JPS59216150A - Electrophotographic iron powder carrier low in saturation magnetization - Google Patents

Abstract

PURPOSE:To obtain a carrier free from edges on black solid parts, and superior in halftone reproducibility and resolution of a formed image without using an expensive material, such as nickel by controlling a content of metallic iron into a specified range smaller than that of the conventional iron powder carrier, and its saturation magnetization into a specified range. CONSTITUTION:An iron powder carrier contg. 70-90wt% metallic iron and having saturation magnetization as low as 130-160emu/g is obtained by treating an iron type carrier contg. 94-97wt% metallic iron in CO2 atmosphere at 300- 700 deg.C for 30min-3hr and reacting it with nascent oxygen. As one of alternative methods, an iron powder contg. 30-90wt% metallic iron and having 90-160 emu/g saturation magnetization is obtained by treating reduced iron powder in the air at about 1,600 deg.C heated by combustion of O2-LPG to rounding the surface, and throwing it into water, or doing likewise. The use of such a carrier permits formation of a high quality image free from brush traces and deformed fine lines of an image by using a magnetic brush.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic image developing carrier for developing electrostatic images formed in electrophotography.

Dry-type electronic copying machines produce copies by a process in which an electrostatic latent image formed on a photoreceptor is visualized using toner, and the powder image is electrostatically transferred to paper and then fixed, but the quality of the image in the copy is affected. The optical system, photoreceptor characteristics, development, transfer, and fixing processes are all involved. Since development is the most important factor among these, various development methods have been studied up to now, and the well-known magnetic brush development method has become the mainstream. In the magnetic brush development method, the developer is a so-called two-component system consisting of toner, which is powder ink, and a ferromagnetic carrier, which serves to triboelectrically charge the toner and simultaneously transport it to the latent image on the photoreceptor. Developers are the most common.

The carriers normally used in two-component developers are iron powder, oxide-coated iron powder whose surface is coated with an extremely thin iron oxide film, or resin-coated iron powder whose surface is coated with various resins to saturate these. Magnetization is 170-190
It is well known that e, m, u, /g.

However, the above iron powder is used as a carrier.

Generally, the disadvantages of developers using oxide-coated iron powder or resin-coated iron powder are as follows: (1) Copied images tend to have dents caused by developer brushes, and fine line images are disturbed. (2) Edge effects tend to appear in peta-black images, and tend to appear in images where the central area is lighter than the peripheral areas.

(3) The reproduction of halftones is poor and it is unsuitable for copying photographs and paintings.

In order to solve these shortcomings and obtain so-called high-quality images, various one-component developing methods have been devised and put into practical use that integrate toner and carrier and develop with toner alone. Although the effect is not apparent, on the contrary, the image density is lower than that of a two-component developer, and the halftones cannot necessarily be said to be sufficiently good.

Currently, in order to obtain high-quality images that have solved all of the above-mentioned drawbacks in the two-component development system, MO, .M'0b (Fe203) x (where M, M The use of soft ferrites such as nickel-zinc ferrite, manganese-zinc ferrite, or [copper] zinc ferrite, etc., is recommended as a carrier, and is actually used. It has been released on the market and has been well received. In other words, by adopting a soft ferrite carrier instead of the conventional iron powder carrier, edge d! The O ferrite carrier produces high-quality images as described above, with good reproduction of medium 11J tones, excellent fine lines and high-resolution images, and can be considered as an alternative to light printing. The reason why it has properties suitable for this purpose has not been fully academically elucidated, but the following are thought to be the main reasons. That is, (1) ultrafine powder with a particle size of around 1 μm is manufactured through the steps of granulation, drying, and sintering, so spherical bodies can be easily obtained, resulting in excellent fine lines and resolution as factors in the spherical shape. (2) Saturation magnetization of soft ferrite is 40 to 80 e, m, u, /11
It is smaller than normal iron powder and the ears formed are soft, suppressing the electrode effect and adjusting the image density, resulting in a uniform image density without any edges in the black areas. (
Replenishment of the consumed toner transferred from the tip of the 3-inch ear to the photoreceptor is carried out smoothly during the stirring process because the ear is soft, and combined with the small residual magnetization of soft ferrite, this results in good image density. bring. (4) First permeability-B (1d
1 bundle density) rate (μ・-H (Ja field. strong)) is large, so it is 40 to 8
A saturation magnetization as small as 0e, m, u, /I is sufficient to increase the effect. (5) The dielectric breakdown voltage is too high, and the potential of the latent image on the photoreceptor does not leak to the carrier, and no plasticity is observed. (6) Since it is composed of a uniform oxide, the carrier does not leak during use. There are several possible reasons for this, such as the fact that no deterioration phenomenon due to resistance change is observed, and therefore the carrier life is long.

As mentioned above, soft ferrite carriers have many properties that are advantageous for obtaining high-quality images, but the price of nickel and copper, which are active ingredients of ferrite, is significantly higher than that of iron, and the desired particle size cannot be achieved in the manufacturing process. Manufacturing costs are high due to poor retention. In addition, in terms of shape, ferrite cannot be changed into various shapes like iron powder carriers and is restricted by shape factors, so even if it is attempted to be applied to current machines, it is often not possible to adopt it due to the structure of the machine.

The inventors conducted various studies to improve the current iron powder carrier to correct the above-mentioned drawbacks of the ferrite carrier, and based on new knowledge, the inventors used the conventional iron powder carrier as a starting material and applied special post-processing to it. In particular, the metal iron content is reduced to 30 to 90 inches (by weight) and the saturation magnetization is t-9.
By suppressing 0 to 160e, m, and u・7g, not only can extremely high-quality images not seen with conventional iron powder-based carriers be obtained, but also the new two-layer carrier has a wide range of application to current machines. The present invention, which has successfully developed a component-based carrier for electrophotography, is advantageous in terms of cost because it does not necessarily require expensive raw materials such as nickel and copper, which are found in ferrite carriers. In terms of image quality, the image is of so-called high quality, with no edges such as black areas, good midtone reproduction, fine lines, and excellent resolution.

Ordinary iron powder-based carrier (metallic iron content 94-97 cm (weight) with a metal iron content of 30-90% and its saturation magnetization f
90-160 e, m, u, /11 (170-190 e, m, u, /1 for normal iron powder carriers
1) There are various methods to reduce this. In other words, in a conventional iron-based carrier 1 co□ atmosphere, 300 to 7
When heat treated at a temperature of 00°C for 30 minutes to 3 hours, CO□ decomposes as shown in formula 1 due to the catalytic effect of iron powder, and the highly active nascent oxygen quickly penetrates through the iron lattice. As a method for reducing saturation magnetization of metallic iron with a metallic iron content of 70 to 90 inches (weight), reduced iron powder or nitrided crushed iron powder is suspended in an oxidizing atmosphere as described in the above-mentioned patent publication No. 19667. By burning it and spheroidizing it due to the surface tension effect during exothermic melting, and pouring it into water, a spherical powder with a metallic iron content of 10 inches or less can be obtained. The metallic iron content can be reduced by 30 to 90% (
Even after partial reduction to weight), the saturation magnetization is 9()”160e,
m, u, /11.

Another method for obtaining iron carriers with low saturation magnetization is that they can also be made from ferrous iron using the method described above. For example, P2
A 5% (weight) Fe-P alloy is used as a master alloy, and an extremely mild steel scale is added to it to adjust the P content to 5 to 15%.The alloy powder is prepared by melting and dewatering in a high-frequency electric furnace or by gas spraying. and annealing.

After undergoing processes such as crushing, grain size adjustment, and magnetic selection, it becomes saturated magnetically 90%
~160 e, m, u, /11.

These low saturation magnetization iron compound powders can be treated with an oxide film to adjust the resistance value in the same way as ordinary iron powder carriers, and can also be coated with a resin to adjust the amount of charge and extend their service life. Although it is possible, the method for producing low saturation magnetization iron is not limited to the method described above.

In addition, the saturation magnetization is 90 to 160 e, m, u, /g
The reason for this is that at 90 e, m, u, 7 g or less, carrier scattering is significant, whereas at 160 e, m, u, 717 or more, when used as a developer, the formed ears do not become soft, so the electrode effect cannot be properly controlled. This is because it is difficult to obtain high-quality images because the uniformity of black areas and the reproducibility of intermediate tones and fine lines are not sufficiently controlled. Furthermore, the reason why the metallic iron content was limited to 30% to 90% CM was that research revealed that the iron content was the optimum amount necessary to achieve the desired saturation magnetization and obtain high-quality images. be.

The present invention will be described in detail below based on Examples.

Example 1 Reduced iron powder (flat shape) manufactured by Nippon Tetsuko Co., Ltd. was heated to 30°C in a C02 atmosphere.
Heat treatment is performed at 500°C to 600°C for minutes to 3 hours, and the metal iron content (hereinafter abbreviated as M-Fs) is t-70 to 90
)-! As a result of changing j, the saturation magnetization is 130 to 16
It became 0 e, mu, /g. This was further oxidized and heat-treated in the air at 300°C to 380°C to reduce the electrical resistance to approximately 8.5.
×1090. After adjusting the diameter to 11 m, magnetic separation was performed to obtain a test sample.

Each sample was mixed with 7% (by weight) toner for S'F-750 (Sharp copying machine) and photographed. Table 1 shows a summary of the actual photographic results using the Electrophotography Society T-yard.

Carriers containing 75 to 90% (by weight) of M and Fe gave images with good reproduction of fine lines and resolution, but when the content was less than 70%, fogging and carrier scattering occurred. Further, as a comparative sample, a carrier untreated with co2 gas having M and PE of 97% (by weight) had insufficient fine line and resolution.

After developing sample No. 4 on A4 paper 8000 times with the above 5F-750, the image density at proper exposure was initially 1.25 using a Macbeth densitometer (RD514) (hereinafter abbreviated as 1.D). Although it was slightly lower than (1, D, 1.30), the other evaluations were almost the same as the initial stage.

Example 2 Reduced iron powder manufactured by Nippon Tetsuko Co., Ltd. was exposed to oxygen at an atmospheric width of about 1,600°C.
It was projected into LPG combustion gas to form a spherical surface, and then poured into water. After drying, M and Fe were 5% (by weight), so this was reduced at a temperature of about 1000°C to reduce M and Fe to 20.30%.
．． 4-0.50.70.80 and 90 inches (weight), the saturation magnetization is 80e, mu-7g to 16
It liquefied to 0 e, m, u, /9. Disintegration.

Sieve Diameter Heat treated at 300°C to 370°C in the atmosphere for about 15 minutes to adjust the electrical resistance to about 7 x 109 Ω, crn. After magnetic separation, 4 inches (by weight) of toner for RheoDry 8101 (Toshiba copying machine) was mixed. When the chart and Kodak gray scale were photographed, the results shown in Table 2 were obtained. That is, even with M-Fe 20% (weight), fine line resolution and midtone reproduction were good, but carrier scattering was observed; The reproduction was good and no carrier scattering was observed.0 For comparison, it was found that the reproduction of fine lines, resolution, and halftones was inferior to the product of the present invention with a carrier that was almost completely reduced with M and Fe 95 cm (weight). It was done. In addition, after developing sample number 4 30,000 times using A4 paper using the above-mentioned RheoDry 8101, 1. D, is 1
．． 31, hardly any decrease was observed compared to the initial stage (1, D, 1.34), and the other evaluations were also at the same level as the initial stage.

Example 3 Commercially available ferrophosphor (phosphorus content 25% (weight)) 20
1i ultra-mild steel lathe cuttings (C0, 11chi, SiO, 2
%, Mn0.35%, Po, 01%, 50.01f
j) Melt 30 kg in a high-frequency electric furnace, drop the molten metal through a 1-diameter zirconia nozzle, and
CRN2 high pressure water was spouted from the side to atomize the molten metal flow and collect it in water. Collected Fe-10% (
Weight) 2 alloy powder was dehydrated using a centrifuge, dried at 120°C, reduced for 1 hour in a hydrogen stream at 850°C, the reduced product was crushed and adjusted to particle size, and then further treated with an oxide film in the atmosphere. The electrical resistance was approximately 7.2×10 9 Ω-tm. The saturation magnetization was 148 e, m, u, /Ii, so this was designated as sample 1.

Next, as sample 2, the sample of the above sample number 1 and the sample of sample number 5 in Example 1 were mixed in equal amounts, and the saturation magnetization was measured. 153e, m, u, /Ji'
The stain resistance was 7.9 x 10'Ω, which was substandard.

Toner 7 (weight) for SF-750 (Sharp military aircraft) was mixed with each of these two samples, and a live photo test was conducted using an electrophotographic society chart. A summary of the results is shown in Table 3.

Both samples had fine lines and excellent resolution, but the image density at proper exposure after sample number 1 was developed using the above SF 750 800 times using A4 paper was 1. D.
1.28, which was not much different from the initial concentration (1,D・1.32), and the other evaluations were almost the same as the initial values.Table 3

Claims (1)

[Claims] A low saturation magnetization carrier iron powder for electrophotography, which has a metallic iron content of 30 to 90% by weight and a saturation magnetization of 90 to 160 e, m, u/l.