CH652999A5 - METHOD FOR PRODUCING RECONSTRUCTED MICA MATERIALS, RECONSTITUTED Mica PREPREG MATERIALS AND RECONSTITUTED Mica Products and Use of the Mica Material. - Google Patents

Description

The invention is explained in more detail below.

In the present invention, the aspect ratio is defined as follows:

Length and diameter of the mica flakes

Aspect ratio =

(a mor-t r-j tini thickness of the mica flakes

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The particle size distribution is measured by classifying the mica flakes according to a wet method using sieve analysis (Tyler sieves) and weighing them for calculation after drying.

The process for disintegrating unburned mica to form mica flakes with the desired particle sizes and aspect ratios is described, for example, in JA-AS 8899/79 and JA-OS 39984/78 and the like. described. The processes described in these publications are particularly suitable for the easy production of mica flakes with large aspect ratios and desired particle size distributions, since a disintegration device and a classification device are described in these publications.

A slurry containing the following mica flakes made by disintegrating unburned mica should be used to make mica sheets, foils, or sheets:

(A) Mica flakes with a particle size of 1.0 mm or more and an aspect ratio of 150 or more in an amount of 30 to 70 parts by weight.

If the amount is less than 30 parts by weight, the resulting reconstituted mica products or isolated coils have poorer mechanical properties because the mica flake reinforcement is poor. On the other hand, if the amount exceeds 70 parts by weight, the electrical properties of the resulting reconstituted mica products and insulated coils will deteriorate because the large pores are formed in the mica sheets, although the reinforcing effect is increased.

The aspect ratio should be 150 or more. If the aspect ratio is less than 150, the mechanical properties and the electrical properties of the resulting reconstituted mica products and insulated coils deteriorate undesirably.

More preferred particle size distributions, aspect ratios, and amounts within the above ranges are as follows:

Particle size length and aspect ratio wt.

Parts

1.7 mm or more 150 or more 2-25

1.0-1.7mm 150 or more 20-60

(B) mica flakes with a particle size of 0.25 mm or more or less than 1.0 mm in an amount of 20 to 40 parts by weight.

If the amount is less than 20 parts by weight, the closest packing of mica flakes cannot be obtained in the resulting mica sheet, resulting in deterioration in the electrical properties, particularly the dielectric breakdown voltage of the resulting reconstituted mica products or insulated coils. On the other hand, if the amount is more than 40 parts by weight, the mechanical properties of the resulting reconstituted mica products or isolated coils deteriorate because the proportion of mica flakes with smaller particle sizes increases.

If the mica flakes have an aspect ratio of 100 or more, even better results can be obtained. On the other hand, if the aspect ratio is less than 100, there is a fear that the sheet strength of the resulting unfired mica sheet or plate lowers, making the mica sheets difficult to handle. In addition, the electrical properties, in particular the dielectric breakdown voltage of the resulting reconstituted mica products deteriorate, or the electrical and mechanical properties of the resulting insulated coils deteriorate.

(C) mica flakes with a particle size less than 0.25 mm in an amount of 10 to 30 parts by weight.

If the amount is less than 10 parts by weight, it is impossible to sufficiently fill the spaces formed using mica flakes with a particle size of 1.0 mm or more. This means that a larger amount of binder is required to bind the mica sheet or plate to a support material, or that a larger amount of thermosetting resin is required to fill the spaces between the mica flakes when producing insulated coils or prepregs. This causes the electrical properties to deteriorate over time. On the other hand, if the amount is more than 30 parts by weight, the mechanical properties and electrical properties of the resulting reconstituted mica products or insulated coils deteriorate because there is an increase in the proportion of mica flakes with a smaller particle size.

If the mica flakes have an aspect ratio of 100 or more, particularly favorable effects are obtained. On the other hand, if the aspect ratio is less than 100, there is a fear that the sheet strength of the resulting unburned mica sheet deteriorates, which means that the mica sheet becomes difficult to handle and the electrical properties, in particular the dielectric breakdown voltage of the resulting, reconstituted mica products deteriorate or that the electrical and mechanical properties of the resulting isolated coils deteriorate.

In the present invention, the mica sheet slurry contains the mica flakes (A), (B) and (C) as mentioned above. If mica flakes with a particle size of less than 0.25 mm and those with a particle size of 1.0 mm or more are combined, mica sheets with the closest packing of the mica flakes cannot be obtained, since the rates of precipitation of the first and the latter are tenfold or more, and when sheets are used using a wet-type paper making machine, the large mica flakes can collect on one side and the small mica flakes on the other side. Such a mistake can only be eliminated by using the mica flakes (B) in the range mentioned above.

As the unburned mica, there can be used mica which has not been subjected to a firing treatment, and mica which is obtained by making the organic components such as paper, wood, fibers and the like from waste mica, cut mica and the like by completely burning them Air is removed at a temperature at which the crystallization water of the mica is not released (about 600 C or lower) to that at which half or less of the crystallization water of the mica is released.

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If burnt mica is used instead of unburned mica, the mechanical properties, in particular the flexural strength and the flexural modulus, deteriorate considerably in the resulting, reconstituted mica materials, reconstituted mica prepreg materials and reconstituted mica products.

Any of the known methods for making mica sheets (including mica sheets) from the slurry can be used in the present invention. For example, a slurry containing 0.5 to 2% by weight of mica flakes can be used to form sheets thereof, for example, using a Fourdrinier paper machine, a cylinder paper machine, or the like, using the usual conditions.

If necessary, the resulting mica sheet can be glued to a support or underside material. As the support materials, there can be woven sheets, non-woven sheets, films, foils and the like, made of organic materials such as polyesters, polyamides, polypropylenes, or inorganic materials such as glass, alone or in combination, and optionally together with glass yarns, polyester fiber yarns etc. use. In such a case, a binder known per se, such as a thermosetting resin, is used to bond the two materials.

The resulting, reconstituted mica material (in the form of a sheet) can be used to produce reconstituted mica prepreg material by impregnating or coating it with a thermosetting resin composition and, if appropriate, gluing it together with the supporting material and partially curing the impregnated or coated resin.

As the thermosetting resin composition, there can be used an epoxy resin composition, an unsaturated polyester resin composition, a silicone resin composition, and the like, incorporated therein as one or more hardening agents, surfactants, solvents, reactive solvents, and the like as common additives.

The impregnation or coating with the thermosetting resin composition can be carried out according to methods known per se, for example by dissolving the thermosetting resin composition in a solvent such as methyl ethyl ketone, acetone, methanol etc. and using the resulting solution to impregnate the reconstituted mica material or by coating using a coating device known per se, such as a spray nozzle, a brush coating device, etc. After impregnation or coating, the solvent is removed by drying the resulting material using a hot air dryer, infrared rays or the like.

The impregnated or applied resin can be partially hardened by methods known per se.

The same support materials as mentioned above can also be used to make reconstituted mica prepreg material.

The reconstituted mica materials (in the form of sheets or plates) can also be used to produce a reconstituted mica product by impregnating or coating them with the thermosetting resin composition or an inorganic composition and deforming the resulting material under heating and pressure. As the thermosetting resin composition, all of those mentioned above for the production of the prepregs can be used. Masses can be ver652 999 as inorganic materials

that contain aluminum phosphate, borosilicate glass, etc.

The same impregnation or coating methods as described above for the preparation of the prepregs can also be used in this case.

The molding may be carried out with heating at a temperature sufficient to soften the thermosetting resin composition, or at higher temperatures or a pressure sufficient to mold the resulting molded article into one piece, the pressure being maintained for a time which is sufficient to harden the softened, thermosetting resin compound and to deform the product.

The reconstituted mica material (in the form of a foil) with or without support material can also be used to make an insulated coil that includes an electrical conductor and an insulating layer wrapped around the conductor.

The insulating layer can either be produced according to a so-called vacuum impregnation process or according to a so-called prepreg process. There are no particular restrictions on the deformation conditions.

More specifically, the reconstituted mica material is optionally wrapped with a backing material around a conductor, the wrapped mica material is impregnated with a thermosetting resin composition under reduced pressure or under pressure, and the thermosetting resin composition is hardened to form the insulated coil. Alternatively, a reconstituted mica prepreg material can first be prepared by impregnating the reconstituted mica material with a thermosetting resin composition, then partially curing the resin and then wrapping the resulting prepreg material around a conductor, and then curing the resin to obtain an insulating coil.

As the thermosetting resin composition and as the underside material, there can be used those described above, for example, for the production of the reconstituted mica prepreg material.

The insulating layer contains (a) 60 to 85 parts by weight of reconstituted mica material, (b) 15 to 30 parts by weight of thermosetting resin composition and (c) 15 parts by weight or less of the bottom material, the total weight being 100 parts by weight.

The reconstituted mica material is used in the insulating layer in an amount of 60 to 85 parts by weight. If the amount is less than 60 parts by weight, the electrical properties such as the dielectric strength of the insulated coil deteriorate, whereas if the amount is more than 85 parts by weight, the electrical and mechanical properties of the insulated coil deteriorate significantly through more voids between the mica flakes.

The thermosetting resin composition is used in the insulating layer in an amount of 15 to 30 parts by weight. If the amount is less than 15 parts by weight, voids are easily formed in the insulating layer, causing corona discharge and deteriorating the electrical properties of the insulated coil. When stress such as bending or compression or the like is applied to the insulating layer, stress concentration takes place, thereby deteriorating the mechanical properties. On the other hand, if the amount is more than 30 parts by weight, not only the mechanical properties of the insulating coil, but also the electrical properties deteriorate for a long time.

The backing or bottom material is used by adding it to the reconstituted mica material5

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sticks in an amount of up to 15 parts by weight. If the amount is more than 15 parts by weight in the insulating layer, the mechanical or electrical properties deteriorate. For example, if woven sheet or non-woven sheet made of glass fiber is used as a supporting material for the reconstituted mica material in an amount of more than 15 parts by weight, the electrical properties of the resulting insulated coil deteriorate, but its mechanical properties do not deteriorate. If woven sheet material, non-woven sheet material or films made of polyester, polyamide or the like are used as support material for the reconstituted mica material in an amount of more than 15 parts by weight, the mechanical and electrical properties deteriorate with the passage of time of the resulting insulated coil. The same applies when combinations of the above-mentioned films and glass or combinations of the above-mentioned films and yarns made of polyester fibers and the like are used.

The following examples illustrate the invention. In the examples, all parts and percentages are expressed by weight unless otherwise stated.

example 1

The reconstituted mica materials listed in Table 2 are made using slurries containing mica flakes in an amount of about 1% dispersed in water. A Fourdrinier paper machine is used to make the sheets. Table 2 also shows the particle size distribution of the mica flakes used in each material. On the other hand, thermosetting resin compositions or inorganic compositions as listed in Table 3 are produced.

The reconstituted mica material listed in Table 2 is coated with the mass 1 given in Table 3 as an adhesive, which is heated to 60 ° C., in an amount of 100 g / m2 and glued with glass cloth (35 g / m2) as a support material. The mixture is then heated at 80 ° C for 1 h; a partially hardened, reconstituted mica prepreg material is obtained. The resulting prepreg is cut into a band with a width of 30 mm. The tape is wrapped around a conductor (made of copper) with a size of 9.5 mm x 36.5 mm and a length of 1 m eight times with an overlap of the order of 50%. Then the resulting wound conductor is heated to 100 ° C and pressed so that the mass 1 from the reTable 2

Particle size distribution

1.0 mm or more

70

30th

85

15

50

0.25 mm to less

than 1.0 mm

20th

40

15

40

30th

less than 0.25 mm •

10th

30th

0

45

20th

Length and aspect ratio (particle size

^ 1.0 mm) 240 220 235 235 70

Basic weight (g / m2) 200 200 200 200 200

Table 3

Mass component no.

1 bisphenol A type epoxy resin (GY280,

Ciba-Geigy Corp., epoxy equivalent = 250 g equ.) 100 parts

BF3-monoethylamine (BF3-400,

Hashimoto Kasei K.K.) 3 parts

2 monomethylpolysiloxane (KR-220, Shin-

etsu Chemical Industry Co., Ltd.) 100 parts KR-234 (hardening agent for KR-220,

Shin-etsu Chemical Industry Co., Ltd.) 1 part solvent: toluene / isopropyl

alcohol (weight ratio: 2: 1)

Content of non-volatile materials = 10%

3 bisphenol A type epoxy resin (GY260,

Ciba-Geigy Corp., epoxy equivalent = 190 g / eq.) 100 parts

BF3-monoethylamine (BF3-400,

Hashimoto Kasei K.K.) 3 parts

Solvent: methyl ethyl ketone content of non-volatile materials = 20%

4 aqueous solution of aluminum oxide sol

(Alumina sol 100, Nissan Chemical Industries, Ltd.) 100 parts

75% o-phosphoric acid mixed 38.4 parts in 250 parts of water at 60 ° C for 3 h to cause a reaction constituted mica prepreg material, while the mass 1 3 h at 170 C to form an isolated coil with a 3 mm thick insulating layer is hardened. A total of four isolated coils are made in the same way, two of which are used for a test under normal conditions and the rest for a test after thermal decomposition. The bending strength of the coil is measured according to the so-called four-point method (outside distance 550 mm, inside distance 250 mm). Dielectric breakdown voltage tests are performed by increasing the voltage at a rate of 2 kV / sec. The dielectric strength after the decomposition is determined after thermal decomposition at 130 ° C. for 1000 h. The results are shown in Table 4, which shows the average values.

Example 2

Using material 2 listed in Table 2, partially cured, reconstituted mica prepreg materials are prepared in the same manner as in Example 1. Isolated coils are made using the resulting prepreg, and their properties are determined in the same manner as in Example 1. The results are shown in Table 4, which shows average values.

Comparative Example 1

Using material 3 listed in Table 2, partially hardened, reconstituted mica prepreg materials are produced in the same way as in Example 16

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poses. According to the procedure described in Example 1, isolated coils are produced using the resulting prepregs and their properties are determined. The results are shown in Table 4, which shows average values.

Comparative Example 2 Using material 5 listed in Table 2, partially hardened, reconstituted mica prepreg materials are prepared in the same manner as in Example 1. According to the procedure described in Example 1, isolated coils are produced using the resulting prepregs and their properties are determined. The results are shown in Table 4, which shows average values.

Table 4

Example No. Example Comparative Example

12 12

reconstituted mica

material no.

1

2nd

3rd

5

Amount of mass 1 (%)

30th

35

30th

35

Flexural strength (N / m2 • IO4)

1570

1490

1530

1324

dielectric through

impact resistance (kV)

124

112

102

88

dielectric Breakthrough

strength after

Decomposition (kV)

120

104

90

70

Example 3

The reconstituted mica material 1 listed in Table 2 is coated with the mass 2 listed in Table 3 as an adhesive in an amount of 174 g / m2 (content of non-volatile constituents = 10%) and 30 minutes at 80 CC with the formation of partially hardened prepreg mica sheets dried. Eight layers of the resulting mica sheets are placed on top of one another, placed in a press heated to 150 ° C. and pressed for 20 minutes under a pressure of 19.6 • 104 N / m2. The mixture is then heated at 200 ° C. for 2 hours under the same pressure. A heat-resistant mica product is obtained.

The properties of the resulting mica product are determined as follows. The bending strength is measured according to the so-called three-point method (distance 50 mm) at a test speed of 1 mm / min. Weight loss on heating is determined by heating at 500 ° C for 2 hours. Smoke resistance is measured using a sample obtained by winding a nichrome wire (13.2 fi / m) 17 times around a 60 x 140 mm test piece and an alternating current of 115 to 120 V at 3 , 5 A passes through for 5 min. The results are shown in Table 5.

Example 4

The reconstituted mica material 2 listed in Table 2 is coated with the mass 2 listed in Table 3 as an adhesive in an amount of 174 g / m 2 (non-volatile content 10%) and 30 minutes at 80 ° C. to form partially hardened prepreg mica sheets Using the resulting mica sheets, a heat-resistant mica product is produced in the same manner as in Example 3. The properties of the mica product are determined in accordance with Example 3. The results are shown in Table 5.

Comparative Example 3 The reconstituted mica material 4 listed in Table 2 is coated with the mass 2 listed in Table 3 as an adhesive in an amount of 198 gm2 (non-volatile content 10%) and dried at 80 ° C. for 30 minutes to form partially hardened prepreg mica sheets. Using the resulting mica sheets, a heat-resistant mica product is produced in the same manner as in Example 3. The properties of the mica product are evaluated according to Example 3. The results are shown in Table 5.

Comparative Example 4 The reconstituted mica material 5 listed in Table 2 is coated with the composition 2 listed in Table 3, and as an adhesive in an amount of 247 g / m 2 (non-volatile content 10%), and partially at 30 ° C. for 30 minutes at 80 ° C. hardened prepreg mica sheets dried. Using the resulting mica sheets, a heat-resistant mica product is produced in the same manner as in Example 3. The properties of the mica product are determined according to Example 3. The results are shown in Table 5.

Table 5

Example No.

Example 3

4th

Comparative Example 3 4

reconstituted mica

material no.

1

2nd

4th

5

Amount of mass 2 (%)

8th

8th

9

11

Flexural strength (N / m2 -104)

16.0

15.3

13.0

9.4

Weight loss when

Heating (%)

0.8

0.8

0.9

1

Smoke resistance good good good bad

Example 5

Glass cloth (35 g / m2) is placed on the reconstituted mica material 1 listed in Table 2 as a support material. The mass 3 listed in Table 3 is applied as an adhesive to the glass cloth in an amount of 75 g / m 2 (non-volatile content 20%) and then dried at 100 ° C. for 30 minutes. The resulting material is cut into a 30 mm wide band. The tape is wrapped around a conductor (made of copper) of 9.5 mm x 36.5 mm and a length of 1.0 m eight times with an overlap of the order of 50%. Then deaeration takes place at 100 ° C and 0.1 mmHg for 2 h and then is impregnated in a vacuum with the composition 1 listed in Table 3, which is heated to 80 ° C. The pressure is then increased to normal pressure while the coil is immersed in mass 1, and the coil is removed after 1 hour and coated with Lumirror film with a thickness of 50.8 mm (2 mil) (manufactured by Toray Industries , Inc.) covered, so that the coil is prevented from falling out of the mass 1. After curing for 4 hours at 110 ° C. and for 1 hour at 200 ° C., a 3 mm thick insulating layer is obtained. A total of four insulating coils are produced in the same way, two of which are used for the test under normal conditions and the rest for the test after thermal decomposition.

The properties of the isolated coils are evaluated in the same manner as in Example 1. The results are shown in Table 6 as average values.

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Example 6

Using material 2 listed in Table 2, a reconstituted mica tape is made in the same manner as in Example 5. Insulated coils are produced using the procedure described in Example 5. The properties of the isolated coils are evaluated according to Example 1. The results are shown in Table 6 as average values.

Comparative Example 5 Using material 3 listed in Table 2, a reconstituted mica tape is obtained in the same manner as in Example 5. Insulated coils are made according to the procedure of Example 5. The properties of the isolated coils are evaluated according to Example 1. The results are shown in Table 6 as average values.

Comparative Example 6 Using material 5 listed in Table 2, a reconstituted mica tape is obtained in the same manner as in Example 5. Insulated coils are made according to the procedure of Example 5. The properties of the isolated coils are evaluated according to Example 1. The results are shown in Table 6 as average values.

Table 6

Example No. Example Comparative Example

5 6 5 6

reconstituted mica

1

2nd

3rd

5

material no.

Amount of mass 3 (%)

6

6

6

6

Amount of mass 1 after the

Vacuum impregnation

(%)

28

34

29

34

Flexural strength (N / m2 -104)

1590

1490

1520

1340

dielectric through

impact resistance (kV)

128

114

108

90

dielectric Breakthrough

strength after

Destruction (kV)

120

106

94

76

Example 7

The reconstituted mica material 1 listed in Table 2 is coated with the mass 4 listed in Table 3 as an adhesive in an amount of 247 g / m 2 and dried for 5 minutes at 120 ° C. to form partially hardened, reconstituted mica sheets. Three layers of the resulting mica sheets are placed on top of each other and cured for 1 hour while heating at 300 C under a pressure of 98 • 104 N m2 to form a 0.3 mm thick mica laminate. The properties of the mica laminate are listed in Table 7.

Example 8

The material 2 listed in Table 2 is coated with the composition 4 listed in Table 3 in an amount of 247 g / m2. A mica laminate is produced using the procedure described in Example 7. The properties of the mica laminate are listed in Table 7.

Comparative Example 7 The material 3 listed in Table 2 is coated with the composition 4 listed in Table 3 in an amount of 247 g, m 2. A mica laminate is produced using the procedure described in Example 7. The properties of the mica laminate are listed in Table 7.

Comparative Example 8 The material 5 listed in Table 2 is coated with the composition 4 listed in Table 3 in an amount of 278 g / m 2. A mica laminate is produced using the procedure described in Example 7. The properties of the mica laminate are listed in Table 7.

Table 7

Example No. Example Comparative Example

7 8 7 8

reconstituted mica

material no.

1

2nd

3rd

5

Amount of mass 4 (%)

9

9

9

10th

Flexural strength1 (N / m2-104)

21.6

20th

20.3

14.3

Flexural strength after damp

activity absorption2

(N / m2-104)

10.3

9.1

7.35

4.4

Remarks:

1 three-point method, distance 50 mm, test speed

1 mm / min

2 measured after immersing in boiling water for 20 min.

As follows in detail from the examples, since the reconstituted mica materials according to the invention have large aspect ratios, the sheet strength is so good that it is possible to wind them up without using an adhesive. Furthermore, the reconstituted mica prepreg materials and the reconstituted mica products made using the reconstituted mica materials have improved mechanical properties because larger particle size mica flakes are used, and they also have improved electrical properties because a tighter packing is obtained by the Spaces between the mica flakes with larger particle sizes are filled by those with smaller particle sizes. Compared to the known, reconstituted mica products (e.g. materials 3 to 5), the properties improve, although the amount of mass required for impregnation or coating is small. In particular, the properties after decomposition improve over long periods of time, and the properties are better than those that can be obtained with split mica products.

Example 9

The reconstituted mica materials (materials 6 to 10) with a basis weight of 200 g / m2 listed in Table 8 are made using slurries containing mica flakes in an amount of 0.5%, and a Fourdrinier paper machine becomes Production of the sheets used, working at a rate of 5 m / min at 80 to 90 C. Table 8 also lists the particle size distribution of the mica flakes used in each material.

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Table 8

Reconstituted material

\ Gimmer Material No. 6 7 8 9 10 Eigen - ^ ——

Shafts

Particle size distribution

1.0 mm or more

70

30th

85

15

50

0.25 mm to less

than 1.0 mm

20th

40

15

40

30th

less than 0.25 mm

10th

30th

0

45 '

20th

Length and aspect ratio (particle size

^ 1.0 mm) 240 220 235 235 70

Basic weight (g / m2) 200 200 200 200 200

On the other hand, the epoxy resin composition shown in Table 9 is produced.

Table 9

component

Bisphenol A type epoxy resin epoxy resin (GY 280, Ciba-Geigy Corp.,

Epoxy equivalent = 250 g / eq. 100 parts BF3-monoethylamine (BF3-400,

Hashimoto Kasei K.K.) 3 parts

The material 6 listed in Table 8 (reconstituted mica material) is coated with the epoxy resin composition listed in Table 9 and heated to 60 ° C. in an amount of 100 g / m2 and bound to a glass cloth (35 g / m2) as a support material. The mixture is then heated at 80 ° C. for 1 h in order to obtain a partially hardened, reconstituted mica prepreg material. The resulting prepreg is cut into a 30 mm wide prepreg tape. The tape is wrapped around a conductor made of copper with 9.5 mm crosswise, 36.5 mm lengthways and 1000 mm length eight times with an overlap of the order of 50%. The resulting wound conductor is heated to 100 ° C and pressed so that the epoxy resin mass can flow out of the mica prepreg material, while the epoxy resin mass is cured at 170: C for 3 h. An insulated coil with an approximately 3 mm thick insulating layer is obtained. A total of four insulated coils are produced in the same way, two of which are used for tests under normal conditions and the rest for tests after thermal decomposition (130 ° C. during IQ3 h). The dielectric breakdown test is performed by measuring the voltage at a rate of

2 kV / sec increased. The bending strength is determined in accordance with the four-point method (external distance 550 mm, internal distance 250 mm, test speed 5 mm / min). The amount of epoxy resin (adhesive) is measured by heating the insulating layer at 600 ° C for 2 hours.

The results are shown in Table 10 as averages.

Example 10

Using the material 7 shown in Table 8 and the epoxy resin composition shown in Table 9, a prepreg tape is produced in the same manner as in Example 9. Using the resulting prepreg tape, four insulated coils are produced in accordance with Example 9. The properties of the isolated coils are evaluated according to Example 9. The results are shown in Table 10 as averages.

Comparative Example 9 Using the material 8 shown in Table 8 and the epoxy resin composition shown in Table 9, a prepreg tape is produced in the same manner as in Example 9. Using the resulting prepreg tape, four isolated coils are produced in the procedure described in Example 9, the properties of which are determined according to Example 9. The results are in the table

10 given as averages.

Comparative Example 10 Using the material 9 listed in Table 8 and the epoxy resin composition listed in Table 9, a prepreg tape is produced according to Example 9. Using the resulting prepreg tape, four insulated coils are produced in the same way as in Example 9, the properties of which are determined according to Example 9. The results are shown in Table 10 as averages.

Comparative Example 11 Using the material 10 shown in Table 8 and the epoxy resin composition shown in Table 9, a prepreg tape is produced in the same manner as in Example 9. Using the resulting prepreg tape, four insulated coils are produced according to Example 9, the properties of which are determined in the same way as in Example 9. The results are shown in Table 10 as averages.

Example 11

Glass cloth (35 g / m2) is placed on the material 7 listed in Table 8 as a support material. A varnish which was produced by dissolving the epoxy resin composition listed in Table 9 with methyl ethyl ketone and has a nonvolatile content of 20% is applied to the glass cloth in an amount of 75 g / m2 (corresponding to a nonvolatile content of 15 g / m2) applied and then dried at 100 ° C for 30 min. The resulting material is cut into a 30 mm wide prepreg tape. The prepreg tape is wrapped around the same conductor as used in Example 9 eight times with an overlap of the order of 50%. The resulting coil is then dried for 2 hours at 100 ° C. and 0.1 mmHg and impregnated with the epoxy resin composition listed in Table 9 and heated at 80 ° C. at the same pressure. The pressure is then increased to normal pressure while immersing the coil in an epoxy resin composition, and the coil is then removed after one hour and coated with a 50.8 µm (2 mil) Lumirror film (manufactured by Toray Industries, Inc.) so that the coil is prevented from falling out of the crowd. After curing at 110 ° C. for 4 hours and at 170 ° C. for 3 hours, a 3 mm thick insulating layer is obtained.

The properties of the resulting four isolated coils are evaluated according to Example 9. The results are shown in Table 10 as averages.

Comparative Example 12 Using material 10 shown in Table 8, a prepreg tape is made in the same manner as in Example

11 manufactured. Using the resulting prepreg

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According to Example 11, four insulated coils are produced, the properties of which are the same as in Example No.

reconstituted mica material no.

Amount of epoxy resin mass (%)

Flexural strength (N / m2 -104) dielectric. Dielectric strength (kV)

Dielectric Dielectric strength after destruction (kV)

The insulated coils according to the invention have insulating layers with improved mechanical properties, since reconstituted mica materials are used which are produced from mica flakes with larger particle sizes and higher aspect ratios, and they also have insulating layers with improved electrical properties, since the spaces between the larger ones Mica flakes are filled with smaller mica flakes.

Furthermore, if a reconstituted mica material is used in which the spaces between the larger mica flakes are filled with smaller mica flakes, the amount of thermosetting resin composition (which is used as an adhesive) can be reduced. And even if the amount of the thermosetting resin composition is reduced, the initial properties such as the electrical and mechanical properties of the insulated coils do not deteriorate, and good properties are still obtained after the decomposition for a long time (for example, properties after the decomposition during the voltage endurance test ), these properties being equal to or better than those of insulated coils using split mica products.

Example 12

The reconstituted mica materials listed in Table 11 are made using slurries containing mica flakes in an amount of 1% dispersed in water and a Fourdrinier paper making machine. Table 11 also shows the particle size distributions and the aspect ratios of the mica flakes used in each material.

Table 11

Reconstituted mica material

11

12

13

14

15

Particle size distribution

1.7 mm or more

5

15

25th

30th

-

1.0 mm to less than

1.7 mm

25th

40

45

70

10th

0.25 mm to less than

1.0 mm

40

30th

20th

-

50

less than 0.25 mm

30th

15

10th

-

40

game 9 can be determined. The results are shown in Table 10 as averages.

Table 11 (continued)

25 Reconstructed mica material

11

12

13

14

15

Length and side

relationship

30 1.7 mm or more

200

200

100

200

-

1.0 mm to less than

1.7 mm

150

150

100

150

150

0.25 mm to less than

1.0 mm

120

120

80

-

120

35 less than 0.25 mm

120

120

80

-

120

Basis weight (g / m2)

200

200

200

200

200

On the other hand, an epoxy resin composition is prepared as shown in Table 12 on-40.

Table 12

component

45 bisphenol A type epoxy resin epoxy resin (GY 280, Ciba-Geigy Corp.,

Epoxy equivalent = 250 g / eq. 100 parts BF3-monoethylamine (BF3-400,

Hashimoto Kasei K.K.) 3 parts

50

The reconstituted mica material 11 (in sheet form) listed in Table 11 is coated with the epoxy resin composition listed in Table 12 and heated at 60 C in an amount of 100 g / m2 and on glass cloth (WE 05, Nitto 55 Boseki Co., Ltd. ) (35 g / m2) bound as support material. The mixture is then heated at 80 rC for 1 h to form a partially hardened, reconstituted mica prepreg material. The resulting prepreg is cut into a 30 mm wide band. The tape is wrapped around a conductor made of copper of 9.5 mm x 36.5 mm with a length of 1000 mm eight times with an overlap of the order of 50%. The resulting, wound conductor is then heated at 100 ° C. and pressed in such a way that the epoxy resin composition can flow out of the reconstituted mica 65 prepreg material, while the epoxy resin composition is cured at 170 ° C. for 3 hours. An insulated coil with a 3 mm thick insulating layer is obtained. In the same way, a total of four isolated coils are made, by

Table 10

Example Vergi. Example Ex. 11 Vergi. B. 12

9 10 9 10 11

5

7

8th

9

10th

7

10th

18.5

22.4

25.6

26.8

29.7

21.7

29.2

1620

1560

1540

1440

1234

1570

1420

120

132

104

118

86

136

86

118

126

96

108

72

132

78

11

652 999

two of which are used for the test under normal conditions and the rest for the test after thermal decomposition (130 C for 103 h). The dielectric breakdown voltage is determined by increasing the voltage at a rate of 2 kV / sec. The bending strength is determined according to the four-point method (outside distance 550 mm, inside distance 250 mm, test speed 5 m / min). The amount of epoxy resin composition is determined by heating the insulating layer at 600 C for 2 h.

The results are shown in Table 13 as averages.

Example 13

The material 12 listed in Table 11 is coated with the epoxy resin composition listed in Table 12 and heated at 60 ° C. in an amount of 100 g / m2 and bound to glass cloth (35 g / m2) as a supporting material to form a partially hardened, reconstituted mica prepreg material Using the resulting prepreg, four isolated coils are made in the same manner as in Example 12. The properties of the isolated coils are measured according to Example 12. The results are shown in Table 13 as averages .

Comparative Example 13 Material 14 mentioned in Table 11 is coated with the epoxy resin composition listed in Table 12 and heated at 60 ° C. in an amount of 100 g / m2 and bound to glass cloth (35 g / m2) as a support material. The mixture is then heated at 80 ° C. for 1 h to form a partially hardened, reconstituted mica prepreg material. Using the resulting prepreg, four isolated coils are made in the same manner as in Example 12. The properties of the isolated coils are determined in accordance with Example 12. The results are shown in Table 13 as averages.

Comparative Example 14 Material 15 given in Table 11 is coated with the epoxy resin composition listed in Table 12 and heated at 60 ° C. in an amount of 100 g / m2 and bound to glass cloth (35 g / m2) as a support material. The mixture is then heated at 80 ° C. for 1 h to form a partially hardened, reconstituted mica prepreg material. Using the resulting prepreg, four isolated coils are made in the same manner as in Example 12. The properties of the isolated coils are determined in accordance with Example 12. The results are shown in Table 13 as averages.

Table 13

Example No. Example Comparison example

12 13 14 13 14

reconstituted

Mica material no.

11

12

13

14

15

Amount of epoxy resin mass (%)

22.1

23.0

23.5

25.5

23.3

Flexural strength (N / m2 -104) dielectric through

1550

1570

1595

1590

1315

Impact voltage (kV) dielectric through

126

116

106

96

104

impact voltage after destruction (kV)

120

108

92

70

98

Example 15

The reconstituted mica material 11 listed in Table 11 is coated with the epoxy resin composition shown in Table 12 and heated at 60 C in an amount of 25 g / m2 and bound to glass cloth (WE 05) (35 g / m2) as a support material. The mixture is then heated at 80 ° C. for 15 minutes to form a partially hardened, reconstituted mica material. The resulting material is cut into a band with a width of 30 mm. The tape is wrapped around a conductor made of copper of 9.5 mm x 36.5 mm with a length of 1000 mm eight times with an overlap of the order of 50%. Then, the wrapped part is formed into a thickness of 3 mm under pressure. The resulting wound coil is left in a vacuum vessel under a pressure of 1 x 10 "2 mmHg for 30 minutes, and then the epoxy resin composition shown in Table 12, heated at 80 ° C., is poured into the vessel to immerse the wound coil. While After the immersion process, the pressure in the vacuum vessel is increased to normal pressure. After 1 h, the wrapped coil is removed and cured for 3 h at 170 ° C., giving an insulated coil with a 3 mm thick insulating layer. A total of four insulated coils are produced in the same way, the properties of which are determined according to Example 12. The results are given in Table 14 as average values.

Example 16

Material 12 listed in Table 11 is treated in the manner described in Example 15. According to Example 15, four isolated coils are produced, the properties of which are determined according to Example 12. The results are shown in Table 14 as averages.

Comparative Example 15

Material 14 listed in Table 11 is treated in the same manner as in Example 15. According to Example 15, four isolated coils are produced, the properties of which are determined according to Example 12. The results are shown in Table 14 as averages.

Table 14

Example No.

example

Comparative

example

15

16

15

Reconstituted Mica Material No. 11

12

14

Amount of epoxy resin mass (%)

22.0

23.2

25.7

Flexural strength (N / m2 -104)

1560

1570

1580

dielectric breakdown chip

voltage (kV)

128

116

98

dielectric breakdown chip

after destruction (kV)

122

108

68

Reconstituted mica materials, reconstituted mica products, and insulated coils using those that do not have mica flakes with a particle size below 1 mm show poor electrical properties and the electrical properties deteriorate greatly in thermal decomposition for a long time. Furthermore, those products which do not contain mica flakes with a particle size of 1.7 mm or more have the property that their mechanical properties deteriorate. Using the invented

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

652 999

According to the special mica flakes, insulated coils with excellent mechanical properties (flexural strength) and electrical properties can be produced.

Example 17

The reconstituted mica materials listed in Table 15 are added using slurries containing mica flakes in an amount of 0.5% dispersed in water and a Fourdrinier paper forming machine at a rate of 5 m / min 80 to 90 "C. Table 15 also lists the particle size distributions and the aspect ratios of the mica flakes used in each material.

Table 15

Reconstituted mica material no.

16

17th

18th

19th

20th

Particle size distribution

1.7 mm or more

4th

10th

25th

0

20th

1.0 mm to less than

1.7 mm

60

50

40

40

40

0.25 mm to less than

1.0 mm

20th

20th

20th

40

20th

less than 0.25 mm

16

20th

15

20th

20th

Length and side

relationship

1.7 mm or more

200

200

200

-

50

1.0 mm to less than

1.7 mm

200

200

200

200

50

0.25 mm to less than

1.0 mm

120

120

120

120

50

less than 0.25 mm

120

120

120

120

30th

Basis weight (g / m2)

200

200

200

200

200

The reconstituted mica material 16 (in sheet form) listed in Table 15 is coated with the epoxy resin composition given in Table 12, which is heated to 60 ° C., in an amount of 100 g / m2 and with glass cloth (35 g / m2) as a support layer glued. The mixture is then heated at 80 ° C. for 1 h to form a partially hardened, reconstituted mica prepreg material. The resulting pre-preg is cut into a 30 mm wide band. The tape is wrapped around a conductor made of copper of 9.5 mm x 36.5 mm with a length of 1000 mm eight times with an overlap of the order of 50%. Then the resulting wrapped conductor is heated to 100 C and pressed so that the epoxy resin mass can flow out of the reconstituted mica prepreg material while the epoxy resin mass is cured at 170 '' C for 3 hours. An insulated coil with a 3 mm thick insulating layer is obtained. A total of four isolated coils are produced in the same way, two of which are used for a test under normal conditions and two for a test after thermal decomposition (130 ° C. for 10 hours). The dielectric breakdown voltage is determined by increasing the voltage at a rate of 2 kV / sec. Then the bending strength according to the four-point method (external distance 550 mm, internal distance 250 mm, test speed

5 mm / min). The amount of epoxy resin (adhesive) is determined by heating the insulating layer at 600 C for 2 hours. The results are shown in Table 16 as averages.

Example 18

The material 17 listed in Table 15 is coated with the epoxy resin composition shown in Table 12, which is heated to 60 C, in an amount of 100 g / m2 and glued with glass cloth (35 g / m2) as a support material. Then heated at 80 ° C for 1 h to form a partially hardened, reconstituted mica prepreg material. A 30 mm wide tape is cut from the resulting prepreg material and wrapped around the same conductor as used in Example 17, eight times with an overlap of the order of 50%. A total of four isolated coils are obtained in the manner described in Example 17. The properties of the isolated coils are determined in accordance with Example 17. The results are shown in Table 16 as averages.

Example 19

The material 18 listed in Table 15 is coated with the epoxy resin composition shown in Table 12 and heated to 60 ° C. in an amount of 100 g / m2 and glued with glass cloth (35 g / m2) as a support material. Then heated at 80 ° C for 1 h to form a partially hardened, reconstituted mica prepreg material. A 30 mm wide tape is cut from the resulting prepreg material and wrapped around the same conductor as that used in Example 17, eight times with an overlap of the order of 50%, placing a total of four insulated coils on those in Example 17 described way. The properties of the isolated coils are determined in accordance with Example 17. The results are shown in Table 16 as averages.

Comparative Example 16

The material 19 listed in Table 15 is coated with the epoxy resin composition shown in Table 12, heated to 60 ° C., in an amount of 100 g / m2 and glued with glass cloth (35 g / m2) as a support material. The mixture is then heated at 80 ° C. for 1 h to form a partially hardened, reconstituted mica prepreg material. A 30 mm wide tape is cut from the resulting prepreg material and wrapped around the same conductor as used in Example 17, eight times with an overlap of the order of 50%, placing a total of four insulated coils on that in Example 17 way described. The properties of the isolated coils are determined in accordance with Example 17. The results are shown in Table 16 as averages.

Comparative Example 17

The material 20 listed in Table 15 is coated with the epoxy resin composition shown in Table 12 and heated to 60 ° C. in an amount of 100 g / m2 and glued with glass cloth (35 g / m2) as a support material. The mixture is then heated at 80 ° C. for 1 h to form a partially hardened, reconstituted mica prepreg material. A 30 mm wide tape is cut from the resulting prepreg material and wrapped around the same conductor as that used in Example 17, eight times with an overlap of the order of 50%, placing a total of four insulated coils on those in Example 17 described way. The properties of the isolated coils are determined in accordance with Example 17. The results are shown in Table 16 as averages.

12

5

10th

15

20th

25th

30th

35

40

45

50

55

60

65

13

652 999

Example 20

On the reconstituted mica material 17 listed in Table 15, glass cloth (35 g / m2) is layered as a support material. A varnish, prepared by dissolving the epoxy resin composition listed in Table 12 in methyl ethyl ketone and containing 20% non-volatile matter, is applied to the glass cloth in an amount of 75 g / m2 (converted to non-volatile content 15 g / m2) applied and dried at 100'C for 30 min. The resulting material is cut into a 30 mm wide band. The tape is wrapped around the same conductor as used in Example 17, eight times with an overlap on the order of 50%. The resulting coil is then dried at 100 ° C. and 0.1 mmHg for 2 hours and impregnated with the epoxy resin composition listed in Table 12 and heated to 80 ° C. under the same pressure. The pressure is then increased to normal pressure while the coil is immersed in the epoxy resin composition and the coil

Example No.

reconstituted mica material no.

Amount of epoxy resin mass (%)

Flexural strength (kgf / cm2)

dielectric breakdown voltage (kV)

dielectric breakdown voltage after destruction (kV)

The insulated coils according to the invention have insulating layers with improved mechanical properties, since reconstituted mica materials formed from mica flakes with a larger particle size and higher aspect ratio are used, and they also have insulating layers with improved electrical properties, since the spaces between larger mica flakes with smaller ones Mica flakes can be filled.

Furthermore, if a reconstituted mica material is used in which the spaces between larger mica flakes are filled with smaller mica flakes,

Le is removed after 1 hour and covered with a 5.08 µm (2 mil) lumirror film (manufactured by Toray Industries, Inc.) to prevent the epoxy resin mass from flowing out of the coil. After hardening for 5 h at 110 C and for 3 h at 170 C, a 3 mm thick insulating layer is formed. The properties of the resulting four isolated coils are determined in accordance with Example 17. The results are shown in Table 16 as averages.

10th

Comparative Example 18 Using the material 20 listed in Table 15, a tape is made in the manner described in Example 20. Four isolated coils are made using the resulting tape in the same manner as in Example 20. The properties of the isolated coils are determined in accordance with Example 17. The results are shown in Table 16 as averages.

the amount of adhesive (thermosetting resin composition) can be reduced. And even if the amount of the thermosetting resin composition is reduced, the initial properties such as the electrical and mechanical properties 40 of the insulated coils are not deteriorated and the properties after the destruction are excellent for a long period of time (for example, the properties after the destruction by Applying voltage for long periods). These properties are 45 or better than those of insulated coils using split mica products.

Table 16

Example 17 18

19th

Vergi. Example 16 17

Example 20

Comparative Example 18

16 17

18th

19th

20th

17th

20th

19.5 21.0

20.8

24.6

28.8

16.7

27.4

1580 1610

1630

1480

1350

1600

1350

132 118

104

128

90

120

92

128 116

104

120

88

114

86

55

60

S

Claims (9)

652 999 1.7 22 1 1. A process for producing reconstituted mica material by forming into a sheet material a slurry of mica flakes made from disintegrated, unburned mica, and the (A) 30 to 70 parts by weight of mica flakes with a particle size of 1.0 mm or more and a length and aspect ratio of 150 or more, (B) 20 to 40 parts by weight of mica flakes with a particle size of 0.25 mm or more and less than 1.0 mm and (C) contains 10 to 30 parts by weight of mica flakes with a particle size below 0.25 mm. 2nd 23 0.10 0 2nd 0.97 33 33 0.38 9 32 0.18 2.7 19th 2. The method according to claim 1, characterized in that the resulting mica sheet is glued to a support material. 2nd PATENT CLAIMS 3.4 15 0 3rd 652 999 to produce prepreg materials, for example. Products with a higher resin content and poorer mechanical and electrical properties are obtained than if they were deformed under heating and pressure. When heat-resistant, reconstituted mica is produced by using a large amount of heat-resistant, thermosetting resin composition, deterioration in heat resistance or remarkable deterioration in properties takes place over a long period of time. On the one hand, the properties of Phlogopit in terms of heat resistance are slightly better than those of Muskovit, on the other hand, its electrical properties are worse than those of Muskovit, so that it cannot be used for the insulation of high-voltage machines and instruments such as a dynamo. Using disintegrated, unfired mica particles, it is possible to reduce the amount of binder and the time required to process them into reconstituted mica products is shorter compared to the time for disintegrated, fired, reconstituted mica particles is required. However, the mechanical and electrical properties are not sufficient compared to the flake-like mica products. To overcome the disadvantages mentioned above, unburned, reconstituted mica was sold under the trademark Micanite II by U.S. SAMICA Corp. developed. Micanite II is made by disintegrating unburned muscovite flakes in water using ultrasound energy. Its particle size distribution is shown in Table 1 together with the particle size distribution of known, currently used, reconstituted mica materials. Table 1 Average Micanite II (% by weight) Particle size (mm) Known, reconstituted mica 3. The method according to claim 1 or 2, characterized in that the mica flakes (B) with a particle size of 0.25 mm or more and less than 1.0 mm have a length and aspect ratio of 100 or more and that Mica flakes (C) with a particle size below 0.25 mm have an aspect ratio of 100 or more. 4. A method of making reconstituted mica prepreg material by forming into a slurry sheet containing mica flakes made from disintegrated, unburned mica, and the (A) 30 to 70 parts by weight of mica flakes with a particle size of 1.0 mm or more and a length and aspect ratio of 150 or more, (B) 20 to 40 parts by weight of mica flakes with a particle size of 0.25 mm or more and less than 1.0 mm and (C) contains 10 to 30 parts by weight of mica flakes with a particle size of less than 0.25 mm in order to obtain a reconstituted mica material, Impregnating or coating the reconstituted mica material with a thermosetting resin composition and partially curing the impregnated or coated resin. 5. The method according to claim 4, characterized in that the reconstituted mica material impregnated or coated with a thermosetting resin composition is glued to a support material before the partial curing of the impregnated or coated resin. 6. The method according to claim 4 or 5, characterized in that the mica flakes (B) with a particle size of 0.25 mm or more and less than 1.0 mm have a length and aspect ratio of 100 or more and the mica flakes (C) with a particle size less than 0.25 mm have an aspect ratio of 100 or more. 7. A method of making a reconstituted mica product by forming into a slurry sheet containing mica flakes made from disintegrated unfired mica, the slurry (A) 30 to 70 parts by weight of mica flakes with a particle size of 1.0 mm or more and a length and aspect ratio of 150 or more, (B) 20 to 40 parts by weight of mica flakes with a particle size of 0.25 mm or more and less than 1.0 mm and (C) contains 10 to 30 parts by weight of mica flakes with a particle size of less than 0.25 mm and is suitable for producing a reconstituted mica material, Impregnating or coating the reconstituted mica material with a thermosetting resin composition or an inorganic composition and Deformation of the resulting material under heating and pressure. 8. The method according to claim 7, characterized in that the mica flakes (B) with a particle size of 0.25 mm or more and less than 1.0 mm have a length and aspect ratio of 100 or more and the mica flakes (C) with a particle size less than 0.25 mm have an aspect ratio of 100 or more. 9. Use of the reconstituted mica material produced by the method according to claim 1 for producing an insulated electrical coil which has an electrical conductor and an insulating layer wound around the conductor, characterized in that the insulating layer (a) 60 to 85 parts by weight of reconstituted mica material; (b) 10 to 30 parts by weight of a thermosetting resin composition and (c) has 15 parts by weight or less of a support material, the total weight of (a), (b) and (c) being 100 parts by weight. 10. Use according to claim 9, characterized in that the mica flakes (B) with a particle size of 0.25 mm or more and less than 1.0 mm have an aspect ratio of 100 or more and that the mica flakes ( C) with a particle size below 0.25 mm have a length and aspect ratio of 100 or more. 11. Use according to claim 9 or 10, characterized in that the thermosetting resin composition contains as the resin component an epoxy resin, an unsaturated polyester resin or a silicone resin. In the past, as the reconstituted mica, so-called burned, reconstituted mica, which is produced by heating muscovite for dehydration to about 800 ° C, was generally used, the expanded muscovite with stirring in water or with a jet of water to form a slurry Mica flakes or flakes with a particle size as small as about 0.2 to 1.0 mm disintegrate and make mica sheets using the resulting slurry containing the mica flakes. So-called soft, reconstituted mica, which is made by disintegrating and using phlogopite in water to form a mica flake slurry with a particle size as small as about 0.2 to 2.0 mm, was also used Slurry forms mica sheets or sheets. Burnt mica cannot be disintegrated industrially into thin, square flakes of 5 to 10 mm. Since fine cracks appear in the mica flakes or flakes after the crystallization water of the mica emerges, the strength of the mica flakes is low and their effect as a reinforcing material is low. Burnt, reconstituted mica has a density as low as 1.3 to 1.5 g / cm3. and has a large number of pores in the mica foils. A large amount of thermosetting resin composition is therefore required in order to 5 10th 15 20th 25th 30th 35 40 45 50 55 60 65 9 (From the "Catalog" of the U.S. SAMICA Corp.) Micanite II is unburned, reconstituted mica, but has a tensile strength as high as 0.7 to 1.3 kgf / mm2 without the use of a binder, and the corresponding mica sheet has a density as high as 1.6 to Is 1.7 g / cm3. Micanite II, however, has some disadvantages due to the particle size distribution shown in Table 1. This means that since larger particles are used in Micanite II, the strengthening effect of the mica particles is great, which leads to an improvement in the mechanical properties of the processed mica products. On the other hand, since a dense packing cannot be obtained when using larger mica particles, the deterioration of the properties, in particular the electrical properties, is more pronounced for longer periods than with split mica products. “Split mica products” are mica that can be split or delaminated by hand and with a diameter of about 50 mm or more and a thickness of 30 to 50 p.m. Since the The size of this mica is so large that it cannot be deformed into sheets using a wet-type paper machine like reconstituted mica, and is deformed into sheets by hand or in practical production using a semi-automatic machine. The production costs of split mica products thus increase, and finally the split mica products are more expensive than the reconstituted mica products, since the former are not suitable for large-scale production using machines. The properties of split mica products are excellent, even after long periods of time, since larger mica flakes are used than the usual reconstituted mica, and the larger flakes act as an insulator, even after the binder has decomposed. In order to preserve the characteristics of both the split mica products and the reconstituted mica products, a combination of both products has been proposed, for example, in JA-OS 58500/78. According to this proposal, both sides of the split mica sheet or. the plate with reconstituted mica sheets or plates. The resulting product has an improved accuracy in thickness compared to the split mica product, but its properties deteriorate over time compared to the split mica product alone. Insulated electrical coils are manufactured by a process in which a delaminated mica tape is wrapped around a conductor, the wound tape is vacuum-impregnated with a thermosetting resin composition such as an epoxy resin composition, an unsaturated polyester resin, and the resin is cured. A so-called prepreg process is also used, in which a baked mica prepreg tape is wound around a conductor and then deformed under heating and pressure. There are also similar procedures. The prepreg process is preferred because of its initial electrical properties. The other properties are not that good. The vacuum impregnation process using split mica tape is superior in initial mechanical properties and electrical properties after decomposition by the voltage endurance test, but the other properties are not so good. If reconstituted mica is used, an insulated coil with the same or better properties is obtained compared to a coil using split mica. An insulated coil with the same electrical properties as is obtained when using split mica is described in JA-AS 20264/75. According to the process described in this reference, there are disadvantages that the process is necessarily complicated. For example, the raw mica blocks must be wetted with an aqueous solution of hydrofluoric acid or hydrogen chloride, and it is necessary to treat the waste water. The mechanical properties of the resulting, isolated coil are not sufficient since burnt mica was used. In contrast, it is an object of the present invention to eliminate the above disadvantages. This object is achieved with the method and use defined in the claims.