JPH0121504B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to spherical iron powder having excellent storage stability and abrasion resistance and high electrical resistance, and particularly to a spherical iron powder carrier having excellent performance when used as a carrier for a developer for developing electrostatic images. be. For example, in electrophotography, a photoreceptor made of a photoconductive element is given a uniform surface charge in a dark place, and then imagewise exposed to light to form an electrostatic charge image.
This is developed using a developer consisting of toner and carrier to form a visible image. Generally, there are two methods for developing such electrostatic images: liquid development method and dry development method.The liquid development method uses a liquid developer made by dispersing various pigments and dyes as fine particles in an insulating organic liquid. The dry developing method is a developing method that uses fine electrostatic detection powder called a toner, which is made by dispersing a coloring agent such as carbon black in a natural or synthetic resin. This dry development method includes a bristle brush method, an impression method, a powder cloud method, etc. using a developer whose main component is toner only, and a method in which the toner is mixed with a carrier made of magnetic particles or glass beads. A magnetic brush method, a cascade method, etc., which use a body as a developer, are known. In these developing methods, toner particles in a developer adhere to an electrostatically charged image to form a visible image, and this visible image is either fixed directly onto the photoreceptor by heat, pressure, solvent vapor, etc. It is transferred to paper or other support and later fused. Among the above-mentioned developing methods, the present invention provides a carrier of the developer used in the magnetic brush method, in which the toner is stirred together with the toner, thereby imparting a desired charge to the toner, and the toner is transported by the magnetic conveyance means of the magnetic brush. This relates to a carrier that is adhered to the surface of the developer and is transported, and eventually becomes a transport medium for the developer. Conventionally, the carrier for the developer conveyed by the magnetic brush has been a material that is strongly magnetized in the direction of a magnetic field, such as an alloy or compound containing ferromagnetic elements such as ferrite and magnetite, as well as iron, cobalt, and nickel. , or alloys that do not contain ferromagnetic elements but become ferromagnetic by appropriate heat treatment, such as manganese-copper-aluminum or manganese-copper-
A type of alloy called Heusler alloy such as tin, chromium dioxide, etc. are known. However, iron powder or its oxides are generally put into practical use because they are easy to obtain and process raw materials, and are economically advantageous. Such an iron powder carrier is described, for example, in Japanese Patent Publication No. 47-19398, and is produced by heating and nitriding raw iron material in a nitrogen or ammonia stream, pulverizing it, and then denitrifying and classifying it if necessary. It is something that will be done. Since the iron powder carrier has ferromagnetism, it is magnetically conveyed by a magnetic brush, so it functions as a developer conveyance medium and, if the material of the toner in the developer is selected, it can impart an electric charge to the toner by friction. Has a function. However, since such iron powder is a so-called conductive carrier having an extremely low resistance value, when it comes into contact with the latent image charge on the photoreceptor, it leaks the charge, making it impossible to form a toner image having a so-called density. To improve the drawbacks of such iron powder carriers, for example,
Publication No. 48-73358 discloses that pulverized iron powder is heated in an oxygen stream to form an oxide film, and the volume resistance is reduced to approx.
An iron powder carrier with an increased resistance of 10 ⁸ to ^{10 10} Ωcm is disclosed. Although such an iron powder carrier can reduce the leakage of latent image charges to some extent, the oxide film formed on the particle surface is susceptible to mechanical shock and friction, and is chemically and physically unstable. This makes the triboelectricity with the toner uncertain,
A desired toner image cannot be formed. Furthermore, since the iron powder carriers described in the above-mentioned publications are manufactured by pulverizing raw iron materials using a pulverizer, they have irregular shapes with many unevenness. Therefore, when such an iron powder carrier is used as a developer, it has the following drawbacks. (1) Chips and cracks in the carrier tend to occur during the developer transport process, and these damage the surface of the photoreceptor, resulting in the deterioration of the copied image. (2) Frictional resistance increases during the conveyance process of the developer, increasing the torque applied to the developing roller, and furthermore, the fluidity of the developer deteriorates, resulting in a decrease in the developing function. An improved version of these crushed iron powder carriers is the spherical iron powder carrier described in Canadian Patent No. 838,061. After applying anti-oxidation treatment to the iron wire, it is attached to a gas burning gun, and a high-pressure mixed gas of acetylene and oxygen is introduced and burned to melt the iron wire into atomized powder, which is then used as a refrigerant containing an antioxidant. A spherical iron powder carrier is produced by blowing into the powder and granulating it. According to this method, spherical iron powder carriers can be obtained, but since the molten powder is atomized while burning a mixed gas of acetylene and oxygen, the carrier particles are subjected to various anti-oxidation treatments during the process. The inclusion of oxidation products inside and on the particle surface is unavoidable, and the above-mentioned drawbacks of iron oxide powder are inherent. Furthermore, the volume resistivity of the produced iron powder is estimated to be around 10 ⁶ Ω・cm based on the description in the specification, and when an electrostatic charge image is developed with a developer using this powder, leakage of latent image charge occurs. Therefore, a desired toner image cannot be obtained. To improve this problem, for example, the above-mentioned Canadian Patent No. 838061 and Japanese Unexamined Patent Application Publication No. 1988-
Publication No. 37546 discloses a carrier whose core material is spherical iron powder and whose surface is coated with resin.
This makes it possible to mold the surface of the carrier particles to a desired resistance value, and there is no leakage of latent image charge during development.Furthermore, the edge effect makes the fine print highly concentrated and sharp. Although it can produce excellent effects, the iron powder particles that make up the core material are easily oxidized and degraded, and are chemically and physically unstable, so the adhesion between the core material and the resin coating is poor, and it may peel off during use. The reality is that iron powder carriers that are desirable in practice have not been obtained due to drawbacks such as wear and tear. The present invention was made in view of the above circumstances, and its purpose is to have a particle surface that is hard, has excellent wear resistance, is chemically and physically stable, and has high electrical resistance. have,
It is an object of the present invention to provide a developer carrier capable of forming a clear copy image without leaking latent image charges when this is applied to a developer for developing an electrostatic image, for example. Still another object is to provide a developing carrier which has excellent fluidity during development and has excellent developing efficiency. Still another object is to provide spherical iron powder that exhibits excellent adhesion between the core material and the resin coating layer when a resin-coated coating carrier is formed. The above purpose is to contain silicon and manganese from 0.2 to 10
It is formed by a manufacturing method in which a high current is passed through an iron alloy containing % by weight to melt it by electrical discharge, and at the same time, a high-pressure inert gas is introduced to spray the molten alloy, which is then blown into a refrigerant to cool and form it. This is achieved by using spherical iron powder particles in which silicon and manganese are present at a higher density on the surface of the particles. As mentioned above, the spherical iron powder of the present invention contains 0.2 to 10% by weight of silicon and manganese components, preferably 0.3 to 3.0% by weight.
It is made so that these components are distributed in a high density on the surface of iron powder particles, and therefore both inside and on the surface of the particles are chemically and physically stable and have long storage durability. Are better. Furthermore, the iron powder of the present invention is a spherical iron powder with high roundness, and the hardness of the surface of the iron powder particles is large, so that it does not cause wear or breakage during storage or use, and has effective developability over a long period of time. Secured. Furthermore, even when a coating film is formed, a film with excellent adhesiveness can be formed, and since the surface of the iron powder is smooth, an excellent smooth film can be obtained. Furthermore, the particle surface layer exhibits a high electrical resistance of 10 ⁹ to ^{10 12} Ω·cm, which could not be achieved by conventional techniques.
Therefore, when an electrostatic charge image formed on a photoreceptor mounted in a copying machine is developed, a sharp toner image can be formed without leaking the charge of the latent image. The characteristic feature of the spherical iron powder of the present invention is that it contains silicon and manganese at a higher density on the particle surface, as shown in Example 2, which will be described later. } can be clearly recognized. The reason why silicon and manganese are distributed in such a high density on the particle surface will be understood from the following explanation regarding the manufacturing method of the present invention. In order to produce the spherical iron powder of the present invention, for example, 1- to
A known electric wire gun is equipped with a 4 mm diameter iron wire, a high current is passed through the gun, the iron wire is melted by arc discharge, a high pressure inert gas is introduced and atomized, and this is blown into the refrigerant. Cool and shape. In the above-mentioned electric wire gun, the iron wire is heated to several thousand degrees, so all the component metals are melted and mixed, and due to surface tension, manganese and silicon float and precipitate on the iron surface, resulting in a large increase in electrical resistance. It is surmised that iron powder that forms a dense layer and has a high degree of roundness is formed. In addition, in the above manufacturing method, since the molten iron material is atomized with an inert gas, neither the inside nor the surface of the particles will be oxidized.
It is presumed that iron powder that is hard, robust, dense, and chemically and physically stable is formed. The chemical and physical properties of the spherical iron powder thus formed are tested, for example, by the following method. Regarding chemical stability, conduct a salt spray test according to JIS Z 2371 to check for the occurrence of red rust. Regarding the fastness of particles, the hardness (HmV) of not only the surface of the particles but also the inside of the particles is measured using a MicroVickers hardness meter. The degree of ferromagnetism of the particles is determined by measuring the saturation magnetization (σ _s ) using a magnetic balance. For the volume resistance of the particles, the inner diameter of 13 mm was measured on the copper plate.
A cylinder made of vinyl chloride is set up, and a brass electrode is installed at the bottom of the cylinder, which is in close contact with the copper plate and fits into the cylinder. 5 g of sample iron powder is poured down from above to fill it, and 260 g of brass powder is placed on top of it. Place a weight electrode to pressurize the sample iron powder, and apply 50 or 100 V between both electrodes.
Measure by applying a DC voltage of The characteristics of the spherical iron powder of the present invention based on the numerous measurement methods described above were measured in comparison with conventional products in the Examples described below, and in all cases, the iron powder of the present invention was compared with conventional products. As a result, it was confirmed that it had excellent suitability when used for electrophotography. The iron powder of the present invention is not limited to the above-mentioned properties, but also has chemical and physical stability of the iron powder of the present invention, which serves as a core material, even when applied to a carrier with a resin coating, which has been attracting attention recently. It is possible to provide a resin-coated carrier for electrophotography with excellent adhesiveness and abrasion resistance, while making the most of the characteristics as they are. When the spherical iron powder of the present invention is used in a developer for electrostatic image development, it is usually desirable that the particle size is 20 to 1000 μm.
For example, the resin may contain a colorant, a charge control agent, etc. if necessary, and be mixed with a toner having a particle size of 1 to 30μ.
They are mixed and used in parts by weight. The developer thus prepared is suitably used for developing electrostatic images such as electrostatic recording and electrostatic printing electrophotography. EXAMPLES The present invention will be specifically explained below with reference to Examples, but the embodiments of the present invention are not limited thereto. Example 1 Silicon 0.5% by weight, manganese 1.0% by weight, iron
20kg of 1.6mmφ iron alloy wire with a composition of 98.3% by weight was attached to a known electric wire gun, and a high current was passed through it to discharge and melt the wire, while at the same time high pressure nitrogen gas of 4.0kg/cm ² was applied. The molten alloy was introduced and atomized into water at a distance of 30 cm. In this way, 19.5 kg of spherical iron powder (sample No. 1) of the present invention was obtained. Also silicon
A spherical iron powder (Sample No. 2) of the present invention weighing 19.5 kg was obtained in the same manner except that an iron alloy wire containing 2.0% by weight of manganese, 2.5% by weight of manganese, and 95.3% by weight of iron was used. Furthermore, silicon 7.0% by weight, manganese 6.0% by weight, iron
Iron powder of the present invention (sample No. 3) weighing 19.5 kg was obtained in the same manner except that 86.5% by weight iron alloy wire was used. In addition, silicone 0.1% by weight, manganese 0.1% by weight
The other samples used were iron alloy wires containing 99.5% iron.
In the same manner as No. 1, 19.5 kg of spherical iron powder for comparison (sample No. 4) was obtained. Above sample No. 1, sample No. 2, sample
Four types of spherical iron powder, No. 3 and Sample No. 4, respectively.
When sieved to a particle size of 100 to 200 mesh,
Sample No. 1 is 9.5Kg, Sample No. 2 is 9.3Kg, Sample No. 3 is
7.2 kg was obtained for each, but only 3 kg was obtained for comparative sample No. 4. In addition, 2.0% by weight of manganese, 2.5% by weight of silicon,
An iron alloy having a composition of 95.3% by weight of iron was ground in a ball mill and sieved into 100 to 200 meshes to prepare iron powder for comparison (sample No. 5).
Furthermore, an iron alloy having the same composition as Sample No. 5 was melted and atomized using steam using a known method, and the obtained alloy powder was sieved into 100 to 200 meshes to obtain comparative iron powder ( Sample No. 6) was prepared. The following tests were conducted to examine the characteristics of these six types of samples. (1) Measure the chemical composition, weight % saturation magnetization (σ _s ) cgs/emu, volume resistance Ω・cm, microvitkers hardness HmV, apparent density g/cm ³ and other surface properties according to the measurement method described above. , and their values are shown in Table 1.

[Table] However, the apparent density is based on the measurement method specified in JIS Z 2504. The surface smoothness of the particle surface was visually determined from an electron micrograph of the particle, and evaluated on a three-grade scale: good ○, slightly good △, and poor ×. From Table 1, it can be seen that the spherical iron powder of the present invention is significantly superior to the comparative iron powder in terms of resistivity, hardness, surface properties, etc. Next, a salt spray test according to JIS Z 2371 was conducted. As a result, the iron powder of the present invention, Sample No. 1, Sample No. 2, and Sample No. 3, showed no red rust and were chemically stable, but the iron powder for comparison was No. 4 had red rust all over its surface and was found to be chemically extremely unstable. In addition, red rust occurred on a portion of the upper surface of samples No. 5 and No. 6 as well. Figure 1 shows the differential thermal balance measurement results of Sample 1 and Sample 4. Sample 1, which is a product of the present invention, shows no peak of differential heat due to oxidation reaction even when the temperature is increased, and it is clear that the oxidation resistance is high. be. Furthermore, a photograph of the shape of the sample No. 1 particle of the present invention, a distribution photograph of silicon component, a distribution photograph of manganese component, and a distribution photograph of iron component were taken using an X-ray microanalyzer (EPMA), and these photographs are shown in Figure 2. A, b, c, and d were obtained. From these photographs, it is clearly understood that the iron powder of the present invention has a highly rounded spherical shape, and silicon and manganese are distributed at high density on its surface. From the above measurement results, it is understood that the iron powder of the present invention has many excellent properties for use in electrophotography and is extremely useful. Example 2 1 kg of four types of iron powder No. 1 to No. 4 of Example 1 above
Into this, 100 parts of styrene-acrylic resin, 5 parts of carbon black, and 3 parts of negative charge control agent were mixed, kneaded under heating, cooled, crushed and classified, and 20 g each of toner with an average particle size of 15 μm was added. They were mixed to prepare four types of developers. These developers were installed in a modified U-Bix W copier (manufactured by Konishiroku Photo Industry Co., Ltd.).
It has undergone 20,000 durability tests. As a result, the developers using Sample No. 1, Sample No. 2, and Sample No. 3 of the present invention all produced clear images with no major difference from the initial image, but the developer using Sample No. 4 The developer for comparison is
After 3000 times, the density decrease and white spots became noticeable. Further, 20 g of each of the above-mentioned toners were mixed into 1 kg of six types of iron powder of Sample Nos. 1 to 6 of Example 1 to prepare six types of developers. These developers are U-
Installed on each modified Bix W copier and kept at room temperature.
20,000 in an environmental chamber maintained at 35℃ and 80% relative humidity.
We conducted several durability tests. As a result, in the case of the developer using samples No. 1 to No. 3 of the present invention, clear images were obtained with no major difference from the initial image, but with the developer using samples No. 4 and No. 6. In the case of the developer, a decrease in density and background smearing became noticeable around the 5000th time. In addition, in the case of the developer using No. 5, vertical streaks due to scratches on the photoreceptor began to be observed in the image from around the 2500th time. Example 3 Next, a film of polystyrene resin was formed on each of the four iron powders No. 1 to No. 4 of Example 1 by the fluidized bed method. 1kg of iron powder carrier with these resin coatings
Four types of developers prepared by mixing 20 g of the above-mentioned toner each were installed in a modified U-Bix W machine and 50,000 copy tests were conducted on each developer. As a result, the developer using the iron powder of the present invention is
Even after 50,000 copies, a clear image was obtained with no major difference from the initial copy, but the comparison developer using iron powder was 30,000 copies.
Peeling of the resin film was observed around the time of printing, resulting in decreased image density and fogging.

[Brief explanation of drawings]

FIG. 1 is a graph of measurement results showing the oxidation state of iron powder of the present invention and blunt iron powder using a differential thermal balance.
Figure a shows the measurement results for Sample 4 (pure iron powder) of Example 1, and Figure 1B shows the measurement results for Sample 1 of Example 1. Fig. 2 is a photograph showing the metallographic structure of spherical iron powder according to an example of the present invention, Fig. 2 a is a photograph of the shape taken with an X-ray microanalyzer, and Fig. 2 b, c and d are photographs showing the metal structure of spherical iron powder. The amount of Si contained in
This is a photograph of the distribution state of the amount of Mn and the amount of Fe.

Claims (1)

[Claims] 1 Silicon and manganese in iron respectively
A manufacturing method in which a high current is applied to an iron alloy containing 0.2 to 10% by weight to melt it by electrical discharge, and at the same time, high-pressure inert gas is introduced to spray the molten alloy, which is then blown into a refrigerant to cool and form it. A spherical iron powder carrier comprising spherical iron powder particles formed in this way, characterized in that the silicon and manganese are present at a higher density on the surface of the particles.