JPH08137243A - Developing device - Google Patents

Abstract

PURPOSE: To reproduce high image quality in an image forming device using a two-component developer by specifying the relation of the spheroidicity of toner, an average grain size, a carrier diameter and the surface roughness of a developer carrier. CONSTITUTION: When the surface of the developer carrier 4b is roughened in some degree, developers 5c and 5t try to stay on a magnetic pole in a recessed part on the surface of the developer carrier 4b, in accordance with its movement. But when the carrier 4b is moved and a projecting part comes to the magnetic pole, the developers 5c and 5t are moved together with the carrier 4b, to improve the carrying property of the developer. When the surface of the carrier 4b is too roughened, the developing interval between the photoreceptor and the carrier 4b is made irregular. when the toner 5t is in the shape of a sphere whose spheroidicity is >=0.95, the average grain size Dt of the toner 5t is 2 to 6μm and the carrier diameter is defined as Dc, the surface roughness Rz of the carrier 4b is (Dc+2×Dt)×0.25<=Rz<=(Dc+2×Dt)×0.5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing an electrostatic latent image in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a developing device in an electrophotographic image forming apparatus uses a one-component developer containing only toner and a two-component developer containing toner and carrier. Two-component developers have recently been widely used for the reasons that they have good color developing properties for color toners and that they can easily reduce the particle size of toner particles and thus meet the demand for higher image quality. In particular, with regard to the problem of reducing the particle size of toner particles, high image quality can be obtained by reducing the particle size of toner, and in addition, fogging due to poor charging of toner, toner spill from the developing device, toner scattering, etc. It is known to be effective in prevention.

However, as the toner particle size is reduced, the charge amount of each toner becomes smaller. Therefore, a comparison between the non-electrostatic adhesion force and the electrostatic adhesion force due to the individual charging of the toner shows that it is non-electrostatic. The adhesive force tends to be relatively larger. By the way, the non-electrostatic adhesive force between the toner and the developer, the toner and the latent image carrier, and the toner and the sheet impedes the movement of the toner due to the electric field. As a result, toner scattering, density decrease,
There is a risk of causing problems such as uneven density and causing fatal defects for image formation by electrophotography. In order to solve such a problem, Japanese Patent Laid-Open No. 5-19631 discloses a method for making the surface roughness of a developer carrier smoother, specifically, a surface roughness (Rz) of the developer carrier. 0.
A method of making the range from 5 μm to 3 μm is shown.

On the other hand, in order to meet the ever-increasing demand for higher image quality, research is underway to reduce the particle size of toner particles. Conventionally, toner produced by crushing lumps is chemically Since the toner has been manufactured by various processes, the shape of the toner, which was conventionally indefinite, has become close to a sphere. However, when a spherical developer is used, friction between the developer carrying member that carries the developer while rotating and carrying the developer becomes small, and the developer carrying property of the developer carrying member deteriorates. In particular, if the developer bearing member is moved to the developing region again with the developer after completion of development attached, not only the development density on the photoconductor is lowered, but also the history of the previous image remains on the developer bearing member. Distort the image.

Japanese Unexamined Patent Publication (Kokai) No. 4-26874 discloses a method for solving this problem by developing the surface roughness Rz of the developer carrying member.
Is set to 5 μm to 10 μm to improve the transportability of the developer, and the scraper forcibly scrapes the developer off the surface of the developer carrying member.

[0006]

However, in the method of forcibly scraping off the developer by using a member such as a scraper which is in mechanical contact with the developer carrying member, the method of forcibly scraping off the developer causes a long-term use and also a foreign matter. Scratches are caused on either or both of the scraper and the developer carrying member due to the adherence or biting, and image defects such as white spots and black streaks occur along the scratches.

Therefore, an object of the present invention is to solve these conventional problems and to provide a developing device for reproducing high quality image in an image forming apparatus using a two-component developer.

[0008]

SUMMARY OF THE INVENTION A developing device of the present invention which achieves the above-mentioned object, is a cylindrical developer carrier for supporting and rotating a two-component developer composed of toner and carrier, and the developer carrier. In a developing device equipped with a fixed magnet disposed inside, the toner has a spherical shape with a circularity of 0.95 or more, the average particle diameter Dt of the toner is 2 μm or more and 6 μm or less, and the carrier diameter is Is Dc, the surface roughness Rz of the developer carrier is (Dc + 2 × Dt) × 0.25 ≦ Rz ≦ (Dc + 2 × D
It is characterized in that the relationship of t) × 0.5 is satisfied.

The surface roughness is specified in JIS-B0601 as follows. "What is surface roughness?
It refers to irregularities that occur at small intervals on the finished surface of the product, and there are three types: maximum height (Rmax), ten-point average roughness (Rz), and center line average roughness (Ra). " The average roughness referred to in the present invention refers to the above-mentioned "ten-point average roughness (Rz)".

The ten-point average roughness (Rz) is JIS-B06.
According to 01, "From the cross-sectional curve of the surface roughness obtained by a surface roughness measuring device, of the straight lines parallel to the average line of the extracted portion, the one passing the third peak from the highest and the third from the deepest The one that passes through the bottom of the valley is selected, the distance between these two straight lines is measured in the direction of the longitudinal magnification of the cross-sectional curve, and the value is expressed in units of microns. "

[0011]

In the developing device of the present invention, as described above, the surface roughness of the developer carrying member is (Dc + 2 × Dt) × 0.25 or more, that is, the value obtained by doubling the toner particle diameter Dt and the carrier particle. Since it is set to 1/4 or more of the sum of the diameter Dc, the developer carrying property of the developer carrying member is improved,
The spherical toner solves the problem of lowering the transportability of the developer as compared with the irregular toner, and a spherical toner having a high circularity can be used.

Further, in the developing device of the present invention, the surface roughness of the developer carrying member is (Dc + 2 × Dt) × 0.5 or less, that is, the value obtained by doubling the toner particle diameter Dt and the carrier particle diameter Dc.
Since it is set to 1/2 or less of the sum of
Image density unevenness does not occur. Thus, in the developing device of the present invention, since the surface roughness of the developer carrying member is set as described above, it becomes possible to use spherical toner having a circularity of 0.95 or more. The non-electrostatic adhesive force is reduced by the spheroidization of the toner particles, and the toner can follow the transfer electric field at the time of development even when the toner having a small particle size is used. Also, the particle size is 6
Since the toner having a particle size of μm or less can be sufficiently charged and electrostatically held, the toner concentration can have a wide allowable range, which is effective in preventing fog and toner scattering.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of the developing device in this embodiment. The developing device 4 shown in FIG. 1 is a non-magnetic conductive developer carrier 4 whose rotation speed can be arbitrarily set.
b, a fixed magnet 4m with 5 poles built in the developer carrying member 4b, a layer thickness regulating member 6 for regulating the layer thickness of the developer layer on the developer carrying member 4b, and the developer 5 in the developing device 4. Is equipped with an auger 7 for stirring. In the present embodiment, the fixed magnet 4m is a roller-shaped one, but it may be composed of a plurality of block-shaped magnets. The developing device 4 has a distance of 0.4 m between the developer carrying member 4 b and the photosensitive member 1.
It is deployed with a gap of m. The layer thickness regulating member 6 is
It is arranged with a gap of 0.5 mm between the developer carrier 4b and regulates the layer thickness of the developer layer on the developer carrier 4b.

FIG. 2 is a schematic diagram of a magnetic profile on the developer carrier 4b. The horizontal axis represents the angle when the developer carrying member is rotated counterclockwise with the short hand position of the developer carrying member 4b at 3 o'clock in FIG. 1 set to 0 degree, and the vertical axis represents the developer carrying member on the developer carrying member. Magnetic flux density. As shown in FIG. 2, a region (about 2 mm) between the two repulsion magnetic poles for peeling the developer is formed.
At around 70 degrees), a magnetic pole of about 100 Gauss is generated. When the magnetic flux density in this region is zero, the releasability of the developer is further improved, but in this embodiment, the magnetic field in this region was kept at about 100 gauss in order to confirm the effect of the invention.

An arbitrary bias voltage can be applied to the surface of the developer carrying member 4b by a voltage applying device (not shown). The developer 5 is a two-component developer, a non-magnetic polyester toner is used as a toner raw material,
Three types of toners, type A, type B, and type C, which were manufactured differently, were prepared. The type A and type B toners are irregularly shaped toners manufactured by the kneading-pulverization method. The pulverization conditions are different between the type A toner and the type B toner. Type C toner is a spherical toner produced by polymerization. The circularity of these three types of toner was measured. Here, the circularity of the toner is defined as the perimeter of a circle having the same area / the perimeter of the toner with respect to a toner image projected on a plane. In the case of a cube, it is 0.887, which is close to a sphere. It approaches one. The circularity measuring device is an image processing device manufactured by Cambridge Instrument Co., q
Approximately 1,000 of each of the above three types of toners were measured using the Quantimeter 970, and the average value was obtained. As a result, the type A toner was 0.887, the type B toner was 0.940, and the type C toner was 0.985. there were.

The toner particle size is such that, for each toner, the average particle size is 7, 5, 2.5, by changing the sieving point.
The particle size was adjusted to 4 types of 1.5 μm. The carrier is a ferrite type, and after granulating and sintering, apply an appropriate coating agent, and then change the sieving point to obtain an average particle size of about 60, 45, 3
The particle size was adjusted to 4 types of 5 and 20 μm. An appropriate external additive was added to the toner after sizing, and the toner charge amount per the same weight was adjusted to 20 μC / g.

The carrier was prepared by granulating and sintering, applying an appropriate coating agent, and then changing the sieving point. A Coulter counter was used to measure the particle diameters of the toner and carrier. FIG. 3 is a diagram showing the degree of influence of the toner particle size and the carrier particle size on the image graininess. Image graininess is one of the indexes that represent the smoothness of the appearance of the image or the fineness of the image.The index analyzes the image of the microscope image by a computer and frequency-converts the image part and the noise part. , Is calculated numerically. As shown in FIG. 3, it is understood that the graininess is remarkably improved when the toner particle size is reduced. Further, the smaller the carrier particle size is, the better the graininess is, but the graininess is not improved as much as the toner particle size. Although the allowable range of the graininess is below the dotted line in FIG. 3, it was found that the toner having the graininess within this range is a toner having a particle size of 6 μm or less. The toner used in FIG. 3 is type A, but type B and type C
Similar results were obtained with the toner of No. 2.

FIG. 4 is a diagram showing the degree of influence of toner particle size and carrier particle size on fog. Fog is a phenomenon in which toner adheres to non-image portions to impair image quality, and is represented by a value determined by comparing an image with a limit sample. As shown in FIG. 4, it is understood that the larger the toner particle size and the smaller the carrier particle size, the less the fog. Therefore, when using a toner having a small particle diameter, it is preferable that the particle diameter of the carrier is also made small. The permissible limit of fog is around 2 on the vertical axis in FIG. 4, so the toner particle size is 2 μm.
It can be seen that fog cannot be suppressed when the thickness is m or less.

By the way, after the developing process, when the developed toner image is transferred from the photoconductor to the paper, a part of the toner transferred to the paper is returned to the photoconductor due to the influence of the electric field and the like, and the fine line becomes thin. As a result, a phenomenon may occur in which the image quality deteriorates. Therefore, in order to understand the relationship between the transfer of fine lines and the circularity of toner, the fine line transfer efficiency was measured.

FIG. 5 is a diagram showing the relationship between the circularity of toner and the transfer efficiency of fine lines. What is transfer efficiency?
With the machine temporarily stopped, the weight of the toner before transfer on the photoconductor and the weight of the toner after transfer are measured, and the value is calculated by the following equation. Transfer efficiency (%) = (weight of toner after transfer / weight of toner on photoconductor) × 100 As shown in FIG. 5, it is understood that the fine line transfer efficiency is improved when the circularity of the toner is high.

In order to obtain a satisfactory image quality, the transfer efficiency must be 90% or more as a target value, but as shown in FIG. 5, the toner circularity satisfying the condition that the transfer efficiency is 90% or more. Is 0.95 or more. Next, the above-mentioned various developers are added to the developer carrier 4b.
We investigated how they would be transported above. 2 g of the developer is attached to the assembly of the developer carrier and the fixed magnet having the magnetic profile shown in FIG.
After the repulsion magnetic pole is directed downward so that the developer once separated from the developer carrier does not adhere to the developer carrier again, after rotating the developer carrier 4b for a while, The amount of the developer adhering to the developer carrier was measured.

FIG. 6 is a diagram in which the relationship between the surface roughness of the developer bearing member and the remaining amount of the developer is plotted for the developers having various carrier particle sizes. The residual amount of the developer is an index indicating the transportability of the developer, and the developer carrier on which a predetermined amount of the developer is placed is rotated in an offline state, and the developer to be originally peeled off is the developer carrier. It can be obtained by collecting the remaining amount which is not peeled off even after the rotation of, and measuring its weight.

As shown in FIG. 6, it can be seen that as the carrier particle size increases, the residual developer amount increases, and as the surface roughness of the developer carrying member 4b increases, the residual developer amount decreases. The remaining amount of the developer is 0.
It is preferably 1% or less, that is, 10 mg or less.
FIG. 6 shows an example of the C type spherical toner having an average particle size of 7 μm. However, in the case of the A type and B type toners, both can be sufficiently transported even if the surface roughness is smaller than that of the C type toner. Is.

FIG. 7 is a diagram in which the relationship between the surface roughness of the developer bearing member and the remaining amount of the developer is plotted for developers having various toner particle sizes. Although the influence of the toner particle size on the remaining amount of the developer is small, it is understood that the surface roughness may be slightly reduced when the small particle size toner is used. FIG. 8 is a plot of the points at which the respective curves of FIGS. 6 and 7 intersect the target value, that is, the line of the remaining amount of the developer of 10 mg. The toner particle size, the carrier particle size and the developer carrying amount satisfying the target values are plotted. The relationship between body surface roughness is shown. At each carrier particle diameter, a gradual upward linear relationship is found between the toner particle diameter and the developer carrier surface roughness. Expression (1) is obtained by expressing this group of straight lines in an expression.

Rz = (Dc + Dt × 2) × 0.25 (1) However, the surface roughness of the developer carrier is Rz, the carrier particle diameter is Dc, and the toner particle diameter is Dt. In order to satisfy the developer transportability, it is necessary that the value of the surface roughness Rz of the developer carrier is larger than the value on the right side of the expression (1).

Next, the results of examining the surface roughness of the developer carrying member 4b and the density unevenness of the image after development will be described. Density unevenness is obtained by irradiating a solid image of 2 × 2 cm with a light beam having a color filter applied, measuring the amount of reflected light, and digitizing the density of the density. When the density difference is 0.2 or more, "unevenness" is set, and when the density difference is less than 0.2, "unevenness" is set. FIG. 9 is a diagram in which the presence or absence of image density unevenness is plotted by plotting the surface roughness of the developer carrier on the vertical axis and the carrier particle size on the horizontal axis. The toner particle size used is 6 μm.

As shown in FIG. 9, the occurrence of density unevenness depends substantially on the carrier particle diameter. When the surface roughness becomes rougher than the diagonal line in the figure, the density unevenness occurs. If the carrier particle size is sufficiently large, uneven density does not occur. This phenomenon will be considered using the model shown in FIG. FIG. 10 is a model showing the mutual relationship between the developer carrier of the developing device and the developer.

FIG. 10 (a) shows the case where the surface roughness of the developer carrying member is smooth, FIG. 10 (b) shows the case where the surface roughness of the developer carrying member is medium, and FIG. 10 (c) shows the developing process. This is a model when the surface roughness of the agent carrier is rough. When the developer comes on the magnetic pole of the developer carrier, the carrier 5 covered with the toner 5t
The c is connected in a chain due to the influence of the magnetic pole, and is in a so-called spiked state. On a smooth surface as shown in FIG. 10A, even if the developer carrying member 4b moves in the direction of the arrow X, the developer is pulled by the magnet and tries to stay on the magnetic pole, and the developer is conveyed. Hateful.

On the other hand, when the surface of the developer carrying member 4b becomes rough to some extent, as shown in FIG.
With the movement of b, the developers 5c and 5t try to stay on the magnetic poles in the concave portions on the surface of the developer carrying body 4b, but when the developer carrying body 4b moves and the convex portions come on the magnetic poles, 5c,
Since 5t cannot move over the convex portion and moves together with the developer carrier 4b, the developer transportability is as shown in FIG.
Improved compared to (a).

However, as shown in FIG. 10 (c), if the surface of the developer carrying member 4b is made too rough, the developing interval between the photoconductor 1 and the developer carrying member 4b becomes uneven. This unevenness adversely affects the developing electric field at the time of development and causes unevenness in image density. As shown in the model of FIG. 10D, the minimum unit of the developer chain is considered to be the sum of the particle sizes of one carrier particle and two toner particles. Based on the concept of this minimum unit, considering the results of the above-mentioned embodiment,
The occurrence of the image density unevenness depends on this minimum unit, and it can be seen that the image density unevenness occurs when the surface roughness of the developer carrying member exceeds the value of the formula (2) shown below.

Rz = (Dc + Dt × 2) × 0.5 (2) However, the surface roughness of the developer carrying member is Rz, the carrier particle diameter is Dc, and the toner particle diameter is Dt. By combining this equation (2) and the above equation (1), the following equation (3) is obtained. (Dc + 2 × Dt) × 0.25 ≦ Rz ≦ (Dc + 2 × Dt) × 0.5 (3) However, the developer carrier surface roughness is Rz, the carrier particle diameter is Dc, and the toner particle diameter is Dt. .

That is, the surface roughness Rz of the developer carrier.
Of the carrier particle size D
By setting c and the toner particle diameter Dt, it is possible to obtain an image without density unevenness.

[0033]

As described above, according to the present invention,
By setting the surface roughness of the developer carrier to an appropriate range, the developer carrying property of the developer carrier is improved,
Since the spherical toner can be used, the toner can have a smaller particle size, and high-quality image with good graininess can be obtained.

Further, since the surface roughness of the developer carrying member is set within an appropriate range, uneven density of the image does not occur. Further, since the surface roughness of the developer carrying member is set in an appropriate range, it becomes possible to use spherical toner having a circularity of 0.95 or more, and the non-electrostatic adhesive force is reduced by making the toner spherical. However, even if a small particle size toner is used, the toner can follow the transfer electric field at the time of development, and the image quality is improved.

Further, since the spherical toner can be used, the non-electrostatic adhesive force of the toner is reduced, and the particle size is 6
Even if a toner having a small particle diameter of μm or less is used, the toner can sufficiently follow the transfer electric field at the time of development, and fog and toner scattering can be prevented. Further, without providing the developer scraping member, the developer can be completely peeled off from the developer carrying member only by the action of the repulsive magnetic field, so that the surface of the developer carrying member can be prevented from being damaged or worn.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a developing device in this embodiment.

FIG. 2 is a schematic view of a magnetic profile on a developer carrier.

FIG. 3 is a diagram showing influences of toner particle diameter and carrier particle diameter on image graininess.

FIG. 4 is a diagram showing the effects of toner particle size and carrier particle size on fog.

FIG. 5 is a diagram showing a relationship between toner circularity and fine line transfer efficiency.

FIG. 6 is a diagram in which the relationship between the surface roughness of the developer bearing member and the residual developer amount is plotted for developers having various carrier particle diameters.

FIG. 7 is a diagram in which the relationship between the surface roughness of the developer bearing member and the remaining amount of the developer is plotted for developers having various toner particle sizes.

FIG. 8 is a toner particle size at which the residual developer amount satisfies a target value,
The relationship between carrier particle diameter and developer carrier surface roughness is shown.

FIG. 9 is a diagram in which the presence or absence of image density unevenness is plotted with the vertical axis representing the surface roughness of the developer bearing member and the horizontal axis representing the carrier particle size.

FIG. 10 is a model showing the mutual relationship between the developer carrier of the developing device and the developer.

[Explanation of symbols]

 1 Photoconductor 4 Developing Device 4b Developer Carrier 4m Fixed Magnet 5 Developer 5t Toner 5c Carrier 6 Layer Thickness Controlling Member 7 Auger

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number for FI G03G 9/10 15/09 Z (72) Inventor Taku Fukuhara 2274 Hongo, Ebina-shi, Kanagawa Fuji Xerox Ebina Office Co., Ltd.

Claims (1)

[Claims] 1. A developing device comprising: a cylindrical developer carrier that carries and rotates a two-component developer composed of a toner and a carrier; and a fixed magnet disposed inside the developer carrier, The toner is spherical with a circularity of 0.95 or more, and the average particle diameter Dt of the toner is 2 μm or more and 6 μm.
When the carrier diameter is Dc, the surface roughness Rz of the developer carrier is (Dc + 2 × Dt) × 0.25 ≦ Rz ≦ (Dc + 2 × D
A developing device which satisfies the relationship of t) × 0.5.