JP2749869B2 - Developing device - Google Patents

Description

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

[Conventional technology]

Conventionally, in a developing device using a dry type one-component magnetic toner, performing a uniform thin layer coating of a developer on a developer carrier realizes stable charging of the toner and is stable regardless of environmental fluctuations and the number of printed sheets. It is considered to be a very important technique for providing a simulated image. For this reason,
As disclosed in JP-A-57164 and JP-A-58-571645, the developer is formed by forming fine irregularities by sandblasting or the like on a cylindrical metallic developer carrier (hereinafter referred to as a developing sleeve). In addition to improving the transfer force of the toner and stably charging the toner, the developer can be transported at a very small distance (10
(About 0 to 400 μm), a magnetic seal is formed between the ferromagnetic blade and the magnet included in the sleeve, and a thin layer coating of magnetic toner is performed. FIG. 2 shows the developing device in the above proposal. In recent years, with the widespread use of image forming apparatuses such as electrophotographic copiers, their uses have been widely spread,
The demands on the image quality have also become severe. 2. Description of the Related Art In copying images such as ordinary documents and books, it is required to reproduce very finely and faithfully without crushing or breaking even fine characters. In particular, when the latent image on the photoreceptor of the image forming apparatus is a line image of 100 μm or less, thin line reproducibility is generally poor, and the line image is not yet sufficiently sharp. Recently, in an image forming apparatus such as an electrophotographic printer using digital image signals, a latent image is formed by collecting dots of a constant potential, and a solid portion, a halftone portion and a light portion have a dot density. It is expressed by changing. However, if the toner particles do not adhere exactly to the dots and the toner particles protrude from the dots, the gradation of the toner image corresponding to the dot density ratio of the black portion and the white portion of the digital latent image cannot be obtained. There is a problem. Furthermore, when the resolution is improved by reducing the dot size in order to improve the image quality, the reproducibility of a latent image formed from minute dots becomes more difficult, and the resolution and gradation are poor, and the sharpness is low. Image tends to be lacking.

Although the image quality is good in the early stage, the image quality may deteriorate while copying or printing out. It is considered that this development is caused by the fact that only toner particles which are easily developed are consumed first while copying or printing is continued, and the toner particles having poor developability accumulate and remain in the developing machine.

[Problems to be solved by the invention]

When an image was output using fine-grain toner using the developing sleeve shown in the above-described conventional example, the following problems were encountered.

(1) Density due to charge gap The above development is remarkable in a low temperature and low humidity environment. In addition, a toner having a normal particle size generally used (average particle size of 9 to
15 μm), which is considered to be caused by the fine powder (particle diameter: 5 to 6 μm) toner formed on the sleeve. In other words, since the fine powder toner has a large surface area per volume, the application of tribo is excessive (± 20 μc / g or more) and the fine powder toner is strongly restrained on the surface of the developing sleeve by the toner's own reflection power. It has been considered that the normal charging of the toner having the diameter is impaired and the developing ability is reduced, so that a density increase occurs.

In a fine particle toner, the density change due to this charge-up is a more remarkable development. This is because the average particle size of the fine particle toner is 6 to 9 μm, which is almost equivalent to the size of the fine particle toner in the normal particle size toner. That is, since the surface area per volume of the fine particle toner is large, the individual fine particle toner easily becomes tribo-excessive, and the small particle diameter of the fine particle toner further enhances the reflection power of the toner itself, and is strongly restrained by the sleeve surface. It is thought to be. For this reason, when an image is output in a low-temperature and low-humidity environment using the fine-particle toner, a density increase due to the charge-up occurs on about 100 sheets, and it has been difficult to use the fine-particle toner practically.

[Means for solving the problem]

That is, the present invention provides a negatively-chargeable insulating one-component magnetic toner having at least a binder resin and a magnetic powder, and having a particle size distribution of (i) 17 μm or less of magnetic toner particles having a particle size of 5 μm or less. ~ 60%
(Ii) 5-50 magnetic toner particles having a particle size of 6.35-10.08 μm.
(Iii) 2% by volume of magnetic 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 group of magnetic toner particles 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: a positive number of 4.6 to 6.7 N: a dry type one-component developing device having a negatively chargeable insulating one-component magnetic toner satisfying a positive number of 17 to 60, A thin layer made of a composite material of a binder resin, graphite particles, and carbon black particles is formed on the surface of the developing sleeve for transporting the magnetic toner having the tribo by rotation therein, and the surface of the thin layer is formed. Roughness is Ra = 0.3-5μm, Rz = 1.0-30
The present invention relates to a developing device having a range of μm.

In the developing device of the present invention, the surface of the developing sleeve is coated with a conductive coating material in which carbon black and graphite are blended with a binder resin, so that the pigment surface of the conductive pigment projects on the sleeve surface, and By providing an appropriate roughness on the sleeve surface, the density ghost due to charge-up of the insulating one-component magnetic toner is prevented, and the sleeve ghost is reduced.

〔Example〕

FIG. 1 is a structural view of a developing sleeve showing an embodiment of the present invention, and FIG. 5 is a structural view when this is incorporated in a developing device having a ferromagnetic blade 3. Is a ferromagnetic blade arranged at a distance of 250 μm from the sleeve 1. In FIG.
Is a conductive carbon black (CONDUCTEX90 manufactured by Columbia) using 50% by weight of phenolic resin as a binder.
0) is 5% by weight and graphite (Nippon Graphite CSP)
E) is diluted with methyl cellosolve and methanol, and the developing sleeve 1 is coated by spraying with a coating agent comprising 45% by weight of kneaded mixture.
Heat cured at 30 ° C for 30 minutes. Here, it is possible to change the coating pressure at the time of spraying, etc., but as a result of the following experiment, when the fine particle toner is used,
It was found that the surface condition of the coated sleeve in which the density was not generated due to the charge gap was within a certain range.

Experiment 1) The particle size distribution of the developer is as follows: (i) 5 μm or less: 17 to 60% by number (ii) 6.35 to 10.08 μm or less: 5 to 50% by number (iii) 12.70 μm or more: 2% by volume or less (iv ) Volume average particle diameter: 6 to 9 µm (v) Magnetic toner particles of 5 µm or less have the following formula: N / V = -0.05N + k N: Number% of toner particles of 5 µm or less V: Volume% of toner particles of 5 µm or less k : A positive number of 4.6 to 6.7 N: A positive number of 17 to 60 was used.

 For example, the following magnetic toner was used.

The above-mentioned components were put into the steps of mixing, kneading, coarse pulverization, fine pulverization and classification to obtain a classified toner having the following particle size distribution.

(I) 5 μm or less: 35.4 number% (ii) 6.35 to 10.8 μm: 36.9 number% (iii) 16 μm or more: 0.5 volume% (iv) Volume average particle size 6.5 μm (v) N / V = 3.5 This classified product 100 1.2 parts by weight of silica treated with dimethyl silicone oil was added to the parts by weight and mixed to prepare a negatively chargeable insulating magnetic toner.

A coat sleeve of the above formulation was prepared by a spray method. Here, air spray was used, and the gun used was Binks No. 601 and the paint pressure was 0.1 kg / cm ^{2 to 5} kg /
cm ^2, the air pressure pattern adjustment ^{0Kg / cm 2 ~5Kg / cm 2} ,
By adjusting the air pressure for atomization to 0.5 kg / cm ^{2 to 4} kg / cm ² , the surface roughness Ra (center line average roughness) and
A sleeve having Rz (10-point average roughness) was obtained. 3 and 4 show the definitions of Ra and Rz on the sleeve. 23 ° C, 60% RT, 15 ° C, 10% using the above sleeve and toner
When an image was output using the developing device shown in FIG. 5 in three environments of RT, 32.5 ° C., and 85% RT, the density of 5 ^□ (that is, the density of an image of 5 mm × 5 mm square) and the solid density are shown in Table 2. As shown, there was no concentration swell due to the charge through the endurance. However, it was found that each of the comparative sleeves No. 1 and No. 5 had poor developer coating, and was not suitable for practical use. At this time, when observing the upper surface of the sleeve, in the case of the No. 1 sleeve, irregularities (hereinafter referred to as blotches) occurred on the entire surface of the sleeve, and in the case of the No. 5 sleeve, the coat was thick.

Therefore, in the sleeve Nos. 2 to 4 used in the present invention having a surface roughness of Ra = 0.3 to 5.0 μm and Rz = 1.0 to 30.0 μm, a stable thin layer coat without a density increase due to a charge tap is formed. Can be provided.

Furthermore, when a reproduction experiment was performed by changing the values of Ra and Rz, it was confirmed that the sleeves exhibiting Ra = 0.5 to 1.5 μm and Rz = 3.5 to 10.0 μm exhibited almost the same values as the sleeve of No. 3. Was. Further, in the sleeve showing Ra <0.3 μm and Rz <1.0 μm, a blot is generated on the entire surface and Ra> 5.0 μm.
In a sleeve having a thickness of 3 μm and an Rz of 30.0 μm, the coat was thick and a stable image could not be obtained. In the above example, the ratio of carbon and graphite is 1/9, and the ratio of the phenolic resin to carbon and graphite is 1/1.
However, as a result of the study, the ratio of conductive carbon black to graphite as a conductive coating material used as a coating agent was 1/9 to 3/7, and the ratio of phenolic resin to conductive carbon black and graphite was 2/1. No. in the range of ~ 5/10
It turned out that it shows the same characteristics as 2,3,4 sleeves.

In summary, in a developing device using a magnetic toner containing 17 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less as a developer and having a volume average particle diameter of 4 to 9 μm, When the functional coating material is coated on the upper layer of the sleeve: i) The surface roughness of the sleeve is Ra = 0.3 to 5.0 μm, Rz = 1.
By setting the thickness to 0 to 30.0 µm, it is possible to prevent the concentration from being increased due to the charge gap.

ii) preferably Ra = 0.5-1.5 μm, Rz = 3.5-10.0 μm
m is preferred.

When the surface condition of the coat sleeve is in the above range, considering the reason why the density is prevented by the charge gap, the above range (Ra = 0.3 to 5.0 μm, Rz = 1.0) is considered.
(30.0 μm), carbon black particles and graphite particles, which are chemically inert, form irregularities on the surface of the coated sleeve and effectively act as leak sites on the sleeve surface to reduce the contact resistance with the fine particle toner. This is considered to be because the toner particles have a small particle size and a large surface area per volume, and thus suppress the charge-up of the toner particles. Also, Ra is 0.3 μm and Rz is 1.0
If it is smaller than μm, the slipperiness of the coated sleeve surface becomes too large, causing a so-called blotch coating failure. On the contrary, Ra is 5.0 μm and Rz is 10.0 μm.
If it becomes larger, the effect as a leak site expands because the sleeve surface is excessively roughened, and the triboelectricity tends to decrease, and the density tends to decrease. By clogging the sleeve surface, a problem arises in that a uniform thin layer coat, which is an original function of the sleeve, cannot be formed and an image becomes rough. For this reason, the surface roughness of the coast sleeve is Ra = 0.3
5.05.0 μm and Rz = 1.0-30.0 μm. Further, it goes without saying that the fact that the above-mentioned coated sleeve acts as a leak site for the fine toner particles is also effective in preventing a so-called sleeve ghost.

[Other embodiments]

Another embodiment will be described below. FIGS. 6 and 7 show the structure of a developing unit in another embodiment, in which the amount of toner coating is regulated by bringing an elastic metal blade or rubber blade into contact with the sleeve surface. is there. FIG. 6 shows the blade contact in the forward direction with respect to the sleeve rotation direction, and FIG. 7 shows the blade contact in the reverse direction with respect to the sleeve rotation direction. Conventionally, in this method, frictional charging is positively applied to toner particles at a contact portion between a sleeve, toner particles, and a blade, and stable triboelectric application can be performed. However, when the blast sleeve and the elastic blade are used for the fine particle toner, the tribo is excessively applied compared with the case where the ferromagnetic blade in the conventional example is used, so that the density increase due to the charge is easily generated. For this reason, it has been extremely difficult to make the best use of the combination of the fine particle toner and the elastic blade. Then, when an elastic blade was used for the coat sleeve as shown in FIGS. 6 and 7, it was found that the effect was obtained from the following experiment.

Experiment 2) The developer used in Experiment 1 and No. 2, 3, and 4 sleeves were
A urethane rubber having a thickness of 1.0 mm was used as a blade. 23 ° C, 60% RT, 15
The images were output in an environment of 10% RT, 32.5 ° C, and 85% RT.
Up to 00 sheets, 5 ^□ (5 mm × 5 mm) and solid density were stable, and no density loss due to the charge-up occurred and no coating failure occurred. At this time, when the elastic blade comes into contact with the sleeve in the forward direction and the reverse direction with respect to the rotation direction of the sleeve, it is desirable that the elastic blade is in contact with the sleeve in both cases. Therefore, uniform coating cannot be performed on the sleeve, and a stable image cannot be obtained.

The surface roughness of the coated sleeve is Ra = 0.3 to 5.0 μm,
By setting Rz in the range of 1.0 to 30.0 μm, even when an elastic blade is used, it is possible to prevent the toner particles from increasing in density due to the charge gap. In addition, by using the elastic blade, even in a high-temperature and high-humidity environment, sufficient tribo can be applied to the toner particles, and a stable image can be output regardless of the environment.

〔The invention's effect〕

As described above, in a developing apparatus using a magnetic toner containing 17 to 60% by number of magnetic toner particles having a particle diameter of 5 μm or less and having a volume average particle diameter of 6 to 9 μm, the toner is synthesized on the surface layer of the sleeve. The resin is coated with a conductive coating material containing carbon black and / or graphite, and the surface roughness of the sleeve at this time is set to Ra = 0.3 to 5.0 μm and Rz = 1.0 to 30.0 μm. This makes it possible to prevent the density reduction and sleeve ghost caused by the charge gap evenly.

Therefore, an image excellent in fine line reproducibility and gradation can be stably provided by using the fine particle toner which has been difficult to use conventionally.

[Brief description of the drawings]

FIG. 1 is a perspective view of a developing sleeve in Example 1, FIG. 2 is a conventional example, and FIG. 3 is a center line average roughness Ra.
FIG. 4 is a diagram showing the definition of the 10-point average roughness Rz, FIG. 5 is a diagram showing the configuration of the developing device in the first embodiment, and FIG. 6 is a diagram showing the configuration in the second embodiment. FIG. 7 shows a configuration diagram of the developing device, and FIG. 7 shows a configuration diagram of the developing device in the second embodiment. 1 ... sleeve, 2 ... flange, 3 ... ferromagnetic blade, 4
... Hopper, 5 ... Toner, 6 ... Magnet, 7 ... Drum, 8 ... Elastic blade, 9 ... Conventional sleeve

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Otsuka Yasumasa 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Akihiko Takeuchi 3-30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc. (72) Inventor Koichi Tanikawa 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takayasu Yunomo 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Stocks In-company (56) References JP-A-55-117173 (JP, A) JP-A-62-168162 (JP, A) JP-A-61-23171 (JP, A) JP-A-61-122675 (JP, A) JP-A-61-208069 (JP, A) JP-A-56-14263 (JP, A)

Claims (3)

(57) [Claims] 1. A negatively chargeable insulating one-component magnetic toner having at least a binder resin and a magnetic powder,
(I) 17 to 60% by number of magnetic toner particles having a particle size of 5 μm or less
(Ii) 5-50 magnetic toner particles having a particle size of 6.35-10.08 μm.
(Iii) 2% by volume of magnetic 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 group of magnetic toner particles 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: a positive number of 4.6 to 6.7 N: a dry type one-component developing device having a negatively chargeable insulating one-component magnetic toner satisfying a positive number of 17 to 60, A thin layer made of a composite material of a binder resin, graphite particles and carbon black particles is formed on the surface of the developing sleeve for transporting the magnetic toner having the tribo by rotation and enclosing, and a surface of the thin layer is formed. Roughness is Ra = 0.3-5μm, Rz = 1.0-30
a developing device having a size in the range of μm. 2. The developing device according to claim 1, wherein a ferromagnetic metal blade is arranged at a minute interval so as to face the developing sleeve. 3. The developing device according to claim 1, wherein a blade made of an elastic material is brought into contact with said developing sleeve.