JPS60229062A - Developing device - Google Patents

Abstract

PURPOSE:To obtain a visible image of high picture quality during both normal development and reversal development by charging a developer contained in a signal developing device sufficiently to the 1st polarity used for the normal development and the 2nd polarity used for the reversal development. CONSTITUTION:A toner 30 is put in the developing device 12 and a toner image is formed on a photosensitive drum 9. The developing device 12 performs development by conveying the toner 30 as shown by an arrow C when a developer sleeve 26 rotates as shown by an arrow C and a magnetic roll 27 rotates as shown by an arrow B. When an agitator screw 28 rotates, the toner 30 is charged sufficiently to the plus or minus polarity and the toner 30 conveyed on the peripheral surface of the developer sleeve 26 reaches a developing area J while its thickness is controlled by a magnetic blade 46 and used for development. The photosensitive layer of a photosensitive drum 9 is formed of selenium as a development condition and the normal development and reversal development are carried out to form an excellent image which has 1.2 maximum image density and neither fogging nor fringing.

Description

[Detailed description of the invention] 10. INDUSTRIAL APPLICATION FIELD The present invention relates to a developing device such as an electrophotographic copying machine or a printer.

2. Prior Art First, an outline of an electrophotographic copying machine using a conventional developing device will be described. The document placed on the document table is irradiated with light by an exposure lamp, and this reflected light passes through an optical system such as a reflecting mirror and lens to an image carrier whose surface has already been charged by a charging electrode (for example, a photosensitive material). body drum). The optical system moves to scan the entire surface of the document, and the photosensitive drum is configured to rotate in synchronization with the movement of the optical system.
When the photoreceptor drum is successively exposed to light reflected from the original, the charge on the surface of the photoreceptor drum disappears depending on the amount of exposure, and an electrostatic latent image is formed. The potential of the area where the amount of exposure due to the reflected light from the original was small is relatively high, and toner with a polarity opposite to that of the photoreceptor drum adheres to this area. The potential of these parts is relatively low, and toner does not adhere to them. In this way, a toner image is formed on the surface of the photoreceptor drum. This toner image is transferred by the transfer pole onto the copy paper fed from the paper feeder. The copy paper onto which the toner image has been transferred is separated from the photoreceptor drum by a separation pole, and after the toner image is fixed on the copy paper by a fixing device, it is sent to a paper discharge tray. - The photosensitive drum continues to rotate during this time, and after residual charges are removed by a static eliminator, residual toner on the surface of the photosensitive drum is removed by a cleaning device, and the drum is subjected to the next copying process.

This copying machine uses regular development (
A positive-positive development method is used.

On the other hand, some recording apparatuses form an electrostatic latent image on a photoreceptor drum using an exposure source (for example, a laser, a cathode ray tube) operated by a recording signal from a data recording section.

When forming an image using such a device, a method is adopted in which a negative latent image is formed by exposing an image area corresponding to a colored area with a small area such as characters, and this is then developed in reverse (negative-positive development). Often. Reversal development is also used to directly obtain a positive record from a negative original.

In reversal development, the toner adheres to the areas of the photoreceptor drum that have been exposed to light and have a low potential of the latent image, so it is necessary to set the toner charge polarity, development bias, etc. to different conditions from those for regular development. be.

For general users, it would be problematic in terms of space and cost for a general user to prepare a dedicated recording device for regular development and reversal development, respectively. Various proposals have been made.

For example, there is a method of storing two types of toners with different charging polarities in separate developing devices and using them depending on whether normal development or reversal development is being performed. Toner boxes for storing replenishment toner must be provided on two sides of the recording apparatus, which inevitably increases the size of the recording apparatus. Another example is to use only one developing device and change the charged polarity of the photoreceptor depending on whether it is regular development or reverse development, but it is technically difficult to manufacture a photoreceptor with similar photosensitive characteristics for both polarities. It is. Furthermore, Japanese Patent Laid-Open Publication No. 128365/1983 has proposed an apparatus in which normal and reversal development is performed using a developing device containing high-resistance magnetic toner. According to this device, regular development and reversal development can be performed using one type of toner, in other words, a single developing device.Therefore, this method simplifies the device and brings about a great practical advantage.

The present inventor uses the above-mentioned toner, that is, one type of toner.
We conducted research on methods for performing regular development and reversal development, but as far as the toners used are concerned, it is not possible to perform regular development or reversal development simply by using a high-resistance magnetic toner, as described in the above-mentioned JP-A-Sho. It was found that it was not possible to obtain high-quality images during both development and development.

3. Purpose of the Invention The purpose of the present invention is to provide a developing device which performs regular development and reversal development using one type of toner, and which can obtain high-quality visible images for both regular development and reversal development. be.

4. Structure of the Invention In other words, the present invention provides a developing device that performs regular development and reversal development, in which the developer contained in a single developing device has a first polarity used for regular development and a reversal development. This invention relates to a developing device characterized in that it is sufficiently charged with a second polarity used in the development.

As described above, in the present invention, the toner has the first polarity,
By being sufficiently charged to the second polarity, it has become possible to obtain high-quality visible images in both regular and reversal development.

Here, the fact that the toner is sufficiently charged to the first polarity and the second polarity means that the toner has a charge distribution curve as shown in Figure 8, for example. In Figure 8, the horizontal axis shows the amount of charge (
μC, #), the content ratio (weight) is plotted on the vertical axis, and the area a defined by the positive side curve of the first polarity (positive) and the negative side curve of the second polarity (negative) Good results were obtained if the ratio of the area defined by the area defined by the sum to the area defined by the ratio was within the range of 3-near to 7:3.

5. Examples Hereinafter, embodiments of the present invention will be described in detail using the drawings.

The charge amount distribution curve shown in FIG. 8 is measured by the method described below. The toner 30 was stirred for m minutes at a rotation speed of 45 rpm using a "micro type see-through mixer" (manufactured by Tsutsui Rikagaku Kiki Co., Ltd.) to charge the toner, and this was charged as described in JP-A-57-
The amount of charge on the toner 30 was measured using the method and apparatus described in Japanese Patent No. 799513. FIG. 9 shows a schematic diagram of this device, in which a nozzle 40 for blowing out toner 30 and an air intake port 41 are provided at one end of a chamber 39 formed by a cylinder 38. 41 is provided with a large number of guides 42 so that the direction of air flow within the chamber 39 is constant.
An r-filter 43 is provided at the other end of the cylinder 38, and the filter 43 is configured to allow air to pass through but not toner 30. Here, chamber 3
When a voltage is applied between the inner wall surfaces 38A and 38B of the cylinder 38 forming the chamber 39, an electric field is generated within the chamber 39 in the direction of the arrow E. Then, if air is sent into the toner 30 from the nozzle 40 in the direction of arrow H through the air intake port 41,
The toner 30 moves inside the chamber 39 in the direction of arrow V due to the force of air.
Fly in the direction of a. The direction of the air flow inside the chamber 39 is fixed in a fixed direction by the guide 42, and if the toner 30 is not charged, it will not flow into the chamber 39.
Even if an electric field exists within it, it will match the direction of the air flow.
However, when the toner particles 30A are electrically charged, a force acts in the direction of the arrow Fe or the arrow Fr under the influence of the electric field.

FIG. 9 shows that the toner particles 30A are moved in the direction of Fe due to electrostatic force.

The toner particles 30A then adhere to a point at a distance from the center wire of the chamber 39 of the first passer 43. If the amount of toner particles 30A attached to each part of the first passer 43 is calculated, a charge distribution curve as shown in FIG. 8 can be obtained for the toner 30. Note that the charge distribution curve of the toner 30 described below is based on an inner diameter of the chamber 39 of 46 mm.
φ, the voltage applied between the inner wall surfaces 3&A and 38B of the chamber 39 is 1.5 KV, and the wind speed is 075 m/sec.
, is the result of measuring the distance l from the nozzle 40 to the filter 43 under the condition of 100 fins.

Note that, as described above, the most important point of the toner 30 is the relative ratio of the amount of charge on the positive side and the amount on the negative side. Therefore, when measuring the charge amount distribution of toner, consistent results can be obtained not only by the above-mentioned charging method using the microscopic see-through mixer but also by other charging methods. Therefore, when measuring the charge amount distribution, it is not necessary to use the above-mentioned specific charging method.

The developer used in this developing device.

This resistance value was measured by the method described below.

Cross-sectional area 1. Sample (toner) in Od cell from 0.03 to
0D8cIrL to a depth h), and from above, 1k
The current value A is measured when a weight of 17 is applied and a voltage is applied such that it becomes 104 V/, and the resistance value is calculated using the following formula.

(2) Resistance value λ (07 cm)=-xh Next, the toner used in the present invention will be explained.

The toner 30 is mainly formed from a resin and a finely divided ferromagnetic material, and may also contain a colorant.

As the resin component, a thermoplastic resin is preferably used, which provides insulation to the toner 30 and has properties suitable for heat fixing.

Advantageously used thermoplastic resins include, for example, styrenes such as styrene and parachlorostyrene, vinylnaphthalenes, such as vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, and the like. vinyl esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloro-ethyl acrylate,
Esters of α-methylene aliphatic monocarboxylic acids with phenyl, α-methyl chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide, e.g. vinylmethyl ether,
Vinyl ethers such as vinyl isobutyl ether and vinyl ethyl ether, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone, such as N-vinylpyrol, N-
Homopolymers made by polymerizing monomers such as N-vinyl compounds such as vinylcarbazole, N-vinylindole, and N-vinylpyrrolidone, copolymers made by copolymerizing a combination of two or more of these monomers, or mixtures thereof. , or, for example, rosin-modified phenol-formalin resin, oil-modified epoxy resin, polyurethane resin,
Examples include non-vinyl resins such as non-vinyl thermoplastic resins such as cellulose resins and polyether resins, or mixtures of these and vinyl resins as described above.

Among these resins, especially vinyl resins, 2
It has a glass transition point of 0°C or higher, about 1000 to 500°C.
Those having a weight average molecular weight of 0.000 are effectively used.

In particular, when the toner image transferred onto the copy paper 13 is fixed using a heated roller, a resin containing styrene with good mold releasability, such as styrene-acrylic acid ester, styrene-methacrylic acid ester, etc., is used as the main component. It is preferable to use a styrene-vinyl copolymer resin.

Particulate ferromagnetic materials include substances that are extremely strongly magnetized in the direction of magnetic fields, such as alloys or compounds containing ferromagnetic elements such as ferrite, magnetite, iron, cobalt, nickel, etc., or ferromagnetic elements. Alloys that do not contain manganese but become ferromagnetic through appropriate heat treatment, such as alloys called Heusler alloys that contain manganese and copper, such as manganese-copper-aluminum or manganese-copper-tin, or chromium dioxide. are used effectively, but the use of magnetite is most preferred.

When these ferromagnetic materials are contained in the toner, it is desirable that the average particle size is approximately 0.1 to 1 micron, and the amount contained in the toner is approximately 20-1 microns based on the total amount of the toner.
The content is preferably 70% by weight.

Note that since ferromagnetic materials generally have conductivity, it is not preferable to add a large amount of ferromagnetic materials in order to obtain a highly insulating developer suitable for the method of the present invention.

Since a ferromagnetic material such as magnetite usually has a black color or a color close to black, it itself has an effect as a coloring agent for the toner 30, but a coloring agent may be added if necessary.

Any suitable pigment or dye can be used as the coloring agent. For example, carbon black, nigrosine dye, aniline blue, calco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green offsalate, lamp black, rose bengal, etc. are used singly or in combination. In particular, carbon black is effectively used. However, since carbon black has conductivity, it is desirable to keep its use i relatively low in order to obtain a highly insulating toner 30.

Further, various other additives can be added to the toner 30 as needed.

For example, to control the charge of toner 30, certain dyes and pigments can be added as charge control agents.

As these charge control agents, for example,
Fettsch RUN (Fettsch
warz HBN; Color index N, 26150
), alcohol-soluble nigrosin
; Color index NrL50415), Sudan tief-sc
hwarz BB; Solvent Black 3; Color Index &26150), Brilliant Spirits Shuha) TN, Brilliantsprits
chwarzTN; manufactured by Falpen, Fabriken, Baia), Zapon schwarz X, (Zapon schw
arz
reschwarz (R) G;
O; Color Index Oni 14645), Azo-Oi 1-Black (R)
(manufactured by National, Aniline), and other pigments such as phthalocyanine blue.

Alternatively, chemically treated carbon black and resins having positive or negative charge control groups can be used as a kind of charge control agent.

Furthermore, in order to improve the compatibility of these charge control agents with the resin component, they can be added in the form of salts formed with higher fatty acids, or a compatibility improver can be added separately. In addition, for example, the fixing process is performed using a heating roller 22.
In the toner 30, which is applied to image formation using a method using Salts, relatively low molecular weight polyethylene or polypropylene, higher fatty acids having 28 or more carbon atoms, natural or synthetic paraffins, etc. can be added, and when the resin component is relatively brittle. A plasticizer or the like can be added to modify this.

To manufacture the toner 30, a conventional general toner manufacturing method can be applied as is. For example, various additives such as a resin component, a coloring agent, a particulate ferromagnetic material, and a charge control agent used in combination with these are premixed using a ball mill or the like to uniformly mix and disperse each component. Next, the mixture is kneaded using heated rolls, then cooled and crushed.

In this kneading step, the insulating properties of the toner 30 finally obtained vary greatly depending on the kneading conditions, etc., so in order to reliably obtain toner 3o with high insulating properties,
It is necessary to carry out production based on preliminary experiments to find the optimum conditions for kneading.

Next, in order to obtain a developer having a desired particle size, classification is performed as necessary to produce a toner 30 having an average particle size of, for example, 9 to 12 microns. The particle size of the toner 30 varies depending on the purpose of use, the type of electrostatic image to be developed, etc., but is generally desirably about 5 to 20 microns.
Furthermore, it is also possible to use the most suitable particle size depending on the purpose of use.

Since the toner 30t'i is used without being mixed with a carrier, it is desirable that the toner 30 has a spherical shape as much as possible in order to improve the fluidity of the toner 30 and prevent agglomeration. Further, it is desirable that the particles do not contain developer particles having a relatively small particle size and have uniform particle sizes.

In order to produce developer particles having such a spherical shape, the fine toner powder prepared according to the method described above is further sprayed into hot air to instantaneously melt the surface of each toner particle. It is preferable to make the toner particle surface spherical by surface tension.

Further, in order to improve the fluidity of the toner 30, a fluidity improver may be mixed into the current IM agent. As a fluidity improver, fine powder of hydrophobic silica, hydrophobic titanium white, hydrophobic alumina, etc. is used in an amount of 0.0% per 100 parts by weight of the developer.
It is preferable to add 0.5 to 5 parts by weight, and addition of hydrophobic silica is particularly preferable.

The fluidity of the developer thus obtained is preferably in the range of 20% to 40% in terms of compression ratio.

Next, a copying apparatus using a developing device containing the toner 30 will be explained with reference to FIG.

FIG. 1 is a schematic cross-sectional view of a copying apparatus capable of performing regular development and reversal development. The original 2 held down by the platen cover 4 is irradiated by an exposure lamp 5,
The first mirror unit 7, second mirror unit 7, 'y', and unit 8 guide reflected light from the original 2 to the photosensitive drum 9 while scanning in the direction of arrow A. The photoreceptor drum 9 is already, for example, uniformly charged by the charger 10, and when it is exposed to light reflected from the original 2, the charge on the portion irradiated with light disappears and the portion is not irradiated. The charge on the part remains, 1
1 latent image is formed. This electrostatic first image is formed on the photoreceptor drum 9 by the toner 30 that has been conveyed on the developer sleeve 26 in the developing device 12 adhering to the developing area. This toner image is
Copy paper 1 conveyed by rollers 15 and 16 from 4
3 by the transfer pole 17. The copy paper 13 on which the toner image has been transferred is separated from the photosensitive drum 9 by a separation pole 18 and sent to a fixing device 20 by a conveyor belt 19. The fixing device 20 is composed of a heating roller 22 in which a heater 21 is arranged and a pressure roller 23. The toner image is transferred onto the copy paper 13 by the heat and pressure applied when passing between the rollers 22 and 23. After being fixed, this bale photo paper 13 is then discharged @25 by a paper discharge roller 24.
transported to. Meanwhile, the photosensitive drum 9 continues to rotate during this time, and after the residual charge is removed by the removing electrode 31,
The remaining toner is removed by the cleaning device 1, and the toner is used for the next copying.

Next, changes in the latent image potential of the photoreceptor drum 9 when regular development is performed and reversal development is performed in this copying apparatus will be explained using an example in which the photoreceptor drum 9 is positively charged. First, a case where regular development is performed will be described. When charged by the charger 10, the photosensitive drum 9
The surface of , as shown in FIG. 2, is uniformly Vs.
When exposed to light reflected from the original 2, the reflected light from the image portion of the original 2 is small and the reflected light from the background portion is large, so the latent image potential of the photosensitive drum 9 is as shown in FIG. It comes to show. Here, the part A corresponds to the background of the original 1fr42, and since the amount of reflected light is large, the charge disappears and the potential becomes low. The mouth part corresponds to the image of the original 2, and since the amount of reflected light is very small, the charge does not disappear and the potential of vs is maintained. Then, as shown in FIG. 4, a developing device 1
The toner that is already negatively charged in the photoreceptor drum 2 is attached by electrostatic force, and a toner image is formed on the photoreceptor drum 9.

On the other hand, in the case of reversal development, the charger 1o charges the
As shown in FIGS. 5 and 6, the process is the same as regular development until the potential of the area irradiated with light becomes low due to exposure.
The part C in Figure 6 corresponds to the background part of manuscript 2,
Although the amount of reflected light is small, it maintains Vs, and the second part corresponds to the image of the document 2, and since the amount of reflected light is large, the potential becomes low.

In reversal development, toner must be attached to this low potential area. Therefore, it is necessary to charge the toner in the developing device 12 to the same polarity as that of the photoreceptor drum 9, and to apply a pressure of approximately the same level as VS to the developing sleeve. As a result, toner adheres to the second portion where the potential is relatively low, as shown in FIG.

Developing device 1 provided in the copying machine configured as above
2, it should be noted that insulating magnetic toner 30 having a charge distribution as shown in FIG. 8 is stored, and normal development and reversal development are performed by one developing device 12. Hereinafter, this configuration will be explained in detail.

If the toner 30 stored in the developing device 12 has a charge distribution as shown in FIG. 8, the toner 30 that is negatively charged and the toner 3 that is positively charged are used.
If 0 and 0 are mixed in the developing unit 12, the result is K. During regular development, since the Vs portion of the latent image potential formed by exposure has a positive charge, the positively charged toner 30 in the developing device 12 is repelled and is not deposited on the photosensitive drum 9. No adhesion occurs, and only the negative toner 30 adheres. During reversal development, a bias voltage of approximately the same level as Vs is applied to the developing sleeve 26, so that the potential difference between the developing sleeve 26 and the portion of the photoreceptor drum 9 where Vs is maintained is reduced. Therefore, no electrostatic force acts. Therefore, the negative toner 30 cannot adhere to the portion of the photoreceptor drum 9 where Vs is held. However, as shown in FIG. 6, a potential difference is generated between the portion where the V potential has become low due to exposure and the developing sleeve 26 because a bias voltage of approximately the same level as Vs is applied. An electrostatic force is acting on the . Due to this electrostatic force, the side of the developing sleeve 26 with a high potential is moved from the side of the photosensitive drum 9 with a low potential.
Positive toner 3 (c) (adheres to the side).

That is, even if positively and negatively charged toner 30 as shown in FIG. 8 are mixed in the developing device 12, only the negatively charged toner is used during normal development, and only the positively charged toner is used during reversal development. Only these toners are selectively subjected to development, and no situation occurs in which the toner used for one development interferes with the development of the other. Due to this, even one developing device 12 can perform normal and reversal development.

Since the toner 30 is sufficiently charged positively and negatively within the developing device 12, an image with a constant level of roughness can be formed in both normal development and reverse development.

Hereinafter, specific examples carried out by the present inventor will be described.

Example 1 46% by weight of styrene-acrylic resin was used as the thermoplastic resin, and magnetite (BL-1) was used as the magnetic material.
50% by weight of 00) and nigrosine (
Oil Black SO) 1% by weight, heating roller 22
3ffi-t% of polypropylene (Viscol 660 P) was melted and kneaded as a material having a mold release effect on the toner, crushed, sphericalized by heat treatment, and then classified to obtain a toner having an average particle size of 11 μm.

To 100 parts by weight of this toner, 0.4 parts by weight of hydrophobic colloidal silica R-972 (manufactured by Nippon Aerosil Co., Ltd.) was added as a fluidity improver, and mixed with a type mixer to form Toner 3.
I got 0. When the charge amount distribution of this toner 30 was measured using the apparatus shown in FIG. 9, a charge distribution curve as shown in FIG. 84 could be obtained.

That is, the ratio of the positive charge amount to the negative charge amount is 6.2:3.
It was 8. The reason why the toner 30 formed from the above materials is positively and negatively charged as shown in FIG. 8 is because nigrosine is a substance that is easily charged positively, and hydrophobic silica and magnetite are substances that are easily charged negatively. Due to the effects of both, the toner 30 as a whole is charged to both positive and negative polarities. In addition, the degree of compression as a substitute evaluation for fluidity is 26.
% was rare.

This toner 30 was stored in a developing device 12 whose cross section is shown in FIG. 10, and a toner image was formed on the photosensitive drum 9.

In this developing device 12, the developer sleeve 26 rotates in the direction of arrow C and the magnetic roll 27 rotates in the direction of arrow B, so that the toner 30 is conveyed in the direction of arrow C to perform development. As the stirring screw 28 rotates, the toner 30 is sufficiently charged positively or negatively, and the thickness of the toner 30 conveyed on the circumferential surface of the developer sleeve 26 is regulated by the magnetic blade 46. Development area J
The film arrives at the site and is subjected to development. Toner 3 not subjected to development
0 continues to be transported over developer sleeve 26 and scraped off from developer sleeve 26 by blade 45 . When the toner 3o is insufficient, it is replenished by rotating the replenishment roller 29.

Using this developing device I2, the developing conditions are as follows:
The photosensitive layer is made of selenium, the gap d between the photosensitive drum 9 and the developer sleeve 26 is 0.30+m, and the magnetic blade 46
The gap between and the developer sleeve 26 is 0.35 arp,
The diameter of the current thickener sleeve 26 is 30mm, and the number of rotations is 13mm.
Qrpm.

The rotational speed of the magnetic roll 27 was 1000 rpm.

When normal development and reversal development were performed under the above conditions,
The maximum image stiffness was 1.2, and it was possible to form a good image without blur or frizz. The developer sleeve 26 was grounded during regular development, and 500 V was applied to the developer sleeve by the bias power source 47 during reverse development.

Example 2 The conditions differ from Example 1 in that the constituent materials of toner 3o, nigrosine, are used as Parifast 3804 (manufactured by Orient Chemical Co., Ltd.), and the hydrophobic colloidal silica R-972 is used as 1 (A-
200H (manufactured by Nippon Aerosil Co., Ltd.).

The toner 3o with the above configuration has a compression degree of 24.1%.

The specific resistance value was ti to''n, and the ratio of the amount of charge on the positive side to the amount on the negative side was 4.5:5.5.The developing conditions were as follows: When the charging polarity of the charging electrode 10, the bias voltage, and the polarity of the transfer pole 17 were reversed from those in Example 1, development was performed.
As in Example 1, a good image could be formed. Note that other developing conditions are the same as in Example 1.

Example 3 The difference from Example 2 is that the constituent materials of the toner 30 are Parifast 3804 and Subiron Black TRH (
(manufactured by Hodogaya Chemical Co., Ltd.), and R as the hydrophobic alumina.
0.4 g of X-C (manufactured by Nippon Aerosil Co., Ltd.) was added.

The degree of compression of this toner 30 was 26.3 inches, and the ratio of the amount of charge on the positive side to the amount on the negative side was 4.0:6.0. Even with this toner 30, a good image similar to that of Example 1 could be formed.

When carrying out the present invention, it is also possible to use a developing device as shown in FIG.

FIG. 11 is a sectional view of a developing device including two developing devices 12A and 12B. One developing device 1 shown in FIG.
If only normal development is performed according to step 2, for example, only the negatively charged toner 30 is used, and the positively charged toner 30 remains in the developing device 12. Therefore, as shown in FIG. 11, there are two developing devices, and the developing devices are used to perform regular development and reversal development. First, the developing device 12A performs regular development, the developing device 12B performs reversal development, and the developing device 12A performs reversal development. The positively charged toner 30 is placed in the developing device 12B, and the negatively charged toner 3 (
When there is too much remaining, the developer 12B is used for regular development and the developer 12A is used for reversal development.

By switching in this manner, it is possible to prevent the toner 30 charged to one polarity from remaining in both developing devices.

Note that the present invention can be further modified based on its technical idea. In the embodiment described above, the exposure lamp 5 is used as the exposure source for irradiating the photoreceptor drum 9;
Other light emitting elements such as cathode ray tubes, lasers, and light emitting diodes may also be used. Furthermore, the toner 30 is not limited to insulating magnetic toner, and other toners can also be used.

6. Effects of the Invention As described above, the present invention allows the developer used for regular development and the developer used for reversal development to be stored in a single developing device. There is no need to provide a plurality of , and the developing device can be made smaller.

Then, the developer used for regular development has the first polarity,
The developer used in reversal development is sufficiently charged to the second polarity in the developing device, so both regular development and reversal development provide equally high image quality (sharpness, gradation, maximum density). A visible image of ) is obtained.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG. 1 is a schematic sectional view of a copying apparatus that can perform regular development and reversal development, and FIGS. 2, 3, and 4 show a copying apparatus that can perform regular development. Figures 5, 6, and 7 are diagrams showing potential changes of the photoreceptor drum when reversal development is performed, and Figure 8 is a diagram showing the changes in the potential of the photoreceptor drum when performing reversal development. Figure 9 is a schematic diagram of a device for measuring the charge distribution of developer, Figure 10 is an enlarged sectional view of a developing device, and Figure 11 is a diagram of a developing device consisting of two developing devices. It is an enlarged sectional view. Regarding the symbols used in the drawings, 2...Original 5...Exposure lamp 9...Photosensitive drums 12, 12A, 12B...Developers 26, 26A, 26B...Developer sleeve 27 ,2
7A, 27B...Magnetic roll 28.28A, 28B...
... Stirring screws 29, 29A, 29B, supply roll 30, insulating magnetic toner 46, 46A, 46B, magnetic blades.

Claims (1)

[Claims] 1. In a developing device that performs regular development and reversal development, the developer contained in a single developing device has a first polarity used for regular development and a second polarity used for reversal development. A developing device characterized by being sufficiently charged.