DE1947677A1 - Mica insulation made from large flakes - Google Patents

Description

194-7877

f Dr-In ₈ . {.ANS RUSCHKE

Dipl.-Ipg. Ht I

J3

M 2686

Minnesota Mining and Manufacturing Company, Saint Paul, Minnesota 55101, V.dt.A.

Mica insulation made from large scales.

The invention relates to newly made mica insulation, in particular relates to newly created mica insulation sheets and strips with improved physical properties, especially resistance to breakthrough and severe mechanical abuse.

A break in the electrical insulation occurs if a sharp edge or during use or use Corner of an isolated part forces its Durohbruoh and physically separates the insulation, causing electrical failure caused. A particularly acute breakdown problem exists in high voltage turbine generators with rectangular ones Copper conductors that are isolated from each other and from the earth have to. The insulation used must have unusual electrical and mechanical properties, in particular against breakthrough and severe meohanisohera abuse,

009814/1679

-z-

and must withstand when it is twisted around small angled bends and forced into narrow gaps without doing so tear, splinter or develop voids what elek-t tric failure. It has been found that the resistance to this type of failure is derived from the The result of a laboratory test that measures the force required to pass a sharp edge can be predicted to force electrical insulation.

Mica has excellent electrical, mechanical, and thermal properties Properties, but is thick and inflexible in its naturally occurring state. Lamellar mica crystals are manual to non-contiguous ADD flattening decoated, laid by hand or by machine in overlapping patterns and covered with a resinous material for the purpose Forming an insulating sheet, which for most purposes is a barrier to mechanical abuse and breakthrough has adequate strength. However, machine-laid sheets are thick, often discontinuous, and tend to Flaking, are non-uniform and must be used in thick layers to have adequate electrical properties to achieve. Hand-laid insulating sheets are expensive, difficult to manufacture and also tend to flake.

U.S. Patents 2,405,576, 2 54-9 88u, and 2 614 U55 describe newly created mica insulating sheets, made from naturally occurring mica, which are too thin Dandruff in the absence of an inactivating atmosphere, compressing the dandruff and drying under heat and pressure getting produced. U.S. Patent 3,131,114 describes the wide scale size of about 3.5 to 4 mm mesh (U.3. Standard Sieve) for use for newly created mica flake insulation sheets with enclosed glasflooken. Such well-known mica lamb arches produced have good ones

009.8.-U / 1679

electrical properties and are significantly more pliable and uniform than sheets of mica flake, but they are opaque and depend on an impregnating resin for resistance to thermoset breakage. When impregnated with soft resin, the arcs lack strength due to physical abuse and deformation, while arcs impregnated with hard resin crack and splinter during use, which is expressed in a deterioration in electrical insulation property. ^:

Despite the long-recognized utility of mica sheets or strip insulation with both resistance to breakdown and physical abuse of mica flakes, and the electrical superiority, uniformity, poor strength, and flexibility of newly created mica, -. such a product has not previously been available. ■ '

"t

This invention applies to newly made mica insulation sheets and! -strip, which has excellent resistance to breakthrough and physical abuse with electrical superiority, uniformity, thinness and flexibility from newly created mica.

Insulating sheets and strips made in accordance with this invention have excellent electrical and physical properties, being flexible, dense, uniform, continuous, translucent, non-flaky, and retain their electrical properties such as arc resistance and corona resistance, dielectric strength and low electrical properties Heavy duty power factor at. In addition, these sheets are ideally suited for insulating sheets, wrappings and strips with significantly improved strength ^; ability to break through and mechanical abuse during i. the application and use. The insulating dyes of this invention! are ideally suited for technical use in the '

0098U / 1679

Isolation of DC traction motors, AC motors, and transformers are particularly well suited for Insulation of the rectangular conductors of high voltage turbine generators. These glinimer sheets can be used around the sharp angled bends including the right angle bends be bent at the edges of right-angled conductors and hung into narrow cracks without the danger electrical failure.

Surprisingly, it has been discovered that a newly created mica insulating sheet can be produced from large mica flakes, in order then to have a strength in the unimpregnated state against break-through that is more than 200 # i larger than the wide flake size range of known newly produced mica sheets, while still having the Maintains advantageous uniformity, flexibility and electrical properties j. The mica used to make these bows! scales are considerably larger than the average size of mica dome used to make known arches. At least 40% by weight of the flakes are larger than 14 mesh (US Standard Sieve), at least 70 % are larger than 35 mesh and at least 90% are larger than 60 mesh. Preferably, at least 50 % of the flakes are larger than 14 mesh, at least 80 % larger than 35 mesh, and at least 95% larger than 60 mesh. Known mica insulation sheets use a broad scale distribution of about 3.5 to 400 mesh, mainly about 35 to 400 mesh. It is believed that the large surface area of the individual flakes allows a large overlap area which increases the cohesion between the flakes, eliminates internal voids in the arch to increase the specific gravity and create a continuous arch. It is also believed that the large surface area of the large soles contributes to the excellent resistance to breakthrough and physical abuse.

009814/1879

1947877

The strength and the resistance to abuse of the Mica insulating sheets are illustrated by tensile strength (ASTM test D-828). One of a wide range of scale sizes known insulating sheet manufactured (commercially available from Integrated Mica Corporation under the trade name "Acim") has an average tensile strength of

about 28 to 33 kg / cm while sheets made according to this invention have an average tensile strength of about 245 to 350 kg / cm.

The freedom from internal voids that the arch of this Invention is characterized by its specific gravity of about 1.6 to 2.5 explained, which is about 2.7 to 2.8-fold specific gravity of solid muscovite corresponds to * A well-known, newly produced mica insulating sheet has an i specific gravity of about 0.9 to 1.5, which clearly shows that it contains a large number of voids. The specific. Mica sheet weight is easily determined by the Mercury Intrusion Method, which is included in the American Instrument Company Bulletin 2405-A.

Muscovite and phlogopite mica larger than about 3 mesh is can be used to make these large mica flakes. After a pre-wash with water to remove Dust and small fragments are sent to the mica blocks with jets of water which are practically parallel to the mica blocks the cleavage plane, as described in U.S. Patent No. 2,405,576. The scales are made with the appropriate U.S. Standard screen classified and reclassified into a mica insulating sheet using standard papermaking techniques which has an overlapping arrangement of large mica, the surfaces of which are in abutting relationship. In Scales split in this way are very thin and have a large surface area compared to their thickness. at

009814/1679

The individual mica flakes adhere to the Neüzüsämmenverbindung due to natural cohesive forces in contrast to mica flakes, which have to be bonded together with resin j.

After the newly created Glimmeriso Animal Arch has been manufactured, the arch can be impregnated with inorganic resin such as boron phosphates or potassium borates or organic resin such as shellac, epoxy, alkyd, polyester or silicone resin, etc., the choice of resin being dependent on the cost balance, the Temperature resistance, the flexibility and the required 'electrical strength depends. Inorganic or organic binders, fibers and threads can optionally be incorporated into the sheet. For certain industrial applications it is useful to put the impregnated insulating sheets made from large flakes on a tape such as a polymeric film or ge '. to pile up woven or non-woven products, either _t ; using the impregnating resin as an adhesive, j or by applying a separate adhesive between J the tape and the insulating sheet. The improved breakdown strength of newly made mica insulating sheets from large flakes is not dependent on the saturating resin or the backing web, allowing the use of a variety of soft resins that maintain the flexibility of the insulating sheet.

Dar resistance to breaking will be determined by installing a 1.25 1.25 χ χ 7.5 om large Flußstahlstänge with a '0.0008 mm thick refinement on all sides in each terminal of a pressure cell containing tensile tester. Both rods are inserted at right angles at the edge to each other so that only one point of contact occurs when the rods touch. The selected sample is brewed between the bars and the machine clamps closed at a speed of 1.25 cm / minute. The right-angled edges are created by the mica

009814/1679 '

Forced to bend until they touch each other, creating one Complete an electrical circuit that lights a lamp, indicating that the breakdown is complete is. The tensile tester recorder gives an accurate reading of the Force required to force the sharp edges through the mica arch.

The following examples, ta which all parts, unless otherwise indicated, parts are, illustrate the preparation of Isolierbb'gen and strips of this invention to oegrenzen without their area.

Description of the preferred embodiment.

example 1

This example involves breaking up mica blocks into flakes and making a newly made mica sheet from large flakes. Indian muscovite scrap is broken into thin flakes by exposure to jets of water as described in U.S. Patent No. 2,405,576. The wet mica flake slurry was classified by washing the flakes using a series of standard tfSA sieves, discarding any under 14u mesh flakes. The classified flakes are recombined in a 1 percent mica slurry in water such that 52% by weight of the flakes throughout the slurry are greater than 14 mesh, 85 # greater than 35 mesh, and 93 # greater than 60 mesh.

The newly created sheet was then produced using technical paper mill equipment which - in conjunction - comprised a stirrer, a storage box and a cylinder ^ - paper machine with an endless moist press drive belt, the moist mica flake from the cylinder sieve

^# 009814/1679

conveyed to a damp steel press roll, with the speed of the cylinder screen was 8 cm / second. An endless woven cotton belt carried the damp paper tape to a dry section of the machine where the paper was dried by passing it through a steel cylinder was sent, which were heated to about 6ü to 8ü ° C. The delivery speed of the mica flake slurry to the paper machine determines the thickness of the insulating sheet obtained. The sheet thickness can be from about u.0127 to about j

0.75 mm fluctuate. If thicker sheets are required, you can! the sheets stacked on top of each other or in the ^ sandwich method ■ be connected to each other. Mica insulating sheets produced in this manner have an unusually high degree of Uniformity of the scale structure as evidenced by the uniformly shaped Gives transparency seen when an arc is held against a light source.

An insulating sheet made in the manner described above has an average thickness of 0.063 mm when tested according to ASTM Test D-374, Method C, a tensile strength of about 280 kg / om when tested according to ASTM test D-828 mm, a dielectric strength of about 643 volts per 0.0254, when tested according to ASTM test D-149, a through crushing strength of about 3 kg, a specific gravity of about 1.7 and yielded a serviceable insulating sheet without impregnation . This mica sheet was impregnated, rolled up and slit as described in Examples 2 to 5.

An insulating sheet using the broad 3.5 to 400 mesh * flake size distribution of the prior art as disclosed in U.S. Patent 3,131,114 was prepared and tested in the same manner. It had an average thickness of 0.072 lam, a tensile strength of about 14 kg / om, a dielectric strength of about 350 volts each

0098 U / 1679

ü, 025 mm, a breakdown strength of about 0.9 kg and a specific gravity of about 1.2.

Example 2

This example describes the impregnation of a portion of the rebuilt mica insulation sheet of Example 1 from large flakes with a polyester / epoxy resin. A mixture of “IOD parts of polyester-epoxy resin and one part of tertiary amine [tris- (2,4,6-dimethylaminomethyl) phenol] was prepared according to Example 2 of US Pat. No. 3,027,279. The impregnating resin was coated with methyl ethyl ketone 25 # solids diluted and applied to the mica sheet using a customary immersion and flow process. The impregnated paper was then ^{dried for about 15 minutes at 65 °} C. and then cured for 10 minutes at 200 ^° C. The finished insulating sheet was tough, flexible and fully cured The resin content of the impregnated sheet was determined by weighing both before and after coating and found to be about 20% by weight.

When the impregnated sheet was tested in the manner described in Example 1, the average thickness was found

of 0.112 mm, a tensile strength of about 700 kg / one, one dielectric strength of 690 volts per 0.0254 mm and a breakdown strength of about 3.5 kg.

Impregnating a Gliramerisulierbogens using the known in the art, wide 3 _S 5 to 4Ou mesh Schuppengröüenverteilung in the same way with the moving around of the resin gave a sheet 0.119 mm diok was "2NC t" resin contained and a Durohbreohwlderstand of 1.5 kg exhibited.

Btisplel 3

Part of the great. scales newly created

009814/1679

-ιυ-

arc of example 1 was described in example 2 Denen! Way impregnated with an isooctyl acrylate / acrylic acid / ipoxy terpolymer resin and 0.45 % uranyl nitrate hexahydrate as a catalyst, j

That. Copolyraerharz was made by initially putting in one

Stainless steel tank 9OU kg isooctyl acrylate, 13 kg!

Acrylic acid, and 8 kg of tertiary dodecyl mercaptan together!

were mixed. A charge of 125u kg of toluene was j

then overall in a glass-lined 5 5Ou liter boiler \

give, and then add 65 kg of the mixture in the tank

ί sets. The kettle was flushed with nitrogen and under con-; Constant stirring ^{heated to 80 0} C, while constantly a gentle: nitrogen flow was maintained through the kettle. Then: 3 separate 10 kg batches of azobisisobutyronitrile dissolved in 1 toluene were added at equal intervals over a period of approximately 50 minutes; where each! Feed was 22 % solids. During this period the mixture from the tank was continuously added at a rate of about 17 kg per minute. After a further 50 minutes, 9 kg of 20% strength acobisisobutyronitrile in toluene were added and the temperature was kept at 80 ° C. for a further 21/2 hours. Then 55 kg of 3,4-epoxyeyclohexylmethyl-3,4-epoxy-oyclohexanecarboxylate with an average molecular weight of about 260 and a viscosity of about 500 centipoise at 24 ⁰ C (Union Carbide SRL-4221) were added and thoroughly I lent interfered. The mica arch then became like in example! Impregnated and 2 minutes 10, after drying at 100 C and ■ 10 Biinütigem curing at 200 ^W C, the resin content to 20% \ Issstimmt. The clinging impregnated insulating sheet was connected with a 0.04 »on strong, non-woven tape made of heat-born polyethyleneterephthalate fibers by means of a coating * whale.

Bi® Durohbreahfestlgkeit this öchiofet blower is essential as the ice-cream known mica sheet » ψ ± ο m 009814/1679"'

-in-

is described in Example 1, with a similar impregnation and! Coating. r

Example 4

This example illustrates the impregnation of part of the mica insulating sheet of Example 1 with soft pliable Silicone resin by coating a woven glass cloth impregnated with resin and then layering it on top of one Polyethylene terephthalate film.

Polysiloxane resin (commercially available from General Elec- 'trio Company under the trade designation SR-32) was diluted in: toluene to 35 # solids. A woven 0.05 mm thick glass cloth was impregnated with this resin according to the conventional dip-j and flow method and to a portion of the mica-ΐ arc ~ jj coated of Example 1 by means of Aufschichtwalzen the layer structure was 4 minutes at 200 ⁰ C dried. The layer structure contained 10 % resin, was 0.2 mm thick and had a break through strength which was superior to that of a known, similarly saturated and layered mica insulating sheet as described in Example 1.

The non-coated mica exposed surface was then coated with the above-described silicone resin saturant to the reverse roll coating technique and dried for 4 minutes at 12O ⁰ C. The tacky mica surface was then coated onto 0.006 mm thick biaxially oriented polyethylene terephthalate film with the aid of coating rollers, rolled into a jumbo roller , and

; then divided into 2 cm wide strip rolls. The resin content of the laminate was 15 # and the breakdown resistance was that of the one described in Example 1 in FIG Similar to impregnated and coated known mica insulating sheets.

0098U / 1679

Example 5

This example illustrates the lay-up of polyester film tape on the impregnated Glazier arch made from large scales of Example 2. After the impregnation and the subsequent 15-minute drying at 65 ° C the impregnated Glimmerbogeη cooled and with the help of rotating Pressure rollers coated on 0.012 mm thick biaxially oriented polyethylene phthalate film. The breakthrough strength was that of a known, as described in Example 1, similarly impregnated and coated mica insulating sheet think.

-Patent claims-

0098U / 1679

Claims (6)

-13- Claims newly created mica insulation sheet from an overlapping of non-impregnated mica flakes, characterized in that at least 40 wt .- # of the individual flakes larger than 14 mesh, at least 70% by weight of the individual flakes larger than 35 mesh, and at least 90% by weight of the individual scales are larger than 60 mesh. 2. insulating sheet according to claim 1, further characterized in that that it is impregnated with an epoxy, polyester, silicone, alkyd, or acrylic resin. 3. insulating sheet according to one of the preceding claims, wide characterized in that it is coated on a fibrous tape or polymeric film. 4 * Layer structure according to claim 3, further characterized in that the tape consists of fibers of polyethylene terephthalate, and the polymeric film consists of biaxially oriented polyethylene terephthalate . 5. Article according to one of the preceding claims, further characterized in that it is wound around itself in roll form and in that it can be extracted from it without de-compensation or reading can be handled. 6. A process for the manufacture of the article of claim 1, characterized in that naturally occurring mica is broken down in the absence of a non-activating atmosphere into pellets, the pellets are classified in order to obtain a class of large pellets in which at least 40 wt of the balls are larger than 14 mesh, and the balls of the class obtained in the previous session 009814/1679 large shed reassembled to form a Glimraer insulating sheet will. 00381471671