JPS607782B2 - Electrophotographic materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic material using titanium oxide as a photosensitive pigment, and particularly to an electrophotographic material using a rutile crystal containing a small amount of anatase crystal as titanium oxide.

In electrophotography, the surface of a photosensitive material is uniformly charged by corona discharge, then imagewise exposed to attenuate the charge in the exposed area to form an electrostatic latent image, and then an electroscopic colored toner is applied to the electrostatic latent image. A visible image is formed on a photosensitive material by depositing it on the photosensitive material.

It goes without saying that the photosensitive material used in this method must have the necessary electrophotographic properties, but in particular it must have charging properties that allow its surface potential to reach a high value in a short time after the charging operation starts. , light retention properties such that the surface potential is maintained for the time required for operation without decreasing after the charging stops, and light attenuation properties such that the surface potential quickly attenuates in accordance with the exposure amount after the start of exposure. (Photosensitivity) is basically essential. Electrophotographic materials currently in practical use include photosensitive pigments such as selenium, polyvinylcarbazole, subsalt oxide, and cadmium sulfide dispersed in a resin binder.

Titanium oxide, especially high-purity products with a rutile crystal structure, is known to have properties as a photosensitive pigment, and its application to electrophotography has been considered. (Comparatively, it has poor photosensitivity and color retention, so it has not yet been put into practical use.) The present inventors have developed titanium oxide, especially titanium oxide produced by the gas phase oxidation method of titanium tetrachloride, which yields the rutile crystal structure with the highest purity among the currently industrialized technologies, the so-called chlorine method. While conducting research on its use as a photosensitive pigment, it was surprisingly discovered that when produced under special reaction conditions in which a small amount of anatase type crystals were mixed, excellent electrophotographic properties were brought about. A similar tendency was confirmed in titanium oxide produced by the so-called sulfuric acid method, which involves heating and hydrolyzing a titanium sulfate solution and calcination of the resulting hydrated titanium oxide.

An object of the present invention is to provide an electrophotographic light-sensitive material using titanium oxide that has improved electrophotographic properties, particularly chargeability, color retention, and photosensitivity.

Another object of the present invention is to provide an electrophotographic light-sensitive material whose electrophotographic properties are generally improved to a practically practicable degree and which also has a high degree of whiteness. The present invention is an electrophotographic photosensitive material in which a photosensitive layer in which titanium oxide as a photosensitive pigment is dispersed in a resin binder is laminated on a conductive substrate, the titanium oxide being 0} titanium halide. '2} Hydrolyze the titanium halide and then sinter the obtained hydrated titanium oxide, or '3}
It is produced as a rutile noanatase crystal mixture by hydrolyzing titanium salt and then calcining the obtained hydrated titanium oxide, and is characterized by that 3Z to 40% of the total Ti02 is anatase type crystals. This is an electrophotographic light-sensitive material. The titanium oxide used in the present invention is produced as a rutile noanatase crystal mixture, and is produced, for example, as follows.

In the chlorine method, titanium oxide is obtained by reacting titanium tetrachloride vapor with oxygen at high temperatures, but in the industrial production of pigment-grade titanium oxide, 100% rutile crystals are usually used. Something with structure is generated. Therefore, in order to obtain a rutile noanatase crystal mixture, for example, it is necessary to remove all or most of aluminum trichloride, water, etc., which are generally used as additives, from the reaction system, and to form anatase. By adding a small amount of boron compound to the reaction system, bringing titanium tetrachloride and oxygen into contact in a high-temperature reaction chamber, and adjusting the mixing speed, we further controlled the reaction temperature and reaction. Conditions such as time are adjusted to obtain the desired rutile/anatase mixing ratio. In addition, in the sulfuric acid method, rutile seeds are added during heating and hydrolysis of an aqueous titanium sulfate solution, and the resulting hydrated titanium oxide is calcined to cause crystal rearrangement from anatase to rutile. The desired rutile/anatase mixing ratio can be achieved by reducing the amount of rutile added compared to when 100% rutile is expected, adjusting the type and amount of firing additives, firing temperature, and firing time, etc. of titanium oxide can be produced. The thus obtained rutile/anatase crystal mixture in which 3 to 40% of the total Ti02 has an anatase crystal structure and the remaining 60 to 97% has a rutile crystal structure is used as a photosensitive pigment in the photosensitive material of the present invention. It will be done.

When the content of anatase is higher than the above range, charging property,
The result is poor dark retention and slightly poor light sensitivity. In addition, when going through a firing process such as in the case of manufacturing by the sulfuric acid method, if the firing is insufficient, for example, at 500 qo for 2 hours, even if the anatase content is within the above range, the chargeability and dark retention will deteriorate. On the other hand, if the film is overfired at 1000 o'clock for 2 hours, the photosensitivity will be reduced, so care must be taken. It has also been found that it is desirable that the titanium oxide has a slightly larger particle size than pigment grade titanium oxide, which usually has a median particle size distribution of about 0.2 to 0.4.

That is, the titanium oxide which is a rutile/anatase crystal mixture preferably has a median particle size distribution of 0.41 or more, preferably in the range of 0.6 to 5 degrees. If the particle size is too small, photosensitivity will decrease. On the other hand, if it is too large, for example 1
If the titanium oxide contains a considerable amount of coarse particles of 0 or more, the image will become rough, which is undesirable.According to the conventional wisdom, the titanium oxide used in the present invention should contain as few colored impurities or impurities derived from raw materials or additives as possible. It is desired that Fe, M
It is necessary to suppress the total amount of n, Ni, Co, V, Cr, P, AI, Si, etc. to 0.1% or less in terms of oxides.

However, Zn, Ca, Mg, Li, Ba and Sr are 0.
It is known that the presence of 01 to 5 mol% in the crystal structure of titanium oxide improves the electrophotographic properties, and it is desirable to add it in the firing process when producing the titanium oxide of the present invention, for example, by the sulfuric acid method. bring results. The electrophotographic material of the present invention can be prepared according to conventional methods except for using the titanium oxide described above as a photosensitive pigment.

That is, this photosensitive pigment is mixed into a resin binder at a concentration of 35 to
It is dispersed at a ratio of 6% by volume and coated on a conductive substrate to a thickness of usually 10 to 30 mm, and dried to form a photosensitive material. Usually, when kneading titanium oxide and a resin binder, one type or a combination of two or more types of various processing agents for improving electrophotographic properties are used. For example, dyes such as anthraquinones, phthalenes, xanthenes, cyanines, triphenylmethanes, azos, azines, and oxazines are used as spectral sensitivity property improvers, while amines and organic dyes are used as spectral sensitivity property improvers. Acids, silane coupling agents, resins, metal soaps, and alcohols having 6 or more carbon atoms are used as pre-exposure fatigue inhibitors, the above-mentioned dyes, phenols, and amines are used as pre-exposure fatigue inhibitors, and metals are used as charging property improvers. Soaps, organic acids, phenols, amines, silane coupling agents, resins, alcohols having 6 or more carbon atoms, and the like can be used. Such a processing agent may be simply added and kneaded when titanium oxide and the resin binder are kneaded, but due to the characteristics of electrophotography, it is preferable to first strongly adsorb the processing agent on the surface of the pigment particles and then knead with the resin binder. It will be done. That is, between before and after the kneading of the treatment agent and titanium oxide, heating is usually carried out for more than 90 minutes, preferably for 120 to 25,000 hours, preferably for 1 to 4 hours, preferably for 2 to 3 hours, and then kneaded with a resin binder and coated. If the processing agent is dried at a temperature lower than the heating temperature mentioned above, the processing agent is closely adsorbed and retained on the surface of the pigment particles, so that an improvement effect beyond that originally possessed by the processing agent is brought about, and the effect of improving other photographic properties is also improved. Sometimes. As the resin binder, a resin having film-forming properties and high electrical insulation properties can be appropriately selected and used. For example, acrylic resin, alkyd resin, polyester resin, vinyl resin, polyurethane resin, various natural resins, synthetic rubber, amino resin,
Polyolefin resin etc. can be used. Conductive Motomura is
Any material with higher conductivity than the photoconductive layer may be used, such as paper or cloth coated with a conductive substance commonly used in electrophotography, a metal sheet, a plastic sheet coated with metal, or a thin layer of metal foil. Use paper, etc. The light-sensitive material of the present invention has a high degree of whiteness due to the excellent pigment properties of titanium oxide, and can produce good images with fine grains.

Furthermore, since titanium oxide has a high dielectric constant and a large charge retention capacity, the photosensitive layer can be made thinner and the whole material is lighter. Furthermore, continuous tone reproducibility is extremely excellent, and images comparable to silver halide photography can be obtained, which has the great advantage of being applicable to color printing. Next, examples according to the present invention will be described.

Example 1 Specified titanium oxide obtained by vapor phase oxidative decomposition of titanium tetrachloride 27.5 mm, Alloset spots 04XC (acrylic resin, manufactured by Nippon Arrow Chemical Co., Ltd.) 13.0 mm, xylene 12 mm, mixed pigment Methanol solution of MD-19 (NK-1410, Cresyl Violet, Uranine, Eriochrome Black T and Azururo; Dye-1) at 3.44 [,
Dioctyl azelate 0.72 mm and glass beads 1
03 was placed in a 240M glass container, shaken well with a quick mill, and the glass beads were separated to obtain a coating liquid.

This coating solution was applied onto aluminum laminated paper using a 50-m doctor blade, dried for one coat on a loo dryer to make photosensitive paper, and this was left in a room for two days and nights to be used as a sample for measuring electrophotographic properties. . Among the electrophotographic properties, chargeability and scale retention were determined by drawing charging curves and scale attenuation curves by the turntable method (dynamic method) using Kawaguchi Denki's SP-42 matrix paper analyzer. The potential Vo reached by charging and the potential V2 after being left for 20 seconds in the tray after charging.

is read, and the chargeability is determined by Vo, and V2o/Vox
A value of 100 indicates floor retention. The light attenuation property was determined by charging to 300 V' with a scorotron charger, then irradiating with light while measuring the potential with a surface potentiometer (JII Kuchi Denki SSV Rho 30), and the potential was the same as the potential just before exposure (30
The time tl/10 seconds required for the voltage to decay from 0V to one-tenth (30V) was measured and is shown here. For exposure, a 150W tungsten bulb was used, and the light was separated into blue, green, and red by a dichroic filter, and the illuminance was adjusted so that each illuminance was 43 lux for blue, 1350 lux for green, and 720 lux for red on the sample surface. Irradiated. The rutile/anatase ratio of titanium oxide was obtained by measuring the diffraction intensities of 100 planes of rutile and anatase on crushed titanium oxide using an X-ray diffraction method, and measuring the relationship between the intensity ratio and the rutile/anatase ratio in advance. It was determined by reading it on a correlation curve.

The median diameter of titanium oxide was determined by Joyce's centrifugal sedimentation method.
A cumulative particle size distribution curve was drawn using a disc-type measuring device manufactured by Revell Inc., and its median value was determined. The test results are shown in Table 1.
Table 1 Example 2 In Example 1 above, titanium oxide was dispersed in Isopar daylight, and zinc naphthenate was used as Zn in an amount of 0.2% by weight (Ti0
2 standards), heat for 30 minutes at the boiling point (approx. When using titanium oxide, a photosensitive material was prepared in the same manner as in Example 1 except that the treatment was carried out in an amount of 0.02% by weight based on titanium oxide, and the electrophotographic properties were measured to obtain the results shown in Table 2.

Table 2 Example 3 An aqueous solution of titanium sulfate was heated and hydrolyzed in the presence of a small amount of rutile species to obtain hydrated titanium oxide having a relatively large particle size.

1 mol % of zinc oxide (based on Ti02) was added to this hydrated titanium oxide, and the mixture was fired in an electric furnace adjusted to 800 oo. By appropriately changing the firing time, titanium oxide with different ratios of rutile and anatase was produced, and after firing, it was crushed to make a photosensitive pigment, and mixed dye MD-19 (dye-1) and surface treatment were added to the same machine as in Example 2. A photosensitive material was prepared by performing the above steps, and the electrophotographic properties were measured to obtain the results shown in Table 3. The median diameter of this titanium oxide was measured in the same manner as in Example 1, and was found to be 0.6 to 0.8 mm.

Table 3

Claims (1)

[Claims] 1 An electrophotographic photosensitive material comprising a photosensitive layer in which titanium oxide as a photosensitive pigment is dispersed in a resin binder is laminated on a conductive substrate, and the titanium oxide is prepared by (1) dispersing titanium halide (2) hydrolyzing a titanium halide and then calcining the resulting hydrated titanium oxide; or (3) hydrolyzing a titanium salt and then calcining the resulting hydrated titanium oxide. An electrophotographic light-sensitive material characterized in that 3 to 40% of the total TiO_2 is anatase-type crystals, which are produced as a rutile/anadase crystal mixture.