JP3120460B2 - Electrophotographic developer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic method, an electrostatic recording method, a toner an electrostatic latent image of two or more colors in an electrostatic printing method or the like
And a two-component developer developed with

[0002]

2. Description of the Related Art Electrophotography is widely used in copiers and printers, and among them, stabilization of the characteristics of photoreceptor and developer is the most important in improving the reliability of these products. Many researches and developments have been promoted as important elemental technologies. Among them, organic photoconductors have attracted attention because of their low cost, stability, etc., but the organic photoconductors have a problem that when charged at a high potential, the photoconductor is easily destroyed and the life is shortened. .

Further, with the recent progress in colorization of office documents, multi-valued surface potentials of photoconductors have been used to develop toners of two or more colors. In such a system, since the surface potential of the photoconductor is divided and used, it is necessary to develop with a smaller electrostatic contrast than before.

On the other hand, in the developing method, magnetic brush development is currently mainstream, and a two-component developer mainly composed of a carrier and a toner is used. When the electrostatic contrast is not high, it is effective to use a developer using a binder-dispersed carrier containing a binder resin and magnetic fine particles as main components among these two-component developers. That is, the binder-dispersed carrier has a high developing efficiency, so that the image density is high even under a low contrast potential, and a copy image with good resolution can be obtained.

In a method of developing toner of two or more colors by increasing the surface potential of a photoreceptor, a second method is used.
There is a problem that the tip of the magnetic brush on the developing sleeve after the developing device disturbs the toner image on the photoreceptor developed earlier, especially when the toner image is developed under a low contrast potential. The image is disturbed to a large extent because the electrostatic adhesion between the photoconductor and the photoconductor is weak.

However, in such a developing system,
The use of a binder-dispersed carrier at least for the developer after the second development is effective in preventing the toner image on the photosensitive member from being disturbed because the tip of the magnetic brush is relatively soft. No. 6,086,045.

The disadvantage of such a binder-dispersed carrier is that the magnetic force is relatively weak and the particle size is often small.
The electrostatic attraction force acting on the carrier from the photoconductor is larger than the magnetic attraction force required for the carrier to be carried on the developing sleeve, and is applied to the image area or non-image area on the photoconductor. Carriers may tend to adhere.

As a method for solving the above-mentioned problem in the binder dispersion type carrier, for example, a particle size of 18 to 70 μm is used.
In order to use carriers having a volume resistance of 10 ⁸ to 10 ¹² cmΩ at a speed of 1000 m and a magnetic field of 1000 Oe,
Adjusting to 200 gauss or more
657), a method of adjusting the coercive force of the carrier to 60 to 250 Oe in order to prevent aggregation of the carrier due to the magnetic force (Japanese Patent Application Laid-Open No. 60-147750), reducing the average particle size of the carrier, A method of using a sharp-cut carrier having a narrow distribution and adjusting the coercive force to 100 Oe or less to prevent a decrease in developing ability (Japanese Patent Laid-Open No.
JP-A-223471), a method of adding alumina particles to the toner surface in order to improve the flowability of the developer (Japanese Patent Application Laid-Open No. 62-129860), and a method of adding titania particles in the same manner (Japanese Patent Application Laid-Open No. 62-129860). Japanese Unexamined Patent Publication No. 62-129861) and the like have been proposed.

On the other hand, to use a two-component developer in a system in which the electrostatic contrast cannot be increased as in the above-described developing method, it is necessary to reduce the adhesive force between the toner and the carrier to some extent. The reason is that the toner must be removed from the carrier and adhered to the electrostatic image by an electrostatic attraction force proportional to the electrostatic contrast, and if the charge of the toner is high, the electrostatic image can be formed with a small amount of toner. This is because the charge is neutralized and a large amount of toner cannot be attached.

However, in order to reduce the charge amount of the toner,
It is necessary to increase the ratio of the toner to the carrier. As a result, frictional charging occurs between the toners, and the contact with the carrier becomes insufficient. Therefore, there is a problem that the amount of the toner of the opposite polarity increases. There is also a problem that the toner adheres to the surface of the carrier with the use of the developer and the amount of the toner of the opposite polarity increases. These opposite polarity toners cause the toner to adhere to the background of the photoreceptor and hinder long-term use of the developer.

From this, it is always stable at a low charge amount,
There has been a demand for a developer in which the reverse polarity toner does not increase even when used for a long time. In particular, in order to reproduce a low-contrast electrostatic image, it is necessary to obtain a toner having a large amount of charge that is stable over a long period of time. For example, JP-A-62-129860, JP-A-62-129861, 62-1
JP-A-29866 describes that a toner having stable triboelectric charging properties can be obtained over a long period of time by adding and mixing a certain kind of inorganic oxide on the surface of the toner.

However, even if these inorganic oxides are added to the toner surface, if the difference between the charge sequence on the carrier surface and the charge sequence on the toner surface is large, the amount of triboelectric charge of the toner increases, and the desired low charge The amount of toner could not be stably obtained for a long period of time. Further, the charge exchange property between the carrier and the toner is deteriorated, and the charging speed is reduced. Therefore, when the toner is added, the amount of the toner of the opposite polarity increases, and there is a problem that fog occurs.

[0013]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems and provides a developer which can be developed at a high density even if the electrostatic contrast is low, and which does not cause carrier adhesion on the surface of a photoreceptor. More specifically, the charge content is low, the charge distribution is narrow, the content is stable over a long period of use, and the content of the particle size that easily adheres to the photoreceptor is reduced. It is intended to provide a developer comprising a carrier and a toner. Another object of the present invention is to provide a method of developing toner of two or more colors by multiplying the surface potential of a photoreceptor so that a toner image developed on the photoreceptor is transferred to a developing device thereafter. It is an object of the present invention to provide a developer which is not disturbed by a magnetic brush made of the developer.

[0014]

According to the present invention, there is provided a developer used in an electrophotographic system for developing with two or more colors of toner.
Using a carrier obtained by dispersing magnetic fine particles in a binder resin, the average particle size of the carrier is 40 μm or more,
The ratio of particles having a particle size of 31 μm or less is 25% by weight or less, and the coercive force in a 5000 Oe
0 is at Oe or more and a volume resistivity on the carrier surface is 10 ¹² [Omega] cm or less of the conductive fine particles 0.0
An electrophotographic developer, wherein the developer is added at a ratio of from 0.05 to 10% .

As a method for producing the binder-dispersed carrier used in the present invention, a method of melt-kneading a binder resin and a magnetic powder and pulverizing and classifying, or a method of melt-kneading the binder resin and the magnetic powder, spray cooling and granulating. And the like.

As the binder resin for the carrier used in the present invention, all general thermoplastic resins can be used, and specifically, styrenes such as styrene and chlorostyrene; ethylene, propylene, butylene, isobutylene, etc. Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate and vinyl butyrate;
Α of methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, phenyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate, etc.
-Homopolymers or copolymers of vinyl ethers such as methylene aliphatic monocarboxylic acid esters such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone and vinyl isopropenyl ketone. The most typical binder resins are polystyrene and
Examples include styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene, and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, and wax can be exemplified.

The weight average particle size of the carrier used in the developer of the present invention is 40 μm or more, more preferably 45 μm.
The above is appropriate. In addition, the carrier particle size 31
The amount of the fine powder having a size of less than μm is suitably 25% by weight or less, more preferably 20% by weight or less of the total carrier.

Further, the coercive force of the carrier used in the developer of the present invention is 2 in a magnetic field of 5000 Oe.
0 or more, more preferably 30 or more is suitable.

The magnetic powder used in the carrier according to the present invention comprises:
Any material can be used as long as it satisfies the value of the coercive force in the carrier.Specifically, triiron tetroxide, γ-iron sesquioxide, various ferrites,
Examples include chromium oxide and various metal powders. The content of the magnetic powder is usually about 30 to 95% by weight, preferably 45 to 90% by weight, based on the total amount of the binder resin.

Further, conductive fine particles are added to the surface of the carrier used in the developer of the present invention. Although carbon black can be used as the conductive fine particles, inorganic oxide fine particles are preferable. As the conductive inorganic oxide, an inorganic fine powder which is added to a usual electrophotographic toner for the purpose of charge adjustment and powder fluidity adjustment can be used, and is not particularly limited. These conductive inorganic oxide particles used in the present invention have a volume resistance of 10 ¹² Ωcm or less, more preferably 10 ¹⁰ Ωcm or less. Specific examples include titanium oxide, silica, alumina, zinc oxide, magnesium oxide, tin oxide, iron oxide and the like. It is appropriate that the particle size be 1 μm or less, more preferably 0.1 μm or less.
The conductive fine particles used in the present invention may be subjected to a surface treatment for the purpose of hydrophobicity, charge adjustment, and the like, if necessary.

The amount of the conductive fine particles used in the present invention added to the carrier is 0.005 to 10%, and more preferably 0.05 to 10%.
Suitably, it is 1 to 5%. The method of adding the conductive fine particles to the carrier surface is not particularly limited, as long as it is a commonly used mixing device. Specific examples include a V-type blender, a cement mixer, a paint shaker, a Henschel mixer, a kneader coater and the like. The addition of the conductive fine particles may be performed before or at the same time as the addition of the toner at the time of preparing the developer.

The toner used in the present invention is not particularly limited, and may be any chargeable toner in which a colorant is dispersed in a binder resin and which is used in a usual electrophotographic method.

[0023]

In general, if the carrier has a large particle diameter, a small amount of fine powder, and a large magnetic force, it is possible to prevent the carrier from adhering to the photoreceptor (microcarrier over). However, the life of the carrier is shortened and the resolution is reduced. In 1-pass n-color (one-process multicolor development), there was a disadvantage that the previous image was disturbed.

According to the present invention, by adding conductive fine particles to the surface of a binder-dispersed carrier, an excessive increase in the total charge of the carrier can be suppressed. It is excellent in environmental stability because it can suppress carrier adhesion to the photoconductor without significantly increasing the particle size and magnetic force of the carrier. Made it possible.

Further, since the conductive fine particles on the carrier surface have low electric resistance, excessive toner charging is suppressed,
Since the charge in the contact area easily moves to the non-contact carrier surface, which contributes to the improvement of the charge exchange property and the charging speed, and even if a small amount of toner or the like adheres to the carrier surface, the charge amount does not significantly decrease. Even when the electrostatic contrast is low, high density development can be stably performed for a long time.

In the carrier of the present invention, the average particle size is 4
The amount of fine powder having a particle size of 0 μm or more and a particle size of 31 μm or less is 25 wt% or less, the coercive force in a 5000 Oe magnetic field is adjusted to 20 Oe or more, and the volume resistance of the conductive fine particles added to the carrier surface is 10 ¹² Ωcm. By doing so, carrier adhesion to the surface of the photoreceptor could be significantly reduced. Further, even when the electrostatic contrast is low, development of high density can be stably performed for a long time.

[0027]

The present invention will be described more specifically below with reference to examples and comparative examples. However, the present invention is not limited by these examples. (Example 1) 30 parts of a styrene / n-butyl methacrylate copolymer 70 parts of a magnetic powder (MG-Z, manufactured by Mitsui Kinzoku Co., Ltd.) were kneaded by a pressure kneader, pulverized by a jet mill, and classified by an air classifier. A dispersion type carrier having a coercive force of 45 Oersted in a magnetic field of 5000 Oersted was obtained in which a ratio of an average particle size of 48 μm and a particle size of 31 μm or less was 15% by weight in a magnetic field of 5000 Oersted. To 100 parts of this carrier, titanium dioxide fine powder (P-25, manufactured by Titanium Industry Co., Ltd .: 10 ⁶ Ωc)
m) 0.2 parts were added using a V blender. Styrene / n-butyl methacrylate copolymer 84 parts Polypropylene wax (660P, manufactured by Sanyo Chemical) 5 parts Carbon black (R330, manufactured by Cabot) 8 parts Charge control agent (Bontron N-04, manufactured by Orient Chemical) 3 parts Was kneaded, pulverized, and classified to obtain a toner having an average particle diameter of 11 μm. To 100 parts of this toner, 0.5 part of silica fine particles (R972, manufactured by Nippon Aerosil Co., Ltd.) was mixed using a Henschel mixer. The above-mentioned carrier and toner were mixed at a ratio of a toner concentration of 8% by weight to obtain a developer.

Example 2 30 parts of a styrene / n-butyl methacrylate copolymer 70 parts of a magnetic powder (MG-Z, manufactured by Mitsui Kinzoku Co., Ltd.) were kneaded by a pressure kneader, pulverized by a jet mill, and pneumatically classified. After classification, a dispersion type carrier having a coercive force of 45 Oersted in a magnetic field of 5000 Oersted was 21% by weight at a ratio of 46 μm in average particle size and 31 μm or less in particle size. To 100 parts of this carrier, 0.2 part of titanium dioxide fine powder (P-25, manufactured by Titanium Co., Ltd.) was added using a V blender. Using this carrier,
The developer was adjusted in the same manner as in Example 1.

Example 3 Bisphenol A ethylene oxide adduct-terephthalic acid copolymerized polyester 20 parts Magnetic powder (EPT1000, manufactured by Toda Kogyo Co., Ltd.) 80 parts was kneaded with a pressure kneader, pulverized by a jet mill, and air classifier. To obtain a dispersed carrier having a coercive force of 110 Oersted in a magnetic field of 5000 Oersted at a ratio of 24% by weight having an average particle size of 43 μm and a particle size of 31 μm or less. To 100 parts of this carrier, 0.2 part of titanium dioxide fine powder (P-25, manufactured by Titanium Co., Ltd.) was added using a V blender. Using this carrier,
The developer was adjusted in the same manner as in Example 1.

Comparative Example 1 In Example 1, the average particle size of the carrier was 38 μm and the particle size was 31 μm by pulverizing with a jet mill and adjusting classification conditions with an air classifier.
The developer was adjusted in the same manner as in Example 1 except that the following ratio was changed to 28% by weight.

Comparative Example 2 In Example 1, ferrite powder having a particle size of 0.5 to 1 μm was used as the magnetic powder, and the same operation was carried out so that the ratio of the average particle size was 45 μm and the particle size was 31 μm or less was 20% and 5000 Oe. The carrier whose coercive force in the magnetic field of 18 Oersted was manufactured. Thereafter, a developer was prepared in the same manner as in Example 1.

Comparative Example 3 Example 1 was repeated except that the addition of fine titanium dioxide powder to the carrier was omitted.
A developer was prepared by the same composition and operation as described above.

(Actual Machine Test) The above developer was evaluated using the following image forming system. This system uses a low-potential part, a medium-potential part, and a high-potential part, and the low-potential part and the high-potential part of the electrostatic latent image having different potential colors when the medium-potential part is used as a background part potential. A two-color image forming system is used in which the toner is overlaid and developed and transferred onto the copy at one time. Although the developer of the present invention is effective irrespective of the polarity of the toner, in the present embodiment, the developer is used in combination with a positively charged black toner.
The system parameters were set as follows.

An OPC drum for a laser printer having an outer diameter of 84 mm was used as a photoreceptor drum.
It was uniformly charged to 800V. Next, the emission wavelength 780
Using a semiconductor laser writing device of nm, reverse exposure (image area exposure) was performed.
An electrostatic latent image having a surface potential of V was formed, and development was performed using a negatively charged red toner (manufactured by Fuji Xerox Co., Ltd.) under a developing bias of -650 V. Subsequently, regular exposure (non-image portion exposure) is performed by an exposure lamp, and the non-exposed portion-70 is exposed.
An electrostatic latent image having a surface potential of 0 V and an exposed portion of −50 V was formed, and the developer of Examples 1 to 3 and Comparative Example 1 was used.
Development using a positively charged black toner was performed. At this time, the developing bias was -400 V, and the electrostatic contrast was 30.
It was 0V. When the image quality was evaluated by the above process, the results shown in Table 1 were obtained.

[0035]

[Table 1]

That is, as in Examples 1 to 3, the average particle size is relatively large, the amount of fine powder is reduced, and the coercive force is increased.
Further, in a developer comprising a carrier and a toner to which a conductive inorganic oxide is added on the surface, the carrier does not adhere to the surface of the photoreceptor and a low charge amount is stably maintained even after 100,000 copies. Thus, it is possible to efficiently develop even a latent image having a low electrostatic contrast, and to exhibit excellent developer performance with a long life without a decrease in density or fogging. In addition, although experiments were conducted with other electrostatic contrasts as application to the developer of the example, it was possible to sufficiently utilize even at 500 V or less.

[0037]

According to the present invention, by adopting the above-mentioned structure, there is no carrier adhesion on the surface of the photoreceptor and excessive toner charging at the initial stage can be suppressed. Speed can be maintained. As a result, the charge distribution is narrow and a stable charge amount can be maintained even at a low charge, a latent image with a low electrostatic contrast can be efficiently developed, a carrier image is not generated in a copy image portion or a non-image portion, and a long-life development is performed. Agents and photoreceptors can be provided.
In particular, when the developer of the present invention has a low electrostatic contrast,
For example, it has an effect of enabling development at 500 V or less, and is suitable for application to a multicolor system without image disturbance.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tetsu Torigoe 1600 Takematsu, Minamiashigara-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. Takematsu Office (56) References JP-A-63-274966 (JP, A) JP-A-2-2 43566 (JP, A) JP-A-1-101500 (JP, A) JP-A-1-298371 (JP, A) JP-A-63-127260 (JP, A) Photo Industry Separate Volume “Imaging” Part 2, Showa 63 July 30, 2008, Photo Industry Publishing Co., Ltd., p. 63 (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/107 G03G 9/113

Claims (1)

(57) [Claims] 1. A developer used in an electrophotographic system for developing with a toner of two or more colors, wherein a carrier obtained by dispersing magnetic fine particles in a binder resin is used. A ratio of particles of 31 μm or less is 25% by weight or less, a coercive force in a 5000 Oe magnetic field is 20 Oe or more,
An electrophotographic developer, wherein conductive particles having a volume resistance of 10 ¹² Ωcm or less are added to the surface of the carrier at a ratio of 0.005 to 10% .