JPH01174565A - Pigment dispersion liquid - Google Patents

Abstract

PURPOSE:To provide a dispersion of a pigment such as organic photoconductive pigment, characterized by specific shear rate and dispersion specific viscosity, having excellent dispersibility and dispersion stability and useful for the production of photosensitive material for electrophotography. CONSTITUTION:The objective dispersion has a shear rate Ds of <=10sec<-1> in the measurement of apparent viscosity and has a dispersion specific viscosity of 1-20, preferably 2.5-20 defined by the formula and measured by using a halogenated hydrocarbon solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a dispersion of a pigment such as an organic photoconductor pigment used in the production of an electrophotographic photoreceptor.

[Conventional technology]

An electrophotographic photoreceptor has a basic structure in which a photosensitive layer is formed on a conductive substrate. As a photoconductive material for forming this photosensitive layer, selenium has conventionally been commonly used, and other inorganic photoconductive materials such as cadmium sulfide and zinc oxide are also known.

However, in recent years, attempts have been made to improve film formability by using organic photoconductor pigments and to increase productivity by producing by coating.

The dispersibility and stability of this organic photoconductor pigment greatly affect the electrophotographic properties of a photoreceptor produced from the resulting dispersion.

An indicator of the dispersibility of this type of pigment is viscosity, and a change in viscosity is an indicator of dispersion stability.

If the dispersion stability is poor, the electrophotographic properties of the resulting photoreceptor are more likely to deteriorate by the time the photoreceptor is manufactured, even if the dispersion is allowed to stand still in a sealed container. When taking photographs, defects such as black spots and streaks tend to occur.

Regarding such dispersion stability, JP-A-60-177347 discloses that when a single cylindrical rotational viscometer is used and the rotational speed is 6 Orpm, the dispersion specific viscosity of formula (I) below is 0.8 to It is taught that a dispersion having a molecular weight of 2.5 is desirable from the viewpoint of dispersion stability in producing a photoreceptor.

[Problems that the temple is trying to solve]

In the prior art described in the above publication, the shear rate Ds is 7
The apparent viscosity is measured under the condition of 1.65 ec-'.

By the way, the dispersion liquid used when manufacturing electrophotographic photoreceptors uses a halogenated hydrocarbon solvent as a dispersant and an organic photoconductor pigment as a dispersoid, and is generally a non-Newtonian fluid and has pseudoplastic properties. Shows fluid behavior.

For such a non-Newtonian fluid, as in the prior art, the apparent viscosity is measured under a high shear rate, the dispersion specific viscosity is determined, and this is used as an index of the dispersion stability of the dispersion,
Even if a dispersion liquid having a dispersion specific viscosity in the range of 0.8 to 2.5 is used, a dispersion having excellent dispersion stability cannot be obtained.

Therefore, the main object of the present invention is to provide a dispersion liquid which has not only good dispersibility but also excellent dispersion stability.

[Means for solving problems]

The present invention for achieving the above object has the following gist.

When measuring the apparent viscosity, the shear rate Ds≦10 sec-
1 and having a dispersion specific viscosity defined below in the range of 1 to 20 when a halogenated hydrocarbon solvent is used as a solvent.

...(1) (Function) In the present invention, since the apparent viscosity is measured in a low shear rate region, it is important to note that the dispersion liquid for producing a photoreceptor exhibits pseudoplastic fluid behavior. Therefore, it is not only more reasonable, but also that the dispersion specific viscosity is within the range of the present invention, the dispersibility,
In particular, the dispersion stability is excellent as shown in the examples below.

[Specific structure of the invention]

The present invention will be explained in more detail below.

In the present invention, the apparent viscosity is measured using a cone-and-plate rotary viscometer, such as the "E-type viscometer" manufactured by Tokyo Keiki Co., Ltd., under conditions where the shear rate Da is 10 sec-' or less at 25°C. Perform with the number of revolutions.

Further, when a halogenated hydrocarbon solvent is used as a solvent, the dispersion specific viscosity of the above formula (1) is 1 to 20, preferably 2.8.
~20. When the dispersion specific viscosity is less than 1, the pigment is not sufficiently dispersed, and when it exceeds 20, the dispersion stability is poor.

The factors that should be selected to set the dispersion specific viscosity within the range of 1 to 20 include the degree of dispersion of the pigment (for example, the particle size distribution of the pigment, the average particle diameter, etc.), the type of dispersion machine, the dispersion operation conditions, and the formulation of the dispersion liquid. (particularly pigment concentration and binder resin content).

When the above dispersion is used for producing a total photoreceptor,
A dispersion is applied onto a conductive substrate.

The photoreceptor to be finally obtained by employing the present invention includes a single-layer photoreceptor in which an organic photoconductor pigment is dispersed as a charge-generating material in a charge transporting material layer on a conductive substrate; There is a functionally separated photoreceptor in which a charge transporting material layer is formed on a static substrate and a charge generating material layer is formed thereon.

In any case, the organic photoconductor pigments according to the present invention used as charge-generating materials include azo pigments, anthanthrone pigments, perylene pigments, phthalocyanine pigments,
Quinacridone pigments, cyanine pigments, biryllium pigments, thiopyrylium pigments, indigo pigments, scaric acid pigments, polycyclic medium non-based pigments, and the like can be used.

As pigment dispersants, alcohol solvents such as methanol, ethanol, and isopropyl alcohol, acetone,
Ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone, aromatic solvents such as benzene, toluene, xylene, and chlorobenzene, DMF, D
Various solvents such as MAC can be used. As a means of dispersion,
Methods such as a sand mill, colloid mill, attritor, and ball mill can be used.

Binder resins include polyvinyl butyral, formal resin, polyamide resin, polyurethane resin, cellulose resin, polyester resin, polysulfone resin,
Polycarbonate resin, acrylic resin, styrene resin, etc. are used.

When constructing a functionally separated photoreceptor, the charge generation layer can be formed by coating the above dispersion directly on a conductive substrate or on an intervening adhesive layer, and a charge transport layer is formed on the charge generation layer. Formed by coating. It is also possible that the charge generation layer is coated on the charge transport layer. The thickness of the charge generation layer is 5μ or less, preferably o, oi-iμ.
It is desirable to form a thin film layer with a thickness of . Most of the incident light is absorbed by the charge generation layer to generate a large amount of charge, and the generated charge carriers need to be injected into the charge transport layer without being deactivated by recombination or trapping. Thickness is preferred.

Coating is done by dip coating method, spray coating method,
spinner coating method, bead coating method, Meyer bar coating method, blade coating method,
This can be carried out using a coating method such as a roller coating method or a curtain coating method. For drying, it is preferable to dry to the touch at room temperature and then heat dry. Heat drying can be carried out at a temperature of 30 to 200° C. for a period of 5 minutes to 2 hours, either stationary or with ventilation.

The charge transport layer is electrically connected to the charge generation layer described above, and has the function of receiving and taking charge carriers injected from the charge generation layer in the presence of an electric field, and transporting these charge carriers to the surface. have. At this time, as described above, this charge transport layer may be laminated on or under the charge generation layer. However, it is desirable that the charge transport layer is laminated on the charge generation layer.

The material for transporting charge carriers in the charge transport layer (hereinafter simply referred to as charge transport material) is preferably substantially insensitive in the wavelength range of electromagnetic waves to which the charge generation layer is sensitive. The term "electromagnetic waves" used herein includes a broad definition of "light rays" including T-rays, X-rays, ultraviolet rays, visible light, near-infrared rays, infrared rays, far-infrared rays, and the like. When the photosensitive wavelength range of the charge transport layer coincides with or overlaps that of the charge generation layer, charge carriers generated in both layers trap each other, resulting in a decrease in sensitivity.

As the charge transport material, any known material can be used, and examples thereof include hydrazone derivatives, pyrazoline derivatives, triphenylamine derivatives, polyvinylcarbazole, and the like.

In addition to these organic charge transport materials, inorganic materials such as selenium, selenium-tellurium, amorphous silicon, and cadmium sulfide can also be used.

Further, these charge transport materials can be used alone or in combination of two or more.

When the charge transport material does not have film-forming properties, a film can be formed by selecting an appropriate binder. Examples of resins that can be used as binders include acrylic resin,
polyarylate, polyester, polycarbonate, polystyrene, acrylonitrile-styrene copolymer,
Insulating resins such as acrylonitrile-butadiene copolymers, polyvinyl butyral, polyvinyl formal, polysulfone polyacrylamides, polyamides, chlorinated rubber, or organic photoconductive polymers such as poly-N-vinylcarbazole, polyvinylanthracene, polyvinylpyrene, etc. Can be done.

As the conductive substrate, the substrate itself is conductive, such as aluminum, aluminum platinum, copper, zinc, stainless steel, vanadium, molybdenum, chromium, titanium, nickel, indium, gold, and platinum. In addition, aluminum, aluminum alloy,
Plastics (e.g., polyethylene, polypropylene,
Polyvinyl chloride, polyethylene terephthalate, acrylic resin, polyfluorinated ethylene, etc.), conductive particles (e.g. carbon black, silver particles, etc.) coated on plastic with a suitable binder, conductive particles coated on plastic or paper. It can be used for impregnated substrates, plastics with conductive polymers, etc.

A subbing layer having barrier and adhesive functions can also be provided between the conductive layer and the photosensitive layer.

〔Example〕

Next, the effects of the present invention will be clarified by examples.

(Example) In a sand grinder, using glass beads as the grinding media, a dispersion liquid having the following formulation was heated at 1500 rpm.
Dispersion was carried out for 250 minutes at a rotational speed of .

The glass peas were added in a volume of 45 ld.

(Comparative example) Pigment: 1.2wt/νO2%, binder resin: 0.6%
It was the same as the example except that wt/vow%, the rotation speed during dispersion was 650 rp+n, and the dispersion time was 8 hours.

Results> For each dispersion, changes over time in dispersion specific viscosity immediately after production were investigated, and the results shown in Table 1 were obtained.

Table 1: The apparent viscosity was measured using a cone-plate rotational viscometer at a shear rate of 9,605 ec at 25°C.
After rotating at -', this was stopped and the value after 1 minute was based.

On the other hand, each dispersion liquid was sealed tightly and allowed to stand for one month. When the dispersion liquid was visually observed, no sedimentation of the pigment was observed in the dispersion liquid in the example, whereas in the dispersion liquid in the comparative example, precipitation of the pigment was observed. 25% sedimentation was observed.

Further, photoreceptors were manufactured using each dispersion liquid, and changes in sensitivity between the time of manufacture and one month later were examined, and the results shown in Table 2 were obtained.

According to the above results in Table 2, it can be seen that the stability of the dispersion according to the present invention is significantly superior to that of the comparative example.

〔Effect of the invention〕

As described above, according to the present invention, a dispersion liquid having excellent dispersibility and stability can be obtained.

Claims (1)

[Claims] (1) When measuring the apparent viscosity, the shear rate Ds≦10se
c^-^1, and when a halogenated hydrocarbon solvent is used as a solvent, the dispersion specific viscosity defined below is 1 to 20.
A pigment dispersion liquid characterized by being in the range of . Dispersion specific viscosity = Apparent viscosity of pigment dispersion / Apparent viscosity of solution excluding pigment components