JPH06301243A - Carrier for developing electrostatic charge image and its production - Google Patents

Abstract

PURPOSE:To uniformly form a developer layer on a magnetic roll, to prevent the falling of a carrier and the roughening and drop-out of an image, to ensure electrostatic charge stability of the carrier and to prevent the occurrence of unevenness of an image and the deterioration of image quality by using specified magnetic powder as core particles. CONSTITUTION:When core particles are coated with a coating resin while keeping a dry state and applying shearing force to obtain a carrier for developing an electrostatic charge image, magnetic powder having 30-60mum average particle diameter and including <=25wt.% particles having <=20mum particle diameter is used as the core particles. A copolymer of a fluorine-contg. vinyl monomer such as vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoro-ethylene, monochloroethylene or trifluoroethylene or a polymer of styrene or a styrene deriv. such as chlorostyrene or methylstyrene may be used as the coating resin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image developing carrier used for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic recording method or the like with a two-component developer, and a method for producing the carrier. .

[0002]

2. Description of the Related Art A method of visualizing image information through an electrostatic latent image such as electrophotography is currently used in various fields. In the electrophotographic method, an electrostatic latent image is formed on a photosensitive member by a charging and exposing process, the electrostatic latent image is developed with a developer containing toner, and then transferred and fixed to be visualized. The developer used here includes a two-component developer composed of a toner and a carrier and a one-component developer such as a magnetic toner which is used alone as a toner. In the two-component developer, the carrier is a developer. It is widely used at the present time because it has functions such as good controllability because it is divided into functions such as stirring, carrying, and charging and is separated as a developer. In particular,
A developer using a resin-coated carrier has excellent charge controllability, and is relatively easy to improve in environmental dependency and stability over time. Further, as a developing method, a cascade method or the like has been used in the old days, but at present, a magnetic brush method using a magnetic roll as a developer conveying unit is mainly used.

Problems with the magnetic brush method include a decrease in image density due to charge deterioration of the developer, a remarkable background stain, an image roughening due to the adhesion of the carrier to the image, and an image accompanying the consumption of the carrier. There were problems such as uneven density. Adhesion of the carrier to the image is induced charge injection and adhesion to the image portion due to the decrease of the resistance of the carrier.
In addition, it is considered that the toner adheres to the edge portion due to excess charge of carrier after development.

As described above, in order to obtain a high-quality image, it is very important to control the charge and resistance of the carrier, and it is necessary to consider impact resistance, abrasion resistance, developer life and the like. There is. As a carrier satisfying these required characteristics, a resin coating type carrier has been actively studied,
Also in the production method, a method of dissolving a coating resin in a solvent, mixing it with core particles, and forming a coating by removing the solvent has been put to practical use, but in order to obtain a sufficient amount of coating and a problem of solvent toxicity. There is also a manufacturing problem, such as a long time being required.

Therefore, a coating method in which core particles and a coating resin are dry-mixed and then heated to melt and solidify the coating resin (JP-A-54-35736 and JP-A-62-10).
6475) and a dry coating method of forming a coating while applying an impact force to a mixture of core particles and resin particles for coating (see Japanese Patent Laid-Open No. 2-87167). However, the former method makes it difficult to use a resin that has a high viscosity when melted, and in the process of cooling and solidifying the coating resin,
There is a problem that aggregation of carriers is likely to occur. In the latter method, since impact force is applied, the core particles may be destroyed, and when a resin having a high softening point is used as the coating resin, it becomes difficult to form a coating film. However, there are great restrictions on the selection of core particles and coating resin.

In order for the resin coating type carrier to satisfy the required characteristics, it is important that the coat layer is uniformly formed on the carrier. Despite the importance of the particle size distribution of the core particles in the dry coating method, the particle size distribution of the core particles is now important in order to obtain a carrier on which a resin coating layer that is smooth and has good uniformity without aggregation of core particles is formed. Has not been fully considered.

[0007]

Therefore, the present invention is to provide a carrier for developing an electrostatic image having the following characteristics by forming a uniform coating by a dry coating method and a method for producing the same. Uniform formation of the developer layer on the magnetic roll to prevent carrier spills, image roughening, and image dropouts, to secure the charge stability of the carrier, and to prevent image unevenness and image quality due to developer consumption due to carrier adhesion. Prevent deterioration.

[0008]

Means for Solving the Problems The present invention provides a carrier for developing an electrostatic charge image in which a core resin is coated with a coating resin while keeping a dry state and applying a shearing force. The particle size is in the range of 30-60 μm, and
An electrostatic charge image developing carrier characterized by using a magnetic powder having an amount of particles of 20 μm or less of 25% by weight or less, and an average particle size of 30 to 60 μm, and a particle size of 20 μm. Manufacture of a carrier for developing an electrostatic charge image, characterized in that magnetic powder core particles having an amount of the following particles of 25% by weight or less and coating resin particles are mixed and heated in a dry state while applying a shearing force. Is the way.

[0009]

In the resin-coated carrier particles, in order to have excellent chargeability with the toner and to obtain stable image quality, it is usually necessary to increase the amount of the coating resin to prepare for abrasion and toner sticking and extend the life of the developer. It is normal. However, if the coating resin amount is increased, the carrier surface undergoes yield deformation under pressure,
In many cases, cohesiveness appears in the carrier and the fluidity deteriorates.

The cohesiveness of the carrier largely depends on the amount of coating resin, and in the case of ordinary ferrite or magnetite granulated powder,
The cohesiveness is observed in the region of 1% or more by weight, and it is considered that it depends on the molecular weight and softening point of the resin, but in the study of the present inventors, it also depends largely on the particle size distribution of the core particles. found. That is, if the fine powder side of the core particles is increased, even if the mixing is continued during cooling, it is not possible to sufficiently transmit the shearing force between the core particles, and even in the process of forming the film, the small particles or the small particles and the large particles are mixed. Tend to agglomerate, and uniform coated particles cannot be obtained. As a result, instability of triboelectric charging due to deterioration of fluidity of the carrier, roughness of developer layer formation on the magnetic roll, and the like are caused, resulting in deterioration of image quality.

Therefore, the present inventors have determined that the average particle size is 30 to
A magnetic powder core particle having a particle size of 60 μm and a particle size of 20 μm or less in an amount of 25% by weight or less, and more preferably 10% by weight or less, and a coating resin particle are subjected to shearing force in a dry state. By mixing and heating while adding and manufacturing, it succeeded in eliminating the above-mentioned fault.

The coating resin used in the present invention includes vinylidene fluoride, tetrafluoroethylene, hexafluoropropylene, monochlorotrifluoroethylene, monochloroethylene, trifluoroethylene, and other vinyl-based fluorine-containing monomer copolymers; styrene. , Styrenes such as chlorostyrene and methylstyrene; methyl methacrylate, methyl acrylate, propyl acrylate,
Α such as lauryl acrylate, methacrylic acid, acrylic acid, butyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate
-Methylene aliphatic monocarboxylic acid esters; nitriles such as acrylonitrile and methacrylonitrile; 2-
Vinyl pyridines such as vinyl pyridine and 4-vinyl pyridine; vinyl ethers; vinyl ketones; olefins such as ethylene, propylene and butadiene; and silicon homopolymers or copolymers such as methyl silicon and methyl phenyl silicon. It is possible,
Furthermore, polyesters containing bisphenol, glycol, etc. can also be used. The amount of the coating resin compounded is about 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the carrier.

As the core particles used in the present invention, known particles can be used. In particular, ferrite, which is lighter in weight and has less stress in the developing device, is preferable.

[0014]

【Example】

[Example 1] (Production of carrier) Spherical Cu-Zn ferrite (manufactured by Powdertec Co., average particle size 40 µm, ratio of particles having an average particle size of 20 µm or less 8.6%) 100% by weight Styrene-methacrylate copolymer 0.5% by weight % The above components were mixed with a 1 liter small kneader (made by Irie Shosha Co., Ltd.) with a stirring blade at 40 rpm for 10 minutes, and the heat medium temperature was 20
After setting the temperature to 0 ° C and stirring and kneading for 40 minutes as it is, turn off the heater and stir while cooling for 50 minutes to obtain 63μ.
The resin-coated carrier was obtained by sieving with a m sieve. When the obtained carrier was observed by a scanning electron microscope, no aggregation of core particles was observed, and it was confirmed that the resin coating layer was uniformly formed.

(Manufacture of Toner) Styrene-n-butyl methacrylate 84 wt% Carbon (BPL manufactured by Cabot) 10 wt% Charge control agent (Bontron No4 manufactured by Orient) 2 wt% Polyethylene wax (400P manufactured by Mitsui Petrochemical Co., Ltd.) 4% by weight The above components were kneaded and pulverized to obtain a toner having an average particle size of 11 μm.

(Manufacturing / Testing Method of Developer) A developer was prepared by dry-mixing the toner and the carrier at room temperature for 20 minutes so that the toner concentration was 4% by weight. This developer was subjected to an image quality maintenance test using an FX5030 modified machine manufactured by Fuji Xerox Co., Ltd.

Comparative Example 1 A developer was prepared in the same manner as in Example 1 except that ferrite having an average particle size of 70 μm was used as the core particles of the carrier, and an image quality maintaining test was conducted. .

[Comparative Example 2] The same as Example 1 except that as the core particles of the carrier, ferrite having an average particle size of 47 μm and an amount of particles having a particle size of 20 μm or less of 28% was used in Example 1. A developer was prepared in this manner, and an image quality maintenance test was conducted.

Comparative Example 3 The same carrier composition as in Example 1 was mixed for 10 minutes with a 1 liter small kneader,
Stop mixing and set the heat transfer medium temperature to 200 ° C in a stationary state, heat for 60 minutes, and then turn off the heater to 60
After cooling for 1 minute, the resin-coated carrier was obtained by sieving with a 63 μm sieve. When the obtained carrier was observed with a scanning electron microscope, the agglomeration of nuclear particles was very large, and the surface of the nuclear particles was exposed, and the coating film was non-uniform in most cases. Using this carrier, a developer was prepared in the same manner as in Example 1 and an image quality maintenance test was conducted.

(Results of Image Quality Evaluation) In Comparative Examples 1 and 2, the initial image quality was good, or the deterioration of the image quality due to carrier adhesion and the dropout of the image quality became noticeable from about 2,000 sheets, especially in Comparative Example 2, 20,000. The unevenness of the image density occurred due to the decrease of the developer from the number of sheets. In Comparative Example 3, carrier adhesion to the black image portion occurred from the initial stage, and image omission and fog occurred remarkably, and the image quality maintenance test was stopped. On the other hand, when the developer of Example 1 was used, the initial image quality was good, and the image quality after 100,000 sheets remained in good condition without any problems. It is considered that this is because the uniform coating of the core particles greatly contributes to the reduction of cohesiveness.

[0021]

According to the present invention, by adopting the above-mentioned constitution, it becomes possible to form a uniform resin film by the dry film forming method, and it is possible to prevent the agglomeration of the core particles and to prevent the core particles from coagulating. In addition, the developer layer can be formed uniformly, the charge stability of the carrier can be secured, and excellent image quality can be obtained.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masahiro Takagi 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Satoru Ishigaki 1600 Takematsu, Minamiashigara City, Kanagawa Prefecture, Fuji Xerox Co., Ltd.

Claims (2)

[Claims] 1. An electrostatic charge image developing carrier comprising a core particle coated with a coating resin while maintaining a dry state and applying a shearing force, wherein the core particle has an average particle size of 30 to 6
A carrier for developing an electrostatic charge image, which comprises magnetic powder having a particle size of 0 μm and a particle size of 20 μm or less in an amount of 25% by weight or less. 2. A magnetic powder core particle having an average particle size in the range of 30 to 60 μm and an amount of particles having a particle size of 20 μm or less is 25% by weight or less, and a coating resin particle, in a dry state. A method for producing a carrier for developing an electrostatic charge image, which comprises mixing and heating while applying a shearing force.