JPH1144998A - Electrophotographic developing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prolong the life of a developer and to prevent insufficiently electrified toner or cloud from occurring, by setting the electrified amount of toner in developer to a value equal to or under the critical electrified amount of the toner when the developer is replenished with toner. SOLUTION: In the case of replenishing two-component developer consisting of at least toner and magnetic carrier with toner, the electrified amount of the toner in the developer is set to a value equal to or under the critical electrified amount of the toner. By keeping the electrified amount of the toner equal to or under the value of the critical electrified amount of the toner, the toner is replaced. As a result, the developer is moved to an area C from an area B by gravity and motive power transmitted from a developer carrying member 2. At this time, a magnet roll 3 is rotated, so that the developer is carried while it is stirred by the magnetic force on a non-magnetic plate 5. The insufficiently electrified toner which is easily isolated from the developer is removed by stirring at that time. In an area D, the developer is carried by the magnetic force of the roll 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic image forming method for forming a toner image using an electrostatic latent image.

[0002]

2. Description of the Related Art In electrophotography, a developing method using a two-component developer containing a toner and a carrier has characteristics that the toner is easily charged and the toner particles are hardly agglomerated. It is widely used despite that. In the developing method using a two-component developer, charge is applied to the toner by frictional charging between the toner and the carrier, and the charged toner is statically charged on the electrostatic latent image formed on the latent image carrier. An image is formed by being electrically attached. In such a developing method, the mechanical stress when the toner and the carrier are rubbed, the binder property of the toner and the external additive are fused to the carrier surface, and the charging performance of the carrier is deteriorated. External additives such as silica and titanium oxide externally added to the toner in order to control the fluidity and chargeability of the toner are buried in the toner, or the toner is degraded from the toner. However, there is a problem that a normal charge cannot be applied to the image and the image is deteriorated. In order to avoid such a problem that the toner is poorly charged due to the mechanical stress applied to the developer, a proposal has been made to reduce the mechanical stress applied to the developer in the developing device. For example, Japanese Patent Application Laid-Open Nos. 6-3963 and 7-92815 propose that the mechanical stress applied to the developer is reduced by defining the magnetic flux density of the developing roll, thereby extending the life of the developer. I have.

[0003] However, it has been found that reducing the stress on the developer is not enough to actually extend the life of the developer. For example, in the continuous print mode, a developer is used when a solid image having a gradation such as a photograph, a painting, or a map is mainly printed, and when a line mainly image such as characters or ruled lines is printed. There is a great difference in the life of the developer, and the life of the developer is significantly reduced when an image mainly printed on a line is printed.
This difference is greatly affected by the chargeability of the developer based on the balance between the consumption amount and the supply amount of the toner.

When printing is performed with a large image area such as a solid image, a large amount of toner is consumed, so that the amount of replenished toner increases, and the replacement of toner in the developer becomes severe. As a result, even when continuous printing is performed, the time during which the toner stays in the developer is shortened, and the charge amount of the toner is settled to a low level. On the other hand, when an image having a small image area such as a line image is mainly used for printing, replacement of the toner in the developer does not occur so frequently. As a result, the time during which the toner stays in the developer is prolonged, and the charge amount of the toner is settled at a high level.

[0005] Comparing the developer in the case where the solid image is mainly printed and the developer in the case where the solid image is printed, the phenomena such as the deterioration of the carrier and the deterioration of the toner are mainly performed in the line image. Is remarkably observed in the developer continuously performed. This is because the developer is mixed in the developing device while the toner exchange is small, so that the charge amount of the toner is increased and the electrostatic force acting between the toner and the carrier is increased. This is considered to be a result of an increase in the stress applied to the developer as a whole due to the application of the mechanical stress.

[0006] Even if the carrier and the toner are not significantly deteriorated, when a new toner is replenished to the developer in a state where the charge amount of the toner in the developer is high, poorly charged toner is likely to be generated. For example, when continuous printing is performed in the mainstream of the line image and the charge amount of the toner is increased, the solid image is switched to the mainstream printing and the continuous printing is performed, and the fog due to the toner cloud often occurs. . This means that when continuous printing is performed on an image that consumes a large amount of toner, such as a solid image, a large amount of new toner is supplied. On the other hand, since the developer prints continuously in the mainstream of the line image, the amount of charge of the toner originally in the developer is high, and the toner in the developer adheres firmly to the electrostatic force. Because the carrier surface is covered in the degraded state, it is difficult for new toner to contact the carrier surface. As a result, it is considered that the toner was not efficiently charged, and the new toner could not hold a sufficient charge amount, resulting in a cloud.

When such a state continues for a long time, the amount of charge of the toner originally attached to the carrier further increases with time, and the adhesive force between the toner and the carrier further increases.
The above-mentioned cloud is likely to be generated, and if the state further progresses, it leads to phenomena such as toner deterioration and carrier deterioration. Therefore, in order to extend the life of the developer, it is necessary to control not only the stress of the developer but also the charge amount of the toner.

SUMMARY OF THE INVENTION The present invention has been made in view of such a phenomenon. More specifically, the present invention is directed to developing a two-component developer by controlling the toner charge amount within an appropriate range. It is an object of the present invention to provide an electrophotographic developing method capable of extending the life of an agent and preventing the occurrence of poorly charged toner and cloud.

[0008]

The above object is achieved by an electrophotographic developing method having the following features. That is,
According to the present invention, when replenishing a toner to a two-component developer comprising a toner and a magnetic carrier, the charge amount of the toner in the developer is set to a value equal to or less than the critical charge amount of the toner, and the toner and the carrier are replenished. It is characterized in that the electrostatic adhesion acting between them is not increased more than necessary.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION As a result of intensive studies by the present inventors on the behavior of toner in a developer, the following phenomena have become apparent. That is, when an uncharged toner is added to a developer composed of a toner and a carrier, the degree of mixing of the toner varies depending on the charge amount of the toner in the developer. If the charge amount is equal to or lower than the toner saturation charge amount at the critical toner concentration of the developer, the charged toner adhering around the carrier and the newly added charged toner are charged. Replacement of no toner (Replacing
It turns out that happens). Here, the critical toner concentration is defined as a toner concentration corresponding to a point at which the proportionality of the slope is broken when the saturation charge amount of the toner in the developer is plotted against the toner concentration. Note that the toner concentration at this time is changed by 1 ± 0.5 wt%. The saturated charge amount of the toner at the critical toner concentration is defined as the critical toner charge amount.

FIG. 1 shows the toner concentration in the developer [TC
(Wt%): Toner Concentration], the saturation charge amount of the toner in the developer [TV (μC / g): Tribo Valu
e]], the point where the proportional relationship between the two is broken is shown. Here, the saturated charge amount means that 200 to 300 ml of a developer is placed in a cylindrical container made of polyethylene or glass having a diameter of 100 to 150 mm at the bottom and a height of 150 to 200 mm, and the container has an amplitude of 3 in the vertical direction.
While mixing the developer at 0 cm and a shaking speed of 60 times per minute, the charge amount of the toner at that time was measured by a blow-off method every 3 minutes, and the value of the charge amount of the toner measured continuously three times was Mean value when the average value is within ± 5%.

Considering the phenomenon shown in FIG.
In a region where the TC is low, that is, in a region where the surface area of the toner is small relative to the surface area of the carrier, the toner is frequently contacted with the carrier. Therefore, the longer the mixing time, the better the toner is charged. It is also in this region that the TV varies according to the mixing conditions. However, if the mixing is performed for a certain time or more, the charge amount is saturated. In the region where TC is low, T
V indicates the maximum charge amount that the toner can have, and is a substantially constant value. In such a state, it can be said that the entire surface of the toner is uniformly contacted with the carrier and the entire surface of the toner is uniformly charged to the saturation level.

When TC is increased from such a state,
After a certain TC, the TV gradually decreases. In this region, the TC is high, that is, the toner covers the carrier surface. In a state where the toner covers the surface of the carrier, the toner can only locally contact the carrier. Therefore, the charge amount of the toner is small, and the electrostatic adhesion of the toner to the carrier is also small. In addition, since the toner can only locally contact the carrier, charging is stabilized in a relatively short time. When a new toner is added to such a developer, the toner originally contained in the developer has a low charge amount and a small electrostatic adhesion to the carrier, so that the carrier is replaced with the new toner (Replacing). ) Is easily performed.

These will be described with reference to FIGS. 2 to 5. FIG. 2 shows the case where the toner concentration in the developer is low, that is, the case where the probability that the entire toner surface contacts the carrier is high, and the mixing time , The state where the entire surface of the toner is charged. Since the amount of electric charge of each toner particle is large and the electrostatic force acting between the toner particles and the carrier is large, the toner hardly separates from the carrier. FIG. 3 shows the case where the toner concentration in the developer is high, that is, the case where the toner surface can only partially contact the carrier. The toner is locally charged, and the charge amount of each toner particle is shown. Is also lower,
The electrostatic force acting between the toner and the carrier is small, and the toner is easily separated from the carrier.

When new toner (uncharged toner) is added to the toner in the state shown in FIG. 2 or FIG.
If the toner that is originally in contact with the carrier has a large charge amount, the toner and the carrier have a large adhesive force.
4 does not occur (FIG. 4), but if the charge amount of the toner originally in contact with the carrier is low as shown in FIG. 3, the adhesion between the toner and the carrier is small. Replacing) occurs easily (FIG. 5).

The present invention utilizes this phenomenon.
That is, when toner is supplied to at least the two-component developer in the developing device, by keeping the toner of the developer in such a state, the toner adhering to the carrier is constantly replaced with new toner. . As described above, since the metabolism of the toner with respect to the carrier occurs efficiently, the charge amount of the toner does not increase more than necessary. A phenomenon such as embedding or release of the external additive can be prevented, and the life of the developer can be drastically extended. Next, an example in which replacement of toner is confirmed experimentally will be described. (Experimental Example 1) The following black toner and Sian toner were prepared as toners, and the following polymer carriers were prepared as carriers. Black toner: polyester (number average molecular weight: 3,300,
(Weight average molecular weight: 9,800, Tg = 60 ° C.) 93% by weight of carbon black and 7% by weight of carbon black are kneaded and pulverized to obtain a base toner having an average particle diameter of 7 μm. ₂ Fine powder was externally added to the toner surface by 2.0% by weight. Sian Toner: Polyester (Number average molecular weight: 3,3
00, weight average molecular weight: 9,800, Tg = 60 ° C) 9
After 2% by weight and 8% by weight of Sian pigment are kneaded and pulverized to obtain a base toner having an average particle diameter of 7 μm, a 40 nm TiO ₂ fine powder obtained by subjecting the base toner to a hydrophobic treatment is added to the surface of the toner by 2.0% by weight. Attached. Carrier: styrene-acrylic copolymer (number average molecular weight: 23,000, weight average molecular weight: 98,000, T
g = 78 ° C.) 30% by weight, and 70% by weight of granular magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) are kneaded.
It was pulverized and classified to obtain a polymer carrier having an average particle size of 45 μm. When the magnetic properties were measured, the saturation magnetization was 55 emu.
/ G.

First, the relationship shown in Table 1 was obtained when the relationship between the TC of the developer and the saturation charge amount was determined for the developer containing the black toner at various ratios.

[0017]

[Table 1]

For this developer, the saturated charge amount of the toner is -20 (μC / g), the critical toner concentration is 21% by weight, and the critical toner charge amount is -18 μC / g.

Next, 40 g of black toner and 160 g of carrier
Was mixed to obtain a mother developer having a toner concentration of 20% by weight. The developer at this time was 100-400 times with an optical microscope.
Observation at twice magnification confirmed that almost the entire carrier surface was covered with black toner. 200 g of this mother developer was placed in a cylindrical container made of polyethylene having a bottom diameter of 105 mm and a height of 180 mm (capacity:
Then, the developer was stirred up and down at an amplitude of 30 cm and a shaking speed of 60 times per minute, and the stirring time was changed to obtain a developer having a different toner charge amount. To each of the mother developers thus obtained, 40 g of Sian toner was added, followed by stirring by shaking 10 times. This was used as a sample developer, and sieved with a 28 μm mesh to remove excess toner. The developer was observed with an optical microscope at a magnification of 100 to 400 times focusing on the toner attached to the carrier. The results in Table 2 were obtained.

[0020]

[Table 2]

From the above results, when a new toner is added to the developer, the charge amount of the toner originally attached to the carrier is -18 μC / C, which is the critical charge amount of the toner.
If it is less than g, it can be seen that replacement with new toner added later (Toner Replacing) occurs.

(Experimental Example 2) The following black toner and cyan toner were prepared as toners, and the following polymer carriers were prepared as carriers. Black toner: polyester (number average molecular weight: 3,300,
(Weight average molecular weight: 9,800, Tg = 60 ° C.) 93% by weight of carbon black and 7% by weight of carbon black are kneaded and pulverized to obtain a base toner having an average particle diameter of 7 μm. ₂ Fine powder was externally added to the toner surface by 1.0% by weight. Sian Toner: Polyester (Number average molecular weight: 3,3
00, weight average molecular weight: 9,800, Tg = 60 ° C) 9
After 2% by weight and 8% by weight of Sian pigment are kneaded and pulverized to obtain a base toner having an average particle diameter of 7 μm, a 40 nm SiO ₂ fine powder obtained by subjecting the base toner to a hydrophobic treatment is added to the surface of the toner by 1.0% by weight. Attached. Carrier: styrene-acrylic copolymer (number average molecular weight: 28,000, weight average molecular weight: 98,000, T
g = 78 ° C.) 30% by weight, and 70% by weight of granular magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) are kneaded.
It was pulverized and classified to obtain a polymer carrier having an average particle size of 45 μm. When the magnetic properties were measured, the saturation magnetization was 55 emu.
/ G.

First, the relationship shown in Table 3 was obtained when the relationship between the TC of the developer and the saturation charge amount was determined for the developer containing the black toner at various ratios. .

[0024]

[Table 3]

With this developer, the saturated charge amount of the toner is -23 (μC / g), the critical toner concentration is 21% by weight, and the critical toner charge amount is -20 μC / g.

Next, 40 g of black toner and 160 g of carrier
Was mixed to obtain a mother developer having a toner concentration of 20% by weight. The developer at this time was 100-400 times with an optical microscope.
Observation at twice magnification confirmed that almost the entire carrier surface was covered with black toner. 200 g of this mother developer was placed in a cylindrical container made of polyethylene having a bottom diameter of 105 mm and a height of 180 mm (capacity:
Then, the developer was stirred up and down at an amplitude of 30 cm and a shaking speed of 60 times per minute, and the stirring time was changed to obtain a developer having a different toner charge amount. To each of the mother developers thus obtained, 40 g of Sian toner was added, followed by stirring by shaking 10 times. This was used as a sample developer, and sieved with a 28 μm mesh to remove excess toner. The developer was observed with an optical microscope at a magnification of 100 to 400 times focusing on the toner attached to the carrier. The results in Table 4 were obtained.

[0027]

[Table 4]

From the above results, when a new toner is added to the developer, the charge amount of the toner originally attached to the carrier is -18 μC / C, which is the critical charge amount of the toner.
If it is less than g, it can be seen that replacement with new toner added later (Toner Replacing) occurs.

(Experimental Example 3) The following black toner and cyan toner were prepared as toners, and the following polymer carriers were prepared as carriers. Black toner: polyester (number average molecular weight: 3,300,
(Weight average molecular weight: 9,800, Tg = 60 ° C.) 93% by weight of carbon black and 7% by weight of carbon black are kneaded and pulverized to obtain a base toner having an average particle diameter of 7 μm. 0.8% by weight of the fine powder was externally added to the toner surface. Sian Toner: Polyester (Number average molecular weight: 3,3
00, weight average molecular weight: 9,800, Tg = 60 ° C) 9
2% by weight and 8% by weight of Sian pigment are kneaded and pulverized to form a base toner having an average particle diameter of 7 μm, and then a 40 nm PMMA fine powder obtained by subjecting the base toner to a hydrophobic treatment is externally added to the toner surface by 0.8% by weight. did. Carrier: styrene-acrylic copolymer (number average molecular weight: 28,000, weight average molecular weight: 98,000, T
g = 78 ° C.) 30% by weight, and 70% by weight of granular magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) are kneaded.
It was pulverized and classified to obtain a polymer carrier having an average particle size of 45 μm. When the magnetic properties were measured, the saturation magnetization was 55 emu.
/ G.

First, the relationship shown in Table 5 was obtained when the relationship between the TC of the developer and the saturation charge amount was determined for the developer containing the black toner at various ratios. .

[0031]

[Table 5]

For this developer, the saturated charge amount of the toner is -18 (μC / g), the critical toner concentration is 21% by weight, and the critical toner charge amount is -16 μC / g.

Next, 40 g of black toner and 160 g of carrier
Was mixed to obtain a mother developer having a toner concentration of 20% by weight. The developer at this time was 100-400 times with an optical microscope.
Observation at twice magnification confirmed that almost the entire carrier surface was covered with black toner. 200 g of this mother developer was placed in a cylindrical container made of polyethylene having a bottom diameter of 105 mm and a height of 180 mm (capacity:
The developer was stirred at an amplitude of 30 cm vertically and at a shaking speed of 60 times per minute, and the stirring time was changed to obtain a developer having a different toner charge amount. To each of the mother developers thus obtained, 40 g of Sian toner was added, followed by stirring by shaking 10 times. This was used as a sample developer, and sieved with a 28 μm mesh to remove excess toner. The developer was observed with an optical microscope at a magnification of 100 to 400 times focusing on the toner attached to the carrier. The results in Table 6 were obtained.

[0034]

[Table 6]

From the above results, when a new toner is added to the developer, the charge amount of the toner originally attached to the carrier is -16 μC / C, which is the critical charge amount of the toner.
If it is less than g, it can be seen that replacement with new toner added later (Toner Replacing) occurs.

Next, an example of a developing apparatus for performing the electrophotographic developing method of the present invention will be described. FIG. 4 is a schematic view of the developing device. The developing device includes a developer conveying member 2 rotatably disposed with a small gap between the OPC photosensitive member 1 and the surface thereof, and a magnetic pole disposed inside the developer conveying member 2. N and S symmetrically magnetized magnet rolls 3 having a pitch of 2 mm, a spacer member 4 for providing a gap between the developer conveying member 2 and the magnet roll 3, a partial non-magnetic plate 5, a toner hopper It consists of Since the developer conveying member 2 is in contact with the magnet roll 3, it moves following the magnet roll 3. Reference numeral 7 denotes a developer supply port. The photoconductor 1, the developer transporting agent 2, and the magnet roll 3 rotate in the direction of the arrow. The developer conveying member 2 is driven by a magnet roll 3.

According to the electrophotographic developing method of the present invention, when the toner is replenished to a two-component developer comprising at least a toner and a magnetic carrier, the charge amount of the toner in the developer is equal to the critical charge amount of the toner, or It is characterized in that it is set to a value less than that. That is, it is necessary to satisfy such a condition at least in the region A in FIG. The developer satisfying such conditions in the area A falls into the area B. In the area A, since a gap is provided between the developer transport member 2 and the magnet roll 3, the magnetic force acting on the developer is reduced, and the developer drops naturally. In the area B, the toner dropped from the toner hopper and the toner dropped naturally from the area A are mixed.
Here, the magnetic force from the magnet roll hardly acts, there is no aggregation of the developer due to magnetism, and the developer contacts each other in a state where each developer is loosened, so that the mixing property is extremely good. At this time, the control is not performed such that the toner concentration of the developer is replenished by the amount used as in the related art. However, as described above, at least in the area A, the charge amount of the toner in the developer becomes the critical charge of the toner. It is done to make the value equal to or less than the amount. "Is the charge amount of the toner in the developer equal to the critical charge amount of the toner,
The phrase "reducing the value to a value less than or equal to" is, in practice, performed in such a state that the toner concentration always exceeds the critical toner concentration, but is not limited to this method. In short, it is only necessary that the charge amount of the toner in the developer in at least the region A be equal to or less than the critical charge amount of the toner.

As described above, when the charge amount of the toner is maintained below the value of the critical charge amount of the toner, the replacement of the toner (Tone) is performed.
r Replacing) occurs. Replace Toner (Toner Re
As a result, the developer in the state in which the toner has adhered in multiple layers moves from the area B to the area C by gravity and the power transmitted from the developer conveying member 2. In the region C, the developer is magnetically attracted to the magnet roll 3 via the non-magnetic plate 5. At this time, since the magnet roll is rotating, the developer is conveyed on the non-magnetic plate 5 while being stirred by a magnetic force. The agitation at this time removes the poorly charged toner that is easily released from the developer. In the area D, the developer is transported by the magnetic force of the magnet roll.

Here, the developing apparatus for carrying out the electrophotographic developing method of the present invention will be described in more detail. Normal
The developing device for two-component developer mixes toner and carrier,
A “developer preparation unit” that keeps the toner concentration of the developer uniform and a toner charge amount in the developer at a desired value by stirring, and a “developer” that conveys the prepared developer to a development area. Transport section ". Specific examples of the configuration of the “developer preparation unit” include a configuration using a stirring blade called a paddle and a configuration using a stirring rotary shaft with a spiral groove called an auger. In such a developing device, it is required that the “developer conveying unit” conveys the developer adjusted in the “developer preparing unit” without stress. For example, when a mechanical force is strongly applied to the developer in the “developer conveying section”, the charge amount of the toner increases, and the state of the developer controlled by the “developer preparation section” is broken. In the so-called magnetic pole fixed type sleeve rotation method, which has a sleeve that can rotate around a generally used fixed magnetic pole, tumbling of the developer on the sleeve occurs, which causes stress on the developer and increases the charge amount of the toner. May be used, for example, by using a lower rotational speed,
A device such as lower magnetic force is used.

As a developing device free of such stress due to tumbling, for example, there is a developing device which conveys a developer by a movement of a magnetic pole of a magnetic force generating member. In such a developing device, there is no stress due to tumbling, but when the developer is transported by the movement of the magnetic force generating member, the developer on the developer transporting member has a magnetic brush shape corresponding to the pitch of the magnetic poles of the magnetic force generating member. For example, when the N pole and the S pole are adjacent to each other, when observing the shape of the magnetic brush of the developer, the portion corresponding to the magnetic pole of the magnetic force generating member has a high spike of the developer magnetic brush, and the portion corresponding to the magnetic pole of the magnetic force generating member corresponds to In the portion where the developer magnetic brush has fallen, the ears of the developer magnetic brush are low. When the developer is transported by the movement of the magnetic force generating member, the high and low portions of the developer magnetic brush will alternately enter the development area, causing image density unevenness according to the magnetic pole pitch. May be.

Since the difference between the heights of the spikes of the developer magnetic brush on the magnetic pole and between the magnetic poles decreases as the distance between adjacent magnetic poles decreases, the magnetic force generating member is magnetized at a narrow magnetic pole pitch. Magnetic material is used. A magnetic force generating member having a magnetization pitch of 3 mm or less, preferably 2 mm or less is used. Regarding the arrangement of the magnetic poles, it is preferable that the N and S alternating symmetrical magnetizations be used. Any material that can transport the agent may be used.

The magnetic force generating member may be any material that is generally used as a permanent magnet. For example, a metal magnet magnetized on a metal material such as ferrite, magnetite, or iron, or a magnetite powder or a ferrite powder dispersed in a polymer. Magnetic materials such as those called normal plastic magnets magnetized on magnets and those called normal sheet magnets magnetized on sheets made by dispersing magnetite powder or ferrite powder in polymer or rubber Can be used as long as it generates the following.

Since it is necessary to apply a developing bias to the developer conveying member, it is necessary that the resistance is low and the surface has a uniform electric resistance value. Further, a portion where the magnetic force exerted by the magnetic force generating member may be provided on the developer conveying member may be provided with a portion where the magnetic force is strong and a portion where the magnetic force is weak. The aim is described.

The portion where the magnetic force generating member exerts a strong magnetic force on the developer conveying member refers to the developer conveying area, and the portion where the magnetic force generating member exerts a weak magnetic force on the developer conveying member is the developing portion. It indicates a region where the developer is separated from the agent transport member and mixed with the toner. As a method of peeling the developer from the developer transport member, there is a method of pressing a peeling agent called a scraper against the developer transport member to peel the developer, but in such a method, the developer transport member is removed. ,
Alternatively, the scraper may be worn and the peeling performance may be reduced. Further, there is a case where the life of the developer is significantly reduced due to the stress of the developer by the scraper. In the present invention, by providing a portion where the magnetic force exerted by the magnetic force generating member on the developer conveying member is provided, the developer can be separated without applying a stress, so that the problem of shortening the life of the developer does not occur. .

A method of forming a portion on the developer carrying member where the magnetic force exerted by the magnetic force producing member is weak, for example, by disposing a tubular developer carrying member around a cylindrical magnetic force producing member, The gap between the magnetic force generating member and the tube-shaped developer conveying member may be increased, or a magnetic material having high magnetic permeability such as permalloy may be interposed between the developer conveying member and the magnetic force generating member. In order to provide a gap between the developer conveying member and the magnetic force generating member, a spacer may be provided, or a gap may be provided by applying tension to the developer conveying member.

As for toner replenishment, the developer separated from the developer conveying member is mixed with excess toner to increase the toner concentration once, and then, while stirring, removes excess toner and then returns to the developing area. It is preferable from the viewpoint that replacement of new toner is promoted by taking the form of being transported. In a region where the toner concentration of the developer is increased, it is effective to increase the effective charging area of the developer and to improve the mixing property between the developer and the toner by minimizing the magnetic restraining force acting on the developer. At this time, by allowing the developer to spontaneously fall into the toner pool by the action of gravity, the mixing property between the developer and the toner can be further improved.

After the toner concentration is once increased, the developer is agitated by the developer agitating means, thereby increasing the efficiency of toner replacement. As a method of stirring the developer, a method using vibration, impact, rotation by mechanical means, or an electric means for vibrating the developer by an alternating electric field is used. By means, the aim can be achieved with a simpler configuration. For example, a region for holding the developer by the magnetic force of the magnetic force generating member via a fixed non-magnetic plate is provided in the developer stirring region. The magnetic pole of the magnetic force generating member moves to transport the developer. At this time, the developer on the non-magnetic plate can be stirred by the magnetic force. With this configuration, the developer can be stirred while transporting the developer with a simple configuration.

As the developer, a known two-component developer is used. The toner is not limited to magnetic and non-magnetic. Known carriers such as metal fine particles such as ferrite, magnetite, and iron, or metal particle carriers obtained by coating the surfaces of these metal fine particles with a polymer, or polymer carriers obtained by adding a magnetic powder to a polymer are used. Can be

Next, an embodiment will be described.

Example 1 The black toner used in the above experimental example,
Using the same toner and carrier as the Sian toner and the carrier, and using the developing device shown in FIG. 6,
The measurement of the charge amount of the toner in the developing device and the actual continuous print test were performed. The development conditions and the like are as follows. (Developing conditions) Photoreceptor OPC (φ84) ROS LED (400 dpi) Process speed 100 mm / s Latent image potential Background part = −600 V, image part = −100 V Developer transport member Non-magnetic endless film (100 μm thick, polycarbonate resin those obtained by dispersing carbon black click in. electrical resistance = 10 ⁶ Ω · cm) magnet roll flux density = 22mT (developer conveying the member) roll diameter = ø20 roll rotation speed = 250 mm / s developer conveying member Maximum gap between the photoconductor and the magnet roll = 2 mm Distance between the photoconductor and the developer conveying member = 0.5 mm Thickness of the developer layer = 0.5 mm Development bias DC component = −550 V AC component = 1.5 kV _PP (1. 5 kHz) Toner The above-mentioned polyester-based black toner having a particle diameter of 7 μm. Carrier The aforementioned polymer carrier with a particle size of 45 μm

First, a toner and a carrier were mixed to prepare a developer having a toner concentration of 20% by weight. By changing the stirring time of the developer at this time, the following three developer samples having different charge amounts of the toner were prepared. Sample a: toner charge = −15 μC / g Sample b: toner charge = −18 μC / g Sample c: toner charge = −12 μC / g

The three types of developers were supplied from the developer supply port 7 and the magnet roll 3 was rotated. Since the developer conveying member 2 is in contact with the magnet roll 3, it moves following the magnet roll 3. In the area A, since a gap is provided between the developer transporting agent 2 and the magnet roll 3, the magnetic force acting on the developer is reduced, and the developer spontaneously falls. In the area B, the developer drops from the toner hopper. Mixes with toner. Here, the magnetic force from the magnet roll hardly acts, there is no aggregation of the developer due to magnetism, and the developer comes into contact with the toner in a loosened state, so that the mixing property with the toner is extremely good.

At this time, the toner concentration of the developer in all of the samples a, b and c is in a state where the toner concentration is not controlled at all, and varies from 50 to 300% by weight. Observation of the developer at this time with an optical microscope revealed that the toner had adhered in multiple layers around the carrier. When the charge amount of the toner is measured while blowing the toner around the carrier from the outside in order from the air, the charge amount of the toner attached from the second layer to the outside around the carrier is almost 0 μm.
It was confirmed that the toner was poorly charged because it was near C / g, was hardly charged, and was easily released. It is considered that these toners could not be brought into direct contact with the surface of the carrier and were not easily charged by friction with the carrier, so that the toner was poorly charged. On the other hand, it was found that the toner in the first layer around the carrier was charged and was difficult to be released from the carrier. It is considered that these toners can be brought into direct contact with the carrier surface, so that the toner is charged by friction with the carrier, and adheres to the carrier by electrostatic force.

As described above, the developer in the state in which the toner adheres in multiple layers around the carrier moves to the area C by the gravity and the force transmitted from the developer conveying member 2. In the region C, the developer is magnetically attracted to the magnet roll 3 via the non-magnetic plate 5. At this time, since the magnet roll is rotating, the developer is conveyed on the non-magnetic plate 5 while being stirred by a magnetic force. The agitation at this time removes the poorly charged toner that is easily released from the developer.

In the area D, the developer is transported by the magnetic force of the magnet roll. Under these conditions, a continuous print test of 10,000 sheets was performed while measuring the toner concentration of the developer conveyed to the developing area and the charge amount of the toner. As a result, in Samples a and b, a small amount of toner cloud began to be generated at about a level of no practical problem from about 8,000 sheets, but the image density was constant and the practicability was confirmed. At this time, the charge amount of the toner in the developer on the magnet roll 3 is -13 to -15 [mu] C.
/ G and an almost constant value. Further, the toner density is 18 to 20 even though the toner density is not controlled.
The value was almost constant as% by weight. However, in Sample c, the image density began to decrease around 1000 sheets or more,
The toner cloud began to be generated around 1500 sheets, and the test was interrupted at 2000 sheets. Investigation of the developer on the magnet roll 3 at this time reveals that the amount of toner charge in the developer is -20 μC / g until the first 1000 sheets.
, But the charge distribution has widened,
The charge distribution continued to widen, and the amount of toner charge in the developer tended to gradually decrease with variation. The toner concentration also varied from 18 to 30% by weight.

After completion of the print test, these developers were taken out, 40 g of the above-mentioned Sian toner was added to 200 g of the developer, and the resultant was placed in a polyethylene container.
After stirring for 2 seconds and sieving with a mesh having a mesh size of 28 μm, the developer was observed with an optical microscope.
It was confirmed that the black toner and the Sian toner adhered to the carrier in almost equal amounts. However, in the sample c, the carrier remained covered with the black toner, and the Sian toner did not adhere to the carrier at all and existed as free toner. That was confirmed.

Further, these developers are put into pure water and subjected to ultrasonic cleaning to separate the toner from the carrier and to dry the carrier.
0g to make a mother developer with a toner concentration of 20wt%,
200 g of this mother developer was supplied with
The developer was placed in a cylindrical container made of polyethylene having a height of 180 mm (capacity: about 1100 ml), and the developer was stirred up and down 120 times at an amplitude of 30 cm and a shaking speed of 60 times per minute to check the charge amount of the toner. . As a result, in Samples a and b, the charge amount of the toner showed a value of around −15 μC / g, whereas in Sample c, the charge was only about −7 μC / g. Observation of the carrier surface with an SEM confirmed that the carrier surface was covered with foreign matter that was considered to be a toner binder component. Therefore, it is possible to maintain a stable image density for a long period of time by maintaining the charge amount of the toner in the developing device at a value equal to or less than the critical charge amount of the toner, and replenishing and stirring the toner at a critical toner concentration or more. confirmed.

[0057]

[Example 2] In Example 1, the toner was sphericalized by hot air to obtain a spherical toner.
A print test of 000 sheets was performed. As a result, the image density was constant in sample a and sample b as in Example 1, and no toner cloud was generated. The charge amount of the toner in the developer on the magnet roll 3 is -14 to -1.
The value was 5 μC / g, which was more stable than that of Example 1. In addition, the toner concentration was 19 to 20% by weight, which was more stable than that of Example 1, even though the toner concentration was not controlled. Further, a continuous print test of 5000 sheets was performed, and as a result, a small amount of toner cloud began to be generated, and the image density also began to decrease. In sample c, although the image density was more stable than in Example 1, the image density began to decrease around 3000 sheets or more, and a toner cloud was generated around 3500 sheets and the test was stopped at 5000 sheets. Investigation of the developer on the magnet roll 3 at this time reveals that the toner charge amount in the developer is the first 300
Until the 0th sheet, -20 μC / g was maintained, but thereafter, there was a tendency to gradually decrease with variation. The toner concentration also varied from 18 to 30% by weight.
It was the same result as. These results are thought to be due to the fact that the toner was made spherical, the fluidity was increased, and the adhesion to the carrier was reduced, so that the toner was smoothly replaced and the deterioration of the developer was reduced.

[0058]

Example 3 In Example 2, the carrier was made spherical by hot air to form a spherical carrier, and a 10,000 sheet print test was performed under the same conditions as in Example 1. As a result, the image density was constant in sample a and sample b as in Example 1, and no toner cloud was generated. The charge amount of the toner in the developer on the magnet roll 3 is -14 to-
The value was 15 μC / g, which was more stable than that of Example 1. Further, the toner concentration was 19 to 20% by weight, which was more stable than that of Example 1, even though the toner concentration was not controlled. Further, as a result of continuous printing test of 10,000 sheets, a small amount of toner cloud began to be generated from over 8,000 sheets.
Samples having practically no problem were obtained up to 0000 sheets. In sample c, although the image density was more stable than in Example 1, the image density began to decrease around 6,000 sheets, and a toner cloud was generated around 6,500 sheets, and the test was stopped at 8,000 sheets. Investigation of the developer on the magnet roll 3 at this time reveals that the amount of toner charge in the developer is -20 .mu.
C / g was maintained, but then tended to gradually decrease with variation. 18 ~
The variation was 30% by weight, and the result was similar to that of Example 1. These results are thought to be due to the fact that the toner and the carrier were made into spheres, so that the fluidity was increased, and the adhesion of the toner to the carrier was reduced, whereby the toner was smoothly replaced and the deterioration of the developer was reduced. Can be

[0059]

As described above, according to the present invention, it is possible to provide a developing device capable of maintaining a stable image density for a long period of time.

[0060]

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a relationship between a toner concentration in a developer and a saturation charge amount.

FIG. 2 is a conceptual diagram illustrating a case where the entire toner surface is charged.

FIG. 3 is a conceptual diagram illustrating a state where a part of the toner surface is charged.

FIG. 4 is a conceptual diagram showing a case where new toner is added to the toner in the state of FIG. 2;

FIG. 5 is a conceptual diagram illustrating a case where new toner is added to the toner in the state of FIG. 3;

FIG. 6 is a schematic view showing an image developing apparatus for carrying out the present invention.

[Explanation of symbols]

(1) ... OPC photoreceptor (electrostatic latent image carrier) (2) ... developer transport member (3) ... magnetic force generating member (magnet roll) (4) ... spacer member (5) ): Partial non-magnetic plate (6): Toner hopper (7): Developer supply port (8): Mesh screen (9): Toner transport auger A: Toner charging toner in contact with the area B · · · toner supply section C · · · toner preparation section D · · · toner transport unit T · · · toner particles CA · · carrier T _O · · originally carrier keep the amount specified value Particles _TN New toner particles

Claims (4)

[Claims] In an electrophotographic developing method using a developer containing a toner and a magnetic carrier, at least when the toner containing the toner and the magnetic carrier is replenished with the toner, the charge amount of the toner in the developer is reduced. An electrophotographic development method characterized in that the value is equal to or less than the critical charge amount. 2. The electrophotographic developing method according to claim 1, wherein the toner has a spherical shape. 3. The electrophotographic developing method according to claim 1, wherein the carrier has a spherical shape. 4. The electrophotographic development method according to claim 1, wherein when replenishing the toner to the developer containing the toner and the magnetic carrier, the toner concentration in the developer is equal to or higher than the critical toner concentration. .