JP2712039B2 - Developing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a developing device used in an apparatus for forming an image by electrophotography, and more particularly to a developing device capable of controlling the toner concentration of a two-component developer.

2. Description of the Related Art In a developing apparatus using a two-component developer composed of a mixture of magnetic particles and toner particles, toner particles in the developer are consumed every time a developing operation is performed, and magnetic particles (ie, carriers) are consumed. Remain, the toner concentration in the developer decreases with each development operation. Therefore, in order to always maintain the toner concentration in the developer at a constant value, the toner concentration of the developer being used in the developing device must always be accurately detected, and toner must be supplied in accordance with the detection result. No.

For this reason, conventionally, for example, a developing device as shown in FIG. 6 has been devised as a developing device capable of detecting the toner concentration of the developer in use.

The developing device shown in FIG. 6 uses the method for detecting the developer concentration disclosed in Japanese Patent Application Laid-Open No. 53-107853. In the this device, the sensor 1 for toner density detection in the interior of the developer container 100 in which the developer D ₁ of the two-component system are accommodated
01 is provided to drive the screw feeder 103 of the toner replenishing tank 102 based on a signal obtained by the sensor 101, and supplies the toner T _1, the developer D ₁ to be attached to the photosensitive drum 111 Adjust the density. That is, as shown in the figure, a sensor 101 disposed near a developing sleeve 104 as a developer carrier has a light emitting element 105 and a light receiving element 106, and is adsorbed on the developing sleeve 104 and immediately below the sensor 101. Irradiate the developer D ₁ on the developing sleeve 104 moving to the light generated from the light emitting element 105 through the transparent glass window 107,
The light reflected by the attached developer on the developing sleeve 104 is incident on the light receiving element 106 via the infrared transmission filter 108.

The light receiving element 106 converts the incident light into an electric signal, compares the electric signal with a reference value in a differential amplifier 109, amplifies the difference, and amplifies the difference.
The motor 110 that drives the motor 3 is controlled.

(Problems to be Solved by the Invention) Incidentally, in the case of such a conventional example, in order to always accurately detect the toner concentration, it is necessary that the developer does not adhere to the detection unit of the means for detecting the toner concentration. .

Therefore, in the apparatus shown in FIG. 6, a transparent glass window 107 of the sensor 101 arranged close to the developing sleeve 104, a transparent glass window in ears D ₁₀ of the developer D ₁ formed on the sleeve 104 by rubbing the 107, and to prevent the adhesion of the developer D ₁ of the to the glass window 107 surface.

However, on the developing sleeve 104 to generate at all times a fixed position the bristles D ₁₀ is very difficult, the magnetic particles of the developer D ₁ made of a conductive material such as iron oxide powder, in recent years because are subjected to resin coating to improve durability, charging can occur on the developer D transparent glass window 107 resistance is high in _1,
In such a conventional example, the developer D _{1 is} applied to the glass surface 107a of the transparent glass window 107 because the glass contact angle of the transparent glass window 107 itself is small, so that the substance easily adheres to the glass surface 107. However, there is a drawback that the toner is liable to adhere, and high-accuracy concentration detection cannot be performed.

Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and an object of the present invention is to prevent the developer from adhering to the means for detecting the toner concentration and to always obtain an accurate developer. An object of the present invention is to provide a developing device capable of detecting density.

(Means for Solving the Problems) In order to achieve the above object, according to the present invention, there is provided a developer container containing a developer having toner particles and magnetic particles, and a developer container carrying the developer. A developing device having a developer carrier to be carried out and a detection window for optically detecting a toner concentration rubbed by the developer, wherein a negatively charged polarity of the toner particles of the developer is reduced; The detection window is coated with a fluororesin, and the surface of the detection window is negatively charged by friction with the developer.

(Operation) In the present invention having the above configuration, the developer is carried out of the container by the developer carrier. In this case, the developer is
It has toner particles with negative charge polarity and polar particles with positive charge polarity, and the surface of the detection window that comes in contact with the developer is coated with fluororesin, so that the rubbing received from the developer The force decreases and becomes negatively charged. Therefore, the detection window provided for detecting the toner density is unlikely to cause slidable charging, and the polarity when charged is negative, so that the developer is prevented from adhering to the surface.

(Embodiment) An embodiment of the developing device of the present invention will be described below with reference to FIGS.

In FIG. 1, 1 is a photosensitive drum as an image carrier that rotates in the direction of arrow A, 2 is a magnet roller, 3 is a developing sleeve as a developer carrier that rotates in the direction of arrow B,
Reference numeral 4 denotes a developer container containing a developer D composed of toner T and magnetic particles coated with a resin, 5 denotes a developer agitator, 6 denotes a toner replenishing tank, 7 denotes a screw feeder for replenishing the toner T, and 8 denotes a screw feeder. A drive motor 9 for the screw feeder, a blade 9 as a regulating member for controlling the layer thickness of the developer D adsorbed on the developing sleeve 3, and a bias 10 for applying a developing bias voltage to the developing sleeve 3 A power supply, 90 is a detection window formed on the wall of the blade 9 and fitted with glass 91 as a transparent member, and 11 is a detection window.
One surface of 90 glass 91 (surface not in contact with developer D)
A toner concentration detector (toner concentration detecting means) for the developer D, which is installed facing the surface, amplifies the difference between the output signal of the toner concentration detector 11 and a reference value to generate a control signal for the motor 8. Control circuit.

Further, a coating film 91a made of a fluororesin described later is formed on a surface of the glass 91 on the inner side of the developer container 4 (a surface in contact with the developer).

As shown in FIG. 2, the toner concentration detector 11 includes a light emitting element 11b, a light receiving element 11c, a light receiving element 11d for generating a reference signal, slits 11e and 11f, etc., inside a detector body 11a. The front opening of the body 11a is the blade 9
The body 11a is aligned with the blade 9 so that
It is detachably attached to.

In FIG. 1, a portion of the developing device excluding the photosensitive drum 1 is included.

In the above configuration, the developing sleeve 3 is
When the developer D in the developer container 4 is attracted to the developing sleeve 3 by the magnetic field of the developing sleeve 3 while being rotated by the magnetic field of the developing sleeve 3 in synchronization with the rotation of after raising the developer container 4 in the direction of P _1, a lower end and the amount of the developer D only vessel 4 outside equal to the layer thickness of which is determined by the gap between the outer peripheral surface of the developing sleeve 3 of the blade 9 And is supplied to the outer peripheral surface of the photosensitive drum 1.

On the other hand, the developer D blocked by the blade 9
And rubs the surface of the coating film 91a of the glass 91 while rising along the inner wall surface of the blade 9 to the arrow P ₂ direction is inverted downward to thereafter arrow P ₃ at shown as the developer container 4.

As the fluororesin, for example, PFA (trade name, ethylene tetrafluoride-perfluorovinyl ether copolymer)
After coating this PFA on the glass 91 of the detection window 90, the coating film 91 is baked at a high temperature.
a is formed. Here, the thickness of this glass 91 is 0.6 mm
The thickness of the coating film 91a is 6 μm.

In this embodiment, as shown in FIG. 1, a detection window 90 is provided in a blade 9 extending in a direction intersecting the circumferential direction of the surface of the developing sleeve 3, particularly in an axial direction of the sleeve 3, and is further fitted into the window 90. Since the coating film 91a made of fluororesin is formed on the surface of the glass 91 in contact with the developer D, compared with the conventional example in which the detection surface of the toner concentration detector faces the development sleeve, the developer D on the surface of the coating film 91a is reduced. Has a small rubbing force, and as a result, rubbing charging on the surface of the glass 91 is unlikely to occur. The rubbing force is large at the lower portion of the blade 9 and small at the upper portion due to the pushing force of the developer D, but the overall rubbing force is much smaller than that of the conventional example, and forms the coating film 91a. Since the fluororesin has good releasability, the adhesion of the developer D to the glass 91 is prevented.

By the way, the present applicant formed an image from the initial stage up to 100,000 sheets using the developing apparatus having the above-mentioned configuration, and measured a triboelectric charging state on the surface of the glass 91 during the image formation.

This measuring method is to measure the surface potential of the coating film 91a by grounding the entire back surface of the PFA coating film 91a of the glass 91 with a conductive tape or the like.

In the above measurement, the potential due to the triboelectric charging became substantially constant near -40 V as shown in FIG. In the present embodiment, as the polarity of the developer D, the toner T is minus,
The carrier is configured to be positive. When the charge potential of the coating film 91a increases as shown in FIG. 3, the carrier adheres to the surface. Note that there is a correlation between the charging potential and the film thickness of the coating film 91a, but when a limit value of the film thickness of the coating film 91a was examined, when the film thickness of the coating film 91a was 60 μm or more, the charging potential was −100 V.
As described above, it has been confirmed that when the polarity of the toner T is negative, carrier adhesion occurs and causes a problem. Further, it was confirmed that when the polarity of the toner T was positive, toner adhesion occurred and became a problem.

Now, when detecting the toner concentration of the developer D, the developer D rising along the detection window 90 is irradiated with infrared light or the like from the light emitting element 11b through the detection window 90, and this infrared light is After being reflected by the developer D, the reflected light is converted into an electric signal by the light receiving element 11c. On the other hand, the light emitted backward from the light emitting element 11b enters the reference signal generating light receiving element 11d through the slit 11f, and is converted into an electric signal by the light receiving element 11d.

The electric signal generated from the light receiving element 11c and the electric signal generated from the reference signal generating light receiving element 11d are input to a control circuit 12, where the difference between the two input signals is amplified and used as a control signal for the motor 8. Output from the control circuit 12.
Therefore, if the reflected light from the developer D reaches the light receiving element 11d correctly, the toner concentration can be detected with high accuracy and always stably, and the toner concentration of the developer D in the developer container 4 can be always set to a predetermined value. Can be held.

FIG. 4 shows a difference signal between the electric signal generated from the light receiving element 11c and the electric signal generated from the light receiving element 11d in this embodiment. In this embodiment, the difference signal is set to 0 V when the initial toner concentration of the developer D is 6%.

Thus, in the same figure, the difference increases as the toner density increases, while the difference signal decreases as the toner density decreases. As a result, the toner density and the voltage of the difference signal change abnormally. It is understood that there is no proportionality. That is, according to the developing device of the present invention, the glass of the detection window 90
The developer D does not adhere to the surface of the coating film 91a of 91,
It has been proved that accurate toner concentration detection can always be performed.

FIG. 5 shows another embodiment of the developing device according to the present invention, which is a type in which development is performed upward. In the present embodiment, the same reference numerals are given to the same parts as in the above embodiment. In this embodiment, a developing sleeve 3 having a magnet roller 2 is provided above a developer container 4. Is rotated in the direction of arrow B, thereby performing the same development as in the above embodiment. The blade 9 for regulating the thickness of the developer D is provided so as to cross the surface of the developing sleeve 4, and the blade 9 has a detection window 90 in which a transparent glass 91 is fitted. . The lower surface of the glass 91 is coated with a fluororesin as described above, and the upper surface of the blade 9 is provided with a toner concentration detector.
11 is provided, and the toner T is supplied based on the detection signal.

Thus, also in the present embodiment, the developer D flows along the glass 91 not facing the developing sleeve 3 as shown by the arrow P, so that the developer D
Can be prevented from adhering. Note that the other configuration and operation are the same as those of the above-described embodiment, and the description thereof will be omitted.

(Effect of the Invention) As described above, in the present invention, the charge polarity of the toner particles of the developer is set to minus, the charge polarity of the magnetic particles is set to plus, and the surface of the detection window that contacts the developer is coated with a fluororesin. Because the film is formed, the transparent member of the detection window is less likely to be triboelectrically charged, the polarity when charged is negative, and the developer is used on the transparent member because of the use of a highly releasable fluororesin. There is no occurrence of such a situation that sticks. As a result, according to the present invention, it is possible to always accurately and stably detect the toner concentration in the developer and the detection window, and it is possible to always control the toner concentration in the developer to a constant value. Becomes

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an essential part of an embodiment of the developing device according to the present invention, FIG. 2 is a sectional view taken along line II-II of FIG.
FIG. 4 is a graph showing the state of frictional charging of the glass surface of the detection window in the embodiment, FIG. 4 is a graph showing the relationship between the output of the toner concentration detector of the embodiment and the toner concentration, and FIG. FIG. 6 is a schematic longitudinal sectional view showing another embodiment, and FIG. 6 is a schematic longitudinal sectional view showing a conventional developing device. DESCRIPTION OF REFERENCE NUMERALS 1 photosensitive drum (image carrier) 3 developing sleeve (developer carrier) 4 developer container 9 blade (regulating member) 11 toner concentration detector (toner concentration detecting means) ) 90: detection window 91: glass (transparent member) 91a: fluororesin coating film D: developer, T: toner

Continuation of the front page (56) References JP-A-63-18377 (JP, A) JP-A-55-134876 (JP, A) JP-A-57-37374 (JP, A)

Claims (2)

(57) [Claims] A developer container containing a developer having toner particles and magnetic particles; a developer carrying member carrying the developer and being carried out of the developer container; and a toner concentration rubbed by the developer. And a detection window for optically detecting the developer, wherein the charge polarity of the toner particles of the developer is minus, the charge polarity of the magnetic particles is plus, and the detection window is covered with a fluororesin. A developing device characterized in that the surface of the detection window is negatively charged due to friction with the agent. 2. The coating thickness of the fluororesin coating is 60
The developing device according to claim 1, wherein the thickness is within μm.