CA1199768A

CA1199768A - Foil manufacture

Info

Publication number: CA1199768A
Application number: CA000433321A
Authority: CA
Inventors: Gottfried Deutschmann; Helmut Gsellmann
Original assignee: Isovolta Osterreichische Isolierstoffwerke AG
Current assignee: Isovolta AG
Priority date: 1982-07-27
Filing date: 1983-07-27
Publication date: 1986-01-28
Also published as: AT387356B; AU1774583A; ZA835471B; EP0113741B1; JPS60500048A; AU565559B2; IN158759B; WO1984000515A1; DE3368223D1; IT8322223A0; IT1163849B; EP0113741A1; ATE24145T1; ATA288782A

Abstract

ABSTRACT OF THE DISCLOSURE
A process for the production of an electrical insulating foil com-prising substantially a thin-layer of electrical grade mica powder and a hardenable synthetic resin comprising forming a paste of electrical grade mica and a hardenable synthetic resin and optional fillers and/or reinforcement materials, forming a strand of said paste and subjecting the pasty strand to a calender or ribbon press to reduce the strand thickness into a thin-layer.

Description

76~3 STATE OF THE ART
The use of area insulatiny materials based on fine mica for the electrical insulation of coils and conductor rods of heavy-duty electrical machines is known and the said insulating materials are usually made of a support material such as glass fiber cloths or thermostable plastic foils bonded to a fine mica paper impregnated with a thermosetting resin which acts as a binder. The thermosetting resin in the said insula-ting material is in the B-state. The said area electrical insulating materials are applied to the element to be insula-ted such as a conductor rod as a tape or as a wide material and the coated element is heated in a coil press to cure the insulation and form the final product.
The preparation of the known area insulating materials is relatively expensive as the fine mica paper has to be prepared from mica in a suitable manner and then the support material and the fine mica paper are coated with the thermosetting resin and finally bonded together by calendering.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an inexpensive method of producing an electrically insulating foil made of a hard-enable synthetic resin and electrical grade mica and the foil pro-duced thereby.
It is another object of the invention to provide a novel method of electrically insulating elements and the elements pro-duced thereby.
These and other objects and advantages of the invention will become obvious from the following detai]ed description.

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THE INVENTION
The invention provides a process for the production of an electrical insulating foil comprising substantially a thin-layer of electrical grade mica powder and a hardenable syn-thetic resin with a thickness of 0.1 to 0.5 mm comprising the steps oE
forming a pas-te of electrical grade mlca powder and a hardenable substantially solvent free synthetic resin and optional fillers and/or reinforcement material, forming a strand of said paste and evenly distributing the pasty strand over the entrance of a calender or a ribbon press to reduce the strand thickness into a thin-layer 0.1 to 0.5 mm thick. The foil preferably has a thick-ness of about 0.2 mm.
The expression "electrical grade mica" means mica mater-ia] free of all electrically conductive compounds or materials such as metals and the preferred mica is muscovite or phlogopite based powder with a grain range of 0.03 to 2.8 mm. The pasty strand preferably contains 35 to 70% by weight, more preferably 45 to 65% by weight, of the mica powder and up to 20% by weight of fillers and/or reinforcing materials.
The hardenable synthetic resin mixture may be based on an epoxy resin, a polyester resin or a silicone resin. Preferred are mixtures of epoxy resins with epoxy equivalents of 150 to 800.
The hardenable resins will contain a hardener such as an amine dissolved in a reactive thinner such as diphenyl glycidyl e-ther, butanediol diglycidyl ether or more preferably a low viscosity cycloaliphatic epoxy resin. The hardenable synthetic resin may be used in the liquid state.
In a preferred embodiment of the invention, a mixture of '~

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resin and mica and optional filler and/or reinforcement materials is added to an extruder and the hardener is separately added to the extruder whereby mixing of the pasty material takes place in the extruder itself.
In a preferred embodiment of the invention, the pasty strand is supplied to the calender nip or the nip of the ribbon press between two incoming webs of sheet type ma-terial and prefer-ably the thin layer produced in the calender or ribbon press is permanently bonded to at leas-t one of the sheet type webs or advantageously a fiber fabric web is placed between the pasty - 2a -'' '~' ~3 ~ ~ a~
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strand and one of the webs of sheet material before entry into the calender nip or nip of the ribbon press. The fiber fabric web is permanently bonded to the thin foil produced thereby.
While the production of the resin foils using an extruder followed by calendering is known, one skilled in the art would not expect the calender-ing of a strand of a mixture of mica powder and resin would produce a foil or thin layer in which the mica powder particles are oriented essentially parallel to the foil surfaces by the thickness reduction of the strand in the calender.
The particle orientation of the mica par~icles parallel to the layer surfaces is similar to tha-t of mica in known mica paper which is important to obtain high electrical strength values.
Referring now to the drawing:
The Figure is a schematic view of an apparatus for carrying out the process of the invention.
The apparatus of the Figure comprises a heatable double screw extruder 1 with only one of the two screws 2 being illustrated in the drawing. The extruder housing is connected to feed hopper 4 by feed inlet 3 into which mi.ca powder 6 is metered from supply tank 5 by metering spiral 7 and inlet feed 3 is also connected via line 8 and proportioning pump 9 to heatable storage vessel 10 for the hardenable resin. A second feed inlet 12 offset relative to inlet 3 in the direction of arrow 10 is connected via line 13 and proportion-ing pump 14 to storage vessel 15 holding hardener solution 31. The extruder 1 is provided with orifice 16 for extrusion of a round strand and can pivot in oscillation at the point of orifice 16 as indicated by 17 in a direction perpendicular to the drawing plane.
Following the extruder is a calendar with a pair of heatable calendar rolls 18 which enclose nip 19 and provided with a draw-off device for foil product 20 comprising two guide rollers 21 and 22, a pair of draw-off rollers 23 and a winding device 24. The ca.lender is also provided with unrolling devices 25, 26 and 27 to feed two separate foils 28 in tape form and glass fiber fabric 29 to ni~ 19.
To produce an area electrical insulating material in ribbon form with a thickness of 0.2 mm consisting of a foil of a thermosetting epoxy resin and mica powder on one surface and a fiber glass fabric web on the other surface, a muscovite-based mica powder with about 50% by weight having a grain size o 0.08 to 0.10 mm and about 50% by weight having a grain size of 1.5 to 1.8 mm is placed in storage tank 5 and an epoxy resin mixture 30 consisting of 7 parts by weight of epoxy resin with an epoxy equivalent of 200 and 3 parts by weight of epoxy resin with an epoxy equivalent o 420 is placed in heatable storage vessel lO. A latent amine hardener in solution in a reactive thinner 31 is placed in storage vessel 15 and the fiber glass fabric 29 has a thickness of 0.04 mm. The separating foils 28 made of polyethylene terephthalate have a thickness of 0.03 mm.
Mica powder 6 and liquid epoxy resin 30 are continuously fed together in a wei.ght ratio of 58:41 respectively through inlet 3 and are intimately mixed in first mixing ~one 32 of extruder l. At inlet 12, l part by weight of hardener solution 31 is added to the mica-resin mixture whereby extruder screws

2 transports a uniform mixture of resin-mica-hardener solution to orifice 16.
The temperature of the mixture in the extruder is maintained at about 100C over the entire screw length and is lowered to 85 to 90C at orifice 16.
By oscillation of the extruder in the area of orifice 16 in a direction per-pendicular to the drawing plane, the pa.sty strand 33 continuously issuing from orifice 16 is supplied to nip 19 with even distribution over the total width thereof between two separating foils 28 fed from unwind.ing devices 25 and 27.

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Fiber glass web 29 is supplied from unwinding device 26 between one of separat-ing foils 28 and pasty strand 33.
The material of the pasty strand 33 is continuously transformed between heated calender rollers 18 maintained at 75C into a thin foil which becomes permanently bonded to fiber glass fabric web 29. The flaky particles of mica powder in the foil are predominantly oriented parallel to the layer plane due to the calendering effest which is desired. The laminated material 20 emerging from the nip is drawn-off via guide rollers 21 and 22 with the aid of draw-off rollers 23 and is then wound at 24.
The separating foil 28 applied to fiber glass fabric 29 is removed from laminate 20 by a special rewinding device and the laminate is then ready for use as an area electrical insulating material after cutting into narrower strips, if desired.
The temperature contro] in the treatment of the mixture of mica powder, epoxy resin and hardener during the method is such that the resin is brought into the B state. Instead of being bonded with the glass fabric web 29, the ~hin -foil produced from the mixture of mica powder, epoxy resin and hardener can be bonded in the calendar also with other sheet type materials, in particular support materials such as plastic foils, synthetic fiber fabrics and the like. The method of the invention can advan~ageously be employed also quite generally for the production of foils which are to contain besides a hardenable resin mixture, instead of the mica powder or a part thereof, other Eillers and/or reinforcement substances such as carbon black, iron powder, reinforcement fibers and the like.
Various modifications of the products and processes of the invention may be made without departing from the spirit or scope thereof and it is to be understood that the invention is intended to be limited only as defined in the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the production of an electrical insulating foil comprising substantially a thin-layer of electrical grade mica powder and a hardenable synthetic resin with a thickness of 0.1 to 0.5 mm comprising the steps of forming a paste of electrical grade mica powder and a hardenable substantially solvent free synthetic resin and optional fillers and/or reinforcement material, forming a strand of said paste and evenly distributing the pasty strand over the entrance of a calender or a ribbon press to reduce the strand thickness into a thin-layer 0.1 to 0.5 mm thick.

2. The process of claim 1 wherein the mica powder is based on muscovite or phlogopite.

3. The process of claim 1 wherein the paste contains 35 to 70% by weight of mica powder.

4. The process of claim 1 wherein the paste contains 45 to 65% by weight of mica powder.

5. The process of claim 1 wherein the paste contains up to 20% by weight of fillers and/or reinforcing materials.

6. The process of claim 1 wherein the resin is in the liquid state.

7. The process of claim 1 wherein the resin is an epoxy resin.

8. The process of claim 1 wherein the resin is a polyester resin.

9. The process of claim 1 wherein the resin is a silicone resin.

10. The process of claim 1 wherein the pasty strand is between two webs of sheet material while being calendered or pressed by a ribbon press.

11. The process of claim 10 wherein the pasty strand is permanently bonded to at least one of the webs of sheet material.

12. The process of claim 10 wherein a fiber fabric web is provided between the strand and web of sheet material and the fabric web and foil layer are permanently bonded together.