JPH0477307B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to an electrophotographic photoreceptor having high sensitivity in the long wavelength range, which is formed by forming a charge generation layer and a charge transport layer on a conductive support, and particularly relates to an electrophotographic photoreceptor having high sensitivity in the long wavelength range. The present invention relates to an electrophotographic photoreceptor having properties. [Background of the Invention] An electrophotographic photoreceptor has an inorganic or organic photoconductor layer provided on a conductive support. Organic photoconductors generally have lower photosensitivity than inorganic photoconductors, so various sensitization methods have been devised, but the most effective method is to create a charge-generating layer that generates charges when the photoreceptor is irradiated with light. and a charge transport layer that efficiently transports the charges generated in the charge generation layer. Such electrophotographic photoreceptors usually contain organic substances such as monoazo dyes, disazo dyes, squaric acid dyes, quinocyanine pigments, nonmetallic or metal phthalocyanine pigments, or inorganic substances such as tellurium, arsenic, and selenium pigments as charge generating substances. Polymer is used as the charge transport material.
Conductive support using N-vinicarbazole, hydrazo compounds, pyrazoline compounds, oxadiazole compounds, trinitrofluorenone, and various nitro- and cyano-substituted compounds, either alone or dispersed or dissolved in a resin. Laminated layers are used on the body. Incidentally, in an electrophotographic copying machine using such a photoreceptor, first, the surface of the photoreceptor is charged by corona irradiation, and then imagewise exposure is performed to create an electrostatic latent image. Copying is performed by attaching toner to the electrostatic latent image to create a toner powder image, which is then transferred to paper or the like. Therefore, photoreceptors are required to have charging properties, sensitivity, resolution, optical properties, etc. depending on the process, as well as stability of these properties, toner cleanability, and abrasion resistance. Furthermore, in recent years, a system has been devised as a type of high-speed printer that uses a laser as a light source and prints by electrophotography. In particular, when a semiconductor laser is used as a light source, the light source section can be made very small, making it possible to reduce the size of the printer and also to significantly reduce power consumption. However, since the oscillation wavelength of a semiconductor laser is usually a long wavelength of 770 nm or more, the sensitivity of the conventional electrophotographic photoreceptor described above is not sufficient, and a photoreceptor with high sensitivity, especially in the long wavelength range, is required. ing. Therefore, as mentioned above, improvements in sensitivity can be achieved by making the photoreceptor multi-layered or adding a sensitizer, and by forming a protective layer or insulating layer on the surface of the photoreceptor, or adding a lubricating agent to improve durability, cleaning properties, and resistance. Although various improvements have been attempted, such as improving abrasion properties, no solution has been obtained that satisfactorily satisfies the various demands. [Object of the Invention] An object of the present invention is to provide an electrophotographic photoreceptor that has sufficient sensitivity even in the oscillation wavelength range of a semiconductor laser, and particularly has excellent resolution and durability. [Summary of the Invention] The composite electrophotographic photoreceptor of the present invention includes a charge generation layer comprising a τ type, τ′ type, η type, or η′ type metal-free phthalocyanine and a silicone resin on a conductive support, and preferably , is composed of a charge transport layer consisting of an oxazole compound having the following structural formula and a silicone resin, and the charge generation layer has a τ, τ', η or η' type metal-free phthalocyanine and the silicone resin in a weight ratio of 1/3 to 1/3.
3/1, preferably the charge transport substance oxazole compound and silicone resin are in a weight ratio of 1/2 to 1/2.
It is characterized by being used at a blending ratio of 5. [In the formula, Y is

【formula】

【formula】

[Formula] and

[Formula] represents at least one heterocyclic group selected from the group consisting of (however, Z represents O or S, and the heterocyclic group may be substituted); and R ₁ and R ₂ are alkyl groups having 3 or less carbon atoms. ] Normally, the wavelength range to which a photoreceptor is sensitive depends on the absorption wavelength range of the charge-generating material, as long as the charge-transporting layer used does not interfere with the light absorbed by the charge-generating material. Many studies have been carried out on long wavelength absorbing charge generating substances, and for example, a method has been found for Se, CdS, etc. to increase the sensitivity in the long wavelength region by adding a sensitizer, but this It has insufficient environmental resistance to water and humidity, and also has problems in terms of toxicity. The τ-type metal-free phthalocyanine is defined as follows. That is, the bragg angle (2θ±0.2 degrees) is 7.6,
It has a strong X-ray diffraction pattern at 9.2, 16.8, 17.4, 20.4 and 20.9. In particular, the infrared absorption spectrum has four absorption bands with the strongest intensity of 751±2 cm ^-1 between 700 and 760 cm ^-1 , and two absorption bands with almost the same intensity between 1320 and 1340 cm ^-1 , 3288 It is desirable to have a characteristic absorption of ±3 cm ^-1 . τ' type metal-free phthalocyanine is defined as follows. That is, for the 1.541 Å X-ray of CuKα ₁ /Ni, the Bragg angle (2θ±0.2 degrees) is 7.5, 9.1,
This is a new metal-free phthalocyanine crystal polymorph with strong X-ray diffraction patterns of 16.8, 17.3, 20.3, 20.8, 21.4 and 27.4. In particular, the infrared absorption spectrum
Four absorption bands with the strongest strength at 753±2cm ^-1 between 700 and 760cm ^-1 and two absorption bands with almost the same strength between 1320 and 1340cm ^-1 at 3297±3cm ^-1 It is desirable that the material has a high level of absorption. η-type metal-free phthalocyanine is defined as follows. That is, 100 parts by weight of metal-free phthalocyanine,
It is a mixture crystal of 50 parts by weight or less of a mixture of one or more of metal-free phthalocyanine having a substituent on the benzene nucleus, a phthalocyanine nitrogen isomer which may have a substituent on the benzene nucleus, or a mixture of two or more metal phthalocyanines. Absorption spectrum is 700
Four absorption bands with the strongest intensity at 753±1cm ^-1 between ~760cm ^-1 , two absorption bands with almost the same intensity between 1320 and 1340cm ^-1 , and a characteristic characteristic at 3285±5cm ^-1 It has good absorption. According to the study conducted by the present inventor, η-type metal-free phthalocyanine has a black angle (2θ±
0.2 degree) has an X-ray diffraction pattern showing strong peaks at 7.6, 9.2, 16.8, 17.4 and 28.5, and 7.6,
Examples include those having an X-ray diffraction pattern showing strong peaks at 9.2, 16.8, 17.4, 21.5 and 27.5. η' type metal-free phthalocyanine is defined as follows. That is, 100 parts by weight of metal-free phthalocyanine,
It is a mixture crystal of 50 parts by weight or less of a mixture of one or more of metal-free phthalocyanine having a substituent on the benzene nucleus, a phthalocyanine nitrogen isomer which may have a substituent on the benzene nucleus, or a mixture of two or more metal phthalocyanines. Absorption spectrum is 700
Four absorption bands with the strongest strength at 753 ± 1 cm ^-1 between ~760 cm -1 and two absorption bands with almost the same strength between 1320 and 1340 cm ^-1 , characteristic at 3297 ^± 5 cm ^-1 This is a new metal-free phthalocyanine crystal polymorph with a unique absorption property. According to the inventor's study, η′-type metal-free phthalocyanine has a particularly black angle (2θ±0.2 degrees).
7.5, 9.1, 16.8, 17.3, 20.3, 20.8, 21.4 and 27.4
7.5, 9.1.16.8, 17.3, 20.3, 20.8, 21.4, 22.1,
It is desirable to have an X-ray diffraction pattern showing strong peaks at 27.4 and 28.5. In addition, the maximum value of the photosensitive wavelength range of all τ type, τ′ type, η type, and η′ type metal-free phthalocyanine is 790 ~
In the 810nm range. The τ-type and τ'-type metal-free phthalocyanine according to the present invention are produced in the following manner. That is, α-type metal-free phthalocyanine is heated to 50 to 180°C, preferably 60 to 180°C.
A metal-free phthalocyanine having a τ' crystal form is prepared by milling at a temperature of 130° C. with stirring or mechanical strain for a time sufficient to effect crystal conversion. The α-type phthalocyanine used in the present invention is a “phthalocyanine compound” by Moser and Thomas.
(Moser and Thomes “Phthalocyanie
For example, metal-free phthalocyanines are metal phthalocyanines that can be demetallized with acids such as sulfuric acid, such as lithium phthalocyanine, sodium phthalocyanine, and other suitable methods. Those made directly from phthalodinitrile, aminoiminoisoindolenine, alkoxyiminoisoindolenine, etc. are used by acid treatment of metal phthalocyanine containing calcium phthalocyanine, magnesium phthalocyanine, etc. Metal-free phthalocyanine obtained by a well-known method is preferably dissolved in sulfuric acid or converted into a sulfate at a temperature below 5°C, and then poured into water or ice water to re-precipitate or hydrolyze to obtain α-type metal-free phthalocyanine. is obtained.
At this time, if an inorganic pigment dissolved or dispersed in sulfuric acid or a reprecipitation solution is used, an α-type metal-free phthalocyanine containing an inorganic pigment can be obtained. The inorganic pigment may be any water-insoluble powder used as a color filler, such as titanium white, zinc white, white carbon, calcium carbonate, etc., and may be used in the form of powder in a variety of ways. Examples include metal powder, alumina, iron oxide powder, and kaolin. The α-type metal-free phthalocyanine containing this inorganic pigment is much more easily crushed and made into fine particles when it is made into a pigment, and is effective in saving labor and energy. The α-type metal-free phthalocyanine subjected to such treatment is preferably used in a dry state, but a water paste form can also be used. Dispersion media for stirring and kneading may be those commonly used for pigment dispersion, emulsification, and the like, such as glass beads, steel beads, alumina balls, and flint stones. However, distributed media is not necessarily required. As the crushing aid, those commonly used as crushing aids for pigments may be used, and examples thereof include common salt, sodium bicarbonate, and sulfur salt. However, this crushing aid is not necessarily required. If a solvent is required during stirring, kneading, and crushing, it may be liquid at the temperature during stirring and kneading.
For example, alcoholic solvents, i.e. glycerin,
1 from the group of ethylene glycol, diethylene glycol or polyethylene glycol solvents, cellosolve solvents such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ketone solvents, ester ketone solvents, etc.
It is preferable to select more than one type. Typical devices used in the crystal transition process include general stirring devices, such as homomixers, dispersers, agitators,
There are stirrers or kneaders, Banbury mixers, ball mills, sand mills, attritors, etc. The temperature range in the crystal transition step of the present invention is 50~
It is carried out within a temperature range of 180°C, preferably 60-130°C. It is also an effective method to use crystal nuclei as in the usual crystal transition process. The α-type phthalocyanine used in producing the η-type and η′-type metal-free phthalocyanine according to the present invention and the metal-free phthalocyanine having a substituent on the benzene nucleus, or even if the benzene nucleus has a substituent, the phthalocyanine nitrogen is more The structure or metal phthalocyanine is the ``phthalocyanine compound'' of Moser and Thomes mentioned above.
Those obtained by known methods such as "Phthalocyanine Compounds" and other suitable methods are used. For example, α-type metal-free phthalocyanine can also be obtained by the same formulation as described above, and may also contain other inorganic pigments. In addition, phthalocyanine nitrogen isostructures include various porphins, such as copper tetrapyridinoporphyrazine in which one or more of the benzene nuclei of phthalocyanine is replaced with a quinoline nucleus, and metal phthalocyanines include copper, nickel, Various materials such as cobalt, zinc, tin, and aluminum can be mentioned. In addition, as substituents, amino group, nitro group,
Examples include alkyl groups, alkoxy groups, cyano groups, mercapto groups, halogen atoms, and relatively simple examples include sulfonic acid groups, carboxylic acid groups, or metal salts thereof, ammonium salts, and amine salts. Furthermore, various substituents can be introduced to the benzene nucleus via an alkylene group, a sulfonyl group, a carbonyl group, an imino group, etc., and these are conventionally known in the technical field of phthalocyanine pigments as aggregation inhibitors or crystal conversion inhibitors. (for example, USP No. 3973981,
(see Publication No. 4088507), or unknown ones. Known methods for introducing each substituent will be omitted. In addition, things that are not publicly known are described as reference examples in the examples. In the present invention, the mixing ratio of α-type metal-free phthalocyanine and metal-free phthalocyanine having a substituent on the benzene nucleus, or a phthalocyanine nitrogen isomer or metal phthalocyanine which may have a substituent on the benzene nucleus is 100/50 (by weight). (ratio) or higher, preferably 100/30 to 100/0.1 (weight ratio). If the ratio exceeds this ratio, the resulting η-type and η'-type phthalocyanines tend to bleed, reducing their suitability as pigments. In the present invention, mixing in the above-mentioned ratio may be done by simply mixing, or by mixing before acid pasting the α-type metal-free phthalocyanine. The method of stirring or milling the mixture thus mixed may be the one normally used for dispersing, emulsifying, or mixing pigments, and examples of dispersion media for stirring or kneading include glass beads, steel beads, alumina balls, and flint. A stone is an example, but a dispersion medium is not necessarily required. The grinding aid, the solvent during kneading, the materials and equipment used in the crystal transition step are the same as those for the τ-type and τ'-type metal-free phthalocyanine described above. The temperature range in the crystal transition process of η-type and η′-type metal-free phthalocyanine is 30 to 220°C, preferably
Perform within the temperature range of 60-130°C. At higher temperatures, it is easy to transition to the β type, and at lower temperatures, it takes time to transition to the η and η' types. It is also an effective method to use crystal nuclei as in the usual crystal transition process. Incidentally, a charge generating substance generates charges by light passing through the charge transport layer, and the generated charges must be efficiently injected into the charge transport layer by an electric field. Therefore, it is necessary to form the charge-generating material on the conductive support with appropriate thickness and adhesion. Specifically, it is necessary to uniformly disperse the τ-type metal-free phthalocyanine and dissolve the silicone resin. It is formed by applying an organic solvent onto a conductive support and drying it. Silicone resin is used here because silicone resin is less susceptible to corona irradiation than other thermoplastic resins and thermosetting resins, and when modified, it has conductive support and good adhesion. The charge generation layer swells when the charge transport layer is applied because it forms a three-dimensional network structure by heating and hardening, and has good solvent resistance.
This is because there is no problem with peeling or elution.
The reason why the mixing ratio of τ-type phthalocyanine and silicone resin in the charge generation layer is set to 1/3 to 3/1 by weight is that if the resin component is too small, the charge generation substance will not adhere well to the conductive support. On the other hand, if the amount is too large, charge movement becomes difficult to occur during light irradiation, resulting in problems such as decreased sensitivity of the photoreceptor and failure of the surface potential to completely return to zero during light irradiation. The organic solvent is preferably one that can disperse the charge generating substance well and dissolve the resin component well, and such solvents include tetrahydrofuran, methyl ethyl ketone, dioxane, toluene, xylene, methylene chloride, 1,2-dichloroethane, 1, 1,2-trichloroethane, 1,
1,2,2-tetrachloroethane and the like can be used. The thickness of the charge generation layer formed in this way is
It is desirable to have a thickness of 0.1 to 3 μm. The reason for this is that when the thickness of the charge generation layer is 0.1 μm or less, the sensitivity is low and the surface residual potential upon irradiation with light becomes large, which poses a practical problem. Conversely, the residual potential also increases when the thickness is 3 μm or more. The thickness of such a charge generation layer can be adjusted by appropriately changing the solid content concentration of the coating liquid depending on the type of charge generation substance and resin used. On the other hand, fluctuations in the resolution of the photoreceptor, resolution during repeated use, and various electrophotographic properties are mainly affected by the surface physical properties of the charge transport layer, the corona ions of the charge transport material and resin components during repeated use, and the stability against light. Gender etc. have a big influence. The present inventors conducted various studies on methods for improving these characteristics of photoreceptors, and found that the following structural formula is used as a charge transport material: [In the formula, Y is

【formula】

【formula】

[Formula] and

[Embodiments of the invention]

Reference Example 1 α-type metal-free phthalocyanine (Monolite Fast Bull GS manufactured by ICI) was extracted and purified three times with heated dimethyl formaldehyde. This operation transformed the crystal form to the β form. Next, a portion of this β-type metal-free phthalocyanine was dissolved in concentrated sulfuric acid, and this solution was poured into ice water to cause reprecipitation, thereby transforming it into the α-type. This reprecipitate was washed with aqueous ammonia, methanol, etc., and then dried at 70°C. Next, the α-type metal-free phthalocyanine refined above was placed in a sand mill together with a grinding aid and a dispersant, and kneaded at a temperature of 100±20° C. for 15 to 25 hours.
After confirming that the crystal form has changed to the τ type by this operation, take it out from the container, thoroughly remove the grinding aid and dispersion medium with water and methanol, etc., and dry it to form a τ type with a clear greenish color. Blue crystals of metal phthalocyanine were obtained. Table 1 shows the infrared absorption spectra of the α-, β-, and τ-type metal-free phthalocyanines thus obtained. The units of numbers in the table are cm ^-1 , the strength of absorption is expressed as w (weak), m (medium), and s (strong), and sh indicates shoulder. As is clear from Table 1, the absorption wave number of the τ type metal-free phthalocyanine at 700 to 800 cm ^-1 is different from that of the α and β types.

【table】

[Table] Example 1 1 part by weight of τ-type metal-free phthalocyanine (average particle size: 0.3φ×1 μm) obtained in the above reference example, epoxy-modified silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR-5240,
Solid content 15% by weight) 6 parts by weight, methylphenylsiloxane compound (manufactured by Shin-Etsu Chemical Co., Ltd., KP-323)
0.005 parts by weight and 40 parts by weight of tetrahydrofuran were kneaded in a ball mill for about 5 hours to prepare a coating liquid for the charge generation layer. This coating liquid was applied onto aluminum foil with a thickness of 100 μm using an automatic applicator and dried at 130° C. for 2 hours to form a charge generation layer with a thickness of 0.5 μm. Next, as a charge-generating substance, an olefin having the following structural formula Using 1 part by weight of a xazole compound, straight silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR-255,
2 to 12 parts by weight (solid content 50% by weight) and 0.005 parts by weight of the methylphenylsiloxane compound KP-323 are dissolved in 15 to 25 parts by weight of tetrahydrofuran so that the blending ratio of the oxazole compound and the resin component is 1/1, 1/
Six types of coating liquids for the charge transport layer were prepared, each having a thickness of 2, 1/3, 1/4, 1/5, and 1/6. These coating liquids were applied onto the charge generation layer prepared above using an automatic applicator and dried at 130°C for 2 hours to form a charge transport layer with a thickness of approximately 15 μm. A photographic photoreceptor was obtained. Comparative Examples 1 and 2 The procedure was the same as in the above example except that the α- and β-type metal-free phthalocyanine obtained in the above reference example was used, and the blending ratio of the oxazole compound and silicone resin in the charge transport layer was 1/4 by weight. Two types of composite electrophotographic photoreceptors were produced. Next, the electrophotographic characteristics of each photoreceptor produced in Example 1 and Comparative Examples 1 and 2 were measured. For the measurement, we used an electrostatic recording paper tester SP-428 (manufactured by Kawaguchi Electric). We charged the corona charger in dynamic mode for 10 seconds with the power supply voltage of -5 kV, left it in the dark for 30 seconds, and then charged it with a tungsten lamp.
10 lux (measured value at rest) was irradiated. During this time, the surface potential of the photoreceptor was recorded with a recorder, and the potential V ₀ after charging was completed, the potential V ₃₀ after being left for 30 seconds, and the half-reduced exposure amount
E ₅₀ (unit of exposure amount lux·s required for V ₃₀ to reach V ₃₀ /2) was read. Furthermore, in a similar measurement system, a halogen lamp (600W) was used as the light source.
In particular, we measured the half-decreased exposure amount E ⁸⁰⁰ ₅₀ (erg/cm ² ) for light with a wavelength of 800 ± 1 nm, and determined the sensitivity and
1/E ⁸⁰⁰ ₅₀ was calculated. The illuminance when using 800nm monochromatic light as the light source is approximately 20nW/ ^m2 . The results are shown in Table 2. As is clear from Table 2, the photoreceptor using τ-type phthalocyanine of Example 1 was superior to the photoreceptors using α- and β-type phthalocyanine of Comparative Examples 1 and 2, especially for long wavelength light of 800 nm. It has sensitivity.

[Table] Next, using each photoreceptor of Example 1, negative
After irradiating with a 5 kV DC corona, a resolution evaluation pattern of the Society of Photographic Society Test Chart No. 1-R was closely exposed to form an electrostatic latent image on the photoreceptor. Next, after applying a plastron toner to this latent image to form a toner powder image, this powder image was transferred and fixed onto a transfer paper, and the resolution was evaluated. As a result, as shown in Table 2, higher resolution was obtained as the amount of the charge transport material in the charge transport layer was smaller. However, too little charge transport material resulted in a significant decrease in photoreceptor sensitivity. Examples 2 to 5 After forming a charge generation layer on aluminum foil in the same manner as in Examples 1 to 6, the following structure was used as a charge transport material. Using 1 part by weight of the oxazole compound of formula, 8 parts by weight of alkyd modified silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR-5206, solid content 50% by weight) (Example 2), and 8 parts by weight of epoxy modified silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR-5206, solid content 50% by weight) as the silicone resin. manufactured by ES-100IN, solid content 45% by weight) 8.9
parts by weight (Example 3), 5.3 parts by weight of urethane-modified silicone resin (K, R-302A, manufactured by Shin-Etsu Chemical Co., Ltd., solid content 75% by weight) (Example 4), polyester-modified silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd., KR- 5203, solid content
50) In 8 parts by weight (Example 5), 0.005 parts by weight of methylphenylsiloxane compound KP-323 was dissolved in 20 to 25 parts by weight of tetrahydrofuran, and the blending ratio of the oxazole compound and the resin component was 1/4. Four types of charge transport layer coating liquids were prepared, each having different types. Next, these coating liquids are applied onto the charge generation layer prepared above using an automatic applicator.
Each layer was dried at 130° C. for 2 hours to form a charge transport layer with a thickness of about 15 μm, and four types of composite electrophotographic photoreceptors were obtained. The initial electrophotographic characteristics and resolution of each of these photoreceptors were first measured in the same manner as described above. Next, in order to evaluate the durability of each of these photoconductors, we used Hitachi's laser beam printer SL-
The photoreceptor of the present invention was pasted on a 1000C photoreceptor drum, 50,000 copies were made in copy mode, and the electrophotographic characteristics and resolution were measured in the same manner as above. The results are shown in Table 3. As is clear from Table 3, there is almost no change in the electrophotographic characteristics and resolution of the photoreceptor of the present invention before and after repeated use.
Furthermore, as a result of a detailed examination of the surface of the photoreceptor, it was found that there was almost no wear or damage on the photoreceptor caused by the toner cleaning brush, and there was no change in the cleaning performance of the toner.

〔Effect of the invention〕

As described above, the electrophotographic photoreceptor of the present invention has high sensitivity in the long wavelength region, excellent resolution, durability, etc., and is particularly suitable as a photoreceptor for semiconductor laser beam printers.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor comprising a charge generation layer and a charge transport layer formed on a conductive support, wherein the charge generation layer is a τ, τ', η or η' type metal-free phthalocyanine. 1. An electrophotographic photoreceptor comprising a mixture of one selected from the following and a silicone resin in a weight ratio of 1/3 to 3/1. 2. An electrophotographic photoreceptor according to claim 1, wherein the charge transport layer is made of a compound of the following structural formula and a silicone resin in a weight ratio of 1/2 to 1/5. . [wherein, Y is at least one heterocyclic group selected from the group consisting of [formula] [formula] [formula] and [formula] (however, Z represents O or S, and the heterocyclic group is substituted n represents 0, 1 or 2, and R ₁ and R ₂ are an alkyl group having 3 or less carbon atoms. 3. The electrophotographic photoreceptor according to claim 1, wherein the charge generation layer has a thickness of 0.1 to 3 μm, and the charge transport layer has a thickness of 10 to 30 μm.