JPS649361B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a ferromagnetic powder with a lubricating layer characterized by imparting lubricity with fatty acids. It is characterized by coating the surface with a metal that reacts. As is well known, magnet manufacturing methods can be broadly divided into casting methods and powder methods. Recently, the number of magnets manufactured using powder methods such as ferrite, rare earth cobalt, and sintered alnico has rapidly increased. Although the powder method has various advantages, it also has the following disadvantages. That is, the density is lower than the bulk, and the orientation of the ferromagnetic powder is low. One of the main causes of decreased density and orientation is surface friction of ferromagnetic powder. When ferromagnetic powder is press-molded, the density of the compact increases as the press pressure increases, but as the press pressure increases, the frictional force between the powders or between the powder and the mold surface increases. For this reason, a contradiction arises in that even if the density increases, the orientation decreases. Under conditions of high press pressure, it is necessary to reduce the surface friction coefficient of ferromagnetic powder. As a method for reducing the surface friction coefficient of ferromagnetic powder, a method commonly used for ferrite and the like is to mix a small amount of paraffin into the powder. However, in the conventional method, the orientation deteriorates under high pressure, and in order to improve the magnetic properties, it is necessary to further lower the surface friction coefficient of the ferromagnetic powder by one rank in order to increase the density and orientation. There is a need. On the other hand, as is well known, regular packing of powder
If we apply a filler smaller than the 5th sphere using Horsfield filling, the calculated void ratio will be 3.9%. However, the actual void ratio is 15 to 20% even if the powder particle size distribution is adjusted and a small amount of paraffin is added as a lubricant.
It's smaller and more difficult. In powder compaction, the density will be higher if pressure is applied from both the top and bottom surfaces rather than from one side. Moreover, if the powder particle size becomes too small, the density after powder compaction will become small. These causes are due to powder friction. On the other hand, for permanent magnets, the critical radius of a single domain particle is
Rc is Rc=9γ/4πMs (γ: domain wall energy,
Ms: magnitude of spontaneous magnetization), here are a few examples:
It is shown in Table 1. Single magnetic domains are usually on the order of submicrons, and as the grain size increases, magnetic properties change.
Among other things, the coercive force increases, but the density decreases. The situation is shown in Table 2. In a magnet, the strength of magnetization per unit volume is proportional to the density, and the maximum energy product (BHmax) is proportional to the square of the density, so
Increasing the density is one of the essential elements for improving the performance of powder magnets. In particular, the influence of density is extremely large in resin- and metal-bonded magnets. On the other hand, sintered magnets shrink by 20 to 30% during the sintering process, increasing their density, so they are less affected by pores.

【table】

[Table] Table 3 also shows the orientation caused by press pressure.
The experimental results of the authors are shown below. The supplied powder is
It has a hexagonal crystal structure. Press molding is performed while applying a magnetic field, and the X-ray diffraction intensity from the (220) and (006) planes of the crystal is _{measured at 220} ,
₀₀₆ was measured, _and the ratio _220/006 was taken as the orientation index, which is shown in Table 3. Even when a strong magnetic field is applied, if the pressing pressure is 1 ton/cm ² or more, the easy axes of magnetization are not aligned, and the deviation between the easy axis of the particles and the direction of the magnetic field becomes large. easy

[Table] When the angle between the axis and the external magnetic field is θ, the relationship between θ and coercive force, and between θ and residual magnetic flux density is expressed as Stonen−
When calculated using Wohlfath's theory, the results are shown in Figures 1 and 2. The coercive force and the residual magnetic flux density are each normalized to be 1 when θ=0. If θ shifts even slightly from 0, both the coercive force and the residual magnetic flux density decrease, and the proportion of the coercive force is significant. In order to align the axes of easy magnetization, it is important to increase the magnetic field and decrease the surface friction coefficient of the magnetic powder. To generate a magnetic field of 25 KOe or more, it is necessary to increase the size of the device or use superconducting coils, which is the limit of the current industrial level. On the other hand, the moment that the magnetic powder receives during magnetic field compaction is: Moment due to magnetic field = vMsHSinθ Moment due to frictional force = Kμrp v: Volume of ferromagnetic powder Ms: Magnetization size per unit volume H: External magnetic field θ: External magnetic field Angle formed by spontaneous magnetization K: Unbalance coefficient of stress applied to the ferromagnetic powder μ: Coefficient of surface friction of the ferromagnetic powder r: Radius of the ferromagnetic powder P: Press stress between the easy direction of the magnetic field (direction of spontaneous magnetization) and the external When the angle with the magnetic field is 0°, the moment due to the magnetic field is 0, and even if θ deviates slightly from 0°, the moment due to the magnetic field to restore the angle does not work much. Therefore, even if a large external magnetic field is applied, due to the small moment due to frictional force,
The axis of easy magnetization is rotated and does not return to its original state. To reduce the moment due to frictional force,
In addition to the surface friction coefficient μ, it is also effective to lower K. K can be decreased by making the powder shape more spherical, and μ can be decreased by lowering the surface friction coefficient of the ferromagnetic powder. However, since K is greatly influenced by the crystallinity of the ferromagnetic material, it is difficult to significantly improve this. The object of the present invention is to reduce the surface friction coefficient of ferromagnetic powder under conditions of high pressure. The fatty acid in the present invention refers to carboxyl group 1
Among the carboxylic acids RCOOH, which have a chain structure, it is a general term for those that have a chain structure. R is CnHm (n: an integer of 5 or more, m: a positive integer), and is a saturated or unsaturated alkyl group. In addition, in the present invention, metals that chemically react with fatty acids include Cu, Ag, Se, Te,
As, Sb, Bi, Sn, Pb, Al, Ga, In, Zn, Cd,
This was established through experiments with Mg and Lanthanide. Furthermore, the ferromagnetic powder in the present invention refers to permanent magnet material and ferrite powder. Hereinafter, the present invention will be specifically described in detail with reference to Examples. Example 1 After degreasing and cleaning 100g of SmCo ₅ powder with a metal cleaner, it was electrolessly plated with copper using a Fehling liquid. The composition of Fehling's liquid used was as follows: copper sulfate 70 gr/l potassium sodium tartrate 350 sodium hydroxide 100 37% formalin 150 c.c./l, and the SmCo powder was stirred well in this liquid for 1 minute. Approximately 0.1-0.2 μ of Cu is deposited on the surface of SmCo ₅ .
After washing and drying the plated SmCo ₅ powder,
Mix and react thoroughly with 0.2gr of stearic acid at 70°C in an argon atmosphere, and then remove after cooling. Thereafter, 2.5g of epoxy resin was added as a binder, stirred and mixed well, and the coefficient of friction was measured. The coefficient of friction of the ferromagnetic powder was 0.1, which is a better result than the current coefficient of 0.3 to 0.4. Example 2 After degreasing and cleaning 100g of SmCo ₅ powder with a metal cleaner, electroless tin plating with the following composition was performed. Stannous sulfate 2gr/l Sulfuric acid 10 Temperature 90℃ Stir the SmCo ₅ powder in this solution for 30 seconds.
Approximately 0.1-0.2 μ of Sn is precipitated on the SmCo ₅ surface. After washing and drying the plated SmCo ₅ powder, it was thoroughly mixed and reacted with 0.2gr of stearic acid at 70℃ in an argon atmosphere. After cooling, 2.5gr of epoxy resin was added as a binder and mixed with good stirring. After that, the friction coefficient was measured. The coefficient of friction of the ferromagnetic powder SmCo ₅ was 0.1, which is a better result than the current coefficient of 0.3 to 0.4. Example 3 After degreasing and cleaning 100g of SmCo ₅ powder with a metal cleaner, it was mixed with 0.5g of Zn powder, stirred and mixed in an argon atmosphere at 500℃, and the surface of the SmCo ₅ powder was
Deposit 0.1-0.2μ of Zn. After cooling, the mixture was sufficiently mixed with 0.2 gr of stearic acid at 70° C. in an argon atmosphere, and after cooling, 2.5 gr of epoxy resin was added as a binder, stirred and mixed well, and the coefficient of friction was measured. The friction coefficient of ferromagnetic powder SmCo ₅ is
0.1 gave better results compared to the current 0.3-0.4. In the examples, the current one is one in which stearic acid is not attached to SmCo ₅ and a metal that reacts with stearic acid is not attached, but stearic acid is directly attached to SmCo ₅ , and then mixed with an epoxy resin. The difference between the current method and the present invention is that the carboxyl group reacts with the powder and forms a chemical bond, so even when mixed with the epoxy resin, stearic acid remains firmly attached to the powder surface. In addition, in the case where fatty acids are simply physically adsorbed, when ferromagnetic powders are pressed at a pressure of 1 ton/cm ² or more, the fatty acid film is cut and the ferromagnetic powders come into contact with each other. However, if the fatty acids are adsorbed through a chemical reaction, the fatty acid film is broken during pressing, and the ferromagnetic powders do not come into contact with each other. Now, Examples 1 to 3 only describe a part of the present invention. In addition to the above, the metals that coat the ferromagnetic powder include Ag, Se, Te, As, Sb, Bi, Pb, Al,
Using Ga, In, Cd, Mg, and Lanthanide, the surface friction coefficient of the powder can be made approximately 0.1 using the same method as in the example. The thickness of these coated metals is 0.001μ~
1μ is preferred. If it is less than 0.001μ, the metal coating will be non-uniform and there will be uncoated areas, and if it is more than 1μ, the non-magnetic portion will become too large and the magnetic properties will deteriorate significantly. In addition, as a ferromagnetic powder, as an example in the example
Although SmCo ₅ was written, RmTn (R: rare earth element,
T: transition element, m, n: positive integer), ferrite,
The material is not limited to alnico, Mn-Al-C, Mn-Bi, etc. As RmTn, (SmPr)
(Co, Fe, Cu, Zr) ₅ , (MMA) (Co, Fe, Cu,
There are many examples, such as Zr) ₅ , (Smpr) ₂ (Co, Fe, Cu, Zr) ₁₇ , etc. By changing the elements R and T in small amounts, various magnets are created, and these belong to the present invention. Furthermore, stearic acid was shown in the example as a fatty acid, but linoleic acid (C ₁₇ ), oleic acid (C ₁₇ ),
Chain fatty acids around C ₂₀ such as erucic acid (C ₂₁ ), stearic acid (C ₁₇ ), napecanoic acid (C ₁₈ ), and aragic acid (C ₁₉ ) are suitable for reducing the coefficient of friction. C less than ₁₀ is liquid at room temperature and has excellent lubricity at low temperatures. or,
Unsaturated fatty acids exhibit strong acidity when the double bond is close to the carboxyl group, increasing their reactivity with metals.
There are many desirable things. The amount of fatty acid required for lubrication is not limited to 0.2 gr as in the example, as long as it can cover the surface of the powder with at least one molecule. These ferromagnetic powders with a lubricating layer according to the present invention are made of organic polymers (epoxy, nylon, vinyl chloride, polypropylene, EP rubber, diene rubber, urethane rubber, acrylic polymer, polyvinyl polymer, polyester polymer). , phenolic polymers, xylene polymers, melamine polymers), inorganic polymers (silicon polymers, phosphorus polymers, sulfur polymers), metals (Sn, Pb, In, Sb,
Bi, Zn, Cd, Al, Mg), etc. alone or in combination as a binder. Furthermore, the highly oriented green body is sintered as is without a binder, resulting in high density,
Highly oriented magnets can be created. In the example, in the conventional method, the maximum energy product of the magnet was 8.2MGOe, but in Example 1
Then, the average of the four samples was 9.1MGOe, and in Example 2
9.8MGOe, and 9.5MGOe in Example 3, which significantly improved the magnetic properties. As described above, the present invention applies completely new knowledge regarding the lubrication of ferromagnetic powder to provide a manufacturing method that makes effective use of non-oriented grains that have been wasted in the past, and improves the performance of powder magnets. This will greatly contribute to the

[Brief explanation of drawings]

FIG. 1 shows the orientation dependence of the holding force. FIG. 2 shows the orientation dependence of the residual magnetic flux density.

Claims (1)

[Claims] 1 A method comprising the steps of coating the surface of ferromagnetic powder with a metal that chemically reacts with fatty acids to a thickness of 0.001 to 1 μm, and coating the ferromagnetic powder coated with the metal that chemically reacts with fatty acids with fatty acids. A method for producing ferromagnetic powder with a lubricating layer.