Curable composition

Abstract

A curable composition includes a curable resin and a magnetic body, wherein the magnetic body comprises magnetic particles and a surface treatment agent present on a surface of the magnetic particles. The curable composition has low viscosity, and fluidity, and capable of effectively cured without causing curing shrinkage or the like to form a cured product having desired physical properties.

Claims

1. A curable composition, comprising: a curable resin and a magnetic body, wherein the magnetic body comprises magnetic particles and a surface treatment agent present on a surface of the magnetic particles, wherein the surface treatment agent has an acid value in a range of 10 to 400 mg KOH/g, or an amine value in a range of 5 to 400 mg KOH/g.

2. The curable composition according to claim 1, wherein the curable composition has a room-temperature viscosity of 10,000 cP or less at a shear rate of 100 s.sup.?1.

3. The curable composition according to claim 1, wherein the curable composition has dielectric breakdown strength of 10 kV/mm or more, or the curable composition is configured to form a cured product having dielectric breakdown strength of 10 kV/mm or more.

4. The curable composition according to claim 1, wherein the curable resin comprises an alkenyl group, an acryloyl group, a methacryloyl group, an epoxy group, an oxetane group, an alkenyl group, a hydrogen atom bonded to a silicon atom, an isocyanate group, a hydroxyl group, a phthalonitrile group or a carboxyl group.

5. The curable composition according to claim 1, wherein the curable resin is a polysilicone resin, polyimide, polyether imide, polyester imide, an acrylic resin, a vinyl resin, an olefin resin, a polyurethane resin, an isocyanate resin, an acrylic resin, a polyester resin, a phthalonitrile resin, polyamic acid, polyamide or an epoxy resin.

6. The curable composition according to claim 1, wherein the magnetic particles are multi-domain type magnetic particles.

7. The curable composition according to claim 1, wherein the surface treatment agent is a polyol-based compound, a polysiloxane-based compound, an alkyl phosphoric acid-based surface treatment agent, an alkylcarboxylic acid-based surface treatment agent, an alkyl sulfonic acid-based surface treatment agent, an acid compound containing a long-chain alkyl group, an acrylic copolymer containing an acidic functional group or an amino group, an aromatic acid-based surface treatment agent or a block copolymer containing an acidic functional group or an amino group.

8. The curable composition according to claim 1, wherein the magnetic body comprises 0.01 to 30 parts by weight of the surface treatment agent relative to 100 parts by weight of the magnetic particles.

9. The curable composition according to claim 1, wherein the magnetic body further comprises a secondary surface treatment agent bonded to the surface treatment agent.

10. The curable composition according to claim 9, wherein the secondary surface treatment agent is a polyurethane-based surface treatment agent, a polyurea-based surface treatment agent, a poly(urethane-urea)-based surface treatment agent compound or a branched polyester-based surface treatment agent.

11. The curable composition according to claim 9, wherein the magnetic body comprises 0.01 to 30 parts by weight of the secondary surface treatment agent relative to 100 parts by weight of the magnetic particles.

12. The curable composition according to claim 1, comprising 0.01 to 60 parts by weight of the magnetic body relative to 100 parts by weight of the curable resin.

13. An electric motor, comprising: a stator in which one or more slots are formed; windings present in the slots of the stator; and a cured product of the curable composition of claim 1, wherein the cured product is present in the slots.

14. The electric motor according to claim 13, wherein the slot has an opening area in a range of 0.5 to 10 cm.sup.2.

15. A method for manufacturing an electric motor, comprising: introducing the curable composition of claim 1 into one or more slots into which windings are introduced, the slots being formed in a stator; and applying an alternating magnetic field capable of induction heating of the magnetic body in the curable composition.

16. The curable composition of claim 1, wherein the magnetic particle has a coercive force in a range of 1 kOe to 200 kOe.

17. The curable composition of claim 1, wherein the magnetic particles have a saturation magnetization value at room temperature of 20 emu/g to 150 emu/g.

18. The curable composition of claim 1, wherein the magnetic particles have an average particle size of ranging from 20 nm to 300 nm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIGS. 1 and 2 are schematic diagrams of an exemplary stator.

(2) FIG. 3 is a schematic diagram showing a state where a winding is introduced into the stator.

(3) FIG. 4 is a view illustratively showing a process of introducing a curable composition into a slot of a stator to which a winding is introduced.

EXPLANATION OF REFERENCE NUMERALS

(4) 100: stator 101: slot 102: winding 200: nozzle

MODE FOR INVENTION

(5) Hereinafter, the present application will be described in detail by way of examples and comparative examples, but the scope of the present application is not limited to the following examples.

(6) 1. Measurement Method of Viscosity

(7) A viscosity of a curable composition was measured using a Brookfield DV2LV viscometer. Using the viscometer, the viscosity was measured at room temperature by adjusting the rpm to satisfy a condition of a shear rate of 100 s.sup.?1 using a spindle #16.

(8) 2. Evaluation Method of Room-Temperature Stability

(9) Room-temperature stability of a curable composition was confirmed by introducing the curable composition prepared in Example or Comparative Example into a vial of 20 mL in an amount of about 10 mL and then evaluating the time point when phase separation of the magnetic body and the curable resin occurred while keeping the temperature at room temperature. The room-temperature stability was evaluated by evaluating the time point when the phase separation or precipitation of the magnetic body was confirmed visually and confirming the time of the time point.

(10) 3. Dielectric Breakdown Strength

(11) Dielectric breakdown strength was evaluated according to ASTM D149 standard for a cured product of a curable composition. The cured product was made into a specimen that the width and height lengths are each 100 mm or so and the thickness is 1 to 3 mm, and the dielectric breakdown strength was measured according to the standard and then converted to the dielectric breakdown strength per unit thickness.

(12) 4. Evaluation of Hardness

(13) A cured product of a curable composition was molded into a specimen that the width and height lengths are each 100 mm or so and the thickness is 12 mm or so, and hardness was measured with a durometer according to ASTM D2240 standard.

(14) 5. Evaluation of Filling Rate

(15) After a cured product of a curable composition was formed inside the slot of the stator, into which the windings were introduced, by the method described in Examples or Comparative Examples, the stator was cut to check the amount of the cured product filled in the slot, and then the percentage of the volume of the cured product was obtained relative to the entire slot internal volume, thereby determining a filling rate.

Production Example 1. Magnetic Particles (A)

(16) As magnetic particles (A), MnOFe.sub.2O.sub.3 particles were applied. The magnetic particles (A) had an average particle size of about 100 nm, a coercive force of about 94 kOe and a saturation magnetization value of about 80 emu/g or so when measured by FESEM (field effect scanning electron microscope) and DLS (dynamic light scattering). Here, the coercive force and the saturation magnetization value were measured under an external magnetic field of 1 Tesla to a vibrating sample magnetometer (SQUID-VSM, Korea Basic Science Institute) using an H-S curve (VSM curve).

Production Example 2. Production of Magnetic Body (A)

(17) The magnetic body (A) subjected to the surface treatment of the magnetic particles of Production Example 1 was produced in the following manner. As the surface treatment agent, a surface treatment agent (BYK-180) having an acid value of about 94 mgKOH/g and an amine value of about 94 mgKOH/g was applied. The surface-treated magnetic body (A) was produced by uniformly mixing the magnetic particles (A) of Production Example 1 and the surface treatment agent in a weight ratio of 100:10 (magnetic particles:surface treatment agent) using a planetary mixer.

Production Example 3. Production of Magnetic Body (B)

(18) The magnetic body (A) of Production Example 2 was further surface-treated to produce a magnetic body (B). At this time, as the additional surface treatment agent, a mixture of poly(urethane-urea) having an amine value of about 25 mgKOH/g and a molecular weight (Mw) of about 20,000 and polyurethane with a molecular weight (Mw) of about 20,000 or so formed by urethane reaction of HMDI (hexamethylene diisocyanate) and PG (polypropylene glycol) (mixing ratio:about 1:3 (poly(urethane-urea):polyurethane)) was used. The used poly(urethane-urea) included hexamethylene diisocyanate as a diisocyanate compound, propylene diamine as a polyamine and ethylene glycol as a polyol in a weight ratio of 1:5:4 (diisocyanate:polyamine:polyol). The magnetic body (B) was produced by uniformly mixing the magnetic body (A) produced in Production Example 2 and the surface treatment agent in a weight ratio of 100:0.5 (magnetic body (A):surface treatment agent) using a planetary mixer.

Production Example 4. Production of Magnetic Body (C)

(19) The magnetic particles of Production Example 1 and a surface treatment agent (BYK-220S) having an acid value of 100 mgKOH/g or so were uniformly mixed with a planetary mixer in a weight ratio of 100:5 (magnetic particles:surface treatment agent) to produce a primary surface-treated magnetic body. The mixing was performed by blending the magnetic body and the surface treatment agent so that the concentration of the magnetic particles in the epoxy resin applied in Example 3 was about 5 weight %. Subsequently, a branched polyester-based surface treatment agent (hyperbranched polyester) (BYK-2152) and the primary surface-treated magnetic body were uniformly mixed with a planetary mixer in a weight ratio of about 10:1 (magnetic body:BYK-2152) to produce a magnetic body (C).

Example 1

(20) The curable polyester imide having a room-temperature viscosity (condition of shear rate of 100 s.sup.?1) of about 4,000 to 6,000 cP as measured by the above method and a temperature index of 180? C., the magnetic body (A) of Production Example 2 and a leveling agent (BYK 333) were mixed to prepare a curable composition. Here, the ratio of the magnetic body in the curable composition was about 5 weight %, and the ratio of the leveling agent in the curable composition was about 0.5 weight %. The viscosity of the prepared curable composition was about 4,530 cP or so (shear rate 100 s.sup.?1) at room temperature. The relevant curable composition was coated in a film form (thickness:about 2 mm) and the curing by induction heating was performed by applying an alternating magnetic field. The alternating magnetic field was applied for 2 minutes so that the applied alternating magnetic field intensity was about 25 mT or so, and the frequency at the time of applying the alternating magnetic field was about 340 kHz or so. The application of the alternating magnetic field was performed using a coil from AMBRELL (AMBRELL, EASY HEAT 820, ? 30 mm, 3 turns solenoid type coil).

(21) On the other hand, as shown in FIG. 1, a cylindrical stator was prepared. The slots were formed radially in the stator, as shown in FIG. 1, and the openings were in the form of rectangles having a width of about 5 mm or so and a length of about 20 mm or so. Windings (102) (copper wires) were introduced into the slot, as shown in FIG. 3. As the windings, those having a circular cross section having a diameter of 4.5 mm or so were used, and 5 relevant windings were introduced into one slot. Then, the curable composition was injected into the slot in the manner shown at the leftmost portion of FIG. 4 and the curable composition was filled inside the slot by tilting the stator as in the middle and rightmost views of FIG. 4. Subsequently, the curable composition was cured in the same manner as described above and the filling rate was evaluated. At the time of evaluating the filling rate, the stator was cut in a direction perpendicular to the longitudinal direction, and a portion where the cured product of the curable composition was present was confirmed using a UV lamp, whereby the filling rate of the cured product was obtained.

Example 2

(22) A curable composition was prepared in the same manner as in Example 1, except that the magnetic body (B) of Production Example 3 was applied as the magnetic body. The viscosity of the prepared curable composition was about 4,810 cP or so (shear rate 100 s.sup.?1) at room temperature. A specimen and a stator were prepared in the same manner as in Example 1 using this curable composition, and applied to the evaluation. However, in the case of Example 2, the application time of the alternating magnetic field was adjusted to a level of about 90 seconds.

Example 3

(23) A curable epoxy resin (manufactured by Kukdo Chemical Co., Ltd., room-temperature viscosity: 10,000 cP, epoxy equivalent 200, bisphenol A type epoxy resin), the magnetic body (C) of Production Example 3 and a cationic initiator (manufactured by Samsin Chemical Co., Ltd., B2A) were mixed to prepare a curable composition. Here, the ratio of the magnetic body in the curable composition was about 5 weight %, and the ratio of the cationic initiator in the curable composition was about 0.2 weight %. The viscosity of the prepared curable composition was about 6,100 cP or so (shear rate 100 s.sup.?1) at room temperature. A specimen and a stator were prepared in the same manner as in Example 1 using this curable composition, and applied to the evaluation. However, in the case of Example 3, the application time of the alternating magnetic field was adjusted to a level of about 80 seconds.

Comparative Example 1

(24) A curable composition was prepared in the same manner as in Example 1, except that the magnetic particles (A) of Production Example 1 were applied. The viscosity of the prepared curable composition was about 4,340 cP or so (shear rate 100 s.sup.?1) at room temperature. A specimen and a stator were prepared in the same manner as in Example 1 using this curable composition, and applied to the evaluation. However, in Comparative Example 1, the application time of the alternating magnetic field was adjusted to about 3 minutes or so.

Comparative Example 2

(25) A curable composition was prepared in the same manner as in Example 3, except that the magnetic particles (A) of Production Example 1 were applied. The viscosity of the prepared curable composition was about 6,800 cP or so (shear rate 100 s.sup.?1) at room temperature. A specimen and a stator were prepared in the same manner as in Example 1 using this curable composition, and applied to the evaluation.

(26) The evaluation results of the respective examples and comparative examples were summarized and described in Table 1 below.

(27) TABLE-US-00001 TABLE 1 Room- Dielectric temperature breakdown Filling stability strength Hardness rate Example 1 96 hours 20 kV/mm 87 89% 2 480 hours 20 kV/mm 87 92% 3 360 hours 20 kV/mm 91 86% Comparative 1 72 hours 19 kV/mm 85 79% Example 2 96 hours 19 kV/mm 90 74%

(28) From the results of Table 1, the curable composition of the examples exhibited extraordinarily excellent room-temperature stability and filling rates as compared with the comparative examples. Also, in the case of the comparative examples, it could be confirmed that the partially phase-separated portions were visually observed even in the cured products, and other physical properties were also poor.