solution containing the material, or when using the in-situ polymerization method, the monomer is dissolved. By dissolving the sensitizing dye in the solution, the sensitizing dye can be adsorbed onto the surface of the zinc oxide powder particles at the same time as the capsule wall is formed.

The solvent used when using the coacervation method may be any solvent as long as it dissolves the material, but the advantageous ones are that it is inexpensive, non-toxic to the human body, and has a low boiling point. It is a solvent that satisfies conditions such as being suitable and having a small latent heat of vaporization. Specific examples include hydrocarbons (preferably aromatic hydrocarbons), halogenated hydrocarbons, alcohols, ketones, and esters, although they vary somewhat depending on the material used. Typical of these solvents are:
Hydrocarbons include n-hexane, riboin, benzene, toluene, xylene, etc. Halogenated hydrocarbons include chloroform, dichloroethane, chlorobenzene, etc. Alcohols include methanol,
Examples of ketones include acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.; examples of esters include methyl formate, ethyl formate, ethyl acetate, and butyl acetate.

In addition, when using the coacervation method, the non-solvent used must be one that is miscible with the above-mentioned solvent but does not dissolve the material, and
A compound having a high boiling point is preferable because the entire system can be heated to a necessary temperature in order to heat the formed capsule wall film and further polymerize or crosslink it. By polymerizing or crosslinking the capsule wall film without taking it out of the system, the zinc oxide powder coated with the material that has not yet been polymerized or crosslinked can be removed. Agglomeration of the zinc oxide powder particles, which occurs when separated from the liquid phase, can be avoided. Preferred nonsolvents include water, saturated chain hydrocarbons, halogenated hydrocarbons, alcohols, ketones, esters, and ethers (eg, diethyl ether). In addition, in practical terms, high boiling point isoparaffins are preferred as non-solvents because of the benefits mentioned above.
Examples include those with a boiling point of 115 to 300°C (according to ASTM method), a specific gravity of 0.70 to 0.79 (ASTM method D445), and an aniline point of 70 to 90°C (ASTM method D1133). For example, Isopar E, G, and H manufactured by Etsuo Kagaku Co., Ltd.
There is the same L and the same M.

The combination of the above solvent and non-solvent can be arbitrarily selected depending on the materials and operating conditions, but for example, when methyl ethyl ketone or ethyl acetate is used as the solvent, a combination such as Isopar, which is a high boiling point isoparaffin, is used as the non-solvent. It can be used as

When using the isocyteur polymerization method, the same solvent as in the coacervation method can be used.

The capsule wall film formed as described above is preferably a polymeric material having a cross-linked three-dimensional network structure, but if the material deposited on the surface of the zinc oxide powder particles is not such a material, As mentioned above, the capsule wall film-forming system can be crosslinked or hardened by heating it as it is, or by adding a crosslinking agent or hardening agent, or by taking the solid material out of the system and heating it. is preferred.

The thickness of the capsule wall film formed in the present invention is 5 Å to 1 μm, preferably 10 to 1000 Å, and more preferably 20 to 100 Å. It is preferable to separate the zinc oxide powder on which the capsule wall has been formed by filtration or the like, and then perform a drying operation to drive out the solvent and non-solvent remaining in the capsule wall.

A photoconductive composition made of zinc oxide produced by the method of the present invention is dispersed in a solution of a binder resin such as acrylic resin or melamine resin to form a coating solution for forming a photosensitive layer. and polyethylene terephthalate film, polyethylene film,
A conductive layer made of aluminum, copper, zinc, etc. is laminated on a support made of polypropylene film, nylon film, or a laminate of these films and paper, or an intermediate layer is further provided on this conductive layer as necessary. An electrophotographic photoreceptor is manufactured by applying the coating liquid for forming a photosensitive layer onto a substrate provided with a layer to form a photoconductive photosensitive layer.

Since the photoconductive composition produced by the method of the present invention has a capsule wall film formed by a coacervation method or an in-situ polymerization method on the surface of particles of photoconductive zinc oxide powder, As is clear from the examples below, an electrophotographic photoreceptor having a photosensitive layer made of the photoconductive composition can be produced by corona discharge, etc., which is conventionally considered essential for the development of photoconductivity of zinc oxide. It exhibits sufficient photoconductivity even in an atmosphere where no oxidizing active species (O ₃ , O ₃ ^- , O ₂ ^-, etc.) are present, so it can be used, for example, to exhaust air around a corona charger in an electronic copying machine. This prevents oxidative deterioration of the photosensitive layer, resulting in long printing durability such as being able to withstand copying processes of 10,000 copies or more, excellent gradation reproducibility and resolution, and low memory effect.
Furthermore, the capsule wall film allows a stable state in which the photoconductive composition is sufficiently dispersed in the photosensitive layer coating solution, and the formation of the photosensitive layer can be suitably achieved.

The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

Example 1 0.5 g of free acid rose bengal obtained by acid decomposition of ordinary rose bengal disodium salt was added to 100
ml of methyl ethyl ketone, and 100 g of photoconductive zinc oxide powder dried under reduced pressure at a temperature of 120° C. was added to this solution and dispersed in a ball mill for 1 hour. The methyl ethyl ketone was evaporated and rose bengal was adsorbed. Sensitized zinc oxide powder was obtained.

100 g of this sensitized zinc oxide powder was dispersed in a mixed solvent of 50 ml of Isopar H (manufactured by Etsuso Petrochemical Co., Ltd.), an isoparaffinic non-solvent, which had been dehydrated and dried using a conventional method, and 150 ml of methyl ethyl ketone, which had been dehydrated and dried in the same manner. , and also silicone polyol KR302A
[Manufactured by Shin-Etsu Chemical Co., Ltd.] 1.0g and isocyanate
0.5 g of KR302B (manufactured by Shin-Etsu Chemical Co., Ltd.) was added and subjected to ultrasonic dispersion for 1 hour. Next, by gradually evaporating methyl ethyl ketone from this system using a rotary evaporator, the silicone polyol and isocyanate were deposited on the surface of the particles of the sensitized zinc oxide powder, and then 150 ml of Isopar H was added, and while stirring, temperature 130
C. for 1 hour to produce a photoconductive composition in which a capsule wall film made of a cured silicone urethane resin was formed on the surface of the sensitized zinc oxide powder particles. This composition was filtered through a glass filter, and Isopar H was removed by evaporation.

The photoconductive composition thus obtained is dispersed in a binder resin solution by a known method, and the resulting coating solution for forming a photosensitive layer is applied onto a conductive support.
It was dried to produce an electrophotographic photoreceptor.

When this electrophotographic photoreceptor was attached to an electronic copying machine U-Bix 2000R (manufactured by Konishiroku Photo Industry Co., Ltd.) and a live copy test was conducted, it was found that even after more than 10,000 copying processes, the image remained clear and clear. A copy image was formed. Also, when the resolving power of this electrophotographic photoreceptor was investigated using test patterns, it was 8/1.
It has a resolution as high as mm, and when the gradation reproducibility was examined using a 150 line screen, it was found to be fully satisfactory.

Example 2 100 g of dried photoconductive zinc oxide powder was added to a mixture of 30 ml of methyl isobutyl ketone and 70 ml of toluene in which 0.5 g of free acid rose bengal was dissolved, and the mixture was dispersed in a ball mill for 1 hour. was filtered through a glass filter (25G3) to obtain sensitized zinc oxide powder adsorbed with rose bengal.

100 g of this sensitized zinc oxide powder was dispersed in a mixed solvent of 50 ml of non-solvent Isobar H dried in a conventional manner and 150 ml of methyl ethyl ketone dried in the same manner, and further 1.0 g of silicone polyol KR302A and 0.5 g of isocyanate KR302B were added. The mixture was subjected to ultrasonic dispersion for 1 hour. Next, by gradually evaporating methyl ethyl ketone from this system using a rotary evaporator, the silicone polyol and isocyanate were deposited on the surface of the particles of the sensitized zinc oxide powder, and then 150 ml of Isopar H was added, and the temperature was increased while stirring. Heat treatment was performed at 130° C. for 1 hour to produce a photoconductive composition in which a capsule wall film made of a cured silicone urethane resin was formed on the surface of the sensitized zinc oxide powder particles. The composition was filtered and Isopar H was removed by evaporation.

Using the photoconductive composition thus obtained, an electrophotographic photoreceptor was produced in the same manner as in Example 1, and the same photographic test as in Example 1 was conducted.
Even after more than 10,000 copy processes, clear copied images were still obtained. In addition, in a resolving power test using a test pattern, it was found that it had a resolving power as high as 8/1 mm.

Example 3 100 g of dry photoconductive zinc oxide powder in a mixed solution of 150 ml of methyl ethyl ketone and 50 ml of Isopar H in which 0.5 g of free acid erythrosine was dissolved.
After dispersing in a ball mill for 1 hour, 1.0 g of silicone polyol KR302A and 0.5 g of isocyanate KR302B were added and further dispersed in a ball mill for 1 hour. Next, by evaporating methyl ethyl ketone from this system using a rotary evaporator, erythrosine, silicone polyol, and isocyanate were deposited on the surface of the zinc oxide powder particles, and then 150 ml of Isopar H was added, and the temperature was raised to 130°C while stirring. A photoconductive composition was prepared in which a capsule wall film made of a cured silicone urethane resin containing a sensitizing dye was formed on the surface of the zinc oxide powder particles.

Using the photoconductive composition thus obtained, an electrophotographic photoreceptor was produced in the same manner as in Example 1, and the same photographic test as in Example 1 was conducted.
Even after more than 10,000 copy processes, clear copied images were still obtained.

Example 4 Sensitized zinc oxide powder as in Example 1
100g of two-component urethane resins Coronate L and Desmorphen 800 [Nippon Polyurethane Co., Ltd.]
] 1.0g and 1.6g each in 200ml of ethyl acetate
The mixture was added to a solution dissolved in a mixed solvent of 200 ml of Isopar H and was subjected to ultrasonic dispersion for 1 hour, and then heated to a temperature of 50° C. under reduced pressure using an aspirator to remove ethyl acetate with stirring. Isopar is applied to this residual liquid.
Add 200ml of H and keep the temperature at 300℃ for 3 hours while stirring.
After heating, the solid matter was filtered out using a glass filter and further dried for 3 hours to produce a photoconductive composition having a capsule wall made of urethane resin.

Example 5 Sensitized zinc oxide powder as in Example 1
Add 100 g to a 200 ml solution of dry ethyl acetate containing 1.5 g of silicone varnish KR214 (manufactured by Shin-Etsu Chemical Co., Ltd.) and 1.0 g of isocyanate Coronate HL (manufactured by Nippon Polyurethane Co., Ltd.), and stir this. Meanwhile, 400 ml of Isopar H was added dropwise using a separatory funnel over a period of 2 hours, and the system was further heated at a temperature of 300°C for 3 hours, and the solid matter was filtered out. A photoconductive composition having a capsule wall was prepared by vacuum drying at .degree. C. for 3 hours.

Example 6 Sensitized zinc oxide powder as in Example 1
100 g of silicone epoxy resin ES1001N [manufactured by Shin-Etsu Chemical Co., Ltd.], 2.2 g, and 0.06 g of curing agent D-15 [manufactured by Shin-Etsu Chemical Co., Ltd.] were mixed into 200 g of methyl ethyl ketone.
ml and dispersed in a ball mill for 2 hours, then add isopar to this while stirring.
200 ml of H was added dropwise over a period of 2 hours, then heated to 150°C for 3 hours while stirring, the solid matter was filtered out, and 500 ml of toluene was added.
The photoconductive composition was washed with water five times and dried under vacuum at a temperature of 100° C. for 3 hours to produce a photoconductive composition having a capsule wall made of a cured silicone epoxy resin.

Example 7 Sensitized zinc oxide powder as in Example 1
100g and two-component urethane resins Takerak A-310 and Takenate A-3 [Takeda Pharmaceutical Co., Ltd.
] 1.2g and 0.1g respectively, and dry acetone.
Add to 100ml and disperse for 3 hours using a ball mill.
This dispersion was added dropwise using a separating funnel into 1000 ml of Isopar H heated to 120°C and vigorously stirred, and the heating was maintained for 2 hours, after which the solid matter was filtered out with a glass filter and the temperature
A photoconductive material having a capsule wall was produced by drying at 120° C. for 3 hours under reduced pressure.

An electrophotographic photoreceptor was produced in the same manner as in Example 1 using the photoconductive compositions produced in Examples 4 to 7 above, and a photographic test was conducted in the same manner as in Example 1. Even with the electrophotographic photoreceptor made of the conductive composition, clear copied images were still obtained even after copying processes over 10,000 times.

Example 8 A photoconductive composition having a capsule wall film was produced in exactly the same manner as in Example 1, except that rose bengal disodium salt was used in place of the diluent acid rose bengal in example 1. An electrophotographic photoreceptor was produced using this photoconductive composition in the same manner as in Example 1, and the same photocopying test as in Example 1 was conducted. Image obtained.

Furthermore, similar results were obtained when crystal violet was used as a sensitizing dye instead of rose bengal.

Example 9 100 g of dried photoconductive zinc oxide powder was added to a solution of 0.5 g of free acid Rose Bengal dissolved in 100 ml of methyl ethyl ketone and dispersed in a ball mill for 1 hour, and then the methyl ethyl ketone was evaporated to dryness and the remaining solids were ground. A sensitized zinc oxide powder was obtained.

100g of this sensitized zinc oxide powder was mixed with 1.0g of silicone polyol KR302A and isocyanate.
The mixture was added to a solution of 0.5 g of KR302B dissolved in dry methyl ethyl ketone and subjected to ultrasonic dispersion for 1 hour. Next, this dispersion was heated under reflux for 6 hours, and then the solid matter was filtered off and dried to produce a photoconductive composition having a capsule wall made of silicone urethane resin.

Using the photoconductive composition thus obtained, an electrophotographic photoreceptor was produced in the same manner as in Example 1, and the same photographic test as in Example 1 was conducted.
Even after more than 10,000 copy processes, clear copied images were still obtained.

Comparative Example: Into 100 ml of methyl ethyl ketone in which 0.5 g of free acid rose bengal was dissolved, 100 g of photoconductive zinc oxide powder dried under reduced pressure at a temperature of 120°C was added and dispersed in a ball mill for 1 hour, and then the methyl ethyl ketone was evaporated to dryness to form a residue. The solid material was pulverized to obtain sensitized zinc oxide powder.

This sensitized zinc oxide powder was directly dispersed in a binder resin solution in the same manner as in Example 1, and the resulting coating solution for forming a photosensitive layer was applied and dried on a conductive support, and a comparative electrophotographic photosensitive layer was prepared. Made the body. Example 1 for this comparative electrophotographic photoreceptor
When we conducted a similar live-action test, we found that after 1,000 copying processes, the copied images were already blurry. Also, the resolution test using the test pattern is
The resolution was low at 6.3 lines/1 mm, and when we checked the gradation reproducibility using a 150 line screen, we found that it was not sufficiently reproduced.

Claims (1)

[Claims] 1. A pigment is adsorbed onto the surface of zinc oxide, and then a capsule film of epoxy resin or urethane resin is formed by a coacelvation method or an in-situ polymerization method, or by a coacelvation method or an in-situ polymerization method. 1. A method for producing a photoconductive composition, which comprises adsorbing a dye while forming a capsule film of epoxy resin or urethane resin, and subjecting the composition to heat treatment if necessary.