JPH0424650A - Two-component developer and method for managing developer - Google Patents

Abstract

PURPOSE:To obtain a desired separating power even if any developers are used regardless of sp. gr. and shapes by allowing the use with various developing means and specifying the coverage indicating the ratio at which toners covers the surfaces of carriers at the value larger than a prescribed value. CONSTITUTION:The carriers and toners are agitated and electrified by a bucket roller 74. The developers supplied by respective buckets 74a to the lower part of a developing sleeve 71 are transported in an arrow (d) direction on the outer peripheral surface of the developing sleeve 71. Electrostatic latent images are developed when the developers pass a developing region A. The mixing ratio of the two-component developers is regulated not by weight % of the toners based on the weight of the carriers but by the coverage indicating the ratio at which the toners covers the surfaces of the carriers so that the coverage attains the prescribed value or above. The contact probability of the toners and carriers incorporated into the developers is equaled in this way if the coverage is equal even in the case of various kind of the developers. The developers with which the desired separating power is obtainable are thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-component developer used in a multicolor image forming apparatus that simultaneously forms a multicolor image using a plurality of colors, and a method for managing the same.
In particular, the present invention relates to a developer and a method for managing the developer that improves the ability to separate mixed colors during development.

[Conventional technology]

For example, black and red (color) as a two-color image forming device
The simultaneous two-color copying machine reads black and red images with a light-receiving element, and exposes two different locations on the photoreceptor drum in the circumferential direction with laser light of two different wavelengths modulated accordingly. ,
A latent image of each color image is formed. Here, in order to improve the visibility of the image, the exposure position of each color is normally charged and exposed on the upstream side of the black image in the rotational direction, and developed in the first developing device containing red toner. . Further, after the red color is developed, black color is recharged and exposed, and then developed in a second developer containing black toner.

Therefore, the red toner is scraped by the developer in the second developing device and mixed into the second developing device, and during black development, an image that is originally black becomes an image that is a mixture of black and red. There is. As a conventional color mixture separation technique for preventing this, the one disclosed in Japanese Patent Application Laid-Open No. 72158/1983 is known.

A two-component developer consisting of red toner and carrier is stored in a first developing device located upstream of the photoreceptor drum.
A two-component developer consisting of black toner and carrier is stored in a second developing device located on the downstream side. The red toner and black toner used here are non-magnetic, and when the red toner is mixed into the second developing device containing the black toner, it has the property of being charged to opposite polarities due to frictional charging. have different physical properties. The red toner having such characteristics and mixed into the second developing device adheres to the non-image area (charged area) of the photosensitive drum during development by the second developing device, and is removed from the second developing device. Since the adhered red toner has the same polarity as the applied voltage of the transfer charge 10, it is not transferred to the paper, but remains adhered to the photoreceptor, and is scraped off and collected by a cleaner. In this way, color mixture separation is automatically performed during development.

In the case of color toners that are charged to opposite polarities when mixed, the separation ability is determined by the physical property difference between the color toner and black toner described above, that is, the difference in the charging series, as well as the mixing ratio of the carrier of the second developer and the black toner, For example, the ratio of toner to carrier (
It depends on the toner concentration Tc (% by weight), the stirring time of the second developer, and the strength of stirring. FIG. 5 is a graph showing an example of the relationship between the mixing ratio and the separation ability, in which the horizontal axis represents the toner concentration T as the mixing ratio, and the vertical axis represents the separation ability. At this time, the toner diameter is 12 μm and the carrier diameter is 36 μm.
m, toner specific gravity 1.15, and carrier specific gravity 2.30. As is clear from Figure 5, the higher the toner concentration, the higher the separation ability; conversely, when the toner concentration is 3%
If it is less than that, there will be no separation ability.

This is because when the toner concentration is low, not much black toner adheres around the carrier, and the mixed color toner comes into contact with the carrier rather than the black toner, and the color toner is charged to the same polarity as the black toner, resulting in a difference in physical properties. It is thought that this decreases the separation ability.

Similarly, as the stirring time increases, the probability of contact with carriers increases and the separation ability decreases. Therefore, in order to maintain separation ability, it is necessary to always maintain the mixing ratio above a certain level.

[Problem to be solved by the invention]

However, the probability of contact between toner and carrier varies depending on the particle size of the toner and carrier, and in reality, even if the toner concentration is the same, the separation ability will differ depending on the specific gravity and shape of the toner and carrier used. Therefore, it has been difficult to determine and maintain the separation ability of various developers based on the mixing ratio expressed in weight percent.

The present invention has been made based on this knowledge, and by specifying the mixing ratio of toner and carrier not by toner concentration but by coverage ratio, it is possible to use any desired material regardless of specific gravity and shape. An object of the present invention is to provide a developer and a method for managing the developer that can obtain the separation ability of .

[Means to solve the problem]

The two-component developer according to the present invention is used in a multicolor image forming apparatus that obtains images of multiple colors using a plurality of developing means arranged at different positions in the rotational direction around a rotating photoreceptor.
In a developer having two components: toner and carrier,
The developer management method is characterized in that the toner is used in each developing means and has a coverage rate larger than a predetermined value, which indicates the ratio at which the toner covers the surface of the carrier. It is housed in a plurality of developing means arranged at different positions in different directions, and has toner and carrier,
In a developer management method for controlling the mixing ratio of the carrier and toner of two-component developers having different colors and physical properties, a coating indicating the ratio of toner covering the surface of the carrier of the developer stored in each developing means. The method is characterized in that the ratio is maintained at a value larger than a predetermined value.

[Effect]

In the two-component developer of the present invention, the mixing ratio of the two-component developer is not defined by the weight percent of the toner with respect to the carrier, but by the coverage ratio indicating the ratio of the toner covering the surface of the carrier, and the coverage ratio is not less than a predetermined value. This is how it should be. As a result, even if various developers are used, if the coverage ratio is the same, the probability of contact between the mixed toner and the carrier can be made equal, and the desired separation ability can be obtained.

Further, in the developer management method of the present invention, since the developer is managed to maintain a predetermined coverage rate, the separation ability can always be maintained at a constant level.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on drawings showing embodiments thereof.

FIG. 1 is a sectional view showing a schematic configuration of a two-color laser beam printer, which is a two-color image forming apparatus using a two-component developer and a method for managing the developer according to the present invention, together with a block configuration of a control system.

In the figure, 1 is a photoreceptor drum, and the surface has a-
A photoconductive film such as 5i is formed. The photosensitive drum 1 is installed so as to be rotatable in the direction of arrow a, and a first charging charger 2, a first optical system 3, a first developing unit 4, and a second charging unit are arranged around the photosensitive drum 1 in order along the direction of rotation. A charger 5, a second optical system 6, a second developer 7, an eraser lamp 8, a transfer charger 9, a blade-type cleaning device 10, and a main eraser lamp 11 are installed.

1st. The second charger 2.5 uniformly applies a constant charge (positive polarity in this embodiment) to the surface of the photoreceptor drum 1 by its corona discharge.

1st. The second optical systems 3 and 6 are connected to the first optical system. Second driver circuit 32
．． 62, the first. This is for forming a predetermined image as a negative electrostatic latent image on the surface of the photoreceptor drum 1 using laser light from the second laser diode (hereinafter referred to as LD) 3L61. Each driver circuit 32.62 is controlled by the image control section 22 described below. For example, the first optical system 3 creates ruled lines as an image, and the second
Depending on the optical system 6, predetermined characters printed within the ruled lines are created as an image.

1st. The second developing devices 4 and 7 are of a magnetic brush type and include a developing sleeve 41 containing a magnetic roller. The first developer 4 contains a first developer made of a mixture of insulating color toner (for example, red toner) and small-diameter magnetic carrier, and the second developer 7 contains an insulating developer with a diameter of 12 μm. A second developer consisting of a mixture of black toner and a magnetic carrier having a diameter of 36 μm is contained therein. Further, the color toner is located in a more negative direction than the black toner on the triboelectric charging array, and when the color toner mixes into the second developing device 7, it comes into contact with the black toner and is triboelectrically charged to a negative polarity. This charging characteristic is opposite in polarity to the charging characteristic (positive polarity) of the photoreceptor drum 1. Further, in this embodiment, each toner is triboelectrically charged to a positive polarity, and the carrier is triboelectrically charged to a negative polarity.

Here, the mixing ratio (toner concentration) of the second developer is 3 in terms of weight ratio.
% or more, and in this example, 6%
I try to replenish toner when the amount falls below.

When the mixing ratio is expressed in terms of toner concentration (% by weight), the separation ability changes depending on the properties of the toner and carrier, as described above. Therefore, in the present invention, the mixing ratio is considered from the viewpoint of the probability of contact between the toner and the carrier, and the mixing ratio is expressed by the coverage ratio.

The coverage C is defined by the following equation (1).

N' C= xloo...(1) However, N: Limit number of toners (number of toners that cover the surface of one carrier without any gaps) N': Actual number of toners (number of toners that actually cover the surface of one carrier) (number of toners) Here, in the case of plane approximation, the limit number of toners N is expressed by the following equation (2) as shown in Journal of Electrophotography, Vol. 25, No. 4 (1986), p. 270.

r: toner radius R: carrier radius

That is, in the above case, if the periphery of one carrier is covered with toner without any gaps, a total of 57 pieces of black toner will cover the carrier.

On the other hand, the toner concentration Tc is mc + mt mc: Toner weight mt: carrier weight It is indicated by.

Therefore, when the toner concentration is 3%, The relationship between and carrier weight mc is Toner weight mt C Wt becomes.

Here, the weight WLwc of each toner and carrier is the true specific gravity of black toner ρt=1.15, true specific gravity of carrier ρ
. = 2.30, Wt = πr3 ・ ρ, ...
(5) wc = πR3・ρ. ...
(6) Also, the actual number of toners per carrier N'
becomes c Wt C .

Therefore, toner concentration Tc The actual number of toner N' is When is 3%, equation (7) w　　　　　　m　C 97r3 ρt =1.67 becomes.

Substituting this and the result of equation (2) into equation (1), when the toner concentration TC of the second developer is 3%, the coverage C is 3%, that is, the coverage is 2.89% or less. In this case, the probability of contact between the mixed color toner and the carrier increases, and the second
Since the separation ability of the developer decreases as shown in FIG. 5, it is sufficient for the developer of the present invention to have a coverage ratio C of greater than 2.89%.

However, this is a value obtained by determining the limit number N of toners by a planar approximation, and if this is made into a three-dimensional approximation as described on page 270 of the above-mentioned academic journal, this value will change slightly.

On the other hand, the first. As the second developing device 4.7, multiple developing devices of the same type are prepared, each containing a developer containing various toners with different tones, and it is possible to form a two-color image using any combination of colors. In order to do so, it is said to be replaceable.

Next, the structure and general operation of the developing device will be explained using the second developing device 7 as an example.

FIG. 2 is a sectional view of a main part showing the structure of the second developing device 7. As shown in FIG.

As shown in FIG. 2, the second developing device 7 has an N pole and an S pole in the circumferential direction.
A magnetic roller 72 whose poles are sequentially magnetized is built into the developing sleeve 71, and a scraper 73 is provided on the outer peripheral surface of the developing sleeve 71.
The tips of a and 73b are pressed together.

Further, a bucket roller 74 including a bucket 74a is provided near the developing sleeve so as to be rotatable in the direction of arrow e.
Furthermore, a developer guide plate 75 is located close to the developing sleeve 71.
, a carrier collection roller 76, and a duct 79 are provided.

The carrier recovery roller 76 rotatably accommodates a magnetic roller 77 therein, and the tip of a scraper 78 is pressed against its outer peripheral surface. Further, a dust collector equipped with a suction fan (not shown) is connected to the duct 79.

The developing sleeve 71 and the magnetic roller 72 are driven to rotate in the direction of the arrow C, and the developer receives a conveying force in the direction of the arrow C by the rotation of the developing sleeve 710, and is transferred in the direction of the arrow d by the rotation of the magnetic roller 72. Upon receiving the conveying force, the developing sleeve 71 is conveyed in the direction of arrow d on the outer peripheral surface due to the difference in the re-conveying force.

That is, the carrier and toner are agitated and charged by the packet roller 74, and the developer supplied to the lower part of the developing sleeve 71 by each brush 74a moves the outer peripheral surface of the developing sleeve 71 in the direction of arrow d as described above. transported to. When the developer passes through the development area A, it develops the second electrostatic latent image formed by the second optical system 6, and is then scraped off by the scraper 73a. Further, as the developing sleeve 71 rotates in the direction of arrow C, the developer transported in the same direction is transferred to the scraper 73b.
It will be scraped off.

On the other hand, the carrier attached to the surface of the photosensitive drum 1 is captured by the outer peripheral surface of the carrier recovery roller 76 by the magnetic force of a magnetic roller 77 rotatably provided in the carrier recovery roller 76, and the magnetic roller 77 is used for developing. The magnetic roller 72 in the sleeve 71 is rotated synchronously in the direction of the arrow f by the magnetic force, thereby being transported on the outer peripheral surface of the carrier recovery roller 76 in the direction of the arrow g, and is scraped off by the scraper 78 .

Next, the image control section 22 will be explained with reference to FIG.

This image control section 22 is connected to the first image control section 22. Second driver circuit 32
．． 62 to generate a desired image signal, and also to generate a signal for creating a reference image for toner supply control. It also includes image selection means 20 that gives priority to the second image when there is an overlap between the first image and the second image.

That is, CPLI21 using a microcomputer
The first stroke sample number M1 outputted from the reading circuit 23a and the second stroke sample number M2 outputted from the reading circuit 23b are read, respectively.
When the image selection means 20 inputs an image priority signal (operated by the operator) that gives priority to the second image, both image signals M+2M2 are compared in the comparison circuit 24, and only the signal M of the overlapping portion is input. ' is inputted to the erasing circuit 26 via the memory circuit 25, where the overlap point signal M' is erased from the first stroke sample number M1, and the signal is inputted to the memory circuit 26.
7a.

Further, the second image sample number M2 is stored as it is in the storage circuit 27b. The image signals in the memory circuits 27a and 27b are read by driver circuits 32 and 62, and converted into laser light signals by operating the first and second LDs 31.61. Here, a first don't counter 50 for detecting the light emission time of the first LD 31 is interposed between the first driver circuit 32 and the memory circuit 27a, so that the consumption amount of color toner can be detected. The first dot counter 50 counts the light emission time of the first LD 31 per a certain period of time, that is, the number of dots in a certain period of time.
Given to PU 21.

Further, the converted laser light signal is scanned on the surface of the photoreceptor drum 1 in the axial direction (main scanning direction) to form a negative electrostatic latent image. Incidentally, a sensor 33 is installed at the scan start end of the first optical system 3 with respect to the photoreceptor drum 1. This sensor 33 is for instructing the driver circuit 32.62 to start reading an image, and outputs this instruction signal when laser light is incident on the sensor 33. A delay circuit 28 is interposed with respect to the second driver circuit 62, and reading of the second image sample number is started after a certain period of time from the instruction signal from the sensor 33. here,
The fixed time is the time required for the image formation start point of the photoreceptor drum l to reach the second exposure position from the first exposure position.

On the other hand, when the image selection means 20 does not issue an image priority signal, the first image sample number M is stored as it is in the storage circuit 27a without passing through the comparison circuit 24.

The reference image pattern circuit 29 stores a reference image pattern for toner replenishment control, and controls the first and second driver circuits 32 and 62 to change the image on the photoreceptor drum 1 for each image formation. First, reference latent images for controlling the toner of the first developer and those for controlling the toner of the second developer are formed at one end separated from the forming section with their positions shifted in the rotational direction. This reference latent image is applied to the first and second developing devices 4.
At step 7, the image is reversely developed under the same conditions as the image, and transferred together with the image onto the transfer paper 16. Immediately after the transfer, one density detection sensor 18 detects the density at a certain timing.

The density detection sensor 18 is an optical type consisting of a light emitting element and a light receiving element, and detects the amount of toner adhering to the reference image as a reflection density. The detected value here is the toner replenishment control circuit 19.
The toner density Te (weight %) in the developer in each of the developing units 4 and 7 is compared with the reference reflection density when it is at a set value (for example, 6%).

When the detected reflection density is lower than the reference reflection density, a toner replenishment signal is issued, and the first and second toner replenishment means 4
2.43 is activated to replenish a predetermined amount of toner into the developer in the first and second developing devices 4 and 7. As a result, the coverage is always maintained at a predetermined value (2,89%) or higher, and the separation ability does not decrease.

Note that when the properties of the developer change, the toner concentration to be controlled changes. For example, when the specific gravity of the carrier and toner is the same as that described above, the toner particle size is 16 μm, and the carrier particle size is 36 μm, the toner concentration T that maintains the coverage rate of 2.89% is (1) ~ From formula (8), N=38.8,
N'=1.12, and Tc=4.2%. Therefore, if the toner concentration is maintained at 6%, a predetermined separation ability can be obtained even with such a developer.

FIG. 3 is a block diagram showing a schematic configuration of the CPLI 21, in which the first L dots counted by the first dot counter 50
The light emitting time of D31 is given to the comparing section 210 in the CPU 21, where the light emitting time of the first LD31 and a predetermined value are compared. A signal of the comparison result is given to the separation control section 211, and when the light emission time of the first LD 31 is longer than a predetermined value, a separation signal indicating this is given to the drive control section 212 in order to shift to a separation mode to be described later. The drive control unit 212 controls the drive of the photoconductor drum 1 and various devices around it, and upon receiving a separation signal, controls the photoconductor drum motor,
1st. The second chargers 5 and 9 and the second developing device 7 are turned on and off.

Further, the CPU 21 receives a control signal and an image signal sent from a host computer (not shown), processes the control signal, sends it to the drive control section 212, processes the image signal, and sends it to the first drive control section 212.
．． Output the second image sample number M+2Mz.

Next, the image forming operation will be explained. FIG. 4 is a diagram illustrating the image forming operation, in which the photosensitive drum 1 is rotated at a constant speed in the direction of arrow a, and first, the first charging charger 2 performs a first charging. The surface of the photosensitive drum 1 is charged to a potential of Vo. continue,
A first exposure is performed in the first optical system 3, and the potential of the image area is reduced to approximately 0.times., forming a negative electrostatic latent image of the image, such as a ruled line. Then, in the first developing device 4, the first
The image is developed. During this development, V is applied to the developing sleeve 41.
This is reversal development, which is performed while applying the developing bias b, in which the positively charged color toner TC adheres to the image area (charge erased area).

Next, second charging is performed in the second charging charger 5,
The surface of the photoreceptor drum 1 is almost ■. is returned to the potential of Subsequently, a second exposure is performed in the second optical system 6, and the potential of the image area is reduced to approximately OV, forming a negative electrostatic latent image of an image such as a character within a ruled line. Then, the second developing device 7 performs second development. This development is performed while applying a development bias of Vb to the development three 771,
This is a reversal development in which positively charged black toner TB adheres to the image area (charge erased area), and a second image is formed overlapping the first image.

At this time, the color toner TC mixed in the second developing device 7 comes into contact with the black toner TB and is frictionally charged to a negative polarity. This charging polarity is the opposite polarity (negative polarity) to the charging polarity (positive polarity) of the surface of the photoreceptor drum 1, so that the color toner TC that is negatively charged has a charging potential of
. Since the transfer charger has the same polarity (negative polarity), it is removed from the surface of the photoreceptor drum 1 by the cleaning device 10 without being transferred to the transfer paper 16.

However, when the toner concentration Tc becomes 3% or less, the probability of contact between the color toner TC and the carrier increases, and the color toner TC contacts the carrier instead of the black toner TB.
It will be charged to the same polarity as the black toner TB. Therefore, the above-described toner replenishment operation is performed when a toner concentration of 6% is detected.

On the other hand, the transfer paper 16 is conveyed as a continuous paper in the direction of the arrow on the path shown by the dashed line in FIG.
The toner TC is discharged with negative polarity.

After TB is transferred, the toners TC and TB are melted and fixed by a fixing device (not shown). This completes the printing operation.

Note that the charge on the photosensitive drum 1 is erased by an eraser lamp 8 immediately before the transfer process.

The photosensitive drum 1 continues to rotate in the direction of arrow a even after the transfer, residual toner is removed by a cleaning device 10, and residual charge is erased by a main eraser lamp 11.

On the other hand, a portion of the color toner mixed into the second developing device 7 may not be charged but may be neutralized by contact with the carrier. The color toner whose charge amount has been neutralized to almost zero in this way tends to become dusty smoke, and becomes dusty smoke in the area B on the upstream side in the developer conveyance direction to the development area. This toner powder smoke is collected and removed through a duct 79 in the second developing device 7, which is maintained at negative pressure by a suction fan.

Note that in this example, a toner concentration of 3% results in a coverage rate of 2.89%.
A developer was used, but this is just an example; the toner concentration that gives a coverage rate of 2.89% was calculated based on the properties of the toner and carrier. Needless to say, it can be used as an inventive developer.

〔effect〕

As explained above, since the two-component developer of the present invention has a coverage rate larger than a predetermined value, the probability of contact between the mixed toner and the carrier is suppressed, and the toner mixed into the second developing means comes into contact with the stored toner. The separation ability is maintained at the required level by being charged to the opposite polarity. In addition, in the developer management method of the present invention, the mixing ratio of toner and carrier in the two-component developer is managed so that the coverage is equal to or higher than a predetermined value, so that separation ability is similarly maintained, and this method Accordingly, an equivalent effect can be achieved in which image formation with less color mixture can be performed during multicolor image formation.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a schematic configuration of a two-color laser beam printer, which is a multicolor image forming apparatus using a two-component developer and developer management method according to the present invention, together with a block configuration of a control system. A sectional view of main parts showing the structure of the second developing device, the third
FIG. 4 is a block diagram showing the configuration of the CPU, FIG. 4 is a diagram showing the image forming operation, and FIG. 5 is a graph showing the relationship between separation ability and mixing ratio. ■...Photosensitive drum 4...First developer 7...
Second developing device 19... Toner replenishment control circuit 43...
・Second developer toner supply means TB...black toner T
C...Color toner patent Applicant: Minolta Camera Co., Ltd. Agent Patent attorney: Noboru Kono Fire brother diagram 1st charge v 2nd charge diagram Figure

Claims (1)

[Scope of Claims] 1. Toner and carrier used in a multicolor image forming apparatus that obtains images of multiple colors using a plurality of developing means arranged at different positions in the rotational direction around a rotating photoreceptor. A two-component developer, characterized in that the developer is used in each developing means and has a coverage ratio indicating a ratio of the toner covering the surface of the carrier that is larger than a predetermined value. 2. A two-component developer that is housed in a plurality of developing means disposed at different positions in the rotational direction around a rotating photoconductor and has a toner and a carrier, each having a different color and physical properties; A developer management method for managing a mixing ratio of a developer, characterized in that a coverage ratio indicating a ratio of toner covering the surface of a carrier of a developer stored in each developing means is maintained at a value greater than a predetermined value. Management method.