JPH045983B2 - - 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. Furthermore, although photoreceptors having a Cds binder resin photoconductive layer have been widely put into practical use, they are still 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, Υ, 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 low potential area, that is, the intermediate tone, was It was confirmed that it was never repeated. 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. Purpose of the invention The present invention has been made in view of the above facts.
The purpose is to provide an image forming method that has excellent gradation reproducibility and can always produce good images. Summary of the Invention The summary of the present invention is that the benzene nucleus of phthalocyanine and phthalocyanine molecules exhibits a characteristic that the dark decay rate after image exposure changes depending on the exposure illuminance as a photoreceptor. A phthalocyanine derivative substituted with at least one electron-withdrawing group selected from groups and carboxyl groups is mixed with an inorganic acid capable of forming a salt with phthalocyanine, and then precipitated with water or a basic substance. A material having a photoconductive layer formed by dispersing the obtained phthalocyanine-based photoconductive material in a binder resin is used, and the time from image exposure to the photoreceptor to development is about 0.1 to 0.4 seconds. 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 a phthalocyanine derivative with an inorganic acid that can form a salt with phthalocyanine, and then precipitating it with water or a basic substance.The thus obtained product is dispersed in a binder resin and applied to make it photoconductive. It forms a layer. 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. that's all,
It is desirable to set the ratio to preferably 0.002 or more, and examples of 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 the composition of copper phthalocyanine and dinitro copper phthalocyanine is separated, 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 the copying machine shown in FIG. 1, 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 a This is an eraser lamp. Although not shown, the copying machine is also provided with a surface electrometer, an illuminance meter, etc. for measurement purposes. First, the photoreceptor was uniformly charged to a predetermined surface potential Vo by the corona charger 2, and the dark decay characteristic starting from Vo was measured. (Hereinafter, this dark decay characteristic is referred to as Vo dark.) The measurement results are as shown in Figure 2. In the figure, curve A shows Vo when the initial surface potential Vo is about 500V, and curve B shows Vo when Vo is about 400V. In the dark, the Vo 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 Vo decreases approximately linearly, but in the case of photoreceptors with a photoconductive layer containing a special α-type phthalocyanine pigment, a shoulder is formed as described above. and then rapidly attenuates. For curve A,
Vo gradually decreases with the dark decay time, but it does not decrease much until 15 seconds, and it decreases rapidly 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 Vo intersects the shoulder tangent, as shown in curve A. At curve A, Tin is 15.9 seconds, and at curve B, where Vo is approximately 400V, Tin is 13.8 seconds. Incidentally, Tin becomes short due to repeated use of the photoreceptor, and also depends on various factors such as ambient temperature, corona current, and inclusion of phthalocyanine pigment. Especially when the corona current is high, Tin becomes extremely short due to the amount of ozone generated, but this can be prevented to some extent by ozone exhaust.
Generally, Tin is at least 3 seconds and at most 1 minute. However, even if we take a low-speed copying machine as an example, there is no machine that requires more than 3 seconds from charging to image exposure, so the Vo dark characteristic described above does not pose a problem. However, the photoreceptor containing the special α-type phthalocyanine pigment exhibits not only the above-mentioned unique characteristic of Vo dark, but also 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 Vo was 500V,
When the dark decay characteristics immediately after exposure were examined under exposure illuminances of 6.3 lux and 7.5 lux (exposure time was constant), a rapid potential decay was observed, contrary to Vo dark. In other words, under exposure with an exposure illuminance of 6.3 lux, the initial surface potential Vo decreases to Vi of 400V, as shown by curve C, and the dark decay starting from Vi causes a rapid potential decay and the dark decay time but
It drops below 5V in less than 0.5 seconds. Even when the exposure illuminance is 7.5lux, Vi is approximately 3000, but it is curved.
As shown in 0D, a rapid potential decay also occurs.
When this is applied to the copying machine shown in FIG. This means that the image will not be developed at all because it will be broken. In other words, if a copy document is made of a black image (for example, black text) and a gray image (an intermediate image such as a photograph or thin text) and is charged to Vo and exposed to the image, the potential corresponding to the black image area will be approximately Vo. As it is, the potential does not decrease to at least the above-mentioned Tin, but the gray image area decreases 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. Particularly, since the bias voltage 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 explain in more detail 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 changed from 1.2 lux to 300 lux. used the same plate-shaped photoreceptor as the one described above, which was produced using the same manufacturing method, and used a reciprocating electrostatic characteristic device as a measuring device. In addition, it was performed with the intervention of an irradiation shutter, and 100
It was opened for ~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 illuminance
1 second for 30lux curve E5, 50lux curve E6
It is very 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. In view of the above facts, the image forming method according to the present invention requires a time of approximately 0.1 from image exposure to development.
By setting the time to between 0.4 seconds and 0.4 seconds, a good image with excellent gradation reproducibility can be obtained. The time from image exposure to development (hereinafter referred to as Tid), that is, the latent image portion formed by image exposure through the exposure slit 3 in FIG. 1 arrives at the magnetic brush developer 4. time until
The reason for setting Tid to approximately 0.1 to 0.4 seconds is that if it is less than 0.1 seconds, even if the speed is increased, it will not be sufficient to reach the development stage, and the sensitivity of the photoreceptor will decrease. This is because not only a part of the halftone image cannot be reproduced, but also the gradation reproducibility itself deteriorates. To explain specifically, Figure 4 shows the surface potential when changing the time Tid from image exposure to development.
It is a light attenuation characteristic that shows the relationship between Vo and exposure amount. Curve F1 has Tid of 0.25 seconds, F2 has Tid of 0.39 seconds, and F
3 is the light attenuation curve when Tid is 0.67 seconds.
As is clear from the figure, each curve F1, F2, F
The slope degree of 3 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, deteriorates, and it turns out that it is better to shorten Tid in order to widen the halftone reproduction range. Further, from this, desired gradation reproduction can be obtained by changing Tid. In Figure 5, the left vertical axis is the time Tin until the shoulder of the dark decay curve starting from the surface potential Vo occurs, the right vertical axis is the exposure amount E1/2 required to halve Vo, and the horizontal axis is Tid. Tin and Tid were measured by changing the rotational speed of the photoreceptor 1 in FIG. 1 and by changing the development position (experimentally, the measurement position) with respect to the fixed image exposure position. 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 photoconductor rotation speed, It is the corona current μA of corona charger 2 required to charge the photoconductor to 500V Vo, seconds/period is the time required for one rotation of the photoconductor, and θ is the image exposure The probe position located counterclockwise from the position as well as Tid, Tin, and E1/2 at each probe position are shown.

[Table] In Fig. 5, ○ and ● represent the relationship between Tin, Tid, and E1/2Tid at θ=25°, and △ and ▲ represent 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. Also, although not shown, Tin has a Tid of 0.1 seconds, especially
It decreases rapidly in less than 0.05 seconds, and in this sense Tid is
It is important that the time is 0.1 seconds or more. in this way
The reason why Tin becomes shorter is because it is closely related to the corona current It, and Tin becomes shorter depending on the amount of ozone generated. On the other hand, when looking at the relationship between E1/2 and Tid, Tid
It can be seen that the longer the time, the higher the sensitivity becomes.
For example, when Tid is 0.12 seconds, E1/2 is 9.3lux・sec, whereas at 0.5 seconds, E1/2 is 5.9lux・sec, and at 0.67 seconds.
Sensitivity has improved considerably at 5.0lux・sec. 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 is the number of Kodakku Brake scale reproduction steps and the horizontal axis is
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, using the photoreceptor having the special α-type phthalocyanine binder resin photoconductive layer, an image forming experiment was conducted using the copying machine shown in FIG. 1 at Tid of 0.15, 0.3, 0.39, and 0.55 seconds, respectively. Except for the case of 0.55 seconds, good images with excellent gradation reproducibility were obtained.
Good images were obtained by setting Tid to 0.1 to 0.4 seconds. Note that the photoreceptor used in the present invention includes, for example, a special α-type phthalocyanine binder resin photoconductive layer and an ε
It may have a structure in which a type phthalocyanine binder resin photoconductive layer is laminated, or it may have a structure in which two layers of special α type are laminated on a substrate and each layer has a different content of phthalocyanine pigment. Furthermore, the present invention is not limited to the slit exposure type copying machine as shown in FIG. It can also be carried out on machines. Effects As is clear from the above explanation, according to the image forming method according to the present invention, it is possible to obtain a good image with excellent gradation reproducibility. It is easy to implement because it only needs to be set within a certain range. Furthermore, the above-mentioned time setting has excellent effects such as flexibility in obtaining desired gradation reproduction.

[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. FIG. 6 is a diagram showing the relationship between the time, photosensitivity, and the time from image exposure to development. FIG. 6 is a diagram showing the relationship between gradation reproducibility and the time from image exposure to development. 1...Photoconductor, 2...Corona charger, 3...
...Exposure slit, 4...Magnetic brush developer, Tid
...Time from image exposure to development, Tin...Time until the shoulder of the dark decay curve appears.

Claims (1)

[Claims] 1. Phthalocyanine and phthalocyanine molecules exhibiting the characteristic that the dark decay rate after image exposure changes depending on the exposure illuminance as a photoreceptor in an image forming method in which an image is obtained through the steps of charging, image exposure, development, and transfer. The benzene nucleus is a nitro group,
A phthalocyanine derivative substituted with at least one electron-withdrawing group selected from a cyano group, a halogen atom, a sulfone group, and a carboxyl group is mixed with an inorganic acid that can form a salt with the phthalocyanine, and then mixed with water or a basic acid. A photoconductive layer formed by dispersing a phthalocyanine-based photoconductive material obtained by precipitation with a substance in a binder resin is used, and the time from image exposure to development on the photoreceptor is about 0.1 to An image forming method characterized in that the time is 0.4 seconds.