JPH0619320A - Detection of toner concentration - Google Patents

Abstract

PURPOSE:To exactly detect the toner concn. of a developer contg. toner particles which do not substantially reflect the light of a wavelength region of detecting light over a long period of time by using the developer mixed with magnetic carrier particles higher in the spectral light reflectivity in a prescribed wavelength region than that of the toner particles. CONSTITUTION:The two-component developer 7 mixed with the nonmagnetic toner particles and the magnetic carrier particles is housed in a container 6 of a developing device 5. The magnetic carrier particles provided with the higher spectral reflectivity in the wavelength region of the detecting light which is detected by a photodetector 21 and is converted to an electric signal than the spectral reflectivity of the colornts of the toner particles by contg. a magnetic material having the spectral reflectivity higher than the spectral reflectivity of the colornts of the toner particles are used as the magnetic carrier particles. For example, the magnetic carrier particles formed by using maghemite (gamma-Fe2O3) which is a brown coloring pigment having magnetism and coating the surfaces of such cores with a resin in order to improve triboelectrostatic chargeability, environmental stability and durability are used as the magnetic cores of the magnetic carrier particles.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art When an electrostatic latent image is developed by using a so-called two-component developer in which toner particles and carrier particles are mixed, the toner particles gradually decrease. It is necessary to replenish the particles in the two-component developer in the developing device.

Therefore, there is provided 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 toner according to 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 the two-component developer, the developer is irradiated with light as described in JP-B-60-7792. Then, there is a method in which the light in the infrared wavelength region reflected by the developer is received by the light receiving element and an electric signal corresponding to the received light amount is formed.

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

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

The iron powder is coated with a resin colored in white to irradiate the light of a two-component developer containing carrier particles that reflect light, and the reflected light is detected to detect the toner density. This method is described in JP-A-58-55954.

However, while the carrier particles are used for a long time, the white resin thin layer is peeled off from the surface of the core material (black magnetic material), and the reflectance of the carrier particles decreases. Therefore, it becomes gradually 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 a toner concentration of a developer containing toner particles that does not substantially reflect light in a wavelength region of detection light for a long period of time. It is to be.

[0010]

According to the toner concentration detecting method of the present invention, the toner contained in the developing device for developing the electrostatic latent image is toner particles and the spectral reflectance in a predetermined wavelength region is the toner particles. Using a developer mixed with magnetic carrier particles having a spectral reflectance in the predetermined wavelength region higher than toner particles by including a magnetic material higher than a coloring material,
The toner concentration of the developer is detected by irradiating the developer with light, receiving the reflected light in the predetermined wavelength region reflected by the developer with a light receiving element, and forming an electric signal corresponding to the received light amount. To do.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENT A container 6 of a developing device 5 in which the present invention can be used in FIG.
A two-component developer 7 containing non-magnetic toner particles and magnetic carrier particles is contained therein.

A developing sleeve 8 made of a non-magnetic material is arranged at the opening of the container 6 so as 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 the developing area where the toner is attached to the electrostatic latent image. The layer thickness of the developer conveyed to the developing area is regulated by the blade 10.

A developing bias voltage in which a DC voltage is superimposed on an AC voltage is applied to the developing sleeve 8 by a power source 11. This improves the developing efficiency.

The developer which has passed through the developing area and returned to the container 6 is released from the sleeve 8 and agitated in the container 6.

Reference numerals 12 and 13 denote stirring screws arranged in the container. The screws 12 and 13 respectively rotate in the directions of the arrows to stir the developer 7 to frictionally charge the toner particles with the carrier particles and to make the toner concentration of the developer 7 uniform over the longitudinal direction of the sleeve 8.

The screw 12 is from the back side to the front side in the drawing,
The screw 13 moves the developer from the front side to the back side. The partition wall 14 between the screws 12 and 13 is provided with developer passage openings on the back side and the front side, respectively. Through these openings, the developer 7 travels from the screw 12 to the screw 13, and from the screw 13 to the screw 12. Moving.

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

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

A detector 23 for the toner concentration of the developer 7 is arranged 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.

This detector 23 is provided with a window 19 made of a transparent material such as glass or acrylic resin, which is arranged so as to come into contact with the two-component developer 7 carried on the developing sleeve 8, and one end through this window 19. A light emitting diode (LED) 20 that irradiates the developer 7 with light in the infrared region from the side, and the light in the infrared region reflected by the developer 7 is received through the window 19 and an electrical signal corresponding to the amount of received light is received. And a second photodiode 22 that directly receives the light in the infrared region emitted from the other end side of the LED 20 and generates an electric signal corresponding to the amount of received light. is 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 to form a reference signal, that is, a standard signal. In the illustrated example, the reference signal is formed using the infrared light from the LED 20 received by the second photodiode 22 without passing through the developer 7, but another reference signal forming means may be used instead.

As shown in FIG. 2, the output signal of the first photodiode 21 is amplified by the amplifier 24, and the output signal A /
The digital signal C is converted 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 into the digital signal R by the A / D converter 27. This signal R is a reference signal corresponding to a predetermined target toner density.

Both signals C and R are control circuit (cpu) 2
8 is transmitted. The cpu 28 calculates the difference between the signals C and R, and the motor 18 is operated through the drive circuit 29 for a time corresponding to this difference or for a predetermined time at the rotation speed corresponding to this difference.
To rotate. That is, the developer 7 in the developing device 5 is replenished with the toner particles in an amount corresponding to the difference from the hopper 15.

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 received light amount of the first photodiode 21 becomes larger than the received light amount corresponding to the target toner concentration, the toner is replenished to the developer 7 as described above. In this way, 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. As such toner particles,
5 to 15 wt% in 80 to 90 wt% binder resin
% Carbon black and a dispersion of a small amount of charge control agent can be used.

For example, polyester resin 80 to 90 wt
% To 5% by weight of carbon black, and a toner having an average particle size of 6 to 10 μm in which a metal complex of an alkyl-substituted salicylic acid is further dispersed as a negative charge control agent. Titanium oxide TiO ₂ is used as a fluidity improver. 0.5-2 wt%
Can be used as an external additive. Other silica may be used as the external additive.

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

As described above, the toner colored with carbon black has a light absorption property from the visible region to the infrared region and does not substantially reflect light. Therefore, the toner density depending on the amount of reflected light of the toner is used. No detection can be done.
Therefore, as described above, in order to detect the toner concentration by the amount of reflected light of the carrier, a technique using a carrier in which a magnetic material surface such as ferrite is coated with a resin colored in white has been proposed. There is. However, this prior art has the above-mentioned drawbacks.

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

For example, magnetic carrier particles 30a magnetic core 3
1 (FIG. 3 (a), maghemite (γ-Fe ₂ O ₃ ) which is magnetic and has a brown coloring pigment is used, and triboelectrification, environmental stability and durability are provided on the surface of the core 31. For improvement, a resin having a mean particle size of 40 to 60 μm coated with 0.5 to 2 wt% of resin can be used.In FIG. 3 (a), reference numeral 32 is a thin layer of the resin, and maghemite is a developer. It has sufficient magnetic properties to be used as a component.

Acrylic resins, polyester resins, fluororesins, silicone resins and the like can be used as the resin forming the coat thin layer 32. The resin forming the thin coat layer 32 may be any resin as long as it can transmit light in the wavelength region of the detection light, and need not be colored.

The light from the LED 20 is emitted by the carrier particles 30.
Penetrates the coat thin layer 32 of and enters the surface of the core 31,
Then, the coating thin layer 3 is reflected again on the surface of the core 31.
2 and is emitted outside the carrier particles 30.

Such carrier particles reflect both visible light and infrared light.

As an example, in the case of an LED, the peak value of the light intensity distribution is at a wavelength of 950 nm, and the spectrum half-width (in the light intensity distribution, the distribution width at an intensity level of ½ of the peak value) is 45 nm. Irradiate with light, wavelength band having sensitivity is 840 to 1150 nm, maximum sensitivity wavelength is 970 nm
With a photodiode of 0.1 mW
When detected under conditions of / 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 to 2%.

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

A straight line B in FIG. 4 is a two-component composition in which a black toner obtained by mixing cyan, magenta, and yellow pigments into a binder resin for coloring is mixed as a toner, and a black carrier in which ferrite particles are thinly coated with a resin is mixed as a magnetic carrier. 3 is a straight line showing the relationship between the toner concentration and the output voltage of the photodiode 21 when a developer (developer for Canon color copying machine CLC-500) is used.

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

In the straight line B in FIG. 4, the detection sensitivity is 200 mV.
/ Wt%. On the other hand, in the straight line A, the detection sensitivity is 150 mV / wt%. This enables accurate detection of toner density and accurate control of toner replenishment.

In any case, the thin coat layer 32 is the core 31.
Even if it is peeled off, the spectral reflectance of the carrier particles does not change so much, and the toner concentration can be accurately detected over a long period of time.

On the other hand, as in the above-mentioned prior art, when the core is coated with a resin colored in white, peeling of the coating layer from the core is prevented and sufficient reflectance is obtained. If this is the case, the thickness of the coat layer must be increased considerably. Then, the volume resistance of the carrier particles reaches 10 ¹⁸ Ωcm, and in that case, the triboelectric charges are excessively accumulated in the carrier particles, so that the triboelectric charges cannot be sufficiently imparted to the toner, and the effect of the developing bias voltage is reduced. In some cases, the developing efficiency may be lowered and the developing efficiency may be lowered.

On the other hand, in the present invention, the resin coating layer 3
Since 2 may be thin, the above inconveniences can be easily solved. Incidentally, in the case of the carrier particles, the volume resistivity is 1
0, which is the ^{8 ~10 10 Ωcm.}

The following example 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 binder 33 of the resin described above is used. That is, in the present embodiment, styrene-acrylic resin is used as a colored magnetic material such as maghemite (γ-Fe ₂ O).
_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
It was a brown carrier having a thickness of 0 μm and an electric resistance of 10 ¹³ to 10 ¹⁴ Ωcm. In the same manner as in the previous example, the two-component developer was irradiated with infrared light and the toner density was detected by the reflected light from the carrier. The detection sensitivity was 140 mV / wt.
%, Which was sufficient for practical use.

In the above examples, magnetic powder containing maghemite as a magnetic substance having light reflectivity was used as a carrier, and this was mixed with a toner to be used as a two-component developer. Magnesium (γ-Fe ₂ O ₃ ) which is a brown magnetic material is dispersed in styrene-acrylic resin to have a weight average particle diameter of 10 μm, and infrared-reflective magnetic powder is used as a brown toner. Magnetite, which is a black magnetic substance, is dispersed in a polyester resin, and the infrared ray absorbing magnetic powder having a weight average particle diameter of 10 μm is used as a black toner. These brown toner and black toner are mixed to form a developer. 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 in a weight ratio of 50% so that the brown toner is positively charged by friction with the black toner and the black toner is negatively charged 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 and 2 kHz are set. A bias is applied to perform non-contact development. Here, if the latent image potential is negative with respect to the developing sleeve 8, development is performed with brown toner,
If it is positive, development is performed with black toner. The transfer voltage is switched to negative for positive toner and positive for negative toner.

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

When an OPC negatively charged one is used as the image bearing member 4, the image portion is exposed when the toner is negative, and the non-image portion is exposed when the toner is positive. Should 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 the light reflection method. However, it was difficult to control the concentration to be constant, but in the present invention, since the light-reflecting type magnetic powder is used for the brown toner, even the mixed brown and black toners are brown. The density of these toners can be detected by detecting the amount of reflected light of the toners.

Therefore, in the present embodiment, a means for supplying black toner and brown toner is provided, and black or brown toner is supplied according to the detected density, so that one developing device can always stably and selectively operate. It is now possible to develop two colors.

As a result of examining each of the above examples, particles (magnetic carrier particles or magnetic toner particles) having a spectral reflectance of 20% or more in the wavelength region of detection light (infrared light in the above examples), 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 detection light is used, the mixing ratio of both particles by the detection light is practically sufficient. It has been found that it can be detected with accuracy and the mixing ratio can be accurately controlled.

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

Further, the developer may be irradiated with light in a wide wavelength range such as emitted light 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 carrier particles, it is also possible to use particles which are made of a magnetic material such as maghemite which is reflective to detection light, without being coated with a resin or the like.

[0058]

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

[Brief description of 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 toner density detection sensitivity.

[Explanation of symbols]

 5 Developing Device 7 Two-Component Developer 8 Developing Sleeve 20 LED 21 First Photo Sensor 22 Second Photo Sensor

Claims (4)

[Claims] 1. The toner according to claim 1, wherein the developer contained in a developing device for developing the electrostatic latent image contains toner particles and a magnetic material having a spectral reflectance in a predetermined wavelength region higher than a coloring material of the toner particles. Using a developer mixed with magnetic carrier particles having a spectral reflectance in the wavelength region higher than that of toner particles, irradiating the developer with light, and reflecting in the developer in the predetermined wavelength region. A toner concentration detection method in which light is received by a light receiving element and an electric signal corresponding to the amount of the received light is formed to detect the 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 concentration detecting method according to claim 1, 2 or 3, wherein the predetermined wavelength region is a wavelength region of infrared light.