JPH02223962A - Magnetite carrier particle and its production - Google Patents

Abstract

PURPOSE:To improve resolution, solid-black uniformity, etc., by forming the above carriers of spherical particles having >=95% spheroidization rate and <=65mum average particle size and allowing the control of saturation magnetization between 40 and 90emu/g. CONSTITUTION:Both iron oxide powder 3 and gaseous nitrogen for transportation are charged into a combustion flame gas and the iron powder is melted to a spheroidal shape in the flame 2. The concn. of the oxygen in the gas is controlled and the molten iron is dropped into water 12 in a cooling container 13, by which the molten iron is rapidly cooled. The surface thereof is coated with a resin at need. Since such production process is adopted, spherical particles having <=500e coercive force, >=40emu/g saturation magnetization, >=10<4>OMEGA.cm electric resistivity, <=3g/cm<3> bulk density, >=95% spheroidization rate, high surface smoothness and <=65mum average particle size are obtd. The control of the saturation magnetization is possible between 40 and 90emu/g. The resolution, solid-black uniformity, etc., are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier for an electrostatic image developer used in electrophotography, electrostatic recording, electrostatic printing, or the like.

[Conventional technology]

Development methods for electronic copying can be roughly divided into wet development methods and dry development methods, but since the former uses an organic solvent as a carrier, problems such as operability and odor pollution have been pointed out, and it is currently covered by a U.S. patent. Nα2786439 Publication (195
The magnetic brush development method, which is the dry development method described in a), is the mainstream. In this magnetic brush development method, a two-component developer, which is a mixed powder of magnetic carrier and toner, is used as a developer for visualizing images, and the carrier is currently a spherical or irregularly shaped iron powder carrier. (for example, Japanese Patent Publication No. 47-19398), ferrite carriers (for example, Japanese Patent Publication No. 53-15040), composite carriers (for example, Japanese Patent Publication No. 167150/1982), magnetite carriers (for example, Japanese Patent Publication No. 151551/1982) is used, and its surface layer is further coated with an organic polymer.

However, iron powder carriers have a large bulk density and the surface layer is stabilized with iron nitride, etc., so with long-term use, the stable layer on the carrier surface may be destroyed or a toner film (commonly called (spent toner) is formed, the resistance of the carrier particles changes significantly, and the amount of triboelectric charging becomes unstable, resulting in a disadvantage that the density of the image decreases and fog increases.

Therefore, instead of the iron powder carrier, a magnetite carrier, also known as r-iron ferrite 1, was developed, which has a uniform composition even inside and whose surface is stable without undergoing chemical changes in a practical environment. Magnetite carriers have a saturation magnetization larger than that of ferrite carriers and smaller than that of iron powder carriers, so they are attracting attention as carriers that fall between iron powder and ferrite.

[Problem to be solved by the invention]

However, since conventional magnetite carriers are first manufactured by a ferrite manufacturing method represented by kneading, granulation, firing, and crushing using iron oxide powder as a raw material, a kneader for kneading the raw materials, A granulator is required to granulate the particles into the desired spherical shape, a calcination furnace is required to advance the ferrite reaction, and a pulverizer is required to crush the clusters that are generated as the particles sinter during calcination. However, since it is a batch process, it is not suitable for mass production, and as a result, the production cost is higher than that of iron powder carriers. Second, in the conventional granulation and firing method, particles sinter and form clusters during firing as described above, but this phenomenon
In addition, in the subsequent crushing process, it is virtually impossible to separate crushed fragments from healthy carriers in the particle size range of 50- or less, so conventional methods Therefore, it was difficult to manufacture carriers with a thickness of 50 μm or less. Thirdly, in the crushing process, the spherical particles, which are the basic specifications of the carrier, are crushed, which has the disadvantage of lowering the yield and worsening the spheroidization rate. In addition, the fourth raw material is iron oxide Cpet.
os) 100%, so there was a drawback that the saturation magnetization could only be changed arbitrarily like a ferrite carrier.

Therefore, an object of the present invention is to solve the above-mentioned problems by reducing FeO-Fe, O generated from steel materials during the steel manufacturing process.

By introducing a thermal spray flame method using iron oxide as a raw material, we have provided a completely new continuous manufacturing method that does not require the conventional kneading, granulation, calcination, and crushing steps. The object of the present invention is to provide magnetite carrier particles having the following particle diameters, high surface smoothness, high sphericity, and magnetic control.

[Means to solve the problem]

The above-mentioned problems of the present invention are as follows: Firstly, compared to conventional iron oxide powder raw materials, a large amount of P is generated in the steel manufacturing process, for example, in a heating furnace.
It is possible to reduce the raw material cost by using inexpensive mill scale, which has eOFe5Oa as the main composition, and remove impurities from this mill scale powder by, for example, pickling treatment, dry it, and grind it to a predetermined particle size. By introducing a thermal spray flame method in which particles are put into a combustion flame gas together with a transport gas and melted into spherical particles using surface tension, the kneading, granulation, calcination, and crushing processes that were previously required are completely unnecessary. This makes it possible to produce spherical particles continuously, in large quantities, and at low cost using an extremely simple process.Secondly, by using the thermal spray flame method, there are no sintered clusters even in the small particle size range, so it is possible to produce spherical particles in advance. Firstly, carrier particles of 65 μm or less can be easily manufactured by crushing the raw materials to a predetermined particle size. Thirdly, since a crushing process is not required, carrier particles with high surface smoothness and high sphericity can be manufactured. Fourthly, by controlling the flame temperature and oxygen concentration in the flame during thermal spray flame treatment, the problem can be solved by making it possible to control the saturation magnetization.

The magnetite carrier of the present invention can generally be obtained by the following method.

FIG. 1(a) is a schematic diagram showing an apparatus for implementing the method for manufacturing magnetite carrier particles according to the present invention, and FIG. 1(b) is a front view of a thermal spray burner in the same implementing apparatus.

As shown in FIG. 1(b), on the front of the thermal spray burner 1,
Between the rows of flame holes 10 arranged on two concentric circles,
Similarly, rows of powder holes 11 arranged on concentric circles are arranged in a sandwich shape.

A flame 2 of oxygen-propane is ejected from the flame hole 10, and iron oxide powder 3 is ejected together with gas from the powder hole 11. The iron oxide powder is stored in a hopper 5, and is supplied to the thermal spray burner 1 through the powder transport pipe 4 together with, for example, nitrogen gas. On the other hand, as combustion supporting gas and fuel gas, oxygen and propane (or acetylene) are supplied to the thermal spray burner 1 through the oxygen supply pipe 6 and the propane supply pipe 7 via the control device 8 . Since the oxygen supply pipe 6 and the propane supply pipe 7 meet inside the thermal spray burner 1, a mixed gas of oxygen and propane is generated, and this mixed gas is ejected from the flame hole 10 to form the flame 2.

Due to the heat of the formed flame 2, the iron oxide powder 3 ejected together with nitrogen gas melts, reacts with the oxygen remaining in the flame 2, changes to Fe, 04, and at the same time becomes spherical due to surface tension. The magnetic powder is poured into the water 12 in the cooling container 13.
A large quantity of magnetite carriers can be produced by collecting the solidified magnetic powder, which is then pickled to remove non-standard carriers. Furthermore, in this production method, by selecting the mill scale and adjusting the oxygen/propane ratio, Fe, PeO + FezO
It becomes possible to freely control the generation rate of a+FezO+, etc.

〔Example〕

The invention will be explained in further detail in the following examples.

Example-1 Mill scale generated in a slab heating furnace was pickled, dried, and ground to a particle size of 100Al11 or less using a dry grinder as a raw material, and propane (15Nnf/hr) was used as fuel gas.
, oxygen (75Nrrr/hr) as combustion supporting gas.

Using nitrogen (22 N rd / hr) as the powder transport gas, mill scale (304 cg / hr) was subjected to thermal spray flame treatment with the equipment shown in Figure 1 (a), and pickling and 1 classification and 1 crystal quality inspection were carried out. , produced a given magnetite carrier.

Table 1 shows the characteristic values of the produced magnetite carrier. FIG. 2 shows a surface electron micrograph of the magnetite carrier, and FIG. 3 shows a cross-sectional photograph of the same. From FIG. 2, it can be seen that the surface is extremely smooth and the particles are spherical with a sphericity of 95% or more. Furthermore, it can be seen from FIG. 3 that a dense and uniform structure is formed throughout the interior. In addition, a commercially available developing machine was filled with 400cc of carrier, and a magnetic roll of 12
As a result of rotating the carrier at 0 rpm for a time equivalent to 20,000 copies, no damage to the carrier was observed.

Example 2 A sample prepared in the same manner as in Example 1 was coated with 1% by weight of silicone oil using a transfer/fluid coating device. When this developer was used in a copying machine that uses a selenium photoreceptor, image evaluation was carried out using the electrophotographic society test chart, and there was no carrier scattering, and the resolution was 81.
A good image with 11 characteristics was obtained.

Example-3 Based on the conditions of Example-1, the oxygen/propane ratio was changed from 4 to
A magnetite carrier was manufactured by adjusting the temperature within a range of 5.

The results are shown in Table 2. From this table, it can be understood that the saturation magnetization of the magnetite carrier can be controlled by controlling the oxygen/propane ratio.

Table 2 [Effects of the Invention] As explained above, the magnetite carrier particles according to the present invention are made from iron oxide generated from steel materials in the steel manufacturing process, pickled to remove impurities, dried, and reduced to a particle size of 100 nm or less. After crushing, it is put into combustion flame gas together with transportation gas,
The Fe3O4 production ratio is controlled by melting and spheroidizing in the flame and controlling the oxygen concentration in the gas, followed by rapid cooling.
Because the manufacturing method is characterized by coating the surface with resin as necessary, the coercive force is less than 500e and the saturation magnetization is 40.
It is composed of magnetite with physical properties of emu/g or more, electrical resistivity of 104 Ω・1 or more, and bulk density of 3 g/cd or less, and has a spheroidization rate of 95% or more, high surface smoothness, and an average grain size. It is a spherical particle with a diameter of 65 μm or less, and has the characteristics that the saturation magnetization can be controlled between 40 emu/g and 90 emu/g, and the following effects can be obtained.

(1) Manufacturing costs are low because inexpensive mill scales can be used and continuous, large-scale production can be achieved through a simple process that does not require any cross-wire, granulation, firing, or crushing steps.

(2) Since the particles are fine particles of 65 nm or less, the developer has improved resolution, density, and solid black uniformity.

(3) By using the thermal spray flame method, carrier particles with higher surface smoothness and higher sphericity than conventional products can be obtained, which reduces developer torque, reduces the amount of spent toner, and reduces the amount of spent toner. It becomes a developer with excellent developability and stability of image density.

(4) Since the saturation magnetization can be controlled, the degree of freedom in designing the copying machine developing engine is increased.

[Brief explanation of the drawing]

FIG. 1(a) is a schematic diagram of an implementation apparatus of the present invention, FIG. 1(b)
) is a front view of a thermal spray burner in an apparatus for implementing the present invention,
FIG. 2 is a surface electron micrograph of the magnetite carrier particle structure obtained by the present invention, and FIG. 3 is a cross-sectional photograph of the same. l... Thermal spray burner, 2... Flame, 3... Iron oxide powder, 4... Powder transport pipe, 5... Hopper, 6...
Oxygen supply pipe, 7... Propane supply pipe, 8... Control device, 9... Nitrogen gas supply pipe, 10... Flame hole, 11
...Powder hole, 12...Water, 13...Cooling container.

Claims (2)

[Claims] (1) Coercive force 500e or less, saturation magnetization 40emu/g or more, electrical resistivity 10^4Ω・cm or more, bulk density 3g/c
For magnetite particles of m^3 or less, the spheroidization rate is 9
5% or more, spherical particles with high surface smoothness, average particle size of 65 μm or less, and saturation magnetization of 40 emu/g to 90 em
Magnetite carrier particles characterized in that they are controllable between u/g. (2) FeO-Fe_ generated from steel materials during the steel manufacturing process
An iron oxide raw material whose main composition is 3O_4 is put into combustion flame gas together with a transport gas, and while it is spheroidized in the flame,
In the manufacturing method of magnetite produced by rapid cooling, the product particle size is controlled by crushing the raw material in advance, the Fe_3O_4 ratio produced by controlling the flame temperature and the oxygen concentration in the flame, and the acid A method for producing magnetite carrier particles, which comprises removing impurities by washing or magnetic separation, and coating the surface with a resin if necessary.