Composite thin film insulator, manufacturing method thereof, and electric rotating machines using the composite thin film insulator

Abstract: The present invention is aimed at improving adhering property of a thin film insulator, which is used for insulation among layers and to the earth of electric apparatus such as induction motor coils, between mutual thin film insulators and between the thin film insulator and a conductive body. The thin film insulator relating to the present invention is composed of a polyester film 1a, polyester unwoven cloth sheets 1b, a reconstituted mica paper 2, and epoxy resin 3, wherein the mica paper 2 is adhered on a surface of a laminated plastic film·unwoven cloth sheet 1, which is formed previously by adhering the polyester unwoven cloth sheet 1b to each of upper and lower surfaces of the polyester plastic film 1a without any binder by heating and melting, by impregnating the epoxy resin 3 into the polyester unwoven cloth sheet 1b and the mica paper and heating for curing.

Description: Background of the Invention (1) Field of the Invention: The present invention relates to a composite thin film insulator, a manufacturing method thereof, and electric rotating machines using the composite thin film insulator, for instance, insulating material used as tapes or sheets for insulation between layers of conductors and to the earth in an induction motor, and especially relates to composite thin film insulators using mica. (2) Description of the Prior Art: Conventionally, reconstituted mica tape which is superior in insulating performance is used for insulation between layers and to the earth of coils in electric motors. Mica in the reconstituted mica tape can not be used alone as an insulator because mica itself is inferior in mechanical properties such as bending strength, tensile strength, and elongation. Therefore, mica is used as composite tape reinforced by adhering a backing such as film such as polyester film, unwoven fabrics such as polyester unwoven cloth, or glass cloth, with a binder, as disclosed in, for example, EP-A-413179, EP-A-406477, WO-A-8100986 and GB-A-1426575 Especially, in accordance with current advancements in decreasing size and weight of electric motors, insulating material with improved heat resistance and decreased insulating thickness is required for use in coils. Therefore, reinforced material which is reinforced by adhering plastics film which has high heat resistance and thin insulating thickness is widely used. The reconstituted mica tape with adhered plastics film is generally contained in an iron core slot after being wound around a coil, impregnated with a non-solvent type resin such as epoxy resin, and cured by heating so as to adhere the conductor and the tape, the tapes mutually, and the iron core slot. Further, in the case of a coil for large size electric motors, semi-cured insulating tape comprising the reconstituted mica, a backing, and a semi-cured binder for adhering is wound around a coil, and subsequently, the semi-cured insulating tape is cured by heating with a heat-pressing machine so as to adhere the conductor and the tape, and the tapes mutually, with the semi-cured binder contained in the insulating tape. For instance, JP-A-3077203, corresponding to EP-A-413179, discloses such insulating materials for electric rotating machines as described above. Actually, the reconstituted mica having adhered plastics film backing, which is wound around a coil, forms an insulating layer with the binder, and the materials act effectively against various stresses on the coil. For instance, both the plastics film and the reconstituted mica are effective against electrical stress, the plastics film is effective against mechanical stress, and the plastics film is effective against thermal stress, and integrally the reconstituted mica has a superior performance. However, among materials which mutually adhere tight with the binder to form the insulating layer, the adhering force between the plastics film and the reconstituted mica is relatively weak, and further, differences in linear thermal expansion coefficients exist among the various materials. Accordingly, the insulating layer has the disadvantage that separation may occur between the plastics film and the reconstituted mica due to repeated heat cycles over a long period of operation. Even if the degree of separation between the plastics film and the reconstituted mica is small when it first occurs, the separation is deemed to be a problem because the degree of separation grows due to repeating thermal stresses and added mechanical stresses such as vibration of the electric motor, and finally the separation causes breakage of the insulating layer. Summary of the Invention The object of the present invention is to provide a composite thin film insulator, which suffers less or no separation by heat cycles over a long use period and insulation breakage by repeated thermal stress and added mechanical stress, and also to provide a manufacturing method thereof, and electric rotating machines using the composite thin film insulator. The invention provides a method of manufacturing a composite thin film insulator as set out in claim 1. The invention further provides a composite thin film insulator as set out in claim 5. Furthermore, the invention provides an electric rotating machine as set out in claim 7. In accordance with the present invention, the reconstituted mica and the unwoven cloth sheet can be adhered tightly with a binder, and the unwoven cloth sheet and the plastics material film, the surface of which is smooth and not easily adhered, are mechanically adhered by melting with heating and pressing without a binder. Therefore, the unwoven cloth can be adhered tightly with both the plastics material film and the reconstituted mica. Accordingly, insulators in a balanced adhering condition can be provided, and superior insulation, in which the insulating layer does not easily separate, can be achieved by using the above insulator of the present invention for coil insulation of electric motors. Brief Description of the Drawings FIG. 1 is a partial perspective view of the composite thin film insulator which is an embodiment of the present invention, and FIG. 2 is a flow sheet for explaining manufacturing steps of the composite thin film insulator shown in FIG. 1. Detailed Description of the Embodiments Hereinafter, the present invention is explained in detail referring to the embodiment shown in FIGs. 1 and 2. FIG. 1 shows an embodiment of the present invention in which polyester film 1a for the plastics film, polyester unwoven cloth sheet 1b for the unwoven cloth sheet, the reconstituted mica 2, and epoxy resin 3 for the binder were used. As shown in FIG. 1, the composite thin film insulator embodying the present invention comprises polyester film 1a, polyester unwoven cloth sheets 1b adhered by melting to both upper and lower surfaces of the polyester film 1a, and reconstituted mica 2 adhered to a surface of polyester unwoven cloth sheet 1b with epoxy resin 3. FIG. 2 is a flow sheet indicating manufacturing steps of the composite thin film insulator shown in FIG. 1. First, a polyester film 1a and polyester unwoven cloth sheets 1b which are lapped at both upper and lower surfaces of the polyester film 1a are laminated by heating and pressing treatment to obtain a laminated sheet 1 of which lapped portions are adhered by melting. Subsequently, epoxy resin 3 is applied at a surface of one of the polyester unwoven cloth sheets of the laminated sheet 1, a reconstituted mica paper 2 is laid on the epoxy resin carrying surface of the polyester unwoven cloth sheet to impregnate the epoxy resin 3 into both the reconstituted mica paper 2 and the polyester unwoven cloth sheet 1b, and the reconstituted mica paper 2 and the polyester unwoven cloth sheet are adhered together by heat treatment to cure the epoxy resin 3. Consequently, a composite thin film insulator composed of an integrated body of the laminated sheet 1 and the reconstituted mica paper 2 is formed. After rolling the insulator up, the roll is cut into tapes and sheets having various designated widths depending on their use, and the tapes and sheets are used as insulators between layers and to the earth of coils for electric motors. Strength against separation occurring between respective adjacent materials (Mica-Unwoven cloth and Film-Unwoven cloth) of the composite thin film insulator manufactured in a manner according to the invention explained above is, as shown in Table 1, approximately 2.5 times the strength of conventional composite polyester film-reconstituted mica paper insulating material (Mica-Film) which has been used for insulation with respect to earth of coils for electric motors, and it reveals that adhesion among materials in the composite thin film insulator embodying the present invention is significantly improved. Material Bonding method Strength against separation (relative value) Mica - Film Binder 100 Mica-Unwoven cloth Binder 250 Film-Unwoven cloth adhering by melting 350 Consequently, when the composite thin film insulator of the present invention is used as an insulator to the earth of a coil for an electric motor, separation between respective materials in the composite thin film insulator and between overlapped portions of the composite thin film insulator due to thermal stress caused by heat cycles such as operation and stop can be prevented. In the present embodiment, an example of composition materials of thermal classes B - F classes in the thermal resistance classification is illustrated. However, for the plastics films, other films such as polyamide film, polyimide film, polyamide imide film, or composite films wherein other high polymer materials are chemically combined to the above films as a main component can be used. Further, for the unwoven cloth sheet, various unwoven cloths other than polyester fiber which is shown in the present embodiment such as polyamide fiber, glass fiber, or ceramic fiber can be used. As for the binder, silicone resin, polyimide resin, or unsaturated polyester resin and the like can be used. The above described materials can be used in various combinations depending on conditions such as the thermal resistance classification, or the use environment. By using the composite thin film insulator explained in the above embodiment for insulation of electric rotating machines, such as for insulating among layers or with respect to earth of stator coils and rotator coils, a superior insulator having a strong adhesion strength against thermal stresses caused by heat cycles can be provided. In the invention, because the reconstituted mica and the unwoven cloth sheet are adhered tightly with a binder, and the unwoven cloth sheet and plastics material film, the surface of which is smooth and hard to adhere, are adhered mechanically by melting with heating and pressing without using a binder, the unwoven cloth sheet can be tightly adhered to both plastics material film and the reconstituted mica. Therefore, no separation is generated even by heat cycles during a long operation period, and no breakage of insulation occurs even if repeated thermal stresses and mechanical stresses are added. Accordingly, the composite thin film insulator of the present invention is very effective in use as an insulator.

Claims: A method for manufacturing a composite thin film insulator comprising the steps of; adhering an unwoven cloth sheet (1b) at each of upper and lower surfaces of a plastics material film (1a) by melting to form a laminated sheet (1), and adhering a mica sheet (2) at a surface of one of said unwoven cloth sheets (1b) of the laminated sheet (1) with a binder (3). A method according to claim 1, comprising the steps of; lapping said unwoven cloth sheets (1b) at the upper and lower surfaces of the plastics material film (1a), heating and pressing said plastics material film (1a) lapped with said unwoven cloth sheets (1b) to form said laminated sheet (1) by mutual adhesion due to melting, applying a heat-curable resin (3) as a binder at a surface of at least one of (i) one of said unwoven cloth sheets (1b) of the laminated sheet (1) and (ii) said mica sheet (2), joining the unwoven cloth sheet (1b) and the mica sheet (2) together by means of the resin (3), with impregnation of the resin (3) into both the unwoven cloth sheet (1b) and the mica sheet (2), and adhering the unwoven cloth sheet (1b) and the mica sheet (2) together by heating the resin (3) to cure it. A method according to claim 1 or 2, wherein said plastics material film (1a) is composed of an insulating material selected from polyester, polyamide, polyimide, polyamide-imide, or is a composite film having a main body of polyester, polyamide, polyimide or polyamide-imide which is chemically combined with another high polymer material, said unwoven cloth sheet (1b) is an insulating unwoven cloth sheet composed of any one of polyester fibre, polyamide fibre, glass fibre and ceramic fibre, said mica sheet (2) is composed of reconstituted mica foil, and said binder (3) is an adhesive material composed of any one of epoxy resin, silicone resin, unsaturated polyester resin and polyimide resin. A method according to claim 1 or 2, wherein said binder (3) to adhere the laminated sheet (1) and the mica sheet (2) is cured to form an integrated insulator in either a dry condition wherein said resin is cured completely, or a semi-cured condition wherein said resin is cured incompletely. A composite thin film insulator composed of a plastics material film (1a), unwoven cloth sheets (1b) adhered to each of upper and lower surfaces of said plastics material film (1a) by melting, and a mica sheet (2) which is adhered to a surface of one of said unwoven cloth sheets (1b) by a binder. A composite thin film insulator according to claim 5, wherein said plastics material film (1a) is composed of an insulating material selected from polyester, polyamide, polyimide, polyamide-imide, or is a composite film having a main body of polyester, polyamide, polyimide or polyamide-imide which is chemically combined with another high polymer material, said unwoven cloth sheet (1b) is an insulating unwoven cloth sheet composed of any one of polyester fibre, polyamide fibre, glass fibre and ceramic fibre, said mica sheet (2) is composed of reconstituted mica foil, and said binder (3) is an adhesive material composed of any one of epoxy resin, silicone resin, unsaturated polyester resin and polyimide resin. An electric rotating machine comprising a stator, a stator coil arranged in a slot of said stator, a rotor coil arranged in a rotor slot at a location so as to cooperate magnetically with said stator coil, and a rotor supported in a rotatable manner in a concentric relationship with said stator, characterised by composite thin film insulator material composed of a plastics material film (1a), unwoven cloth sheets (1b) adhered to each of upper and lower surfaces of said plastics material film (1a) by melting, and a mica sheet (2) which is adhered to a surface of one of said unwoven cloth sheets (1b) by a binder (3), said insulator material insulating between layers and with respect to earth of at least one of said stator coil and said rotator coil.

Inventors: KANO IKUSHI, KOIDE TOSHIYUKI, MARUYAMA SYOICHI, KANO, IKUSHI, KOIDE, TOSHIYUKI, MARUYAMA, SYOICHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1995
Main classification: B32B19
IPC codes: H01B3, H02K3, B32B19