EP1634306A2

EP1634306A2 - High strength soft magnetic powder composite material

Info

Publication number: EP1634306A2
Application number: EP04741767A
Authority: EP
Inventors: Wolfgang Von Gentzkow; Peter Donner; Jürgen Huber; Gerhard Piecha; Michael Schreyer
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2003-06-13
Filing date: 2004-06-09
Publication date: 2006-03-15
Also published as: WO2004112062A3; WO2004112062A2

Abstract

The invention relates to a high strength soft magnetic powder composite material which comprises a soft-magnetic powder and an oxazolidinone-modified epoxide resin.

Description

description

Soft magnetic powder composite with high mechanical strength

Soft magnetic materials are required in all electrical machines, such as motors and generators, but also in transformers, chokes, transformers, relays, electroacoustic transducers and in many sensors and actuators for guiding the magnetic flux. You determine their shape, component size, performance and efficiency. So far, due to the high magnetic flux densities required, almost exclusively solid iron and iron alloys and - to reduce eddy current losses - packages made of electrically insulated sheets made from these materials have been used. However, the use of sheet metal packages means a not inconsiderable effort, since the sheets have to be painted, punched, compacted and fixed. It reaches its limits when it comes to realizing complex three-dimensional structures.

For this reason, attempts are increasingly being made to implement magnetic flux guidance with highly filled, soft-magnetic powder composite materials with as many degrees of freedom as possible in the shaping and thus to partially replace the laminated cores. Powder composite materials with volume fill levels of more than 80 percent are necessary for this. Commercially available matrix systems based on thermosets show in the iron / plastic composite material with such high filling levels

Flexural strength values of maximum 110 MPa at room temperature (Table 2). This level of strength is not sufficient for many manufacturing processes. These matrix systems cannot be used for applications with complex structures and high mechanical loads. It is known to produce components for magnetic flux guidance in electrical machines, such as stator and rotor of electric motors, from a soft magnetic iron / plastic compound. In DE 2 038 351, iron powder / casting resin systems are unpressurized

Gap filling in the king core used in hysteresis disc motors. DD 45 170 uses, for example, polyester resin in the liquid state as a binder. The non-tack-free and non-storage stable compound is then processed in a continuous process (eg extrusion process). In DD 142 409, a pressure-atomized pure iron powder is mixed with a cold-curing epoxy resin / hardener mixture that is liquid at room temperature to form a flowable compound, molded, cured at room temperature for 24 hours and post-cured at 80 ° C. for 2 hours. No information is given on the filling levels achieved and the mechanical strengths achieved after hardening. However, one prepared in accordance with the described embodiment, so _ß rreicht one maximum filler contents of 80% by weight. DE 2 147 663 describes a similar process with heat-curing epoxy resins of thermal class F. The epoxy resin mixture used for this, which is obviously solid at room temperature, is applied to the iron powder via a solution. The curing takes place at 160 ° C. In the exemplary embodiment given for this purpose, a comparatively low mechanical strength of 85 MPa is described with a degree of filling of 83% by weight. SU 1080220 A describes phenol / formaldehyde resins as binders for the iron powder. The specified test specimens with densities between 6.8 g / cm ^ and 7.0 cm ^ achieve a maximum strength of 75 MPa.

No. 5,321,060 describes iron particles with thermoplastic materials, such as polyphenyl ether, polyether sulfone, polyether imide or for the production of soft magnetic composite materials

Polycarbonate, dry mixed. Subsequently, these iron powder / polymer dry mixtures are small amounts Solvents added, which are removed after intensive mixing. Test specimens are molded and post-cured from such compounds at high temperatures. However, our own experiments on thermoplastic-bonded iron powders show that the level of mechanical properties of the composite materials contained is very low.

WO 99/03622 A1 uses soft-annealed spattery iron powders in combination with a lubricant (wax or polymer). WO 95/29490 A1 describes phenol-formaldehyde resins for binding the spicy iron powder particles. In WO 99/09565 A1, the spattery metal particles are coated with different adhesion promoters or thermoplastics. Compounds produced in this way have the major disadvantage that they are not flowable even under high pressures of 800 MPa and can only be pressed. It is therefore not possible to take geometrically complex structures. After pressing, these have to be worked out mechanically from the pressings using complex machining processes. Another disadvantage is that after the pressing, a complex sintering process must be carried out at 500 ^° C., in which the plastic binder is removed. In some cases, temperatures of 700 to 800 ^° C. are even given. The composites obtained are known to be very brittle and fragile.

All the cited documents show that despite the use of various reactive resins and thermoplastic materials and despite being more complex

Processing methods the mechanical properties of the composite materials obtained are unsatisfactory.

Proceeding from this, the object of the invention is to provide a soft magnetic powder composite material with high mechanical strength. This object is achieved by the inventions specified in the independent claims. Advantageous refinements result from the dependent claims.

The invention relates to soft magnetic iron powder composites, produced by mixing a predominantly spherical iron powder in a multimodal distribution with an oxazolidinone-modified epoxy resin. Such compounds are free-flowing and therefore very easy to dose. They point after the melting of the

Reaction resin component despite very high filling levels of up to 98% by weight of iron powder have a very good flowability during processing and, after hardening, give composite materials with a very high magnetic permeability and a very high mechanical strength.

If commercially available epoxy resins based on chain-extended bis-phenol-A (or F) -diglycidyl ether, which are solid at room temperature, are used to produce iron / plastic composite materials, insufficient values are obtained for the flexural strength at room temperature (Table 2). Surprisingly, it has now been found that composites with oxazolidinone-modified epoxy resins have a significantly higher level of flexural strength than can be achieved with commercially available epoxy resins. This is surprising, since it is generally assumed that a high content of secondary aliphatic OH groups, as is present in the chain-extended bisphenol-A (or F) diglycidyl ether, increases the adhesion to fillers and intercalation components. Since there are no secondary OH groups in the oxazolidinone-modified epoxy resins and nevertheless significantly better mechanical property values are obtained, it is assumed that during the curing of the oxazolidinone-modified epoxy resin, connection structures with high structures are found between the oxazolidinone structures and the surface of the iron powder Form binding energy that brings about the high mechanical strength of the composite material.

To produce the soft magnetic powder composite materials according to the invention, compounds are produced which contain the following components:

1. One or more oxazolidinone-modified structures having prepolymeric epoxy resin compounds obtained by chemical reaction of commercially available epoxy resins with polyisocyanates.

2. One or more difunctional or polyfunctional epoxy resin components.

3. Mainly spherical iron powder in a multimodal distribution.

4. Polymerization initiators or amine or phenolic hardeners.

5. Reaction accelerator

6. Common additives such as flow aids, wetting agents, adhesion promoters, etc.

After the addition of the polymerization initiators, the compounds which can be used according to the invention can be cured anionically or cationically. If amine or phenolic hardeners are added, the hardening is carried out by a polyaddition reaction.

To produce the iron / plastic compounds that can be used according to the invention, the iron powder and the corresponding amount of oxazolidinone-modified epoxy resin are mixed together. This can be done at elevated temperature, that is to say after the epoxy resin, which is solid at room temperature, has been melted, without the addition of solvents. However, the compound is produced particularly advantageously if the oxazolidinone-modified epoxy resin is dissolved in a very low-boiling solvent, for example dichloromethane, and is applied to the iron powder from this solution. If you work with a solution, the solvent is removed again after an intensive mixing process. This can be done, for example, in a ventilated stirred tank, a fluid mixer or with the help of a heated rolling mill. The powdered iron / plastic compound obtained is then further processed in a shaping process. This is done, for example, in a pressurizable tool, particularly advantageously in a press, at an elevated temperature. At the temperatures used during the pressing process, the oxazolidinone-modified epoxy resin passes through a melting phase with low viscosity, which, supported by the spherical particle shape of the iron powder, gives the compound a surprisingly good fluidity for highly filled mixtures. In this state, undercuts in the press mold can also be perfectly filled with molding compound during the molding process. This is an important prerequisite for the implementation of complex component geometries. In addition, the low melt viscosity during the shaping before hardening enables a very good and complete wetting of the iron surface with the reaction resin.

The use of oxazolidinone-modified epoxy resins, as described in EP 0 828 774 B1, is particularly advantageous. These form one-component compounds which are stable in storage with the iron powders and which can be cured very quickly thermally by polymerization to give the powder composite materials according to the invention.

After processing the iron / plastic compounds in the molding process, powder composites are used excellent mechanical property level and very good ^■ soft magnetic properties.

Examples

Example 1: Preparation of the curable iron / plastic compound

3.98 g of the epoxy-functional reaction resin are dissolved together with 0.02 g of l-cyanoethyl-2-phenylimidazole as a catalyst in about 20 g of dichloromethane. In the case of the reaction resin II modified with oxazolidinone, 4 g or 3 g of reaction resin are dissolved. Since this resin already contains the reaction accelerator, no further catalyst is required. 96 or 97 g of the multimodal iron powder mixture with a predominantly spherical particle shape are added to the solution and mixed very intensively. Once the solvent has evaporated to the extent that a pasty mixture is present, it is calendered on a roller mill for approx. 5 minutes (roller temperature maximum 120 ° C) for intimate mixing and for wetting the iron surface with reactive resin as well as for removing the solvent. The so-called "fur" obtained is then comminuted and stored in a vacuum cabinet for at least 16 h at room temperature and reduced pressure of a maximum of 100 mbar to completely remove the solvent. Table 1: Composition of iron-plastic composites with different thermoset matrix systems

!) Oxazole. -modif. Epoxy resin I according to EP 0 113 575 Al ²⁾ oxazole. -modif. Epoxy resin II according to EP 0 828 774 B1, sufficient reaction accelerator is already contained in the epoxy resin

Example 2: Production and testing of the test specimens

To process the compound, the dried powder is placed in a mold for producing a plate-shaped test specimen, which is then first heated in a press without pressure. At 100 ° C, a pressure of approx. 130 MPa is built up over the die of the tool, the mold is brought to a temperature of 170 to 190 ° C and this state is maintained for 60 minutes. The test specimen is then removed from the mold and can be post-hardened if necessary at temperatures ≥ 150 ° C. Bars for the three-point bending test are then sawn out of the test specimen. Table 2: Mechanical property values of iron / plastic composites with various thermoset matrix systems and flow behavior of the corresponding compounds

To determine the magnetic properties (Table 3), 80 g of iron / plastic compound, consisting of the amounts of oxazolidinone-modified epoxy resin II and iron powder in a ring shape given in Table 3 at a pressure of 40 - 50 kN / cm ² and a temperature of 100 ° C - 170 ° C hot pressed.

Table 3: Magnetic property values of iron / plastic composites

To determine the flow length, 46 g of the iron / plastic compound described in Example 1 are placed in the storage volume of a spiral flow mold and with a Stamp at 100 ° C / 400 MPa in the semicircular, 5 mm wide and deep, spiral flow channel. After opening the flow mold, the flow length can be measured.

Claims

claims

1. White magnetic composite material, characterized by - prepolymeric epoxy resin compounds having one or more oxazolidinone-modified structures, - a soft magnetic powder.

2. Composite material, characterized in that the prepolymeric epoxy resin compounds having one or more oxazolidinone-modified structures are obtained by chemical reaction of epoxy resins with polyisocyanates.

3rd Composite material, that is, that the composite material contains di- and / or polyfunctional epoxy resin components.

4. Composite material according to one of the preceding claims, characterized in that the soft magnetic powder is iron powder, in particular iron powder in a multimodal distribution.

5. Composite material according to one of the preceding claims, characterized in that the composite material contains polymerization initiators.

6. Composite material according to one of the preceding claims, characterized in that the composite material is amine and / or phenolic

Contains hardener.

7. Composite material according to one of the preceding claims, characterized in that the composite material contains reaction accelerators.

8. Composite material according to one of the preceding claims, characterized in that the composite material contains conventional additives.

9. Production method for producing a soft magnetic composite material, in which a soft magnetic powder and oxazolidinone-modified epoxy resin are mixed together.

10. Magnetic body containing a soft magnetic composite according to one of claims 1 to 8.

11. Electrical machine containing a magnetic body according to claim 10.