JPH0140341B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a photoreceptor used in a laser printer device, and more particularly to a photoreceptor for a semiconductor laser printer that has high photosensitivity in the oscillation wavelength region of a semiconductor laser. Conventionally, Se, Se-Te-
A large number of materials are known, including CdS, ZnO, and organic photoconductors, and several of these have actually been put into practical use in electrophotographic copiers and laser printers that use He--Ne lasers as input. However, there are still only a few photoreceptors that are sensitive to the oscillation wavelength region of semiconductor lasers, that is, the near-infrared region, and only CdS, As--Te--Se systems, and phthalocyanine are mentioned. However, the former two are hazardous substances (Cd is designated as a hazardous substance under the Poisonous and Deleterious Substances Control Law and is a Class 2 substance under the Specified Chemical Substances Hazard Prevention Regulations; Se is a poisonous substance under the Poisonous and Deleterious Substances Control Law), so they cause pollution. There are major drawbacks in terms of manufacturing efficiency, such as safety and hygiene during manufacturing, and the need for vapor deposition equipment for the As-Te-Se system when manufacturing photoreceptors. Also
Although CdS has good photosensitivity, it has low charging properties and has the disadvantage of requiring a special charging method. On the other hand, phthalocyanine pigments have been known for a long time to exhibit photoconductivity, and their application to photoreceptors for copying machines and laser printers has been studied for a long time in the field of electrophotography. In order to produce a photoreceptor using this phthalocyanine pigment, since it does not have film-forming properties when used alone and is difficult to vapor-deposit, the phthalocyanine pigment and binder are dispersed in an organic solvent to create a photoconductive coating liquid. Coat on a conductive substrate using a blade, bar coater, roll coater, etc.
Formed on a photoreceptor film of several micrometers. In order to charge the photoreceptor film formed as described above, a corona charger as shown in FIG. 1 is used to positively charge it at a discharge voltage of +6.8 KV, for example. In the figure, 1 is a discharge electrode, 2 is a shielding electrode, 3 is a conductive support, and 4 is a photoreceptor film coated on the conductive support. The ratio of the phthalocyanine pigment to the binder, which is a resin for dispersing the phthalocyanine pigment, or the pigment dispersion rate (phthalocyanine pigment/phthalocyanine pigment + binder x 100) was plotted as a parameter, with the vertical axis representing the charging potential and the horizontal axis representing the film thickness. The second example of the charging characteristics of the photoreceptor is
As shown in the figure. From FIG. 2, in order to increase the charging potential, the pigment dispersion rate may be lowered or the photoreceptor film thickness may be increased. When the pigment dispersion rate is low, there is a proportional relationship between the charging potential and the photoreceptor film thickness, but as the pigment dispersion rate increases, the relationship deviates from linearity. For example, when the pigment dispersion rate is 40wt%, the film starts to deviate from linearity when the film thickness exceeds several μm, and when the film thickness exceeds 10μm, the charging potential is approximately 500V.
Saturation occurs at a certain level. Therefore, in order to maintain linearity in the relationship between charging potential and film thickness and to increase the charging potential to about 300 V or more, it is desirable that the pigment dispersion rate be low to some extent. However, if the pigment dispersion rate becomes too low,
Although a proportional relationship can be obtained between the charging potential and the photoreceptor film thickness, and a high charging voltage can be obtained, the ratio of resin increases, and it becomes difficult for the charge generated in the phthalocyanine by light irradiation to move, resulting in a lack of conductivity. This has the disadvantage that the charge is slowly removed from the support. Therefore, it is preferable that the pigment dispersion rate is approximately 35 wt%. Phthalocyanine pigment and binder are dispersed in an organic solvent so that the pigment dispersion rate is 35wt%, and this dispersion is mixed with a doctor blade.
FIG. 3 shows the spectral sensitivity curve of a photoreceptor prepared by coating it onto a conductive substrate using a barcoder, roll coater, etc. so that the dry film thickness was 7.0 μm. In the figure, the vertical axis is the reciprocal 1/E1/2 of the half-decreased exposure amount E1/2 from the charging potential +500V, and the horizontal axis is the irradiation wavelength (600 to 900 nm). Note that the smaller the half-life exposure amount E1/2, the higher the sensitivity. Therefore, the third
A large value on the vertical axis 1/E1/2 in the figure indicates high sensitivity, and a small value indicates low sensitivity. From the spectral sensitivity curve in Figure 3, it can be seen that phthalocyanine pigments have a wide range of sensitivity from the visible region to the near-infrared region, but for copying machines and laser printers,
The disadvantage is that the sensitivity is still insufficient, especially in the oscillation wavelength region of semiconductor lasers. The present invention eliminates the above-mentioned disadvantage of low photosensitivity especially for semiconductor laser printers.
Light-sensitive in the near-infrared region, non-polluting and light-resistant.
By adding tetrathiafulvalene to a phthalocyanine pigment with excellent chemical resistance, we have achieved dramatic sensitization, creating a photoreceptor for printers that has high photosensitivity to semiconductor laser light and is pollution-free, inexpensive, and easy to manufacture. It is on offer. The present invention provides an electrophotographic photoreceptor in which a photoreceptor film in which phthalocyanine is dispersed in a resin is formed on a conductive substrate, wherein the photoreceptor film contains tetrathiafulvalene. Ru. The present invention will be explained in detail below. Since the photoreceptor is easy to manufacture, the present inventor has intensively investigated various sensitization methods with the aim of utilizing this [phthalocyanine binder] type photoreceptor. First, in order to investigate where the lack of sensitivity of the [phthalocyanine pigment-binder] dispersed photoreceptor (P ₁ ) originates, we investigated the surface potential of the above sample.
Wavelength is applied to a photoreceptor charged to 400V.
We irradiated it with 632.8 nm light and observed changes in surface potential over time. Figure 4 shows the results. The figure shows the light attenuation characteristics of the photoconductor, with the vertical axis representing the surface potential and the horizontal axis representing the light irradiation time.The solid line in the figure represents the dark state when light is irradiated, and the dotted line represents the dark state when no light is irradiated. It is attenuation. The relationship between the residual potential rate n and the irradiation energy E ₀ is shown in FIG. Figure 5 shows the latent image potential obtained t seconds after light irradiation as ΔVt, and the irradiation energy required to obtain ΔVt as E ₀
The residual potential rate η=[1-ΔVt/V ₀ ] is plotted on the vertical axis in order to understand the state of photosensitivity, and E ₀ is plotted on the horizontal axis on a logarithmic scale. Note that V ₀ is the surface potential at the start of light irradiation. Note that the curve P ₁ in Fig. 5 is the phthalocyanine pigment + binder dispersed photoreceptor P ₁
shows the optical attenuation characteristics of This result shows that the attenuation immediately after light irradiation is extremely small, that is, the irradiation energy is not used efficiently. (This phenomenon immediately after irradiation is hereinafter referred to as induction phenomenon). That is, [phthalocyanine pigment + binder]
It has been found that this induction phenomenon must be eliminated in order to make the dispersion type photoreceptor highly sensitive. For this reason, we have made extensive efforts to investigate the sensitizing effects of a large number of compounds. In order to investigate the sensitizing effects of a number of compounds, a photoreceptor having a laminated structure _P2 as shown in FIG. 7 was formed and its charging characteristics were investigated. That is, the sixth
As shown in the figure, the basic structure is a structure _P1 in which a charge generation layer 4 in which a phthalocyanine pigment is dispersed in a resin is formed on a conductive support 3, and a compound whose sensitizing effect is to be examined is placed on the charge generation layer 4 using a resin. A layer dispersed therein is formed to form a laminated structure _P2 as shown in FIG. In this way, in addition to being able to use the same base conditions for many compounds, it is also possible to avoid reactions or interactions between the compound whose sensitizing effect is to be tested and the phthalocyanine pigment, making it easier to evaluate the presence or absence of a sensitizing effect. It can be done. In addition, in terms of process, it is sufficient to form a large number of photoreceptors with the P ₁ structure and then apply a coating liquid containing a predetermined compound thereon to form the photoreceptor, so it is possible to investigate a large number of compounds. It's convenient. After charging the photoreceptor having the laminated structure P ₂ formed in this way, it was irradiated with light with a wavelength of 632.8 nm, the time change in surface potential was measured, and the residual potential rate η
The relationship between = (1-ΔVt/V ₀ ) and irradiation energy E ₀ was determined. Among the sensitizing effects of many compounds investigated, photoreceptor P ₂ containing tetrathiafulvalene was found.
The characteristics shown by curve _P2 in FIG. 5 were obtained. Although the half-decrease exposure amount is not much different or larger than that of the conventional _P1 , a comparison of the initial state shows that the induction phenomenon has disappeared. The present inventor focused on this point and sought to improve the properties of the composition of tetrathiafulvalene, the structure of the photoreceptor, and the method of forming it. The induction phenomenon is thought to be because carriers generated in the phthalocyanine pigment due to light irradiation are difficult to move across the interface between the phthalocyanine and the binder. In other words, if there is an electronically active molecule, such as tetrathiafulvalene, that allows charge to easily move around the phthalocyanine pigment, the carrier transfer rate will improve.
Induction phenomenon is eliminated. In the photoreceptor having the laminated structure _P2 shown in FIG. 7, only the phthalocyanine pigment near the interface 7 comes into contact with the tetrathiafulvalene, resulting in poor efficiency. Therefore, as shown in FIG. 8, by using a layer 8 in which a phthalocyanine pigment and an electronically active compound such as tetrathiafulvalene are simultaneously mixed and dispersed in a resin, the phthalocyanine pigment and an electronically active compound can be mixed together. The photoconductor P ₃ has been developed with improved carrier mobility and improved carrier mobility. The photosensitivity of this photoreceptor _P3 will be exemplified in the following examples, but it has become dramatically more sensitive to light in the near-infrared region than the conventional photoreceptor _P1 . (Example 1) The composition listed in Table 1 was placed in a polyethylene wide-mouth bottle (1) and milled for 80 hours. This coating liquid was applied onto an aluminum plate by a doctor blade method so that the film thickness after drying was 8.0 μm.

[Table] This photoreceptor is equipped with a corona charger (discharge voltage
When charged at 6.8 KV), the surface potential of photoreceptor A was 340V and that of photoreceptor B was 300V. When irradiated with light having a wavelength of 632.8 nm (irradiation intensity 10 μW/cm ² ), the photosensitivity characteristics were as shown in FIG. 9.
It can be seen from FIG. 9 that the photoreceptor of the present invention has significantly higher sensitivity than conventionally known photoreceptors. In other words, the photosensitivity characteristic of the conventional photoreceptor is curve B.
As shown by the (dotted line), the irradiation energy E ₀ is 3
The potential attenuation is extremely small at ~4 μJ/cm ² . Furthermore, although the half-decrease exposure amount is as large as 10 μJ/cm ^{2 ,} the photosensitivity characteristics of the photoreceptor of the present invention are as shown by curve A (solid line).
The induction phenomenon has been improved, and the half-decrease exposure has become 4 μJ/cm ² , making it highly sensitive. Note that tetrathiafulvalene used as a sensitizer in the present invention is It has the structure LRMelty (J.Qrg.Chem, 39, 2456
(, 74)) and MV Lakshmikan Than et al. (J.Org.
Chem 41 , 879 (76)) describes its synthesis method. (Example 2) A coating liquid having the following composition was formed on a photoreceptor in the same process as in Example 1.

[Table] The maximum charging potential of the photoreceptor with a film thickness of 6.2 μm was 570V, and the half-reduction exposure amount (for a wavelength of 632.8 nm) from the surface potential of 500V was 5 μJ/cm ² . As is clear from the above explanation, by using a photoreceptor in which the phthalocyanine of the present invention and tetrathiafulvalene, which is an electron-donating compound, are dispersed in a resin, it is possible to improve Compared to a photoreceptor in which the photoreceptor is dispersed in a resin, the sensitivity can be dramatically increased. In this example, a photoreceptor material having a laminated structure of a charge generation layer in which phthalocyanine is dispersed in a resin and a layer (charge transport layer) in which electronically active tetrathiafulvalene is dispersed in a resin, phthalocyanine and tetra Although we have described a photoreceptor material in which a mixture with thiafulvalene is dispersed in a resin, it goes without saying that a layer in which a phthalocyanine is dispersed in a resin and a mixture of phthalocyanine and an electronically active compound such as tetrathiafulvalene can also be used. The photoreceptor material may have a structure in which either a layer in which an electronically active compound such as tetrathiafulvalene is dispersed in a resin is laminated.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of a corona charger that charges a photoreceptor, Figure 2 is the charging characteristics of a photoreceptor with phthalocyanine dispersed in resin, Figure 3 is the spectral sensitivity curve of the photoreceptor, and Figure 4 is the photoreceptor. Light attenuation properties of the body, 5th
9 and 9 are light attenuation characteristics of the conventional photoconductor and the present invention, FIG. 6 is a conventional photoconductor, and FIGS. 7 and 8 are schematic diagrams of the structure of the present invention photoconductor.

Claims (1)

[Scope of Claims] 1. An electrophotographic photoreceptor in which a photoreceptor film in which phthalocyanine is dispersed in a resin is formed on a conductive substrate, wherein the photoreceptor film contains tetrathiafulvalene. Photoreceptor for use. 2. The electrophotographic photoreceptor according to claim 1, wherein the phthalocyanine is copper phthalocyanine.