JPH0623854B2 - Electrophotographic photosensitive material - Google Patents

Description

TECHNICAL FIELD The present invention relates to an electrophotographic light-sensitive material containing titanium dioxide as a photosensitive layer component, and more specifically, it contains a novel condensed titanium dioxide having improved photosensitivity. The present invention relates to an electrophotographic photosensitive material.

[Technical background of the invention and its problems]

Titanium dioxide is the most used pigment as it has high hiding power and tinting power and provides excellent gloss to the coating. Most of this commercial product is anatase type or rutile type with an average particle size of 0.15 to 0.35μ,
In order to improve the dispersibility, gloss, weather resistance and the like according to the purpose, a surface treatment with a hydrated oxide such as aluminum or silicon is applied.

On the other hand, a large amount of zinc oxide is used as a photoconductive substance of an electrophotographic photosensitive material, and a technique of applying titanium dioxide in place of this is being researched and developed.

Titanium dioxide as the photoconductive substance is introduced in, for example, Japanese Patent Publication No. 47117/1972. It has anatase type crystal structure and consists of particles with an average particle size of 0.05-0.15μ, with at least 70% by weight of the particles 0.08-0.18.
It is in the μ range.

Recently, with the development of electrophotographic technology, a higher quality image has been required, and at the same time, there is a market demand for the development of a photoconductive titanium dioxide having further excellent electrophotographic characteristics.

[Object of the Invention]

An object of the present invention is to provide an electrophotographic photosensitive material excellent in electrophotographic characteristics using a novel condensed titanium dioxide as a photoconductive substance, and to meet the above market demand.

[History and outline of invention]

The present inventors have been researching and developing for a long time a technique of using titanium dioxide as a photoconductive substance in place of zinc oxide, and a certain titanium dioxide is used as a binder (binder resin) compatible with it. It was clarified that when used together with various auxiliaries, an image having high resolution and sharpness and sharpness can be produced as compared with the case of zinc oxide.

The present inventors, as a result of continuing research and development to meet the above market demand, are sintered aggregates of fine primary particles, having a rutile type crystal structure, and an oil absorption of 35 to
The present invention has been completed by finding that the object can be achieved by an electrophotographic light-sensitive material using 65, which is a novel condensed titanium dioxide as a photoconductive substance.

That is, the present invention is (1) in an electrophotographic photosensitive material comprising a conductive support and a photosensitive layer containing titanium dioxide and a binder as main components, wherein the titanium dioxide is a fine primary particle. An electrophotographic light-sensitive material, which is a sintered agglomerate, has a rutile type crystal structure, and is an aggregated titanium dioxide having an oil absorption of 35 to 65. (2) An aggregated titanium dioxide is baked. A condensed titanium dioxide obtained by the presence of at least one compound containing an element selected from the group consisting of lithium, zinc, magnesium, calcium, strontium and barium, in the aforementioned hydrous titanium dioxide. The electrophotographic light-sensitive material of (1), (3) the condensed titanium dioxide is one treated with a mineral acid, the electrophotographic light-sensitive material of (1) or (2), (4) ore The acid is hydrofluoric acid The electrophotographic light-sensitive material according to claim (3), and (5) the gloss ratio of 45 ° -45 ° specular gloss to 45 ° -0 ° specular gloss of the photosensitive layer surface is 0.7 to 2. The electrophotographic photosensitive material according to any one of claims (1) to (4).

The condensed titanium dioxide according to the present invention is obtained by, for example, heating a titanium-dissolved acidic aqueous solution and hydrolyzing it in the presence of rutile-type seed crystals for hydrolysis to calcinate a precipitate at 700 to 900 ° C. to sinter the primary particles. Can be manufactured.

Examples of the titanium-dissolved acidic aqueous solution include aqueous solutions of titanium sulfate, titanium tetrachloride and the like.

The rutile type seed crystal for hydrolysis is used for promoting rutile formation and controlling the particle size in the thermal hydrolysis of pigment-grade titanium dioxide, and its example is 19
1974 The Rona Press Company
ld Press Company) Issued "Titanium" (TITANIUM)
160 to 173, Japanese Patent Publication No. 32-415, and the like.

The rutile-type seed crystal for hydrolysis suitable for producing the condensed titanium dioxide of the present invention is a fine titania sol having a rutile-type crystal structure, and this fine-grained titania sol shows a peak of a rutile-type crystal when measured by an X-ray diffraction method. It is a sol of hydrated titanium oxide. The average crystallite size is usually about 50 to 120Å. This microtitania sol has, for example, (1) TiO ₂ of 150 to 220
g / titanium tetrachloride aqueous solution is heated at the boiling point for 2 to 10 hours to hydrolyze (2) 150-220 g / titanium sulfate aqueous solution or titanium tetrachloride aqueous solution as TiO ₂ is maintained at 5 to 30 ° C. Colloidal precipitate neutralized with alkaline aqueous solution such as sodium oxide and aged for 1 to 10 hours at 60 to 80 ° C. (3) Amorphous titanium hydroxide such as metatitanic acid or orthotitanic acid is aqueous sodium hydroxide solution. Put in 80
It can be produced by heating at 80 ° C to the boiling point for 1 to 10 hours, filtering and washing, and then heating in an aqueous hydrochloric acid solution at 80 ° C to the boiling point for 1 to 10 hours.

In the above-mentioned structural example of condensed titanium dioxide, the difference from the case of general pigment grade titanium dioxide in the thermal hydrolysis condition is that the temperature is preferably as low as 65 to 85 ° C.

The hydrous titanium dioxide obtained by adding rutile type seed crystals for hydrolysis to a titanium-dissolved acidic aqueous solution and heating it
Calcination is preferably performed at ~ 900 ° C, preferably 750-850 ° C, but the difference from the case of general pigment grade titanium dioxide in the calcination step is that the calcination temperature is low and phosphoric acid and phosphoric acid compounds such as It is not necessary to add a sintering inhibitor such as orthophosphoric acid or an alkali metal compound such as potassium hydroxide. If the calcination temperature is too low, the desired rutile titanium dioxide cannot be fired. I won't.

The desired fired product thus obtained is usually roughly crushed and then classified. In this coarse pulverization, if the pulverization energy is large, the aggregated titanium dioxide is broken into primary particles. Therefore, under conditions where calcination can be performed under good control, it is preferable to carry out classification without coarse pulverization.

The condensed titanium dioxide according to the present invention is a secondary particle having a rutile type crystal structure, and has a shape like a grape or an irregularly divided shape as shown in the electron micrograph of FIG. The individual primary particles corresponding to each grain are sintered with the adjacent ones, but this sintering is not the strength over the entire surface of the primary particles, and the agglomeration of the primary particles is sparse. The aggregated titanium dioxide particles are rich in voids. This can be understood by the irregularities, cavities, and shades of the condensed titanium dioxide particles shown in the photograph of FIG. Most of these condensed titanium dioxide particles are 1 to 5
The size is μ.

As described above, the condensed titanium dioxide according to the present invention has a shape and size as compared with pigment-grade titanium dioxide or titanium dioxide as a light-guiding substance for electrophotography described in JP-B-47-29117. Is basically different.

The condensed titanium dioxide according to the present invention has a large oil absorption amount of 35 to 65, as evidenced by its shape. Pigment-grade titanium dioxide is not preferred to have a large value because of the properties required as a pigment, and its oil absorption is generally in the range of 15 to 25. The oil absorption amount referred to herein is measured as follows.
That is, 2 to 5 g of a sample dried at 105 to 110 ° C. for 2 hours is put on a glass plate, and refined linseed oil having an acid value of 4 or less is dropped little by little from a buret to the center of the sample and kneaded with a spatula each time. The operation of dropping and kneading is repeated, and the amount of the refined linseed oil is obtained with the end point when the whole is gathered into one rod for the first time, and the oil absorption amount is calculated by the following formula.

In the production of the condensed titanium dioxide according to the present invention, an appropriate amount of a sintering inhibitor such as phosphoric acid and potassium hydroxide was used in the calcination step as described in the above Japanese Patent Publication No. 47-29117. Most of the fired products at this time are primary particles.
The average particle diameter (Haywood diameter, weight basis) of this primary particle titanium dioxide is usually in the range of 0.05 to 0.25 μ (provided that the same pulverization and classification as in pigment-grade titanium dioxide).

Further, in the production of the condensed titanium dioxide according to the present invention, the calcined product when the calcination temperature is 1000 ° C., the primary particles are densely fused to each other due to sintering, and the oil absorption amount is about the size of voids. Unlike titanium dioxide, it has a small value.

The electrophotographic light-sensitive material using the condensed titanium dioxide of the present invention is disclosed in Japanese Patent Publication No. 58-40177 in order to improve its electrophotographic characteristics.
As described in the specification, before calcination of hydrous titanium dioxide, at least one compound containing an element (metal) selected from the group consisting of lithium, zinc, magnesium, calcium, strontium and barium is present. It is effective to let This improvement brings about favorable effects on electrophotographic characteristics such as initial potential, dark decay rate, and light decay half-life. As the compound containing these metals, oxides, hydroxides, halides, nitrates, sulfates and organic acid salts thereof can be used. The addition amount of these compounds is generally 0.001 to 5 mol% with respect to TiO ₂ as the metal, preferably 0.01 to 5 mol%, especially if the metal is lithium 0.02-0.2 mole% relative to TiO ₂ as Li, zinc otherwise 0.1 to TiO ₂ as the metal
5 mol% is preferable. Zinc has a significant effect on the improvement of dark decay properties as compared with other metals.

In order to improve the electrophotographic characteristics of the electrophotographic photosensitive material using the condensed titanium dioxide of the present invention, it is effective to treat the calcined condensed titanium dioxide with a mineral acid.

Examples of the mineral acid include sulfuric acid, nitric acid, hydrochloric acid and hydrofluoric acid, and hydrofluoric acid is one of them. The mineral acids may be used alone or in combination.

Mineral acid treatment is usually performed using an aqueous solution of mineral acid and its concentration is 0.00
It is carried out by suspending condensed titanium dioxide in the one specified by 05 to 20 and immersing it.

If the mineral acid is sulfuric acid, nitric acid, hydrochloric acid, etc.
It may be processed according to the description in the specification. However, strong agitation that destroys the shape of condensed titanium dioxide must be avoided. It is preferable to treat these mineral acids with 0.1 normal or more, preferably 0.1 to 10 normal, and the higher the concentration, the lower the processing temperature and the shorter the processing time. For example, in a high-concentration aqueous solution of 6 to 10 N, it is about 0 at about 60 ° C.
Treatment for 5 to 2 hours is sufficient. When the concentration is low, the desired effect can be obtained by heating or prolonging the treatment time. For example, a low-concentration aqueous solution of 0.1 to 2N has a boiling point of about 1
It is recommended that the treatment be performed for 3 hours.

When the mineral acid is hydrofluoric acid, it can be treated according to the description in JP-B-63-35977, but in the case of the condensed titanium dioxide according to the present invention, it is surprisingly different from the description in the specification in that the fluorine content It has been found that it is better to treat the so that it does not substantially remain. Therefore, it is not necessary to dare to carry out the high temperature immersion treatment, and it is desirable that the cleaning be sufficiently performed. Hydrofluoric acid is usually used as an aqueous solution for treatment, and its concentration is usually 0.0005.
-20 normals, preferably 0.05-10 normals. Also in this case, it is necessary to avoid strong agitation that destroys the shape of the condensed titanium dioxide during the dipping treatment.

In the above-mentioned nucleic acid treatment, if the concentration is too low, the desired effect cannot be obtained, and if it is too high, the solubility of titanium dioxide increases, which is not preferable. In the same process,
For mineral acids, water-soluble fluorine compounds such as ammonium fluoride,
Coexistence of potassium fluoride, lithium fluoride, zinc fluoride and the like may bring about a more desirable effect. The solid matter that has been subjected to the immersion treatment with a mineral acid is thoroughly washed so that anions do not substantially remain, and then dehydrated and dried if desired. The electrophotographic light-sensitive material utilizing the condensed titanium dioxide obtained by the mineral acid treatment as described above has a photosensitivity, a dark decay rate, and a moisture resistance as compared with those not subjected to this treatment as shown in the test examples below. Excellent electrophotographic characteristics such as performance.

The condensed titanium dioxide according to the present invention is suitable as a photoconductive substance as described above. To prepare an electrophotographic photosensitive material of so-called CPC method using the titanium dioxide, titanium dioxide powder is used. It can be carried out by dispersing in a binder to prepare a coating liquid, coating the coating liquid on a conductive support, and drying to form a photosensitive layer on the support. As the conductive support, various ones may be used, but ones to which conductivity is imparted by coating, impregnating or filling various conductivity-imparting agents on, for example, paper or plastic film. Or
A conductive substrate such as a metal plate which is usually used in electrophotography can be used. Various kinds of binders may be used as the binder for forming the photosensitive layer. For example, acrylic resin, alkyd resin, polyester resin, vinyl resin, silicone resin, amino resin, polyurethane resin. And the like, and these may be used alone or in combination.

Furthermore, in producing an electrophotographic photosensitive material using the condensed titanium dioxide of the present invention, for example, photosensitivity, charging speed,
Various modifiers can be added to improve electrophotographic properties such as dark decay and their stability over time. Examples of the improving agent include, as spectral sensitivity improving agents, cyanine-based, xanthene-based, phthalein-based, triphenylmethane-based, diphenylmethane-based, oxazine-based, thiazine-based, and anthraquinone-based dyes, alone or in appropriate combination thereof. Can be used. In the above, the photosensitive layer composed of the condensed titanium dioxide according to the present invention is dye-sensitized so as to have a spectral sensitivity in a relatively long wavelength region, particularly in the near infrared region to the infrared region. Various kinds of sensitizing dyes can be used in the case of exposing with the laser beam light using a semiconductor laser which has been attracting attention. Those having a polar group such as a carboxyl group, a sulfonyl group and a hydroxyl group and having 3 or more methine groups are desirable. In order to increase the stability of the sensitizing action of the sensitizing dye, it is extremely desirable to use various organic acids or their acid anhydrides together. As the organic acid or the acid anhydride thereof, various ones can be used. For example, an aromatic cyclic acid such as phthalic acid or phthalic anhydride or an aliphatic dicarboxylic acid such as an acid anhydride thereof or maleic anhydride. Cyclic anhydrides and the like may be used, and it may be more desirable to use a higher fatty acid compound such as stearic acid in combination with these acid anhydrides.

The electrophotographic light-sensitive material of the present invention produced as described above has a 45 ° -45 ° specular gloss and 45 ° -0 ° on the surface of its photosensitive layer.
Gloss ratio to specular gloss is 0.7 to 2, preferably 0.7 to
It is 1.

The reason why the electrophotographic light-sensitive material of the present invention exhibits excellent electrophotographic properties when it is in a specific gloss ratio range has not been theoretically elucidated, but it is used as a photoconductive substance. Depending on the shape of the condensed titanium dioxide, its size, its filling state, etc., the titanium dioxide dispersed in the binder of the photosensitive layer becomes a state in which incident light is easily diffused, and in the photosensitive layer important as an electrophotographic photosensitive material. It is presumed that the utilization factor of light is increased, and as a result, electrophotographic characteristics such as photosensitivity are improved.

The present invention will be further described below with reference to Examples and Comparative Examples.

Example of the present invention

Example 1 200 g / aqueous solution of titanium tetrachloride was hydrolyzed at 75 ° C. for 2 hours in the presence of a rutile type seed crystal for hydrolysis to precipitate hydrated titanium oxide. This rutile type seed crystal for hydrolysis was prepared by aging 200 g / titanium tetrachloride aqueous solution of TiO ₂ at 20 ° C. while neutralizing the solution by adding sodium hydroxide, and aging the colloidal precipitate at 70 ° C. for 2 hours. It is a thing. This seed crystal was made to exist in a ratio containing 8 mol% Ti with respect to Ti in the titanium tetrachloride aqueous solution. The hydrous titanium dioxide precipitate produced by this hydrolysis was decanted twice, washed with water, filtered, repulped and neutralized with ammonia. The TiO ₂ yield by hydrolysis was 95%. ZnO fine powder corresponding to 2 mol% of TiO _{2 in} the neutralized product was added to the neutralized product, mixed, and filtered. The precipitate cake was dehydrated and then calcined at 780 ° C. for 2 hours.

This calcined product is put into water and a slurry (TiO ₂
g /), a small amount of water glass was added as a dispersant, the pH was adjusted to about 10 with sodium hydroxide, and the mixture was stirred. Then, the static classification method was used to remove particles of about 5 μm or more, and hydrofluoric acid was added to the obtained slurry to reduce the hydrofluoric acid concentration in the slurry to 3
The content was adjusted to wt%, and the mixture was gently stirred and immersed for 1 hour. After the treatment, the solid matter in the slurry was filtered, washed and dried at 300 ° C to obtain the condensed titanium dioxide according to the present invention. This had the shape seen in the electron micrograph of FIG. 1, and its oil absorption was 47.

Then, as a sensitizing dye for the condensed titanium dioxide,
1- (2-Carboxyethyl) -4- [3- (3-ethylbenzothiazoline-2-ylidene) -1-propen-1-yl] quinolinium iodide was applied by a conventional method. The processing amount is Ti
It is 0.003% by weight with respect to O ₂ .

16 g of condensed titanium dioxide coated with a sensitizing dye, 0.6 g of zinc naphthenate (8% by weight of Zn), Aroset 5804XC 12.7 g, and 14.4 ml of xylene are lightly mixed with a paint shaker containing glass beads to paste. And

Apply 15μ of this paste on a conductive paper with a doctor blade.
Then, the electrophotographic light-sensitive material of the present invention (Sample A) was obtained by applying the solution to a thickness of m and drying at 120 ° C. for 3 minutes. This was subjected to measurement of photosensitivity, dark decay rate and specular gloss, and the results are shown in Table 1.

The photosensitivity was represented by the time required for the potential to decrease to 60 V by continuous exposure after 300 V charging by the dynamic method of Kawaguchi Denki Paper Analyzer. Therefore, the smaller this value, the better the sensitivity. The exposure was performed using a tungsten light source, adjusting the illuminance on the surface of the photosensitive material with white light to be 1000 lux, and performing it through a red light filter.

The dark decay rate is based on Kawaguchi Denki's paper analyzer (EPA-81
00), from the potential V ₀ when corona charging is performed at −6 KV for 20 seconds by the dynamic method and the potential V ₂₀ when corona charging is stopped immediately after reaching V ₀ and left in the dark for 20 seconds, (V _0-
It was determined as V ₂₀ ) / V ₀ × 100. The gloss ratio of the photosensitive layer surface
45 ° -45 ° specular gloss (x) and 45 ° -0 ° specular gloss (y) were measured with a gloss meter (GM-26 type manufactured by Murakami Color Research Laboratory), and the value was (x) / (y ).

Example 2 The procedure of Example 1 was repeated except that hydrochloric acid was added instead of hydrofluoric acid (concentration of hydrochloric acid in the slurry was 3%) to obtain the condensed titanium dioxide according to the present invention. It was This had an oil absorption of 46.

Then, the electrophotographic photosensitive material of the present invention (Sample B) was processed in the same manner as in Example 1 and subjected to measurement of photosensitivity, dark decay rate and specular gloss in the same manner as in Example 1, and the results are The results are shown in Table 1.

Comparative Example Titanium dioxide was obtained in the same manner as in Example 1 except that the calcined product obtained in Example 1 was sufficiently pulverized as an aqueous slurry by a sand grinder.
This product had an oil absorption of 21, and an electron micrograph of this product is shown in FIG.

The titanium dioxide was treated in the same manner as in Example 1 to obtain an electrophotographic photosensitive material (Sample C), and subjected to measurement of photosensitivity, dark decay rate and specular gloss in the same manner as in Example 1. The results are shown in Table 1.

As is clear from the results in Table 1, Sample A according to the present invention
In the cases of B and B, the photosensitivity is excellent and the dark attenuation rate is superior to that of the sample C of the comparative example.

〔The invention's effect〕

The present invention provides a novel electrophotographic light-sensitive material that uses condensed titanium dioxide and has excellent electrophotographic characteristics, and has a great industrial contribution.

[Brief description of drawings]

FIG. 1 is an electron micrograph showing the particle structure of condensed titanium dioxide used as a photoconductive substance of the electrophotographic photosensitive material of the present invention (Example 1), and FIG. 3 is an electron micrograph showing the particle structure of titanium dioxide used as a photoconductive substance. Magnification is 10,000
Double.

Claims (5)

[Claims] 1. An electrophotographic photosensitive material obtained by laminating a photosensitive layer containing titanium dioxide and a binder as main components on a conductive support, wherein the titanium dioxide is a sintered aggregate of fine primary particles. Which is a condensed titanium dioxide having a rutile type crystal structure and an oil absorption of 35 to 65. 2. A condensed titanium dioxide obtained by allowing at least one compound containing an element selected from the group consisting of lithium, zinc, magnesium, calcium, strontium and barium to be present in hydrous titanium dioxide before calcination. It is titanium dioxide, It is characterized by the above-mentioned.
The electrophotographic light-sensitive material of (1). 3. The electrophotographic light-sensitive material according to claim 1, wherein the condensed titanium dioxide is treated with a mineral acid. 4. The mineral acid is hydrofluoric acid.
The electrophotographic light-sensitive material of (3). 5. A 45 ° -45 ° specular gloss of the photosensitive layer surface and a 45 °-
The electrophotographic light-sensitive material according to any one of claims (1) to (4), characterized in that the gloss ratio to 0 ° specular gloss is 0.7 to 2.