JPS62119552A - Electrophotographic developer - Google Patents

Abstract

PURPOSE:To enhance copy density, to reduce fog, to render brush striations inconspicuous, and to improve reproducibility of halftone and edge effect by specifying a mixing ratio of magnetite to iron oxide power to adjust a carrier. CONSTITUTION:The electrophotographic developer is prepared by mixing a toner with the carrier composed of magnetite and the iron oxide powder having a mixing weight ratio of magnetite to iron oxide of 90-40:10-60. The carrier mixture has a particle diameter of, preferably, 20-200mum, and if <=20mum, forma tion of a magnetic brush deteriorates, hindering development, and if >=200mum, striations are produced on black solid parts by the magnetic brush. Too mush magnetite beyond the range of said mixing ratio cannot solve the problem of the edge effect, and too much iron oxide powder cannot solve the problems of striations on the black solid parts, and deterioration of gradation.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an electrophotographic developer. For more details,
The present invention relates to a two-component developer consisting of toner and carrier.

<Problems to be solved by conventional technology and invention> Conventionally,
A method for developing an electrostatic latent image with toner is to hold a two-component developer containing toner and a magnetic carrier in a magnet and slide the brush-shaped developer over the electrostatic latent image. Magnetic brush development is well known.

Iron oxide powder is generally used as a magnetic carrier, but a developer containing this carrier and toner has poor gradation and halftone reproducibility. It has the disadvantage of causing the phenomenon of fine streaks.

In recent years, it has been proposed to use ferrite and maginetabut as magnetic carriers, but when these carriers are used, the electrical resistance of the developer becomes υ higher than when iron oxide powder carriers are used. An edge effect is likely to occur in the resulting image, and since the magnetic brush has short bristles, the developing interval between the photoreceptor and the developing sleeve must be narrowed, which is disadvantageous in terms of design accuracy.

The inventors have discovered that the above-mentioned problems can be solved by using a carrier prepared by adjusting a predetermined mixing ratio of iron oxide powder and iron oxide powder, and have arrived at the present invention.

In other words, the gist of the present invention is to provide an electrophotographic developer characterized in that the weight mixing ratio of Magnetame and acid iron oxide powder is in the range of Magnetact iron dioxide powder = 90 to Da 0:10 to Otsu 0. Exists.

The carrier used in the present invention preferably has a nearly spherical shape, and its minimum particle size is preferably the same as or larger than the maximum particle size of the toner. The latter iron oxide powder is known per se, and those having a flat shape or a slightly rounded shape by thermal treatment, mechanical treatment, etc. are used.

The particle size of the mixed carrier is preferably in the range of 20 to 200 pm; if the particle size is less than 20 μm, the magnetic brush will not stand up properly and development will be hindered;
pm or more, a magnetic brush is preferably in the range of 60, preferably Magnetact: Iron oxide powder -30~! rO knee o-
Go range is good. Outside this range of mixing ratio, if there is too much magnetite, the disadvantage of the edge effect will not be resolved, while if there is too much dispersed iron powder, the disadvantages will be the occurrence of brush lines in solid black areas and poor gradation. It is preferable that the resolved diameter is the same as or larger than the particle size of the iron oxide powder, and the resistance is higher, and the iron oxide powder has a lower resistance.

Furthermore, both carriers can adjust resistance, improve environmental dependence,
To improve durability, the surface of the carrier may be coated with a suitable resin.

31 The toner used in the present invention is made from a binder resin and additives selected from pigments, dyes, charge control agents, mold release agents, etc., and is produced by mixing, kneading, pulverizing, and classifying these materials. υ
It is obtained as particles with a particle size of 5 to 30 μm.

Note that the obtained toner may be a magnetic toner containing magnetic powder if necessary, or may be a magnetic toner containing a fluidity improver,
An external additive treatment may be performed in which part or all of the toner surface is coated with a fine additive having a particle size smaller than that of the toner, such as a photoreceptor abrasive.

<Examples> Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

Example/-5 and Comparative Examples 1 to 3 A selenium photoconductor was prepared using a developer consisting of a toner prepared as described below and a carrier prepared by mixing magnetor/to and iron oxide powder in the weight ratios shown below. The copied images were evaluated by regular development using an RPC copying machine equipped with the following.

(1) Toner Styrene/acrylic resin 100 parts by weight Low molecular weight polypropylene Cocarbon plaque
6 Chromium Alloy Dye After mixing the above compositions, kneading them using a hot roll, cooling them, coarsely grinding them with a hammer mill, finely grinding them with an ultra-high speed jet mill, and then classifying them with a wind classifier to determine the particle size. 5～koSμ
A toner of m was prepared. As a post-treatment, 0.2% by weight of hydrophobic silica, which is a fluidity improver, was externally added to the toner using a high-speed stirrer. The toner thus produced is referred to as toner A.

Those shown in Table 1 were used.

Table 1 Carrier characteristics The shape was determined by observing with an optical microscope.

The particle size was determined by measuring the particle size distribution using a method according to JIS Z-Zagoi, and was expressed as the particle size of the sieve mesh having a weight ratio of 70 or more.

Electrical resistance is determined by placing a carrier in an insulating tube at a given weight.
SUS electrodes were provided on the top and bottom, and when a DC voltage was applied between both electrodes, the current value was measured with a microammeter, and determined by converting it into static resistance.

The above toner A and carriers B, C, and D were mixed in a predetermined ratio to obtain developers ① to ②. Then, using each developer, PPC
The results of evaluating the copied images using the copying machine are shown in Table 2 below.

In Example/-5, almost good results were obtained in terms of comprehensive copy image evaluation, but in Comparative Examples 1 to 3, results were inferior to those in Examples.

<Effects of the Invention> When the developer of the present invention is used, a copy image with high copy density, less fog, less noticeable brush lines, good halftone reproducibility, and improved edge effect can be obtained.

Applicant: Mitsubishi Chemical Industries, Ltd. Agent: Patent Attorney Hase - 1 other person

Claims (1)

[Claims] (1) A toner is obtained by mixing a carrier consisting of magnetite and iron oxide powder, and the weight mixing ratio of magnetite and iron oxide powder in the carrier is 90 to 40:10 to 60. An electrophotographic developer characterized by being in the range of