JPH04329553A - carrier for electrophotography - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Description [0001] [Industrial Application Field] The present invention relates to a carrier for electrophotography, and more specifically, a coated carrier for two-component magnetic brush development, which can be mixed with a toner. This invention relates to an electrophotographic carrier that has been improved so as to constitute a developer with high image quality and long life. [0002] Conventionally, as a developer for developing an electrostatic charge image formed on a latent image holding surface of an electrophotographic photoreceptor,
Two-component developers consisting of a carrier and a toner are known. Development methods using two-component developers include the cascade method and the magnetic brush method.
As a high-speed development method, a magnetic brush method is widely used in which a magnetic carrier is used and a brush-like carrier formed on a magnet is brought into contact with a photoreceptor. This method is
Since the toner supply capacity is high and the tip of the magnetic brush acts as a developing electrode very close to the photoreceptor, it has the characteristic of providing good image quality not only for line drawings but also for solid black screens. [0003] Recently, coated carriers in which the surfaces of magnetic core particles are coated with resin have been proposed and put into practical use as magnetic carriers. Such a coat carrier is
It is characterized in that it is difficult for the toner to become spent during development, and as a result, the amount of charge is stabilized, and the life of the developer can be extended. [0004] Problems to be Solved by the Invention [0004] However, the above-mentioned magnetic coated carrier becomes highly resistant or insulated due to its resin coating, and no longer plays the role of a developing electrode during development.As a result, in particular, Problems such as edge effects and lack of uniformity in solid black areas have been pointed out. As a method for compensating for the above-mentioned problems of magnetic coated carriers, a method is known in which, for example, a small amount of conductive fine powder of metals, semimetals, and their oxides is added to the developer as an external additive. However, although the conductive fine powder as described above has the role of suppressing the increase in resistance of the developer and promoting the effect of the coat carrier as a development electrode, it has too strong abrasive action. This may cause unnecessary wear and tear on the photoreceptor when cleaning the toner. That is, streak-like polishing scratches are generated on the surface of the photoreceptor due to the conductive fine powder, causing image defects, and the film of the photoreceptor is severely thinned, resulting in a decrease in the electrical or optical performance of the photoreceptor. Conductive materials also sometimes have the problem of being transferred onto paper and contaminating the copied image. The present invention has been made to solve the above-mentioned problems of conventional developers, and its purpose is to reduce the amount of charge on the toner during repeated use without unnecessary wear and tear on the photoreceptor. without increasing, i.e.
An object of the present invention is to provide an electrophotographic carrier capable of maintaining high image quality in line drawing areas and solid black areas without causing a decrease in image density. [Means for Solving the Problems] That is, the gist of the present invention is a coated carrier formed by coating the surface of magnetic core particles with resin, and in measuring the dynamic resistance of the coated carrier, The present invention relates to an electrophotographic carrier characterized by having a breakdown voltage in the DC voltage range of 500V. The present invention will be explained in detail below. The electrophotographic carrier of the present invention is basically constructed by coating the surface of magnetic core particles with a resin, similarly to conventional magnetically coated carriers. Examples of the magnetic material include magnetite and various ferrites represented by the general formula MO.nFe2 O3. In the above general formula, M specifically represents Fe, Cu, Zn, Mg, Ni, Co, Mn, Cd
etc., and the combination may be one type or two or more types. Further, the composition of the ferrite may be non-stoichiometric and may contain small amounts of metal elements and others. The magnetic material is used as core particles with a volume average particle diameter of 10 to 300 μm. Examples of resins include silicone resins or modified products thereof, fluorine resins, acrylic resins, styrene resins, epoxy resins, polyester resins, polyamide resins, cellulose resins, acetal resins, petroleum resins, polycarbonate resins, Examples include vinyl chloride-vinyl acetate copolymer resin. These resins may be used alone or in combination of two or more. [0012] The electrophotographic carrier of the present invention has the following features:
In measuring dynamic resistance, the point is to have a breakdown voltage in the DC voltage range of 100 to 500V. That is, the present invention provides a magnetic coated carrier with a breakdown voltage characteristic that occurs within a predetermined range, so that the electrostatic image on the photoreceptor can be transferred from a place with a low surface potential without causing unnecessary wear on the photoreceptor. In other words, it is possible to reproduce high-quality images from halftones to line drawings and solid black areas. [0013] The dynamic resistance according to the present invention is measured by using a magnetic brush type commercially available copying machine, changing the photoreceptor to an A1 blank tube, applying a DC voltage between the magnetic brush and the A1 blank tube, This is carried out by accommodating only the coated carrier in a developer tank, rotating a magnetic brush, and measuring the current-voltage value when the carrier ear comes into contact with the A1 blank tube, which is a counter electrode. Breakdown voltage refers to the voltage at which the current value suddenly rises in the above measurement, and in the electrophotographic carrier of the present invention, the breakdown voltage is in the DC voltage range of 100 to 500V. be. The breakdown voltage actually varies depending on the model used, such as the shape of the developer tank, doctor gap, interval of the development gap, magnetic brush rotation speed, etc., so in each model, the photoreceptor is replaced with an A1 tube. Changed and measured. FIG. 1 is a graph showing the voltage-current characteristics of magnetic coated carriers obtained in Examples described later, in which (A) and (B) are coated carriers of the present invention; ) is a coat carrier for comparison. As is clear from FIG. 1, the magnetic coated carrier of the present invention has a distinct breakdown voltage in the DC voltage range of 100-500V. The magnetic coated carrier of the present invention is basically prepared by coating magnetic core particles with a coating resin dissolved in an appropriate solvent and drying the coated resin by, for example, a flow coater method or a spray dryer method. Manufactured. The coating method may be either random coating or layered coating, but it is preferable to provide a non-uniform resin coating layer on the surface of the magnetic core particles. The electrical properties of the resulting coated carrier are determined by the resistance value and surface condition of the magnetic core particles, the resin composition, the resin concentration in the coating solution, and the ratio of the magnetic core particles to the resin (coating thickness). It is necessary to select the above conditions appropriately to obtain the desired magnetic coated carrier, but it is preferable to use magnetic core particles with a small resistance value, and The film thickness is preferably in the range of 0.05 to 3 μm. In addition, in the case of the above-mentioned layered coating, it is possible to adopt a method in which the above-mentioned operation is repeated and then sieved and the passed portion is obtained as a coat carrier. resistance adjustment,
Various fillers can also be added for the purpose of increasing strength and adjusting friction. The electrophotographic carrier of the present invention constitutes a developer in combination with a toner, and is used as a developer for magnetic brush development. As the toner, a conventionally known toner mainly consisting of a binder resin, a colorant, a charge control agent, etc. can be used as is. [0017] As the binder resin, polystyrene,
Including styrene resins such as styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, and styrene-butadiene copolymer, polyester resin, epoxy resin, phenol resin, coumaron resin, chlorinated paraffin, and xylene resin. , vinyl chloride resin, polyethylene, and polypropylene. In addition to being used alone, these binder resins can also be used in two ways.
More than one species can also be used together. The coloring agent is not particularly limited, but examples include carbon black, aniline black, quinacridone magenta, rhodamine B, brilliant carmine 6B.
, phthalocyanine blue, Victoria blue, industhrene blue, phthalocyanine green, malachite green, benzidine yellow, Hansa yellow, quinoline yellow and the like. The ratio of the above binder resin and colorant used is 0.00 parts by weight of colorant per 100 parts by weight of binder resin.
It ranges from 1 to 30 parts by weight, preferably from 0.5 to 10 parts by weight. Even when two or more types of colorants are used together, the ratio of binder resin and colorant to be used is preferably within the above range. As the charge control agent, all known ones can be used. For example, for positively charging properties, nigrosine dyes, triphenylmethane dyes, quaternary ammonium salts, styrene/aminoacrylate copolymers, polyamine resins, etc. can be used, and for negatively charging properties, metal-containing azo dyes can be used. , metal salts of alkylsalicylic acids, etc. can be used. The metal in the metal-containing azo dye includes Cr,
Examples include Co, Fe, Al, and the like. The amount of the charge control agent used is 0.1 to 10 parts by weight per 100 parts by weight of the binder resin.
parts by weight, preferably in the range of 0.5 to 5 parts by weight. 2
Even when more than one type of charge control agent is used in combination, the amount of the charge control agent to be used is preferably within the above range. Further, the charge control agent may be used by being mixed into the binder resin or by being attached to the toner surface. In addition to the above, auxiliary agents such as various plasticizers and release agents may be added to the toner for the purpose of adjusting thermal properties, physical properties, etc. Examples include low molecular weight polyolefin for improving offset properties, colloidal silica, titania, alumina, etc. for improving fluidity. Furthermore, magnetic fine powder can be contained in the toner due to the development mechanism. Examples of the magnetic powder include alloys or compounds containing elements exhibiting ferromagnetism, such as ferrite and magnetite. And the magnetic fine powder is
It is in the form of a fine powder with an average particle size of 0.05 to 1 μm and is used by dispersing it in a resin in an amount of 60% by weight or less. [0022] The carrier for electrophotography of the present invention as described above usually contains 1 to 1 to 10 parts by weight of toner per 10 parts by weight of carrier.
It is used in a mixture of 10 parts by weight to provide a developer with high image quality and long life. [Examples] The present invention will be explained in more detail by examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof. In addition, in the examples, "part"
is "parts by weight". Example <Preparation of Toner A> Toner raw materials having the following formulation were melt-kneaded in a heated roll mill, cooled, and then coarsely ground using a hammer mill, and then finely ground using an air jet type pulverizer. The obtained fine powder was classified to obtain a toner having a volume average particle diameter of 9.8 μm by Coulter Counter method. Furthermore, fine particle silica (Aerosil R9) was added to this toner.
72 (manufactured by Nippon Aerosil) was added externally using a mixer to prepare toner a. Styrene/n-butyl acrylate copolymer
100 copies
Carbon black #40 (manufactured by Mitsubishi Kasei)
7 parts Quaternary ammonium salt Bontron P-51 (manufactured by Orient Chemical) 2 parts Polypropylene wax Viscole 550P (manufactured by Sanyo Chemical)
Part 2 [0025] <Preparation of toner b>
A toner having a volume average particle diameter of 11.3 μm was obtained using toner raw materials having the following formulation and in the same manner as toner a. Further, 0.1 wt % of fine particle silica (Aerosil R972, manufactured by Nippon Aerosil) was externally added to this toner using a mixer to prepare toner b. polyester resin

100 parts (polycondensate of propylene oxide adduct of bisphenol A and fumaric acid) Quinacridone pigment (C.I. Pigment Red
122) 5 parts Quaternary ammonium salt Bontron P-51 (manufactured by Orient Chemical)
Part 3 <Preparation of Toner C> A toner having a volume average particle diameter of 10.3 μm was obtained using toner raw materials having the following formulation and in the same manner as in the preparation of toner a. Furthermore, fine particle silica (Aerosil R9) was added to this toner.
72 (manufactured by Nippon Aerosil) was added externally using a mixer to prepare toner C. Styrene/n-butyl acrylate copolymer
100 copies
Carbon black MA-8 (manufactured by Mitsubishi Kasei)
Part 6
Metal-containing dye Bontron S-34 (manufactured by Orient Chemical Co., Ltd.) 1 part Polypropylene wax Viscole 550P (manufactured by Sanyo Chemical Co., Ltd.) 2 parts
5 kg of μm ferrite (B-700, manufactured by Kanto Denka) was placed in a flow coater and while flowing, a coating solution with the following formulation was sprayed under heating at 80°C, and then dried for 1 hour to complete the coating layer. . As a result of measuring the dynamic resistance of the obtained coated carrier, the breakdown voltage was 190V. polyvinylidene fluoride
Part 11 Polystyrene

9 parts Methyl ethyl ketone
200 copies 0028] Furthermore,
The above breakdown voltage was measured using a commercially available copying machine (SF8400 manufactured by Sharp Corporation) and a developing device in which the photosensitive drum was replaced with an Al blank tube. <Preparation of Coated Carrier B> 5 kg of ferrite carrier (B-700, manufactured by Kanto Denka) having a volume average particle diameter of approximately 100 μm as a core particle was placed in a flow coater and while flowing, a coating liquid having the following formulation was heated at 90°C. The coating layer was then dried at 150° C. for 2 hours to complete the coating layer. The breakdown voltage of the coated carrier obtained was 250V. Silicone resin (KR311, manufactured by Shin-Etsu Chemical) 10 parts toluene
100 parts <Preparation of coated carrier C> Volume average particle size of core particles is approximately 1
00μm ferrite carrier (DFC-150, manufactured by Dowa Iron Powder) 5kg was placed in a flow coater and while flowing, a coating solution with the following formulation was sprayed under heating at 80℃, and then dried for 1 hour to complete the coating layer. I let it happen. As a result of measuring the dynamic resistance of the obtained coated carrier, breakdown did not occur up to 500V. polyvinylidene fluoride
6 part polystyrene
4
methyl ethyl ketone
200 parts <Preparation of developer> The above toners a to c and coated carriers A to C were combined as shown in Table 1 to prepare developer samples (1) to (2). The developer was prepared by mixing 4 parts of toner and 96 parts of carrier using a V-type mixer. [Table 1] Carrier (A
) (B) (C)
(Breakdown voltage) 190v 25
0v Greater than 500v ────────
──────────────────────────
Toner (a)
■
■ Toner (b)
■
■ Toner (c)
■
<Evaluation of developer> When initial copying was carried out using a commercially available copying machine (SF8400 manufactured by Sharp Corporation, photoreceptor: organic photoconductor), carrier C was The developer used was
Although the image was good in the line drawing area, the image density was low in the solid black area, and an image with strong edge effects was obtained. On the other hand, the developers using carriers A and B had good quality in line areas, high image density in solid black areas, and good, uniform images. Furthermore, when we conducted a continuous photographic test of 30,000 sheets of developer sample (3), it was found that the change in image quality was small and good image quality could be maintained over a long period of time. Effects of the Invention The magnetically coated carrier of the present invention as described above can maintain high image quality in both line drawing areas and solid black areas, and also maintains the initial image quality even when used continuously for a long period of time. Can be maintained stably.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the voltage-current characteristics of magnetic coated carriers obtained in Examples, in which (A) and (B) are coated carriers of the present invention, and (C) is a comparative coated carrier. It is a coat carrier for.

Claims (2)

[Claims] 1. A coated carrier formed by coating the surface of a magnetic core particle with a resin, characterized in that it has a breakdown voltage in the DC voltage range of 100 to 500 V when measuring the dynamic resistance of the coated carrier. A carrier for electrophotography. 2. The electrophotographic carrier according to claim 1, wherein the magnetic core particles are ferrite or magnetite.