JP3150223B2 - Toner density detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to electrophotography and the like.
The present invention relates to a method for detecting a toner concentration of a developer contained in a developing device for developing an electrostatic latent image.

[0002]

2. Description of the Related Art When an electrostatic latent image is developed using a so-called two-component developer in which toner particles and carrier particles are mixed, the toner particles gradually decrease. The particles need to be replenished into the two-component developer in the developer.

For this reason, a toner concentration control device comprising a toner concentration detection device for detecting the toner concentration of the developer in the developing device and a toner replenishment control device for replenishing the toner in accordance with the detected signal. The toner concentration of the developer is kept constant.

As a method for detecting the toner concentration, that is, the ratio of the amount of toner particles in a two-component developer, the developer is irradiated with light as described in JP-B-60-7792. Then, there is a method in which light in the infrared wavelength region reflected by the developer is received by a light receiving element and an electric signal corresponding to the received light amount is formed.

In this method, the carrier particles contain iron powder or ferrite particles such as Fe, Cu, Ni, etc. as the magnetic material, and therefore exhibit a black color and do not substantially reflect light in the infrared wavelength region. On the other hand, toner particles are effective for detecting the toner concentration of a two-component developer that substantially reflects light in the infrared wavelength region.

However, in the case of a black toner containing carbon black as a coloring material, light in the infrared wavelength region is not substantially reflected. The above method cannot be applied to a method for detecting the toner concentration of a two-component developer in which such toner particles are mixed with the above carrier particles.

[0007] A two-component developer containing carrier particles which reflects light by coating an iron powder with a white colored resin is irradiated, and the reflected light is detected to detect the toner concentration. The method described above is described in JP-A-58-55954.

However, while the carrier particles are used for a long time, the white resin thin layer is separated from the surface of the core material (black magnetic material) and disappears, and the reflectance of the carrier particles decreases. Therefore, it becomes increasingly difficult to accurately detect the toner density.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a toner concentration detecting method capable of accurately detecting the toner concentration of a developer containing toner particles which does not substantially reflect light in the wavelength region of detection light over a long period of time. It is to be.

[0010]

According to the toner concentration detecting method of the present invention, a toner contained in a developing device for developing an electrostatic latent image has toner particles and a toner having a spectral reflectance in a predetermined wavelength region. By having a magnetic material higher than the coloring material and a resin layer provided on the magnetic material and transmitting light of a predetermined wavelength, the spectral reflectance in the predetermined wavelength region is mixed with magnetic carrier particles higher than the toner particles. Using developer
The developer is irradiated with light, reflected light of the predetermined wavelength region reflected by the developer is received by a light receiving element, and an electric signal corresponding to the received light amount is formed to detect the toner concentration of the developer. I do.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG.
The inside contains a two-component developer 7 in which non-magnetic toner particles and magnetic carrier particles are mixed.

At the opening of the container 6, a developing sleeve 8 made of a non-magnetic material is arranged to face the electrostatic latent image carrier 4 such as an electrophotographic photosensitive member or a dielectric. Inside the developing sleeve 8, a magnet 9 is arranged stationary.

The developing sleeve 8 rotating in the direction of the arrow carries the two-component developer 7 by the magnetic force of the magnet 9 and conveys it to a developing area where toner adheres to the electrostatic latent image. The thickness of the developer transported to the developing area is regulated by the blade 10.

A power supply 11 applies a developing bias voltage obtained by superimposing a DC voltage on an AC voltage to the developing sleeve 8. Thereby, the development efficiency is improved.

The developer that has passed through the developing area and returned to the container 6 is separated from the sleeve 8 and is stirred in the container 6.

Numerals 12 and 13 are stirring screws arranged in the container. The screws 12 and 13 rotate in the directions of the arrows to stir the developer 7, frictionally charge the toner particles with the carrier particles, and equalize the toner concentration of the developer 7 over the longitudinal direction of the sleeve 8.

The screw 12 is moved from the back side to the front side in the drawing.
The screw 13 moves the developer from the near side to the far side. The partition 14 between the screws 12 and 13 is provided with a developer passage opening on the back side and the front side, respectively, through which the developer 7 flows from the screw 12 to the screw 13 and from the screw 13 to the screw 12. Moving.

The chamber in which the screw 13 is provided in the container 6 is supplied with non-magnetic toner particles 16 contained in the hopper 15. That is, the toner particles 16 in the hopper 15 are supplied to the two-component developer 7 in the container 6 of the developing device 5 by rotating the supply roller 17 by the motor 18.

The fresh non-magnetic toner particles replenished from the hopper 15 and the two-component developer mixed well by the screws 13 and 12 are again sleeved by the magnetic force of the magnet 9 in the chamber where the screw 12 is provided. Pumped to 8.

A toner concentration detector 23 for the developer 7 is disposed immediately before the developer layer thickness regulating blade 10. The detector 23 detects the toner concentration of the developer 7 carried on the sleeve 8.

The detector 23 has a window 19 made of a transparent material such as glass or acrylic resin, which is disposed so as to come into contact with the two-component developer 7 carried on the developing sleeve 8, and one end through the window 19. A light emitting diode (LED) 20 for irradiating the developer 7 with light in the infrared region from the side, and an infrared signal reflected by the developer 7 is received through the window 19, and an electric signal corresponding to the amount of received light is received. And a second photodiode 22 that directly receives infrared light emitted from the other end of the LED 20 and generates an electric signal corresponding to the amount of received light. are doing.

The output signal of the first photodiode 21 corresponds to the toner density of the developer 7. The output signal of the second photodiode 22 is used for forming a reference signal, that is, a reference signal. In this example, the reference signal is formed using infrared light from the LED 20 received by the second photodiode 22 without passing through the developer 7, but may be replaced with another reference signal forming means.

As shown in FIG. 2, the output signal of the first photodiode 21 is amplified by the amplifier 24,
The signal is converted into a digital signal C by the D converter 26. This signal C corresponds to the toner density of the two-component developer 7.

On the other hand, the output signal of the second photodiode 22 is amplified by the amplifier 25 and converted to a digital signal R by the A / D converter 27. This signal R is a reference signal corresponding to a predetermined target toner density.

The two signals C and R are supplied to a control circuit (cpu) 2
8 is transmitted. The cpu 28 calculates a difference between the signals C and R, and outputs a time corresponding to the difference via the driving circuit 29 or a certain time at a rotation speed corresponding to the difference.
To rotate. That is, the amount of toner particles corresponding to the difference is supplied from the hopper 15 to the developer 7 in the developing device 5.

In the present invention, when the toner concentration of the developer 7 decreases, the amount of light received by the first photodiode 21 increases.
Therefore, when the amount of received light of the first photodiode 21 becomes larger than the amount of received light corresponding to the target toner density, toner is supplied to the developer 7 as described above. Thus, the toner concentration of the developer in the container 6 is maintained at the target toner concentration.

The toner particles are colored black with carbon black. Such toner particles include:
5-15 wt% in 80-90 wt% binder resin
% Of carbon black and a small amount of a charge control agent dispersed therein.

For example, a polyester resin of 80 to 90 wt.
% To 5 to 15 wt% of carbon black, further metal complexes of alkyl-substituted salicylic acid using a toner having an average particle size of 6~10μm which is dispersed as a negative charge control agent, this titanium oxide TiO ₂ as a flow improver 0 0.5 to 2 wt%
Can be used externally. In addition, silica may be used as the external additive.

As the binder resin, a polystyrene resin or a styrene-acrylic copolymer can be used.

As described above, the toner colored with carbon black has a light absorption characteristic from the visible region to the infrared region and does not substantially reflect light. No detection can be performed.
For this reason, as described above, in order to enable detection of the toner concentration based on the amount of reflected light from the carrier, a technique using a carrier in which a magnetic material surface such as ferrite is coated with a resin colored white is proposed. I have. However, this prior art has the disadvantages described above.

Therefore, in the present invention, a magnetic material having a higher spectral reflectance in the wavelength region of the detection light that is received by the light receiving element (21) and converted into an electric signal than the coloring material of the toner particles is used as the magnetic carrier particles. By using the magnetic carrier particles, magnetic carrier particles having a higher spectral reflectance in the wavelength region than the toner particles are used.

For example, the magnetic carrier particles 30a and the magnetic core 3
1 (FIG. 3 (a), using maghemite (γ-Fe ₂ O ₃ ), which is magnetic and has a brown coloring pigment, has a triboelectric charging property, environmental stability, and durability on the surface of the core 31. In order to improve the performance, a resin having an average particle diameter of 40 to 60 μm coated with 0.5 to 2 wt% of a resin can be used, and in Fig. 3 (a), 32 is a thin layer of the resin. It has sufficient magnetic properties to be used as a component.

As a resin constituting the thin coat layer 32, an acrylic resin, a polyester resin, a fluororesin, a silicone resin, or the like can be used. The resin constituting the coat thin layer 32 may be any resin that can transmit light in the wavelength region of the detection light, and need not be colored.

The light from the LED 20 is applied to the carrier particles 30.
Through the coat thin layer 32 and enter the surface of the core 31;
Then, the light is reflected on the surface of the core 31, and the coat thin layer 3 is again formed.
2 and exits out of the carrier particles 30.

Such carrier particles reflect both visible light and infrared light.

As an example, in the LED, the peak value of the light intensity distribution is at a wavelength of 950 nm, and the infrared half width of the spectrum (distribution width at an intensity level of 1/2 the peak value on the light intensity distribution) is 45 nm. Irradiated with light, the wavelength band having sensitivity is 840 to 1150 nm, the maximum sensitivity wavelength is 970 nm
Irradiating light intensity on the light receiving surface 0.1mW
/ Cm ² and an open-circuit voltage of 250 mV, the carrier particles had a spectral reflectance of about 40%.

On the other hand, when the toner particles were irradiated as described above and received as described above, the spectral reflectance of the toner particles was 1-2%.

FIG. 4 shows the toner concentration (toner particle weight / (toner particle weight + carrier particle weight) × 1) when a two-component developer in which the above carrier particles and toner particles were mixed was used.
00) and the output voltage of the photodiode 21 is shown by a straight line A.

A straight line B in FIG. 4 is a two-component mixture of a black toner obtained by mixing cyan, magenta, and yellow pigments in a binder resin as a toner and a black carrier in which ferrite particles are thinly coated with a resin as a magnetic carrier. 4 is a straight line showing the relationship between the toner density and the output voltage of the photodiode 21 when a developer (a developer for a color copier CLC-500 manufactured by Canon Inc.) is used.

In the latter case, the carrier particles do not substantially reflect the infrared light, and the toner particles substantially reflect the infrared light. Therefore, when the toner concentration of the developer decreases, the amount of light received by the photodiode 21 decreases.
In C-500, toner concentration is detected by infrared light reflected from the developer, and toner replenishment is controlled).

On the straight line B in FIG. 4, the detection sensitivity is 200 mV.
/ Wt%. On the other hand, on the straight line A, the detection sensitivity is 150 mV / wt%. As a result, accurate detection of toner density and accurate control of toner replenishment have become possible.

In any case, the coat thin layer 32 is
Even when the toner particles are separated from the carrier, the spectral reflectance of the carrier particles does not change so much, and accurate detection of the toner concentration can be performed over a long period of time.

On the other hand, when the core is coated with a resin colored in white as in the above-described prior art, the coating layer is prevented from peeling off from the core, and a sufficient reflectance is obtained. If this is the case, the thickness of the coat layer must be considerably increased. As a result, the volume resistance of the carrier particles reaches as high as 10 ¹⁸ Ωcm, and in that case, the frictional charges are excessively accumulated in the carrier particles, so that it is impossible to impart sufficient frictional charges to the toner, and the effect of the developing bias voltage is reduced. In some cases, the developing efficiency is reduced, and the developing efficiency is reduced.

On the other hand, in the present invention, the resin coat layer 3
Since 2 may be thin, any inconvenience can be easily solved. Incidentally, in the case of the carrier particles, the volume resistivity is 1
0 ⁸ to 10 ¹⁰ Ωcm.

The following embodiment is characterized in that as the carrier particles 30 of the two-component developer, a carrier in which maghemite fine powder 34 is dispersed in the above-mentioned resin binder 33 is used. That is, in the present embodiment, maghemite (γ-Fe ₂ O), which is a colored magnetic material, is added to styrene-acrylic resin.
_The magnetic powder in which ₃ ) is dispersed is used as a carrier.

The carrier at this time has an average particle size of 40 to 5
The carrier was a brown carrier having a thickness of 0 μm and an electrical resistance of 10 ¹³ to 10 ¹⁴ Ωcm. When the two-component developer was irradiated with infrared light and the toner concentration was detected by the reflected light from the carrier in the same manner as in the previous embodiment, the detection sensitivity was 140 mV / wt.
%, Which was sufficient for practical use.

In the above embodiment, a magnetic powder containing maghemite as a magnetic material having light reflectivity was used as a carrier, and this was mixed with a toner to be used as a two-component developer. Magnetite (γ-Fe ₂ O ₃ ), which is a brown magnetic substance, is dispersed in a styrene-acrylic resin, and a magnetic powder having a weight average particle diameter of 10 μm and having infrared light reflectivity is used as a brown toner. Then, magnetite, which is a black magnetic substance, is dispersed in a polyester resin, and the weight average particle diameter is 10 μm. Used as

At this time, the brown toner is positively charged by the charge control agent, and the black toner is negatively charged by the charge control agent. These toners are mixed at a weight ratio of 50% so that the brown toner is stably charged positively by friction with the black toner, and the black toner is stably charged negatively by friction with the brown toner.

In this state, a thin layer of a mixed toner of two colors of brown toner and black toner is formed on the developing sleeve 8 of FIG. 1, the distance between the developing sleeve 8 and the image carrier 4 is set to 300 μm, and 2 kVpp, 2 kHz A non-contact development is performed by applying a bias. Here, if the latent image potential is negative with respect to the developing sleeve 8, development is performed with brown toner,
If positive, development is performed with black toner. The transfer voltage is switched to minus for positive toner and to plus for negative toner.

When developing with a brown toner, the black toner functions as a carrier, and when developing with a black toner, the brown toner functions as a carrier.

When a negatively charged OPC is used as the image carrier 4, the image portion is exposed when the toner is negative, and the non-image portion is exposed when the toner is positive. May be formed.

As described above, when a developer in which two color toners are mixed is used in one developing device, conventionally, the toner density (mixing ratio) of the two colors of the developer is detected by a light reflection method. Although it was difficult to control the concentration to be constant, the present invention uses light reflection type magnetic powder for the brown toner. By detecting the amount of reflected light of the toner, the density of the toner can be detected.

Therefore, in this embodiment, a means for replenishing black toner and brown toner is provided, and black or brown toner is replenished according to the detected density. It is now possible to perform two-color development.

As a result of examination of each of the above examples, it was found that particles (magnetic carrier particles or magnetic toner particles) having a spectral reflectance of 20% or more in the wavelength region of the detection light (in the above example, infrared light) If a developer mixed with particles (non-magnetic toner particles or magnetic toner particles) having a spectral reflectance of 5% or less in the wavelength region of the detection light is used, the mixing ratio of both particles can be practically sufficient by the detection light. It was found that detection was possible with high accuracy and that the mixing ratio could be accurately controlled.

In each of the above embodiments, the detection light is infrared light, but may be visible light or ultraviolet light.

The developer may be irradiated with light in a wide wavelength range, such as light emitted from a tungsten lamp, and the reflected light may be received by a light receiving element through a filter that transmits only light of a specific wavelength. Good.

Further, as the above-mentioned carrier particles, those which are not coated with a resin or the like but are made of a magnetic material having a detecting light reflecting property such as maghemite alone can be used.

[0058]

According to the present invention, the toner concentration of the developer can be accurately detected for a long time by the reflected light detection method.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example of a developing device to which the present invention can be applied.

FIG. 2 is an explanatory diagram of a toner supply control circuit.

FIG. 3 is an explanatory diagram of carrier particles that can be used in the present invention.

FIG. 4 is an explanatory diagram of a toner density detection sensitivity.

[Explanation of symbols]

 Reference Signs List 5 developing device 7 two-component developer 8 developing sleeve 20 LED 21 first photo sensor 22 second photo sensor

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-58-55954 (JP, A) JP-A-64-40952 (JP, A) JP-A-64-40953 (JP, A) JP-A-63-55954 149676 (JP, A) JP-A-61-155938 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/08 114-115 G03G 9/10-9/113

Claims (4)

(57) [Claims] 1. A developer contained in a developing device for developing an electrostatic latent image, comprising toner particles, a magnetic material having a higher spectral reflectance in a predetermined wavelength region than a coloring material of the toner particles, and a magnetic material provided on the magnetic material. A developer having a resin layer that transmits light of a predetermined wavelength, and having a spectral reflectance in the predetermined wavelength region mixed with magnetic carrier particles higher than toner particles. A toner concentration detecting method for irradiating, and receiving, at a light receiving element, reflected light in the predetermined wavelength region reflected by the developer, and forming an electric signal corresponding to the received light amount to detect a toner concentration of the developer. 2. The toner concentration detecting method according to claim 1, wherein the spectral reflectance in the predetermined wavelength region is 20% or more for carrier particles and 5% or less for toner particles. 3. The toner concentration detecting method according to claim 1, wherein the coloring material of the toner is carbon black or magnetite, and the magnetic material of the carrier particles is maghemite. 4. The toner density detecting method according to claim 1, wherein the predetermined wavelength region is a wavelength region of infrared light.