JP3155421B2 - Developing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, with the spread of image forming apparatuses such as electrophotographic copying machines and laser beam printers, the uses thereof have been diversified and the demands for the image forming apparatuses have become strict. For this reason, there is a strong demand for an image forming apparatus that can stably supply an image having excellent fine line reproducibility and gradation using a toner having a small particle diameter.

In general, small-sized toner particles are often excessively charged due to friction with devices (developing sleeves and elastic blades) in a developing device. If a developing operation is performed using the excessively charged toner, There is a problem in that the density of the image is reduced and sleeve ghost occurs during development.

Therefore, a developing device which does not cause the above-mentioned problem even when a toner having a small particle diameter is used and which is excellent in fine line reproducibility and gradation is proposed (Japanese Patent Application Laid-Open No. 2-306274). FIG.
As shown in FIG. 1, such a developing device 100 includes a developing sleeve 102 disposed to face a photosensitive drum 111 and a magnetic roller 103 having a plurality of magnetic poles non-rotatably disposed in the developing sleeve 102. And an elastic blade 104 that contacts the developing sleeve 102 and regulates the layer thickness of the toner.
And a magnetic toner having a small particle size (17 to 60
Toner having 10% by volume and a volume average particle diameter of 6 to 9 μm) 10
5 comprises a developing device main body 101 and the like.

On the outer peripheral surface of the developing sleeve 102,
The resin is coated with a conductive film in which carbon black and / or carbon graphite is blended. Under normal circumstances, even when the small particle size toner 105 is used, the image density does not decrease and sleeve ghost does not occur during continuous printing. It has become.

The film coated on the developing sleeve 102 has a surface roughness Ra = 0.3 to 5 in order to form a uniform thin layer of toner on the developing sleeve and to stably charge the toner. 0.0 μm, Rz = 1.0-30
μm.

[0007]

However, in the above-mentioned conventional developing device, when a small particle size toner having a volume average particle size of 6 to 9 μm is used, there is a problem that the density at the end of the image is reduced during intermittent printing. Was.

[0008] Small particle size toner 105 in developing device main body 101
Is charged by the friction caused by the rubbing with the developing sleeve 102 and the strong friction with the elastic blade 104, but all the toner conveyed to the developing area by the developing sleeve 102 moves to the photosensitive drum 111 side. In many cases, the toner is circulated together with the developing sleeve 102 without being consumed, and each time the developing sleeve 102 and the elastic blade 104 receive a further charge. Even in this case, in the case of continuous printing under a normal environment, there is no particular problem with the developing device 100, but when an image with a low printing rate is intermittently printed in a low-temperature and low-humidity environment, the toner charge amount is usually Therefore, the developing device 100 cannot cope with the problem, and the image density is reduced. This phenomenon is noticeable at the edges of the image,
The cause is considered as follows.

As shown in FIG. 5, an elastic blade 104 is bonded to a sheet metal 106, and the sheet metal 106 is
At 08, the elastic blade 104 is attached to and supported on the mold portion 109 of the developing container 101, so that the elastic blade 104 is brought into contact with the developing sleeve 110 with a certain pressure. The toner carried on the developing sleeve 110 is provided with a triboelectric charge by strong friction between the elastic blade 104 of the toner and the developing sleeve 110, and a uniform thin coating on the developing sleeve 110 is performed.

At this time, the contact pressure of the elastic blade 104 against the developing sleeve 110 is set at 1 in order to obtain a good image.
0 g / cm to 50 g / cm is optimal. 10g / cm
In the following, less charge is applied to the toner, the density is reduced, and unevenness occurs in the thin layer coating of the toner, and uneven density occurs in a solid black or halftone image. 50g / c
If m or more, it is known that the contact pressure against the developing sleeve 110 is too high, and excessive charging of the toner occurs, and the density decreases due to charge-up.

As described above, the elastic blade 104 is attached to the mold part 101 by the screws 107 and 108. The elastic blade 104 is made of a rubber member such as urethane. The rubber is an elastic body, and when the rubber is bent and comes into contact with the developing sleeve 110, the contact pressure tends to be higher at the ends A and B of the elastic blade 104 than at the center C. This is because, as the number of prints increases, the displacement of the rubber becomes larger at the end portions A and B than at the center portion C. When the developing device is used, the blade contact pressure is set to 30 g / cm to 40 g / cm. Even if the contact pressure is measured after a large number of puddings, the elastic blade 104
In the end portions A and B, the thickness exceeds 50 g / cm. As a result, the toner is charged up at the end of the elastic blade 104, and correspondingly, the density is reduced at the end of the image.

This problem can be solved by making the longitudinal width of the developing sleeve sufficiently larger than the printing width of the image, and separating the region where the contact pressure at the end of the elastic blade 104 is high from the image region. However, since the longitudinal direction of the developing device becomes large, there is a disadvantage that the image forming apparatus becomes large in size.

An object of the present invention is to prevent the toner from being charged up at the end of the elastic blade even if the contact pressure of the elastic blade against the developing sleeve is high at the end of the elastic blade. It is an object of the present invention to provide a developing device capable of obtaining an undeveloped image.

[0014]

The above object is achieved by a developing apparatus according to the present invention. In summary, the present invention is a magnetic toner in which the developer has at least a binder resin and a magnetic powder, and the particle size distribution of the toner is (i) 17 to 60% by number of toner particles having a particle size of 5 μm or less.
(Ii) 5 toner particles having a particle size of 6.35 to 10.08 μm.
(Iii) 2% by volume of toner particles having a particle size of 12.70 μm or more.
(Iv) having a volume average particle diameter of 6 to 9 μm, and (v) a toner particle group having a particle diameter of 5 μm or less is represented by the following formula: N / V = −0.05N + k N: the number% of toner particles having a particle diameter of 5 μm or less V: volume% of toner particles of 5 μm or less k: positive number of 4.6 to 6.7 N: positive number of 17 to 60 To form a conductive coating made of a binder resin and carbon black and / or a composite material of carbon black, and the surface roughness of the coating is Ra = 0.3 to
In a developing device having a range of 5.0 μm, a developer regulating blade made of an elastic body is in contact with the developer carrier, and the surface roughness of the film corresponds to an image edge. The developing device is characterized in that it is 10% to 30% higher at the end of the developer carrier than at the center.

Preferably, the length from the fixed end to the free end of the blade is longer at the end of the blade than at the center.

[0016]

【Example】

Embodiment 1 FIG. 1 is a perspective view showing a developing sleeve together with an elastic blade according to an embodiment of the present invention, and FIG. 2 is a sectional view showing a developing device incorporating the developing sleeve.

As shown in FIG. 2, the developing device 4 has a developing sleeve 1 disposed to face the photosensitive drum 9 and a plurality of magnetic poles disposed in the developing sleeve 1 in a non-rotating manner. It comprises a magnetic roller 6, an elastic blade 3 which comes into contact with the developing sleeve 1 to regulate the layer thickness of the toner, a developing device main body 7 containing a magnetic toner 8 having a small particle diameter as a developer, and the like.

As shown in FIG. 1, a developing sleeve 1 has on its surface a conductive coating 2 formed by coating, and the coating 2 is a composite material in which carbon black and / or graphite is mixed with a resin. Consists of The elastic blade 3 is in contact with the developing sleeve 1.

The ten-point average roughness Ra of the surface of the developing sleeve 1 on which the conductive film 2 is formed is determined by measuring the end A of the elastic blade 3,
In the end region of the developing sleeve 1 corresponding to B, R _A and R _B are set, and in the other region corresponding to the central portion C, R _C is set so that they satisfy the following formula.

With the configuration of R _A = R _B = 1.2 R _C or more, the amount of toner coating per unit area on the developing sleeve 1 is M / S _A , M / S in the area corresponding to the elastic blade ends A and B. S _B and M in the area corresponding to the center C
/ When S _C, R _A, by R _B is greater than _{R C, M / S A>} M / S C, the relationship of _{M / S B> M / S} C hold.

At this time, the contact pressure of the elastic blade 3 is F _A , F _B , F _{C at} the portions A, B, C of the elastic blade, respectively.
Then, F _A > F _C and F _B > F _C are satisfied. However, as described above, in the area corresponding to the ends A and B of the elastic blade 3, the toner coat amount M / S _A on the developing sleeve 1 is obtained. , M / S _B is large, so that the toner on the developing sleeve 3 is not excessively charged even if the contact pressure at the ends A and B of the elastic blade 3 is large, and the charge of the toner is increased. Is prevented.

As disclosed in Japanese Patent Application Laid-Open No. 2-306274, when a fine particle toner having a volume average particle diameter of 6 to 9 μm is used, a conductive material composed of a composite material containing carbon black and graphite as a binder resin is used. In a developing sleeve having a coating on the surface, the surface roughness is Ra =
It is said that 0.3 to 5.0 μm is good. This allows
When Ra is small, blotching is prevented, and when Ra is large, poor coating and rough images are prevented.

The amount of change in the surface roughness between the end of the developing sleeve 1 and the center other than that required to eliminate the low density at the end of the image during intermittent printing was determined by the following experiment. Determined by

An image forming experiment was performed using the developing device of FIG. 2 for development. The developing sleeve 1 was formed as follows.

50% using a phenolic resin as a binder
5% of conductive carbon black (CONDUCTEX 900 manufactured by Columbia) and 45% (more than weight%) of graphite (CSPE manufactured by Nippon Graphite) are mixed and kneaded,
After dilution with methyl cellosolve and methanol, the resulting coating film is coated on a sleeve substrate by a spray method, and the coating film is heat-cured at 150 ° C. for 30 minutes to form a conductive film 2, thereby obtaining a developing sleeve 1. Was.

The surface roughness of the developing sleeve 1 can be changed by changing the coating pressure or the like at the time of spraying the coating material. At the center.

Specifically, an air spray method was used, the gun used was Binks No. 601, and the paint pressure was set at 0.
^{1Kg / cm 2 ~5K / cm 2} , 5Kg / cm 2 air pressure pattern adjustment, 0.5 Kg air pressure atomizing
/ Cm ^{2 to 4} kg / cm ² . As a result, Table 1
As shown in FIG. 5, five types of developing sleeves No. 5 having the same surface roughness Ra at both the end portion and the center portion. 1 to 5 and five types of developing sleeves No. 1 whose end is higher than the center. 6 to 10 were obtained.

[0028]

[Table 1]

The magnetic toner as a one-component developer has a particle size distribution of (i) a particle size of 5 μm or less: 17 to 60% by number (ii) a particle size of 6.35 to 10.08 μm: 5 to 50% by number ( iii) Particle size of 12.70 μm or more: 2% by volume or less (iv) Volume average particle size: 6 to 9 μm (v) A group of toner particles having a particle size of 5 μm or less is represented by the following formula: N / V = −0.05 N + k N: 5 μm or less V: volume% of toner particles of 5 μm or less k: positive number of 4.6 to 6.7 N: positive number of 17 to 60 For example, the following magnetic toner was used.

100 parts by weight of styrene / butyl acrylate / divinylbenzene copolymer (copolymer weight ratio: 80 / 19.5 / 0.5, weight average molecular weight: 320,000) Iron trioxide (average particle size: 0.2 μm) 80 parts by weight Cr complex of azo dye 1 part by weight Low molecular weight propylene-ethylene copolymer 4 parts by weight Ingredients are mixed, kneaded, coarsely ground, finely ground and classified according to the above formulation, and the mixture is subjected to the following particle size distribution. A classified toner product was obtained.

(I) 5 μm or less: 35.4 number% (ii) 6.35 to 10.08 μm: 36.9 number% (iii) 16 μm or more: 0.5 volume% or less (iv) Volume average particle size: 6.5 μm (v) N / V = 3.5 To 100 parts by weight of this classified product, 1.2 parts by weight of silica treated with dimethyl silicone oil was added and mixed to prepare a negatively chargeable insulating magnetic toner.

15 ° C., 10% R. T. An image was formed by intermittent printing at a process speed of 15 ppm (15 sheets / min. For A4) under the environment described above. As a result, Tables 2 and 3
Shown in

[0033]

[Table 2]

[0034]

[Table 3]

As shown in Tables 2 and 3, the developing sleeve No. In the cases of Nos. 1 to 5, both the density of 5 square (5 cm square image) density and the solid black density were such that as the number of image formed sheets increased to as many as 1000 sheets and 5000 sheets, the density of the edges was reduced due to the charge-up of the toner. On the other hand, the developing sleeve No. In Nos. 6 to 10, even when the number of images formed became large, the density of the image edge portion was not low.

As a result of further study, in order to prevent the image end portion from having a low density, the surface roughness of the end portion of the developing sleeve 1 corresponding to the image end portion is set to be smaller than that of the other central portions by 1%.
It has been found that it should be 0-30% higher, preferably 20% higher. Also, the portion where the surface roughness is increased is 5 to 5 times the toner coat width in the longitudinal direction of the developing sleeve 1 on both sides.
It has been found that the width should be 20%, preferably 10%.

In summary, according to the present invention, the one-component developer has a volume average particle diameter of 6 to 9 having the above-mentioned particle size distribution.
In a developing device using a developing sleeve 1 having a conductive coating containing carbon black and / or graphite as a resin, the Ra of the developing sleeve surface is 0.3 to 5.0 μm. Within this range, Ra at the end of the developing sleeve is higher than that at the center. (2) The degree of raising Ra at the end of the developing sleeve is 10 to 30%, preferably 20%, and (3) The portion where Ra at the end of the developing sleeve is increased is a width on one side, which is 5 to 20 times the toner coat width in the longitudinal direction of the developing sleeve.
%, Preferably 10%.

As described above, according to the present invention, the elastic blade 3
Prevents the toner from charging up at the end of the developing sleeve where it comes in contact with high pressure, and prevents the density at the image end from decreasing.
A good image without low density can be obtained.

Embodiment 2 When an image forming apparatus having a high process speed is used,
Opportunities for applying charge to the toner by the elastic blade 3 increase. Therefore, as in the first embodiment, the surface roughness of the end of the developing sleeve 1 is increased, the amount of toner coating on the developing sleeve 1 is increased at the end, and the elastic blade is brought into contact with the end of the developing sleeve. Even if prevention of toner charge-up due to high pressure is attempted, charge-up is unavoidable and density is reduced. Therefore, in the present embodiment, the following is performed.

FIG. 3 is a plan view showing the elastic blade in this embodiment. The present embodiment is characterized in that the free length on the supporting side of the elastic blade 10 bonded to the supporting metal plate 11 for attachment to the developing container is longer at the end of the elastic blade 10 than at the other central part. . Other configurations are the same as in the first embodiment.

Thus, in the developing device 4 shown in FIG.
The contact nip with the developing sleeve 1 at both ends of the elastic blade 10 is widened, and the contact pressure per unit area of the elastic blade 10 can be reduced at both ends of the developing sleeve 1. Therefore, even if the process speed of the image forming apparatus is high, by incorporating the developing device having such an elastic blade 10, when forming an image by intermittent printing,
The occurrence of low density at the end of the image can be prevented. That is, by setting the free length of the end of the blade 10 corresponding to the end of the developing sleeve 1 to be long and reducing the contact pressure of the elastic blade 10 to the end of the developing sleeve 1, the process speed is high and the fine particles are fine. Even when the chance of applying the triboelectric charge to the toner increases, the toner does not charge up, and a decrease in the density at the end can be prevented.

In this embodiment, the developing device is set to 30 πcm
By applying the present invention to an image forming apparatus having a high process speed of 45 πcm / sec and 45 πcm / sec, it was possible to obtain an image having a low density at the end.

As a result of further study, (1) in order to stabilize the application of triboelectric charge to the toner, the contact pressure of the elastic blade to the developing sleeve was set to 10 to 50 g / cm in linear pressure, and (2) (3) By increasing the free length of the end of the elastic blade, the contact pressure of the elastic blade at both ends of the developing sleeve can be reduced within the above range, and (3) the portion of increasing the free length of the end of the elastic blade. Of the elastic blade is 5 to 20%, preferably 10%, of the width in the longitudinal direction of the elastic blade.

As described above, in this embodiment, the surface roughness of the end of the developing sleeve 1 is increased, and the contact pressure of the elastic blade 10 is reduced at both ends. Even when the present invention is applied to a forming apparatus, an image can be formed by intermittent printing without causing a low density at an end.

[0045]

As described above, in the developing device of the present invention, a conductive film made of a binder resin and carbon black and / or a composite material of carbon black is formed on the surface of the developing sleeve, Ra = 0.3
In addition, the surface roughness of the coating was increased by 10 to 30% at the end of the developing sleeve corresponding to the end of the image from the center in this range, so that the elastic blade applied to the developing sleeve. Even if the contact pressure is high at the end of the blade, charge-up of the magnetic toner of the one-component developer at the end can be prevented, and a developed image without a decrease in density at the image end can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a developing sleeve and an elastic blade in one embodiment of the present invention.

FIG. 2 is a sectional view showing a developing device incorporating the developing sleeve of FIG. 1;

FIG. 3 is a plan view showing an elastic blade according to another embodiment of the present invention.

FIG. 4 is a cross-sectional view illustrating a conventional developing device.

FIG. 5 is a perspective view of the developing device of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Developing sleeve 2 Conductive thin film 3 Elastic blade 4 Developing device 6 Magnet 7 Developing container 8 Magnetic toner 9 Photosensitive drum 10 Elastic blade 11 Support metal plate

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazuo Ono 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Norio Hashimoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inside (72) Inventor Masaharu Okubo 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Takayasu Yunomo 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. ( 56) References JP-A-2-306274 (JP, A) JP-A-6-1101031 (JP, A) JP-A-3-125364 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , (DB name) G03G 13/08-13/095 G03G 15/08-15/095 G03G 9/083

Claims (2)

(57) [Claims] The developer is a magnetic toner having at least a binder resin and a magnetic powder, and has a particle size distribution of: (i) 17 to 60% by number of toner particles having a particle size of 5 μm or less.
(Ii) 5 toner particles having a particle size of 6.35 to 10.08 μm.
(Iii) 2% by volume of toner particles having a particle size of 12.70 μm or more.
(Iv) a volume average particle diameter of 6 to 9 μm, and (v) a toner particle group having a particle diameter of 5 μm or less is represented by the following formula: N / V = −0.05 N + k N: the number% of toner particles having a particle diameter of 5 μm or less V: volume% of toner particles of 5 μm or less k: positive number of 4.6 to 6.7 N: positive number of 17 to 60 To form a conductive coating made of a binder resin and carbon black and / or a composite material of carbon black, and the surface roughness of the coating is Ra = 0.3 to
In a developing device having a range of 5.0 μm, a developer regulating blade made of an elastic body is in contact with the developer carrier, and a surface roughness of the coating corresponds to an image edge. A developing device that is 10% to 30% higher at the end of the developer carrier than at the center. 2. The developing device according to claim 1, wherein the length from the fixed end to the free end of the blade is longer at the end of the blade than at the center.