JP2734365B2 - Electrophotographic photoreceptor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic photoreceptor,
More specifically, the present invention relates to an electrophotographic photoreceptor having an intermediate layer provided between a conductive support and a photoconductive layer.

[0002]

2. Description of the Related Art In recent years, an organic electrophotographic photosensitive member has been widely used as an electrophotographic photosensitive member for a copying machine or a laser beam printer. Among them, a function-separated type organic electrophotographic photoreceptor in which a photoconductive layer is composed of a charge generation layer and a charge transport layer is increasingly used as a photoreceptor having a high degree of freedom in design of characteristics and high sensitivity. .

The charge generation layer is mainly formed of a charge generation material and an adhesive, and phthalocyanine pigments, bisazo pigments, and the like are often used as the charge generation material. On the other hand, the charge transport layer is formed by a charge transport material and an adhesive, and various compounds such as a hydrazone compound and a styryl compound are used as the charge transport material. The charge generation layer and the charge transport layer are formed by dispersing or dissolving the respective components in a solvent and coating the dispersion on a conductive support such as aluminum.

Further, in order to prevent fogging due to the surface properties of the conductive support, or to prevent deterioration of the charging ability of the photoreceptor caused by charge injection from the conductive support during charging, a photoconductive layer is used. An insulating intermediate layer is provided between the photoconductor and the conductive support (for example, an intermediate layer of a photoreceptor described in JP-A-1-238677). As the intermediate layer, a polymer compound such as polyamide, polyvinyl alcohol, polyvinyl butyral, and epoxy resin is used.

In such an electrophotographic photosensitive member having an intermediate layer between the conductive support and the photoconductive layer, the intermediate layer has a role of controlling charge injection from the conductive support to the photoconductive layer. I have. Therefore, it is necessary to have a resistance value that does not deteriorate the charging performance of the electrophotographic photoreceptor, a certain level of sensitivity, and a conductivity sufficient to reduce the residual potential to a certain level or less.

Therefore, it is desirable that the resistance of the intermediate layer be in a certain range. However, since the characteristics of an electrophotographic photosensitive member vary depending on the specifications of an apparatus using the same, the resistance value of the intermediate layer cannot be clearly limited. However, when the specific resistance value of the intermediate layer is 10 ¹⁵ Ω · cm or more, a problem that the residual potential becomes large occurs. When the specific resistance value is 10 ⁴ Ω · cm or less, a problem that the charging ability is too low seems to occur.

[0007]

Conventionally, an insulating polymer compound has been used as the intermediate layer as described above.
Some photoconductors using these polymer compounds as an intermediate layer exhibit good characteristics under normal temperature and normal humidity environment if the thickness of the intermediate layer is appropriate, but the intermediate layer under high temperature and low humidity environment The electric resistance of the molecular substance increases, and as a result, injection of charges from the photosensitive layer to the conductive support is hindered, resulting in a decrease in sensitivity and an increase in residual potential.

For example, when a polyamide resin is used for the intermediate layer, when a running test is performed, the residual potential does not rise at a moderate humidity, but rises at a low humidity. This seems to be because under moderate humidity, water molecules are adsorbed to the amide bond in the molecular chain of the polyamide resin which is originally an insulator, thereby giving the polyamide resin an appropriate conductivity. . Therefore, it is considered that the insulator becomes an original insulator under low humidity, and the residual potential increases.

Further, in a high-temperature and high-humidity environment, the electric resistance of the intermediate layer is reduced due to water absorption of the intermediate layer, so that the effect of preventing charge injection is weakened, and the charging ability of the photoreceptor is reduced. there were. Furthermore, in addition to these characteristics of the intermediate layer, the photoconductive layer itself has temperature characteristics such as low sensitivity to light at low temperatures and a decrease in charging ability at high temperatures. In addition, the charging ability and sensitivity of the photoreceptor fluctuate greatly in various environments, and undesired phenomena such as fogging and fluctuation in print density have occurred.

An object of the present invention is to provide an electrophotographic photoreceptor which improves the conventional intermediate layer and exhibits good characteristics under various environments.

[0011]

It is considered that the above-mentioned problems are caused by changes in the electrical characteristics of the intermediate layer under various temperatures and humidity, and by the temperature characteristics of the photoconductive layer. The present inventors have studied a method for controlling the characteristics of the photoconductor by controlling the charge injected from the conductive support to the photoconductive layer via the intermediate layer, and have reached the present invention.

That is, in an electrophotographic photosensitive member having a photoconductive layer formed on a conductive support, a powder having a positive resistance temperature coefficient and a powder having a negative resistance temperature coefficient are provided between the conductive support and the photoconductive layer. It has been found that the above-mentioned problem can be solved by providing an intermediate layer containing. And, in particular,
Barium titanate BaTiO ₃ powder with positive temperature coefficient of resistance
If the powder having a negative resistance temperature coefficient is a powder mainly containing at least one of cobalt oxide CoO, nickel oxide NiO, manganese oxide MnO, and iron oxide FeO, humidity and temperature It was found that good characteristics were obtained with respect to.

First, the powder mainly composed of BaTiO3 having a temperature coefficient of positive resistance used for the intermediate layer will be described.
BaTiO3 is silicon Si, aluminum Al , nickel Ni, cobalt Co, chromium Cr, manganese Mn,
Lantern La , samarium Sm, dysprosium Dy,
A ceramic is produced by including at least one kind of yttrium Y as a trace impurity, and the ceramic has a unique property that its specific resistance is greatly increased near the Curie point (positive temperature coefficient, abbreviated as PTC characteristic). The PTC characteristics vary depending on the amount of impurities to be added or the firing conditions when producing the ceramic.
The Curie point can be changed by substituting a part of Ba atom with another atom or substituting a part of Ti atom with another atom.

When one of the impurities, for example, Mn, is added to BaTiO ₃ , the specific resistance greatly changes around 120 ° C. The temperature range used for the electrophotographic photoreceptor is 1
Since the temperature is about 0 to 40 ° C., the temperature at which the specific resistance changes is preferably about 0 ° C. or less.

To lower the Curie point of BaTiO3,
Some of the Ba atoms are strontium Sr and calcium C
a, magnesium Mg or lead Pb may be replaced by at least one atom, or a part of Ti atoms may be replaced by zirconium Zr or tin Sn. For example, by replacing 30% of Ba atoms with Sr, the temperature at which the specific resistance changes becomes about −10 ° C., the specific resistance at 0 ° C. is about several hundred kilohms, and the specific resistance at 40 ° C. Ten megaohm ceramics can be made.

Next, a powder having a negative resistance temperature coefficient used together with the ceramic powder containing BaTiO3 as a main component will be described. As powder with negative temperature coefficient of resistance , C
Ceramic powder mainly composed of oO, NiO, MnO, and FeO can be used. These are ceramics having a negative resistance temperature coefficient by replacing each metal with a monovalent metal. NiO will be described as an example. In the case of NiO, a part of NiO is lithium L
By substituting with i, a ceramic having a negative temperature coefficient of resistance can be obtained. This is because divalent Ni is replaced by monovalent Li, so that holes close to the number of Li are introduced into the crystal, and Ni
This is because O becomes a P-type semiconductor.

According to a third aspect of the present invention, the intermediate layer is formed of a ceramic powder having a positive temperature coefficient of resistance, a ceramic powder having a negative temperature coefficient of resistance, and an adhesive. Therefore, the resistance value is not significantly affected by humidity. This is because the powder has no water absorption. Therefore, there is nothing like the above-mentioned polyamide resin.

As for the temperature characteristics of the photoconductive layer, an ordinary photoconductive layer often has a characteristic that the sensitivity is low at a low temperature and the sensitivity is high at a high temperature. Therefore, in order to reduce the temperature characteristics of the electrophotographic photoreceptor, it is necessary to increase the resistance value of the intermediate layer as the temperature rises by using powder having a positive resistance temperature coefficient.

A ceramic having a normal temperature coefficient of positive resistance generally has a large temperature change in resistance. Taking the above-mentioned BaTiO ₃ -based ceramic as an example, the specific resistance at 0 ° C. is about several hundred kilohms, and that at 40 ° C. The resistance is several tens of megaohms and the temperature change of the resistance is extremely large. As described above, when the temperature change of the resistance of the ceramic is larger than the temperature characteristic of the sensitivity of the photoconductive layer, the temperature characteristic of the resistance of the intermediate layer in the intermediate layer consisting of only the ceramic having a positive resistance temperature coefficient and the adhesive is changed. Although possible to some extent, control over a sufficiently wide temperature range becomes difficult.

The temperature change of the resistance when a ceramic having a positive temperature coefficient of resistance is used can be suppressed to a small value by the composition of the ceramic, but at the same time, the temperature at which other characteristics, for example, the specific resistance greatly changes, that is, the Curie temperature Characteristic changes, such as a change in the point and a change in the specific resistance value as a whole, also occur, and much labor is required to obtain a ceramic having the required characteristics.

On the other hand, since the intermediate layer according to the present invention contains a powder having a positive resistance temperature coefficient and a powder having a negative resistance temperature coefficient, a sudden temperature change due to a ceramic having a positive resistance temperature coefficient can be suppressed.
The temperature coefficient of the resistor can be controlled over a considerable temperature range. Therefore, even if a plurality of electrophotographic photoconductors having different characteristics of the photoconductive layer are prepared, by changing the mixing ratio of the above-described powder, the temperature characteristics of the sensitivity can be relatively easily and easily improved. A photoconductor can be realized.

The intermediate layer of the present invention is formed by dispersing a powder having a positive resistance temperature coefficient and a powder having a negative resistance temperature coefficient in a binder to form a coating material (intermediate layer coating material) and applying it to a conductive support. be able to.

As the powder having a positive temperature coefficient of resistance, the above-mentioned Mn is used.
Ba _0.7 Sr _0.3 TiO ₃ ceramic to which Ni has been added, and Ni substituted with Li as a powder having a negative temperature coefficient of resistance.
The case where O is used will be described. First, although the ceramic has a positive temperature coefficient of resistance, the characteristics of the ceramic vary depending on the firing conditions. However, the ceramic exhibits a resistance of about 10 ^{5 at} 0 ° C. and about 10 ⁸ Ω · cm at 40 ° C. This is roughly pulverized and then further finely pulverized using a ball mill to obtain a powder. Li-substituted NiO
Is 0, although the resistance value varies depending on the Li substitution amount and the firing temperature.
It shows a resistance value of about 10 ⁵ at ° C and about 10 ⁴ Ω · cm at 40 ° C. The intermediate layer paint can be prepared by determining the mixing ratio of these powders according to the temperature characteristics of the photoconductive layer and dispersing and mixing the powder in a binder. This intermediate layer paint is applied on a conductive support and dried to form an intermediate layer.

The type of the binder resin used herein is not particularly limited as long as it has a film-forming property and has an adhesive property to a conductive support. However, the resistance value of the intermediate layer and the temperature / humidity characteristics differ depending on the type of the resin and the mixing ratio of the ceramic and the resin.

For example, when a polyvinyl butyral resin is used, if the ratio of the resin exceeds 80% by volume, the resistance value is large, and the temperature characteristic of the resistance does not show the positive temperature characteristic, which is not desirable as an intermediate layer. In the case of this combination of materials, the resin ratio is desirably 10 to 70% by volume.

The electrophotographic photoreceptor using the intermediate layer of the present invention exhibits stable characteristics under various environments because the resistance of the intermediate layer becomes small in the low temperature range where the sensitivity of the photoconductive layer becomes low. Charge injection from the photoconductive support is relatively easy to occur, which prevents a decrease in the sensitivity of the photoconductor at low temperatures, and in a high-temperature region where the sensitivity of the photoconductive layer increases, the resistance of the intermediate layer increases and the conductivity increases. It is considered that the charge injection from the photosensitive support is suppressed to some extent, and therefore, the increase in the sensitivity of the photoreceptor at a high temperature is suppressed. Further, the electrophotographic photoreceptor of the present invention is hardly affected by humidity. This is because the ceramic used for the intermediate layer has a stable resistance to humidity.

Next, the conductive support used in the present invention will be described. As the conductive support, it is possible to use a conventionally used material, for example, a metal such as aluminum, copper, and stainless steel, or a drum made of plastic or the like on which gold, palladium, conductive carbon, or the like is deposited or applied.

Examples of the charge generation material used in the charge generation layer of the photoconductive layer formed on the intermediate layer include metal-free phthalocyanine pigments, phthalocyanine pigments such as metal phthalocyanine pigments, anthraquinone pigments, monoazo, and the like. Known materials such as bisazo pigments may be used. And it can be used alone or in combination of two or more.

Examples of materials used for the charge transport layer of the photoconductive layer include known materials such as hydrazone compounds, carbazole compounds, oxadiazole compounds, indole compounds, and pyrazoline compounds.

When forming a charge generation layer and a charge transport layer,
Polymeric material with film forming properties, for example, polycarbonate,
Polyester, acrylic resin, etc., dichloromethane,
It is dissolved in a solvent such as chlorobenzene or tetrahydrofuran, and the above-mentioned charge generating substance and charge transporting substance are mixed into a solution of the polymer substance to form a paint, which is sequentially coated on the conductive support on which the intermediate layer is formed. , Formed by drying.

[0031]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited by these examples.

Example 1 BaTi _0.8 Sn _0.2 containing 0.1 mol% of Mn as a powder having a positive temperature coefficient of resistance.
O ₃ was used and was produced by the following method.
BaCO ₃ , TiO ₂ , and SnO ₂ were weighed so as to have the above-mentioned material composition. Next, 0.1 mol of MnCO ₃ was weighed with respect to 1 mol of the substance, and these were mixed for 10 hours in a ball mill using ethanol as a dispersion medium.

After mixing in a ball mill, the mixture was filtered, dried, and calcined in an electric furnace at 1100 ° C. for 2 hours. Subsequently, these were pulverized by a grinder and 1400 in an electric furnace.
C. for 5 hours. This calcined product is pulverized again by a refraction machine, and then ZrO 2 of φ2 is used as a dispersion medium with ethanol.
_{Using 2} balls, ball mill pulverized, particle size almost 1μ
powder with positive temperature coefficient of resistance of m, BaTi with Mn added
_0.8 Sn _0.2 O ₃ was prepared.

Next, as a powder having a negative resistance temperature coefficient, Fe
Was prepared by the following method using FeO in which 0.1 mol% of Li was replaced with Li. First, FeO, LiCO ₃
Was weighed so as to have the above-mentioned composition, and mixed with a grinder. Next, this mixture was fired at 1100 ° C. for 2 hours. Subsequently, pulverization was performed under the same conditions as in the above method to obtain a powder having a negative resistance temperature coefficient.

Next, the aforementioned temperature coefficient of positive resistance of BaTi
70 parts by weight of a powder of _0.8 Sn _0.2 O ₃ , 20 parts by weight of a Li-substituted FeO powder having a negative temperature coefficient of resistance, and 10 parts by weight of a polyamide powder were weighed and dispersed in methanol to give a solid content of 50% by weight. An intermediate layer paint was made.

Next, 4 parts by weight of X-type titanyl phthalocyanine, 4 parts by weight of polyvinyl butyral resin, and 92 parts by weight of tetrahydrofuran were mixed with a paint shaker to prepare a charge generating paint.

Next, 15 parts by weight of 4-dibenzylamino-2-methylbenzyldihydride-1,1-diphenylhydrazone as a charge transporting substance and polycarbonate 15
Parts by weight were dissolved in 70 parts by weight of dichloromethane to obtain a charge generating paint.

Next, an electrophotographic photosensitive member was prepared using the above-mentioned paint. The creation was as follows. First, thickness 1mm,
An intermediate layer paint is applied by dip coating onto an aluminum tube having an outer diameter of 30 mm and a length of 250 mm.
And dried to form an intermediate layer having a thickness of 20 μm. next,
The charge generating paint is applied on the intermediate layer in the same manner,
Drying was performed at 30 ° C. for 30 minutes to form a charge generation layer having a thickness of 0.3 μm. Finally, using a charge transport coating, the coating is applied in the same manner and dried at 110 ° C. for 30 minutes.
A charge transport layer having a thickness of μm was formed. FIG. 1 shows the first embodiment.
1 is a partial cross-sectional view of an electrophotographic photosensitive member according to the present invention. In the figure, an intermediate layer 2 and a conductive support 1 of an aluminum tube are provided.
The charge generation layer 3 and the charge transport layer 4 are sequentially formed.

Example 2 As a powder having a temperature coefficient of positive resistance, Ba _0.7 Sr _0.3 Ti containing 0.2 mol% of Mn was added.
O ₃ was used, and the same production process as in Example 1, that is, the raw materials were weighed, mixed, temporarily calcined, pulverized, main calcined, and pulverized to prepare a powder having a positive resistance temperature coefficient. However,
Here, SrCO ₃ was used instead of SnO ₂ as a raw material. In addition, NiO in which 0.1 mol% of Ni was replaced with Li was used as the powder having a negative resistance temperature coefficient, and a powder was prepared in the same manner as in Example 1.

An intermediate layer paint was prepared in the same manner as in Example 1.
An electrophotographic photoreceptor was prepared using the same conductive support, charge generation paint and charge transport paint as in Example 1.

Comparative Example 1 After forming a 0.2 μm polyamide resin as an intermediate layer, a charge generation layer and a charge transport layer were sequentially applied and dried in the same manner as in Example 1 to form an electrophotographic photosensitive member. It was created.

The electrophotographic photosensitive members obtained in Examples 1 and 2 and Comparative Example 1 were measured using an electrophotographic photosensitive member tester (manufactured by Gentec Corporation) under the following conditions.

A corona charge of -4 KV was performed, and the surface potential (V ₀ ), the potential (Vd) after leaving in a dark place for 5 seconds, and the potential (Vi after giving a light amount of 1.2 μJ / cm ² with a halogen lamp). ) Was measured to determine the dark decay DDR5 (Vd / V ₀ ). Temperature and humidity of the measurement environment are 10 ° C, 20% (LL condition), 24 ° C, 40% (NN condition), 35 ° C, 85%
(HH condition).

FIG. 2 shows the evaluation results. As is clear from FIG. 2, in the electrophotographic photoreceptor of the present invention, under each environment,
Characteristics such as charging ability, dark decay, and sensitivity are stable.

[0045]

As described above, since the intermediate layer of the electrophotographic photosensitive member of the present invention contains a powder having a positive resistance temperature coefficient and a powder having a negative resistance temperature coefficient, the temperature coefficient of resistance is considerably reduced. Can control. Therefore, even if a plurality of electrophotographic photoconductors having different characteristics of the photoconductive layer are prepared, by changing the mixing ratio of the above-described powder, the temperature characteristics of the sensitivity can be relatively easily and easily improved. A photoconductor can be realized.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view of an electrophotographic photosensitive member according to an embodiment of the present invention.

FIG. 2 is a table showing evaluation results of Examples 1 and 2 of the present invention and Comparative Example 1.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 conductive support 2 intermediate layer 3 charge generation layer 4 charge transport layer

Claims (5)

(57) [Claims] 1. An electrophotographic photosensitive member having a photoconductive layer formed on a conductive support, wherein a powder having a positive resistance temperature coefficient and a negative resistance temperature coefficient are provided between the conductive support and the photoconductive layer. An electrophotographic photoreceptor comprising an intermediate layer containing a powder. 2. The powder having a temperature coefficient of positive resistance contained in the intermediate layer is a powder containing barium titanate BaTiO ₃ as a main component, and the powder having a temperature coefficient of negative resistance is cobalt oxide Co.
2. The electrophotographic photosensitive member according to claim 1, wherein the powder is a powder mainly containing at least one of O, nickel oxide NiO, manganese oxide MnO, and iron oxide FeO. 3. The electrophotographic photoreceptor according to claim 2, wherein said powder having a positive resistance temperature coefficient and said powder having a negative resistance temperature coefficient are each a semiconductor ceramic. 4. The powder having a temperature coefficient of positive resistance of silicon Si, aluminum Al , nickel Ni, cobalt C
o, at least one of chromium Cr, manganese Mn, lanthanum La , samarium Sm, dysprosium Dy, yttrium Y, and barium titanate Ba
4. The electrophotographic photoreceptor according to claim 3, wherein TiO3 includes a material in which a part of titanium Ti atoms is replaced with at least one of tin Sn and zirconium Zr. 5. The powder having a temperature coefficient of positive resistance of silicon Si, aluminum Al , nickel Ni, cobalt C
o, at least one of chromium Cr, manganese Mn, lanthanum La , samarium Sm, dysprosium Dy, yttrium Y, and barium titanate Ba
Part of barium Ba atom of TiO3 is replaced with strontium S
r, calcium Ca, magnesium Mg or lead Pb
4. The electrophotographic photoreceptor according to claim 3, wherein the electrophotographic photoreceptor contains a compound substituted with at least one atom of the following.