JP2000305355A - Developing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device and an image forming apparatus capable of reducing toner scattering to eliminate background contamination and preventing a decrease in image density caused by using a conventional magnetic toner. I will provide a. SOLUTION: The developer 3 having the magnetic toner carried on a developing sleeve 4 is blocked by a doctor, and the developer stored in a developer storage portion A is changed by a toner supply port 8a due to the internal pressure of the developer itself and its own weight. To the toner hopper 8
In the developing device 10 which takes in the replenishing toner 3a from the toner, the saturation magnetization value in a magnetic field of 4.0 × 10 ⁵ A / m is 1.25 × 10 ^{−2 to} 5.65 × as the magnetic toner.
Using a magnetic toner of 10 ⁻² A / m · g, the carrier coverage of the developer carried on the developing sleeve regulated by the doctor is 30 to 130%. As a result, background contamination can be suppressed to a level that does not cause a problem, and a decrease in image density can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, etc. and a developing device used for the same, and more particularly, to a magnetic toner on a developer carrier having a magnetic field generating means disposed therein. And a developing device for carrying a developer containing a magnetic carrier and the developer, transporting the developer to a development area facing the latent image carrier, and developing the latent image formed on the latent image carrier. And an image forming apparatus having the same.

[0002]

2. Description of the Related Art Conventionally, this type of developing device does not require a toner density detecting means such as a toner density sensor.
2. Description of the Related Art There has been known a toner density self-control system which replenishes toner by movement of a developer and controls the toner density within an appropriate range. In the developing device using the toner concentration self-control system, the toner concentration detecting means can be simplified and the toner replenishing mechanism can be simplified, so that the size and cost of the device can be reduced. Becomes possible.

As a developing device utilizing such a toner concentration self-control system, for example, a magnetic carrier layer is formed on a developer carrier in a container, and the magnetic carrier layer is formed in a toner supply section in the container. The toner is stored so as to be in contact with the toner, and the magnetic carrier in the magnetic carrier layer is moved by the rotation of the developer carrier having a magnet fixedly arranged therein, so that the toner is taken into the magnetic carrier layer by the toner supply unit. In a developing device in which a developer in which a toner and a magnetic carrier are mixed is regulated in a layer thickness by a developer regulating member and transported to a development area, the magnet does not have a magnetic pole facing the toner replenishing unit, and the developer is carried. It has a magnetic pole on the downstream side of the toner supply section and the upstream side of the regulating member with respect to the rotation direction of the body, and has a magnetic pole downstream of the toner supply section and upstream of the regulation member. A developing device is provided at a position within a range where the magnetic field of the magnetic pole reaches, facing the developer carrier, and has a shielding member that forms a region filled with the magnetic carrier layer between the developer carrier and the developer carrier. It has been proposed (Japanese Patent Publication 5-6)
No. 7233).

According to this developing device, the developer remaining in the region surrounded by the shielding member and the developer carrier on the upstream side of the developer regulating member has a high toner concentration and a large bulk of the developer. When becomes, it becomes difficult to move the filling rate of the region increases, except for the developer passing through the developer regulating member,
There is almost no movement of the developer in this area. Conversely, when the toner density decreases due to the consumption of the toner and the bulk of the developer becomes small, the filling rate of the area decreases, the developer becomes easy to move, and the toner is taken into the developer.
Then, when the toner density of the developer increases and the bulk of the developer increases, the developer in the area hardly moves again, and the taking in of the toner stops. Thus, the developing device can automatically control the toner concentration in the developer.

However, in the developing device disclosed in the above publication, when the amount of the developer existing in the region filled with the magnetic carrier layer becomes slightly larger, the developer except for the one passing through the developer regulating member is used. Almost does not work.
For this reason, when an image is formed with a slightly larger amount of toner consumption, it becomes difficult to supply new toner to the developer that contributes to development. On the other hand, if the magnetic carrier is set in an amount larger than the required amount, the toner concentration is significantly reduced, and even if the toner concentration becomes insufficient, the flow of the developer for taking in the toner does not occur. When the toner consumption further progresses, the toner density becomes almost 0 wt%, and a desired image density may not be obtained. Therefore, in order to activate the movement of the developer existing in the above-mentioned area, it is preferable to set a small amount of the developer in the case of this developing device. However, if the amount of the developer is too small, the toner density may be reduced. Is excessively high in some parts, and insufficient charging of the toner easily causes problems such as background contamination and in-machine contamination due to toner scattering. In addition, such problems as contamination on the ground and in-machine contamination due to scattering of the toner are also caused by insufficient charging of the toner due to a short route from the supply of the toner to the developer to the conveyance of the toner to the development area. It is thought that there is.

As described above, in the developing device disclosed in the above publication, the amount of developer cannot be increased as compared with the conventional two-component developing device. When applied to a fast high-speed machine, the toner cannot be charged sufficiently, and there is a possibility that background contamination and toner scattering may occur.

In order to solve such a problem, the present applicant discloses in Japanese Patent Application Laid-Open No. 9-22178 a developer carrier for carrying and transporting a developer containing a toner and a magnetic carrier. A magnetic field generating means disposed inside the developer carrier, a developer regulating member for regulating the amount of developer carried and conveyed by the developer carrier, and a developer blocked by the developer regulating member. A developer accommodating portion to be accommodated, and a developer adjacent to the developer accommodating portion from an upstream side of the developer carrying direction on the developer carrying member, wherein the contained toner is carried by the developer carrying member. And a toner storage portion having a toner replenishing opening in contact with the developer in the developer storage portion, wherein the developer blocked by the developer regulating member is moved by the internal pressure of the developer itself and its own weight in the developer storage portion. When it is moved to the toner supply opening side, And transporting the developer having taken in the toner from the toner storage section to the developer regulating member side along the surface of the developer carrier, and regulating the developer carrier to a predetermined amount by the developer regulating member. A developing device for supplying the above developer to a developing area facing the image carrier, wherein a magnetic toner is used as a toner constituting the developer, has been proposed.

[0008] In this developing device, a developer layer (hereinafter, referred to as a main layer) which is mainly carried by a developer carrier and transported.
It is referred to as "first developer layer". After the developer is regulated to a predetermined amount by the developer regulating member, the developer is supplied to a development area facing the image carrier. Then, when the bulk of the developer changes in accordance with the change in the toner concentration in the developer, the development of the developer accommodating portion which has moved to the toner replenishing opening mainly at a position distant from the surface of the developer carrier. By changing the degree to which the developer of the developer layer (hereinafter, referred to as “second developer layer”) closes the toner supply opening, the amount of toner taken in by the developer of the first developer layer can be reduced. The density is changed according to the toner consumption, and the toner concentration of the developer is automatically controlled.

Further, in this developing device, by using a magnetic toner as a toner constituting the developer, the magnetic binding force due to the magnetic field generated by the magnetic field generating means can be reduced by the first type.
By acting not only on the magnetic carrier but also on the magnetic toner in the developer layer, the frictional force between the magnetic carrier and the magnetic toner is increased. Thereby, the toner in the developer can be sufficiently charged. As a result, a sufficiently charged toner can be supplied to the developing area even when the image forming apparatus is used in a high-speed image forming apparatus as compared with the case where a non-magnetic toner is used, thereby reducing background contamination and toner scattering. Can be.

Further, since the toner is magnetized by the magnetic effect of the magnetic field generating means, the binding force of the magnetic carrier to the toner is increased, and background contamination and toner scattering by the toner having a relatively small charge amount can be reduced. . Further, when the magnetic field generating means is disposed at a position opposite to the toner replenishing opening of the toner containing section, the magnetic force of the magnetic field generating means causes the toner from the toner containing section to move toward the developer carrier. Since the toner is drawn, the toner replenishing property is improved, and the followability of toner replenishment when the toner consumption rate is high, such as when a solid black image is formed, is improved.

[0011]

However, when a magnetic toner is used as the toner constituting the developer in this manner, the toner binding force on the magnetic carrier also increases due to the magnetic bias effect of the magnetic toner. Due to this magnetic bias effect, the magnetic toner having a small charge amount can be attracted to the magnetic carrier by the magnetic force acting on the magnetic toner itself. As a result, it is possible to reduce background contamination and the like due to the toner having a relatively small charge amount as described above. However, if the toner restraining force is excessively increased, the toner suction force to the latent image bearing member side in the developing area is reduced. There has been a problem that the toner restraining force cannot be overcome, and the developing ability is reduced to lower the image density.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to reduce development of toner by reducing toner scattering and preventing a decrease in image density. It is an object to provide an apparatus and an image forming apparatus.

[0013]

In order to achieve the above object, according to the present invention, a developer carrying member for carrying and transporting a developer containing a toner and a magnetic carrier is provided. Magnetic field generating means disposed inside the developer carrier, a developer regulating member for regulating the amount of developer carried and conveyed by the developer carrier, and a development blocked by the developer regulating member A developer accommodating section for accommodating a developer, and a toner accommodating section having a toner supply port adjacent to the developer accommodating section from the upstream side of the developer carrying direction on the developer carrying section,
The developer blocked by the developer regulating member is moved to the toner supply port side by the internal pressure of the developer itself and its own weight in the developer accommodating portion, and the developer taking in the magnetic toner from the toner accommodating portion is The developer is conveyed to the developer regulating member side along the surface of the developer carrying member, and the developer on the developer carrying member regulated to a predetermined amount by the developer regulating member is moved to a developing area opposed to the latent image carrier. in the developing apparatus for supplying, as the toner, 4.0 × ¹⁰ 5 saturation magnetization in a magnetic field of a / m is ^{1.25 × 10 -2 ~5.65 × 10 -} 2 a /
The carrier coverage of the developer carried on the developer carrying member regulated by the developer regulating member is set to 30 to 130% using a magnetic toner of m · g.

In this developing device, the saturation magnetization value is
1.25 × 10^-2~ 5.65 × 10 ^-2A / m · g
Contains a certain magnetic toner, and is used as the developer regulating member.
Carrier coverage in developer more regulated is 30 to 13
Development is performed using a 0% developer. This allows
Dirt can be reduced to a level that causes little
You. Details will be described later.

In particular, the invention according to claim 2 is characterized in that, in the developing device according to claim 1, the linear velocity ratio of the developer carrier to the latent image carrier is set to 1.5 or more. is there. When a magnetic toner is used, the toner has a larger toner binding force than a non-magnetic toner, so that the developing ability is lower than that of a non-magnetic toner. To solve this problem, for example, a method of increasing the developing bias to increase the developing ability can be considered. However, this method causes problems such as shortening the life of the latent image carrier and the like and making it impossible to save power. There is. Therefore, in claim 2, the developing capability is improved by using a method of increasing the developing capability by setting the linear speed ratio of the developer carrier to the latent image carrier to 1.5 or more.

[0016] The invention of claim 3 is the invention of claim 1 or 2.
Wherein the charge amount of the magnetic toner is 7 to 3
It is characterized by being 5 μC / g. When the carrier coverage of the developer used for development is high, the image may be affected by the amount of charge of the magnetic toner contained in the developer in some cases. Specifically, as the charge amount of the magnetic toner decreases, the problem due to background contamination increases,
Conversely, as the charge amount of the magnetic toner increases, the image density decreases. In particular, when the linear velocity ratio of the developer carrying member to the latent image carrying member is small, background stain is likely to occur. In view of this, in the present invention, the charge amount of the magnetic toner is set to 7 to 35 [mu] C / g, background smear is suppressed to a level that hardly causes a problem, and a decrease in image density is prevented.

According to a fourth aspect of the present invention, there is provided an image forming apparatus comprising: a latent image carrier for carrying a latent image; and a developing device for developing the latent image formed on the latent image carrier. Is the developing device according to claim 1, 2 or 3. In this image forming apparatus, by using the developing device described in each of the above-mentioned claims, it is possible to effectively reduce background contamination and prevent a decrease in image density.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) as an image forming apparatus will be described. First, the configuration and operation of the entire copying machine according to the present embodiment will be described. FIG.
1 is a schematic configuration diagram of a copying machine that performs development using a developer 3 including a magnetic toner and a magnetic carrier that is a magnetic particle.
This copier has a scanner unit 1 for reading image information of a document.
1 and an exposure device 12 for forming an electrostatic latent image on the photosensitive drum 1 as a latent image carrier based on image information read by the scanner unit. In the scanner unit 11,
The image information of the document placed on the contact glass 11a is read by the light receiving device 11b, and the image information is sent to the central processing unit 13. Based on the received image information, the central processing unit 13 includes a laser diode 12a and a polygon mirror 12b as light sources of the exposure device 12.
To form an electrostatic latent image on the photosensitive drum 1.

Around the photoreceptor drum 1, a charger 14 as a charging means for uniformly charging the surface of the photoreceptor drum, and a developer for transferring an electrostatic latent image formed on the photoreceptor drum to a developer. A developing device 10 for developing in step 3, a transfer device 15 for transferring a toner image developed and formed by the developing device to a transfer paper, and a cleaning device for cleaning the surface of the photosensitive drum after the transfer. A cleaning device 16 is provided.

In the copying machine having the above construction, the surface of the photosensitive drum 1 is uniformly charged by the charger 14 and the exposure device 12 controls the photosensitive drum 1 based on the image information of the original read by the scanner section 11. Light exposure is performed by irradiating the surface with a laser. As a result, an electrostatic latent image is formed on the photosensitive drum 1. Here, for example, when the present invention is applied to a printer, an electrostatic latent image is formed based on image information output means for outputting image information, for example, a personal computer.

The electrostatic latent image on the photosensitive drum 1 is developed by the developing device 10, and a toner image is formed on the photosensitive drum. After that, the toner image is transferred onto a transfer paper (not shown) by the transfer device 15.
In this way, the toner image transferred to the transfer sheet is fixed on the transfer sheet under the action of a fixing device (not shown). On the other hand, the transfer residual toner remaining on the photosensitive drum 1 at the time of this transfer is removed by the cleaning device 16, and the cleaned photosensitive drum 1 is subjected to the next image forming step.

Next, the configuration of the developing device 10 in the copying machine will be described. FIG. 2 is a partial cross-sectional view illustrating a schematic configuration of the developing device 10 according to the present embodiment. The developing device 10 is arranged on the side of the photosensitive drum 1. The developing device 10 includes a casing 2 having an opening toward the photosensitive drum 1, a developing sleeve 4 made of a non-magnetic material as a developer carrier partially exposed from the opening, A magnet roller 5 as a magnetic field generating means fixedly arranged inside the developing sleeve, a doctor 6 as a developer regulating member for regulating the amount of the developer carried on the developing sleeve, and the doctor stops the progress. And a toner hopper 8 serving as a toner storage section for storing a supply magnetic toner (hereinafter referred to as “supply toner”) 3a. Have.

The developer 3 in the developer accommodating portion is placed on the developing sleeve at a position facing the developer accommodating portion A of the magnet roller 5 fixedly disposed inside the developer sleeve 4. A magnetic pole 5a for carrying is provided.

The toner hopper 8 has a toner supply port 8a adjacent to the developer accommodating section A on the upstream side in the developer transport direction and facing the surface of the developing sleeve 4. In the space adjacent to the toner supply port 8a, there is arranged an agitator 9 as a toner stirring member for feeding the supply toner 3a contained in the toner hopper 8 while stirring it toward the toner supply port 8a. ing. As shown by a broken line in the figure, the position of the rotating shaft and the length of the fin of the agitator 9 are set so that the outermost track does not contact the developer.

Next, the operation of the developing device 10 in this embodiment will be described. In the developing device 10, the developer 3 accommodated in the developer accommodating portion A rotates with the rotation of the developing sleeve 4 rotating in the direction of arrow a in the drawing.
It is conveyed to the doctor 6 side. The developer 3 on the developing sleeve 4 conveyed in this manner is regulated and thinned by the doctor 6, and is conveyed to a developing area facing the photosensitive drum 1 rotating in the direction of arrow b in the drawing. In this developing area, the toner in the developer is supplied to the electrostatic latent image formed on the photosensitive drum 1 in a contact or non-contact manner, and the electrostatic latent image is visualized and developed.

After the development is performed as described above, the developer 3 on the developing sleeve 4 is conveyed to the toner supply port 8a side as the developing sleeve rotates. Then, the developer returns to the developer accommodating section A while taking in the supply toner 3a supplied from the toner supply port 8a.
The internal pressure of the developer 3 containing the replenishing toner 3a in the regulating section by the doctor 6 increases, and the toner in the developer is frictionally charged. As described above, the toner in the developer can be charged by the internal pressure of the developer 3 stored in the developer storage portion A. Therefore, a paddle or a screw for charging or stirring the developer is used. There is no need to provide a complicated stirring and conveying mechanism.

On the other hand, a part of the developer 3, which is not transported to the developing area and is prevented from proceeding by the doctor 6, is removed by the internal pressure and gravity of the developer itself in the developer accommodating section A. It moves toward the supply port 8a.
The developer 3 that has moved to the vicinity of the toner supply port 8a is drawn toward the developing sleeve 4 by the magnetic force of the magnetic pole 5a of the magnet roller 5, and is conveyed to the doctor 6 with the rotation of the developing sleeve. In this way,
The developer 3 whose progress is prevented by the doctor 6 circulates in the developer accommodating section A.

In the developing device of this embodiment, when the amount of the replenishing toner 3a supplied to the developer 3 increases and the toner concentration increases, the bulk of the developer increases accordingly. The toner overflows from inside the agent container A and closes the toner supply port 8a. As a result, the amount of toner taken up by the developer 3 is reduced, and the toner concentration of the developer is maintained at a certain concentration or less. Conversely, when the toner concentration of the developer 3 decreases, the bulk of the developer decreases and the toner supply port 8
a is not blocked. As a result, a predetermined amount of replenishing toner 3a is supplied to the developer 3 from the toner replenishing port, and the toner concentration of the developer is always maintained at a constant level.
As described above, in the present embodiment, since the toner concentration of the developer 3 is controlled within a substantially constant range, complicated toner concentration control using a toner concentration sensor, a supply member, or the like is not required.

Since the toner in the developer 3 is a magnetic toner, it is magnetized by a magnetic field generated by a magnet roller 5 provided inside the developing sleeve 4. When the toner in the developer 3 is magnetized, a magnetic bias effect is obtained, and problems such as toner scattering and background contamination can be reduced. Further, there is obtained such an advantage that the toner replenishing property is improved and the solid black followability is improved.

On the other hand, when the magnetic toner is used as described above, the toner binding force by the magnetic carrier also increases due to the magnetic bias effect of the magnetic toner. If the toner restraining force at this time is excessively increased, the toner attraction force due to the electrostatic latent image on the photosensitive drum 1 cannot overcome the toner restraining force in the developing area, and the developing capability is reduced to reduce the image density. May be lowered.

Therefore, in this embodiment, the content of the magnetic material is
20 × 50 wt%, 4.0 × 10 ⁵A / m (about 500
0 Oe) in a magnetic field of 1.25 × 10^-2
~ 5.65 × 10^-2A / m · g (about 10 to 45 em
u), and is regulated by the doctor 6 described above.
Carrier coverage when controlled is 30-130%
Development is performed using the developer 3. This makes the magnetic
By effectively utilizing the magnetic bias effect of the toner, the toner
Image with high image density while reducing scattering and dirt
Formation is possible.

Next, in the case where development is performed using the above magnetic toner, the conditions of the saturation magnetization value of the magnetic toner which can effectively prevent background contamination and prevent a decrease in image density can be prevented. The measurement performed to derive the carrier coverage of the magnetic toner will be described. First, the saturation magnetization value contained in the magnetic toner is changed by changing the amount of magnetic material contained in the magnetic toner used in the copying machine according to the present embodiment, and the image density of the image formed by the copying machine is changed. (Hereinafter referred to as “ID”) and the evaluation of background contamination was performed. The evaluation in this measurement is an evaluation when developing is performed using the above-described developing apparatus while the developing bias is set to 300 V in an environment of a temperature of 20 ° C. and a humidity of 60%.

The above ID was measured using a Macbeth densitometer. It is desirable that the value of this ID is 1.4 or more and at least 1.6 or less. If the ID value is within this range, a high-quality image with almost no problem can be obtained. In addition, the background dirt was evaluated by adopting a rank evaluation (1 is the lowest and 5 is the highest rank) determined from the background dirt determination criteria based on the research results of the applicant. In this criterion, the background dirt does not cause a problem in a normal image when the rank evaluation is 4 or more.

FIG. 3 is a graph showing the ID value and the background contamination evaluation when the amount of the magnetic material of the magnetic toner is changed. FIG. 4 is a graph showing the ID value and the background contamination evaluation when the saturation magnetization value changes in response to the change in the amount of the magnetic material. Considering the relationship between the magnetic material amount of the magnetic toner and the ID value based on FIG. 3, the magnetic material amount is about 40 wt%.
In the following cases, the ID is constant at approximately 1.45, and the ID sharply drops when the amount of the magnetic substance exceeds about 40 wt%. When the amount of the magnetic material becomes 50% by weight or more, the ID is less than 1.4. If the value is more than this, the image becomes thin and the image quality is deteriorated. As a result, it can be considered that an image having a desired ID can be obtained if the amount of the magnetic material in the magnetic toner is set to 50 wt% or less.

Considering the relationship between the amount of the magnetic substance of the magnetic toner and the background contamination, the amount of the magnetic substance is about 30 wt.
%, The background stain does not cause a problem in a normal image, and its evaluation is almost constant. When the amount of the magnetic substance is less than about 30 wt%, the evaluation of the background dirt sharply drops. When the amount of the magnetic substance becomes about 20 wt% or less, the evaluation of the background contamination is 4 or less. As a result, it can be considered that if the amount of the magnetic substance of the magnetic toner is set to 20 wt% or more, it is possible to obtain an image that does not cause a problem in the background image with respect to a normal image. As a result, by setting the amount of the magnetic substance of the magnetic toner in the range of 20 to 50 wt%, it is possible to prevent background contamination due to a small magnetic bias effect and to reduce image density due to an excessively large magnetic bias effect. The drop can be prevented.

On the other hand, as shown in FIG.
Saturation per unit weight of the magnetic toner corresponding to the range
The magnetization value is 4.0 × 10⁵1.25 × in a magnetic field of A / m
10 ^-2~ 5.65 × 10^-2A / m · g. Follow
And the saturation magnetization value is 4.0 × 10⁵1. In a magnetic field of A / m
25 × 10^-2~ 5.65 × 10^-2A / m · g
If development is performed using magnetic toner, the magnetic bias effect can be reduced.
Prevents background contamination due to small size and magnetic bias
Prevents reduction of image density due to excessive effect
be able to.

However, when the saturation magnetization value of the magnetic toner is changed by changing the amount of the magnetic material as described above, the specific gravity of the magnetic toner changes. When the specific gravity changes in this manner, even if the toner concentration of the developer containing the magnetic toner is the same, the state of the magnetic toner adsorbed on the magnetic carrier of the developer, that is, the carrier coverage of the magnetic toner Will be different. The carrier coverage also affects the background stain and ID of the formed image.

Then, next, the carrier coverage of the magnetic toner constituting the developer used in the copying machine according to the present embodiment is changed to measure the ID of the image formed by the copying machine and to remove the background stain. An evaluation was performed. This carrier coverage T
n can be calculated by the following equation (1).

[0039]

(Equation 1)

[0040] where the symbols C is the toner concentration in the developer (wt%), the symbol r is the toner particle diameter radius ([mu] m), the symbols R are the carrier particle diameter radius ([mu] m), the symbol [rho _t is the toner The true specific gravity (g / cm ³ ), ρ _c is the true specific gravity of the carrier (g
/ Cm ³ ). Note that, in the equation shown in Expression 1, it is necessary to satisfy a condition that the surface of the magnetic carrier can be regarded as a plane when viewed from the toner, that is, R >> r.

FIG. 5 is a graph showing the ID value and the background contamination evaluation when the carrier coverage is changed. FIG.
Considering the relationship between the carrier coverage and the ID based on the following equation, when the carrier coverage is about 30% or more, the ID is almost constant at 1.45, and the carrier coverage is less than about 30%. The ID sharply drops around. When the carrier coverage becomes smaller than 30%, the ID falls below 1.4, and at a value higher than this, the image becomes thin and the image quality deteriorates. As a result, if the carrier coverage of the magnetic toner constituting the developer is 30% or more,
It can be considered that an image having a desired ID can be obtained.

Considering the relationship between the carrier coverage and the background contamination, the carrier coverage is about 100%.
In the following cases, the background stain is not a problem in a normal image, and its evaluation is almost constant. When the carrier coverage exceeds about 100%, the evaluation of the background contamination sharply drops. When the carrier coverage exceeds 130%, the evaluation of the background contamination is 4 or less. As a result, if the carrier coverage of the magnetic toner is set to 130% or less, it is possible to obtain an image that does not cause a problem with a normal image regarding background contamination. As a result, by setting the carrier coverage of the magnetic toner in the range of 30 to 130%, it is possible to effectively prevent background contamination and prevent a decrease in image density.

As described above, the saturation magnetization value is 4.0 × 10 ⁵ A
/ M in a magnetic field of 1.25 × 10 ^{−2 to} 5.65 × 10
By using a magnetic toner of ⁻² A / m · g and setting the carrier coverage of the magnetic toner to 30% to 130%, it is possible to effectively prevent background contamination and prevent a decrease in image density. be able to.

By the way, in the developing device using the magnetic toner as described above, the toner binding force of the carrier is higher than that of the non-magnetic toner due to the magnetic bias effect between the magnetic toner and the magnetic carrier. When the toner constraining force is increased in this manner, a case may occur in which the toner suction force for adhering to the electrostatic latent image formed on the photosensitive drum 1 in the developing area cannot overcome the toner constraining force. It may lead to a decrease in performance.

As a method of preventing such a decrease in the developing ability, a method of increasing the developing bias by increasing the developing bias can be considered, but it is disadvantageous in terms of the life of the photosensitive member and power saving. Therefore, in the present embodiment, a method of increasing the developing speed by increasing the linear velocity ratio of the developing sleeve 4 to the photosensitive drum 1 is adopted.

Therefore, the above-mentioned photosensitive drum 1
By changing the linear velocity ratio of the developing sleeve 4 according to the present embodiment,
The ID of the image formed by the copying machine was measured. this
In the measurement, the saturation magnetization value was 1.25 × 10^-2A / m · g
And 5.65 × 10 ^-2A / m · g
ID of the image formed when using the magnetic toner of
Measurement. The conditions for this measurement were as follows.
It is the same as the measurement of ID for quantity.

FIG. 6 shows the photosensitive drum 1 described above.
Indicates the ID value when the linear velocity ratio of the developing sleeve 4 is changed.
This is a graph. In this figure, the ID value is the linear velocity
It increases as the ratio increases. In addition, the above saturation magnetization
The higher the value, the higher the toner binding force of the carrier.
5.65 ×, which is the maximum saturation magnetization value set in the embodiment
10^-2Developing ability is most likely to decrease when A / m · g
And the image density tends to decrease. Therefore, based on FIG.
Consider the relationship between the above linear velocity ratio and the ID value
And when the linear velocity ratio is 1.5 or more, the saturation magnetization value
Is 5.65 × 10 ^-2ID even in case of A / mg
Can be kept at 1.4 or more. As a result,
Setting the linear speed ratio to 1.5 or more will reduce the development capacity.
Can effectively prevent the image density from lowering.
You. In practice, the linear velocity ratio is set to 3.5 or less.
You.

When the carrier coverage is high and the linear velocity ratio of the developing sleeve 4 to the photosensitive drum 1 is small, the toner that forms background stains on the photosensitive drum is recovered by the scavenging force. The probability of occurrence is reduced, and soiling is likely to occur. Also,
Generally, when the charge amount of the toner is small, the background stain tends to occur, and when the charge amount of the toner is large, the image density tends to be insufficient.

Therefore, in this embodiment, the carrier coverage of the magnetic toner is set to 30 to 130% in order to further effectively prevent the occurrence of background contamination by setting the charge amount of the toner to an appropriate range. When it is within the range, the charge amount Q / M per unit weight of the magnetic toner is changed to measure the ID value of the image formed by the copying machine according to the present embodiment and to evaluate the background contamination. Was.

FIG. 7 shows the relationship between the charge amount Q / M of the magnetic toner of the developer used in the copying machine according to the present embodiment and the ID,
6 is a graph showing a relationship between the charge amount and background contamination. Considering the relationship between the charge amount Q / M of the magnetic toner and the ID value with reference to FIG. 7, when the charge amount is 35 μC / g or less, the ID is 1.4 regardless of the carrier coverage.
The above can be held. On the other hand, considering the relationship between the charge amount Q / M of the magnetic toner and the background stain evaluation, when the charge amount is 7 μC / g or more, the background stain evaluation becomes 4 or more regardless of the carrier coverage. As a result, when the charge amount Q / M of the magnetic toner is set in the range of 7 to 35 μC / g, background contamination can be effectively prevented and a decrease in image density can be prevented.

In the above measurement, the developing bias was set to 3
Although the case where the voltage is set to 00 V has been described, the same result can be obtained even when the developing bias is actually higher than that.

[0052]

According to the first to fourth aspects of the present invention, it is possible to reduce background scattering by reducing toner scattering and to prevent a decrease in image density caused by using a conventional magnetic toner. There is an excellent effect that it can be done.

In particular, according to the invention of claim 2, there is an excellent effect that a decrease in image density can be more effectively prevented.

Further, according to the third aspect of the present invention, there is an excellent effect that it is possible to reduce the scattering of the toner to eliminate the background stain and to prevent the image density from lowering.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an entire copying machine according to an embodiment.

FIG. 2 is a partial cross-sectional view illustrating a schematic configuration of a developing device of the copying machine.

FIG. 3 is a graph showing a relationship between a magnetic substance amount of a magnetic toner of a developer used in the copying machine and ID, and a relation between the magnetic substance amount and background contamination.

FIG. 4 is a graph showing the relationship between the saturation magnetization value of magnetic toner of the developer and ID, and the relationship between the saturation magnetization value and background contamination.

FIG. 5 is a graph showing a relationship between the carrier coverage of the developer and ID, and a relationship between the carrier coverage and background contamination.

FIG. 6 is a graph showing a relationship between a linear velocity ratio of a developing sleeve to a photosensitive drum of the copying machine and ID.

FIG. 7 is a graph showing a relationship between a charge amount of a magnetic toner of a developer used in the copying machine and an ID, and a relationship between the charge amount and a background stain.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor drum 2 casing 3 developer 3a replenishing toner 4 developing sleeve 5 magnet roller 5a magnetic pole 6 doctor 7 developer storage case 8 toner hopper 9 agitator 10 developing device 11 scanner unit 12 exposure device 13 central processing unit 14 charger 15 Transfer device 16 Cleaning device

Claims (4)

[Claims] A developer carrying member for carrying and transporting a developer containing a toner and a magnetic carrier; a magnetic field generating means disposed inside the developer carrying member; A developer regulating member for regulating the amount of developer carried and conveyed, a developer accommodating portion for accommodating the developer blocked by the developer regulating member, and a developer carrying member provided in the developer accommodating portion; A toner container having a toner replenishing port adjacent from the upstream side in the developer transport direction, and the developer blocked by the developer regulating member is supplied to the developer container by the internal pressure of the developer itself and its own weight in the developer container. The developer, which has been moved to the toner supply port side and has taken in the magnetic toner from the toner accommodating portion, is conveyed to the developer regulating member side along the surface of the developer carrier, and a predetermined amount is conveyed by the developer regulating member. On the developer carrier regulated to In the developing device supplies the image bearing member opposed to the developing region, as the toner, 4.0
The saturation magnetization value in a magnetic field of × 10 ⁵ A / m is 1.25 × 1
Using a magnetic toner of 0 ^{-2 to} 5.65 x 10 ^-2 A / m · g, the carrier coverage in the developer carried on the developer carrier regulated by the developer regulating member is 30 to
A developing device characterized in that the ratio is 130%. 2. A developing device according to claim 1, wherein a linear velocity ratio of said developer carrier to said latent image carrier is set to 1.5 or more. 3. The developing device according to claim 1, wherein the charge amount of said magnetic toner is 7 to 35 μC / g. 4. An image forming apparatus comprising: a latent image carrier for carrying a latent image; and a developing device for developing a latent image formed on the latent image carrier. An image forming apparatus, comprising: the developing device according to any one of (2) and (3).