JPH0414795B2 - - 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. It has many advantages such as relatively easy particle friction control, toner particle agglomeration is less likely to occur, and the magnetic brush 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 the developer is applied with an oscillating electric field. There is a non-contact method called the jumping method, which uses means such as vibration to cause the toner to fly toward the image carrier.
Although the latter method has some difficulties in terms of development conditions, it has the advantage that it is suitable for forming multicolor images because the same screen can be repeatedly developed without streaks on the developed image surface.

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, and the toner particles also adhere to the background part of the image. So-called fogging occurs, and it becomes difficult to prevent fogging even by applying a DC bias voltage to the developer transport carrier. It becomes difficult to control the triboelectric charging of toner particles, causing problems such as agglomeration becoming more likely to occur.

In addition, the thickness of the developer layer formed on the developer transport carrier is made thinner than the gap between the image carrier and the developer transport carrier, and so-called non-contact development is performed in which toner particles are ejected to the image carrier surface under an alternating electric field. Under these conditions, the van der Waals force becomes strong, so that the fine toner particles strongly adhere to the carrier and become difficult to fly.

The transfer and flight of the toner to the image bearing member is due to the traction force that acts between the latent image and the charged toner particles, but the amount of charge on each particle forming the toner is not necessarily the same, and the toner may have opposite polarity. It also contains charged particles, and toner with a large amount of charge is greatly influenced by the electric field in the development area, tends to adhere to the latent image, and is consumed preferentially. Therefore, if you continue copying while replenishing toner, toner with a low charge amount and toner charged with the opposite polarity will accumulate in the developer.
The proper bias conditions for development may deviate, or the surface of the carrier particles may be covered with low-charging toner particles.
Unfavorable developments such as deterioration of developability due to a decrease in the amount of charge, fogging caused by toner with opposite polarity, and toner scattering occur frequently.

Although toner miniaturization is an extremely effective means for improving image quality, it has been difficult to advance miniaturization beyond a practical limit because the above-mentioned side effects become more pronounced with miniaturization. .

[Purpose 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 above-mentioned troubles. It is in.

[Structure of the invention]

The above purpose is to supply a two-component developer mainly consisting of carrier particles and toner particles to the surface of a developer transporting carrier, and placing the two-component developer layer formed on the surface of the developer transporting carrier under an oscillating electric field. In a developing method for developing an image on the surface of an image carrier, the toner particles contain 2% by weight of a toner charged with an opposite polarity and having an absolute value of a charge amount larger than an absolute value of an average charge amount of the toner particles. The content of toner having a charge amount that is twice or more the average charge amount of the toner particles is 20% by weight or less, and 1/5 of the average charge amount, including the following:
Toner content with charge amount below 10% by weight
This was achieved by a developing method characterized by the following.

In general, development conditions such as bias voltage and oscillating electric field strength are set to the optimum conditions that will give the best image, depending on the properties of the developer including the average charge amount of the toner. The amount has a wide distribution, and some particles are included that have a charge lower than the average charge or are charged to the opposite polarity.

The various problems associated with the miniaturization of toner as described above are mainly caused by these particles, and toners with a finer average particle size can be produced without problems if they do not contain these particles. can be used.

Particularly under non-contact development conditions under an oscillating electric field, the toner particle diameter consumed for development is highly selective, so the toner charge distribution is important, and it is desirable to use a toner with a narrow distribution.

The present invention achieves the above-mentioned effect by using a toner having a narrow charge distribution, in particular, which does not contain particles that are charged with opposite polarity or whose charge amount is significantly low relative to the average charge amount. The aim is to obtain high-quality images without such troubles.

In the present invention, it is basically preferable that the toner is composed only of toner that forms the toner image to be obtained on the image carrier (that is, toner having a desired polarity, hereinafter simply referred to as toner to be deposited on the image carrier). may contain a small amount of toner of opposite polarity (meaning the polarity opposite to that of the toner to be adhered).

The inventors conducted various experiments and found that good images with little fogging were obtained with toners that did not substantially contain toner of opposite polarity that had a charge amount greater than the absolute value of the average charge amount of all toners. Ta.
(If it is less than 2% by weight of the toner, it can be considered that it is not substantially contained.) In the method of the present invention, an oscillating electric field is applied, and this amplitude and frequency are determined by the average charge amount of all toner. The setting is such that the toner to be deposited on the image carrier having a charge amount approximately equal to is sufficiently vibrated to fly and adhere onto the image carrier. Therefore, if there is a toner of opposite polarity that has a larger absolute value of charge amount than the average charge amount of all toners, the oscillating electric field will have an opposite phase to the direction in which the toner to be attached flies toward the image carrier. This seems to be because toner of opposite polarity sometimes adheres to the image carrier.

More preferably, the toner charged to the opposite polarity accounts for 10% by weight or less, preferably 5% by weight or less of the total toner. If the amount is 10% by weight or less, the toner does not contain a toner of opposite polarity that has the same amount of charge as the toner to be deposited on the image carrier, and is substantially composed of unipolar toner. It can be said that it is working.

Further, if the amount is 1% by weight or less, even if copying is continued while toner is replenished and toner of opposite polarity continues to increase, a considerable volume can be copied until the amount exceeds 10% by weight, which is desirable.

Further, it is desirable that the toner used in the method of the present invention has an average charge amount of 1 to 100 μC/g, particularly preferably 5 to 50 μC/g.

In addition, it is preferable that the content of particles having a charge amount that is twice or more than the average charge amount of the toner is 20% by weight or less, further preferably 10% by weight or less, of the total toner particles, and/or 1/5 of the average charge amount. The content of low charge particles with an electrical charge is 10% by weight or less, and further 5% by weight
The following is desirable. When the content of highly charged particles exceeds 20% by weight, deterioration of developability occurs.
Particles with a low charge amount hardly contribute to development under normal development conditions set with respect to the average charge amount, and if their content exceeds 10% by weight, they cause various troubles as described above.

The electrification of toner particles varies not only depending on the materials of the toner and carrier, but also on their mixing ratio, stirring conditions, and the like.

The amount of charge of toner particles is described in Japanese Patent Application No. 117430/1983, which is similar to JP-A-57-79958.
It can be measured by the method described in No. 117431.

In other words, a magnet (if the toner contains a magnetic material, it has a magnetic force that does not attract the toner) is placed in the flow path of the toner particles discharged from the mesh part to the outside of the developer container and headed toward the suction pipe using a blow-off device. A carrier is provided to collect the toner, and only the toner is introduced into the suction pipe, and the toner having different amounts of charge under an electric field is separated and collected on a filter by the method described in the specification of Japanese Patent Application No. 117431/1982.

The filter that collected the toner particles is then mounted on an image analyzer that is driven by a computer. The image analyzer is from Bausch.
The Omnieon is manufactured by (and Lomb). The image analyzer includes a microscope with a pedestal for supporting the filter and a computer. When the computer is turned on, a program is started that controls the microscope and creates a histogram of the charge distribution of the toner particles. In this way, the toner charge amount distribution is measured.

It is necessary to set the above-mentioned conditions while taking into consideration the actually measured charging state of the toner.

Further, the toner used in the method of the present invention may be composed of irregularly shaped particles, but it is particularly preferably composed of spherical particles, and a mixture of irregularly shaped particles and spherical particles may also be used. It is possible.

The toner particles have better fluidity and are better charged by friction with the carrier particles. Therefore, they form a developer layer together with the carrier particles at an appropriate concentration, and are separated from the developer layer during development. It exhibits excellent performance in that it is selectively attracted to electrostatic images, etc., and is easily transferred from the image carrier surface. This is because the spherical shape makes the contact areas between toner particles and carrier particles, and between toner particles and the surface of the image bearing member constant, reducing non-uniform forces that are difficult to control, such as van der Waals forces. This is thought to be largely related to the fact that it does not cause charge concentration or discharge neutralization unlike needle-like protrusions, edges, or elongated shapes. For this purpose, it is particularly preferable that the toner particles are spherical so that the ratio of the major axis to the minor axis is at least 3 times or less.

Such spherical toner particles are made of a resin such as styrene resin, vinyl resin, ethyl resin, rosin modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, and a coloring component such as carbon. In addition, in the case of magnetic toner, metals such as iron, chromium, nickel, and cobalt, or compounds and alloys thereof, such as triiron tetroxide, γ-ferric oxide, and chromium dioxide. , manganese oxide, ferrite,
A ferromagnetic or paramagnetic material such as a manganese-copper alloy is melted and kneaded with fine particles, then dissolved in a solvent, and the liquid is sprayed into hot air from a nozzle in the form of a mist, and the sprayed mist drops form a solvent. The spray drying method obtains spherical particles by evaporating the particles, or by pulverizing the melt-kneaded and solidified material and blowing the obtained particles into hot air to melt the resin content in the particles. A flow coater method in which the resin is polymerized and precipitated in a solution of a prepolymer from which coloring components have been separated, or
Instead of the flow coater method, toner particles can be obtained by a method of stirring toner particles in hot water to soften the resin to form spheres, and then filtering and drying the particles. Note that the toner particles may be microencapsulated, and the above manufacturing method and spheroidization treatment can be applied to such toner particles as well. Furthermore, it is of course possible to use the melt-kneaded, cooled and pulverized toner as it is as an amorphous toner.

The toner thus obtained is made up of particles of various sizes, but generally the toner has a property that as the average particle size of the toner particles becomes smaller, the amount of charge qualitatively decreases in proportion to the square of the particle size. Therefore, in order to obtain a toner with a narrow charge distribution suitable for the method of the present invention, it is preferable to classify the toner particles to make them uniform in particle size. The toner can be classified using a known classification means that is normally used for classifying fine powder, such as a wind classifier.

As mentioned above, toner particles must be made fine in order to obtain high-quality images, but when toner particles are made fine, the adhesion force due to Van der Waals force becomes stronger, making it difficult for toner particles to separate from carrier particles. Once a single toner particle adheres to a non-image area on the surface of the image carrier, it cannot be easily removed by rubbing with a conventional magnetic brush, causing fogging. 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 using spherical toner particles as described above and by performing development with a developer layer under an oscillating electric field. That is, the toner particles attached to the developer layer are easily transferred from the developer layer to the image area or non-image area on the image carrier surface due to electrically applied vibrations.
If the surface of the image carrier is rubbed with the developer layer, the toner particles attached to the non-image area of the image carrier can be easily removed or moved to the electrostatic image area. It becomes like this. Furthermore, if the thickness of the developer layer is made thinner than the gap between the image carrier surface and the developer transport carrier, toner particles with a low charge amount will almost never migrate to image areas or non-image areas. 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 with 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, as described above, when the thickness of the developer layer is made thinner than the gap between the image carrier surface and the developer transport carrier, toner particles with a large amount of charge are exposed to the oscillating electric field in the image area and non-image area. vibrates below,
Depending on the strength of the electric field, the carrier particles also vibrate, and the toner selectively transfers to the electrostatic image area on the image carrier surface, which greatly reduces the adhesion of the carrier to the image carrier surface. Reduced. Toner particles directed to the non-image area due to the electric field 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. In addition, in order for the toner particles to follow the electric field, the average charge amount of the toner particles should be greater than 1 μC/g (preferably 5 to 5 μC/g).
50μC/g) is desirable. Particularly when the particle size is small, a high amount of charge is required.

Among the toners obtained in this way, it is preferable that the toner particles are magnetic particles containing fine magnetic particles, and it is particularly preferable that the amount of fine magnetic particles does not exceed 60% by weight, especially not more than 30% 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. Furthermore, in the case of color toner, it is difficult to obtain clear colors.

Next, regarding the carrier, if the average particle size of the magnetic carrier particles is generally large, the developer layer formed on the developer transport carrier will be rough, so the electrostatic image will be imaged while being vibrated by an electric field. Even if the toner image is developed, unevenness tends to appear in the toner image, and the toner concentration in the developer layer becomes low, resulting in problems such as the inability to perform high-density development. In order to solve this problem, the average particle size of the carrier particles can be made smaller, and the experimental results show that the effect begins to appear at 50 μm or less, and when it becomes 30 μm or less, problem ○B actually occurs. It turned out to be gone. The average particle size was measured as a weight average particle size using Omnicon Alpha (manufactured by Possilom) and Coulter Counter (manufactured by Coulter). In addition, the problem of ○B can also be solved by making the magnetic carrier finer particles for the problem of ○B.
The problem is resolved when the toner concentration in the developer layer increases and high-density development is performed. However, if the carrier particles are too fine, they tend to adhere to the surface of the image carrier or become easily scattered.
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. ,5μ
It becomes noticeable below m. A portion of the carrier particles adhering to the image bearing surface is transferred onto the recording paper along with the toner, and the remaining part is removed from the image bearing surface 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 the carrier particles transferred onto the recording paper (○) are not fixed on the recording paper by themselves and easily fall off, and the carrier particles remaining on the surface of the image carrier (○) are easily removed. There is a problem in that when the particles are removed by the cleaning device, they tend to damage the surface of the image bearing member, which is a photoreceptor.

The above-mentioned problems ◯◯◯◯◯ that occur when using particularly finely divided carrier particles can be solved by forming magnetic carrier particles together with a substance that can be fixed to the recording paper, such as a resin. In other words, the magnetic carrier particles are formed with a substance that can be fixed on the recording paper, so that even if they adhere to the recording paper, the carrier particles will be fixed by heat or pressure, and the cleaning device will remove any remaining particles. Even when the toner is removed from the image carrier surface together with the toner, the image carrier surface is not damaged. Therefore, even if the carrier particles have an average particle size of 5 to 15 .mu.m or less, the above-mentioned problem (C) does not actually cause any trouble. Note that if carrier particles adhere to the image bearing member, it is effective to provide a recycling mechanism.

Furthermore, when the carrier particles are spherical, the agitation properties of the toner and the carrier and the transportability of the developer are improved, and aggregation of toner particles and toner particles and carrier particles is made less likely to occur.

From the above, in the carrier used in the present invention, the average particle size of the magnetic carrier particles is preferably 50 μm or less, particularly preferably 30 μm or less, and
It is preferable that the magnetic carrier particles are formed together with a substance such as a resin that can be fixed on the recording paper, and are further spherical.

For such magnetic carrier particles, choose spherical magnetic particles with the same resistance as possible in magnetic toner, or choose spherical magnetic particles with resin, palmitic acid, stearin, etc. similar to those in toner. It is obtained by coating it in a spherical shape with fatty acid wax such as acid, or by making spherical particles of resin or fatty acid wax containing dispersed magnetic particles, and the spherical shape is made by hot air or hot water similar to that used in toner. In the case of a dispersed type, a spray drying method can also be applied. As for the average particle size, a preferable carrier can be obtained by selecting the average particle size using a conventionally known average particle size selection means, if necessary.

In addition to the above-mentioned effects, making the carrier particles spherical with a resin or the like as described above makes the developer layer formed on the developer transport carrier uniform, and also makes the developer layer more uniform. It also has the effect of making it possible to apply a high bias voltage to the carrier. That is, the fact that the carrier particles are made spherical by resin or the like is 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, preventing the occurrence of locally low resistance areas and uneven layer thickness. As a result, even if a high bias voltage is applied to the developer transport carrier, the electric field will not be concentrated on the edge portion, and as a result, even if a high bias voltage is applied to the developer transport carrier, it will discharge to the image bearing surface and disturb the electrostatic latent image. This provides the effect that voltage breakdown does not occur. The fact that this high bias voltage can be applied means that when the 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. This means that it can be done.
As mentioned above, wax can be used to make the carrier particles spherical, which produces the above-mentioned effects.However, from the viewpoint of the durability of the carrier, it is preferable to use resins such as those mentioned above. Preferably, insulating magnetic particles are formed so that the resistivity is 10 ³ Ωcm or more, particularly 10 ¹³ Ωcm or more. This resistivity is calculated by placing particles in a container with a cross-sectional area of 0.05 cm ² and tapping them, then applying a load of 1 Kg/cm ² on the packed particles, and applying a voltage of 1000 V/cm between the load and the bottom electrode. This value is obtained by reading the current value when a voltage that generates an electric field is applied, and 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.

In summary, the magnetic carrier particles are spherical so that the ratio of the major axis to the minor axis is at least 3 times or less, and therefore, the magnetic carrier particles are spherical in shape, so that charge concentration and discharge at needle-shaped parts and edge parts are prevented. Proper conditions are that there are no easily raised protrusions and that the resistivity is 10 ³ Ωcm or more, preferably 10 ¹³ Ωcm or more, and such magnetic carrier particles can be obtained by the method described above. can.

In the developing method of the present invention, the amorphous or spherical toner particles having a defined charge amount distribution as described above and carrier particles, particularly preferably spherical carrier particles, are used in the same manner as in conventional two-component developers. A developer mixed in the same proportions is preferably used, but if necessary, a fluidizing agent to improve the fluidity and slippage of the particles and a cleaning agent to help clean the surface of the image carrier are mixed therein. 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-based surfactant, etc. can be used. 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 layer thickness of the developer layer on the sleeve surface, the above-mentioned wave-like movement sufficiently covers 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. Note that it is preferable that the rotating magnet body and the sleeve are conveyed in the same direction by rotation. In the case of the same direction, image reproducibility is better than in the opposite direction. However, it is not limited to these.

Further, the thickness of the developer layer formed on the developer transport body is preferably such that the adhered developer is sufficiently scraped off by a thickness regulating blade to form a uniform layer. The gap between the developer transport carrier and the image carrier is preferably several 10 to 2000 μm. If the surface gap between the developer transport carrier and the image carrier becomes narrower than several tens of micrometers, it becomes difficult to form a developer layer that acts uniformly on the gap, and it becomes difficult to apply sufficient toner particles to the developing area. If the gap becomes much larger than 2000μm, stable development will not be possible.
The counter electrode effect decreases, making it impossible to obtain sufficient development density. In this way, when the gap between the developer transport carrier and the image carrier becomes extremely narrow, 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. The thickness of the developer layer may be set so that the developer and the image carrier come into contact with each other, but the gap and the thickness of the developer layer should be set so that the developer layer does not come into direct contact with the surface of the image carrier as much as possible. It is particularly preferable to set the conditions so that they are close to each other. This prevents scratches and fog from occurring due to rubbing of the developer layer in toner development such as electrostatic images.

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. It is also preferable to use a bias voltage that is a superimposition of a DC voltage that prevents toner particles from adhering to non-image areas and an AC voltage that facilitates the separation of toner particles from 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 is carried out by an apparatus as illustrated in FIGS. 1 to 3.

In FIGS. 1 to 3, 1 rotates in the direction of the arrow, and a photoreceptor such as SeCdS, ZuO, amorphous silicon, or organic photoconductor is formed on its surface by a charging exposure device (not shown). 2 is a sleeve made of a non-magnetic material such as aluminum; 3 is a magnet body provided inside the sleeve 2 and having a plurality of N and S magnetic poles alternately in the circumferential direction on its surface; This sleeve 2 and the magnet body 3 constitute a developer transport carrier. And sleeve 2
The sleeve 2 and the magnet body 3 are rotatable relative to each other, and the figure shows that the sleeve 2 rotates in the direction of the arrow. In addition, the N and S magnetic poles of the magnet body 3 are usually 500
It is magnetized to a magnetic flux density of ~1500 Gauss, and its magnetic force forms a layer of the developer D as described above, that is, a magnetic brush, on the surface of the sleeve 2. 4
5 is a regulating blade made of magnetic or non-magnetic material that regulates the height and amount of the magnetic brush, and 5 is a cleaning blade that removes the magnetic brush that has passed through the developing area A from above the sleeve 2. Since the surface of the sleeve 2 comes into contact with the developer D in the developer reservoir 6, the developer D is supplied thereby.
is a stirring screw that stirs the developer D in the developer reservoir 6 to make the components uniform. 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 to 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, so that the magnetic flux densities of the N and S magnetic poles are approximately equal. In the device shown in Figure 2,
The sleeve 2 rotates in the direction of the arrow, but the magnet 3 is fixed, and in the device shown in FIG. 3, the magnetic flux densities of the N and S magnetic poles of the fixed magnet 3 are not the same;
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. In addition, as a magnetic pole facing the image carrier 1,
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 surface gap with the image carrier 1 is in the range of several tens to 1000 μm, and the electrostatic image on the image carrier 1 is developed, the sleeve 2 The magnetic brush formed on the surface of the image bearing member moves on the sleeve 2 while vibrating because the magnetic flux density on the surface changes as the sleeve 2 or the magnet 3 rotates. 1 stably and smoothly passes through the gap between the image bearing member 1 and the image bearing member 1, and at this time, a uniform developing effect is imparted to the surface of the image carrier 1, thereby making it possible to stably develop with a high toner density. To do this, in order to prevent the occurrence of fog and to improve the developing effect, an oscillating bias voltage is applied to the sleeve 2 by a bias power supply 10, the base of the image carrier 1 is grounded, and the sleeve 2 and the image An oscillating electric field is formed in the gap between the carriers 1. 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. The waveform of the AC voltage component is not limited to a sine wave, but may be a rectangular wave or a triangular wave. 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. In addition, the voltage value of the AC voltage component is
The frequency is also related; the higher the frequency, the more the magnetic brush will vibrate, which will increase the effect accordingly, but on the other hand, the higher the frequency, the more likely fog will occur and dielectric breakdown, such as that caused by lightning, will occur. However, if the carrier particles of the developer D are made spherical by resin or the like, dielectric breakdown can be prevented, and fogging can also be prevented by 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.

As described above, FIGS. 1 to 3 show an example in which an oscillating bias voltage is applied to the developer transport carrier, but the developing method of the present invention is not limited thereto. It is also possible to improve the developing effect by providing vibration to the magnetic brush by extending several electrode wires 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. Further, 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. 58-183152
The present invention can also be applied to a color image forming method in which an image carrier is repeatedly developed and a plurality of toners are superimposed, as described in the specifications of No. 58-187000 and No. 58-187001.

This will be explained in detail below using examples.

[Example 1] 100 parts by weight of styrene/acrylic resin (Himer up110 manufactured by Sanyo Chemical Co., Ltd.), 10 parts by weight of carbon black (MA-100 manufactured by Mitsubishi Chemical Corporation), and 5 parts by weight of nigrosine were kneaded and ground, and then A non-magnetic toner having an average particle size of about 10 μm was obtained by spheroidization treatment. This was divided into two parts, and one half was used as a sample by passing it through an air classifier to classify it so as not to contain particles of 5 μm or less and 20 μm or more, and the other half was used as a sample.

The average particle size of each of the above samples is 30μ.
An electrostatic copying machine equipped with the developing device shown in Figure 1, in which a developer is prepared by mixing with a carrier consisting of resin-coated spherical ferrite particles having a magnetization of 50 emn/g and a resistivity of 10 ¹⁴ Ωcm. were loaded and a continuous copy test was conducted on each.

In this case, the image carrier 1 is an amorphous silicon photoreceptor, the wind speed 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, outer diameter of sleeve 2 30mm, rotation speed
100 rpm, magnetic flux density of N and S magnetic poles of magnet body 3 is 900
Gauss, its rotation speed is 1000 rpm, the thickness of the developer layer
0.6 mm, the gap between the sleeve 2 and the image carrier 1 is 0.5 mm, that is, 500 μm, the bias voltage applied to the sleeve 2 is a DC voltage component of -250V, an AC voltage component of 1.5kHz,
It was set to 500V. That is, in this embodiment, the developer layer contacts the image carrier 1 to perform development. Development was carried out under conditions such that the toner ratio of the developer D in the developer reservoir 6 was 10% by weight relative to the carrier, corona transfer was performed on plain paper, and the image was fixed by passing through a heat roller fixing device at 140°C. The object was visually evaluated.

Further, when the charge amount distribution of the toner particles during development was measured by the method described above, the distribution curve shown in FIG. 4-1 was obtained. The average charge amount of both samples was approximately 15 μC/g. The sample does not contain particles with opposite polarity charge, and the amount of charge is 1/5 of the average charge amount.
The content of particles with a charge amount of 3 μC/g or less and 30 μC/g or more, which is twice or more, is approximately 0.5% by weight and 3% by weight, respectively.
In terms of weight percent, the sample is suitable for the method of the present invention, whereas the sample contains particles with a particle size of 3 μC/g or less, including those with opposite polarity charge, of about 17 weight percent, and particles with a particle size of 30 μC/g or more, which accounts for about 30 weight percent. was occupied.

When using the sample developer, the obtained image of the object was extremely clear with no edge effect or fog, and with high density. However, I was able to obtain a stable and unchanging image from beginning to end. After obtaining 50,000 sheets of recording paper, the toner charge amount distribution was measured, and the distribution curve shown in FIG. 4-2 was obtained. The average charge amount was approximately 13μC/g, but as you can see from this figure, the charge amount was -
Exceeds 13μC/g (absolute value of charge amount
Toner of opposite polarity to the toner to be deposited on the image carrier (greater than 13 μC/g) was not substantially observed.

On the other hand, in the case of a developer using a toner sample, the initial image was almost the same as the sample, but as copying continued, the average charge amount of the toner decreased, and the density and sharpness of the image decreased. At the same time, fogging occurred and increased, and after replenishing toner appropriately and obtaining 30,000 sheets of recording paper, the toner charge distribution was measured on the sample in the same way as the sample, and the distribution as shown in Figure 4-2 was obtained. A curve was obtained. The average charge amount was approximately 12μC/g, but the charge amount was -
Many toners with opposite polarity exceeding 12 μC/g were observed.

[Example 2] A kneaded product having the same composition as in Example 1 was prepared with an average particle size of approximately
After crushing and spheroidizing to 5 μm, it was divided into two parts, and one half was classified using an air classifier so as not to contain particles with a particle size of 3 μm or less and 10 μm or more, and used as a sample, and the other half was used as a sample as it was.

Mix the sample with a carrier consisting of thermally spheronized magnetic particles with an average particle size of 20 μm, magnetization of 30 emu/g, and resistivity of 10 ¹⁴ Ωcm or more, each of which is dispersed at 50% by weight in a fine ferrite resin. A developer is prepared and loaded into an electrostatic copying machine equipped with the developing device shown in FIG.
A continuous copying test was conducted under conditions of 20% by weight.
Further, the amount of charge of the toner particles in the developing device was measured, and a charge amount distribution curve shown in FIG. 5-1 was obtained. The average charge amount was about 20 μC/g for both samples, but the sample did not contain particles with opposite polarity charge, and the charge amount was less than 4 μC/g, which is 1/3 of the average charge amount, and 2 times the average charge amount.
The content of particles of 40 μC/g or more was 5% or less in all cases, which was suitable for the method of the present invention. On the other hand, although the sample does not contain particles with opposite polarity, the charge amount distribution is extremely wide, with particles below 4 μC/g accounting for approximately 15% of the total amount, and particles exceeding 40 μC/g accounting for approximately 25% by weight.
It accounted for %.

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
150 rpm, 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 0.5 mm,
Gap between sleeve 2 and image carrier 1 is 0.7mm or 700μ
The bias voltage applied to the sleeve 2 was 1000 V with a DC voltage component of -200 V and an AC voltage component of 2 kHz. In this embodiment, the developer layer on the sleeve 2 is formed thinner than the gap between the image carrier 1 and the sleeve 2. The transfer and fixing conditions were the same as in Example 1.

In the case of the developer using the toner sample, the obtained copy image was of better quality than that of Example 1, which had no edge effect or fog and had a high density. I was able to obtain a stable and unchanging image from beginning to end. After obtaining 50,000 sheets of recording paper, the toner charge amount distribution was measured, and the distribution curve shown in FIG. 5-2 was obtained.

The average charge amount was approximately 18 μC/g, but as can be seen from this figure, toner with a polarity opposite to that of the toner that should adhere to the image carrier with a charge amount exceeding -18 μC/g was not substantially observed. Nakatsuta.

On the other hand, in the case of a sample, the initial image was similar to that of a developer using a sample, but as copying continued, the amount of charge on the toner decreased, and as a result, the density and sharpness of the image rapidly deteriorated. The fog also increased after 30,000 sheets of recording paper were obtained, and when the number of sheets reached 50,000 sheets, there was a large difference in image quality from the sample. After obtaining 30,000 sheets of recording paper, the sample was measured in the same manner as the sample, and the distribution curve shown in FIG. 5-2 was obtained. The average charge amount is approximately 17μC/g, which is -17μC/g.
Although no toner with a reverse polarity exceeding 10% was observed, the toner with a reverse polarity accounted for more than 10% by weight of the total toner. Also, a problem with the image quality appeared before and after obtaining 50,000 sheets of recording paper. The average charge amount at that time is 15μC/g
, and many toners with opposite polarity exceeding -15 μC/g were observed.

As mentioned above, the quality of the images obtained in this example was at a higher level overall than in Example 1, but the difference between the samples was larger than in Example 1, and the method according to the present invention It has been demonstrated that this method is particularly effective under development conditions in which the developer layer does not come into direct contact with the image carrier.

[Example 3] Using the toner sample and carrier used in Example 2, a copying test was conducted by changing the ratio of toner particles to carrier particles in the developer reservoir of the developing device in two stages: 20% by weight and 40% by weight. I went to
The copying machine used in the test was the same as in Example 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 gap between sleeve 2 and image carrier 1 is 0.7 mm, or 700 μm, and the bias voltage applied to sleeve 2. The DC voltage component was -200V, and the AC voltage component was 2kHz and 1000V. However, when the ratio of toner particles is 40% by weight, the DC voltage component is set to -350V, which is the optimal value at that time, and everything else is the same. All transfer and fixing conditions were also the same as in Example 1. When the charge of toner particles was measured, when the ratio of toner particles to carrier particles was 20% by weight, the amount of charge on toner particles and its distribution were similar to the curve in Figure 5-1, but when the ratio was 40% by weight. , the average charge amount is
It decreased to 10μC/g. The distribution expanded as shown in Figure 6, and particles with opposite polarity were also generated, reaching 2.5μC/g.
Below, particles with a charge amount of 25 μC/g or more each accounted for 20% of the total particles.

In the case of a toner particle ratio of 20%, the obtained copy image is extremely clear with no edge effect or fog, and has a high density, and has higher resolution and higher density than the image in Example 2. It was excellent in that respect. Subsequently, toner was replenished as appropriate and 50,000 sheets of recording paper were obtained, but it was possible to obtain stable and unchanged images from beginning to end. On the other hand, when the toner particle ratio was 40%, the initial image quality was good, but the sharpness of the image deteriorated as copying continued. After obtaining 50,000 sheets of recording paper, we measured the charge amount distribution of the toner and found that the average charge amount was 8 μC/g, but there was a lot of toner with the opposite polarity exceeding -8 μC/g, which caused fogging. It was also big.

As shown in this embodiment, the method of the present invention can be carried out by adjusting not only the toner itself but also factors that affect the charging of toner particles, such as the amount of carrier.

As mentioned above, it is better to perform development with a toner having the most preferable charge amount distribution described in this specification, but as the charge amount distribution widens as the developer is used, the image quality gradually deteriorates. is deteriorating. However, as long as toner of opposite polarity (hereinafter referred to as "problematic toner") having a charge amount larger than the absolute value of the average charge amount does not substantially appear, the toner is excellent and has no practical problems, although it has deteriorated.

In addition, if a toner of the present invention with a wide charge amount distribution is used as the initial toner and a problematic toner appears after a few repetitions of development, and such deteriorated toner is continued to be used. This invention also uses all the constituent elements of the present invention in its initial stage, and is therefore included in the technical scope of the present invention.

〔Effect of the invention〕

As seen in the above examples, the method of the present invention allows fine toner with an average particle diameter of 20 μm or less to be used without fogging without deterioration in image quality due to continuous use of developer, even when using a fine carrier with a diameter of 50 μm. Recorded images with high density and clarity can be obtained. 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.

Furthermore, if the toner in the two-component developer has magnetism, it goes without saying that a magnetic latent image can also be visualized under similar development conditions.

[Brief explanation of drawings]

FIGS. 1 to 3 are partial schematic sectional views showing examples of an apparatus for carrying out the present invention, and FIGS. 4 to 6 are toner charge amount distribution charts. DESCRIPTION OF SYMBOLS 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...Protection resistor, A...
...Development area, D...Developer, T...Toner particles,
N, S...magnetic pole.

Claims (1)

[Scope of Claims] 1. A two-component developer mainly consisting of carrier particles and toner particles is supplied to the surface of a developer transporting carrier, and the two-component developer layer formed on the surface of the developer transporting carrier is subjected to an oscillating electric field. In the developing method of developing the image on the surface of the image bearing member, the toner particles are charged with two toner particles charged with opposite polarity and having an absolute value of the amount of charge larger than the absolute value of the average amount of charge of the toner particles. Including weight% or less,
The content of toner having a charge amount that is twice or more the average charge amount of the toner particles is 20% by weight or less, and the content of toner having a charge amount of 1/5 or less of the average charge amount is 10% by weight. A developing method characterized by the following. 2. The developing method according to claim 1, wherein the carrier particles are spherical particles. 3. The developing method according to claim 1, wherein the magnetic field is temporally varied in the region where the developer layer is vibrated by the oscillating electric field. 4. The developing method according to any one of claims 1 to 3, wherein the carrier particles have an insulating resistivity. 5. The developing method according to claims 1 to 4, wherein the carrier particles have an average particle diameter of 50 μm or less.