JPH0452938B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pigment dispersion, and more particularly to a pigment dispersion that improves the dispersion stability of a photoconductive organic pigment. Conventionally, as electrophotographic photoreceptors made of inorganic photoconductive materials, those using selenium, cadmium sulfide, zinc oxide, etc. have been widely used. On the other hand, electrophotographic photoreceptors made of organic photoconductive substances include photoconductive polymers typified by poly-N-vinylcarbazole and 2,5-bis(p-diethylaminophenyl)-1,3,4-oxa Those using low-molecular organic photoconductive substances such as diazole, and furthermore, those in which such organic photoconductive substances are combined with various dyes and pigments are known. An electrophotographic photoreceptor using an organic photoconductive substance has good film forming properties, can be produced by coating, has extremely high productivity, and has the advantage of being able to provide an inexpensive photoreceptor. Further, it has the advantage that color sensitivity can be freely controlled by selecting the sensitizer such as dye or pigment to be used, and a wide range of studies have been carried out to date. In particular, recently, with the development of a functionally separated photoreceptor in which an organic photoconductive pigment is used as a charge generation layer and a so-called charge transport layer made of the aforementioned photoconductive polymer or a low-molecular organic photoconductive substance is laminated, Significant improvements have been made in the sensitivity and durability, which were considered to be drawbacks of conventional organic electrophotographic photoreceptors, and they have come into practical use. Furthermore, various compounds and pigments that are suitable for functionally decomposed photoreceptors have also been discovered. Since such a functionally separated photoreceptor has a structure of at least two layers, a charge generation layer and a charge transport layer, charge carriers generated by light absorption in the charge generation layer are injected into the charge transport layer, increasing the charge on the photoreceptor surface. This causes electrostatic contrast to disappear, and the role played by the charge generation layer in this process is extremely important. In other words, how to generate a large number of charge carriers uniformly, how to efficiently inject the generated charge carriers into the charge transport layer, and how smoothly to flow opposite charge carriers to the support. Many of the electrophotographic properties, such as characteristics and image properties, are largely due to the charge generation layer. It is generally believed that the more uniform, extremely thin and smooth the charge generation layer is formed, and therefore the finer the charge generation particles, the better the electrophotographic properties will be. Therefore, the biggest problem in practical application is how to stably obtain an ultra-thin layer, and to do so, there is the problem of dispersibility, which is how to disperse the pigment, which is a charge-generating substance, into fine particles, and the problem of cohesiveness of the dispersion liquid. The problem of dispersion stability, which is produced as a stable liquid without oxidation, must be solved. A common method for producing finely divided pigment dispersions is to grind the pigment together with a binder using a sand mill, pole mill, roll mill, attritor, etc., and if the dispersion conditions are optimized, it can be achieved to a certain level. It is possible to atomize the particles up to Furthermore, it is not difficult to produce a fine pigment dispersion of 0.1 μm or less if this technology is combined with technology to make the pigment into fine particles from the synthesis and purification stage and to maintain the fine particles. but,
Generally speaking, the finer the pigment particles, the more
Factors that inhibit stability as a coating solution, such as cohesiveness and thixotropy, increase inversely proportionally, and dispersibility and dispersion stability are often contradictory. Regarding dispersion stability, in the pigment field with a long history, there are almost established methods such as measuring the matching of pigment, binder, and solvent using SP values, etc., and adding additives called dispersion stabilizers. It is no exaggeration to say that there is still no established method for stabilizing pigment dispersions for electrophotography, and that we are still searching in the dark. The present inventor has made various efforts to improve the stability of fine particle dispersions of pigments, but
As a result, it has been discovered that in the case of pigment dispersions with strong cohesiveness, a value called dispersion specific viscosity is a factor that influences the cohesiveness. That is, an object of the present invention is to provide a method for producing a photoconductive composition containing a particulate organic pigment, and also to provide a method for producing a stable dispersion of a particulate organic pigment. An object of the present invention is to provide a method for manufacturing an electrophotographic photoreceptor having high sensitivity characteristics and stable potential characteristics during long-term use. The present invention is characterized by finding a stable dispersion state having a dispersion specific viscosity defined below. Dispersion specific viscosity = viscosity of pigment dispersion / viscosity of solution excluding pigment components, that is, a photoconductive composition is produced by applying and drying a pigment dispersion having a dispersion specific viscosity in the range of 0.8 to 2.5. be. Dispersion specific viscosity is a value similar to the specific viscosity obtained by dividing the viscosity of a polymer solution by the viscosity of only the solvent.It is the viscosity of the stock solution consisting of the solvent, binder, additives, etc., that is, the viscosity of the solution excluding pigment components. This is the value obtained by dividing the viscosity, and indicates the rate at which the viscosity changes due to the presence of fine pigment particles. Dispersion specific viscosity varies depending on the combination of pigment, solvent, and binder, mixing ratio of pigment and binder, solid content concentration, etc., but is 0.8 to 2.5, more preferably 1.1.
When the value is in the range of ~1.6, the stability of the dispersion becomes outstandingly good. Regarding the method for manufacturing the photoconductive composition of the present invention,
I will explain in more detail. Examples of photoconductive organic pigments include azo pigments, phthalocyanine pigments, quinacridone pigments, cyanine pigments, pyrylium pigments, thiapyrylium pigments, indigo pigments,
Scaric acid pigments, polycyclic quinone pigments, and the like can be used as charge-generating materials for electrophotographic photoreceptors. The pigment can be used in powder or paste form along with the binder resin in alcoholic solvents such as methanol, ethanol, and IPA, ketone solvents such as acetone, MEK, MIBK, and cyclohexanone, and aromatic solvents such as benzene, toluene, xylene, and chlorobenzene. , 1,4-dioxane, THF, DMF,
Dispersed in various solvents such as DNAC. As the binder resin, polyvinyl butyral, formal resin, polyamide resin, polyurethane resin, cellulose resin, polyester resin, polysulfone resin, styrene resin, polycarbonate resin, acrylic resin, etc. are used. Sand mill, colloid mill,
Methods such as attritor, pole mill, roll mill, etc. can be used. The dispersion conditions are optimized by changing the ratio of pigment to binder, changing the solid content concentration, and examining the dispersion method among the above combinations of organic pigment, binder, and solvent, but the dispersion specific viscosity depends on the concentration of the coating solution. must be controlled so that it is within the range of 0.8 to 2.5. In the method of the present invention, the atomized dispersion of organic pigment is extremely stable, with no agglomeration for over 1 year when left in a sealed container, and over 3 months in a model system of an actual coating machine that incorporates circulation, filtration, and stirring. and maintain a state with no viscosity change. When this is used as an electrophotographic photoreceptor, improvements are seen in sensitivity characteristics and charge characteristics during long-term use, as is clear from the embodiments described below. The charge generation layer can be formed by coating the above-mentioned dispersion directly onto the conductive support or onto the adhesive layer.
It can also be formed by coating on the charge transport layer described below. The thickness of the charge generation layer is 5μ or less,
Preferably, it is a thin film layer with a thickness of 0.01 to 1 μm. Most of the incident light is absorbed by the charge generation layer, generating many charge carriers, and the generated charge carriers must be injected into the charge transport tank without being deactivated by recombination or trapping. , it is preferable to set the film thickness as described above. Coating can be carried out using coating methods such as dip coating, spray coating, spinner coating, bead coating, Meyer bar coating, blade coating, roller coating, and curtain coating. For drying, it is preferable to dry to the touch at room temperature and then heat dry. Heating sensation: 5 minutes to 2 at a temperature of 30℃ to 200℃
It can be carried out stationary or under blown air for a period of time within a range of hours. The charge transport layer is electrically connected to the charge generation layer described above, and has the function of receiving charge carriers injected from the charge generation layer in the presence of an electric field and transporting these charge carriers to the surface. ing. At this time, this charge transport layer may be laminated on or under the charge generation layer. However, it is desirable that the charge transport layer is laminated on the charge generation layer. Since the photoconductor generally has the function of transporting charge carriers, the charge transport layer can be formed by the photoconductor. The substance that transports charge carriers in the charge transport layer (hereinafter simply referred to as charge transport substance) is preferably substantially insensitive to the wavelength range of electromagnetic waves to which the charge generation layer is sensitive. The term "electromagnetic waves" used herein includes a broad definition of "light rays" that includes gamma rays, X-rays, ultraviolet rays, visible light, near infrared rays, infrared rays, far infrared rays, and the like. When the photosensitive wavelength range of the charge transport layer coincides with or overlaps that of the charge generation layer, charge carriers generated in both trap each other, resulting in a decrease in sensitivity. Charge transport substances include electron transport substances and hole transport substances, and electron transport substances include chloranil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, and 2,4,7-trinitro-9-fluorenone. , 2, 4, 5, 7-
Tetranitro-9-fluorenone, 2,4,7-
trinitro-9-dicyanomethylenefluorenone, 2,4,5,7-tetranitroxanthone,
Examples include electron-withdrawing substances such as 2,4,8-trinitrothioxanthone, and polymerized versions of these electron-withdrawing substances. Examples of hole-transporting substances include pyrene, N-ethylcarabazole, N-isopropylcarbazole,
N-Methyl-N-phenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-3-methylidene-9-ethylcarbazole, N,N-diphenylhydrazino-
3-methylidene-10-ethylphenothiazine,
N,N-diphenylhydrazino-3-methylidene-10-ethylphenoxazine, p-diethylaminobenzaldehyde-N,N-diphenylhydrazone, p-diethylaminobenzaldehyde-N
-α-naphthyl-N-phenylhydrazone, p-
Pyrrolidinobenzaldehyde-N,N-diphenylhydrazone, 1,3,3-trimethylindolenine-ω-aldehyde-N,N-diphenylhydrazone, p-diethylbenzaldehyde-3-methylbenzthiazolinone-2-hydrazone hydrazones such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, 1
-Phenyl-3-(p-diethylaminostyryl)
-5-(p-diethylaminophenyl)pyrazoline, 1-[quinolyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]- 3-(p-
diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[6-methoxy-pyridyl(2)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrizoline, 1- [pyridyl(3)]-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[lepidyl(2)]-3-(p-
diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-
3-(p-diethylaminostyryl)-4-methyl-5-(p-diethylaminophenyl)pyrazoline, 1-[pyridyl(2)]-3-(α-methyl-p-
diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, 1-phenyl-3-
(p-diethylaminostyryl)-4-methyl-5
-(p-diethylaminophenyl)pyrazoline,
1-Phenyl-3-(α-benzyl-p-diethylaminostyryl)-5-(p-diethylaminophenyl)pyrazoline, spiropyrazoline and other pyrazolines, 2-(p-diethylaminostyryl)
-6-diethylaminobenzoxazole, 2-
Oxazole compounds such as (p-diethylaminophenyl)-4-(p-dimethylaminophenyl)-5-(2-chlorophenyl)oxazole, 2
Thiazole compounds such as -(p-diethylaminostyryl)-6-diethylaminobenzothiazole, triarylmethane compounds such as bis(4-diethylamino-2-methylphenyl)-phenylmethane, 1,1-bis(4-N,N -diethylamino-2-methylphenyl)heptane, 1,
Polyarylalkanes such as 1,2,2-tetrakis(4-N,N-dimethylamino-2-methylphenyl)ethane, triphenylamine, poly-
N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polyvinylacridine,
Examples include poly-9-vinylphenylanthracene, pyrene-formaldehyde resin, and ethylcarbanol formaldehyde resin. In addition to these organic charge transport materials, inorganic materials such as selenium, selenium-tellurium, amylphous silicon, and cadmium sulfide can also be used. In addition, these charge transport substances may be one or two types.
More than one species can be used in combination. When the charge transport material does not have film-forming properties,
A film can be formed by selecting an appropriate binder. Resins that can be used as binders are:
For example, insulating resins such as acrylic resin polyarylate, polyester, polybonate, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral, polyvinyl formal, polysulfone, polyacrylamide, polyamide, chlorinated rubber, or poly-N- Mention may be made of organic photoconductive polymers such as vinylcarbazole, polyvinylanthracene, polyvinylpyrene. Since the charge transport layer has a limit in its ability to transport charge carriers, it cannot be made thicker than necessary. Typically it is between 5 microns and 30 microns, with a preferred range between 8 microns and 20 microns. When forming the charge transport layer by coating, an appropriate coating method as described above can be used. In this way, a photosensitive layer having a laminated structure of a charge generation layer and a charge transport layer is provided on a substrate having a conductive layer. As the substrate having the conductive layer, materials that are themselves conductive can be used, such as aluminum, aluminum alloy, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, and platinum. In addition, plastics (e.g., polyethylene, polypropylene, polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyethylene fluoride, etc.), conductive particles (e.g. carbon black,
A substrate made of plastic coated with silver particles (silver particles, etc.) together with a suitable binder, a substrate made of plastic or paper impregnated with conductive particles, a plastic containing a conductive polymer, etc. can be used. A subbing layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer. The subbing layer is made of casein, polyvinyl alcohol, nitrocellulose, ethylene-acrylic acid copolymer, polyamide (nylon 6, nylon 66, nylon
610, copolymerized nylon, alkoxymethylated nylon, etc.), polyurethane, gelatin, aluminum oxide, etc. Undercoat layer thickness: 0.1 micron to 5 micron,
Preferably, 0.3 micron to 3 micron is appropriate. When using a photoreceptor in which a conductive layer, a charge generation layer, and a charge transport layer are laminated in this order, and the charge transport material is an electron transport material, the surface of the charge transport layer must be positively charged, and exposure after charging is required. Then, in the exposed area, electrons generated in the charge generation layer are injected into the charge transport layer, and then reach the surface and neutralize the positive charge, causing a decrease in surface potential and creating an electrostatic contrast with the unexposed area. . A visible image can be obtained by developing the electrostatic latent image thus formed with a negatively charged toner. This can be directly fixed, or the toner image can be transferred to paper, plastic film, etc. and then developed and fixed. Alternatively, a method may be used in which the electrostatic latent image on the photoreceptor is transferred onto an insulating layer of transfer paper, then developed and fixed. The developer, type, developing method, and fixing method may be any known developer or known method, and are not limited to specific ones. On the other hand, when the charge transport material consists of a hole transport material, the surface of the charge transport layer must be negatively charged.
After charging, when exposed to light, holes generated in the charge generation layer in the exposed area are injected into the charge transport layer, and then reach the surface and neutralize the negative charge, causing a decrease in the surface potential and static electricity between the exposed area and the unexposed area. Electrocontrast occurs. During development, it is necessary to use a positively charged toner, contrary to the case where an electron transport material is used. Another specific example of the present invention is an electrophotographic photoreceptor in which the photoconductive organic pigment described above is contained in the same layer as a charge transport material. At this time, a charge transfer complex compound consisting of poly-N-vinylcarbazole and trinitrofluorenone can be used in addition to the above-mentioned charge transport substance. The electrophotographic photoreceptor of this example can be prepared by dispersing the aforementioned organic photoconductor and charge transfer complex compound in a polyester solution dissolved in tetrahydrofuran, and then forming a film thereon. Each photoreceptor contains at least one type of pigment, and if necessary, pigments with different light absorptions are used in combination to increase the sensitivity of the photoreceptor or to obtain a punctochromatic photoreceptor. 2
It is also possible to use more than one species. The electrophotographic photoreceptor of the present invention can be used not only for electrophotographic copying machines, but also for laser printers and CRTs.
It can also be widely used in electrophotographic applications such as printers. Further, the photoconductive composition of the present invention can be used not only for the above-mentioned electrophotographic photoreceptor but also for solar cells and optical sensors. Hereinafter, the present invention will be explained according to examples. Example 1 (Comparative Example 1) In a 500 ml beaker, 80 ml of water and 16.6 ml of concentrated hydrochloric acid (0.19
mole)

Add 6.53g (0.029mol) of diamine represented by the formula,
The mixture was stirred while cooling in an ice-water bath to bring the liquid temperature to 3°C.
Next, add 4.2g (0.061mol) of sodium nitrite to 7ml of water.
Add the solution dissolved in water dropwise over 10 minutes while controlling the temperature within the range of 3 to 10℃. After finishing, add the solution at the same temperature.
Stirred for 30 minutes. Carbon was added to the reaction solution to obtain a tetrazotized solution. Next, put 700ml of water into 2 beakers and dissolve 21g (0.53mol) of caustic soda, then naphthol AS.
(3-hydroxy-2-naphthoic acid anilide)
16.2 g (0.061 mol) was added and dissolved. Cool this coupler solution to 6℃ and reduce the liquid temperature to 6-10℃.
Add the above-mentioned tetrazotization solution while controlling the temperature at
The mixture was added dropwise over 30 minutes with stirring, and then stirred at room temperature for 2 hours and further left overnight. After filtering the reaction solution, it was washed with water to obtain 19.08 g of a crude pigment. Next, each 400ml of N,
Washing was repeated five times with N-dimethylformamide. Thereafter, washing was repeated three times with 500 ml each of MEK to obtain 67.32 g of MEK base of purified pigment.
Pigment solid content in MEK baset is 2.5%, yield is 75
It was %. Moreover, the obtained pigment has the following structure. Next, 50 g of the above paste pigment was added to a solution prepared by dissolving 5 g of butyral resin (degree of briralization: 63 mol %) in 240 ml of MEK (methyl ethyl ketone), and dispersed with an attritor for 2 hours. Further, as a comparative example, a dispersion liquid treated in the same manner with 2 g of butyral resin was prepared. The average particle size of the dispersion of the present invention was 0.10, and that of the comparative example was 0.28. On the other hand, for dispersion specific viscosity measurement, the viscosity of a solution in which 2 g of the above butyral resin was dissolved in 110 ml of MEK was measured, and for a comparative example, the viscosity of a solution in which 0.8 g of butyral resin was dissolved was measured, and from the viscosity of the above dispersion, the dispersion specific viscosity I asked for

[Table] The viscosity was measured using a single cylindrical rotational viscometer "Vismetron type VS-A1" manufactured by Toshiba Systems Corporation. The conditions at that time were as follows. Rotation speed: 60 r.pm (low viscosity rotor used) Time of measurement: 5 minutes after starting Measurement temperature: 30±0.1°C The stability of the above two types of dispersions was tested by the method described in Section 3 below. 1. Leave the cap tightly closed. 2. Stir in the open (replenish the evaporation loss of the solvent as appropriate). 3. Continuous operation using the circulation coating system model (Fig. 1) consisting of a stirring tank, circulation pump, pressure gauge, and filter (1 in the figure indicates the circulation tank, 2 ( indicates the pressure gauge, 3 indicates the filter, 4 indicates the pump, and 5 indicates the liquid reservoir.) The evaluation method is to check whether the paper becomes clogged over time (does the pressure gauge increase)? Cohesiveness was determined based on whether granular deposits were observed on the dried film, and stability of the dispersion was determined based on changes in viscosity over time.

[Table] It was found that the stability of Example-1 was significantly increased compared to Comparative Example-1. Next, place an ammonia solution of casein on an aluminum plate (casein 11.2 g, 28% ammonia water 1 g, water
222 ml) was applied using a Mayer bar so that the film thickness after drying was 1.0 micron, and dried. The previously dispersed pigment dispersion was applied onto this casein layer using a Mayer bar so that the film thickness after drying was 0.3 microns.
A charge generation layer was formed by drying. Next, 5 g of p-diethylaminobenzaldehyde-N,N-diphenylhydrazone and 5 g of polymethyl methacrylate resin (number average molecular weight 100,000) were added.
Sample 1 was obtained by dissolving 1.g in 70 ml of benzene and coating the charge generation layer with a Mayer bar so that the film thickness would be 12 microns after drying, and drying to form a charge transport layer. On the other hand, for comparison, the dispersion liquid prepared as the above-mentioned comparative example was applied and dried in exactly the same manner as described above on the day after dispersion to prepare comparative sample 1. The electrophotographic photoreceptor prepared in this way was used with electrostatic copying paper manufactured by Kawaguchi Electric Co., Ltd. and a test device "Model sp-428".
The sample was statically charged with a corona at -5kV using a 1000V, held in a dark place for 1 second, and then exposed to light at an illuminance of 5lux to examine its charging characteristics. As for the charging characteristics, the surface potential (V _D ) and the exposure amount (E1/2) required to attenuate the potential to 1/2 when the potential is attenuated in the dark for 1 second were measured. This result is the third
Shown in the table.

[Table] Furthermore, in order to measure the fluctuations in the bright area potential and dark area potential during repeated use, the photoreceptor prepared in this example was charged with a -5.6kV corona charger, and the exposure amount was
12lux・sec exposure optical system, developer, transfer charger,
It was attached to the cylinder of an electrophotographic copying machine equipped with a static elimination exposure optical system and a cleaner. This copying machine is configured to produce an image on transfer paper as a cylinder is driven. Using this copying machine, the initial bright area potential (V _L ) and dark area potential (V _D ) and the bright area potential (V _L ) and dark area potential (V _D ) after being used 5000 times were measured. The results are shown in Table 4.

[Table] From the results in Tables 3 and 4, the photoreceptor manufactured by the manufacturing method of the present invention has a high sensitivity and V _D ,
It can be seen that the stability of _VL is also extremely excellent. Examples 2 to 8 (Comparative Examples 2 to 4) Phthalic anhydride 148g, urea 180g, anhydrous chloride No. 1
25 g of copper, 0.3 g of ammonium molybdate, and 370 g of benzoic acid were reacted at 190° C. for 3.5 hours with stirring. After the reaction was completed, benzoic acid was distilled under reduced pressure, followed by washing with water, washing with acid, and washing with water in order to obtain 130 g of crude copper phthalocyanine. This crude phthalocyanine was dissolved in 1,300 g of concentrated sulfuric acid, stirred at room temperature for 2 hours, poured into a large amount of ice water, and the precipitated pigment was separated and washed with water until it became neutral. Next, the mixture was stirred and filtered six times with DMF 2.6, and then twice with cyclohexanone 2.6 to obtain 467 g (solid content: 27%, 126 g) of a cyclohexanone paste of purified copper phthalocyanine. Next, add 95ml of MEK and 15ml of cyclohexanone by changing the amount of cellulose acetate butyrate resin added.
ml of mixed solvent, 18.5 g of cyclohexanone paste (solid content: 5 g) of the above pigment was added, and the mixture was dispersed in a ball mill for 40 hours. Further dilution with MEK was carried out to prepare a dispersion liquid with a reduced solid content concentration.
Samples up to 8 and samples up to Comparative Examples 2 to 4 were created. The correlation between the dispersion specific viscosity, cohesiveness, and viscosity of these dispersions was conducted in the same manner as in Example 1, and the results shown in Table 5 were obtained.

[Table] *The period until the start of aggregation is as in Example 1.
Table 5 shows that dispersion liquids with a dispersion specific viscosity of 2.5 or less are extremely stable.

[Brief explanation of drawings]

The drawing is an explanatory diagram of a circulatory system model in an example. 1...Circulation tank, 2...Pressure gauge, 3...Filter, 4...Pump, 5...Liquid reservoir.

Claims (1)

[Scope of Claims] 1. A pigment dispersion liquid characterized by having a dispersion specific viscosity as defined below in the range of 0.8 to 2.5. Dispersion specific viscosity = viscosity of pigment dispersion / viscosity of solution excluding pigment components