JPS58208772A - Method for inverse development - Google Patents

Abstract

PURPOSE:To obtain many fine copies without the generation of fog and the change of density by using magnetic toner consisting of one component which is agitated in a magnetic field in the method to inversely develop an electrostatic latent image into a toner image by magnetic brush method. CONSTITUTION:After forming an electrostatic latent image on an electrophotographic receptor 4 obtained by forming a photoconductive layer 1 (e.g. a layer obtained by dispersing zinc oxide into a bonding agent) on a conductive supporting element 2, the latent image is developed into a toner image by magnetic toner 7 through a non-magnetic sleeve 8 (to which bias voltage having the same polarity as the surface potential of the photoreceptor 1 is applied) to be rotated relatively to a magnetic roll 10. For said toner, toner obtained by agitating (by using an insulated case 5 and an agitator 6) unmagnetized toner 3 (about <=35wt% of <=15mu grain size and about <=3wt% of <=10mu grain size) consisting of an adhering agent and magnetic powder for 5min-10hr at about 5-60 deg.C under about <=700 gausses of magnetic field generated by a coil 11 is used.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a reversal development method using a magnetic push development method using a one-component magnetic toner in electrophotography.

Conventionally, in the reversal development method in which toner particles are made to adhere to the areas that received light during exposure and are visualized, a magnetic brush development method using a magnet roller is generally known, and was published in Japanese Patent Publication No. 1983. -2705, JP-A-53-112740,
JP-A-53-115299, JP-A-54-98, 24
No. 8 and Japanese Unexamined Patent Publication No. 146243/1983. That is, as shown in FIG. 1, it has, for example, a cylinder-shaped conductive non-magnetic sleeve 8, and the non-magnetic sleeve 8 is rotatably supported relative to a magnet row 210 disposed inside. The non-magnetic strip 8 has the same polarity and potential on the same order as the surface of the photoconductive layer 10 on the photoreceptor 4 on which the latent image is formed, and has a relatively high resistance toner (107 to 1014 Ω). cIIL) is conveyed to the surface of the non-magnetic sleeve 80, brought into contact with the surface of the photoreceptor to be developed, and developed.

The use of one-component magnetic toner in such a developing device is advantageous in that the entire copying machine can be made smaller, maintenance-free, and there is no need to control toner density. When the present inventors performed reversal development using a photoreceptor having a photoconductive layer on a conductive support in which zinc oxide particles were dispersed in a binder, only images with a significantly large amount of capri and low contrast were obtained. It turned out that I couldn't do it.

JP-A-55-134864 discloses a method for obtaining an image with no capri and good contrast by performing reversal development using a magnetic nozzle development method using a one-component magnetic toner. In this method, when performing reversal development using the magnetic brush development method using the above-mentioned -component magnetic toner,
The photoreceptor is charged by suppressing the charging potential to a potential that is extremely lower than the saturation charging potential (the maximum chargeable surface potential of the photoreceptor), for example, about 60% of the saturation charging potential (non-saturated charging), and This is a method of developing by applying a potential to the one-component magnetic toner that has the same polarity as this surface potential and is approximately equal to or slightly higher than this surface potential.

According to this method, it is possible to obtain an image by reversal development that is free from capri and has good contrast, equivalent to an image obtained by normal development using a magnetic plan development method using -component magnetic toner. However, it also has the following drawbacks:

That is, in this method, it is necessary to accurately control the charging potential on the surface of the photoreceptor, and in order to achieve this, a power source for the corona wire and a power source for the grid that controls the amount of charge from the corona wire are required. Since it is necessary to use a so-called scorotron, the cost of the resulting device is inevitably high, and the device itself becomes large. Furthermore, when charging is performed using a scorotron until the charging potential reaches a certain value or higher that allows good development, it takes much longer to charge than when using a corotron, making it difficult to increase the speed 3. In addition, in order to increase the speed, a method of using a scorotron and a corotron in combination is disclosed in Japanese Patent Application Laid-Open No. 144260/1982, but even with this, the drawbacks of the former still remain, and furthermore, it is even more difficult than using a scorotron alone. This inevitably increases the complexity and size of the device, and increases the cost of using the device.

The present inventors previously proposed in Japanese Patent Application No. 56-196627 that in order to solve these problems, by setting the electric resistance value of the -component magnetic toner and its coercive force in a specific range,
It was proposed that images with good contrast without capri can be obtained.

That is, in the electrophotographic developing method of the present invention, an electrophotographic photoreceptor that has been charged to a saturation potential and on which an electrostatic latent image has been formed by image exposure is applied with a potential of the same polarity as the charged potential of the photoreceptor by a bias potential applying means. In an electrophotographic development method in which reversal development is performed by a magnetic brush method using an applied one-component magnetic toner, the -component magnetic toner has an electrical resistance of 107Ω or more and in a range where charge exchange is performed, and 1
It is characterized by the use of a material with a coercive force of 50 millimeters or more, which solves the problems of conventional methods, and makes it possible to obtain images with stable contrast without capri during reverse development as well as normal development. . However, after further research, the present inventors found that the toner has the following properties:
When obtaining reversal development by the reversal development method, there are large changes in density and the degree of capri generation between immediately after the start of development and after copying a large number of sheets at each predetermined applied voltage.
It has been found that there is a problem in that the range of applied potentials in which the density is sufficiently satisfied and there is no capillarity becomes narrow, including the change over time due to the number of copies. Here, in a positive development method (forming a positive image from a positive original and then transferring it to another recording medium) using -component magnetic toner, the image quality changes as the number of copies increases (i.e., the number of copies increases). In order to prevent this phenomenon (as the number of sheets increases, the phenomenon that the background becomes thicker and the density increases, and the dust tail phenomenon around the letters becomes more likely to occur), the particle size distribution of the conventional toner is smaller than the particle size distribution (10 μm). It is known from Japanese Unexamined Patent Publication No. 106466/1983 that the following particles) can be increased.

The above structure was adopted in this method from the point of view of improving the fluidity of the toner, but when such toner was used for reversal development, when developing a negative image, the density change was somewhat small as the number of copies increased. Although it was confirmed that
Capri was very likely to stop, making it impossible to obtain good image quality. As a result of various studies, the inventors of the present invention have discovered that by using a toner stirred in the presence of a magnetic field, the above-mentioned drawbacks can be avoided and good results can be obtained, and the present invention has been achieved. That is, the main purpose of the present invention is to eliminate the drawbacks of conventional magnetic toners, to obtain high-density and clear images that do not cause density changes due to an increase in the number of close-up images in reversal development, and that do not cause capri. The object of the present invention is to provide an inversion method that can set a very wide voltage range.

That is, in the present invention, after charging an electron 4 negative photoreceptor to a saturation potential and forming an electrostatic M image by image exposure, magnetic brush development is performed while applying a bias voltage of the same polarity as the charging potential of the trI\photoreceptor. In the reversal development method in which the silent Fkt latent image is often developed with toner, a one-component magnetic toner containing at least a binder and magnetic powder and stirred in the presence of a magnetic field is used as the toner. This is a reversal development method characterized by the following.

The present invention will be further explained below with reference to the drawings.

FIG.
FIG. 3 is an enlarged cross-sectional view illustrating the state of reversal development using the magnetic brush developing device shown in the figure. A photoconductive layer 1 in which an inorganic photoconductor such as zinc oxide, cadmium sulfide or the like is dispersed in a binder is coated on a conductive support 2 to form a photoreceptor 4. After the photoreceptor 4 is charged to saturation using, for example, a corona charging device, it is imagewise exposed to a blank state. an image is formed. The charged portion of the photoconductive layer 1 is a non-exposed portion, and the uncharged portion is an imagewise exposed portion. A DC power supply 9 is connected (to the negative side in this figure) to supply a bias voltage of the same polarity as the charging to the non-magnetic sleeve 8. This non-magnetic sleeve 8 is hardened and has a multi-polar rotatably arranged 17 girder 10 inside, and the toner powder 7 is conveyed to the surface of the non-magnetic sleeve 8, It is brought into contact with the 4th surface of the photoreceptor, toner is attached to the exposed portion of the photoreceptor surface, and reversal development is performed. Table 1 shows the results of an experiment in which reversal development was carried out using a one-component magnetic toner of Yuzu in such an apparatus.

That is, the experimental results shown in Table 1 relate to bias voltage, image reflection density, and fogging over time.

44 In Table 1, Toner A is a one-component magnetic toner used in the present invention. That is, 40 parts by weight of wax and 60 parts by weight of magnetite.
The magnetic toner consisting of the heavy image area is agitated under a direct current magnetic field and has a coercive force of 270 oersteds and a specific resistance of 1.2×10 12 Ω·. Toner B is a magnetic toner made of the same starting material as Toner A,
Toner C is obtained by subjecting toner B only to stirring treatment in the absence of a magnetic field. Using such toner, a 24.5φ developing device with a magnetic roller that generates a 700 Gauss magnetic field on an 8-pole non-magnetic conductive sleeve,
Fix the sleeve and rotate the magnetic roller to 1000 r.
While the photoreceptor was being rotated at pm, the charged and exposed zinc oxide photoreceptor was subjected to reversal development by applying an insulating pressure to the sleeve. At this time, the zinc oxide photoreceptor was 75cIn/
The film was passed under the developing device at a moving speed of sec. after that,
After the magnetic roller was operated for 20 minutes, an image was obtained again in the same manner. As is clear from the results in Table 1, magnetic toner A according to the present invention showed little change in image reflection density over time, and stable images were obtained that did not change even in the bias voltage range where capriion did not occur. Toner B has a wide bias voltage range in which no capillary occurs, but the initial image reflection degree is extremely low, and the width of the bias voltage range in which both the density and the degree of capillary occurrence are satisfied is extremely narrow. Further, in Toner C, the density change is small, which is preferable, but capri is likely to occur, and the bias voltage range becomes wide, so that it cannot be put to practical use. These results show that the toner used in the present invention is superior, but the reason for this effect is that, as mentioned earlier, the toner surface is made uniform by stirring, and the toner is Since it was weakly magnetized, it was assumed that this was due to its improved fluidity. The present invention performs reversal development using a magnetic brush development method using toner particles stirred at a predetermined temperature for a predetermined time in the presence of a magnetic field. Even if continuous copying is performed, excellent images can be obtained as in normal development. In the specific means, for example, under a magnetic field of 700 Gauss or less at a place where the toner particles come into contact, for a predetermined time of 5 minutes to 10 hours, preferably 5 minutes to 2 hours, and a predetermined temperature of 50
This is achieved by stirring toner particles of ~60C1, preferably Fi20r~4DC. The method of magnetizing the magnetic toner includes a method of applying a direct current magnetic field, a method of applying an attenuated alternating current magnetic field, a method of passing the magnetic toner through these magnetic fields, and the like.

Next, in a preferred embodiment of the present invention, in the particle size distribution of the magnetic toner, particles with a particle size of 15 μm or less account for about 65% by weight or less, and particles with a particle size of 10 μm or less account for about 6% by weight or less. By using it, more favorable effects can be obtained.

The present inventors further conducted experiments using toners having different particle size distributions using the same apparatus and method as described above, and obtained the results shown in Table 2.

The experimental results in Table 2 relate to the bias voltage, image error reflection a degree, and capri in the particle size distribution of the toner.

In Table 2, toner D is
As shown in the figure, particles with a particle size of 15 μm or less weigh approximately 35 ht.
About 3% by weight or less of particles having a particle size of 10 μnL or less and having a particle diameter of 10 μnL or less are present, and the agitation treatment is performed in the presence of a magnetic field. Toner E has the same composition as Toner D, has the same electrical properties, and has been subjected to stirring treatment in the presence of a magnetic field, but has a particle size distribution that contains more small-diameter particles (10 pm or less) as shown in Figure 4. It is. In addition, the broken line in FIGS. 6 and 4 represents S+', the grain size distribution. From the results in Table 2,
Comparing Toner D and Toner E, Toner D has a smaller difference in image reflection density than Toner E even at the initial stage of development and after development at a constant ink pressure. In particular, it can be seen that the range of bias potentials in which capri does not occur is always approximately constant, and that the range of bias potentials in which capri does not occur above a certain concentration can be set wide. Although it is not necessarily clear why such a particle size distribution containing many relatively large particles occurs as an effect of the present invention, it is presumed as follows. In other words, if a relatively small diameter one is used,
As the toner surface area per toner weight becomes larger, the electric attraction force acting between the charged potential of the photosensitive layer and the potential supplied to the toner becomes more dominant than the magnetic attraction force of the magnetic roller during development. It is thought that the resulting capri is removed by increasing the magnetic attraction force by using particles with a relatively large diameter. Next, a specific example of a method for manufacturing the magnetic toner used in the present invention will be described. 751 is obtained by stirring an unmagnetized toner that disrupts the constant particle size distribution in a direct current magnetic field using an apparatus as shown in FIG. That is, the unmagnetized toner 8 produced as described above is placed in an insulating container 9 in the apparatus shown in FIG. The mixture is stirred for 1 hour using a stirrer 11 at room temperature. It's ox.
As another manufacturing example, unmagnetized toner is rotated for 30 minutes on a magnetic roller with a magnetic flux density of 700 Gauss for sleeve table 1 at a net rotation speed of 80 Or, using a magnetic roller as shown in Fig. 1. You can also get it. A preferred embodiment of the magnetic toner obtained in this way is that it has a specific resistance of 107 ohms or more and a high coercive force of 150 or more, particularly in reversal development, a high coercive force of 150 or more. It was mentioned earlier that it was proposed in Japanese Patent Application No. 196627-1983 that it is important to have images without fogging.

The binder used in the magnetic toner of the present invention may be a synthetic resin or a natural resin. Among these, as synthetic resins, for example, polystyrene resin, polyethylene resin, polyester resin, epoxy resin, acrylic resin or copolymers thereof, coumaron resin, indene resin, phthalate resin, waxes, etc. may be used alone or in combination. I can do it.

In addition, magnetic powders include ferrite, magnetite,
An alloy or compound containing an element exhibiting ferromagnetism such as cobalt or nickel, or an alloy that exhibits ferromagnetism by undergoing some kind of aX-physical treatment may be used. A specific example is magnetite (Faao4)
Examples include Co-added manetite, spinel ferrite, and magnetoplano 2ite type ferrite.

As a means of setting the electrical resistance of the toner to an arbitrary value as in the present invention, this can be achieved by adjusting the amount of conductive agent added to the toner, such as carbon black, tin, nickel, aluminum, or the like.

Another embodiment of the present invention is a reversal development method using an electrophotographic photoreceptor having a photosensitive layer formed by dispersing zinc oxide in a binder. The toner resistance that can obtain an image with contrast at i image density is 107Ω・α
As stated in the previous Japanese Patent Application No. 196627/1986, the above is necessary, especially reversal development. On the other hand, image density is determined by the ease of charge exchange between the photoreceptor and toner, that is, the ease of charge exchange from the toner to the photoreceptor surface. This seems to be related to the ease of charge injection. When the photoreceptor is a zinc oxide photoreceptor, the energy level of the zinc oxide electron conductor is relatively low (Photo
chem, Photobiol-16219-241 (
(1972))) Although negative charges are easily injected from the toner, images with contrast can be obtained because a relatively high resistance toner is used.

As described in detail above, by using the magnetic toner according to the present invention, images with small density differences and no capillary formation can be produced even when applied to continuous copying on a recording medium that is saturated and has an image formed thereon. This is a reversal development method.

[Brief explanation of drawings]

Figure M1 is a perspective view showing an example of a magnetic brush developing device used in the present invention, Figure 2 is an enlarged sectional view illustrating the state of reversal development, and Figure 6 is a particle size distribution of the magnetic toner used in the present invention. FIG. 4 is a diagram showing the particle size distribution of a comparative toner, and FIG. 5 is a diagram showing an example of manufacturing a magnetic toner used in the present invention. 1... Photoconductive layer 2... Conductive support 3... Unmagnetized toner 4... Electrophotographic photoreceptor 5... Insulating container 6... Stirrer 7... Magnetic toner 8 ...Non-magnetic sleeve 9...DC power supply 10...Manonet Roshe 11...Coil (6 people) Procedural amendment September 1982, 2Z-1982 Patent Application No. 91606 2. Name of the invention Reversal development method 3. Person making the amendment Relationship with the case: Name of the patent applicant (520) Fuji Photo Film Co., Ltd. Kasumigaseki Building Post Office P.O. Box 49/7 Subject of amendment r (Fe=o , )7, corrected as CoJ. 453-

Claims (4)

[Claims] (1) After charging an electrophotographic photoreceptor to a saturation potential and forming an electrostatic latent image by image exposure, the electrostatic latent image is removed by a magnetic brush development method while applying a bias voltage of the same polarity as the charged potential of the photoreceptor. A reversal development method comprising toner development of a latent image, characterized in that a one-component magnetic toner comprising at least a binder and magnetic powder and stirred in the presence of a magnetic field is used as the toner. Method. (2) The toner has particles with a particle size of 15 μm or less in a weight ratio of about 35 μm or less, and particles with a particle size of 10 μm or less - 7! 2. The reversal developing method according to claim 1, wherein the reversal development method has a plasticity of less than about 6 times. (3) The reversal developing method according to claim 1, wherein the toner has a volume resistivity of 10 Ω·F or more and a coercive force of 150 or more. (4) The reversal developing method according to claim M1, wherein the electrophotographic photoreceptor has a photosensitive layer formed by dispersing zinc oxide in a binder.