JPH0336220B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic photoreceptor for a laser printer. More specifically, the present invention relates to an electrophotographic photoreceptor for laser printers that does not exhibit density unevenness in the form of interference fringes and can reproduce solid images well.

Conventionally, photoreceptors for electrophotographic printers that use a laser as a light source have been made of selenium, selenium-based alloys,
Cadmium sulfide resin dispersions, charge transfer complexes of polyvinylcarbazole and trinitrofluorenone, and the like have been used. Furthermore, gas lasers such as helium-cadmium, argon, and helium-neon are used as lasers, and semiconductor lasers that are small, low cost, and capable of direct modulation have come to be used.

As for photoreceptors, a laminated photoreceptor including a charge transfer layer and a charge generation layer is attracting attention in order to obtain sufficient sensitivity and charging characteristics depending on the wavelength of the laser beam used. Compared to a photoreceptor that uses a single photoconductive layer, in a laminated photoreceptor, photosensitization can depend only on the charge generation layer, so it is relatively easy to use a photoconductive material that is sensitive to the wavelength of the laser light used. You can choose freely.

The charge generation layer of the laminated photoreceptor has the role of absorbing light and generating free charges, and its thickness is 0.1
It is usually as thin as ~5 μm. The charge transfer layer is
A material that has the role of receiving electrostatic charges and transporting free charges and does not absorb image forming light is used, and its thickness is usually 5 to 30 μm.

By the way, when using such a laminated photoreceptor and outputting an image by scanning a line of laser light with a laser printer, there is no problem with line images such as characters, but in the case of solid images, interference fringe-like density may occur. Unevenness appears.

The cause of this is thought to be interference between the light reflected on the surface of the charge transfer layer and the light reflected on the surface of the substrate such as metal. That is, the laminated electrophotographic photoreceptor has a charge generation layer 2 and a charge transfer layer 3 on a base 1, as shown in FIG.
It has a laminated structure. Laser light 4 (emission wavelength is about 0.8 μm for a semiconductor laser, for example, or about 0.8 μm for a helium-neon laser) is applied to this laminated photoreceptor.
0.63 μm), as shown in Figure 2, the reflected light 5 on the surface of the charge transfer layer 3 with large reflection,
Interference occurs with light 6 reflected from the surface of the substrate 1 and emerging from the surface of the charge transfer layer 3. The refractive index of the laminated layer of the charge generation layer 2 and the charge transfer layer 3 is n, the thickness is d ₁ ,
If the wavelength of the laser beam is λ, when nd ₁ is an integral multiple of λ/2, the intensity of the reflected light is maximum, that is, the intensity of the light entering the charge transfer layer 3 is minimum (according to the law of conservation of energy). , nd ₁ is an odd multiple of λ/4, the reflected light is minimal, that is, the light entering the interior is maximal. By the way, d ₁ has a manufacturing certificate of 1μ
It is unavoidable that there will be unevenness in the area of about m. Since laser light has good monochromaticity and is coherent, the above-mentioned interference condition changes in response to the unevenness of _d1 , causing unevenness in the amount of laser light absorbed in the charge generation layer 2,
It is thought that this appears as interference fringe-like unevenness in the density of the solid image. In addition, in a normal copy machine,
Since the light source is not monochromatic, the width of the interference fringe-like density unevenness changes depending on the wavelength, and is averaged out and cannot be seen.

SUMMARY OF THE INVENTION A main object of the present invention is to provide a laminated photoreceptor that does not cause density unevenness due to interference when used in a laser printer.

The electrophotographic photoreceptor for a laser printer according to the present invention is characterized by having a charge transfer layer and a charge generation layer having a transmittance of 10% or less to the laser light used. That is, by controlling the transmittance of the charge generation layer to laser light to be 10% or less, interference of the laser light is prevented and a photoreceptor is provided which can provide a solid image with uniform density.

The electrophotographic photoreceptor for laser printers of the present invention has a structure in which a charge generation layer 2 and a charge transfer layer 3 are laminated on a base 1 as shown in FIG. The transmittance is 10% or less. When the transmittance is 10% or less, the incident laser light enters the charge transfer layer 3, is absorbed by the charge generation layer 2, is reflected on the surface of the substrate 1,
It is absorbed again by the charge generation layer 2, and before it returns to the surface of the charge transfer layer 3, it is absorbed back and forth, so that it is attenuated to 1% or less. A value of 10% or less for the transmittance is a value that, after various experiments, has been used to obtain a solid image with a uniform density that does not pose any practical problems. It is thought that this is occurring, although it is small. In addition, in particular, 5% or less is more suitable.

As shown in Figure 2, if the thickness of the charge generation layer 2 that absorbs laser light is d ₂ cm, and the absorption coefficient of the charge generation layer 2 with respect to the laser light is αcm ^-1 , then the incident light Io and the transmittance are The relationship with I is given by the following equation.

I=Ioexp(-αd ₂ ) To make the transmittance 10% or less, that is, I/Io smaller than 0.1, αd ₂ should be made larger than 2.3. To increase αd ₂ , the thickness of charge generation layer 2
It is sufficient to increase d ₂ or increase the absorption coefficient α. In order to increase α, there are methods such as bringing the peak of spectral absorption of the charge generation layer 2 closer to the emission wavelength of the laser used, and mixing a dye that absorbs laser light into the charge generation layer 2.

Suitable substrates for the photoreceptor according to the present invention include metals such as aluminum, stainless steel, brass, and nickel, or a thin layer of these metals bonded to a plastic sheet or glass with an adhesive; It may be formed by vapor deposition. The charge generation layer of the laminated photoreceptor used in the present invention is formed by using a charge generation substance alone or by mixing it with a polymer. As charge generating substances, monoazo pigments, disazo pigments,
Organic substances such as quinocyanine pigments, perylene pigments, phthalocyanine pigments, squaric acid derivative dyes, pyrylium dyes, and charge transfer complexes of polyvinylcarbazole and trinitrofluorenone are used. Inorganic materials such as amorphous selenium, selenium alloys, cadmium sulfide, and amorphous silicon are also used. The charge transfer layer generally has a transmittance of 80% or more for laser light, and is formed from a charge transfer material alone or mixed with a polymer. As the charge transfer substance, polyvinylcarbazole, pyrazoline derivatives, hydrazone derivatives, oxadiazole derivatives, triphenylmethane derivatives, triphenylamine, trinitrofluorene, etc. are used.

As dyes that absorb laser light, carbon and various dyes corresponding to the emission wavelength of each laser are effective, and cyanine dyes are particularly effective for semiconductor lasers with wavelengths of 750 mμ or more. Cyanine dyes are also called polymethine dyes because they have a long chain of methine groups (-CH=CH-).
As the length increases, the resonance wavelength shifts by about 100 nm to longer wavelengths.

The present invention will be explained below with reference to Examples.

Example 1 1 part by weight of ε (epsilon) type copper phthalocyanine (manufactured by Toyo Ink Co., Ltd., trade name: Lionol Blue ES) and butyral resin (manufactured by Sekisui Chemical Co., Ltd., trade name:
1 part by weight of Eslec BM-2) and 15 parts by weight of isopropyl alcohol were placed in a ball mill and dispersed for 4 hours to prepare a charge generating substance coating liquid. This coating liquid was applied with a wire bar onto an aluminum foil having a thickness of 10 μm which was laminated to a polyester film having a thickness of 75 μm, and was dried to form a charge generation layer. The thickness of the charge generation layer is approximately 0.7 μm. Next, 1 part by weight of a pyrazoline derivative with the following structural formula and polysulfone resin (manufactured by Union Carbide, trade name: P1700)
1 part by weight The mixture was mixed with 6 parts by weight of monochlorobenzene and stirred and dissolved using a magnetic stirrer to obtain a charge transfer substance coating liquid. This solution was applied onto the charge generation layer using a wire bar and dried to form a charge transfer layer. The film thickness is approximately 10 μm. This laminated photoreceptor was attached to an experimental laser printer (charged with negative polarity, which occurs with negative toner) equipped with a gallium-aluminum-arsenic semiconductor laser (emission wavelength: 780 nm, output: 5 mW) to produce an image. As a result, an image with uniform density in the solid image area and sharp line images was obtained.

A charge generation layer with the same thickness was formed on glass using the same charge generation material coating liquid used to prepare the photoreceptor, and the spectral transmittance was measured, and the result was 780 nm.
The transmittance was 4%. In addition, using the same charge transfer substance coating liquid used for photoreceptor production,
When a charge transfer layer of the same thickness was formed on glass and the spectral transmittance was measured, the transmittance was 90% or more in the range of 530 nm to 850 nm.

Comparative Example 1 A charge generation layer was formed in the same manner as in Example 1 using a charge generation material coating liquid having a composition of 1 part by weight of ε-type copper phthalocyanine, 1 part by weight of butyral resin, and 30 parts by weight of isopropyl alcohol. Film thickness is approx.
It is 0.3 μm. A charge transfer layer similar to that in Example 1 was formed on this charge generation layer. When this laminated photoreceptor was attached to the same experimental laser printer as in Example 1 and an image was produced, there was no problem with the line image, but density unevenness in the form of interference fringes appeared in the solid image area.

A charge generation layer of the same thickness was formed on glass using the same charge generation substance coating liquid used to produce the photoreceptor, and the spectral transmittance was measured.
The transmittance was 25%.

Comparative Example 2 Using a charge-generating substance coating liquid having a composition of 1 part by weight of β-type copper phthalocyanine (manufactured by Toyo Ink Co., Ltd., Lionol Blue GLA), 1 part by weight of butyral resin, and 15 parts by weight of isopropyl alcohol, the coating liquid of Example 1 and A charge generation layer was formed in the same manner. Film thickness is approximately 0.7μm
It is. A charge transfer layer similar to that in Example 1 was formed on this charge generation layer. This laminated photoreceptor,
When an image was produced using the same experimental laser printer as in Example 1, there was no problem with the line image, but density unevenness in the form of interference fringes appeared in the solid image area.

A charge generation layer with the same thickness was formed on glass using the same charge generation material coating liquid used to prepare the photoreceptor, and the spectral transmittance was measured, and the result was 780 nm.
The transmittance was 18%. The absorption peak of the ε-type copper phthalocyanine of Example 1 was at a longer wavelength than that of the β-type copper phthalocyanine of Comparative Example 2.

Example 2 1 part by weight of ε-type copper phthalocyanine (manufactured by Toyo Ink Co., Ltd., trade name: Lionor Boole ES) and 0.1 part by weight of a cyanine dye having the following structural formula (manufactured by Japan Photosensitive Color Research Institute, trade name: NK-123). 1 part by weight of butyral resin (manufactured by Sekisui Chemical Co., Ltd., trade name: Eslec BM-2) and 20 parts by weight of isopropyl alcohol were placed in a ball mill and dispersed for 4 hours. It was used as a coating liquid for the load generation layer. This coating liquid was applied to the aluminum surface of the aluminum foil laminated polyester using a wire bar and dried to form a charge generation layer. Film thickness is approx.
It is 0.6 μm. Next, a charge transfer layer similar to that in Example 1 was formed.

Next, 1 part by weight of the same pyrazoline derivative as in Example 1, 1 part by weight of polysulfone resin (manufactured by Union Carbide, trade name: P1700), and 6 parts by weight of monochlorobenzene were mixed, stirred and dissolved using a magnetic stirrer, and charged. It was used as a moving substance coating liquid. This coating liquid was applied onto the charge generation layer using a wire bar and dried to form a charge transfer layer. The film thickness is approximately 11 μm. This laminated photoreceptor is made of gallium-aluminum
Arsenic semiconductor laser (emission wavelength 820nm, output 10
Images were produced by attaching the sample to a laser printer experimental machine (charged with negative polarity, which occurs with negative toner) having a power output of As a result, the density of the solid image is uniform,
A sharp line image was also obtained.

A charge generation layer of the same thickness was formed on glass using the same charge generation substance coating liquid used to produce the photoreceptor, and the spectral transmittance was measured.
The transmittance was 7%.

Example 3 Amorphous silicon was deposited to a thickness of 2 μm on a mirror-finished aluminum cylinder by a capacitively coupled high-frequency glow discharge method to form a charge generation layer. Deposition conditions are silane gas flow rate
10cm ³ /min, gas pressure 6.5Pa, frequency 13.56MHz, high frequency power 100W, substrate temperature 250℃, deposition rate 1μm/min
It's time.

Next, 1 part by weight of trinitrofluorene and a saturated polyester resin (manufactured by Toyobo Co., Ltd., Byron 200)
1 part by weight and 6 parts by weight of monochlorobenzene were mixed and stirred and dissolved using a stirrer to obtain a charge transfer substance coating liquid. This coating liquid was applied onto the charge generation layer by a dipping method and dried to form a charge transfer layer. The film thickness is approximately 12 μm. This laminated photosensitive drum is
Laser printer experimental machine with Ne laser (emission wavelength 633 nm, output 10 mW) (charged with positive polarity)
Then, I took an image. As a result, a solid image with uniform density and sharp line images was obtained. In addition, the same laminated photosensitive drum was used as a semiconductor laser (emission wavelength 780 nm, output 5 mW).
When an image was produced using an experimental laser printer equipped with a laser printer (charged with positive polarity, this phenomenon occurs with positive toner), density unevenness in the form of interference fringes appeared in the solid image area.

When amorphous silicon was deposited to the same thickness on glass under the same deposition conditions as when producing the photosensitive drum, and the spectral transmittance was measured, the transmittance was 2 at 633 nm.
%, and the transmittance was 45% at 180 nm.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a laminated photoreceptor, and FIG. 2 is a diagram illustrating the interference of laser light. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Charge generation layer, 3... Charge transfer layer, 4... Incident laser light, 5... Reflected light on the surface of the charge transfer layer, 6... Charge reflected on the surface of the substrate. Light that has returned to the surface of the moving layer.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor for a laser printer, comprising a charge transfer layer and a charge generation layer having a transmittance of 10% or less to the laser light used. 2. The electrophotographic photoreceptor for a laser printer according to claim 1, wherein the laser is a semiconductor laser. 3. The electrophotographic photoreceptor for a laser printer according to claim 1, wherein the charge generation layer contains a phthalocyanine pigment.