JPS5840177B2 - Kankouseidenshishashinyouzairiyo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photosensitive electrophotographic material containing titanium dioxide as an inorganic photosensitive pigment.

More specifically, after the surface of the photosensitive material is uniformly charged by corona exposure, the charge in the exposed area is attenuated by imagewise exposure to form an electrostatic latent image, and then an electroscopic colored toner is applied to the electrostatic latent image. The present invention relates to a photosensitive material used in so-called electrophotography, which is deposited onto a photosensitive material to form a visible image on the photosensitive material.

Photosensitive electrophotographic materials having a conductive substrate and a photoconductive layer thereon consisting of an inorganic photosensitive pigment and a binder resin have been well known. Zinc, selenium, cadmium sulfide, etc. are known.

In addition, it is known that titanium dioxide can also be used as an inorganic photosensitive pigment.It has excellent pigment properties and produces good white dust on the surface of the photosensitive layer, and has a high dielectric constant, so it can be used to thin the photosensitive layer. It has excellent properties such as a large amount of charge retention even when it is used, a light-sensitive layer due to its low specific gravity, and an ability to easily obtain images with good continuous gradation.

However, such photosensitive materials using titanium dioxide have inferior photosensitivity and charge retention in the dark compared to photosensitive materials using zinc oxide, which are currently in widespread practical use, and also have poor selectivity with respect to binder resins. However, the electrophotographic properties such as chargeability, dark retention, and light attenuation are significantly affected by the type of resin. Furthermore, conventional titanium dioxide for electrophotography is of extremely high purity. It has not been put into practical use because of the necessity of

As a method for improving the electrophotographic properties of titanium dioxide, for example, in Kogyo Kagaku Zasshi Vol. 70, No. 8, p. 1285, for the purpose of improving the photosensitivity of titanium dioxide, high purity titanium dioxide is mixed with nitrates of various metals in the presence of 1,000 ml of titanium dioxide. We proposed to actively incorporate impurities into titanium dioxide by baking it at ℃ for 2 hours, and we measured and studied the photocurrent and dark current.

It has been reported that PbO, CaO, and MgO improve the photosensitivity of titanium dioxide, but Z n Os Li20 and others do not have a positive effect on photosensitivity.

The present inventors investigated the relationship between the photocurrent of titanium dioxide and the electrophotographic properties of a photosensitive layer obtained by dispersing titanium dioxide well in a binder resin and coating it on a conductive substrate. There was no clear correlation between the impurities (ZnO, L
It has been found that some materials (such as i2O) can improve electrophotographic properties when used as a photosensitive layer.

Further detailed research revealed that in the process of the formation or growth of titanium dioxide crystals, i.e., the calcination process of hydrated titanium oxide, the gas phase oxidation process of titanium tetrachloride, or the recalcination process of crystalline titanium dioxide, the following specificities were identified. It has been found that titanium dioxide obtained in the presence of a metal compound exhibits excellent electrophotographic properties when dispersed in a resin.

That is, the present invention provides for the production or growth of titanium dioxide crystals in the presence of one or more compounds containing an element selected from the group consisting of lithium, zinc, magnesium, calcium, strontium, and hyhalium. This is a photosensitive electrophotographic material in which the obtained titanium dioxide is dispersed in a binder resin.

There are various methods for producing titanium dioxide.

There are a method of calcining hydrated titanium oxide obtained by hydrolyzing titanium tetrachloride or titanium sulfate, a method of vapor phase oxidation of titanium tetrachloride with an oxygen-containing gas, a method of thermally decomposing ammonium titanyl sulfate, etc.

In the present invention, in these methods, the metal compound described below is present in the process of generating or growing titanium dioxide crystals.

The process of crystal formation is the calcination process of hydrated titanium oxide,
The term "growth process" refers to a step of gas-phase oxidation of titanium tetrachloride, a step of thermal decomposition of ammonium titanyl sulfate, etc., and a step of re-firing crystalline titanium dioxide.

It is preferable that titanium dioxide contains as little as possible other than the metal compounds present during the above-mentioned generation or growth process.

For example, Fe, Mn, Ni, Co, V, Cr s P
Compounds such as N Al s Si have a strong unfavorable effect on electrophotographic properties, so it is desirable to avoid them as much as possible, but compounds such as Na, B, etc.
Although no favorable effects can be expected, it does not have any adverse effects in small amounts, so it may be included for other purposes, such as controlling the particle shape and particle size of pigments, to the extent that it does not harm the electrophotographic properties. good.

The crystallinity of titanium dioxide generally includes rutile type and anatase type, but in the present invention, it can be used regardless of the crystal form.

Lithium, zinc, magnesium, calcium, coexisting in the process of titanium dioxide crystal formation or growth,
Compounds containing strontium, barium, etc.
These various metal oxides, hydroxides, logenides,
Nitrates, sulfates, organic acid salts, etc. can be used.

The amount of these compounds to be added varies depending on the metal and cannot be unconditionally defined, but is generally 0.001 to 5 mol%, preferably 0.01 to 5 mol% of the metal element based on TiO2.
It is.

In particular, when the metal is lithium, it is preferably 0.02 to 0.2 mol% as Li based on TiO2, and when the metal is zinc or other metals, it is preferably 0.1 to 5 mol% as a metal element based on TiO2.

When the amount is less than the above range, the desired effect cannot be obtained, and when it is too much, the properties of titanium dioxide are impaired and other undesirable effects appear.

Among the above-mentioned metals, zinc has a remarkable effect on improving the dark retention property compared to other metals, as is clear from the results of Examples described later.

Although the reason for this is not clear, it is thought that zinc is the only transition metal in the above group and that it has excellent thermal diffusivity with respect to titanium dioxide.

The processing conditions for the process in which titanium dioxide crystals are generated or grown vary depending on the titanium dioxide manufacturing method employed.

If kept, calcination of hydrated titanium oxide or recalcination of crystalline titanium dioxide is carried out for 1 to 3 hours, preferably 1 to 2 hours, and
The temperature is 980°C, preferably 700-850°C.

At temperatures below 600°C, the formation or growth of titanium dioxide crystals is difficult, and favorable effects cannot be obtained;
Prolonged processing at temperatures above 0.degree. C. causes drawbacks such as a decrease in photosensitivity.

Gas-phase oxidation of titanium tetrachloride takes 5 minutes at most, 900 to 15
The temperature is preferably 1000 to 1300°C.

If the reaction time is too long, the electrophotographic properties may be adversely affected, and if the reaction time is below 900°C, titanium dioxide has poor pigment properties, which is not preferable.

Thermal decomposition of ammonium titanyl sulfate is normally 70
The temperature is 0 to 980°C, preferably 800 to 900°C.

The titanium dioxide treated as described above is pulverized and dispersed in a binder resin to produce the photosensitive material of the present invention.

At that time, commonly known electron affinity substances,
Electron-donating substances, sensitizing dyes, metal salts of organic acids, etc. can also be added.

Alternatively, the substance such as an electron-affinity substance may be fixed or adhered to the surface of titanium dioxide in advance and then dispersed in the resin.

Furthermore, titanium dioxide having a metal salt of an organic acid on its surface can be heat-treated and then dispersed in the resin.

The binder resin to be used may be one that is electrically insulating and has film-forming properties, such as acrylic resin, alkyd resin,
There are polyester resins, vinyl resins, polyurethane resins, various natural resins, synthetic rubbers, amine resins, polyolefin resins, etc., and these can be used alone or in combination of two or more depending on the purpose.

In addition, sensitizing dyes include xanthine type rhodamine B1 fluorescein, uranine, acridine type acriflavine, oxazine type brilliant cresyl blue, triphenylmethane type eosin, eriochrome cyanine R, anthraquinone type alizarin, etc. Cyanine-based NK-79, NK-85, etc. can be used.

The conductive substrate used in the present invention may be any material having higher conductivity than the photoconductive layer, such as paper, cloth or metal sheet coated with a conductive substance commonly used in electrophotography, or a metal sheet. Vapor-deposited plastic sheets, paper laminated with metal boxes, etc. can be used.

Example 1 A titanium sulfate solution obtained by dissolving titanium ore in sulfuric acid is hydrolyzed to precipitate hydrated titanium oxide, and this precipitate is filtered, washed, dried, and then ground to form hydrated titanium oxide powder. Obtained.

Adding a zinc acetate aqueous solution to this hydrated titanium oxide as Zn
After addition and mixing at a ratio of 1 mol % to O2, it was fired in an electric furnace at SOO° C. for 2 hours and pulverized to obtain titanium oxide of about 0.5 μm.

This titanium oxide 8'? And glass peas about 30'? and acrylic resin (trade name Acridic A-405, manufactured by Nippon Reichhold) 4P and zinc naphthenate as Zn.
, oosy and 4 ml of xylene were placed in a glass bottle, mixed in a quick mill for 5 minutes, applied on aluminum foil with a wire applicator, dried by heating at 120°C for 30 minutes, and left in a dark place for 2 days. A photosensitive material of the present invention was obtained.

The thickness of the dried coating film was about 17μ.

The electrophotographic properties of the photosensitive material thus obtained were measured using Paper Analyzer Model 5P-428 manufactured by Kawaguchi Denki, and the results were as shown in the attached table.

The results were evaluated by drawing electrophotographic characteristic curves for both dynamic and static methods using the apparatus.

The charging characteristics are the surface potential (initial potential) reached in 20 seconds with dynamic corona charging, and the retention of surface charge in the dark is the surface potential reached 20 seconds after 20 seconds of dynamic charging. As a percentage of the initial potential,
The photosensitivity was expressed by the optical attenuation half-life when the pre-exposure potential was 200 volts using the static method.

The applied voltage during corona charging was 16KV, and the exposure illuminance was 30KV.
It was set to 0 lux.

Comparative Example 1 A photosensitive material was prepared in the same manner as in Example 1, except that the hydrated iron oxide was calcined as it was at 800° C. for 2 hours and pulverized, and its electrophotographic properties were measured.

Example 2 A photosensitive material was prepared in the same manner as in Example 1, except that a high-purity titanium tetrachloride solution was hydrolyzed in place of the titanium sulfate solution to precipitate hydrated titanium oxide, and its electrophotographic properties were determined. was measured.

Comparative Example 2 A photosensitive material was prepared in the same manner as in Example 2 except that zinc acetate was not added when firing the hydrated titanium oxide, and its electrophotographic properties were measured.

Example 3 In Example 1, calcium acetate was added as Ca in place of zinc acetate at a ratio of 0.5 mol% to TiO2 during firing, and zinc octylate was preliminarily applied to the surface of titanium oxide after firing. A photosensitive material was prepared in the same manner except that zinc naphthenate was not added when dispersing in the binder resin, and its electrophotographic properties were measured.

Comparative Example 3 A photosensitive material was prepared in the same manner as in Example 3, except that no metal salt was added during firing and zinc naphthenate was fixed on the titanium oxide surface in place of zinc octylate. Electrophotographic properties were measured.

Example 4 A photosensitive material was prepared in the same manner as in Example 3 except that lithium acetate was added as Li in place of calcium acetate at a ratio of 0.2 mol% to TiO2 during firing. Electrophotographic properties were measured.

Example 5: During the firing of hydrated titanium oxide, magnesium acetate was added and mixed in place of zinc acetate at a ratio of 0.2 mol% to TiO2, and then fired at 850°C, and in the preparation of photosensitive materials. In this case, acrylic resin (trade name Metalac M Clear, Fujikura Kasei Products) was used, and 0.005% (based on the weight of TiO2) of each of the pigments uranine, rhodamine B, and brilliant cresyl blue was added instead of zinc naphthenate. Except for this, a photosensitive material was prepared in the same manner as in Example 1, and its electrophotographic properties were measured.

Example 6 In Example 5, magnesium acetate was 0.5 mol% as Mg and calcium acetate was 0.5 mol % as Mg, and calcium acetate was
A photosensitive material was prepared in the same manner except that 0.5 mol % of a was added, and its electrophotographic properties were measured.

Example 7 A photosensitive material was prepared in the same manner as in Example 5 except that zinc acetate was added to TiO2 at a ratio of 0.2 mol% as Zn and calcium acetate was added as 0.5 mol% as Ca. Then, its electrophotographic properties were measured.

Claims (1)

[Claims] 1 Containing an element selected from the group consisting of lithium, zinc, magnesium, calcium, strontium, and barium in the process of forming or growing titanium dioxide crystals 1
A photosensitive electrophotographic material in which titanium dioxide obtained in the presence of a species or two or more compounds is dispersed in a binder resin.