JPH022137B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in an electrostatic image developing method, and particularly to an improvement in an electrostatic image developing method using a magnetic brush in an electrophotographic copying machine or the like.

In the conventional electrostatic image developing method using a magnetic brush, carriers having a particle size of about 100 μm are often used. Such large particle diameter carriers have relatively strong magnetic brushes and are excellent in toner conveying force and sliding force on the toner image bearing surface, but the area/volume ratio of the particles is small and the toner particles are It has poor uniformity retention, which may cause blurring during development.

On the other hand, in the same developing method using a magnetic brush, there is an example in which a developer consisting of toner particles with a particle size of about 3 to 15 μ and a magnetic carrier with a small particle size of about 15 to 65 μ is used. JP-A-54-134636
It is known from the publication No. In a developing method using such a carrier with a small particle size, the area/volume ratio of the carrier particles becomes large, which improves the uniform retention of toner particles, and the small particle size of the carrier particles also reduces the sliding force of the magnetic brush. Coupled with the weakening, sweeping marks are less likely to occur, resulting in excellent image reproducibility and good reproducibility in solid areas. However, on the other hand, the formation properties of the magnetic brush are poor, the toner conveying force is weak, and the sliding force of the magnetic brush is also weak, so there are problems such as fogging and toner adhesion to the periphery of the image, that is, a fringe phenomenon is likely to occur. Therefore, it is necessary to take measures such as roughening the surface of the magnetic brush carrier of the magnetic brush device or increasing the magnetic force of the magnet.

The present invention has been made by focusing on the mutually symmetrical advantages and disadvantages of large-grain carriers and small-grain carriers in magnetic brush development, and with the idea of complementing each other's drawbacks with the advantages of the other. To provide an electrostatic image developing method that does not require a complicated magnetic brush device or special additional equipment, can be constructed inexpensively and compactly, and can achieve excellent toner development. It is something.

The developer for forming a magnetic brush used in the method of the present invention is a developer having toner and carrier particles consisting of magnetic particles having a large average particle size, and in which the average particle size is The peak of the magnetic particles with a small diameter is located at a particle size that is one-half or less of the particle size of the peak of the magnetic particles with a large average particle size, and the peak of the magnetic particles with a small average particle size is The particle size of the toner is 25 μm or more and 60 μm or less, and the average particle size of the toner is smaller than the peak particle size of the magnetic particles having the smaller average particle size, thereby making the magnetic brush stronger. It not only takes advantage of the large particle size carrier's ability to reliably transport the toner and sufficiently rub the surface of the toner image carrier, but also ensures that the toner is evenly and sufficiently held by the magnetic brush. carried,
The advantage of the small particle size carrier is that it does not cause scratches, and therefore it is less likely to cause blurring or fringing, making it possible to develop clear toner with excellent reproducibility of solid areas. It exhibits the ideal developing function.

As shown in FIG. 1, in the carrier of the present invention, magnetic particles 2 having a large particle size are attached to the brush ear by a magnet 4 disposed on the surface of a magnetic brush carrier 1 and on the back side thereof. The magnetic particles 3 adhere to the surface of the magnetic particles 2 so as to form a nucleus to form the outer shape of the magnetic brush, and the magnetic particles 3 having a small particle size cling to the surface of the magnetic particles 2 to form a magnetic brush that transports the toner. As a result, the method of the present invention exhibits the advantages of development using a large particle carrier, in which the magnetic brush is strongly formed and has excellent toner conveying force and sliding force on the surface of the toner image bearing member. Furthermore, excellent effects can be obtained in that the advantages of developing using a small-particle carrier, which is excellent in uniformly retaining toner and hardly causes scratches caused by a magnetic brush, can be obtained.

That is, according to the method of the present invention in which the carrier is mixed with toner and used as a developer in a magnetic brush developing device, the toner conveying force of the magnetic brush is large, so it is fully applicable to high-speed development and development with high toner concentration. , The occurrence of fogging etc. is greatly reduced due to the strong sliding force of the magnetic brush;
Extremely excellent results can be obtained, including excellent toner retention, no sweeping marks, excellent image reproducibility, and good reproducibility of solid areas.

The magnetic particles used in the carrier used in the present invention are the same as those used in conventional carriers. In other words, iron powder, particles with an oxide film formed on the particle surface, particles with an insulating resin coating formed on the particle surface, particles consisting of magnetic particles dispersed in an insulating resin, etc. are used, and conventional large particles are used. The carrier of the present invention can also be obtained by mixing a particle carrier and a small particle carrier in appropriate proportions. The most common method for manufacturing the carrier used in the present invention is to produce iron powder by pulverization, classify it using sieves with different meshes to obtain magnetic powders with different average particle sizes, and mix them. It's a method.

In a preferred embodiment of the present invention, the carrier described above, that is, the mixture of magnetic particles having different average particle sizes, has a particle size distribution curve with weight on the vertical axis and particle size on the horizontal axis, which has two peaks. It has a particle size distribution as shown.

In this case, the particle size at the peak position on the smaller particle size side is less than half of the particle size at the peak on the larger particle size side, which effectively takes advantage of the respective advantages of large particle carriers and small particle carriers. This is desirable in taking advantage of the features of the method of the present invention used in

FIGS. 2 and 3 are particle size-weight distribution curves showing examples of the particle size distribution of the carrier used in the present invention.

Figure 2 shows a two-peak distribution with peaks F and R at particle sizes of 50 μm and 120 μm, with the average particle size of small particles showing peak F being 50 μm, and the large particle size showing peak R. The average particle size of the particles was 120 μm, and the weight ratio of small particles to large particles was 1:3.

In the example shown in Figure 3, the particle size of peak F' is 40 μm,
The particle size of peak R′ is 120 μm, the average particle size of small particle size particles is 40 μm, same as peak F′, and the average particle size of large particle size particles is 120 μm, same as peak R′. The weight ratio of diameter particles was 1:4.

High quality visible images were obtained using the carriers shown in FIGS. 2 and 3, respectively.

Examples of the present invention will be further shown below.

Example 1 A carrier made of magnetic particles with an average particle size of 100μ and a carrier made of the same magnetic particles with an average particle size of 25μ are mixed at a weight ratio of 4:1 to make a carrier. A developer was prepared by adding 3% by weight of 7μ toner particles.

When copying was carried out using this developer in a magnetic brush developing device, excellent copies were obtained with extremely good reproduction of fine lines and solid areas and no scratches or fogging.

Example 2 A carrier made of magnetic particles with an average particle size of 120μ and a carrier made of the same magnetic particles with an average particle size of 60μ are mixed at a weight ratio of 5:3 to obtain a carrier,
A developer was prepared by mixing 2.5% by weight of toner with an average particle size of 8μ.

When this developer was used for copying using a magnetic brush developing device, as in Example 1, excellent copies were obtained with no fogging or streaks and good reproducibility of fine lines and solid areas.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing the structure of the magnetic brush ear formed by the carrier used in the present invention, and FIGS. 2 and 3 are graphs showing examples of the particle size distribution of the carrier used in the present invention. . DESCRIPTION OF SYMBOLS 1...Magnetic brush carrier, 2...Magnetic particles with a large particle size, 3...Magnetic particles with a small particle size, 4...Magnet.

Claims (1)

[Claims] 1. A developer comprising carrier particles consisting of magnetic particles with a large average particle size and magnetic particles with a small average particle size, and a toner, wherein the peak of the magnetic particles with a small average particle size is in the particle size distribution of the carrier particles. The particle size is located at half or less of the particle size indicated by the peak of the magnetic particles with a large average particle size, and the particle size of the peak of the magnetic particles with the small average particle size is 25 μm or more and 60 μm or less. An electrostatic image developing method, wherein the average particle size of the toner is smaller than the peak particle size of the magnetic particles having the smaller average particle size.