JP2003307868A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which prevents the deterioration of the developing properties of toner having small particle size, not to mention toner having large particle size, and by which an image free from the deterioration of the quality of solidness is obtained even in the case of using toner whose particle size distribution is wide. <P>SOLUTION: The developing device develops an electrostatic latent image formed on the surface of a photoreceptor drum by laser exposure under a condition that developing bias is applied to a developing sleeve with the toner in two-component developer carried on the developing sleeve. The toner whose particle size distribution is wide and which includes ≤30 num.% toner in the range of d<2M/3, ≤30 num.% toner in the range of 4M/3<d and ≥99 num.% toner in the range of 0<d<2M is used as the toner assuming that the number average particle size of the toner is M and the particle size of the toner is (d). Then, rectangular bias whose frequency is 5 to 20 kHz is applied as the developing bias. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus using an electrophotographic system such as a copying machine and a laser beam printer.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a crushed toner is generally used as a developer in which a lump obtained by kneading a resin and other constituent components is collided with a target to be finely crushed. The characteristics of this pulverized toner are
Generally, the particle size distribution is wide and the composition is the same for all particle sizes.

Generally, the toner flies by the developing electric field E, the force F applied to the toner is described by ^{F = qE-A (q 2} / r 2) ··· (1). Here, q is the charge amount of the toner, r is the distance from the center of charge to the nearest contact point, and A is a constant.

[0004] The equation of motion at this time, the mass of toner m, when an acceleration is a, can be represented by a F = ma = qE-A ( q 2 / r 2) ··· (2), now , acceleration a when the toner flies is, a = E (q / m ) -A (q / m) (q / r 2) becomes (3). From this, it can be seen that when the developing electric field E is constant, the toners having the same q / m have the same acceleration a, that is, the movement characteristic.

Here, the charge amount q and the mass m are represented by the charge density σ of the toner surface and the toner particle size d: q = σS = σBd ² (4) m = Cd ³ ... Since (5), q / m = (σB / C) (d ² / d ³ ) = D / d (6) (where B, C, and D are constants).

In summary, a = D (E / d)-(F / d) (q / r ² ) ... (7) (F is a constant).

[0007]

From the above equation (7),
It can be seen that a toner having a smaller particle size usually develops by moving faster, and a toner having a larger particle size develops thereafter. Furthermore, as the toner has a smaller particle diameter, the effect (mirror power) of the second term of the formula (7) becomes more effective, and the toner cannot fly. That is, it can be seen that the developability is lowered and the image density is lowered.

Therefore, in order to use the toner having a small particle diameter, the developing electric field may be increased, but in practice, the usable particle diameter is determined by the characteristics of the photosensitive drum, and it is currently 7 to.
8 μm toner is used.

In the present specification, the particle size of toner means the Coulter Counter Multisizer (II) manufactured by Coulter Inc.
Type), the one represented by the peak of the number particle size distribution measured with an aperture of 100 μm.

However, in order to improve the quality of the final image,
It is necessary to improve the reproducibility of dots due to development. Therefore, at the development stage, studies are underway using a toner having a smaller particle size and a sharp particle size distribution. However, it is repeated to decrease the developability and sharpen the particle size distribution described above. Due to the classification work, there is a problem that the production yield of toner is reduced.

Further, in order to cope with the increase in speed, it has been studied to improve the fixing property by a treatment such as increasing the colorant of the toner (covering power up). But,
Since the paper P has unevenness on the surface as shown in FIG. 11A, the toner t adhered to the surface of the paper P by transfer as shown in FIG. 11B is as shown in FIG. 11C. By fixing, the mountain portion of the surface is deeply embedded in the fibers of the paper P, and that portion becomes a voluminous portion with a low density, and the entire solid black portion has a feeling of being messy, resulting in deterioration of the solid black quality. was there.

The object of the present invention is not to reduce the developability of small particle size toners, not to mention large particle size toners.
It is an object of the present invention to provide a developing device capable of obtaining an image without deterioration in solid quality even when a toner having a wide particle size distribution is used.

[0013]

The above object can be achieved by the developing device according to the present invention. In summary, the present invention provides an electrostatic latent image formed on the surface of an image carrier by laser exposure.
In a developing device for developing with a toner carried on a developer carrying member while applying a developing bias to the developer carrying member, a toner having a wide number particle size distribution is used as the toner, and a high frequency rectangle is used as the developing bias. A developing device characterized by using a bias.

According to the present invention, preferably, in the toner, the number average particle diameter of the toner is M, and the particle diameter of the toner is d.
In the range of d <2M / 3, 30% or less of the toner is contained, in the range of 4M / 3 <d, 30% or less of the toner is contained, and in the range of 0 <d <2M, 99% or more of the toner is contained. Having a particle size distribution including. More preferably, M / 3 <d
<2M / 3 includes 30% by number or less of toner and 4
The particle size distribution includes 30% by number or less of the toner in the range of M / 3 <d <5M / 3, and 99% by number or more of the toner in the range of 0 <d <2M.

The toner is a one-component developer magnetic toner,
Either a non-magnetic toner of a one-component developer or a non-magnetic toner of a two-component developer is possible. The toner contains at least 3 parts of pigment. The number average particle diameter of the toner is 4 to 10 μm.
Is. The frequency of the rectangular bias is 5 to 20 kHz.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described in more detail with reference to the drawings.

In the following, as an image forming apparatus, a plurality of latent image forming means for digitally forming electrostatic latent images on a plurality of image carriers and an electrostatic latent image formed on the image carriers are provided. An image forming apparatus equipped with a plurality of developing means for developing using a two-component developer of corresponding colors and a plurality of toner replenishing means for replenishing toner to the developing means is adopted. Not only the developing means of various image forming apparatuses but also 1
An image forming apparatus in which one developing unit faces one image carrier or a developing unit in an image forming apparatus in which a plurality of developing units faces one image carrier. Are equally applicable. It can also be applied to the case where a one-component magnetic developer (magnetic toner) or a one-component non-magnetic developer (non-magnetic toner) is used as the developer.

Embodiment 1 First, with reference to FIG. 1, the overall structure of an image forming apparatus in which the developing device of the present invention is installed will be described. In FIG. 1, an image of a document 1 to be copied is projected by a lens 2 onto an image sensor 3 such as a CCD. This image sensor 3
Generates a photoelectric conversion signal corresponding to the density of each pixel, that is, an analog image signal, by decomposing the original image into a large number of pixels. The analog image signal output from the image pickup element 3 is sent to the image signal processing circuit 4, where it is converted into a pixel image signal having an output level corresponding to the density of the pixel for each pixel, and then the pulse width modulation circuit 5 receives the pixel image signal. Sent.

The pulse width modulation circuit 5 has a width (time width) corresponding to the level of each input pixel image signal.
The laser driving pulse of is formed and output. That is, as shown in FIG. 2A, a drive pulse W having a wider width is supplied to a high-density pixel image signal, and a drive pulse I having an intermediate width is supplied to a low-density pixel image signal. Form.

The laser drive pulse output from the pulse width modulation circuit 5 is supplied to the semiconductor laser 6 and causes the semiconductor laser 6 to emit light for a time corresponding to the pulse width. Therefore, the semiconductor laser 6 is driven for a longer period of time with respect to the high-concentration pixel and is driven for a shorter period of time with respect to the low-concentration pixel. Therefore, the photosensitive drum 10 is exposed to a long range in the main scanning direction for high density pixels and a short range in the main scanning direction for low density pixels by the optical system described below. Note that FIG.
In (d), the electrostatic latent images of low, medium, and high density pixels are denoted by reference symbol L,
Indicated by M and H.

Laser light 6 emitted from the semiconductor laser 6
a is swept by the rotating polygon mirror 7, and a lens 8 such as an fθ lens and a fixed mirror 9 that directs the laser beam 6a toward the photosensitive drum 10 are used to move the photosensitive drum 10 in a direction substantially parallel to its rotation axis (main scanning direction). ) To form an electrostatic latent image on the surface of the photosensitive drum 10.

The photosensitive drum 10 is a drum-type electrophotographic photosensitive member which has a photosensitive member such as amorphous silicon, selenium, or OPC on its surface and is rotated in the direction of the arrow. After receiving, it is uniformly charged by the primary charger 12. After that, the laser light modulated corresponding to the above-mentioned image information signal is exposed and scanned, whereby an electrostatic latent image corresponding to the image information is formed.

This electrostatic latent image is subjected to reversal development by a developing device 14 having a two-component developer 13 in which toner and carrier are mixed and visualized as a toner image. Reverse development
This is a developing method in which toner charged to the same polarity as the latent image is attached to the exposed area of the photosensitive drum 10 to visualize the toner.

This toner image is transferred onto the transfer material P conveyed to the photosensitive drum 1 by the transfer material carrying belt 15 by the action of the transfer blade 16. Transfer material carrying belt 1
Reference numeral 5 is stretched between two rollers 17a and 17b, and is rotationally driven in the direction of the arrow in the figure to convey the transfer material P held thereon to the photosensitive drum 10. The transfer material P on which the toner image has been transferred is separated from the transfer material carrying belt 15 and conveyed to the fixing device 19, where heat and pressure are applied to the transfer material to permanently fix the toner image on the surface of the transfer material P. To be done. The transfer residual toner remaining on the photosensitive drum 10 after the transfer is then removed by the cleaner 18.

Although only a single image forming station (including the photosensitive drum 10, the exposing device 11, the primary charging device 12, the developing device 14 and the like) is shown for simplicity of description,
The image forming apparatus is a color image forming apparatus including image forming stations for cyan, magenta, yellow, and black, for example, and the image forming stations are sequentially arranged on the transfer material carrying belt 15 along the moving direction thereof. An electrostatic latent image for each color is sequentially formed on the photosensitive drum 10 of each of the image forming stations, the image of the original being separated, and the electrostatic latent image for each color is developed by the developing device having the toner of the corresponding color, and the transfer material carrying belt 15 is formed. The images are sequentially transferred and transferred onto the transfer material P conveyed by.

An example of the developing device 14 is shown in FIG. The present invention is characterized in that the particle size distribution and the developing bias of the toner used in the developing device 14 are specified to be specific. These will be described later.

As shown in FIG. 3, the developing device 14 is arranged so as to face the photosensitive drum 10, and the lower half of the developing device 14 has a first partition wall 31 extending in a direction perpendicular to the plane of the drawing. It is divided into a chamber (developing chamber) 32 and a second chamber (stirring chamber) 33. In the first chamber 32, a non-magnetic developing sleeve 34 that rotates in the direction of the arrow is arranged at the opening facing the photosensitive drum 10, and a roller-shaped magnet 35 is fixedly arranged in the developing sleeve 34. . A magnetic blade 38 is arranged above the developing sleeve 34 with a predetermined gap therebetween.

Developer stirring screws 36 and 37 are arranged in the first chamber 32 and the second chamber 33, respectively. The screw 36 stirs and conveys the developer 13 in the first chamber 32 in the longitudinal direction of the developing sleeve 34, and the screw 3
7 stirs and conveys the developer 13 in the second chamber 33 in the opposite direction to the above, and in the process, stirs and mixes with the toner 22 replenished from the toner replenishing tank 20 of FIG. Toner supply tank 20
Is connected to a portion of the developing device 14 above the second chamber 33, and supplies the replenishment toner 22 contained therein to the conveying screw 2
The sheet is conveyed by 1 and dropped into the second chamber 33 to be replenished.

The partition wall 31 has a developer passage (not shown) for communicating the first chamber 32 and the second chamber 33 with each other at the front and rear ends in FIG. By the conveyance of the screw 36, the developer 31 whose toner concentration has decreased due to the consumption by the development is transferred from the first chamber 32 to the second chamber 33 through one passage of the partition wall 31 and is conveyed by the screw 37. The developer 31 whose concentration has been restored by the replenishment of the toner 22 in the second chamber 33 is returned from the other passage of the partition wall 31 into the first chamber 32, and thus circulates in the developing device 14.

The two-component developer 13 in the developing device 14 is carried on the developing sleeve 34 by the magnetic force of the magnet 35, and the carried developer is conveyed to the magnetic blade 38 as the developing sleeve 34 rotates. After being regulated to a predetermined layer thickness by the blade 38, the photosensitive drum 10
To a developing area facing the image forming area and is used for developing the latent image on the photosensitive drum 10. During development, the developing sleeve 34 may have a developing bias (rectangular bias,
Pulse bias and / or DC bias) are applied.

As described above, since the toner density of the developer 13 in the developing device 14 decreases due to the development of the latent image, the toner 22 is replenished from the toner replenishing tank 20 to the developing device 14. The toner replenishment is controlled by the density control device so as to keep the toner density of the developer 13 constant or the image density constant.

In this image forming apparatus, as a density control apparatus, a patch image for reference is formed on the photosensitive drum 10,
The patch density is detected by the image density sensor 26 and controlled (patch detection ATR), and the toner density sensor 25 installed in the developing unit 14 detects the toner density of the developer 13 in the developing unit 14. There are two control methods (developer reflection ATR), and toner replenishment control by the developer reflection ATR and patch detection ATR can be performed with a chromatic color developer (color developer) and an achromatic black developer. It is divided.

That is, since the yellow, magenta, and cyan color developers can detect the change in tint by the amount of reflected light,
The developer reflection ATR by the density sensor 25 installed in the developing device 14 is used, and the black developer absorbs light, so the patch detection ATR method is used.

Therefore, at a certain timing during image formation,
The concentration sensors 25 and 26 are operated, and the CPU 27
The amount of toner to be replenished in the developing device 14 necessary for keeping the toner density or the image density of the developer 13 constant is calculated. Then, the rotation time of the motor 23 is obtained from the calculated toner amount, and the conveying screw 2 of the toner supply tank 20 is obtained.
The motor 23 connected to the No. 1 via the gear train 24 rotationally drives the conveying screw 21 to convey the toner 22 in the replenishing tank 20 and replenish it into the developing device 14.

The above-mentioned rectangular bias, pulse bias, DC bias, etc. are applied as the developing bias applied to the developing sleeve 34 of the developing device 14 at the time of developing, but in many studies conducted in the past. According to this, it is known that the development selectivity is generated depending on the type of the development bias.

Specifically, when the case of forming an image on 10,000 sheets is shown, the developing selectivity is 10,000 at the beginning of image formation with respect to the developing bias shown in FIGS. 4 (a) to 6 (a). FIG. 4B to FIG. 6B show the particle size distribution of the toner on one sheet. The particle size distributions shown in FIGS. 4B to 6B are obtained by collecting the developing toner on the developing sleeve at the initial stage of image formation and at the time of 10,000 sheets.
It is the number distribution measured by the Coulter counter described above.

4 (b) to 6 (b), the same toner was used, and the one having a relatively sharp particle size distribution was used (in the solid line in FIGS. 4 (b) to 6 (b)). Particle size distribution).

With the rectangular bias as shown in FIG. 4 (a), as shown in FIG. 4 (b), there is a development selectivity that results in development with fine powder toner (coarse powder toner accumulates in the developing sleeve). With a DC bias as shown in FIG. 5A, as shown in FIG. 5B, the development selectivity is the development with the coarse toner (fine powder toner is accumulated in the developing sleeve), and as shown in FIG. 6A. It is known that with such a pulse bias (double blank pulse bias), as shown in FIG. 6B, the development selectivity is development with toner having these intermediate particle diameters.

Among the developing biases described above, the present inventors have
The study was conducted by focusing on the frequency of the rectangular bias having the selectivity for fine powder development. Currently, the frequency used in the product is about 2 to 6 kHz, but when we investigated even higher frequencies, we found an interesting fact.

First, the frequencies of the rectangular bias are set to 2, 5, 1
FIG. 7 shows the relationship (developing characteristics) between the frequency and the developed image density when the frequency is changed to 0 and 20 kHz. For comparison, the double blank pulse (WB) shown in FIG.
The development characteristics in P) are also shown.

As shown in FIG. 7, the development characteristic of the low frequency rectangular bias is worse than that of the pulse bias (WBP), and the image density does not appear. However, as the frequency is increased, the development characteristic is improved. Especially when the frequency is 20. When the frequency was raised up to kHz, the same development characteristics as the WBP bias were obtained.

Next, FIG. 8 shows the particle size distribution of the developing toner on the photosensitive drum when the frequency of the rectangular bias is changed.
For comparison, the particle size distribution of the developing toner on the photosensitive drum when the WBP bias is used is also shown.

The developing toner is a solid black image developed by 256 levels of laser 256 gradation control.
After developing the latent image on the photosensitive drum, the image forming apparatus was stopped, and a solid black image was taken from the photosensitive drum before being transferred to the transfer paper. The toner used is as shown in FIGS.
It has a relatively sharp particle size distribution shown in (b).

From FIG. 8, the frequencies are 2 kHz and 10 kHz.
As the z and 20 kHz are increased, the development by the small particle size toner and the large particle size toner becomes relatively large,
It can be seen that toner having a wide particle size distribution is used for development, and that toner having a wide particle size distribution can also be developed.

Therefore, in the present invention, a toner having a wide particle size distribution is used as the toner of the two-component developer, and the development is performed by the rectangular bias.

In the present invention, the particle size distribution of a toner used as a toner having a wide particle size distribution is such that the number average particle size of the toner is M, the particle size of the toner is d, and the toner particle size is 30 in the range of d <2M / 3. It is preferable that 30% or less of the toner is included in the range of 4M / 3 <d, and 99% or more of the toner is included in the range of 0 <d <2M. More preferably, 30% by number or less of the toner is included in the range of M / 3 <d <2M / 3, 30% or less of the toner is included in the range of 4M / 3 <d <5M / 3, and 0 <d < 99% or more of the toner is included in the range of 2M.

According to the present invention, by using a high frequency rectangular bias, it is possible to develop with a toner having a wide particle size distribution of a two-component developer. Therefore, the highlight side of a halftone image is a small particle size toner. You can develop more with.

In this embodiment, the rectangular bias frequency is fixed at 20 kHz, and 4 out of 256 gradations of the laser are obtained.
10 (a) to (c) show the results of examining the particle size distribution by developing halftone images of three levels of 8, 96, and 256, collecting the developing toner on the photosensitive drum at that time. The particle size distribution of the toner used is as shown in FIG.

As shown in FIGS. 10 (a)-(c),
When a rectangular bias with a frequency of 20 kHz is used, the halftone image is 96 levels higher than the 256 level, and 48 levels higher than the 96 level. It can be seen that the effect of developing with a toner having a wide particle size distribution is remarkable on the highlight side, and there are many small particle size toners.

As described above, according to the high frequency rectangular bias, the development with the small particle size toner is frequently performed on the highlight side, so that the dot reproducibility is improved and a good image can be obtained.

Example 2 The high frequency rectangular bias used in the present invention enables development with toner having a wide particle size distribution, and therefore this example has the effect of reducing the blur of an image.

In order to see the effect of reducing the ghosting effect on the image, for the black color which is most likely to have the ghosting effect on the image, the covering power of the toner, that is, the black pigment is increased stepwise to develop the image with the rectangular bias. used.

The number of black pigment parts with respect to the black toner is
There were four stages of 2, 3, 4, and 8 parts. The development was performed at a contrast potential where the density of the solid black image was 1.6, and the frequency of the rectangular bias was 20 kHz. The boss reduction effect is
The obtained solid black image was evaluated by 5 persons randomly selected, and each person was evaluated on a scale of 5 points, and expressed as an average point. For comparison, a case where a double pulse bias (WBP) was used as the developing bias was also tried. The results are shown in Table 1.

[0054]

[Table 1]

As can be seen from Table 1, in WBP, the number of pigment parts is 3 points, and the number is 3 points.
However, with a rectangular bias of 20 kHz,
Even if the number of pigment parts was 8, it was 3 points.

This is because the toner having a large particle size develops a solid black image according to the high frequency rectangular bias.
After the obtained toner image was transferred onto the recording paper, the toner was hard to be embedded on the paper due to fixing, and as a result, a good image without a ghost image was obtained.

As described above, by using the high frequency rectangular bias as the developing bias, it is possible to develop a large amount of a solid image from a toner having a wide particle size distribution with a coarse toner, and to reduce the blurring of the solid image.

As described above, according to the present invention, since the high frequency rectangular bias is used as the developing bias, the toner having a wide particle size distribution can be used as the toner of the two-component developer, and the density of the image can be higher than ever. Can be issued. In particular, the highlight side can be developed more with fine powder toner to improve dot reproducibility, and the solid side can be developed more with coarse powder toner to reduce ghosting of a solid image.

[0059]

As described above, according to the present invention,
Since development is performed using a high frequency rectangular bias, even if a toner having a wide particle size distribution is used, not only the large particle size toner but also the small particle size toner is not deteriorated in developability.
It is possible to improve the reproducibility of the highlight part of the image and obtain a good image without deterioration of the quality due to the blur of the solid part.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an image forming apparatus in which a developing device of the present invention is installed.

FIG. 2 is a diagram showing a method of forming an electrostatic latent image by a pulse width modulation method in the image forming apparatus of FIG.

3 is a cross-sectional view showing a developing device installed in the image forming apparatus of FIG.

FIG. 4 is a diagram of a toner particle size distribution showing a rectangular bias and its developing selectivity.

FIG. 5 is a diagram of toner particle size distribution showing a DC bias and its developing selectivity.

FIG. 6 is a diagram of a toner particle size distribution showing a pulse bias and its developing selectivity.

FIG. 7 is a diagram showing the relationship between the frequency of a rectangular bias and the density of a developed image.

FIG. 8 is a diagram showing a relationship between a frequency of a rectangular bias and a particle size distribution of developing toner on a photosensitive drum.

9 is a diagram showing the particle size distribution of the wide particle size distribution toner used in the image forming experiment of FIG.

FIG. 10 is a diagram showing a relationship between three laser gradation levels and a particle size distribution of toner on a photosensitive drum in developing a halftone image with a rectangular bias frequency of 20 kHz according to the present invention.

FIG. 11 is an explanatory diagram showing that, conventionally, ghosting has occurred after fixing on a solid black portion of an image transferred onto a transfer paper due to unevenness on the surface of the transfer paper.

[Explanation of symbols]

10 Photosensitive drum 13 Two-component developer 14 Developer 19 Fixer 34 Development sleeve 39 Development power supply

Continued front page    F-term (reference) 2H005 CA21 EA05 EA07 FA02 FA06                       FA07                 2H073 AA02 AA05 BA04 BA06 BA13                       BA43 CA02 CA03                 2H077 AD36 EA13 EA14

Claims (9)

[Claims] 1. A developing device for developing an electrostatic latent image formed on the surface of an image bearing member by laser exposure with toner carried on the developer bearing member while applying a developing bias to the developer bearing member. 2. A developing device according to claim 1, wherein a toner having a wide number particle size distribution is used as the toner, and a high frequency rectangular bias is used as the developing bias. 2. The toner has a number average particle diameter of the toner M, a toner particle diameter of d, and 30% by number or less of the toner in a range of d <2M / 3, and 4M / 3 <d. 2. The developing device according to claim 1, wherein the developing device has a particle size distribution including 30% by number or less of the toner in a range and 99% by number or more of the toner in a range of 0 <d <2M. 3. The toner is M / 3 <d <2M /, where M is the number average particle size of the toner and d is the particle size of the toner.
The range of 3 includes 30% by number or less of the toner, and 4M / 3 <
30% by number or less of the toner is included in the range of d <5M / 3,
2. The developing device according to claim 1, wherein the developing device has a particle size distribution including 99% by number or more of toner in the range of 0 <d <2M. 4. The developing device according to claim 1, wherein the toner is a one-component developer magnetic toner. 5. The developing device according to claim 1, wherein the toner is a non-magnetic toner of a one-component developer. 6. The developing device according to claim 1, wherein the toner is a non-magnetic toner of a two-component developer. 7. The developing device according to claim 1, wherein the toner contains 3 parts or more of a pigment. 8. The toner has a number average particle diameter of 4 to 10 μm.
The developing device according to claim 1, wherein m is m. 9. The frequency of the rectangular bias is 5 to 20 k.
The developing device according to any one of claims 1 to 8, which has a frequency of Hz.