JPH06322283A - Stably storable x-type metal-free phthalocyanine-containing coating fluid and electrophotographic photoreceptor prepared by using it - Google Patents

Abstract

PURPOSE:To obtain a coating fluid which provides an electrophotographic photoreceptor with no deterioration of dark decay and excellent photosensitivity by incorporating a specified substance in the coating fluid consisting of at least an x-type metal-free phthalocyanine, a binder resin and an org. solvent. CONSTITUTION:The coating fluid consists of at least an X-type metal-free phthalocyanine, a binder resin (e.g. acrylic resin) and an org. solvent (e.g. dioxane), and further contains a phosphate surfactant, pref, phosphatidylcholine and more pref. soya lecithin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a storage-stabilized X-type metal-free phthalocyanine-containing coating liquid and an electrophotographic photosensitive member produced by using the same. , A binder resin, and an organic solvent, mainly phosphoric acid in order to prevent troubles such as change in liquidity and formation of precipitates that may occur during storage after preparation of the coating liquid for electrophotographic photoreceptor production. The present invention relates to a coating liquid in which an ester-based surfactant is present, and an electrophotographic photoreceptor manufactured using the coating liquid.

[0002]

2. Description of the Related Art A photoelectric conversion element using a photoelectric conversion substance, especially an electrophotographic photosensitive member, has been conventionally used in Se and Se / T.
Inorganic substances such as e, Se / As, CdS, Si and ZnO have been used, but none of them are sufficiently satisfactory in terms of width of photosensitive wavelength range, safety, processability, economical efficiency, etc. It has been found that organic compounds having various chemical structures called organic photo-semiconductors (abbreviated as OPC) are excellent materials that supplement the drawbacks of the above-mentioned inorganic substances, and many useful OPCs have been found. There are some that have already been put to practical use.

Among them, phthalocyanines are one of the most excellent OPCs, and have a wide photosensitive wavelength range from the visible light region to the near infrared region, high photosensitivity, stability (durability), and safety. It is well known for its outstanding features such as coating, processability, and economy. Phthalocyanines include metal phthalocyanines that form complex salts with metal ions such as copper, vanadium, iron, cobalt, nickel, titanium, zirconium, indium, germanium, tin, lead, molybdenum, and silicon, or metal-free phthalocyanines. Known and both are known as useful OPCs.

The present invention is particularly applicable to phthalocyanines.
For example, what is called an X-type metal-free phthalocyanine, which has been converted into a crystalline form which is useful as a photoconductive material in electrophotography, as described in JP-B-44-14106. The present invention relates to a coating liquid mainly used for producing an electrophotographic photosensitive member as a photosensitive material, and an electrophotographic photosensitive member produced by using the coating liquid. Such a coating liquid is physically and chemically stored during storage. It must be stable, and the electrophotographic photosensitive member produced by using such a coating liquid must not be inferior in electrophotographic characteristics.

That is, in electrophotography, an electrophotographic photoreceptor layer provided on a conductive support {a color material having a remarkable photoelectric conversion function such as phthalocyanine (which is a charge generating material: C
GM) and, if necessary, a charge transport material (CTM) dispersed in an insulating binder resin and applied, or a laminated structure in which a CGM layer and a CTM layer are overcoated. The present invention relates to electrophotographic photosensitive layers of all structures, but the present invention relates to electrophotographic photosensitive layers of all structures.} After electrostatically charging in the dark, the exposed portion of the exposed portion is imagewise exposed. The electric conductivity is increased, and as a result, a latent image composed of electrostatic charges is formed, and then a dry colored powder or colored powder suspension called toner is brought into contact with the electrostatic latent image to obtain a visible image (development). ) Is the basis of the imaging process.

Since the visible image density corresponds to the electrostatic potential value, it is generally desired that the electrostatic latent image has a potential as high as possible. However, since the electrophotographic photosensitive layer exhibits some dark conductivity, it is unavoidable that the potential at the time of development decreases with time (dark decay) compared to immediately after charging, but the dark decay should be as small as possible. I have to. Since the dark conductivity of the photoreceptor layer mainly depends on the materials constituting it, the materials used must be carefully selected.

In recent years, laser light, which is coherent light, has reached the stage of practical use, and due to its high resolution and high illuminance, it is possible to form an image by scanning exposure even in electrophotography, and it is used to obtain a fine image. Became. Moreover, coupled with the progress of computer technology, it converts the computer-processed image signal into on / off of laser light, and it becomes possible to directly expose computer-processed image information such as so-called computer-to-plate to the photoreceptor. For example, application to a large-sized photosensitive plate used for newspaper printing is being put to practical use. In the case of such a large-sized photosensitive plate, the decrease of the charging potential due to the dark decay during the scanning time required from the start to the completion of the image exposure scanning is not particularly preferable, and the dark resistance of the photosensitive member is reduced by the electrophotographic office work. It must be assembled from materials that are much larger than photoconductors for copiers (PPCs).

Among the phthalocyanines which are excellent OPCs, various metal phthalocyanines have a particularly large polarity because they are complex salts of metal ions and organic ligands, and therefore have a large dark conductivity, and metal phthalocyanines such as titanyloxy. Metal-free phthalocyanines, which have lower sensitivity but much lower dark conductivity than phthalocyanines, especially X-type metal-free phthalocyanines, are selected and used especially in the case of large plate photosensitive plates.

However, probably because X-type metal-free phthalocyanine has a crystallographically stable crystal structure, it often undergoes crystal-type transition and crystal growth with time in an organic solvent. It can be said to be a photosensitive material that is likely to become unusable because the liquid deteriorates during storage. Regarding the crystal type transition, it is possible to prevent it relatively easily by carefully selecting the organic solvent to be used and controlling the temperature during storage, but the cause of the crystal growth is still unclear. Large crystals that did not exist when liquid (for example,
A long needle-like crystal) appears after a lapse of time, the viscosity of the coating liquid increases, the precipitation of crystals occurs, and the non-smoothness of the coated surface is recognized, which often causes the coating liquid to become unusable.

This X-type metal-free phthalocyanine is usually
Phthalonitrile is heated in a basic medium to synthesize β-type phthalocyanine, which is dissolved in concentrated sulfuric acid and added dropwise to water to cause crystal transition to α-type, followed by mechanical grinding of α-type metal-free phthalocyanine. It is obtained by undergoing a crystal transition to an X-type by means of microscopic observation.
It has the appearance of a crushed stone of an order size, and there are no long needle-like crystals. Therefore, if a binder resin or a solvent is selected and a dispersing operation such as a paint conditioner is performed, a coating liquid that can be applied can be obtained. ,
The above-mentioned undesired alterations, especially changes in liquidity due to crystal growth, sedimentation and separation, etc. are often observed.
The frequency of failure can be reduced to some extent by examining the conditions for synthesizing the type phthalocyanine, the purification conditions, the α type milling conditions, the X type dispersion conditions, etc., but it is not yet complete.

Under the circumstances, the present inventor has made various studies to improve the reliability of the storage stability of the coating liquid, and as a result, the present invention has been born.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member which is a practical coating liquid having a high storage stability and high reliability, and which has excellent electrophotographic characteristics, particularly excellent dark decay characteristics. To provide a coating liquid containing at least X-type metal-free phthalocyanine, a binder resin, and an organic solvent. Another object is to provide an electrophotographic photosensitive member having excellent electrophotographic characteristics, particularly excellent dark decay characteristics.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to add a phosphate ester type surfactant to a coating liquid comprising at least an X type metal-free phthalocyanine, a binder resin and an organic solvent. Solved by

That is, although many kinds of surfactants are known for stabilizing the dispersion of the powder in the coating liquid, the powder in the coating liquid such as the system of the present invention is crystallographically The most suitable surfactant for a coating liquid that is a highly unstable new material, and the main purpose of the obtained coating liquid is an electrophotographic photoreceptor, which essentially dislikes the reduction in electrical resistance. There is no literature described, and it had to be found by repeating experiments and tests.

Thus, the inventor of the present invention prevents the crystal growth of the X-type metal-free phthalocyanine powder in the coating liquid, and as a result keeps the liquid properties of the coating liquid stable, and is manufactured using the coating liquid. In order to find a surfactant that makes the electrophotographic photosensitive member excellent, and when experiments and tests were performed patiently on a huge number of samples, it was possible to prevent the precipitation and separation of the powder to some extent, but crystal growth Most of them cannot be prevented, the electric resistance value of the electrophotographic photoconductor in the dark is remarkably reduced, and many are unsuitable for safety and economy. It has been found that only the phosphate ester type surfactant represented by phosphatidylcholine is suitable as the above.

Phosphatidylcholine is also called lecithin, and it is diacyl-L-3-glycerylphosphorylcholine (has two long-chain acyl groups, and the acyl group has 14 to 14 carbon atoms).
22 is common, and the two acyl groups may be the same), is a typical phospholipid, is contained in animal cells and plant seeds, exists as a zwitterion at any pH, and has surface activity. Therefore, it is understood that soybean lecithin from soybean is used as an emulsifier for foods and drugs, and there is no problem in terms of safety and resources.

Incidentally, as described above, it was a surprising fact that phosphatidylcholine was a zwitterion, but the dark resistance (dark decay) of the electrophotographic photosensitive layer containing it was not deteriorated.

[0018]

EXAMPLES Next, the present invention will be described in more detail by way of examples. The parts and% shown below are based on weight unless otherwise specified.

Example 1 P. J. Brachy et al. (Journal of Heterocyclic Chemistry, Vol. 7, p. 1403, 19
100 parts of β-type metal-free phthalocyanine (purple crystal) synthesized with reference to 70 years published as 70% reagent grade sulfuric acid (concentration 97
%) Of 2000%) under ice-water bath cooling, gradually added to dissolve, and filtered using a glass filter. This solution
To 20 000 parts of water (distilled water), while keeping the temperature below 20 ° C., it was added dropwise over 30 minutes, and after standing overnight, the supernatant was removed by decantation, and the precipitate was collected by suction filtration, and the filter cake It was washed with water until it became sexual. Furthermore, it was washed with diluted ammonia water and finally with methanol. This was dried overnight at 70 ° C. to obtain 90 parts of α-type metal-free phthalocyanine.

From the α-type metal-free phthalocyanine thus obtained, 5 g was placed in a agate pot (capacity 250 ml), 7 agate balls (20 mm in diameter) were added, and a planetary ball mill P-5 (Fritsch Japan Co., Ltd.) was added. Made), disk 360 rpm / pot, pot 780 rpm / min.
When the infrared absorption spectrum and the X-ray diffraction pattern were measured after grinding for 24 hours after setting to minutes, three strong absorption peaks were observed at 755, 735 and 717 cm ⁻¹ in the infrared absorption spectrum, In the X-ray diffraction pattern, the Bragg angle 2θ = 7.59, 9.13, 16.66, 17.
24, 22.24, 23.92, 27.20, 28.6
A specific diffraction peak was observed in the range of ± 0.2 degrees around 4,30.47 degrees. From these results,
From the α-type metal-free phthalocyanine obtained above,
It was found in Japanese Patent Publication No. 4-14106 that the same thing as that called X-type metal-free phthalocyanine was produced (sample code: X-1).

Example 2 24 g of α-type metal-free phthalocyanine obtained by the above method
And put it in an alumina pot (capacity 400 ml),
Add 400 g of alumina balls (diameter 10 mm) and
After ball milling for 10 days at 00 rpm, the infrared absorption spectrum and X-ray diffraction pattern were measured. As a result, the same thing as the X-form metal-free phthalocyanine was obtained in the same manner as above. It was found (Sample code: X-2).

Example 3 Using a commercially available reagent, metal-free phthalocyanine (provided to be crystallized α form by X-ray diffraction) as a crude pigment, a sulfuric acid solution was dropped into a large amount of cold water in the same manner as in Example 1. The precipitate was collected by filtration, washed with water, and dried to obtain the same α-type metal-free phthalocyanine as in Example 1. With respect to this, crystal transition to the X type was carried out by a ball mill grinding treatment using an alumina pot and balls in the same manner as in Example 2 (sample symbol: X-3).

Example 4 Using the X-type metal-free phthalocyanine (sample symbol: X-1, X-2 or X-3) produced in Example 1, Example 2 or Example 3, the following formulation was applied. The liquid was prepared. X-type metal-free phthalocyanine 1 part Acrylic resin (binder resin) 6 parts Dioxane (organic solvent) 93 parts To a mixture of these three, 0 parts (blank), 0.01 parts, 0.025 of soya lecithin Part, 0.05
Parts, 0.10 parts or 0.20 parts, and dispersed together with the glass beads by shaking vigorously with a paint conditioner in a closed container for 2 hours, removing the glass beads by sieving and applying a dark blue coating. A liquid was obtained. Each sample was sampled on the day of preparation of the coating liquid, and the viscosity at 20 ° C. was immediately measured using an E-type viscometer. Further, each coating solution was applied onto an aluminum plate subjected to surface anodization treatment using a wire-wound doctor so that the solid coating amount after drying was 6 g / m ^2, and dried at 80 ° C. to obtain a black bag. I put it in and left it for a day. The rest of the coating liquid was stored at 25 ° C or lower in a closed container.

An electrostatic recording tester (SP-42 manufactured by Kawaguchi Electric Co., Ltd.) was used for each of the thus prepared single-layer type electrophotographic photosensitive members.
According to 8), the electrophotographic characteristics were measured. Measurement conditions: Applied voltage + 6kV, light source tungsten
Lamp, sample surface illuminance 2 lux

The measurement results are shown in Table 1. In Table 1, D
D (%) is the surface potential residual percentage after 10 seconds in the dark.

[0026]

[Table 1]

From Table 1, even when soya lecithin, which is one of the phosphoric acid ester type surfactants, is added to the coating liquid, the coating liquid viscosity and the electrophotographic characteristic values relating to the electrophotographic sensitivity and dark decay are almost the same. You can see that they are not affected.

Example 5 The coating solution prepared in Example 4 was stored at 25 ° C. or below for 2 weeks, and the viscosity of each coating solution was measured under the same conditions as in Example 4,
Then, a single-layer type electrophotographic photosensitive member was prepared by applying the same method on an aluminum plate, and the electrophotographic characteristics were measured. The measurement results are shown in Table 2.

[0029]

[Table 2]

As shown in Table 2, when no soya lecithin, which is one of the phosphoric acid ester type surfactants, was added to the coating solution (blank), the viscosity increased remarkably after 2 weeks of storage, and X
In the case of -1, X-2, it was manageable, but the leveling of the coating surface was poor, and it was a poor coating sample in which streaky coating unevenness was observed (therefore, the electrophotographic characteristic values are shown in parentheses). did). In the case of X-3, the viscosity was so high that the viscosity could not be measured with an E-type viscometer (> 600 cp), and according to scanning electron microscope observation, X-type metal-free phthalocyanine was crystallized into needle crystals. Growth and aggregation were also observed, and the coating was impossible (therefore, the electrophotographic characteristic values could not be measured).

On the other hand, when soya lecithin was added to the coating solution, there was almost no increase in viscosity even after 2 weeks of storage, or even if it was, it was within the range of application and deterioration of electrophotographic characteristic values was observed. However, the effect of stabilizing coating solution storage was even dramatic when soya lecithin was added to the coating solution. Of course, no defect was found in the image after charging, image exposure, development and fixing.

[0032]

As is apparent from the examples, at least the X-type metal-free phthalocyanine, the binder resin and the organic solvent are used.
The presence of a phosphoric acid ester-based surfactant in the coating liquid of the present invention makes it possible to obtain an X-type metal-free phthalocyanine-containing coating liquid which is storage-stabilized not only in the liquid properties of the coating liquid but also in the electrophotographic characteristics. I understood. Especially, the effect is remarkable when the phosphate ester surfactant is phosphatidylcholine, and it is practical to use, for example, soya lecithin as the phosphatidylcholine in terms of safety and economy. The electrophotographic photosensitive member produced using the X-type metal-free phthalocyanine-containing coating liquid thus storage-stabilized was excellent in high photosensitivity without deterioration of dark decay.

Claims (4)

[Claims] 1. A storage-stabilized coating liquid comprising at least an X-type metal-free phthalocyanine, a binder resin and an organic solvent, wherein a phosphate ester surfactant is further present. X-type metal-free phthalocyanine-containing coating liquid. 2. The storage-stabilized X according to claim 1, wherein the phosphate ester surfactant is phosphatidylcholine.
Type Metal-free coating liquid containing phthalocyanine. 3. The storage-stabilized X-type metal-free phthalocyanine-containing coating liquid according to claim 2, wherein the phosphatidylcholine is soya lecithin. 4. An electrophotographic photoreceptor manufactured using the storage-stabilized X-type metal-free phthalocyanine-containing coating liquid according to claim 1, claim 2, or claim 3.