JP2003270901A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image forming apparatus which reproduces optimum coloring at all times by suppressing the coloring variation. <P>SOLUTION: At least a developing means 221 and a developer housing part 210 are integrated in the color image forming apparatus 100. A cartridge 201 provided with color toner particles which have a shape factor SF-1 in the range of 100 to 160 and a shape factor SF-2 in the range of 100 to 140 is detachable. A color toner image for density detection is formed by the color toner particles provided in the cartridge 201. The density of the color toner image for density detection is detected by a density detection means 1, and image forming conditions are controlled on the basis of a detection result. The density detection means 1 can be composed of an optical sensor which detects a regular reflected light, or an optical sensor which can detect both of the regular reflection light and a diffuse reflection light. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus using an electrophotographic system, and more particularly, to a cartridge in which at least a developing means and a developer accommodating portion are integrated and which is attachable to and detachable from the apparatus main body. The present invention relates to a color image forming apparatus including a detection unit that optically detects the density of a detection developer image formed on an image carrier for controlling image forming conditions.

Here, examples of the electrophotographic color image forming apparatus include an electrophotographic copying machine, an electrophotographic printer (for example, an LED printer, a laser beam printer, etc.), and an electrophotographic facsimile apparatus.

A cartridge which can be attached to and detached from a color image forming apparatus is one in which at least a developing means and a developer accommodating portion are integrally formed, and the cartridge can be attached to and detached from the main body of the image forming apparatus. Further, the cartridge has at least a developing means and a developer accommodating portion, and is formed into a cartridge integrally with an electrophotographic photosensitive member as an image bearing body together with either or both of a charging means and a cleaning means, thereby forming a color image. A process cartridge detachably attachable to the apparatus main body, or at least a developing means, a developer accommodating portion, and an electrophotographic photosensitive member are integrally made into a cartridge, and detachably attachable to the color image forming apparatus main body. It may be a process cartridge.

[0004]

2. Description of the Related Art Conventionally, as a color image forming apparatus, various systems such as an electrophotographic system, a thermal transfer system and an inkjet system have been used. Among them, the one using the electrophotographic method is superior to the other methods in terms of high speed, high image quality, and quietness, and has become popular in recent years. This electrophotographic color image forming apparatus is also divided into various systems. For example, in addition to the well-known multiple transfer system and intermediate transfer system, a color image is superimposed on the surface of the photoconductor and then collectively transferred. There are a multi-developing method for performing image formation by performing the image formation, and a tandem method in which a plurality of image forming means of different colors are arranged in series and the image is transferred onto a transfer material conveyed by a transfer material carrier. Of these, the tandem method is an excellent method because it can be speeded up and the number of image transfers is small, which is advantageous for image quality.

In addition, in the electrophotographic color image forming apparatus, in recent years, at least a developing means and a developer accommodating portion are integrated for each color, and a cartridge method is adopted which can be attached to and detached from the color image forming apparatus main body. There is something I did. There is also a process cartridge detachable color image forming apparatus in which a cartridge further includes an electrophotographic photosensitive member (hereinafter, simply referred to as “photosensitive member”), a charging unit, a cleaning unit, and the like. Generally, the process cartridge is designed to have its life expired when the toner in the developer accommodating portion is used up, so only one replacement is required, and the maintenance of the device can be performed by the user himself without the need for a service person. Therefore, the operability can be remarkably improved. Further, since it is relatively easy to downsize the apparatus, this process cartridge system is widely used in image forming apparatuses.

FIG. 18 shows a schematic structure of a laser beam printer 150 of a process cartridge removable type as an example of a color image forming apparatus adopting a tandem system. Figure 1
In FIG. 8, an electrostatic adsorption conveyance belt (hereinafter, referred to as “ETB”) 6 is stretched around a driving roller 7, an adsorption counter roller 10, tension rollers 8 and 9, and extends in a direction indicated by an arrow in the figure. Rotate. A yellow process cartridge 201, a magenta process cartridge 202, a cyan process cartridge 203, and a black process cartridge 204 are provided around the ETB 6 as image forming means for forming developer images (toner images) of different colors.
Are arranged in a line, and each process cartridge 20
Photoreceptors 230 (230a to 230d) as image bearing members provided in Nos. 1, 202, 203 and 204 are in contact with transfer rollers 3 (3a to 3d) as transfer means via the ETB 6.

Further, the suction roller 5 is provided upstream of each process cartridge 201 to 204 in the moving direction of the ETB 6.
Are arranged and are in contact with the suction-opposed roller 10 via the ETB 6.

The transfer material S is conveyed from the cassette 20 as a transfer material accommodating portion to the suction roller 5 by a transfer material conveying means such as a pickup roller 19, a conveying roller and a registration roller (not shown). Then, the transfer material S is synchronized with the image formation by each of the process cartridges 201 to 204, a bias is applied when passing through the nip portion formed by the suction roller 5 and the suction counter roller 10, and the transfer material S is statically transferred to the ETB 6. It is electrically adsorbed and conveyed in the direction indicated by the arrow in the figure.

Conventionally, the ETB6 has a thickness of 50 to 20.
PVD with 0 μm and low volume efficiency of about 10 ⁹ to 10 ¹⁶ Ωcm
A resin film such as F, ETFE, polyimide, PET, or polycarbonate, or a rubber substrate having a thickness of about 0.5 to 2 mm, such as EPDM, on which a fluororesin such as PTFE is dispersed in urethane rubber, for example, is used. The one provided as the surface layer is used.

The image forming process in the process cartridge will be described. The yellow, magenta, cyan, and black process cartridges 201 to 204
Have the same structure, the yellow process cartridge 201 will be described below as an example unless otherwise specified.

FIG. 2 shows a schematic structure of a yellow process cartridge. The process cartridge 201 has a drum type photosensitive member, that is, a photosensitive drum 230, as an image bearing member. The photosensitive drum 230 is the process cartridge 2
01 is attached to the apparatus body 100, the apparatus body 1
00 is rotated by a driving means (not shown) in the clockwise direction indicated by an arrow A in the figure at a predetermined peripheral speed, and an electrostatic latent image is formed on the outer peripheral surface by the image forming means. That is, the surface of the rotating photosensitive drum 1 is a charging roller 240 as a charging unit to which a charging bias is applied from the bias power source 241.
Are uniformly charged by. Next, the charged photosensitive drum 230 is scanned and exposed by the laser light L modulated according to the image information from the optical system 30 (30a to 30d) (FIG. 18) as an exposure unit included in the apparatus main body 100, An electrostatic latent image is formed on the surface. Photosensitive drum 23
The electrostatic latent image formed at 0 is then visualized as a toner image by supplying toner by the developing device.

That is, the process cartridge 201 is
The developing device 200 includes a developing container 220 that holds a developing roller 221 that is a developing unit, and a toner container 210 that serves as a developer accommodating portion. Toner container 21
The rotary blade 211 inside 0 is driven to rotate in the clockwise direction indicated by an arrow D in the figure, and supplies the toner t to the developing container 220. The elastic roller 222 as a developer supplying member provided in the developing container 220 is a developing roller 221 as a developer carrier.
It is pressed against and is rotated in the counterclockwise direction indicated by arrow C in the figure to supply the toner t to the developing roller 221.

The toner supplied onto the developing roller 221 serving as a developer bearing member is charged by friction at the contact portion between the elastic blade 223, which is a developer layer thickness regulating member, and the developing roller 221, so that a thin layer is formed. Be converted. Elastic blade 22
3 is in contact with the developing roller 221 on the downstream side in the rotation direction of the developing roller 221 with respect to the pressure contact portion between the developing roller 221 and the elastic roller 222.

The developing roller 221 is in contact with the photosensitive drum 230 and is rotationally driven in the counterclockwise direction indicated by arrow B in the figure.
The contact portion of the developing roller 221 with the photosensitive drum 230 is the developing portion. The thinned toner on the developing roller 221 is supplied to develop the electrostatic latent image on the photosensitive drum 230. At the time of development, a predetermined development DC bias is applied to the development roller 222 from the development bias application power source 224.
Generally, a developing bias in which a DC voltage is superimposed on an AC voltage is applied.

The toner remaining on the developing roller 221 without being used for the development of the electrostatic latent image on the photosensitive drum 230 in the developing portion, the developing container 221 is rotated by the subsequent rotation of the developing roller 221.
It is returned to 0 and is peeled off from the developing roller 221 at the contact portion between the developing roller 221 and the elastic roller 222. Then, the toner is conveyed from the developing container 220 to the toner container 210 again. Further, new toner t is supplied by the elastic roller 222 onto the developing roller 221 from which the toner has been peeled off.

As described above, in this example, the developing roller 22
The developing device 200 in which the developing container 220 holding the developing means such as No. 1 and the toner container 210 as the developer accommodating portion are integrally configured includes a photosensitive drum 230 and a charging roller 240.
Further, the process cartridge 201 is integrally formed with the cleaning device 250 by a frame body to be detachable from the apparatus main body 100. The process cartridge 201 is detachably attached to the apparatus main body via the attachment means 260 provided in the apparatus main body 100.

The toner image formed on the photosensitive drum 230 as described above is subjected to the ETB6 by the transfer process described later.
Is transferred to the transfer material S carried and conveyed by. Further, the toner (transfer residual toner) remaining on the photosensitive drum 230 after the transfer process is removed by a blade-shaped cleaning unit (cleaning blade) 251 included in the cleaning device 250, and is collected in a waste toner container 252.

The above operation / operation cycle is repeated for each of the yellow, magenta, cyan, and black process cartridges 201 to 204. Then, the toner images formed on the photosensitive drums 230 for the respective colors are superimposed on the transfer material S on the ETB 6 to form, for example, a full-color image.

In the actual printing process, ET
B6 moving speed and each process cartridge 201 to 20
In consideration of the distance between the transfer positions of No. 4, at the timing when the positions of the toner images of the respective colors formed on the transfer material S match,
The toner images are formed in the process cartridges 201 to 204, the transfer process is performed, and the transfer material S is conveyed. The transfer material S is used for each process cartridge 201 to 204.
The toner image is completed on the transfer material S while passing through the sheet once.

The photosensitive drums 230 (230a to 230) of the process cartridges 201 to 204 are connected via the ETB6.
At each transfer position where d) and the transfer roller 3 (3a to 3d) face each other, a transfer bias is applied to the transfer roller 3 (3a to 3d) from the bias power source 4 (4a to 4d), and the photosensitive drum 230 (230a to 230a. 230d) The toner image is electrostatically transferred onto the transfer material S from above. In this example, the photosensitive drum 2
Reference numeral 30 denotes a negative polarity OPC photoreceptor, which develops the exposed portion. Therefore, a negative polarity toner is used as the toner,
A positive transfer bias is applied to the transfer roller 3 from the bias power source 4. Here, a low resistance roller is generally used as the transfer roller.

After the toner image is transferred at each transfer position, the transfer material S is separated from the ETB 6 and passed through a conventionally known fixing device 17. Here, the transfer material S is heated and pressed to melt and fix the toner image on the surface.

When the above process is completed, the ETB 6 is neutralized by a neutralization charger (not shown) to prepare for the next printing process. The transfer material S on which the color image is fixed is then ejected outside the machine.

Next, the toner used as the developer will be described.

In recent years, as a toner used as a developer (developing agent), a toner manufactured by a polymerization method (hereinafter, referred to as "polymerized toner") has become widespread instead of a manufacturing method by pulverization. The polymerized toner has a shape factor SF-1 of 100 to
130, and SF-2 is 100 to 115, which is a toner having a substantially spherical shape (hereinafter, “spherical toner”).
Call. ).

SF-1 and SF-2 indicating the shape factor are FE-SEM (S-800) manufactured by Hitachi,
100 toners were randomly sampled, and the image information was introduced into an image analysis device (Luxex3) manufactured by Nikole Co. through an interface for analysis, and the value calculated by the following equation was obtained in the present invention. The shape factors are defined as SF-1 and SF-2.

[0026]

[Equation 1]

FIG. 19 shows AREA (toner projected area), MXL defined to calculate SF-1 and SF-2.
6 illustrates a method of defining NG (absolute maximum length) and PERI (perimeter).

The toner shape factor SF-1 indicates the degree of sphere, and if it is larger than 140, it gradually changes from a sphere to an irregular shape. SF-2 indicates the degree of unevenness, and when it is larger than 120, the unevenness of the surface area of the toner becomes remarkable.

The polymerized toner is superior to the toner produced by the pulverization method (hereinafter referred to as “pulverized toner”) in the following points.

First, unlike pulverized toner having an irregular shape,
Since the toner particles are spherical and have few irregularities, a toner having a small friction coefficient and high releasability can be manufactured. This property is advantageous for many color image forming apparatuses that electrostatically transfer a toner image.

Further, it is possible to manufacture a toner having a fine particle size distribution and a sharp particle size distribution as compared with the pulverization method. As a result, it is possible to deal with smaller dots in order to deal with higher image quality in the future.

Then, a wax can be included in the resin which is the main component of the developer. As a result, this wax is melted during image fixing, and toner is prevented from adhering to the fixing roller. Further, since the low softening point compound can be included in the toner particles, as the speed of printers and copying machines increases,
It is possible to further improve the low temperature fixability.

Next, the image density control will be described.

The toner amount of the printed image varies depending on various conditions such as the temperature and humidity conditions in which the color image forming apparatus is used, the degree of use of the photosensitive member, and the number of prints. The change in the toner amount causes a change in the density of the printed image and is recognized by the user as a change in tint. Therefore, many color image forming apparatuses are equipped with an image density control mechanism that automatically adjusts image forming conditions such as charging potential, exposure amount, and developing bias.

The image density control is to keep the maximum density of each color constant (hereinafter referred to as "Dmax control") and to keep the halftone gradation characteristics linear to the image signal (hereinafter referred to as "Dmax control"). Dhalf control ”).

In general, a density detecting developer image (hereinafter referred to as "density patch") is formed on an image carrier or a transfer material carrier to control image forming conditions, and the density thereof is formed. Is detected by the density detection sensor, and the image forming condition is controlled based on the detection result.

Next, the density detecting sensor will be described in detail.

Generally, for color toners such as yellow, magenta, and cyan (toners of colors other than black are referred to as "color toners"), a sensor for detecting diffuse reflection light provides good density control performance. It has been known. This method is adopted in many color image forming apparatuses. Further, the diffuse reflection light is generated from the color toner, but is hardly generated from the black toner (black toner).

FIG. 20 is a conceptual diagram of diffusely reflected light from the toner detected by the sensor. The solid arrow indicates the irradiation light to the toner t on the ETB 6, and the broken arrow indicates the diffuse reflection light from the toner. Diffuse reflected light is characterized by being diffused uniformly from the toner in all directions.

FIG. 21 is a schematic view of a diffuse reflection light detection type density detection sensor 180. The sensor 180 has a light emitting element 181 and a light receiving element 182. The light emitting element 181 is E
The toner t on TB6 is irradiated with infrared light. The reason for irradiating infrared light is that there is no difference in the spectrum of reflected light when detecting color toners such as yellow, magenta, and cyan. Diffuse reflected light is generated from the toner t, and the light receiving element 182 detects the amount of diffuse reflected light. At this time, the density detection sensor 1 that detects diffuse reflection light
In 80, in order to eliminate the influence of the specular reflection light from the surface of ETB6, the light emitting element 181 and the light receiving element 182 are
The irradiation angle α and the light receiving angle β are configured to be different.

FIG. 22 is a schematic diagram of sensor output characteristics of the sensor 180. The horizontal axis represents the density (a value measured by a Macbeth densitometer RD-918 after a density detection toner image (density patch) is transferred to a transfer material and permanently fixed on the transfer material by a fixing device. The same applies hereinafter.) , The vertical axis is the light receiving element 1
The diffuse reflected light output obtained by 82, the solid line shows the relationship between the toner amount and the diffuse reflected light output. The diffuse reflected light output is
It has a feature of increasing as the toner amount of the density patch increases.

[0042]

However, an electrophotographic color image forming apparatus which employs a cartridge attaching / detaching method in which a developing means and a developer accommodating portion are integrated and uses spherical toner as a developer for a color image. However, with the increase in the number of used cartridges, there may arise a problem that the density after the image forming condition adjustment, which should be kept constant, gradually increases.

This concentration fluctuation occurs relatively gently. However, by changing the cartridge to a new one, the fluctuating concentration is restored to the initial state again. Therefore, the tint variation appears most noticeable immediately after the replacement of the cartridge.

The cause of the problem that the density after adjusting the image forming conditions, which should be kept constant, gradually increases as the number of used cartridges increases will be described below.

The cause of this phenomenon is that the average particle size of the toner contained in the cartridge gradually increases as the number of sheets used (the number of times of image formation) increases, and the average particle size of the spherical toner increases. That is, the output characteristic of the density detection sensor changes.

First, the reason why the average particle diameter of the toner contained in the cartridge gradually increases as the number of used sheets increases will be described. This phenomenon is common not only to spherical toner but also to ground toner.

Explaining with reference to the process cartridge 201 shown in FIG. 2, since the toner having a small particle size has a larger surface area per unit volume than the toner having a large particle size,
Slightly superior in charging characteristics. Electrostatically photosensitive drum 23
Toner particles that are strongly charged,
It has a property of being more easily electrostatically transferred. Therefore, the toner having a small particle size is preferentially consumed in the developing unit, and the toner having a large particle size is not used for the development and has a relatively high probability of remaining on the developing roller 221. The toner remaining on the developing roller 221 is transferred from the developing container 220 to the toner container 2 again.
It is transported to 10. Since the above operation / operation cycle is repeated during the life of the process cartridge 210, the average particle diameter of the toner in the process cartridge 201 gradually increases.

The reason why the average particle size of the toner contained in the cartridge gradually increases as the number of sheets used increases is that toner with a small particle size has excellent charging characteristics and is preferentially used in the developing section. Is to be consumed by.

FIG. 23 shows changes in the average particle diameter of the toner obtained by the print test. The horizontal axis of the figure shows the particle diameter of the toner particles, and the vertical axis of the figure shows the number frequency (%) of the toner particles of each particle diameter. While the average particle size in the initial state shown by the solid line I is 5.5 μm, the average particle size of the toner after printing 25,000 sheets shown by the alternate long and short dash line II is 6.3 μm.
The average particle diameter of the toner after printing 50,000 sheets indicated by the broken lines m and III changes to 7.0 μm. Toner in the initial state (solid line I) and toner after printing 50,000 sheets (broken line II)
The item I) is used in the experiment described later in order to evaluate the amount of concentration fluctuation. Note that here, 50% average particle diameter (D50) is used as the average particle diameter. What is 50% average particle size?
When an integrated distribution curve is drawn for the number of each particle size, the particle size corresponds to 50% of the integrated distribution, and the particle amounts above and below this particle size are equal.

Next, the reason why the density detection sensor output characteristic changes due to the increase in the average particle diameter of the spherical toner will be described. This phenomenon does not occur with irregularly shaped pulverized toner, and is a phenomenon peculiar to spherical toner. When the average particle diameter of the spherical toner changes, the angular distribution of the diffuse reflection light intensity changes. For this reason, the output of the density detection sensor detecting the diffuse reflection light at a specific angle varies.

First, the angular distribution of the diffuse reflection light intensity when the particle size changes will be described. Here, according to the print test result described above, the toner particle size is from 5.5 μm to 7.
The theoretical calculation of the diffused light intensity distribution from the spherical toner when changing to 0 μm is as follows.

The toner has a perfect spherical shape (shape factor SF-1 =
100, SF−2 = 100), the diffuse reflection light intensity distribution from a single toner particle can be calculated from the Mie equation.

Mie's equation shown below solves the vector wave equation derived from Maxwell's electromagnetic equation under continuous conditions on the spherical surface (radius a), and is irradiated by deflection of wavelength λ of unit intensity. It is an analytically obtained scattering function of vertical and horizontal components of scattered light from a spherical particle. i⊥ and i _// indicate the scattering functions of the vertical and horizontal components, respectively. Here, α = 2πa / λ, ψ _n , ζ _n are Riccati-Bessel functions, τ _n is a Hankel function, and P _n1 is a Legendre entrainment function.

[0054]

[Equation 2]

FIG. 24 shows the diffused light intensity angle distribution from the spherical toner calculated by the Mie equation. The vertical axis represents the diffuse reflected light intensity, and the horizontal axis represents the angle. The wavelength λ of light was calculated as 880 nm (light from the infrared light emitting element used for the concentration detection sensor) in the range of 80 ° to 150 °. In the figure, the solid line I indicates the intensity of diffuse reflected light when the toner average particle size is 5.5 μm, and the broken line III indicates the toner average particle size 7.0.
The distribution of diffuse reflection light intensity when μm is shown. According to this calculation result, the diffused light intensity distribution varies depending on the size of the particle size, and the average particle size is 5. 5 in the angle range of 80 ° to 150 °.
The intensity of diffused light from the 5 μm toner tends to increase.

Next, the experimental results of actually measuring the diffused light intensity distribution shape from the density patch will be described.

FIG. 25 shows a spectrophotometer 300 used for measurement.
Indicates. Both the infrared light emitting element 301 and the light receiving element 302 have variable angles, and diffused reflected light at an arbitrary angle can be detected. However, the center lines of the infrared light emitting element 301 and the light receiving element 302 are set to be always inclined to prevent the specular reflection light from entering from the surface of the ETB 6. Using this spectrophotometer 300, infrared light was irradiated onto the density patch and the angular distribution of the diffused light was measured. The density patch is the toner (average particle size 5.5 μm) in the toner container 210 in the initial state of the cartridge obtained by the above print test, and 500
It was prepared with the toner (average particle size 7.0 μm) in the toner container 210 after printing 00 sheets. This toner has a shape factor SF-1 produced by the polymerization method of 100 to 130 and a shape factor S of
F-2 is 100 to 115.

Since this measuring instrument uses the infrared light emitting element as the light source, it is not affected by the difference in the reflection spectra of yellow, magenta and cyan. Therefore, the experimental results for yellow will be described below.

FIG. 26 shows the result of measuring the diffused light from the yellow toner using the spectrophotometer 300. The vertical axis represents the reflected light intensity, and the horizontal axis represents the sensor angle γ with respect to the incident light. The solid line I indicates the process cartridge 201
In the initial state, the intensity of diffuse reflection light from a density patch with an average toner particle size of 5.5 μm, and the broken line III shows the intensity of diffuse reflection light from a density patch with an average toner particle size of 7.0 μm. According to this experimental result, the diffused light intensity distribution changes depending on the size of the particle size, and the diffused light intensity from the toner having an average particle size of 5.5 μm is large in the range of 80 ° to 150 °. This is the same as the result of theoretical calculation.

There are approximately 10 ⁴ to 10 ⁶ toner particles on the laser spot of the irradiation light. At this time, the reflected light is dominated by scattered light from particles having the most frequent particle size, and the particle size distribution of the toner generated by the polymerization method is sharp, so that the actual density patch The measured value of the diffused light intensity distribution has almost the same properties as the diffused light distribution from a single particle obtained by calculation.

As described above, as the theoretical calculation and the experimental result show,
When the average particle size of the toner changes, the angular distribution of the diffuse reflection light intensity changes.

Next, the reason why the output characteristic of the density detection sensor detecting the diffused reflection light at a specific angle changes will be described.

The density detection sensor 180 shown in FIG. 21 detects diffuse reflection light in the direction of 60 ° with respect to the incident light. From the measurement result of the spectrophotometer (FIG. 26), the diffuse reflection light intensity in the direction of 60 ° has a toner average particle diameter of 7.0 μm.
Is different from the case of 5.5 μm and the case of 5.5 μm.
It can be seen that the intensity of diffuse reflection light from the toner of μm is higher. Therefore, the intensity of the diffuse reflection light incident on the light receiving element 182 is 5. When the average particle diameter of the toner is 7.0 μm.
Unlike the case of 5 μm, the sensor output in the case of 5.5 μm is larger. Therefore, when the average particle diameter of the toner changes, the angular distribution of the diffuse reflection light intensity changes, and the sensor output characteristics change.

In summary, the toner having a small particle size has excellent charging characteristics and is preferentially consumed in the developing section. Therefore, the average particle diameter of the toner in the toner container 210 gradually increases as the number of used sheets increases. Then, due to the change in the average particle diameter of the toner, the angular distribution of the diffuse reflection light intensity changes, and the sensor output characteristic changes. As a result, the most noticeable change in color appears immediately before replacement of the cartridge (toner average particle size 7.0 μm) and immediately after replacement (toner average particle size 5.5 μm).

In the image forming apparatus in which the developing means and the developer accommodating portion are separately configured and the toner is replenished to the developing portion on a regular basis, such a variation in color tone does not occur.

Here, the chromaticity difference ΔE in the L × a × b × uniform color space is ΔE = {(L−L ′) ² + (a−a ′) ²
+ (B−b ′) ² } ^1/2 . Generally, for color discrimination, ΔE = 0.8 or more in the adjacent comparison and ΔE in the adjacent comparison.
= 1.6 or more is said to be the discrimination limit.

The cause of the phenomenon that the density gradually increases as the number of used cartridges increases has been described above. This phenomenon is caused by toner shape factors SF-1 and SF-
2 occurs with toner close to 100, and the toner shape is not spherical, that is, it does not occur with irregularly shaped toner having large shape factors SF-1 and SF-2.

Next, the quantitative relationship between the toner shape coefficient and the tint variation will be described. Table 1 shows the average particle diameters of 5.5 μm and 7.0 for four types of toner having different shape factors.
It is the result of measuring the image chromaticity difference ΔE at the time of μm.

[0069]

[Table 1]

(1) Spherical toner produced by polymerization method (SF-1 = 100 to 130, SF-2 = 100 to 1)
15) (2) A toner (SF-1 = 110 to 150, SF-2) produced by a polymerization method and having many polymerization defects.
= 110 to 125) (3) Toner manufactured by a pulverization method and subjected to polishing treatment (treatment for making an irregular shape closer to a sphere) (SF-1 = 14)
(0 to 160, SF-2 = 120 to 140) (4) Toner manufactured by a grinding method and not subjected to polishing treatment (SF-1 = 150 to 175, SF-2 = 140 to 1)
55) Dmax control and Dha for the above four types of toner
If control was performed and 10 patch images with different densities were drawn. The target density (toner amount) of the patch image is 0.1, 0.2, 0.5, 0.7,
1.0 and 1.4. The chromaticity of each patch was measured with a chromaticity meter, and the maximum value of the chromaticity difference between the two was evaluated.

With the toner of (1), the maximum chromaticity difference ΔE = 4.
4, the maximum chromaticity difference ΔE = 3.
For the toners of 2 and (3), the maximum chromaticity difference ΔE = 1.8,
In the toner of (4), the maximum chromaticity difference ΔE is 0.6. The chromaticity difference ΔE = 0.6 is within the range of the reproducibility of the experiment, and shows that the chromaticity variation due to the particle size difference hardly occurs. Since the discrimination limit in the side-by-side comparison is ΔE = 1.6, the toners (1), (2), and (3) exceed the discrimination limit and are detected by the user as a tint variation.

Therefore, the shape factor SF-1 is 100 to 16
0, a spherical toner particle having a shape factor SF-2 in the range of 100 to 140 is used as a developer, and an image forming apparatus in which a cartridge in which a developing unit and a developer accommodating section are integrated is detachable has a tint variation. A concentration control method that does not occur is required.

The cause of the problem that the density after adjusting the image forming conditions, which should be kept constant, gradually increases with the increase in the number of used cartridges has been described above.

Next, the shape factor SF-1 = 150 to 17
5, the reason why the above-mentioned chromaticity difference does not occur when the pulverized toner of SF-2 = 140 to 155 (the above (4)) is used will be described.

FIG. 27 is a conceptual diagram of diffusely reflected light when the pulverized toner is irradiated with light. Since the pulverized toner has an irregular shape, the diffuse reflection light is randomly distributed. Moreover, the shape of each particle is non-uniform and the particle size distribution is flatter than that of the polymerized toner. Therefore, diffuse reflection lights having different distributions are overlapped with each other, and all individual particles have different diffuse light intensity distributions. Therefore, the shape of the diffused light intensity distribution from each toner is not reflected, and the shape of the diffused reflected light intensity distribution hardly changes even if the particle size is different. Therefore, for toners having large shape factors SF-1 and SF-2 and having non-uniform shapes, the sensor output does not change even if the particle size changes, and the tint does not change.

As a color image forming apparatus, a single color Δ
It is desirable to control the density of each color so that E does not exceed the discrimination limit of 1.6 or more in the side-by-side comparison. However, if the above-described tint variations occur in combination, ΔE becomes even larger, and the observer can identify the color difference. Therefore,
From the above evaluation results, the shape factor SF-1 is 100 to 16
No. 0, a spherical toner particle having a shape factor SF-2 in the range of 100 to 140 is used as a developer, and a cartridge in which a developing unit and a developer accommodating section are integrated is detachable, There is a need for a density control method that does not cause a tint variation due to the variation of

The change in tint is relatively easy to catch in the memory of achromatic color or skin color, and is easily pointed out as a problem in the color image forming apparatus. The present invention has been made in view of the above circumstances.

Therefore, an object of the present invention is to provide a color image forming apparatus capable of suppressing the variation of the tint and always reproducing the optimal tint.

[0079]

The above object can be achieved by a color image forming apparatus according to the present invention. In summary, according to the present invention, at least the developing means and the developer accommodating portion are integrated, and the shape factor SF-1 is 100 to 160 and the shape factor SF is 1.
-2 is in the range of 100 to 140, a cartridge including color toner particles is detachable, and the color toner particles included in the cartridge form a color toner image for density detection. In a color image forming apparatus for detecting the density by the density detecting means and controlling the image forming conditions based on the detection result, the density detecting means is an optical sensor for detecting specular reflection light. The image forming apparatus.

According to another aspect of the present invention, at least the developing means and the developer accommodating portion are integrated, and the shape factor S
F-1 is 100-160, shape factor SF-2 is 100-
A cartridge containing color toner particles in the range of 140 is removable, the color toner particles included in the cartridge form a color toner image for density detection, and the density of the color toner image for density detection is detected by a density detection means. In the color image forming apparatus that detects the image density by controlling the image forming condition based on the detection result, the density detecting means is an optical sensor capable of detecting both specular reflection light and diffuse reflection light. A color image forming apparatus is provided. According to one embodiment of the present invention, the detection result of diffuse reflection light is corrected using the detection result of specular reflection light, and the image forming condition is controlled based on the detection result of diffuse reflection light.

In each of the above inventions, according to one embodiment, the color image forming apparatus further includes an electrophotographic photosensitive member and a transfer material carrier or an intermediate transfer member, and the density of the color toner image for density detection. Is detected on the electrophotographic photosensitive member, and either the transfer material carrier or the intermediate transfer member.

In each of the above inventions, the color toner particles are toners purified by a polymerization method, or the color toner particles are toners purified by a pulverizing method and subjected to a surface treatment so as to have a spherical shape. Good.

[0083]

DETAILED DESCRIPTION OF THE INVENTION A color image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Example 1 FIG. 1 shows a schematic configuration of an example of a color image forming apparatus according to the present invention. Color image forming apparatus 100 of this embodiment
Is capable of forming a full-color image on a transfer material S, for example, a recording sheet or an OHP sheet, according to an image information signal from an external host device such as a personal computer communicatively connected to the apparatus main body. It is a laser beam printer that adopts the tandem method and the process cartridge method.

The basic structure and operation of the color image forming apparatus 100 of this embodiment are the same as those of the image forming apparatus 150 described with reference to FIG. 18, and the development for detection is formed for controlling the image forming conditions. The detection means for detecting the density of the agent image is different. Therefore, elements having the same configurations and functions as those of the image forming apparatus 150 in FIG. 18 are designated by the same reference numerals, and detailed description thereof will be omitted.

The image forming apparatus 100 is provided with an electrostatic adsorption conveyor belt (ETB) 6 which is movable in the direction of the arrow in the drawing.
Around the periphery, process cartridges 201 to 204 for yellow, magenta, cyan, and black are arranged in a line as a plurality of image forming units that form images of different colors. Further, a density detection sensor 1 characteristic of this embodiment described later is provided so as to face the ETB 6 downstream of the yellow process cartridge 201 on the most downstream side in the moving direction of the ETB 6.

The process cartridges 201 to 204 for the respective colors mounted in the color image forming apparatus 100 have the same structure as that described with the yellow process cartridge 201 as an example with reference to FIG.

In this embodiment, ETB6 has a thickness of 10
A PVDF resin film of 0 μm and a perimeter of 800 mm was used. The toner used as a developer in each of the process cartridges 201 to 204 is refined by a polymerization method and has a shape factor SF-1 of 100 to 130 and a shape factor SF-2 of 10.
0 to 115.

In this embodiment, the process cartridge 20
Nos. 1 to 204 indicate the cartridge replacement life of A4 paper 5
It is defined as 10,000 prints. That is, at the 5% printing rate of A4 paper, 50,000 sheets of toner are stored in the toner container 210, and the life of the developing portion guarantees image quality up to the number of prints where the toner is used up, and the operation cycle as described above is performed. The process is repeated until the toner in the toner container 210 is used up.

As described above, the toner amount of the printed image varies depending on various conditions such as the temperature and humidity conditions in which the color image forming apparatus is used, the degree of use of the photoconductor, and the number of prints. The change in the toner amount changes the density of the printed image and is detected by the user as a change in tint. Therefore, many color image forming apparatuses 100 are equipped with an image density control mechanism that automatically adjusts image forming conditions such as charging potential, exposure amount, and developing bias.

Next, the image density control method in this embodiment will be described.

The color image forming apparatus 100 of this embodiment is
To keep the maximum density of each color constant (Dmax control),
An image density control mechanism is provided for the purpose of keeping the halftone gradation characteristics linear with respect to the image signal (Dhalf control).

Specifically, in the Dmax control, a plurality of density patches formed by changing the image forming conditions are detected by an optical sensor, the condition for obtaining a desired maximum density is calculated from the result, and the image forming condition is set. change.

FIG. 3 shows the structure of the density patch used in the density control of this embodiment. The density patch is formed by repeating a pattern in which 2 × 3 dots in a 4 × 4 dot matrix are filled. As schematically shown in FIG. 28, when this density patch reaches the position of the density detection sensor (optical sensor) 1, the output voltage of the density detection sensor 1 is changed by the A / D converter 52 of the control unit 50. CP after A / D conversion
It is taken in by U51. The control unit 50 may be a control circuit (controller) that integrally controls the operation of the color image forming apparatus 100. The density patch is generated by a pattern generator circuit as a detection image generation unit, and is input to the image forming sequence of each color. Further, prior to this operation, the sensor output voltage when the light emitting element is turned off (minimum amount of light) is measured. The reflected light intensity when each density patch is measured is equivalent to that obtained by subtracting the sensor output voltage when the light emitting element is turned off. The reflected light intensity calculated in this way is converted into density information by a density conversion table preset in the CPU 51.

The density detection sensor 1 directly detects the toner amount on the ETB 6 in this embodiment.
For the sake of convenience, the following description will be made by replacing the amount of applied toner with the density on the transfer material that is achieved by an actual image (an image obtained by forming and fixing a toner image on the transfer material).

The above operation is repeated several times while changing the developing bias. FIG. 4 shows the relationship between the developing bias and the density. The vertical axis represents density and the horizontal axis represents development bias. In the present embodiment, the developing bias is changed five times, and the developing bias is changed so that the density of the obtained five pieces of density information D1 to D5 becomes higher in the order of D1 to D5. From these density information, the developing bias that makes the density of the density patch the optimum value (herein referred to as "Dt") is calculated. That is, two density patches sandwiching the optimum density value Dt are extracted and
By performing linear interpolation at the points, the developing bias (indicated by Va) at which the density of the density patch becomes the optimum value Dt is calculated.

The above operation is performed for all the colors, and the developing bias for which the image density is optimum for each color is calculated.

On the other hand, in the Dhalf control, in order to prevent the output density from being shifted from the input image signal due to the non-linear input characteristic (γ characteristic) peculiar to electrophotography, a natural image cannot be formed. Image processing is performed to cancel and maintain the input / output characteristics linear.

Specifically, a plurality of density patches having different input image signals are detected by the density detecting sensor (optical sensor) 1 to obtain the relationship between the input signal and the density. The output signal of the density detection sensor 1 is input to the CPU 51 of the control unit 50 in the same manner as described above. From the relationship thus obtained, the image signal input to the image forming apparatus is converted by the controller of the image forming apparatus so that a desired density is obtained with respect to the image signal input from the host computer. The Dhalf control is performed after the image forming condition is determined by the Dmax control.

The density patch formed on the ETB 6 is electrostatically collected by the process device by the cleaning process. During the cleaning process, the photosensitive drum 2
A bias having a polarity opposite to the charging polarity of the toner is applied to 30,
At the transfer portion, the toner is attracted to the photosensitive drum 230 and is scraped off by the cleaning blade 251 like the transfer residual toner. Of course, a blade member or the like for scraping the toner image directly from the ETB 6 may be separately provided.

Next, details of the density detection sensor, which is a feature of the present invention, will be described in detail.

FIG. 5 schematically shows the regular reflection light detection type density detection sensor 1 of this embodiment. The concentration detection sensor 1 has a light emitting element 11 and a light receiving element 12, and is arranged to face the ETB 6. The light emitting element 11 irradiates the toner t with infrared light. In the density detection sensor 1, the light receiving element 12 detects the light reflected in the target angle with the irradiation angle α with respect to the normal line of the surface of the ETB 6.

FIG. 6A is a conceptual diagram of specular reflection light detected by the density detection sensor 1. The solid line shows the irradiation light to the toner t and the specular reflection light from the surface of ETB6. This ETB6
Since the light reflected from the surface of the ETB6 depends on the refractive index and the surface state peculiar to the material of the ETB6 surface, it is not affected by the shape and particle size distribution of the toner particles as the developer. The density control of this embodiment avoids the fluctuation of the density control due to the fluctuation of the toner particle size by utilizing the characteristic of the regular reflection light.

FIG. 7 shows the relationship between the density (toner amount) and the specular reflection light amount. The vertical axis represents sensor output when only specular reflection light is detected, and the horizontal axis represents density. The amount of specular reflection light is ETB6
It becomes maximum when the toner t is not present on the surface. E
When a large amount of toner t is present on TB6, as shown in FIG.
As shown in (B), ETB6 is present in the portion where the toner t is present.
The surface of is hidden and the reflected light is reduced. That is, the amount of reflected light decreases as the amount of toner increases.

Thus, the density detection sensor 1 of this embodiment
Is a detector having high accuracy because the output increases when the toner amount is small, that is, when the density is low. The detectable color toner density (toner amount) is about 1.0 or less. Therefore, the density patch used for the Dmax control needs to be formed in halftone as described above.

Further, a part of the diffuse reflection light from the toner t also enters the light receiving element 12 of the density detecting sensor 1. Figure 8
2 shows the relationship between the amount of specular reflection light and the amount of diffuse reflection light that are incident on the light receiving element 12. The solid line shows the relationship between the regular reflection light amount and the density (toner amount), and the broken line shows the relationship between the diffuse reflection light amount and the density (toner amount). Therefore, the sensor output is the sum of the regular reflection light amount and the diffuse reflection light amount as shown in FIG.

FIG. 10 shows the fluctuation of the sensor output when the toner average particle diameter changes. In the figure, the solid line I is the sensor detection output when the toner average particle diameter is 5.5 μm, and the broken line III is the sensor detection output when the toner average particle diameter is 7.0 μm.
As described above, the density detection sensor 1 is slightly affected by the particle size variation in the control on the high density side, and the sensor output decreases when the average particle size becomes large. Since the density patch is created in halftone, the influence of sensor output fluctuation is small.
The toner of each average particle size is the same as the initial toner of the process cartridge 201 in the above-mentioned print test.
It is the toner after printing 50,000 sheets.

The color image forming apparatus and the density control method in this embodiment have been described above.

The features of the density control shown in this embodiment are summarized as follows.

The characteristics of the regular reflection light detection type density detection sensor 1 are that the sensor output fluctuation is small even if the average particle diameter of the toner changes, and the accuracy is high when the density is low.
In the density control of the present embodiment, by using the specular reflection light detection type density detection sensor 1, the output fluctuation of the density detection sensor caused by the average particle diameter of the toner which changes with time each time the process cartridge is used. Can be suppressed.
Then, the tint after the density control can be stabilized, and the tint variation can be suppressed to the discrimination limit ΔE = 1.6 or less.

Next, the results of evaluating the effects of the present embodiment will be described. Here, the variation in tint when the average particle diameter of the spherical toner changes is evaluated.

Spherical toners having an average particle diameter of 5.5 μm and 7.0 μm (SF-1 = 100 to 130, SF-2 = 100).
~ 115) (each obtained by the above-mentioned print test), Dmax control and Dha, respectively.
If control was performed and 10 patch images with different densities were drawn. The target densities of the patch image are 0.1, 0.2, 0.5, 0.7, 1.0 and 1.4, respectively.
Is. In FIG. 11, the chromaticity of each patch is measured with a chromaticity meter,
It is the result of evaluating the chromaticity difference between the two when the patch image of each target density was created.

As a result, the chromaticity difference ΔE is smaller on the low density side and larger on the high density side. It is considered that this is due to the characteristics of the regular reflection light detection type density detection sensor 1. As described above, the regular reflection light detection type density detection sensor 1 has a smaller toner amount, that is, the lower the density, the larger the sensor output and the higher accuracy, and the higher the density, the lower the accuracy. Therefore, it is necessary to perform the Dmax control on the halftone image, and in this embodiment, the Dmax control is performed on the halftone image as described above. However, since the Dmax control is a control performed to determine the maximum amount of applied toner, the higher the density of the density patch, the higher the accuracy. Further, it is slightly affected by the sensor output fluctuation when the particle size changes. The results shown in FIG. 11 are considered to be due to these.

However, the chromaticity difference ΔE does not exceed the discrimination limit 1.6 in the side-by-side comparison for any of the target densities, and the density control is performed using the density detection sensor 1 of this embodiment. , It is not detected by the user as a color change.

In the density control of the conventional example, the maximum chromaticity difference was 4.4 (Table 1). On the other hand, in the density control of this embodiment, the maximum chromaticity difference was 1.6, and the accuracy could be greatly improved. This is because the output of the regular reflection detection type density detection sensor 1 which is less affected by the particle size variation is used.

As described above, according to the density control of the present embodiment, it is possible to stabilize the tint particularly on the low density side and suppress the chromaticity difference ΔE to be equal to or less than the discrimination limit in the side-by-side comparison. .

Embodiment 2 Next, another embodiment of the present invention will be described. In this embodiment, the light receiving element 12 of the specular reflection light detection type density detection sensor 1 is used.
A method of increasing the detection accuracy by detecting the diffuse reflection light incident on the and correcting it will be described.

Specifically, the density patch formed directly on the ETB 6 and the same patch formed on the black solid image formed on the ETB 6 are detected in combination. As a result, the diffuse reflection component in the reflected light amount is removed and only the specular reflection component is extracted.

Since the main structure of the color image forming apparatus and the image density control method of this embodiment are the same as those of the first embodiment, the elements having the same structure and action are designated by the same reference numerals, Detailed description is omitted.

In this embodiment, a black solid image is formed on the ETB 6 and then a density patch is formed thereon.

As shown in FIG. 12, the density detection sensor 1 arranged to face the ETB 6 has a color toner density patch PA (PA 1, PA 2) formed on the ETB 6 and an ET.
A black solid image U is formed on B6, and the density patches PB (PB1, PB2) of the color toner formed thereon are detected.

The characteristic of the reflected light when the density patch PA of the color toner formed on the ETB 6 is detected is as shown in FIG. On the other hand, as shown in FIG. 12, when the black solid image U is formed on the ETB 6 and the density patch PB of the color toner formed thereon is detected, the characteristic of the reflected light is as shown in FIG.

That is, the characteristic of the reflected light when the density patch PA of the color toner formed on the ETB 6 is detected is
It is the sum of the specular reflection light component and the diffuse reflection light component. On the other hand, the characteristic of the reflected light when the density patch PB of the color toner formed on the black solid image U is detected is that the specularly reflected light component from the surface of the ETB 6 is hidden by the black solid image.
Only the diffuse reflected light component is included. Therefore, by subtracting the diffuse reflection light component from the density patch PB on the black solid image U from the reflection light of the density patch directly formed on the ETB 6, that is, the sum of the regular reflection light component and the diffuse reflection light component, Only the specular reflection light component as shown in 7 is extracted and used for density detection.

Next, the results of evaluation of the effects of the present embodiment will be described. Here, the variation in tint when the average particle diameter of the spherical toner changes is evaluated.

Spherical toners having an average particle diameter of 5.5 μm and 7.0 μm (SF-1 = 100 to 130, SF-2 = 100).
~ 115) (each obtained by the above print test), Dmax control and Dhal
f control was performed and 10 patch images with different densities were drawn. The target densities of the patch image are 0.1, 0.2, 0.5, 0.7, 1.0 and 1.4, respectively. FIG. 14 shows the chromaticity difference between both patches when the chromaticity of each patch is measured with a chromaticity meter and a patch image of each target density is created.

As a result, the chromaticity difference ΔE is smaller on the low density side and larger on the high density side. This is Example 1
As described above, it is considered that this is due to the fact that the Dmax control is performed on the halftone image.

However, the chromaticity difference ΔE does not exceed the discrimination limit 1.6 in the side-by-side comparison for any of the target densities. Further, as can be seen from FIG. 14, the fluctuation of the diffuse reflected light output could be eliminated. That is, Example 1
Although the maximum chromaticity difference was 1.6 in the density control of No. 2, the maximum chromaticity difference of 1.2 was improved in the density control of the present example.

The reason why the accuracy can be improved in this embodiment as compared with the first embodiment is considered as follows.
That is, in Example 1 in which the output from the specular reflection light detection type density detection sensor 1 was directly used, the diffuse reflection light component remained in the sensor, and the cause of the particle size fluctuation remained slightly.
On the other hand, the density control of this embodiment is performed by the density detection sensor 1
The accuracy is improved because the density can be detected only by the specular reflection light output, excluding the influence of the diffuse reflection light output incident on.

As described above, according to the density control of this embodiment, the same effect as that of the first embodiment can be obtained, and the accuracy can be further improved.

Embodiment 3 Next, still another embodiment of the present invention will be described. In the present embodiment, the diffuse reflection light incident on the light receiving element 12 of the regular reflection light detection type density detection sensor 1 is detected and corrected to extract only the regular reflection light component to enhance the detection accuracy on the low density side. Further, a method of correcting the sensor output fluctuation of the diffuse reflection light component by using the specular reflection light component to enhance the detection accuracy on the high density side will be described.

That is, this embodiment is different from the second embodiment in that (1) the sensor output fluctuation of the diffuse reflection light component is corrected by using the specular reflection light component, and (2) the diffusion after correction by the Dmax control is performed. There are three points: using the reflected light output and (3) using the density patch of the solid image.

Since the main structure of the color image forming apparatus and the image density control method of this embodiment are the same as those of the second embodiment, a detailed description is omitted here.

The procedure for correcting the sensor output fluctuation of the diffuse reflection light component using the regular reflection light component will be described below.

Specifically, a reference toner image of color toner for correcting the diffuse reflected light component is formed on the ETB 6, and the sensor output of the diffuse reflected light component and the specular reflected light component is obtained from the reflected light from the reference toner image. Is detected, and the diffuse reflection light component output value is corrected based on the specular reflection light component output value at that time.

To further explain, FIG. 15 shows the relationship between the amount of reflected light from the reference toner image and the density (toner amount) obtained by the density detecting method of the second embodiment. The solid line shows the amount of specular reflection light, and the dotted line shows the amount of diffuse reflection light.

First, the surface output of the ETB 6 is detected by the specular reflection light detection type density sensor 1. The detected value at this time is as shown in FIG.
It becomes P2 out of 5. Next, a reference toner image is formed on ETB6. Here, the reference toner image does not need to have a constant density at all times, and it is important that the reference toner image has a pattern in which both diffuse reflection output and specular reflection output are sufficiently obtained.

In this embodiment, a halftone dither image with an image ratio of 33% was used as the reference toner image. In the color image forming apparatus used in this embodiment, the image density of the 33% halftone dither image is about 0.3 or more,
It falls within the range of 0.7 or less. In this embodiment, the density of the reference toner image was 0.6 (D1 in the figure).

Next, the specular reflection light component and diffuse reflection light component outputs from the reference toner image are derived using the method of the second embodiment. In FIG. 15, the specular reflection light component output and the diffuse reflection light component output are P4 and S2, respectively.

Next, the density D1 of the reference toner image is calculated from the specular reflection output P4 using a density conversion table.
Further, the reference output S1 (calculated value) corresponding to the diffuse reflection light component output for this density D1 is calculated from the density conversion table provided for the diffuse reflection light component output.

The diffuse reflection light value S2 actually obtained from the reference toner image and the reference output S1 (calculated value) calculated for the density D1 of the reference toner image are used to calculate the diffuse reflection light from the following equation. The variation ratio αs of the component output is calculated. αs = S2 / S1

Since the variation ratio αs of the diffuse reflected light component output is obtained by the above procedure, the densities of other toner images (density patches used for density control) are determined by the diffuse reflected light component output value for the toner image. It is calculated after being normalized by αs. This makes it possible to correct the output fluctuation caused by the change in the average toner particle size.

Next, the difference between the Dmax control and the second embodiment will be described.

By performing the above correction, it is possible to detect the density using the diffuse reflection output, and thereby it is possible to perform the Dmax control using the high density patch. The diffuse reflection output is different from the regular reflection output in that the density is 1.0
Since it is possible to detect even with the above, Dmax control can be performed using the density patch of the solid image. Since only specular reflection light output is used in Examples 1 and 2, a high density patch with a density of 1.0 or more cannot be read,
A halftone image is used for Dmax control. However, in order to control the maximum amount of applied toner (corresponding to a density of about 1.4 in this embodiment), it is desirable in terms of accuracy to use a density patch with a direct density of about 1.4.

FIG. 16 is a density patch image used in this embodiment. It is formed by repeating a solid image in which 4 × 4 dots in a 4 × 4 dot matrix are filled.

Next, the results of evaluating the effects of the present embodiment will be described. Here, the variation in tint when the average particle diameter of the spherical toner changes is evaluated.

Spherical toners having an average particle diameter of 5.5 μm and 7.0 μm (SF-1 = 100 to 130, SF-2 = 100).
~ 115) (each obtained by the above print test), Dmax control and Dhal
f control was performed and 10 patch images with different densities were drawn. The target densities of the patch image are 0.1, 0.2, 0.5, 0.7, 1.0 and 1.4, respectively. FIG. 17 shows the results of measuring the chromaticity of each patch with a chromaticity meter and evaluating the chromaticity difference between the two when a patch image of each target density was created.

As a result, the chromaticity difference ΔE is small on both the low density side and the high density side. This is because the maximum toner amount is controlled with high accuracy by performing the Dmax control for the solid image.

By the density control of the present embodiment, the chromaticity difference ΔE for any of the target densities eliminates the fluctuation of the diffuse reflected light output, and further suppresses the hue fluctuation as compared with the first and second embodiments. The discrimination limit of 0.8 or less was achieved.

The maximum chromaticity difference of the density control of Example 2 was 1.2, and the accuracy of the density control of this example was 0.7, which was a maximum chromaticity difference. The reason is considered as follows. The density detection sensor detects the amount of applied toner, but here, for the sake of convenience, the description will be made by converting it to the density on the actual image achieved by the amount of applied toner.

In the second embodiment, the diffuse reflection light component is extracted from the output of the regular reflection light detection type density detection sensor 1 to detect the density, and the accuracy can be improved as compared with the first embodiment.
However, since the output of the specular reflection light is small on the high density side, only the density of about 1.0 or less can be normally detected. Therefore, the Dmax control is performed with a halftone density patch, and the maximum toner application amount is obtained by converting the density into a solid image.

On the other hand, in this embodiment, since the diffuse reflected light output can be used for the density detection, it is possible to detect the density of 1.0 or more. (The color image forming apparatus used in this embodiment defines the toner application amount that achieves the density of 1.4 as the maximum toner application amount.) Therefore, the density patch is formed by the solid image and the maximum toner application amount is set. The development conditions to be achieved can be directly determined. Thereby, the accuracy is improved as compared with the second embodiment.

Since the Dmax accuracy can be improved to prevent the toner from being overloaded in the high density area of the color toner, it is possible to prevent various problems (fixing failure, transfer failure, etc.) that occur when the toner loading amount is large. .

As described above, according to this embodiment, the density patch of the color toner is formed on the ETB 6, and the reflected light is detected by the diffuse reflection type and regular reflection type density detection sensors 1 and 180, and the regular reflection at that time is detected. By correcting the output of the diffuse reflection type density detection sensor 180 based on the output value of the light detection type density detection sensor 1, it is possible to accurately detect the density even if the average particle diameter of the spherical toner changes.

In Examples 1 to 3 described above, the color image forming apparatus having the ETB (electrostatic adsorption conveyance belt) 6 was described as an example, but the present invention is not limited to this. The transfer material carrier is not limited to a belt, and may be a drum shape, a drum shape formed by stretching a sheet on a frame, or the like. Also, the color image forming system is ET
The present invention is not limited to the multiple transfer system including B6, but can be applied to a color image forming apparatus of an intermediate transfer body system, and similar effects can be obtained. As is well known to those skilled in the art, the color image forming apparatus of the intermediate transfer system is, for example, as shown in FIG. Toner images of different colors are sequentially formed on the intermediate transfer belt 6 ', and the toner images are formed by the secondary transfer means 3'on the transfer material S conveyed by the separately provided transfer material conveying means 40. Transfer in a batch to obtain a color image. Even in such a color image forming apparatus, if at least the developing means and the developer accommodating portion are integrally formed into a cartridge and can be attached to and detached from the apparatus main body, the above-described problem may occur. By performing the same image density control as in the above respective embodiments,
The same effect as above can be obtained. The image density control method may be the same as that in each of the above embodiments. Here, ETB6
Is read as an intermediate transfer member, and the entire description in each of the above-mentioned examples is incorporated by reference. 29, elements having the same operations as those of the color image forming apparatus 100 of FIG. 1 are designated by the same reference numerals.

Further, the present invention has a single image carrier (photosensitive drum or the like), and toner images of different colors are sequentially formed on the image carrier by a plurality of developing means, and the toner images are sequentially formed. An image forming apparatus that obtains a color image by transferring to a transfer material on a transfer material carrier, or after transferring to an intermediate transfer body and then collectively onto a transfer material, and further, superimposing a toner image on the image carrier. It is equally applicable to a multi-developing type image forming apparatus which forms a color image by collectively transferring the image onto a transfer material after that. From the above description, it is obvious to those skilled in the art that the principle of the present invention can be applied to color image forming apparatuses of these other types as well, without further explanation.

Further, in each of the above-described embodiments, the density patch and the reference toner image are formed on the ETB 6 (or the intermediate transfer member), and the density detection sensor 1 detects the density patch, but the present invention is not limited to this. Not what is done,
The configuration may be such that detection is performed on the image carrier (photosensitive drum or the like), and the same effect can be obtained.

Further, in each of the above embodiments, the cartridge attachable to and detachable from the color image forming apparatus integrally includes the developing device having the developing means and the developer accommodating portion, the photoconductor, the charging means and the cleaning means. Although the process cartridge has been described as a cartridge, the present invention is not limited to this. For example, the present invention can be equally applied to a developing cartridge detachable image forming apparatus in which the developing means and the developer accommodating portion are integrally formed into a cartridge and can be attached to and detached from the apparatus main body. Can be obtained.

[0158]

As described above, according to the present invention,
At least a developing unit and a developer accommodating portion are integrated, and a cartridge including color toner particles having a shape factor SF-1 of 100 to 160 and a shape factor SF-2 of 100 to 140 is removable, and a cartridge A color toner image for density detection is formed by the color toner particles included in the color toner image, the density of the color toner image for density detection is detected by the density detection means, and the image forming condition is controlled based on the detection result. The apparatus is configured such that the density detecting means is an optical sensor that detects specular reflection light, or the density detecting means is an optical sensor that can detect both specular reflection light and diffuse reflection light. Therefore, it is possible to suppress the variation in tint and always reproduce the optimal tint.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of an embodiment of a color image forming apparatus according to the present invention.

2 is a schematic sectional view of a process cartridge mounted in the color image forming apparatus of FIG. 1 (FIG. 18).

FIG. 3 is a schematic diagram of an example of a density patch.

FIG. 4 is a graph showing an example of a relationship between developing bias and density.

FIG. 5 is a schematic configuration diagram of a regular reflection light detection type density detection sensor.

6A and 6B are conceptual diagrams of specular reflection light detected by a density detection sensor.

FIG. 7 is a conceptual diagram of the output of the density detection sensor.

FIG. 8 is a graph diagram for explaining an amount of specular reflection light and an amount of diffuse reflection light which are incident on the light receiving element of the density detection sensor.

FIG. 9 is a conceptual diagram of an output of a regular reflection light detection type density detection sensor.

FIG. 10 is a conceptual diagram of an output fluctuation of the regular reflection light detection type density detection sensor when the toner average particle diameter changes.

FIG. 11 is a graph showing the evaluation result of the tint variation when the toner average particle diameter in Example 1 changes.

FIG. 12 is a schematic view showing another embodiment of the density patch formed on the electrostatic adsorption and conveyance belt.

FIG. 13 is a graph showing characteristics of reflected light when a density patch formed on a black solid image is detected.

FIG. 14 is a graph showing the evaluation result of the tint variation when the average toner particle diameter is changed in Example 2.

FIG. 15 is a graph for explaining a method for correcting diffuse reflection output by regular reflection output.

FIG. 16 is a schematic view showing another embodiment of the density patch.

FIG. 17 is a graph showing the evaluation result of tint variation when the toner average particle diameter in Example 3 changes.

FIG. 18 is a schematic sectional view of an example of a conventional color image forming apparatus.

FIG. 19 is a schematic diagram for explaining a coefficient defining method for calculating a toner shape coefficient.

FIG. 20 is a conceptual diagram of diffusely reflected light detected by a sensor.

FIG. 21 is a schematic configuration diagram of a diffuse reflection light detection type density detection sensor.

FIG. 22 is a conceptual diagram of diffusely reflected light detected by a sensor.

FIG. 23 is a graph for explaining changes in toner particle number frequency and average particle diameter.

FIG. 24 is a graph showing a theoretically calculated diffuse reflection light intensity distribution.

FIG. 25 is a schematic configuration diagram of a spectrophotometer.

FIG. 26 is a graph showing the angular distribution of diffuse reflection intensity.

FIG. 27 is a conceptual diagram of diffusely reflected light from pulverized toner having an irregular shape.

FIG. 28 is a schematic control block diagram of image forming condition control using a density detection sensor.

FIG. 29 is a schematic configuration diagram of another example of another color image forming apparatus to which the present invention can be applied.

[Explanation of symbols]

1 Regular reflection light detection type density detection sensor 6 Electrostatic adsorption conveyor belt (ETB) 200 developer 201 process cartridge 202 process cartridge 203 process cartridge 204 process cartridge 210 toner container (developer container) 220 developer container 221 developing roller (developing means, developer carrier) 230 Photosensitive drum (image bearing member, electrophotographic photosensitive member) 180 Diffuse reflection light detection type density detection sensor S transfer material t toner

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 115 G03G 15/08 115 115 507 15/16 15/16 15/08 507L (72) Inventor Yoichiro Maebashi Tokyo 3-30-2 Shimomaruko, Ota-ku Canon Inc. F-term (reference) 2H027 DA09 DA10 DE02 DE07 EA05 EB04 EC03 2H077 AA02 DA05 DA31 DA47 DA63 DB08 EA11 GA13 2H200 FA02 GA12 GA23 GA34 GA46 GA47 GA49 GA57 GB12 GB25 HA01 HB12 JA02 JB06 JB39 JC03 JC09 JC19 JC20 PA02 PA19 PB17 PB18 2H300 EB04 EB07 EB12 EC05 EF13 EH16 EJ01 EJ09 EJ22 EJ23 EJ32 EJ43 EJ47 EJ50 GG01 GG02 GG37 QQ02 RR31 RR32 RR35 RR37 RR35 RR37 RR35 RR37

Claims (6)

[Claims] 1. A cartridge comprising at least a developing means and a developer accommodating portion, color toner particles having a shape factor SF-1 in the range of 100 to 160 and a shape factor SF-2 in the range of 100 to 140, is attached and detached. It is possible to form a color toner image for density detection by the color toner particles included in the cartridge, detect the density of the color toner image for density detection by the density detection means, and form an image based on the detection result. A color image forming apparatus for controlling conditions, wherein the density detecting means is an optical sensor for detecting specularly reflected light. 2. A cartridge comprising at least a developing means and a developer accommodating portion, and having color toner particles having a shape factor SF-1 in the range of 100 to 160 and a shape factor SF-2 in the range of 100 to 140. It is possible to form a color toner image for density detection by the color toner particles included in the cartridge, detect the density of the color toner image for density detection by the density detection means, and form an image based on the detection result. A color image forming apparatus for controlling conditions, wherein the density detecting means is an optical sensor capable of detecting both specular reflected light and diffuse reflected light. 3. The color according to claim 2, wherein the detection result of the diffuse reflection light is corrected by using the detection result of the regular reflection light, and the image forming condition is controlled based on the detection result of the diffuse reflection light. Image forming apparatus. 4. An electrophotographic photosensitive member and a transfer material carrying member or an intermediate transfer member, wherein the density of the color toner image for density detection is the electrophotographic photosensitive member and the transfer material carrying member or the intermediate material. The color image forming apparatus according to claim 1, wherein the image is detected on any one of the transfer bodies. 5. The color toner particles are toners refined by a polymerization method.
4. The color image forming apparatus according to any one of 4 above. 6. The color image forming apparatus according to claim 1, wherein the color toner particles are refined by a pulverizing method and subjected to a surface treatment so as to be close to a spherical shape.