JPH0613216A - Oxidation-resistant rare earth/iron permanent magnet bonded with epoxy - Google Patents

Abstract

(57) Summary: The present invention relates to a molded permanent magnet article of oxidation resistant epoxy-bonded rare earth iron, an epoxy resin mixture containing at least one antioxidant component for delaying the oxidation of a molded article. It is characterized by being molded by using. [Effect] The permanent magnet article of the present invention exhibits remarkable oxidation resistance, especially at high temperatures.

Description

Detailed Description of the Invention

The present invention is a process for making iron-neodymium-boron permanent magnets which is generally magnetic and isotropic and is characterized by a coercive force of at least about 5 × 10 ⁶ / 4πA / m (5,000 oersteds) at room temperature. Regarding More particularly, the present invention relates to a method of making an epoxy-bonded magnet of the type described above that is blended with an epoxy antioxidant composition to increase the oxidation resistance of such magnets.

Permanent magnets based on compositions containing iron, neodymium and / or praseodymium, boron are known and are used commercially. Such a permanent magnet is
As the essential magnetic phase, the proportions of iron, neodymium, and boron include, for example, tetragonal crystal grains exemplified by the empirical formula Fe ₁₄ Nd ₂ B.
This magnet composition and its manufacturing method are described in US Pat. No. 4,802,931.
No. The magnetic phase grains are surrounded by a second phase, which is typically rich in rare earths, eg, neodymium, as compared to the essential magnetic phase. Rapid solidification of melts of the above compositions (eg by melt spinning)
However, it is known that magnets based on the above compositions can be produced by making magnetically isotropic platelets of fine particles of ribbon-like fragments. Highly coercive permanent magnets can be formed from these isotropic particles by known methods.

In general, these permanent magnets are characterized by a totally reactive composition that oxidizes upon exposure of the composition to the atmosphere, thereby irreversibly reducing the coercivity that can be obtained from the composition. . This drawback is most apparent at high temperatures. For example, by mixing the powder composition with a suitable epoxy resin and then molding to form a magnetic article,
Many attempts have been made to protect these permanent magnet compositions from oxidation. Certain epoxies are known to have good oxidation resistance. However, although epoxies are generally oxidation resistant, epoxy-bonded magnets can still exhibit some oxidation when blended with rare earth-iron particles.

Therefore, epoxy is blended with a substance that adds sufficient oxidation resistance to the rare earth composition so as to increase the overall oxidation resistance of the molded permanent magnet article, increasing the oxidation resistance of the epoxy bonded permanent magnet article. It is desirable to provide a means of doing so.

A shaped permanent magnet article and a method for forming the same according to the invention have the features specified in claims 1 and 10, respectively.

It is an object of the present invention to provide a means for increasing the oxidation resistance of epoxy bonded permanent magnet articles formed from rare earth permanent magnet materials based on iron, neodymium and / or praseodymium, boron. .

It is another object of the present invention that the above means include blending the epoxy with an antioxidant composition so as to increase the oxidation resistance of the epoxy bonded permanent magnet article.

According to the preferred embodiment of the present invention, these and other objects and advantages are achieved as follows.

In accordance with the present invention, there is provided a method of forming an oxidation resistant epoxy bonded iron-neodymium-boron permanent magnet molded article. Preferably, the thermosetting epoxy resin is uniformly mixed with the composition containing at least one suitable antioxidant and then blended with the iron-neodymium-boron permanent magnet particles. The particles are then subjected to conventional molding, such as compression molding at high temperature or compaction molding at room temperature. Finally, the epoxy is properly cured to form a useful magnet with increased oxidation resistance. Most preferably,
The antioxidant composition used for delaying oxidation of a molded article is
It is present in a preferred amount of about 0.6% by weight, based on the total mass of iron-neodymium-boron particles, and consists of three components, namely, two separate antioxidant compositions and an equivalent amount of the antioxidant composition. However, increased oxidation resistance is observed using only a single antioxidant, or different amounts of the three preferred or single antioxidants.

In general, the epoxies used to mold this type of magnet have been conventionally considered to be sufficiently oxidation resistant. However, it has been determined that the oxidation resistance of this magnet particle encapsulated in an epoxy matrix can be significantly increased by adding an antioxidant composition to the epoxy prior to molding the permanent magnet article.

A particularly advantageous feature of the present invention is that the oxidation resistance of permanent magnet articles is increased even at high temperatures, as compared to conventional methods using only epoxy resins.

Other objects and advantages of the present invention will be better understood from the following detailed description. A rare earth permanent magnet material based on iron, neodymium and / or praseodymium, boron is mixed with an epoxy resin binder containing an antioxidant composition to provide a shaped magnet article featuring increased oxidation resistance.

The composition of the rare earth permanent magnet particles used to form the shaped magnetic article comprises about 40 to 90% iron or a mixture of iron and cobalt and iron on an atomic percent basis (iron is preferably at least 60% of the non-rare earth metal content. ), Neodymium and / or praseodymium must be included in the rare earth metal of about 10-40% (neodymium and / or praseodymium preferably comprises at least about 60% of the rare earth content), and boron of at least 0.5%. Consists of. Preferably, iron comprises at least about 40 atom% of the total composition and neodymium and / or praseodymium comprises at least about 6 atom% of the total composition. Also preferably, the boron content is in the range of about 0.5 to about 10 atomic% of the total composition, although depending on the intended use of the magnet composition, the total boron content may be suitably higher. it can.

[0014] Certain compositions useful in the manufacture of this type of permanent magnet particles are as follows in weight%, Fe ₁₄
It contains a magnetic phase consisting of Nd ₂ B (or equivalent) tetragonal crystals. Rare earth about 27-31.5% (at least about 95% of this component)
% Is neodymium, the rest is essentially praseodymium), about 0.8 to about 1.0% boron, the rest iron.
In some cases about 2 to about 16% cobalt is used instead of iron. In addition, gallium can be added in an amount of about 0.55 to 0.75%.

Particles of this particular composition are typically made by a rapid solidification process. It is foreseeable that permanent magnet compositions having from about 25 to about 40 weight percent rare earth component produced by other methods such as sintering can also be used. Thus, the teachings of the present invention can be applied to a larger group of compositions as described above, in atomic percent, and are commonly referred to as iron-neodymium-boron compositions.

As mentioned above, iron based on a particular composition
Neodymium-boron magnet particles can be made by rapidly solidifying a melt of the composition to produce magnetically isotropic platelets of fine particles of ribbon-like fragments. A commonly used technique is melt spinning. This technique is well known in the art, but other suitable means can be used to form the particles. The average diameter of the particles ranges from about 100 to about 300 microns, but can vary considerably. Each particle contains a tetragonal Fe ₁₄ Nd ₂ B (or its equivalent) that imparts magnetism to the substance.

In general, the magnetism of the melt-spun particles varies as follows, but depends on the actual components of the alloy, especially the amount of iron, cobalt, and rare earths in the composition. Typically, this melt-spun isotropic particle has a particle size of about 0.
Residual magnetic induction (B _r ) in the range of 73 to about 0.83 T (7.3 to about 8.3 kilogauss), about 5.5 × 10 ⁶ / 4π.
To about 6.5 × 10 ⁶ / 4π A / m (5.5 to about 6.5)
Coercive force (H _c ) in the range of Kilo-Oersted, about 8 × 1
0 ⁶ / 4π to about 18 × 10 ⁶ / 4π A / m (8 to about 1
Intrinsic coercive force (H _ci ) in the range of 8 kilo Oersted, about 11 × 10 ⁵ / 4π to about 12.5 × 10 ⁵ / 4π T ·
It has a maximum energy product (BH _max ) in the range of A / m (11 to about 12.5 Mega Gauss Oersted).

Permanent magnet articles formed from these particles by compaction molding with a suitable epoxy at room temperature generally have the following magnetic properties, which properties depend on the actual composition of the alloy. Typically, the remanence induction is in the range of about 0.6 to about 0.7 T (6 to about 7 kilogauss) and the coercive force is about 5 × 10 ⁶ / 4π to about 6 × 10 ⁶ / 4π A / m. (5-
Range of about 6 kilo Oersted), intrinsic coercive force is about 9 x 1
0 ⁶ / 4π to about 16 × 10 ⁶ / 4π A / m (9 to about 1
6 kilo Oersted), the maximum energy product is about 8.5 × 10 ⁵ / 4π to about 9.5 × 10 ⁵ / 4π T ·
It is in the range of A / m (8.5 to about 9.5 Mega Gauss Oersted). Compacted molded permanent magnet articles formed using the epoxy / antioxidant composition in accordance with the teachings of the present invention are generally characterized by magnetism within the above range.

In accordance with the invention, iron-neodymium-boron particles are blended with an epoxy resin mixture containing an epoxy resin and an antioxidant composition. If desired, an accelerator may be included to facilitate the curing of the epoxy resin.

The antioxidant composition preferably comprises three separate but synergistic compounds that retard the oxidation of subsequently shaped particles. The combination of these three separate compounds counteracts the corrosion mechanism that occurs within the iron-neodymium-boron particles when exposed to the atmosphere, presumably by interfering with the ionic charge transfer mechanism during the oxidation-reduction reactions inherent in the oxidation process. Help delay.

The three synergistic compounds are preferably mixed in equal amounts before mixing with the epoxy resin. The three synergistic compounds consist of a primary antioxidant compound, a secondary antioxidant compound, and an antioxidant compound.

Particularly preferred primary antioxidant compositions are:
High molecular weight sterically hindered phenolic antioxidants,
It has an empirical formula of C ₅₃ H ₇₂ O ₈ and a molecular weight of about 836.
2,2-bis [4- {2- (3,5-di-tert-, commercially available from lity Chemicals as Topanol 205.
Butyl-4-hydroxyhydrocinnamoyloxy)}
Ethoxyphenyl] propane. A preferred secondary antioxidant composition has a thioester, empirical formula C ₃₀ H ₅₈ O ₄ S, a molecular weight of about 514, CARST from Morton Thiokol Inc.
It is dilauryl thiodipropinaoat commercially available as AB DLT DP. These two antioxidants probably act by the above mechanism by interfering with the ionic charge transfer mechanism during the oxidation-reduction reaction inherent in the oxidation process.

The preferred metal oxidation inhibitor composition, oxalyl bis (benzylidene hydrazide), has the empirical formula C ₁₆ H ₁₄ O
₂ N ₄ , having a molecular weight of about 294, from Eastman Chemicals
Commercially available as the EASTMAN inhibitor OAHB. This oxidation inhibitor can act by reacting with and deactivating the metal component during the oxidation process.

It has been determined that the three preferred components work synergistically to provide optimum oxidation resistance to the epoxy-bonded iron-neodymium-boron particles. But,
Instead of using equal amounts of synergistic combinations of the three preferred ingredients, any combination of the preferred ingredients, including only a single ingredient or different amounts of each ingredient, and different amounts of suitable substitutes for the ingredients. However, it can be predicted that the magnet particles can be bonded with epoxy. Other suitable alternatives to the individual antioxidant components are other sterically hindered phenols such as bisphenols or thiobisphenols, or other polymers such as amines, more particularly monophenols. , Phenol ethers, aminophenols, diphenylamines, phenylenediamines, quinolines and various other antioxidants. A more detailed list is shown in Table I. Suitable alternatives to oxidation inhibitors can include various other known inhibitors. However, preferred compositions containing equal amounts of the above three compounds are advantageous due to the advantageous synergism resulting in improved resistance to oxidation.

Preferably, each of the three compounds is provided in equal amounts of about 0.
It is present at 2% by weight. Therefore, the total amount attributable to the antioxidant composition is about 0.6% by weight, based on the total mass of iron-neodymium-boron particles. The amount of each component can vary from about 0.01% to about 1.5% by weight, where the total amount attributed to the antioxidant composition is from about 0.03% to about 4.5%.
It can be predicted that the weight percentage can be changed. Clearly, the maximum amount of each component is desired to produce increased resistance to oxidation, but in practice a minimum amount is desired to prevent adverse effects on the density and overall magnetic properties of the molded article made from the particles. Be done. The optimum balance for this is about 0.2 for each component.
Is present in an amount of wt.% And the total antioxidant composition is about 0.6.
Seems to be achieved in weight percent.

The antioxidant composition containing the preferred three components is then mixed with a suitable epoxy resin which provides an adhesive binder for subsequent compaction and molding of the iron-neodymium-boron particles. Preferably, the resin binder is a phenol-formaldehyde type epoxy resin, which is commercially available as a family of compositions known under the trade name Novolak. Other suitable epoxies are bisphenol A-epichlorohydrin based derivatives,
Others can also be included. Prior to the present invention, magnets molded with these epoxies were believed to be sufficiently oxidation resistant, but addition of an antioxidant composition to the epoxy, in accordance with the teachings of the present invention, resulted in oxidation of the metal particles. Decreased,
This increases the overall oxidation resistance of the shaped permanent magnet article.

Preferably, the epoxy resin is present in an amount of about 1.5% by weight, based on the total iron-neodymium-boron particle mass, which amount is predictably about 0.1% to about 10% by weight. Can be changed. If the amount of epoxy is too small,
Insufficient adhesion during subsequent molding of the particles and too high an epoxy content will reduce the overall density and physical properties of the molded magnet. Therefore, about 1.5% by weight of epoxy seems optimal. Compaction of molded parts that can occur when using too much adhesive, without adversely affecting the density or physical properties.
The above amounts ensure a sufficient amount of epoxy for adhesion of the compacted particles during subsequent molding operations.

It should be noted that the epoxy resin binder can be mixed with a suitable accelerator so that the epoxy can be easily cured during subsequent molding operations. The particular accelerator used may vary depending on the particular application and process parameters such as the temperature of the subsequent curing step. The choice of accelerators is known to those skilled in the art and is therefore not discussed in further detail here.

In a particular example, an antioxidant composition having the following composition was mixed with an epoxy resin prior to blending with iron-neodymium-boron particles. The antioxidant composition comprises 2,2-bis [4- {2- (3,5-di-tert-butyl-4-hydroxyhydrocinnamoyloxy)}, a preferred sterically hindered phenolic antioxidant. Ethoxyphenyl] propane, the preferred thioester dilaurylthiodipropionate, and the preferred oxidation inhibitor oxalylbis (benzylidene hydrazide), each in equal amounts, preferably 0.2% by weight of each component, based on the total mass of the particles. The total amount attributable to the antioxidant composition is about 0.6% by weight based on the total weight of iron-neodymium-boron particles.
Met.

The preferred novolac epoxy resin binder can be blended with a liquid or solid accelerator, or the accelerator can be omitted. In a particular example, no accelerator was used. Also, the epoxy could be stored as a mixture if desired, but in the specific examples the epoxy was not a mixture.

The preferred epoxy resin in dry powder form was used in an amount corresponding to about 1.5% by weight, based on the total mass of particles.
Antioxidant composition 0.6 using a conventional V-blender
The wt% and epoxy resin were intimately mixed. Iron-neodymium-boron particles were also added to the V-blender so that the components blend intimately and uniformly. The blending time depends on the size of the mixer used and the amount of the individual components. Preferably, the mixture is mixed until a homogeneous mixture is obtained and the epoxy resin and the antioxidant component are well dispersed in the iron-neodymium-boron particles to ensure good adhesion during the subsequent molding process.

After blending the iron-neodymium-boron particles with the epoxy resin / antioxidant mixture, the mixture was compacted and cured at the appropriate temperature for the epoxy used (and accelerator system if used). In a particular example, the particle mixture was pressed to a density of about 5.8 g / cm ³ in a small cylinder suitable for testing purposes. This is the preferred density for forming shaped magnets from the iron-neodymium-boron particles. The epoxy was then cured at about 171 ° C. Curing temperatures are generally within the knowledge of the art and will vary depending on the particular accelerator (if used) and epoxy resin binder used. The teachings of the present invention of using antioxidants to protect the magnet particles in epoxy bonded magnets are also applicable to the formation of magnets using other techniques such as compression molding or injection molding techniques.

The antioxidant composition was added in an amount of about 0.
The oxidation resistance of molded permanent magnet articles containing the preferred antioxidant reinforced epoxy resin used in an amount of 6% by weight and an epoxy in an amount of about 1.5% by weight was determined using conventional techniques.

The preferred permanent magnet body is at 110 ° C. and 1
Both were subjected to a heat aging test at 25 ° C. 50 at 125 ° C
After 00 hours, the preferred permanent magnet body with antioxidant additive has its second quadrant hysteresis graph (seco).
nd quadrant hysteresis gr
ap), which showed a structural magnetic loss of only 3.4%, whereas the conventional shaped iron-neodymium-boron particles containing no antioxidant composition in the epoxy resin binder had about 1%.
It showed a structural magnetic loss of 0.2%. In the same test at 110 ° C., the preferred iron-neodymium-boron molded articles are 1.
It exhibited a structural magnetic loss of 1%, again an improvement over conventional molded magnets. This structural magnetic loss is 0.7 / 4
It was measured with a load line of π T · A / m (7 Gauss Oersted).

In addition, many other antioxidant compositions were also tested. Generally, a single antioxidant component is about 0.1-1.0.
Weight percent was mixed with an epoxy resin binder to form a molded permanent magnet body as described above. In all cases, the addition of the following antioxidants to the epoxy resin binder increased the oxidation resistance of the permanent magnet body as shown in Table I. Table 1 Oxidation and anticorrosive corrosion ¹⁾ Structure
Loss ²⁾ Control (without antioxidant) 3.5 9.6 Propyl gallate 0.2 7.3 2,6-di-tert-butyl-4-methylphenol 1.0 6.3 N, N-diphenyl-p-phenylenediamine 0.3 4.9 3,5-di -Tert-Butyl-4-hydroxyhydrocarbyl 0.3 1.3 Octadecyl cinnamate 4,4'-thiobis (6-tert-butyl-m-crezo 0.2 1.3 ol) 2,2'-methylenebis (4-methyl-6- tert-bu 0.4 1.1 tylphenol) bis (2,4-di-tert-butylphenol) penta 0.7 1.1 erythritol diphosphate butylhydroxyanisole 0.5 1.9 oxalyl bis (benzylidene hydrazide) 1.2 1.9 4,4-methylenebis (2,6- Dibutylphenone 0.6 1.0) Distearyl thiodipropionate 0.7 1.1 1,1,3-Tris (2-methyl-4-hydroxy 0.3 1. 3-5-tert-butylphenol) 2,2'-methylenebis (4-ethyl-6-tert-1.2 4.3 butylphenol) 2,2'-ethylidenebis (4,6-di-tert-butyl 0.6 3.2 ruphenyl) fluorophos Phyto 3- (3 ', 5'-di-tert-butyl-4-hydroxy 0.9 2.9 cyphenyl) octadecyl propionate tetrakismethylene (3,5-di-tert-butyl-4 0.9 2.2-hydroxyhydrocinnamate) ── ───────────────────────────────── 1) Immerse in 10% NaCl aqueous solution for 10 minutes, then 93%
Weight% increase after 1000 hours exposure at relative humidity. 2) The structural magnetic loss% after aging the formed magnet body at 125 ° C.

From these test results, according to the invention, iron-neodymium-boron particles epoxy-bonded with an epoxy resin solution containing at least one antioxidant compound show an increased resistance to oxidation even at high temperatures. I understand. This is a particularly advantageous feature for the production of shaped high coercivity permanent magnets.

Although the present invention has been described with reference to the preferred embodiment, the amount and number of antioxidant components in the epoxy resin mixture can be varied, or the process parameters used can be altered, or other suitable magnetic materials can be used. It will be apparent that other shapes such as etc. can be adopted by those skilled in the art. This application claims priority from U.S. Patent Application No. 864,242 and
No. 852,426 and the disclosure in the abstract of this application are incorporated herein by reference.

Claims (14)

[Claims] 1. At least about 5 × 10 ⁶ / 4π at room temperature.
A particle mass of iron-neodymium / praseodymium-boron having a coercive force of A / m (5,000 oersteds) and a binder that binds the particles and delays their oxidation, the binder being an epoxy resin and a steric solid. At least selected from the group consisting of hindered phenols, bisphenols, thiobisphenols, phenols, amines, monophenols, phenol ethers, aminophenols, diphenylamines, phenylenediamines, quinolines and thioesters A molded permanent magnet article, characterized in that it consists of one antioxidant composition. 2. The molded permanent magnet article according to claim 1, wherein the antioxidant composition comprises an equal amount of a high molecular weight sterically hindered phenolic antioxidant, a thioester, and an antioxidant. 3. The sterically hindered phenolic antioxidant is 2,2-bis [4- {2- (3,5-di-tert.
-Butyl-4-hydroxyhydrocinnamoyloxy)} ethoxyphenyl] propane, the thioester is dilaurylthiodipropionate, and the oxidation inhibitor is oxalylbis (benzylidenehydrazide). Molded permanent magnet articles. 4. The molded permanent magnet article according to claim 1, wherein the thermosetting resin is a phenol-formaldehyde type epoxy resin. 5. The thermosetting resin is bisphenol A-
The molded permanent magnet article according to any one of claims 1 to 3, which is epichlorohydrin. 6. The antioxidant composition is present in an amount of about 0.03 to about 4.5% by weight based on the total mass of the particles and the epoxy resin is about 0.1 to about the total mass of the particles. About 10.
Molded permanent magnet article according to any of claims 1 to 5, which is present in an amount of 0% by weight. 7. At least about 5 × 10 ⁶ / 4π at room temperature.
An agglomerate of iron-neodymium / praseodymium-boron particles having a coercive force of A / m (5,000 oersteds) and an average diameter of about 100 to about 300 microns, and an epoxy resin mixture for binding the agglomerates of particles. The epoxy resin mixture comprises a phenol-formaldehyde type epoxy resin, and a substantially equivalent high molecular weight sterically hindered phenolic antioxidant, an antioxidant composition of a thioester and an antioxidant, Molded permanent magnet article, characterized in that the components of the epoxy resin mixture work together to provide the necessary adhesion to mold the particles into the permanent magnet article while substantially delaying oxidation of the permanent magnet article. . 8. The sterically hindered phenolic antioxidant is 2,2-bis [4- {2- (3,5-di-tert.
-Butyl-4-hydroxyhydrocinnamoyloxy)} ethoxyphenyl] propane, the thioester is dilaurylthiodipropionate, and the oxidation inhibitor is oxalylbis (benzylidenehydrazide). Permanent magnet articles. 9. The antioxidant composition is present in an amount of about 0.03 to about 4.5% by weight of the total particle mass and the epoxy resin is present in about 0.1 to about the total particle mass. About 10.
Molded permanent magnet article according to claim 7 or 8 present in an amount of 0% by weight. 10. At least about 5 × 10 ⁶ / 4π at room temperature.
It has a coercive force of A / m (5,000 oersted),
Prepare iron-neodymium / praseodymium-boron particle agglomerates having an average diameter of about 100 to about 300 microns.
Phenol-formaldehyde type epoxy resin and sterically hindered phenols, bisphenols, thiobisphenols, phenols, amines, monophenols, phenol ethers, aminophenols, diphenylamines, phenylenediamines, quinolines and An epoxy resin mixture is prepared by mixing with an antioxidant composition consisting of at least one antioxidant selected from the group consisting of thioesters, and the epoxy resin mixture is used to coat the particles sufficiently. Mixing the particles with an epoxy resin mixture and compacting the coated particles to produce an article having a predetermined shape, heating the article at a temperature sufficient to cure the epoxy resin, thereby The epoxy resin mixture substantially retards the oxidation of the permanent magnet article. Comprises forming a useful permanent magnet article molded to method of forming a shaped permanent magnet article. 11. An antioxidant composition in which the antioxidant composition is a substantially equivalent high molecular weight sterically hindered phenolic antioxidant,
The method according to claim 10, which comprises a thioester and an oxidation inhibitor. 12. The sterically hindered phenolic antioxidant is 2,2-bis [4- {2- (3,5-di-te].
rt-Butyl-4-hydroxyhydrocinnamoyloxy)} ethoxyphenyl] propane, the thioester is dilaurylthiodipropionate and the oxidation inhibitor is oxalylbis (benzylidenehydrazide). Method. 13. The epoxy resin is present in an amount of about 0.1 to about 10.0% by weight, based on the total mass of the particles, and the antioxidant composition is about 0.03 to about the total mass of the particles. 13. A method according to any of claims 10 to 12 present in an amount of about 4.5% by weight. 14. The method according to claim 10, wherein the article has a density of about 5.8 g / cm ³ .