JP2002105501A - Spherical porous iron powder and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide iron powder having spherical shape and having over-all porous structure. SOLUTION: The powder particles have 10-300 μm average particle size, at least 100 m2/kg specific surface area, at least 35 s/50 g flowability, <5 min reactivity and about <4 g/cm3 apparent density. The iron powder can be manufactured by heat-treating a basically spherical iron-containing agglomerate in a reducing atmosphere at sufficient temperature over a sufficient length of time in order to form particles composed essentially of iron metal and having over-all porous structure. The resultant particles are then sintered under the conditions of time and temperature long and high enough to obtain required strength thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel iron powder and a method for producing the powder.

[0002]

2. Description of the Related Art Various iron powders are known in the chemical field and are widely used in various applications.

[0003] Thus, iron powders are often used as a raw material for producing iron-containing compounds such as inorganic and organic salts, iron oxide pigments and chelates. Iron powder is also used as an auxiliary material in various chemical treatments and reactions, and the powder is used, for example, as a reducing agent, a catalyst and an extraction medium in a so-called cementation process.

[0004] The rusting reaction of iron powder has two important characteristics, which are used in two important applications: its exothermic (heat generating) nature is a hot-bag. The use of oxygen in applications and the fact that oxygen is consumed during the reaction is used in oxygen absorption applications.

[0005] The iron powder material used in the above mentioned chemical applications must meet several requirements. Iron powder is of high purity, high reactivity, has good fluidity to improve powder handling, has a large active surface area, high reactivity and good permeability for gases and liquids Must have.

[0006] Iron powder is also used as a carrier for toner powder in electrophotography.

[0007] The carrier must meet the following criteria: The carrier must have suitable triboelectric properties to be able to electrostatically retain the toner powder and transfer the retained toner powder to an electrostatic latent image on the photoconductive plate when in contact with the plate. The carrier must have sufficient mechanical strength to protect the carrier particles from breaking and cracking, and good flowability. The carrier particles must have uniform electrical and magnetic properties, be stable to changes in environmental conditions such as humidity, and have sufficient durability to guarantee an acceptable lifetime.

[0008]

At present, there are very few, if any, available iron powder materials useful in all of the above-mentioned applications. The main object of the present invention is to provide such an iron powder.

[0009]

SUMMARY OF THE INVENTION In summary, the present invention relates to powders useful for the above-described applications, as well as methods for making the powders.

The most distinctive feature of the new powder is that the particles have an essentially spherical shape, an overall porous structure and a large specific surface area. Furthermore, the powder has a small apparent density, a large saturation magnetization, high reactivity,
It is characterized by good fluidity.

According to the present invention, the novel powder is prepared by drying a dry powder of an essentially spherical iron-containing mass in a reducing atmosphere,
It is produced by heat treatment at a temperature and for a time sufficient to obtain particles of a generally porous structure consisting essentially of metallic iron. The resulting particles may then be sintered for a time and at a temperature sufficient to obtain the required strength.

According to the invention, a dry powder of essentially spherical mass is produced from a slurry of a selected starting material and a liquid, preferably water.

The starting material may be powdered magnetite and / or hematite, or other iron-containing compounds, such as hydrated iron oxides such as goethite or lepite, or ferric salts. preferable. In this regard, particularly preferred are high purity ores, such as sorted ores. Instead of powdered magnetite and / or hematite ore, artificially prepared magnetite or hematite can of course also be used. The slurry is preferably an aqueous slurry containing, for example, 0.01 to 2% by weight of a binder such as polyvinyl alcohol, methyl cellulose and / or carbowax. Regardless of the source of the starting material,
The majority of particles of this material in the slurry are less than 15 μm,
It preferably has an average particle size of less than 5 μm. Upon spray drying, a spherical mass of particles of the iron-containing starting material is formed. Large particle sizes greater than 15 μm have the potential to be used. However, this use results in more irregularly shaped agglomerates, especially for smaller agglomerate sizes or dimensions.

The size of the spray-dried mass can be controlled and is determined by the conditions during the drying stage, such as the composition of the slurry, the flow rate, the pressure, and the type of use, whether rotating or spray nozzles, and the final powder. Selected by those skilled in the art in light of the intended use of Usually, the particles of the spray-dried powder have an average diameter in the range of about 10 to 250 μm. Factors useful in controlling the porosity of the final powder particles are the starting material particle size or size and sintering conditions.

[0015] As explained above, relatively irregular particles are obtained by this process, for example, by selecting spray drying parameters and raw materials so as to form more irregularly shaped particles. You can also. However, the main purpose is to select the conditions so that essentially spherical particles are formed.

The reduction of the spray-dried powder is important, in order to obtain an essentially pure metallic iron having an overall porous structure and a large specific surface area, so that essentially complete reduction is obtained. , Atmosphere, temperature and time should preferably be selected. However, in some applications,
It may be sufficient or desirable not to carry out a complete reduction to metallic iron. In these examples, the final powder particles comprise a small amount of starting material, such as magnetite or hematite. Thus, the degree of reduction in each particular example can be adjusted by those skilled in the art depending on the intended end use of the powder.

In one embodiment, more than 50% by weight, preferably more than 70% by weight, most preferably 90% by weight
Reduction is carried out until a powder consisting of more than 3 pure metal irons is obtained.

In another embodiment, the reduction is carried out until a powder consisting of more than 95% by weight, preferably more than 97% by weight, of pure metallic iron is obtained.

The reduction is preferably carried out in a continuous or batch furnace in an atmosphere of hydrogen or hydrogen-containing nitrogen, cracked ammonia or carbon monoxide or a mixture thereof. The reduction may be performed in the presence of a carbon-containing material.

In a preferred embodiment of the method of the present invention, about 4
The spray-dried spherical powder is reduced in a hydrogen-based atmosphere at a temperature in the range of 50-700 ° C, preferably about 500-600 ° C, for about 1-4 hours. The time required for the reduction largely depends on the type of furnace used, the amount of material in the furnace, the flow rate of gas, and the like.
Therefore, both a shorter time and a longer time than the above-described 1-4 hours may be required. Basically, reduction to pure iron in pure hydrogen gas
Temperature below 600 ° C, most preferably 530-570
Preferably, it is performed in the range of ゜ C, for example 550 ° C.

Alternatively, the spray-diffused spherical powder mass is reduced in a carbon monoxide-based atmosphere at a temperature in the range of about 700-1300 ° C.

In yet another embodiment of the reduction, the spherical spray-dried material is a carbon-containing material such as graphite at a temperature in the range of about 1100-1300 ° C., preferably about 1200 ° C. It is reduced in existence.

According to a preferred embodiment, the reduction is performed under conditions that allow spherical particles consisting essentially of pure iron to be obtained.

If necessary, and in order to obtain sufficient mechanical strength, the reduced powder is subjected to a sintering treatment, which may be carried out in the same atmosphere as described above or in a modified atmosphere thereof. About 800-1300 ° C, preferably about 8
It is performed at a temperature in the range of 00 to 1100 ° C. This sintering step is performed when the reduction is performed at low temperature,
Of particular importance.

The spray-dried mass may also be subjected to a pre-sintering step in an inert atmosphere to remove the binder and increase the mechanical strength.

Typically, the iron powder particles obtained after reduction and optionally sintering have an average diameter in the range of about 10 to 250 μm. Depending on the particular application, this average diameter can be easily selected from the entire range.
The specific surface area SSA measured by a BET device is usually 100 m ² / kg or more, preferably 300 m ² / kg.
As described above, the powder is basically characterized by a fine microporous structure free of iron oxide. If the reduction is carried out until essentially all oxides have been finally reduced, the powder according to the invention consists of metallic iron and up to 2% by weight, preferably less than 1% by weight, of unavoidable impurities. . The powder according to the invention consists of iron, mostly in metallic form, and up to 3% by weight, preferably less than 2% by weight, of unavoidable impurities. The oxygen content of the powder is usually less than 1% by weight, preferably less than 0.75% by weight.

The apparent density of the formed powder is 0.5 to 4 g.
/ Cm ³ , typically about 1.0-2.5 g / cm ³
Is within the range.

The chemical reactivity of iron powder mainly depends on the purity and specific surface area of the powder.

The specific surface area of ordinary iron powder largely depends on the particle size of the iron powder particles, and their shape and porosity.

The iron powders available are either irregular or spherical in shape. Irregularly shaped powder can be obtained by various methods, for example, a well-known water atomization method.
Alternatively, it can be made by any reduction treatment method, for example, a sponge iron treatment method. In this group, powders with good reactivity are found. However, the flowability of the powder is very poor, when handling the powder, and / or
Or it causes a problem in chemical treatment.

Spherical powders can also be made in various ways, for example by gas atomizing or pyrolysis of pentacarbonyl to form very fine carbonyl iron powders. Although these powders are spherical and have good flow properties, the specific surface area for a given particle size is somewhat smaller, resulting in less reactivity in chemical reactions.

The spherical shape of the iron powder according to the invention, in combination with its overall high porosity structure, each iron particle sufficiently reduces the disadvantages mentioned above. The iron powder according to the invention possesses a unique combination of good flowability and very high reactivity. Furthermore, the specific surface area, and thus the reactivity of the powder, does not depend strictly on the particle size of the powder, but it is also possible firstly to obtain intermediate powder particles having very high reactivity and good flowability.

The preferred powder according to the invention consists essentially of pure (metallic) iron, which means that the reduction of magnetite / hematite is essentially complete. Such a powder has a viscosity of more than 190 emu / g, preferably 200 emu / g.
It is characterized by a saturation magnetization exceeding g. Note that pure iron has a _s value of 200-220 emu / g. Other important magnetic properties that characterize this preferred powder are usually less than 5 emu / g, preferably 3 emu / g.
/ G of less than a small remanence sigma _r, and usually 30Oe
Less, preferably less than 25 Oe. Powders characterized by a high iron content have relatively good conductivity as a result of the high iron content. High conductivity can be easily reduced, for example, by surface oxides and other surface treatments as needed.

The spherical shape and small apparent density of the iron powder according to the present invention make it suitable as a carrier core material which offers considerable advantages over commercially available iron-based carrier core materials. Shall be. According to the current technology, in order to produce a carrier material,
The carrier core is usually coated with a thin resin layer.
The coating is needed to adjust the frictional force, increase the life and adjust the resistivity. The life of today's carrier materials is largely determined by the condition of the resin coating.
In applications, the carrier + toner mixture, commonly referred to as the "developer", causes some interaction phenomena upon movement. The toner powder adheres to the carrier surface, for example, due to sudden collisions or friction between individual carrier particles and is smeared. This application of the toner changes the surface properties of the carrier and thus reduces its life. Carrier particles with large specific gravity or large AD, or irregularly shaped particles, emphasize this problem. Another problem is flaking or delamination of the coating. The area of the coating can be peeled off from the carrier core. This problem is also accentuated when the carrier core has sharp edges, ie, is more irregular in shape. The spherical shape of the iron powder particles according to the present invention,
The small specific gravity of the individual powder particles (or the small A of the powder)
In combination with D), the disadvantages mentioned above are considerably reduced. The low specific gravity and the spherical shape reduce the Hertzian pressure (contact pressure) and friction between individual powder particles in electrophotographic applications. This increases the life of the resin coating and reduces the tendency of the coating to delaminate. The porous structure of the carrier core also improves the adhesion of the resin coating. The spherical and porous iron powder according to the present invention has a very small abrasion effect on the hardware of the machine as compared to the conventional iron-based carrier core materials. further,
Low specific gravity and low AD mean that the weight is reduced for a given carrier core volume as compared to traditional iron-based carrier core materials. The reduction in weight reduces the agitation torque, thereby reducing energy consumption.

According to a particular embodiment of the invention, the iron powder is coated with a resin layer in an amount of 1.5 to 6% by weight. When used as a carrier material, the resin impregnates the porous particles according to the invention.

The state and appearance of the iron powder are very important with respect to the performance as a carrier in electrophotographic applications. Machine manufacturers vary requirements depending on the design of the machine and on the toner of the developer. Some machines prefer a slightly rougher surface profile, while others prefer a smooth surface. This is a further advantage of the material according to the invention. Because various discrete treatments, such as lightly pulverizing to smooth the surface, facilitate surface morphology from somewhat rough or intermediate as-sintered surfaces to very smooth surfaces Because it can be adjusted. This physical treatment can also be overused, which causes more severe deformation of the particles, which can be a real advantage in some applications.

The electrical properties of the carrier core are also very important as properties in the application. The machine is designed for different levels of carriage particle resistivity, voltage breakdown, and charging characteristics.

These properties can be easily adjusted for the iron powder according to the invention. The as-sintered material according to the invention consists mainly of the conductive material iron. Oxidation changes this conductive property to something more resistant. This is another characteristic advantage of the material according to the invention. Depending on the length of the oxidation treatment, the resistivity can be adjusted to a desired value within a range from high conductivity to high resistivity.

[0039] Depending on the choice of oxidation parameters, the state and amount of iron oxide formed can be adjusted.

If the oxidation is carried out for a sufficiently long time, the phase transformation (from iron to various iron oxides) also lowers the magnetic saturation of the material, and not only increases the specific resistance but also reduces the magnetic saturation of the material. can get. This is noted as a deep oxidation case. Oxidation creates some stress on the individual particles, which is reflected in the magnetic properties, ie, remanence and coercivity. This can be easily adjusted to an acceptable level by appropriate heat treatment in a protective atmosphere to relieve stress.

The conductive properties of the material can also be adjusted by surface treatment with various inorganic materials that can be combined with the surface or deep oxidation described above. The inorganic material can be added in various ways, for example as solid particles via a liquid or a gas.

[0042] The reduced particulate material may have undergone an oxidizing or other inorganic treatment to adjust the properties of the carrier core material. The condition and appearance of the particle surface can also be adjusted by various physical treatments, such as by milling. Further, the as-reduced particulate material, or the particulate material after being treated as described above, is coated with a resin material. This can be done in many ways, for example by immersing the material in the volatile organic solvent in the resin material or by spraying the resin solution over a fluidized bed of particulate material. A wide range of organic, organic-metal, inorganic, and metal additives can be added to the resin material to optimize the properties of the carrier material.

Examples of organic solvents that can be used include methyl ethyl ketone, xylene, n-butanol, methyl cyclohexane, methyl isobutyl ketone and toluene. The coated particulate material is heated to a high temperature depending on the nature of the resin material used.

The nature of the resin material that can be used in the present invention is not critical and can be any suitable soluble.

A wide range of additives can be added to the resin material. The purpose of these additives is, for example, to control the charging properties and the flow properties of the electrical and magnetic powders.
These additives can be of various types, including, for example, organic, organic-metal, inorganic, and metal, and are added in the amounts required to obtain the required properties.

The amount of resin material applied to a particular material depends on the nature of the resin used and the type of electrophotographic machine to which the product carrier is supplied (and therefore the electrostatic and electrical suitable for that machine). (Specific resistance characteristic).

In general, the amount of applied resin suitable for the purposes of the present invention ranges from 0.5 to 8%, preferably 1.5 to 6% by weight of the partially reduced magnetized material.

The carrier material coated according to the present invention relates to conventional toners such as, for example, natural resins, synthetic resins, mixtures of natural and synthetic resins, or materials prepared by adding some additives. Can be used.

The invention is illustrated without limitation in the following examples.

Example 1 Magnetite powder having an average particle size of about 1 μm was dispersed in water to form a uniform aqueous slurry of 0.4% by weight of polyvinyl alcohol. Thereafter, the slurry was spray-dried by a spray dryer to form a spherical mass having a diameter of 10 to 150 μm.

The mass was reduced at about 550 ° C. for 80 minutes in a hydrogen atmosphere to convert magnetite to iron. To sinter the material, the temperature was then raised to 900 ° C and held for 40 minutes. Thereafter, the powder was cooled to room temperature and then lightly ground. The spherical particles produced in this way mainly contained iron and had the following properties (magnetic measurements were performed with a BH curve tracer obtained from Ricken Dancy, and SSA was performed with a BET instrument): T). That is, saturation magnetization: 206 emu / g residual magnetism: 2.2 emu / g coercivity: 19 Oe AD: 2.2 g / cc flow rate: 26 seconds / 50 g SSA: 513 m ² / kg

The iron content of the powder was 98.5% by weight, of which 98.4% by weight was pure metallic iron.

Example 2 Magnetite powder having an average particle size of about 3 μm was dispersed in water to form a uniform aqueous slurry. afterwards,
The slurry is spray dried by a spray drier and
A spherical mass having a diameter of 00 μm was formed.

The mass was reduced at about 550 ° C. for 80 minutes in a hydrogen atmosphere to convert magnetite to iron. To sinter the material, the temperature was then raised to 890 ° C and held for 40 minutes. Thereafter, the powder was cooled to room temperature and then lightly ground. The spherical particles thus produced mainly contained iron and had the following properties. That is, saturation magnetization: 206 emu / g residual magnetism: 2.5 emu / g coercivity: 22 Oe AD: 2.0 g / cc flow rate: 28 seconds / 50 g SSA: 515 m ² / kg

The same iron content as in Example 1 was obtained.

Example 3 Hematite powder having an average particle size of about 1.5 μm was dispersed in water to form a uniform aqueous slurry. Thereafter, the slurry is spray-dried by a spray drier and
A spherical mass having a diameter of を 200 μm was formed.

The mass was reduced at about 550 ° C. for 80 minutes in a hydrogen atmosphere to convert hematite to iron. To sinter the material, the temperature was then raised to 900 ° C and held for 40 minutes. Thereafter, the powder was cooled to room temperature and then lightly ground. The spherical particles thus produced mainly contained iron and had the following properties. That is, saturation magnetization: 207 emu / g residual magnetism: 2.8 emu / g coercivity: 23 Oe AD: 1.7 g / cc flow rate: 29 sec / 50 g SSA: 555 m ² / kg

The same iron content as in Example 1 was obtained.

Example 4 To form a uniform aqueous slurry, a mixed powder consisting of 50% hematite and 50% magnetite having an average particle size of about 1.5 μm was dispersed in water.

Thereafter, the slurry is spray dried, ie, spray dried, by a spray drier.
A spherical mass having a diameter of 10 to 200 μm was formed. The mass was reduced at about 550 ° C. for 80 minutes in a hydrogen atmosphere to convert magnetite to iron. To sinter the material, the temperature was then raised to 900 ° C and held for 40 minutes. Thereafter, the powder was cooled to room temperature and then lightly ground. The spherical particles thus produced mainly contained iron and had the following properties. That is, saturation magnetization: 205 emu / g residual magnetism: 2.5 emu / g coercivity: 23 Oe AD: 1.9 g / cc flow rate: 28 seconds / 50 g SSA: 525 m ² / kg

The same iron content as in Example 1 was obtained.

Table 1 below discloses powder properties that are important when applied. Commercially available iron powder was compared with the spherical porous iron powder according to the invention. The spherical porous iron powder according to the invention can be used in a wide range of applications, for example in reactions occurring in thermal bag and oxygen absorption applications, fireworks applications, food and pharmaceutical applications, for example in chemical processing and chemistry. Have a unique combination of properties that make them very suitable as reducing agents, catalysts or auxiliary materials such as so-called cementation extraction media, as chemical processing and reaction reagents, and as electrophotographic carriers I understand.

[Table 1]

The range of particle sizes was obtained by optical inspection using SEM.

The flow rate was measured using a Hall flow meter (Hall flow meter).
meter) according to the ISO 4490 standard.

The apparent density is based on the ISO 3923/1 standard.

Reactivity was measured as half the life of the powder by determining the volume of hydrogen evolved as a function of time when dissolved in diluted hydrochloric acid at room temperature (1: 8). In this way, the lower the number, the higher the reactivity.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K017 AA04 BA06 BB17 CA01 CA07 CA09 EH01 4K018 BA13 BB03 BB04 BB10 BC11 BD01 5E040 AA11 BD01 CA20 HB11 HB17 NN06 NN12

Claims (11)

[Claims] 1. The powder particles have a basically spherical shape, a porous structure as a whole, an average particle size of 10 to 300 μm,
A specific surface area of at least 100 m ² / kg and 35 s / 5
Fluidity of less than 0 g, reactivity of less than 5 minutes, about 4 g / c
Iron powder having an apparent density of less than m ^3. 2. The iron powder according to claim 1, comprising at least 50% by weight, preferably at least 70% by weight, most preferably at least 90% by weight of metallic iron and the balance being a non-reduced iron-containing material. 3. An iron powder as claimed in claim 2, comprising at least 95% by weight, preferably at least 97% by weight, of metallic iron. 4. The iron powder according to claim 1, which has a saturation magnetization of at least 200 emu / g. 5. Less than about 5 emu / g, preferably less than about 3 emu / g
5. The method according to claim 1, wherein the remanence is less than mu / g.
The iron powder according to any one of the above. 6. The iron powder according to claim 1, which has a coercivity of less than 30 Oe, preferably less than 25 Oe. 7. A method for producing an iron powder according to any one of claims 1 to 6, wherein a dry powder of an essentially spherical iron-containing mass is reduced in a reducing atmosphere. Heat-treating at a temperature and for a time sufficient to obtain generally porous tissue particles consisting essentially of metallic iron, and optionally, subsequently forming the powder to achieve the required strength Sintering at a temperature and for a time sufficient for the process. 8. The dry powder of an essentially spherical iron-containing mass is prepared by spray-drying a slurry containing artificially prepared magnetite and / or hematite particles. The method described in. 9. A dry powder of an essentially spherical iron-containing mass is prepared by spray-drying a slurry containing a hydrated iron oxide, such as goethite or lecite, or a ferric salt. A method according to claim 7 or claim 8. 10. The method according to claim 7, wherein a majority of the agglomerates have an average diameter in the range of about 10 to 250 μm. 11. The iron-containing particles in the agglomerate are not more than 15 μm,
2. The composition of claim 1 having an average particle size of less than 5 μm.
The method described in paragraph 0.