JPH046944B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention relates to an image forming method using a photoreceptor having a phthalocyanine binder resin photoconductive layer. Prior Art Various photoreceptors have already been proposed and put into practical use. One example is Se-based materials, which are relatively superior in terms of sensitivity, but have the drawbacks of being harmful and having a low crystallization temperature. Photoreceptors having a CdS binder resin photoconductive layer have also been widely put into practical use, but they are also harmful and have problems in manufacturing and handling. For this reason, in recent years, photoreceptors having a photoconductive layer formed by dispersing a phthalocyanine-based photoconductive material in a binder resin have attracted attention. This type of photoreceptor has the advantage of being pollution-free and easy to manufacture. Phthalocyanine pigments used as photoconductive materials have various crystal forms such as α type, β, γ, ε, σ, and χ, and each crystal form has different electrophotographic properties. Among these, a photoreceptor having a photoconductive layer formed by dispersing a special α-type phthalocyanine pigment in a binder resin, which will be described later, exhibits unique characteristics compared to those of other crystal forms. That is, when the present inventor conducted an image forming experiment on a photoreceptor containing each crystalline phthalocyanine pigment, it was found that the photoreceptor containing the above-mentioned special α-type phthalocyanine pigment had a low potential area, that is, an intermediate tone. It has been confirmed that this is not often reproducible. This is because, as will be explained in detail later, the photoreceptor containing the special α-type phthalocyanine pigment exhibits a unique characteristic in that the dark decay rate after exposure changes depending on the exposure illuminance. However, when this type of photoreceptor is used in a powder image transfer type copying machine, the potential on the photoreceptor falls below the development threshold voltage before development due to the change in the dark decay rate in the high illuminance region, causing the apparent sensitivity changes significantly, significantly affecting tone reproducibility. In addition, the above-mentioned photoreceptor shows significant changes over time, and depending on the electric field strength of the photoreceptor, the occurrence of white spots (white spots) on the image and a decrease in gradation reproducibility are observed, and the dark decay characteristics and light Both sensitivity characteristics become unstable. In addition, the dark decay characteristics and photosensitivity characteristics are not only affected by changes over time, but also depend on the amount of exposure from the light source to remove residual charges during repeated use, making it difficult to obtain good images over a long period of time. Ta. Purpose of the invention The present invention has been made in view of the above facts.
The aim is to ensure excellent electrophotographic properties in general, including gradation reproducibility, light sensitivity characteristics, dark decay characteristics, and repetition characteristics, and to form images that can produce good images over a long period of time. The purpose is to provide a method. SUMMARY OF THE INVENTION The present invention provides phthalocyanine and phthalocyanine molecules, which are used as photoreceptors, and whose photoconductive layer has a film thickness of about 5 to 10 microns, and whose dark decay rate after image exposure changes depending on the exposure illuminance. A phthalocyanine derivative in which the benzene nucleus of is substituted with at least one electron-withdrawing group selected from a nitro group, a cyano group, a halogen atom, a sulfone group, and a carboxyl group is mixed with an inorganic acid capable of forming a salt with the phthalocyanine. After that, a phthalocyanine-based photoconductive material obtained by precipitation with water or a basic substance is dispersed in a binder resin, and the electric field strength per 1 micron of the photoconductive layer during charging is set to about 30 50 volts, the time from image exposure to the photoreceptor to development is approximately 0.1 to 0.4 seconds, and static electricity removal is performed at an exposure amount of approximately 20 to 500 lux·sec. There is an image forming method. Embodiments In the image forming method according to the present invention, a photoreceptor having a photoconductive layer formed by dispersing a phthalocyanine pigment in a binder resin is used, and it is particularly preferable to deposit the photoconductive layer on a conductive substrate to a thickness of approximately A layer with a thickness of 5 to 30 microns is used, and if necessary, an insulating protective layer is layered thereon.
Specifically, the photoconductive layer described above has a characteristic that the dark decay rate after image exposure changes depending on the exposure illuminance, and phthalocyanine pigments having such a characteristic include the following special α-type crystal form. There is. The special α-type crystalline phthalocyanine pigment has a phthalocyanine and a benzene nucleus of the phthalocyanine molecule substituted with at least one electron-withdrawing group selected from a nitro group, a cyano group, a halogen atom, a sulfone group, and a carboxyl group. It is obtained by mixing phthalocyanine with an inorganic acid that can form a salt and then precipitating it with water or a basic substance.The thus obtained product is dispersed in a binder resin and coated to form a photoconductive layer. It is something. In the above, the composition ratio of phthalocyanine and phthalocyanine derivative is such that the number of electron-withdrawing groups in the phthalocyanine derivative is 2 or less, preferably 1 or less, based on the total of phthalocyanine units of phthalocyanine and phthalocyanine derivative, and 0.001. It is desirable to set the ratio to above, preferably 0.002 or more, and
Inorganic acids that can form salts with phthalocyanine include sulfuric acid, orthophosphoric acid, pyrophosphoric acid, chlorosulfonic acid, hydrochloric acid, hydroiodic acid, hydrofluoric acid,
Hydrobromic acid etc. are used. These inorganic acids are those used in conventionally known methods such as phthalocyanine acid pasting method and acid slurry method. As the phthalocyanine, metal-free phthalocyanine, metal phthalocyanine such as copper, nickel, cobalt, zinc, tin, iron, sodium, lithium, calcium, and magnesium, or a mixture thereof can be used. Hereinafter, the image forming method of the present invention will be described in detail when using a photoreceptor having a photoconductive layer containing a special α-type crystal type phthalocyanine pigment. The photoreceptor was created as follows. 40 parts by weight of copper phthalocyanine, 0.5 parts by weight of dinitro copper phthalocyanine
Part by weight was dissolved in 500 parts by weight of 98% concentrated sulfuric acid with thorough stirring. Pour the dissolved liquid into 2000 parts by weight of water,
After precipitating the composition of copper phthalocyanine and dinitro copper phthalocyanine, it is filtered, washed with water, and then separated under reduced pressure.
Dry at 120℃. This composition is a special α-type crystalline phthalocyanine pigment. Next, 10 parts by weight of the composition thus obtained was placed in a ball mill with 40 parts by weight of an organic solvent of butyl acetate:cellosolve (1:1) and dispersed for 20 hours. Subsequently, 32 parts by weight of thermosetting acrylic resin (Acrydik A405, manufactured by Dainippon Ink) and 8 parts by weight of melamine resin (Supervetsucomin J820, manufactured by Dainippon Ink) were mixed with 10 parts by weight of the above dispersion solvent.
Parts by weight were put in a ball mill and kneaded and dispersed for 4 hours to prepare a photoconductive paint. And this paint is 80mm in diameter
A photoreceptor was prepared by coating approximately 10 microns on a mm aluminum drum and drying. The photoreceptor thus obtained was set in a copying machine shown in FIG. 1 or a measuring device corresponding thereto, and the following experiment was conducted. In the figure, 1 is a photoreceptor, 2 is a corona charger for uniformly charging the photoreceptor 1, 3 is an exposure slit, 4 is a magnetic brush developer, 5 is a transfer charger, 6 is a blade cleaner, and 7 is an eraser lamp. It is. First, the photoreceptor was uniformly charged to a predetermined surface potential V ₀ by the corona charger 2, and the dark decay characteristic starting from V ₀ was measured. (Hereafter, this dark decay characteristic is referred to as V ₀ dark.) The measurement results are shown in Figure 2, where curve A is the initial surface potential.
When V ₀ is approximately 500V, curve B is when V ₀ is approximately 400V.
In the V ₀ dark, the V ₀ of the photoreceptor exhibits a unique characteristic in that it gradually decreases until a certain dark decay time, forms a shoulder, and then rapidly decreases. In other words, in the case of photoreceptors such as Se and CdS, the dark decay of V ₀ attenuates almost linearly, but in the case of photoreceptors having a photoconductive layer containing a special α-type phthalocyanine pigment, the shoulder portion decreases as described above. Forms and rapidly decays. For curve A,
V ₀ gradually decreases with the dark decay time, but it does not decrease much until 15 seconds, and then rapidly decreases from about 16 seconds. Here, the time Tin until the shoulder begins to appear in each curve can be determined by finding the point where the horizontal line from the initial surface potential V ₀ and the tangent to the shoulder intersect, as shown in curve A, and it is found that V ₀ is approximately 500V. At curve A, Tin is 15.9 seconds, and at curve B, where _V0 is approximately 400V.
Tin is 13.8 seconds. In this way, Tin is quite long, and if it is always guaranteed to be at least 2 seconds at the very shortest time, then even if we take a low-speed copying machine as an example, there is nothing more required from charging to image exposure. , there is no particular problem. However, as will be clear from the discussion below, Tin is highly dependent on changes in the photoreceptor itself over time, electric field strength, photoconductive layer thickness, exposure amount of the eraser lamp 7, etc., and good images may not be obtained depending on the conditions. This is the situation. Furthermore, the above-mentioned photoreceptor containing a special α-type phthalocyanine pigment has the above-mentioned unique characteristic of V ₀ dark and Tin
In addition to exhibiting instability, it also exhibits the characteristic that the dark decay rate after image exposure changes depending on the exposure illuminance. That is, when the dark decay characteristic (hereinafter referred to as Vi dark) starting from the surface potential Vi after image exposure was measured, the results shown by curves C and D in FIG. 2 were obtained. Specifically, the photoreceptor was charged so that its initial surface potential V ₀ was 500V, and the dark decay characteristics were investigated immediately after exposure by exposing it to light at an exposure illuminance of 6.3 lux and 7.5 lux (exposure time was constant). In contrast to V ₀ dark, a rapid potential decay was observed. In other words, the exposure illuminance
Under the exposure of 6.3 lux, the initial surface potential V ₀ decreases to Vi of 400 V, as shown by curve C,
The dark decay starting from Vi causes a rapid potential decay, and before the dark decay time reaches 0.5 seconds, the voltage reaches 50V.
The following is true. Even when the exposure illuminance is 7.5lux, Vi is omitted.
Although the voltage is 300V, as shown in curve D, a rapid potential attenuation still occurs. When this is applied to the copying machine shown in FIG. This means that the image will not be developed at all. In other words, for example, if a copy document is made up of a black image (for example, black text) and a gray image (halftone image such as a photograph or light text) and is charged to V ₀ and exposed to image, the potential corresponding to the black image area will be approximately Although V remains at ₀ and does not drop to at least the above-mentioned Tin, the gray image area drops to Vi due to image exposure, and as with curves C and D, a rapid potential attenuation occurs from Vi. Therefore, the latent image potential of this gray image area will not be reproduced at all unless it is developed by the magnetic brush developer 4 before the latent image potential becomes equal to or less than the development threshold potential. In particular, since the bias potential applied to the developing electrode of the magnetic brush developing device 4 is at least about 10 V, usually about 50 to 350 V, this becomes a bigger constraint. To further explain how Vi dark changes depending on the exposure illuminance, Figures 3A and 3B show the measurement of the dark decay time when the exposure illuminance was varied from 1.2 lux to 300 lux. In the experiment, the same plate-shaped photoreceptor as above was produced using the same manufacturing method, and a reciprocating electrostatic characteristic device was used as the measuring device. In addition, the irradiation is performed using a shutter,
It was opened for 100 to 110 msec. In Figure 3A, curve E1 represents the Vi dark characteristic when the exposure illuminance is 1.2 lux, curve E2 represents the Vi dark characteristic when the exposure illuminance is 5 lux, and curve E3 represents the Vi dark characteristic when the exposure illuminance is 5 lux.
E4 shows Vi dark characteristics at 20lux, E5 at 30lux, and E6 at 50lux. As is clear from each curve, the dark decay time becomes faster as the exposure illuminance increases. In other words, the dark decay speed of a high-density image of a copy original is slow, but it becomes faster as the density decreases.For example, the time for Vi to decay to 300V in curve E1 is about 10 seconds, whereas the Curve E5 with illuminance 30lux takes 1 second, curve E with illuminance 50lux
6 is extremely fast at 0.4 seconds. This tendency becomes more noticeable as the exposure illuminance increases, and as shown in Figure 3B, curve E7 with an exposure illuminance of 60 lux,
100lux curve E8, 150lux curve E9,
Curve E10 of 300 lux has a progressively faster dark decay, and the time for Vi to decay to 300 V is curve E7.
0.33 seconds, 0.2 seconds on E8, 0.18 seconds on E9, E10
It is 0.15 seconds. As described above, a photoreceptor having a photoconductive layer formed by dispersing a special α-type phthalocyanine pigment in a binder resin has a unique characteristic in that the dark decay rate after image exposure increases as the exposure illuminance increases. However, especially in the case of reproducing a halftone image, the potential of the corresponding latent image falls below the development threshold potential in a very short time, and the latent image must be developed before then. In addition, the Vi dark characteristics shown in FIGS. 2 and 3A and 3B described above have a close relationship in terms of the sensitivity of the photoreceptor. As will be described later, when looking at the light attenuation characteristics of the photoreceptor, the slope of the attenuation curve is relatively strong, that is, it is steep, and depends on the time from image exposure to development. However, depending on the development time, the sensitivity may be high but the gradation reproducibility may be poor, or vice versa, making it impossible to obtain a good image with excellent gradation reproducibility. Furthermore, as mentioned above, the above-mentioned photoreceptor changes significantly over time, and in particular depends greatly on the electric field strength, that is, the potential per micron obtained by dividing the surface potential by the film thickness of the photoconductive layer, and the film thickness of the photoconductive layer itself. Tin,
This not only makes gradation reproducibility and photosensitivity unstable, but also causes noticeable white spots when forming area images, making it impossible to obtain good images over a long period of time. Further, the photosensitivity and Tin of the photoreceptor vary depending on the exposure amount of the eraser lamp 7, and in some cases, a memory effect occurs in which the previous image is reproduced overlappingly with the next image. In view of the above facts, the image forming method according to the present invention is based on the above-mentioned photoreceptor, in which the photoconductive layer has a film thickness of approximately 5.
When charging for image formation, the photoconductive layer is charged to a surface potential of about 30 to 50 volts per micron of the photoconductive layer. By setting the time to about 0.1 to 0.4 seconds and removing residual charges at about 20 to 500 lux·sec, good images can be obtained over a long period of time. First, to explain the time from image exposure to development (hereinafter referred to as Tid), in FIG. The time to reach Tid is approximately 0.1 to 0.4
The reason why it is set in seconds is because if it is less than 0.1 seconds, even if the speed is increased, it will not be enough to reach the development stage, and in addition, the sensitivity of the photoreceptor will decrease, and if it is more than 0.4 seconds, the halftone image will be This is because not only a part of the image is not reproduced, but also the gradation reproducibility itself deteriorates. To explain specifically, Figure 4 shows the surface potential V ₀ when changing the time Tid from image exposure to development.
Curve F1 is a light attenuation characteristic that shows the relationship between
Tid is 0.25 seconds, F2 is Tid 0.39 seconds, and F3 is
This is the light attenuation curve when Tid is 0.67 seconds. As is clear from the figure, the slope of each curve F1, F2, F3 becomes steeper as Tid becomes longer, indicating that the sensitivity becomes higher. However, on the other hand, this means that the gradation, especially the halftone reproduction, will be degraded, and in the end, it is difficult to widen the halftone reproduction range.
It turns out that it is better to shorten Tid. Moreover, from this, desired gradation reproduction can be obtained by changing Tid. In Figure 5, the left vertical axis shows the time Tin until the shoulder of the dark decay curve starting from the surface potential _V0 occurs, the right vertical axis shows the exposure amount E1/2 required to halve _V0 , and the horizontal The relationship is shown with Tid on the axis, and Tin and Tid were measured by changing the rotational speed of the photoreceptor 1 in Figure 1 and by changing the development position (in the experiment) the measurement position with respect to the fixed image exposure position. It is. Specifically, the measurement results are shown in Table 1 below, and a graph plot is shown in FIG. 1st
In the table, RPM is the rotation speed of the photoconductor, It is the corona current μA of corona charger 2 required to charge the photoconductor to V ₀ of 500V, seconds/period is the time required for one rotation of the photoconductor, and θ is the image The probe positions located counterclockwise from the exposure position and Tid, Tin, and E1/2 at each probe position are shown.

[Table] In Figure 5, ○ and ● represent the relationships between Tin and Tid and E1/2 and Tid at θ=25°, respectively, and △ and ▲
are Tin-Tid and E1/2-Tid when θ=45°, and □ and ■ are Tin-Tid and E1/2-Tid when θ=60°.
shows the relationship between First, let's look at the relationship between Tin and Tid.
Tin shows a tendency to saturate as Tid becomes longer.
Further, although not shown, Tin rapidly decreases when Tid is 0.1 seconds, especially 0.05 seconds or less, and in this sense, it is important that Tid is 0.1 seconds or more. On the other hand, E1/2 and Tid
Looking at the relationship, it can be seen that the longer Tid becomes, the higher the sensitivity becomes. For example, when Tid is 0.12 seconds, E1/2 is 9.3lux・sec, but at 0.5 seconds
5.9lux・sec, 5.0lux・sec in 0.67 seconds, which is a considerable improvement in sensitivity. However, as explained in FIG. 4, the increase in sensitivity leads to a decrease in gradation reproducibility. Figure 6 shows the relationship between Tid and gradation reproducibility, where the vertical axis represents the number of Kodak gray scale reproduction steps and the horizontal axis represents the number of Kodak gray scale reproduction steps.
Tid indicates the number of reproduction stages when Tid is 0.25 seconds, 0.39 seconds, and 0.67 seconds, respectively. As is clear from this figure, the tone reproducibility decreases as Tid becomes longer, and since six steps of tone reproduction are generally required to obtain a good image, Tid should be set to a maximum of 0.4 seconds. is necessary. Next, a description will be given of charging by the corona charger 2 so that the electric field intensity is approximately 30 to 50 volts per micron of the photoconductive layer of the photoreceptor. The photoreceptors were fabricated on conductive substrates with a thickness of 7 to 8 microns (sample A) and 11
We prepared three types of laminated photoconductive layers made by dispersing special α-type phthalocyanine photoconductive materials in binder resin, measuring ~12 microns (sample B) and 16 to 17 microns (sample C). The experiment shown in FIG. 7 was carried out with each set in the copying machine shown in FIG.
Incidentally, these photoreceptor samples A to C were immediately after being manufactured. Furthermore, each imaging experiment was conducted under Tid of 0.35 seconds. In Figure 7, the horizontal axis represents the electric field strength (E ₀ , V/μ).
The vertical axis shows the relationship between the white spot rank, Kodakku gray scale gradation reproduction step number, and Tin from the top. Curve H with □ mark
1, H2, H3. Also, sample C is indicated by curves I1, I2, and I3 with a △ mark. The white spot rank is the frequency of occurrence of white spots per unit area when copying an area image (solid black image), and rank 5 is the best without the occurrence of white spots, and rank 1 is the image with the highest frequency of occurrence. Rank 3 or higher is required for practical use. Further, as described above, the number of gradation reproduction stages is required to be six or more stages in order to ensure excellent halftone reproduction. Furthermore, considering the use of low-speed copying machines, Tin requires at least 2 seconds or more. In Figure 7, the electric field strength E ₀ is 30, 40,
As shown in curves G1, H1, and I1, the degree of occurrence of white spots in samples A, B, and C when varying between 50 and 60 V/μ shows that when E ₀ is 30 and 40 V/μ, the ranks are all the same. However, under 50 V/μ, Sample A is ranked 4 and is excellent, but Samples B and C, which have large photoconductive layers, drop to 3 and 2. Further, when E ₀ is 60 V/μ, the white spot ranks are all below 2, which poses a practical problem. On the other hand, the number of gradation reproduction steps is as shown by curves G2, H2, and I2, and except for samples A and B, which have 5 steps when E ₀ is 30 V/μ, all have excellent gradations of 6 steps or more. It shows reproducibility. Next, regarding Tin, this characteristic depends considerably on E ₀ . For example, samples A and B
In this case, when E ₀ is 30V/μ, Tin is 8 seconds, as shown by curves G3 and H3, and at 40V/μ, Tin is 9 to 10 seconds.
seconds, peak 12-13 seconds at 50V/μ, 11 at 60V/μ
Seconds. On the other hand, in sample C, 5 at 30V/μ
At 40V/μ it takes less than 7 seconds, at 50V/μ it takes about 13 seconds, and at 60V/μ it takes 9 seconds. However, all of them are Tin
is at least 2 seconds or more, which is the minimum required, and there is no problem with the characteristics of the photoreceptor in its early stages of use. The same experiment was conducted when E ₀ was 20 V/μ, but fogging was significant in relation to the developing bias voltage, so the results are not shown. After the above experiment was completed, this photoreceptor was stored in a cardboard box at room temperature (20°C) and humidity (50%) for 6 weeks for the purpose of measuring changes over time. However, during this time,
The photoreceptor was removed every week and 120 copies were made continuously. At the seventh week, the same experiment as shown in FIG. 7 was carried out on the photoreceptor, and the results shown in FIG. 8 were obtained. Looking at the relationship between electric field strength E ₀ and white spot rank, as shown by curve G4 in sample A, E ₀ is good at rank 4 at 30V/μ and 42V/μ, and 2 or less at 50V/μ or more. Become. On the other hand, in samples B and C where the photoconductive layer thickness is 11-12 and 16-17μ, respectively, which is thicker than sample A, when E ₀ is 30V/μ, curve H4,
As per I4, the ranks are 4 and 3, respectively, which are permissible ranks, but at 40V/μ or more, they become 2 or less, which poses a practical problem. In addition, in relation to the number of gradation reproduction steps, sample A has 6 or more steps at any electric field strength (curve G5), showing excellent gradation reproducibility, but samples B and C have curve H
5. As shown by I5, there are 5 stages when the voltage is 40V/μ or more.
On the other hand, Tin is shorter overall than when the photoreceptor was first used as shown in FIG. In other words, for samples A and B, as shown by curves G6 and H6,
E ₀ is about 5 seconds at 30/μ, about 8 seconds at 40V/μ, 50V/μ
It is shorter at 8 to 9 seconds at μ and about 6 seconds at 60V/μ. In the case of sample C, as shown by curve I6, the maximum voltage was 7 seconds at 50V/μ, which is about half of the initial value. As described above, the photoreceptor exhibits considerable changes over time. Of course, for Tin, E ₀ is 30 to 60 V/μ
The minimum required time of 2 seconds or less has been measured in the range of
Moreover, it is definitely predicted that it will become unstable at 60V/μ. The photoreceptor was again stored in the cardboard box for 11 weeks, during which time 120 copies were continuously made every week. After 11 weeks had elapsed, that is, 18 weeks after the initial use, the same experiment as shown in FIGS. 7 and 8 was conducted, and the results shown in FIG. 9 were obtained. Although the measurement results of sample C are omitted in the figure, they were all worse than sample B. In Fig. 9, there is a remarkable difference between samples A and B in relation to the white spot rank, and in sample A, as shown by curve G7, E ₀ is 3 or more in the range of 30 to 60 V/μ, especially 30, At 40V/μ, it has the best rank of 5, while in sample B it is as per curve H7.
At 30V/μ, the value is 3, but at 40 and 50V/μ, the image quality is 2 and 1, respectively. On the other hand, when looking at the relationship with the number of gradation reproduction steps, sample A shows 7 at 30 and 40 V/μ.
Sample B has a score of 40, whereas sample B has a score of 40.
At 50V/μ, it is 5 stages or less. Furthermore, in relation to Tin, sample A has E ₀ as shown by curve G9.
30V/μ for 4 seconds or more, 40V/μ for about 10 seconds, 50V/μ
The peak time of 11 seconds for μ and 8 seconds for 60V/μ is guaranteed, which is more than the required 2 seconds, but 20V/μ
It is predicted that the time will be approximately 2 seconds or less, and the fluctuation range of Tin is large at 60V/μ. In sample B, as is clear from curve H9, E ₀ is 30, 40V/
μ is about 3 seconds, which is quite close to 2 seconds, which cannot be said to be preferable. As described above, a photoreceptor having a photoconductive layer formed by dispersing a special α-type phthalocyanine pigment in a binder resin exhibits changes over time depending on the electric field strength and furthermore the thickness of the photoconductive layer itself. From the above-mentioned experiment from the initial stage to the 18th week, it was found that photoreceptors with a photoconductive layer thickness of 11 microns or more (Samples B and C) showed white spots and cracks over time even when the electric field height was varied from 30 to 60 V/μ. Tonal reproducibility, Tin
It can be seen that the characteristics of the product have deteriorated and it is not suitable for repeated use over a long period of time. On the other hand, in sample A with a photoconductive layer thickness of 7 to 8 microns, the electric field strength was approximately
Good results are shown for all characteristics in the range of 30 to 50 V/μ. That is, sample A is E ₀
As long as the voltage is set within the range of 30 to 50 V/μ, the change over time is minimal and good characteristics are maintained even after repeated use over a long period of time. The thickness of the photoconductive layer is not limited to 7 to 8 microns, but even if it is about 5 to 10 microns, similar results with little change over time can be obtained. To explain in more detail about setting the electric field strength to approximately 30 to 50 V/μ, Fig. 10 shows that the electric field strength E ₀ is
The relationship between the number of aging days, white spot rank, gradation reproducibility, exposure amount E _0pA and Tin at 30, 50, and 60V/μ is shown, and curves J1 to J4 are 30V/μ, K1
~K4 is 50V/μ E ₀ , L1~L4 is 60V/μ
Shows the characteristics when E ₀ . First, looking at the relationship with the white spot rank, when E ₀ is 30 or 50V/μ, a good rank of 4 is maintained, but below 60V/μ, it fluctuates drastically and is 2 to 3. The number of gradation reproduction steps is guaranteed to be 6 or more as shown by curves J2 and K2, but when E ₀ is set to 60V/μ, the aging deteriorates significantly to 4 steps. The exposure amount (E _0pt , the exposure amount conversion value of the appropriate image exposure lamp voltage value) is almost stable at any E ₀ , but at 60V/μ, the Vi dark characteristic mentioned above slows down and the film thickness of the photoconductive layer becomes uneven. The occurrence of pinhole images was observed.
Although there is some variation in Tin, all of them are sufficiently longer than 2 seconds. However, there is a considerable difference between E ₀ of 50V/μ and 60V/μ, especially at the beginning of use.
At 60V/μ, Tin is 50 compared to 50V/μ.
The date is 1/2. In addition, in this experiment on changes over time, continuous copying of 120 sheets was performed in 11 times over a period of 130 days, and when E ₀ was 30 and 50 V/μ, good images were obtained from the beginning to the end. However,
At 60V/μ, gradation reproducibility was insufficient and only images with noticeable white spots were obtained. As is clear from this result, it is necessary to set the electric field strength to 30 to 50 V/μ. Finally, static electricity is removed from the photoreceptor using an eraser lamp for approximately 20 to 500 lux・sec to remove residual charges.
The following describes what is done with the exposure amount. 1st
Figure 1 shows the relationship in which the horizontal axis is the exposure amount El of the eraser lamp 7, the left vertical axis is the image exposure amount E1/2 required to halve the predetermined surface potential, and the right vertical axis is Tin. , curve M1 represents the relationship between El and E1/2 at the initial stage of use of the photoconductor, M2 represents the relationship between El and E1/2 after 1000 sheets have been continuously copied, and curve N1,
N2 is for the initial use of the photoreceptor and after continuous copying of 1000 sheets, respectively.
Shows the relationship between El and Tin. The photoreceptor used was the same as that used in sample A described above. It can be seen that each characteristic is generally stable within the range of the exposure amount of the eraser lamp from 20 to 500 lux·sec. but
When the temperature exceeds 500 lux・sec, fluctuations can be seen in both sensitivity E1/2 and Tin, and both become unstable.
Tin is 1000lux・sec, and after repeated copying, it will take less than 2 seconds. The reason for the shortening of Tin is considered to be that when the exposure amount of the eraser lamp 7 exceeds 500 lux·sec, the temperature rises due to heat generation and the Tin becomes faster.
Furthermore, below 20 lux·sec, a memory phenomenon was observed in which the previous copied image was reproduced overlappingly with the next copied image. Therefore, to obtain good images over a long period of time, the exposure amount of the eraser lamp should be approximately 20~
It is necessary to set it to 500lux・sec. Effects As is clear from the above explanation, according to the image forming method according to the present invention, gradation reproducibility, photosensitivity characteristics,
It guarantees excellent electrophotographic properties in general, including dark decay properties and repetition properties, and can obtain good images over a long period of time. In particular, aging of the photoreceptor can be suppressed to a minimum, and even if the photoreceptor has uneven film thickness, the electric field strength can be changed over a relatively wide range, making it easy to obtain the desired good image. can.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a schematic configuration of a copying machine capable of implementing the image forming method according to the present invention, FIG. 2 is a diagram showing dark decay characteristics of a special α-type phthalocyanine binder resin photoreceptor, and FIGS. 3A and 3B Figure 4 shows the dark attenuation characteristics due to changes in exposure illuminance, Figure 4 shows the light attenuation characteristics when the time from image exposure to development is changed, and Figure 5 shows the dark attenuation characteristics until a shoulder occurs. Figure 6 is a diagram showing the relationship between gradation reproducibility and time from image exposure to development, Figures 7, 8, Figure 9 shows the relationship between electric field strength, white spot rank, number of gradation reproduction steps, and Tin, and Figure 10 shows the relationship between number of aging days, white spot rank, number of gradation reproduction steps, image exposure amount, and Tin. 11 are diagrams showing the relationship between the exposure amount of the eraser lamp, the image exposure amount, and Tin. 1...Photoreceptor, 2...Corona charger, 3...
...Exposure slit, 4...Magnetic brush developer, 7...
... Eraser lamp, Tid ... Time from image exposure to development, Tin ... Time until the shoulder of the dark decay curve occurs, E ₀ ... Electric field strength.

Claims (1)

[Claims] 1 In an image forming method in which an image is obtained through the steps of charging, image exposure, development, transfer, and static elimination, the photoconductive layer of the photoreceptor has a film thickness of about 5 to 10 microns and the dark decay rate after image exposure is Phthalocyanine and the benzene nucleus of the phthalocyanine molecule, which exhibit properties that change depending on illuminance, are substituted with at least one electron-withdrawing group selected from a nitro group, a cyano group, a halogen atom, a sulfone group, and a carboxyl group. Using a phthalocyanine-based photoconductive material obtained by mixing a phthalocyanine derivative with an inorganic acid capable of forming a salt with phthalocyanine and precipitating it with water or a basic substance, dispersed in a binder resin, The electric field strength per 1 micron of the photoconductive layer during charging is approximately
30 to 50 volts, the time from image exposure to the photoconductor to development is about 0.1 to 0.4 seconds, and the amount of exposure for static electricity removal is about 20 to 50 volts.
An image forming method characterized in that the image forming method is performed under 500 lux/sec.