JPH058424B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement in a method for developing an electrostatic latent image or a magnetic latent image in an electrophotographic copying apparatus, etc.
Specifically, a two-component developer containing a mixture of carrier particles and toner particles is supplied to the surface of a developer transport carrier.
The present invention relates to an improvement in a method of forming a developer layer on the developer transporting carrier and developing an electrostatic image or a magnetic image on the surface of the image carrier using the developer layer.

[Prior art]

As a method for developing latent images in electrophotographic copying machines and the like, there is a so-called magnetic brush method in which toner is attached to the surface of an image carrier using a magnetic brush formed by adhering developer to the surface of a developer carrying carrier using magnetic force. It is widely used. Development methods using magnetic brushes are further divided into those using a single-component developer consisting of magnetic toner particles and those using a two-component developer consisting of a mixture of magnetic carrier particles and toner particles. Particle friction control is relatively easy, and toner particle aggregation is less likely to occur. It also has many advantages, such as a magnetic brush that stands up well.

To make the toner adhere to the surface of the image carrier from a magnetic brush, there are two methods: a contact method in which the magnetic brush directly rubs the surface of the image carrier, and a method in which the toner layer and the surface of the image carrier are placed close to each other and a vibrating electric field is applied to apply the developer. There is a non-contact method called a jumping method in which the toner is caused to fly toward the image carrier by means of vibration or the like. Although the latter method has some difficulties in terms of development conditions, it has the advantage that it is possible to repeatedly develop the same screen without streaks on the developed image surface, and is suitable for forming multicolor images.

In the two-component development method, a developer consisting of magnetic carrier particles with an average particle size of several tens to hundreds of μm and non-magnetic toner particles with an average particle size of more than ten μm has conventionally been used. Developers have a problem in that because toner particles and even carrier particles are coarse, it is difficult to obtain high-quality images that reproduce delicate lines, dots, differences in shading, and the like. Therefore, in order to obtain high-quality images using this developing method, many efforts have been made in the past, such as coating the carrier particles with resin, improving the magnets in the developer transport carrier, and examining the bias voltage for the developer transport carrier. However, the reality is that stable and fully satisfactory images still cannot be obtained.
Therefore, in order to obtain high quality images, it is considered necessary to make the toner particles and carrier particles even finer. However, when toner particles are made into fine particles with an average particle size of 20 μm or less, especially 10 μm or less, the influence of Van der Waals force appears on the Coulomb force during development, causing toner particles to adhere to the ground area of the image background. This causes so-called fog to occur, and it becomes difficult to prevent fog even by applying a DC bias voltage to the developer transport carrier, and it becomes difficult to control triboelectric charging of toner particles.
Aggregation becomes more likely.

Further, as the carrier particles are made finer, the carrier particles also come to adhere to the electrostatic image area of the image carrier. The reason for this is thought to be that the magnetic bias force was reduced and the carrier particles adhered to the image carrier side together with the toner particles. Note that as the bias voltage increases, carrier particles will also adhere to the ground portion of the image background.

The problem with micronization is that the side effects mentioned above are more noticeable and clear images cannot be obtained, so it is difficult to actually use micronization of toner particles and carrier particles. It was hot.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing method that uses a developer made of finely divided toner particles and carrier particles and that can produce clear images with high reproduction fidelity without deterioration of image quality due to the troubles described above. .

[Structure of the invention]

The above purpose is to form a developer layer by supplying a two-component developer consisting of carrier particles and toner particles onto the surface of a developer transport carrier, and to subject the developer layer on the developer transport carrier surface to an oscillating electric field. In the method of developing a latent image on the surface of an image carrier in a non-contact manner, the carrier particles are formed of spherical particles, and
The resistivity under the electric field of 10 ⁴ V/cm is measured under the following measurement conditions.
A developing method characterized by maintaining insulation of 10 ¹³ Ω・cm or more.

Measurement conditions After putting the carrier particles in a container with a cross-sectional area of 0.50 cm ² and tapping, one
Apply a load of Kg/cm ² and connect the load to the lower electrode.
Obtained by reading the current value when applying a voltage that generates an electric field of 10 ^{2 to 5} V/cm.

This was achieved by the development method described above.

That is, the developing method of the present invention uses particles that maintain insulating properties under a high electric field as the carrier particles of the two-component developer, and by performing development under an oscillating electric field, the particles can be reduced to fine particles without any trouble. This allows the use of carrier particles and toner particles.

When using magnetic particles as a carrier, if the average particle size of the magnetic carrier particles is generally large, (a) the ears of the magnetic brush formed on the developer transport carrier are rough, so that the magnetic brush is Even when an electrostatic image is developed, unevenness tends to appear in the toner image. (b) Since the toner concentration in the panicle is low, problems such as high-density development cannot be performed occur. Said
In order to solve problem (a), it is sufficient to reduce the average particle size of the carrier particles, and as a result of experiments, the average particle size
The effect begins to appear below 50μm, especially at 30μm.
It has been found that the problem (a) practically does not occur under the following conditions. In addition, the problem (b) can also be solved by making the magnetic carrier finer particles in response to the problem (a), since the toner concentration in the spike increases and high-density development can be performed. However, if the carrier particles are too fine, (c) they will adhere to the surface of the image carrier together with the toner particles, or (d) the carrier particles will tend to scatter. These developments are also related to the strength of the magnetic field acting on the carrier particles and the resulting magnetization of the carrier particles, but in general, a tendency gradually begins to appear when the average particle size of the carrier particles becomes 15 μm or less. , becomes noticeable below 5 μm. Some of the carrier particles adhering to the surface of the image carrier are transferred onto the recording paper along with the toner, and the remaining part is removed from the image carrier along with the residual toner by a cleaning device such as a blade or fur brush. With the carrier particles made only of magnetic material, there is a problem that (e) the carrier particles transferred onto the recording paper are not fixed to the recording paper by themselves and are likely to fall off, and (f)
There is a problem in that when the carrier particles remaining on the surface of the image carrier are removed by a cleaning device, they tend to damage the surface of the image carrier made of a photoreceptor.

The above problems associated with the adhesion of the carrier to the image bearing surface can be prevented by increasing the electric field strength of the oscillating electric field during development and suppressing the transfer of the carrier to the image bearing surface. The electric field strength between the body and the developer transport carrier becomes extremely high. That is, an oscillating voltage of several hundred to several kilovolts is superimposed on the surface voltage of several hundred volts of the image carrier and is applied to the developing section, and the distance between the image carrier and the developer transport carrier is 1 to 2 mm. Therefore, a strong electric field of 10 ⁴ to 10 ⁵ V/cm is generated. In order to perform development under such conditions, it is necessary to inject charge into the carrier particles even in a high electric field, and therefore, it is necessary to inject charge into the carrier particles even in a high electric field, which is not necessary in ordinary magnetic brush development. Carrier particles with high electrical resistance are required.

According to the results of studies conducted by the present inventors, in order to provide a sufficient oscillating electric field, the carrier particles must be 10 ⁴ V/cm
It is desirable to have a high resistance of 10 ¹³ Ωcm or more under an electric field of . This resistivity is calculated after the particles are placed in a container with a cross-sectional area of 0.50 cm ² and tapped.
This value is obtained by applying a load of 1Kg/cm ² on the packed particles and reading the current value when applying a voltage that generates an electric field of 10 ^{2 to 5} V/cm between the load and the bottom electrode. The thickness of the carrier particles at this time is about 1 mm. If this resistivity is low, when a bias voltage is applied to the developer transport carrier, charge will be injected into the carrier particles, making it easier for the carrier particles to adhere to the surface of the image carrier, or a breakdown of the bias voltage will occur. It gets easier.

Furthermore, even when using carrier particles having the above-mentioned composition, it is inevitable that some small-sized carrier particles will adhere to the surface of the image carrier during development. This can be solved by forming it with a fixable substance. That is, the magnetic carrier particles are formed by coating magnetic particles with a substance that can be fixed on recording paper, or by being formed of a substance that can be fixed on recording paper containing dispersed magnetic powder.
The carrier particles attached to the recording paper are also fixed by heat and pressure, and even when the carrier particles are removed from the image carrier surface by the cleaning device, the surface of the image carrier is not damaged.
In such magnetic carrier particles, the average particle size of the carrier particles is 5 to 15 μm or less, and even if the carrier particles migrate to the image bearing surface or the recording paper, the above problem (c) can be avoided. In practice, it hardly causes any trouble. In addition, if carrier adhesion as described in (c) above occurs, it is effective to provide a recycling mechanism.

From the above, the average particle size of the magnetic carrier is
A suitable condition is 50 μm or less, particularly preferably 30 μm or less and 5 μm or more, and it is also preferable that the magnetic carrier particles contain a substance that can be fixed on the recording paper. Incidentally, the average particle diameter is a weight average particle diameter and was measured using Omnicon Alpha (manufactured by Boshilom) and Coulter Counter (manufactured by Coulter).

Such magnetic carrier particles may contain iron, iron, similar to conventional magnetic carrier particles as magnetic materials.
Metals such as chromium, nickel, and cobalt, or their compounds and alloys, such as triiron tetroxide, γ
- Ferric oxide, chromium dioxide, manganese oxide, ferrite, manganese - Particles of ferromagnetic or paramagnetic substances such as copper alloys, or the surface of these magnetic particles with styrene resin, vinyl resin, ethyl coated with resin such as rosin-modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, or fatty acid wax such as palmitic acid or stearic acid, or resin containing dispersed magnetic particles. It can be obtained by making particles of fatty acid wax and sorting the particle size using a conventionally known mean particle size classification method.

The carrier used in the method of the invention is also preferably spheroidized by known methods.

Forming the carrier particles into a spherical shape not only improves fluidity, but also makes the developer layer formed on the developer transport carrier uniform, and also makes it possible to apply a high bias voltage to the developer transport carrier. It also gives the effect of saying. That is, the carrier particles are made spherical by resin or the like because (1) Generally, carrier particles tend to be magnetized and attracted in the long axis direction, but by sphericalization, this directionality is lost; , the developer layer is formed uniformly, and local regions of low resistance and uneven layer thickness are prevented from occurring.

(2) As the resistance of the carrier particles increases, the edge portions seen in conventional carrier particles disappear, and the electric field no longer concentrates on the edge portions.
As a result, even if a high bias voltage is applied to the developer transport carrier, the electrostatic latent image will not be disturbed due to discharge on the surface of the image carrier, and the bias voltage will not break down.

It gives the effect of. The fact that this high bias voltage can be applied means that when development under an oscillating electric field in the present invention is performed by applying an oscillating bias voltage, the effects described below can be fully exhibited. That means it can be done.

Taken together, the carrier particles used in the present invention have a resistivity of 10 ¹³ Ω even under an electric field of 10 ⁴ V/cm.
cm or more, and in the case of magnetic carrier particles, such carrier particles are spherical magnetic particles with high resistance or resin-coated carrier particles,
Select magnetic particles that are as spherical as possible and apply a resin coating treatment to them; In a carrier of a magnetic fine particle dispersion system, use magnetic fine particles as much as possible and perform a spheroidization treatment after forming the dispersed resin particles; Alternatively, it can be manufactured by obtaining dispersed resin particles by a spray drying method.

Next, regarding toner, as the average particle size of toner particles becomes smaller, the amount of charge qualitatively decreases in proportion to the square of the particle size, and the adhesion force such as van der Waals force becomes relatively large. Therefore, it becomes difficult for the toner particles to separate from the carrier particles, and once the toner particles adhere to the non-image area of the image carrier surface, they cannot be easily removed by rubbing with a conventional magnetic brush, causing fogging. become. In the conventional magnetic brush development method, such problems become noticeable when the average particle size of toner particles becomes 10 μm or less. The developing method of the present invention solves this problem by performing development using a developer layer, a so-called magnetic brush, under an oscillating electric field. That is, the toner particles adhering to the developer layer are easily separated from the developer layer by the electrically applied vibrations, and are easily transferred to and separated from the image area and non-image area on the surface of the image carrier. When the surface of the image carrier is rubbed with the developer layer, toner particles attached to the non-image area of the image carrier can be easily removed or moved to the image area. If the thickness of the developer layer is made thinner than that between the image carrier surface and the developer transport carrier surface, toner particles with a low charge amount will hardly migrate to the image area or non-image area, and Since there is no friction with the surface of the image carrier, there is no possibility of adhesion to the image carrier due to frictional charging, and toner particles having a particle size of about 1 μm can now be used. Therefore, it is possible to obtain a clear toner image with good reproducibility in which the electrostatic latent image is faithfully developed. Furthermore, since the oscillating electric field weakens the bond between the toner particles and the carrier particles, the adhesion of the carrier particles associated with the toner particles to the image carrier surface is also reduced. In particular, when the thickness of the developer layer is made thinner than the thickness between the image carrier surface and the developer transport carrier surface, toner particles with a large amount of charge vibrate under the oscillating electric field in the image area and non-image area. However, depending on the strength of the electric field, the carrier particles also vibrate, and the toner particles selectively migrate to the image area on the image carrier surface, so that the adhesion of the carrier particles to the image carrier surface is greatly reduced. Reduced. Depending on the electric field, toner particles in the non-image area may or may not reach the non-image area. The same applies to carriers.

On the other hand, as the average particle size of the toner increases, as described above, the roughness of the image becomes noticeable.
Normally, toner with an average particle size of about 20 μm is not a problem in practice for developing fine lines arranged at a pitch of about 10 lines/mm with high resolution.
When the following micronized toner is used, the resolving power is significantly improved, and it becomes possible to provide clear, high-quality images that faithfully reproduce gradation differences, etc. For the above reasons, the appropriate particle size of the toner is an average particle size of 20 μm or less, preferably 10 μm or less. Further, in order for the toner particles to follow the electric field, it is desirable that the average charge amount of the toner particles be greater than 1 to 3 μC/g (preferably 3 to 300 μC/g). Particularly when the particle size is small, a high amount of charge is required.

Such toner can be obtained in the same manner as conventional toner. That is, it is possible to use a toner in which spherical or amorphous non-magnetic or magnetic toner particles in conventional toners are sorted by means of determining average particle size. Among these, it is preferable that the toner particles are magnetic particles containing magnetic particles, and it is particularly preferable that the amount of magnetic fine particles does not exceed 60% by weight. When the toner particles contain magnetic particles, the toner particles are influenced by the magnetic force of the magnet included in the developer transport carrier, so that the uniform formation of the magnetic brush is further improved. The occurrence of fogging is prevented, and furthermore, scattering of toner particles becomes less likely to occur. However, if the amount of magnetic material contained is too large, the magnetic force between the carrier particles and the carrier particles becomes too large, making it impossible to obtain a sufficient developing density. As a result, frictional charging control becomes difficult, toner particles are more likely to be damaged, and toner particles are more likely to aggregate with carrier particles. In particular, when using color toner, the amount of magnetic material must be 30% by weight or less to obtain clear colors.

To summarize the above, the preferred toner in the developing method of the present invention uses a resin as described for the carrier and furthermore fine particles of magnetic material, and a coloring component such as carbon and a charge control agent, etc. are added thereto as necessary. , the average particle size that can be produced by a method similar to the conventionally known toner particle production method is
It consists of particles of 20 μm or less, particularly preferably 10 μm or less. Furthermore, spheroidizing the toner brings about improved fluidity and favorable results in stirring, transporting, and charging the developer.

In the developing method of the present invention, a developer in which carrier particles and toner particles as described above are mixed in the same ratio as in a conventional two-component developer is preferably used, but it is also applicable to higher toner concentrations. I can do it. If necessary, a fluidizing agent for improving the fluidity and sliding of the particles, a cleaning agent for cleaning the surface of the image bearing member, and the like are mixed. As the fluidizing agent, colloidal silica, silicone varnish, metal soap, or nonionic surfactant can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicone, fluorine, etc. can be used as a surfactant. I can do it.

The above are the conditions for the developer, and next, the conditions for the developer transport carrier that forms a developer layer with such developer to develop the electrostatic image on the image carrier will be described.

A developer transport carrier similar to that used in conventional development methods to which a bias voltage can be applied is used as the developer transport carrier, but in particular, a developer transport carrier having a plurality of magnetic poles inside a sleeve on which a developer layer is formed on the surface. A structure in which a rotating magnet is provided is preferably used. In such a developer transport carrier, the developer layer formed on the surface of the sleeve moves in an undulating manner due to the rotation of the rotating magnet, so new developer is continuously supplied. Even if there is some degree of non-uniformity in the thickness of the developer layer on the surface of the sleeve, the above-mentioned wave-like undulations sufficiently cover the effect so that it does not become a problem in practice. It is preferable that the developer conveying speed due to the rotation of the rotating magnet or the rotation of the sleeve is almost the same as or faster than the moving speed of the image carrier. Further, it is preferable that the rotation of the rotating magnet and the rotation of the sleeve are carried in the same direction.
Image reproducibility is better in the same direction than in the opposite direction. However, it is not limited to these.

Further, the thickness of the developer layer formed on the developer transport carrier is preferably such that the adhered developer is sufficiently scraped off by a thickness regulating blade to form a uniform layer. The distance between the developer transport carrier and the image carrier is preferably several 10 to 2000 μm.

The distance between the surfaces of the developer transport carrier and the image carrier is several tens of microns.
If the width is too narrow than m, it will be difficult to form magnetic brush ears that will uniformly develop the area, and it will also be impossible to supply sufficient toner particles to the developing section, resulting in stable development. If the distance is significantly greater than 2000 .mu.m, the opposing electrode effect will deteriorate and a sufficient developed density will not be obtained. In this way, when the distance between the developer transport carrier and the image carrier becomes extreme, it becomes impossible to make the thickness of the developer layer on the developer transport carrier appropriate; ~
In the range of 2000 μm, the developer layer can be formed with an appropriate thickness. So, between
It is particularly preferable to set the thickness of the developer layer to such a condition that the ears of the magnetic brush do not come into contact with the surface of the image carrier and are as close as possible to the surface of the image carrier under the condition that no oscillating electric field is applied. This is because the toner development of the latent image is prevented from having scratches or fog caused by the rubbing of the magnetic brush.

Further, development under an oscillating electric field is preferably carried out by applying an oscillating bias voltage to the sleeve of the developer transport carrier. Further, it is preferable to use a bias voltage that is a combination of a direct current voltage that prevents toner particles from adhering to non-image areas and an alternating current voltage that makes it easier for the toner particles to separate from the carrier particles. However, the present invention is not limited to the method of applying an oscillating voltage to the sleeve or the method of applying a superimposed voltage of DC and AC.

The developing method of the present invention as described above includes the first
This is carried out by an apparatus such as that illustrated in FIGS. 2 and 3.

In FIGS. 1 to 3, reference numeral 1 rotates in the direction of the arrow, and an electrostatic image is formed on the surface of Se, ZnO, CdS, amorphous silicon, organic photoconductor, etc. by charging exposure and sending (not shown). 2 is a sleeve made of a non-magnetic material such as aluminum, and 3 is a magnet body provided inside the sleeve 2 and having a plurality of N and S magnetic poles on the surface in the circumferential direction. , this sleeve 2 and the magnet body 3 constitute a developer transport carrier. The sleeve 2 and the magnet body 3 can rotate relative to each other, and FIGS. 1 and 2 show that the sleeve 2 rotates in the direction of the arrow. Further, the N and S magnetic poles of the magnet body 3 are normally magnetized to a magnetic flux density of 500 to 1500 Gauss, and the magnetic force causes a layer of the developer D as described above, that is, a magnetic brush, to be formed on the surface of the sleeve 2. form. 4 is a regulating blade made of magnetic or non-magnetic material that regulates the height and amount of the magnetic brush; 5 is a developing area A;
This is a cleaning blade that removes the magnetic brush that has passed through the sleeve 2 from above. The surface of the sleeve 2 comes into contact with the developer D in the developer reservoir 6, thereby supplying the developer D, and 7 stirs the developer D in the developer reservoir 6 to make the components uniform. This is a stirring screw. Since the toner particles in the developer D in the developer reservoir 6 are consumed when development is performed, 8 is a toner hopper for replenishing the toner particles T as described above, and 9 is a developer. This is a supply roller having a concave portion on its surface that drops toner particles T into a reservoir 6. A bias power supply 10 applies a bias voltage to the sleeve 2 via a protective resistor 11.

The difference between the devices shown in FIGS. 1, 2, and 3 is that in the device shown in FIG. 1, the sleeve 2 rotates in the direction of the arrow, and the magnet body 3 rotates in the opposite direction of the arrow. , the magnetic flux densities of the N and S magnetic poles are approximately equal, whereas in the device shown in FIG. 2, the sleeve 2 rotates in the direction of the arrow, but the magnet body 3 is fixed, and the In the apparatus, the magnetic flux densities of the N and S magnetic poles of the fixed magnet body 3 are not the same, and the magnetic flux density of the N magnetic pole facing the image carrier 1 is larger than the magnetic flux density of the other N and S magnetic poles. It is. Note that the pole facing the image carrier 1 is as follows:
Of course, the N magnetic poles may be arranged side by side and facing each other as shown in the third figure, or the N and S magnetic poles may be arranged side by side and opposed to each other. By arranging a plurality of magnetic poles to face each other in this manner, it is possible to obtain the effect that development is more stable than when a single pole is posed to face each other.

In the apparatus described above, when the sleeve 2 is set so that the distance between the surfaces of the image carrier 1 is in the range of several tens to 2000 μm, and the electrostatic image on the image carrier 1 is developed, the sleeve 2 The magnetic brush formed on the surface of the sleeve 2 changes its magnetic flux density as the sleeve 2 or the magnet 3 rotates, so the magnetic brush moves on the sleeve 2 while vibrating. By stably and smoothly passing between the toner and the image carrier 1 and imparting a uniform developing effect to the surface of the image carrier 1, stable development with a high toner density is possible. Thereby, in order to prevent the occurrence of fog and to improve the developing effect, a bias voltage having an oscillating AC component is applied to the sleeve 2 by the bias power supply 10 between the base body 1a of the grounded image carrier 1 and the sleeve 2. is being applied.
As mentioned earlier, this bias voltage uses a preferable superimposed voltage of DC voltage and AC voltage.The DC component prevents fogging, and the AC component vibrates the magnetic brush to improve the developing effect. improves. Note that a voltage of 50 to 600 V, which is approximately equal to or higher than the non-image area potential, is normally used for the DC voltage component, and a frequency of 100 Hz to 10 kHz, preferably 1 to 5 kHz, is used for the AC voltage component. Further, the waveform of the AC voltage component is not limited to a sine wave, but may be a rectangular wave or a triangular wave. Note that the DC voltage component may be lower than the non-image area potential when the toner particles contain a magnetic material. If the frequency of the AC voltage component is too low, the effect of imparting vibration cannot be obtained, and if it is too high, the developer will not be able to follow the vibrations of the electric field, resulting in a decrease in developer density and the ability to obtain clear, high-quality images. There is a tendency to disappear. Also,
The voltage value of the AC voltage component is also related to the frequency, but
The higher the height, the more the magnetic brush is vibrated, which increases the effect accordingly, but on the other hand, the higher it is, the more likely it is that fogging will occur, and the more likely it is that dielectric breakdown such as that caused by lightning strikes will occur. However, the fact that the carrier particles of the developer D are insulated and spherical by resin or the like prevents dielectric breakdown, and the occurrence of fog can also be prevented by using the DC voltage component. Note that the surface of the sleeve 2 to which this AC voltage is applied may be coated with an insulating or semi-insulating coating with a resin or an oxide film.

Although FIGS. 1, 2, and 3 have shown examples in which a vibrating bias voltage is applied to the developer transport carrier, the developing method of the present invention is not limited thereto. The developing effect can also be improved by applying vibration to the magnetic brush by extending several electrode wires around the developing area between the carriers and applying an oscillating voltage to them. In that case as well, a DC bias voltage may be applied to the developer transport carrier, or oscillating voltages of different frequencies may be applied. Furthermore, the method of the present invention can be similarly applied to reversal development and the like. In that case, the DC voltage component is set to a voltage approximately equal to the reception potential in the non-image background portion of the image carrier. Furthermore, the method of the present invention can be similarly applied to the development of a photoreceptor having an insulating layer and the development of a magnetic latent image.
It can also be applied to methods of forming a color image by repeatedly developing an image carrier and superimposing a plurality of toners as described in No. 183152, No. 58-187000, and No. 58-187001.

The present invention will be specifically explained below using examples.

Example 1 A resin coating carrier was prepared by spraying a 4% solution of styrene-acrylic resin in methyl ethyl ketone onto spherical ferrite particles having an average particle diameter of about 5 μm placed on a fluidizing bed set at a temperature of 50°C.

Four types of samples were obtained by changing the amount of resin applied as shown below (the numbers are the number of grams of resin per 1 kg of ferrite).

Sample 40 Sample 30 Sample 20 Sample 10 The resistivity of each sample was measured under the conditions described above, and a relationship curve between applied voltage and resistivity as shown in FIG. 4 was obtained. The sample has a resistance of 10 ¹⁴ Ωcm even under an electric field of 10 ⁴ V/cm.
While the sample maintains a resistivity of
Although it has a resistivity of more than 10 ¹⁴ Ωcm under an electric field of 10 ³ V/cm, it decreases to 10 ¹³ Ωcm under an electric field of 10 ⁴ V/cm, and the resistivity of the sample has already decreased at 10 ³ V/cm.
Slightly below 10 ¹⁴ Ωcm, under an electric field of 10 ⁴ V/cm,
10 ¹² Ωcm or less.

The toner contains 100 parts by weight of styrene/acrylic resin (HIMER UP 110 manufactured by Sanyo Kasei), 10 parts by weight of carbon black (MA-100 manufactured by Mitsubishi Kasei), and Nigrosine 5.
Using non-magnetic particles obtained by a crushing and granulation method with an average particle diameter of 10 μm based on parts by weight,
Developers 1 to 4 were prepared by mixing with the carrier samples to 4, and a continuous copying test was conducted using an electrostatic copying machine equipped with the developing device shown in FIG.

In this case, the image carrier 1 is an amorphous silicon photoreceptor, its circumferential flux is 180 mm/sec, the highest potential of the electrostatic image formed on the image carrier 1 is -500V, and the lowest potential is -
100V, the magnetic flux density of the magnetic pole facing the development area A of the magnet body 3 is 1200 Gauss, the thickness of the developer layer is 0.5mm, the distance between the sleeve 2 and the image carrier 1 is 0.7mm, and the bias voltage applied to the sleeve 2 is 100V. is the DC voltage component −
200V, AC voltage component 2kHz, 1000V. In this embodiment, the developer layer on the sleeve 2 is
not in contact with the surface.

Development was carried out under conditions such that the toner particle ratio of the developer D in the developer reservoir 6 was 20% by weight relative to the carrier particles. The average charge amount of toner is 30μC/g
It was hot.

When Developers 1 and 2 were used, the obtained copy image was extremely clear with no edge effect or fog, and had a high density. Excellent in high points. Subsequently, we obtained 50,000 sheets of recording paper, but were able to obtain stable and unchanged images from beginning to end. On the other hand, in the case of the developers 3 and 4, the voltage of the alternating current voltage component that can be applied is limited to about 1/5 of the above voltage, which causes adhesion of the carrier to the image carrier and the copy screen, and roughness of the image. In the case of developer 4, it was particularly noticeable. In this example, where the developer layer and the image carrier layer were not in contact with each other, the resistivity of the carrier under a high electric field was increased.

Example 2 A copying test was conducted by loading the developers 1 to 4 used in Example 1 into the same copying machine as used above. However, the developing conditions were set as follows to prevent the developer layer from coming into contact with the surface of the image carrier 1.

In this case, the conditions of the image carrier 1 are the same as in Example 1, and the outer diameter of the sleeve 2 is also 30 mm, but the rotation speed is
100 rpm, the magnetic flux density of N and S poles is 700 Gauss, the rotation speed is 500 rpm, the thickness of the developer layer is 0.6 mm, the distance between sleeve 2 and image carrier 1 is 0.7 mm, and the bias voltage applied to sleeve 2 is DC voltage component -200V,
The AC voltage component was 2kHz and 1000V. The ratio of toner particles in the developer D in the developer reservoir was 20% by weight relative to the carrier particles. The average charge amount of toner is
It was 30μC/g. The transfer and fixing conditions of the obtained toner image to the transfer paper were as described in the above-mentioned apparatus and Example 1.
It was made the same as.

When developer 1 or 2 is used, the obtained copy image has no carrier adhesion, no edge effect or fog, and is extremely clear with high density, and has higher resolution than the image in Example 1. It was excellent in terms of high concentration and high concentration. Subsequently, we obtained 50,000 sheets of recording paper, but were able to obtain stable and unchanged images from beginning to end. On the other hand, when developer 3 or 4 was used, carrier adhesion and image roughness were significant, as in Example 1, and the effects of the present invention were confirmed.

In addition, in the above embodiment, the results of changing the frequency and voltage of the AC voltage component applied to the sleeve 2 are shown in FIG. FIG. 5 shows the case where developer 1 was used in Examples 1 and 2, and the conditions of the examples are indicated by x marks in the figure.

In FIG. 5, the unmarked range shaded with horizontal lines is the preferred range from which a stable and clear image can be obtained. As is clear from the figure, the range where fogging is likely to occur changes depending on changes in the AC voltage component. Furthermore, in FIG. 5, the low frequency region shaded with scattered dots is a range where uneven development occurs due to the low frequency. It can be inferred from these figures that image formation becomes unstable if the applied voltage of the alternating current component has to be reduced to 1/5 or less.

〔Effect of the invention〕

As seen in the above examples, by employing the method of the present invention, it is possible to use fine carriers with an average particle size of 50 μm or less without adhering to the surface of an image carrier or recorded material, and with an average particle size of 20 μm or less. When used in combination with fine toner, it is possible to obtain recorded images with high resolution and sharpness and no fogging. The effects of the present invention are particularly remarkable in the case of development under conditions where the developer layer and the image carrier do not come into direct contact.

In addition, although only an example of an electrostatic copying machine is given in the above embodiment, the application of the recording apparatus to which the present invention is applied, or the electrostatic image forming method, apparatus, etc. used therein is not limited to this. isn't it.

In the above embodiments, if the toner in the two-component developer has magnetism, it goes without saying that the magnetic latent image can be visualized under the same developing conditions.

[Brief explanation of the drawing]

1 to 3 are partial schematic sectional views showing an example of an apparatus for carrying out the present invention, FIG. 4 shows the electric field dependence of the resistivity of each carrier sample, and FIG. It is a graph showing the development state when changing the AC voltage component of the bias voltage. 1... Image carrier, 2... Sleeve, 3... Magnet, 4
...Regulation blade, 5...Cleaning blade, 6
... Developer reservoir, 7... Stirring screw, 8... Toner hopper, 9... Supply roller, 10... Bias power supply, 11... Protective resistor, A... Development area, D... Developer,
T...Toner particles, N, S...Magnetic poles.

Claims (1)

[Scope of Claims] 1. A two-component developer consisting of carrier particles and toner particles is supplied onto the surface of a developer transport carrier to form a developer layer, and the developer layer on the surface of the developer transport carrier is vibrated. In the method of developing a latent image on the surface of an image carrier in a non-contact manner by placing it under an electric field, the carrier particles are formed of spherical particles, and
The resistivity under the electric field of 10 ⁴ V/cm is measured under the following measurement conditions.
A developing method characterized by maintaining insulation of 10 ¹³ Ω・cm or more. Measurement conditions After putting the carrier particles in a container with a cross-sectional area of 0.50 cm ² and tapping, one
Apply a load of Kg/cm ² and connect the load to the lower electrode.
Obtained by reading the current value when applying a voltage that generates an electric field of 10 ^{2 to 5} V/cm. 2. The developing method according to claim 1, wherein the carrier particles have a size of 5 to 50 μm.