KR20170099968A - Insulating paper - Google Patents

Abstract

The present invention relates to an aramid flock having an average fiber diameter of 10 to 30 mu m and an aramid flock having an average width of 5 to 30 mu m and having an electric insulation strength of 16 kV / mm or more and a non- / g or more. It becomes possible to provide an insulating paper having improved properties by the present invention, in particular, an insulating paper having improved electrical insulating properties and strength.

Description

{INSULATING PAPER}

The present invention relates to an electric insulating paper used in an electric device such as a transformer, a generator, and a motor.

The use of insulating paper has been diversified in accordance with the expansion of use of electronic parts and electric devices. Paper made of cellulose fibers is widely used as an inexpensive electrical insulating material because of its excellent electrical insulation property, and is used for a capacitor, a transformer, a wire covering material, and the like. However, since the insulating paper containing cellulose fibers as a main component is laid using deionized water for the purpose of removing residual ions in the insulating paper, in addition to requiring a dedicated facility, in view of moisture absorption of the cellulose fibers under a high humidity environment, There is a problem that the water content increases and the electric insulation property decreases.

Thus, an aromatic polyamide electric insulating paper which is obtained by blending floc and fibrids of an aromatic polyamide and then subjecting the same to hot calendering is proposed (see Patent Document 1).

Japanese Patent Publication No. 2014-501859

However, electric insulating paper having more excellent characteristics is continuously required.

It is an object of the present invention to provide an insulating paper having improved properties, in particular, an insulating paper having improved electrical insulation and strength.

The present invention relates to an aramid flock having an average fiber diameter of 10 to 30 mu m and an aramid flock having an average width of 5 to 30 mu m and having an electric insulation strength of 16 kV / mm or more and a non- / g or more.

It is preferable that the aramid fibrids contain the fine aramid fibrids having a width of 15 mu m or less in a proportion of 30 fiber count% or more.

The fine aramid fibrids are preferably homogenizer treated or refined.

The aramid flock is preferably made of meta-aramid.

The aramid fibrids are preferably made of meta-aramid.

The insulating paper of the present invention preferably contains 20 to 80% by weight of the aramid flock with respect to the total weight of the insulating paper.

The insulating paper of the present invention preferably contains the aramid fibrid in an amount of 20 to 80% by weight based on the total weight of the insulating paper.

The weight ratio of the aramid flock to the aramid fibrid is preferably 20:80 to 80:20.

The insulating paper of the present invention may further include at least one kind of binder made of a polymer other than aramid.

The insulating paper of the present invention may further include at least one kind of filler.

It is preferable that a part of the aramid flock and a part of the aramid fibrid are thermally adhered.

The insulating paper of the present invention preferably has a basis weight of 20 to 500 g / m 2.

The present invention relates to an electric insulator including the insulating paper, and an electric device including the electric insulator, for example, a transformer, a generator or an electric motor.

The insulating paper of the present invention has excellent properties as an electric insulating paper. In particular, the insulating paper of the present invention has improved electrical insulation and strength.

As a result of intensive investigations, the inventors of the present invention have found that an insulating paper comprising an aramid flock having an average fiber diameter of 10 to 30 占 퐉 and an aramid fibrid having an average width of 5 to 30 占 퐉 has an insulating proof strength of 16 kV / And an insulated paper having a non-insulative strength of 30 mN · m 2 / g or more can be realized. Thus, the present invention has been completed.

Particularly, the present inventors have found that when the relatively thin aramid fibrids having a predetermined width or less are present in the aramid fibrids at a predetermined ratio, the properties as electrical insulating paper, in particular the electrical insulation and the strength, are improved. Therefore, in the insulating paper of the present invention, it is preferable that the aramid fibrids contain fine aramid fibrids having a width of 15 탆 or less in a proportion of 30% or more of the number of fibers.

Here, the "% of the number of fibers " means the ratio of the number of the fine aramid fibrids occupying in the total number of the aramid fibrids present on the surface of the insulating paper of the present invention. Particularly, Means the ratio of the number of the fine aramid fibrids occupying in the total number of the aramid fibrids present in the area range (for example, 60,000 mu m ² ). The "number of fibers%" can be determined, for example, by SEM (scanning electron microscope) observation or the like. Thus, in other words, the fine aramid fibrids are 30% or more based on the number of the aramid fibrids contained in the insulating paper of the present invention.

The insulating paper of the present invention is composed of "aramid flock" and "aramid fibrid" means that the insulating paper of the present invention consists only of the aramid flock and the aramid fibrid, and the case of the aramid flock and the aramid fibrid, Quot; includes " and " including "

[Aramid]

In the present invention, " aramid " means an aromatic polyamide. The term " aramid " in the present invention means that at least 60 mol%, preferably at least 70 mol%, more preferably at least 80 mol%, still more preferably at least 90 mol% of the amide bonds in the aromatic ring ≪ / RTI > is directly bonded to the polymer backbone.

The aramid is classified into para-aramid, meta-aramid and copolymers thereof depending on the substitution position of the amide group to the benzene ring. Examples of the para aramid include polyparaphenylene terephthalamide and copolymers thereof, poly (paraphenylene) -copoly (3,4'-diphenyl ether) terephthalamide (poly (paraphenylene) 4'-diphenyl ether) terephthalamide) and the like. Examples of the meta-aramid include poly (metaphenylene isophthalamide) and copolymers thereof. These aramids are industrially produced, for example, by conventionally known interfacial polymerization, solution polymerization and the like, and can be obtained as commercial products, but the present invention is not limited thereto. In the present invention, meta-aramid is preferably selected. The meta-aramid is characterized by being soluble in a general-purpose amide solvent, capable of wet molding using a polymer solution as a starting material, excellent in heat-sealability, and excellent in heat resistance and flame retardancy. Of the meta-aramids, poly (meta-phenylene isophthalamide) is preferably used because it has good molding processability, thermal adhesiveness, flame retardancy and heat resistance.

[Aramid flock]

"Aramid floc" is a short fiber made of aramid. The (average) fiber length of the flocs is preferably in the range of 1 to 50 mm, more preferably in the range of 2 to 40 mm, and still more preferably in the range of 3 to 30 mm. If the average fiber length is less than 1 mm, the strength of the insulating paper may be reduced. If the average fiber length exceeds 50 mm, "winding" and "binding" of the flock among the insulating paper tend to occur, which is not preferable because it tends to cause defects.

The average fiber length can be obtained, for example, by averaging the length of a predetermined number (for example, 100) of aramid flocs as raw materials for the insulating paper of the present invention. Alternatively, the length of the aramid flocs present in the predetermined area range (for example, 55 mm 2) on the surface of the insulating paper of the present invention may be measured and observed by a stereomicroscope.

The aramid flocs in the insulating paper of the present invention have a (number) average fiber diameter of 10 to 30 mu m. The average fiber diameter of the aramid flock is preferably 12 to 28 占 퐉, more preferably 14 to 26 占 퐉, and even more preferably 16 to 24 占 퐉. The average fiber diameter can be obtained, for example, by averaging the predetermined number (for example, 100) of the aramid flocs as the raw material of the insulating paper of the present invention. Alternatively, the width of the aramid floc present in a predetermined area range (for example, 60,000 mu m ² ) on the surface of the insulating paper of the present invention may be measured by SEM observation or the like and averaged.

The fineness of the aramid flock is preferably 0.1 to 10 denier, more preferably 0.5 to 8 denier, and even more preferably 1 to 6 denier. Here, " denier " is a unit expressed in mass (grams) per 9,000 m of fibers. If the fineness is smaller than 0.1 denier, mutual winding in water becomes large, which may cause deterioration of the performance of insulating paper. On the other hand, if the fineness is more than 10 denier, the diameter of the flock becomes excessively large, which may result in deterioration of the aspect ratio, deterioration of the mechanical reinforcement effect, and poor uniformity of insulating paper.

The aramid floc used in the present invention is preferably made of meta-aramid. As the meta-aramid, polymethenylene isophthalamide and copolymers thereof are preferable. For example, it can be produced by co-polymerization of m-phenylenediamine and isophthalic acid chloride. Meta-aramid flocs are commercially available. For example, " Conex (registered trademark) " of Daikin Co., Ltd. can be used, but the present invention is not limited thereto.

[Aramid fibrids]

The term " aramid fibrids " is a film-like or fibrous fine particle made of aramid and may also be referred to as aramid pulp (for aramid fibrids, see Japanese Patent Publication No. 35-11851 and Japanese Patent Publication No. 37-5752 Reference). Since the fibrids have super-oily properties such as ordinary wood (cellulose) pulp, they can be dispersed in water and then formed into a sheet form by a paper machine.

The aramid fibrids used in the present invention are preferably made of meta-aramid. As the meta-aramid, a polymethenylene isophthalamide and a copolymer thereof are preferable, and for example, it can be produced by co-polymerization of m-phenylenediamine and isophthalic acid chloride. The meta-aramid fibrids can be produced by a wet precipitation method according to the method described in, for example, Japanese Patent Publication No. 35-11851, a solution containing meta-aramid.

The aramid fibrids can be subjected to the so-called high-temperature treatment for the purpose of maintaining the quality suitable for grass as in the case of ordinary wood pulp. This defoaming treatment can be carried out by a grass paddy processing machine having a mechanical cutting action such as a disk refiner, a beater and the like.

The aramid fibrids in the insulating paper of the present invention have an average width of 5 to 30 mu m. The average width of the aramid fibrids is preferably 7 to 22 占 퐉, more preferably 9 to 20 占 퐉, and still more preferably 11 to 18 占 퐉. The average width can be obtained, for example, by averaging the widths of predetermined numbers (for example, 100) of the aramid fibrids as raw materials for the insulating paper of the present invention. Alternatively, the width of the aramid fibrids present in the predetermined area range (for example, 60,000 mu m ² ) on the surface of the insulating paper of the present invention may be measured by SEM observation or the like and then averaged.

The aramid fibrids in the insulating paper of the present invention preferably contain fine aramid fibrids having a width of 15 m or less in a proportion of 30% or more of the number of fibers. Here, the " width " means the maximum width in the width direction (diameter) of the aramid fibrids. The content of fine aramid fibrids having a width of 15 탆 or less is more preferably 40 fiber number% or more, more preferably 50 fiber number% or more, and still more preferably 60 fiber number% or more.

The upper limit of the mixing ratio of the fine aramid fibrids having a width of 15 탆 or less contained in the aramid fibrids is not particularly limited, but is preferably 90% or less of the number of fibers, more preferably 80% or less of the number of the fibers, % Or less is more preferable.

The fine aramid fibrids can be produced by refining the aramid fibrids. The kind of the finer treatment is not particularly limited and may be homogenizer treatment or refiner treatment although it may be non-mechanical fineness treatment such as ultrasonic treatment. Particularly, a double disc refiner or a conical refiner is preferable. Therefore, it is particularly preferable that the aramid fibrids are treated with a double disc refiner or a conical refiner.

[Insulation paper]

The insulating paper of the present invention is in the form of a porous sheet mainly composed of the aramid flock and the aramid fibrids, and has an electric insulation strength of 16 kV / mm or more and a non-infrared heat intensity of 30 mN · m2 / g or more. The dielectric strength of the insulating paper of the present invention is preferably 20 kV / mm or more, more preferably 24 kV / mm or more, and still more preferably 28 kV / mm or more. The non-inscribed strength of the insulating paper of the present invention is preferably 32 mN · m 2 / g or more, more preferably 34 mN · m 2 / g or more, and still more preferably 36 mN · m 2 / g or more.

The dielectric strength and the non-thermal strength are usually in a trade-off relationship. Therefore, if the blending ratio of aramid fibrids is increased to increase the dielectric strength, the non-thermal strength is lowered. On the other hand, if the blending ratio of aramid floc is increased to increase the non-thermal strength, the dielectric strength is lowered. However, in the present invention, for example, fine aramid fibrids having a width of 15 mu m or less in the aramid fibrids are contained in a proportion of 30% or more of the number of the fibers in a proportion of at least 30 fibers to progress the fineness of the aramid fibrids, It is possible to increase the dielectric strength by a relatively small amount of aramid fibrids, and on the other hand, it is possible to use a relatively large amount of aramid flocs, and it is possible to increase the non-luminescent strength. Therefore, the insulating paper of the present invention has both a high dielectric strength and a high non-luminescent strength.

The thickness of the insulating paper of the present invention is preferably 10 to 1000 占 퐉, more preferably 20 to 800 占 퐉, and still more preferably 30 to 500 占 퐉. The basis weight of the insulating paper of the present invention is preferably 10 to 1000 g / m 2, more preferably 20 to 500 g / m 2, and still more preferably 30 to 300 g / m 2.

The insulating paper of the present invention preferably contains 20 to 80% by weight, more preferably 30 to 70% by weight, and more preferably 40 to 60% by weight of the aramid flock with respect to the total weight (total weight) More preferable.

The insulating paper of the present invention preferably contains 20 to 80% by weight, more preferably 30 to 70% by weight, and more preferably 40 to 60% by weight of the aramid fibrid with respect to the total weight of the insulating paper .

The mixing ratio (weight ratio) of the aramid flock / aramid fibrids is preferably 20:80 to 80:20, and the mixing ratio of the aramid flock / aramid fibrid to the aramid floc is preferably 30:80 to 80:20, : 70 to 70: 30 is more preferable.

The insulating paper of the present invention can be produced by, for example, a method of mixing the aramid flock and the aramid fibrids followed by sheeting. Specifically, for example, there are a method of dry-mixing the aramid flock and the aramid fibrids followed by forming a sheet using an air flow, a method of dispersing and mixing the aramid flock and the aramid fibrids in a liquid medium, Permeable nets, belts or the like to form a sheet, drying the liquid by removing the liquid, and the like. The latter method is preferable, and the wet aging method in which water is used as a liquid medium is preferable .

In the wet granulation method, an aqueous slurry containing at least the aramid floc and the aramid fibrid is supplied to a paper machine and dispersed, followed by dewatering, embedding, and drying to form a sheet. Examples of the paper machine include a paper machine, a grinder paper machine, an inclined paper machine, and a combination paper machine in combination. In the case of production in a combination paper machine, a composite sheet comprising a plurality of paper layers can be obtained by sheet-forming and combining slurries having different blend ratios. Additives such as a dispersing agent, an antifoaming agent, and an emulsifying agent may be used as needed during the agitation.

The insulating paper obtained as described above can be improved in density, crystallinity, heat resistance, dimensional stability, mechanical strength and the like, for example, by thermo-compressing between a pair of rolls at high temperature and high pressure. As a result, it is preferable that a part of the aramid flock and a part of the aramid fibrid are thermally fused. The conditions of the hot press may be, for example, in the case of using a metal roll, at a temperature of 100 to 350 캜 (preferably 200 to 350 캜) and a linear pressure of 50 to 400 kg / cm, Do not. A plurality of insulating paper sheets may be laminated upon thermal pressure. The above-mentioned hot-press working may be performed a plurality of times in an arbitrary order. However, the insulating paper of the present invention preferably retains its porosity.

[bookbinder]

The insulating paper of the present invention may further include at least one kind of binder made of a polymer other than aramid, if necessary. The resin to be used as the binder may be in the form of a water-soluble or dispersible polymer added directly to the paper-making dispersion or may be in the form of a mixture of the aramid fibers and the aramid fibers to be activated as a binder by heat applied during the drying or subsequent additional compression and / Or in the form of a thermoplastic binder fiber of a mixed resin material. Examples of the water-soluble or dispersible polymer include water-soluble or water-dispersible thermosetting resins such as a polyamide resin, an epoxy resin, a phenol resin, a urea resin, a urethane resin, a melamine formaldehyde resin, a thermosetting polyester resin and an alkyd resin . Particularly useful are water-soluble polyamide resins. An aqueous solution or dispersion of a thermoplastic resin such as poly (vinyl alcohol), polypropylene, polyester, poly (vinyl acetate) or the like may also be used.

[filler]

The insulating paper of the present invention may further include at least one kind of filler, if necessary. The filler is not particularly limited, but an inorganic filler is preferable. For example, inorganic fillers such as clay such as mica, graphite, kaolin and bentonite, carbon nanotubes, aluminum nitride, aluminum oxide, boron nitride, magnesium oxide, Thermally conductive fillers.

[Other components]

The insulating paper of the present invention may contain other fibers made of materials other than aramid, if necessary. Examples of other fibers include heat-resistant fibers such as aromatic polyester fibers, aromatic polyether ketone fibers and para-aramid fibers.

The para-aramid fiber is obtained by polycondensation of a para-oriented aromatic dicarboxylic acid and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is bonded to the aromatic ring at the para position or its corresponding orientation (for example, 4,4'- For example, at an orientation position in which the polymer is stretched in the opposite direction (e.g., coaxial or parallel to stretch in the opposite direction, such as rhenylene, 1,5-naphthalene, 2,6-naphthalene, , Poly (4,4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylene dicarboxylic acid amide), poly (paraphenylene-2,6-naphthalene dicarboxylic acid Amide), and other aromatic polyamides having a structure close to the para-orientation type can be specifically exemplified. These aromatic polyamides are prepared by polymerizing a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide.

Examples of the para-oriented aromatic diamine include paraphenylenediamine (hereinafter also referred to as PPD), 4,4'-diaminophenyl, 2-methyl-paraphenylenediamine, 2-chloro-paraphenylenediamine, 2 , 6-naphthalenediamine, 1,5-naphthalenediamine, and 4,4'-diaminobenzanilide.

Examples of the para-oriented aromatic dicarboxylic acid halide include terephthaloyl chloride (hereinafter also referred to as TPC), 4,4'-benzoyl chloride, 2-chloroterephthaloyl chloride, 2,5-dichloroterephthaloyl chloride Chloride, 2-methylterephthaloyl chloride, 2,6-naphthalenedicarboxylic acid chloride, and 1,5-naphthalenedicarboxylic acid chloride.

The insulating paper of the present invention can function as an electric insulating paper. The insulating paper of the present invention may have an electrical resistance of at least 10 ¹³ ? Cm, preferably at least 10 ¹⁵ ? Cm, according to the method of volume resistivity of ASTM D-257.

The insulating paper of the present invention has excellent properties as an electric insulating paper, and is particularly useful as a component of an electrical insulator because it has improved electrical insulation and strength. For example, the insulating paper or the laminated body of the present invention can be used as a component of an electric insulator constituting an electric device such as a transformer, a generator, and a motor. The insulating paper or the laminate of the present invention may be impregnated with a resin such as phenol resin, epoxy, polyimide, etc., but it can exhibit excellent electrical insulation even if it is not impregnated with a resin.

Therefore, the present invention is a paper comprising an aramid flock having an average fiber diameter of 10 to 30 占 퐉 and an aramid flock having an average width of 5 to 30 占 퐉 and having an insulating proof strength of 16 kV / mm or more and a non- An electrical insulation method using paper having a specific surface area of 30 mN · m 2 / g or greater, in particular an electrical insulation improvement method, or an aramid flock having an average fiber diameter of 10 to 30 μm and an aramid fibrid having an average width of 5 to 30 μm As paper, it has an aspect of use for electrical insulation of paper having an insulation strength of 16 kV / mm or more and a non-insulation strength of 30 mN · m 2 / g or more, in particular, for improving electrical insulation. The above description applies to the aramid flock and the aramid fibrids.

Example

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples, but the scope of the present invention is not limited to the examples.

[Assessment Methods]

(Average fiber width)

Each of the raw material slurry for aquatic plants obtained in the following Examples and Comparative Examples was diluted and dropped onto a prepalam so as to be a uniform thin film and dried. The scale was enlarged to 100 to 400 times with a scanning electron microscope to observe the three fields at random, The average fiber diameter (diameter) was calculated by measuring 30 fiber diameters randomly. The ratio of the number of fibers having a fiber width of 15 m or less in the fibers measured at the same time was calculated.

(Dielectric strength)

Measured according to ASTM D-149.

(Non-luminescence intensity)

Measured according to JIS P8116: 2000.

[Example 1]

(Raw material composition)

The meta-aramid fibrid fibers were subjected to a comprehension treatment for 30 minutes at a gravimetric fiber weight concentration of 1.2% using a standard grinder in water. After the treatment, the slurry of the raw material was screened using an 8-cut screen, . Subsequently, the raw slurry from which the micro-untreated fibers were removed was treated twice at a valve pressure of 10 to 20 MPa using a low-pressure homogenizer at a weight concentration of 1.2% of the crumbled fiber to obtain a fibrid fiber slurry for aquatic plants. Table 1 shows the results of the fiber width test in SEM.

Then, the aramid flock fibers were subjected to a dispersion treatment in water for one minute at a gravimetric fiber weight concentration of 0.3% using a standard grinder in water to obtain a flock fiber slurry for aquatic plants with an average fiber width of 17 탆. Each of the obtained fibrin fiber slurry for aquatic plants and flock fiber slurry for aquatic plants was mixed in order so that the weight ratio of the crushed fiber after the water sheet was 50:50.

(Sheet)

A raw sheet was prepared so that the raw material mixture slurry for aquatic plants would have a basis weight of 115 g / m 2 on a dry weight basis, and a wet sheet was prepared using a 120-mesh wire in a square water-type machine, and dehydration in a press machine, heating Followed by drying to obtain a water-containing dry sheet. Subsequently, heating and pressing treatment of the water-containing dry sheet was conducted between metal rolls heated to 300 占 폚 to obtain a test sheet.

[Example 2]

A test sheet was obtained in the same manner as in Example 1 except that the fibrin fiber slurry treated with the slurry was treated 10 times with a low pressure homogenizer to prepare a fibrid fiber slurry for a few seconds.

[Example 3]

(Raw material composition)

The meta-aramid fibrid fiber was subjected to a comprehension treatment for 30 minutes at a weight concentration 1.2% of desiccated fiber using a standard grinder in water. After the treatment, the raw slurry was subjected to refiner treatment in a double disc refiner (manufactured by Aikawa Iron Works). This treatment was carried out at a beating density of 0.9% and eight passes. Thus, a fibrid fiber slurry for aquatic plants was obtained.

Then, the aramid flock fibers were subjected to a dispersion treatment in water at a weight concentration of 0.3% for 1 minute using a standard grinder in water to obtain a flock fiber slurry for aquatic plants with an average fiber width of 17 탆. Each of the obtained fibrin fiber slurry for aquatic plants and flock fiber slurry for aquatic plants was mixed in order so that the weight ratio of the crushed fiber after the water sheet was 50:50.

(Sheet)

A raw sheet was prepared by using a 120-mesh wire in a square-shaped water-based machine and dewatering in a press machine, heating in a rotary dryer (photographic dryer) Followed by drying to obtain a dry sheet of several seconds. Subsequently, heating and pressing treatment of the water-containing dry sheet was conducted between metal rolls heated to 300 占 폚 to obtain a test sheet.

[Comparative Example 1]

A test sheet was obtained in the same manner as in Example 1, except that the fibrin fiber slurry subjected to roughening treatment was subjected to low-pressure homogenizer treatment without being subjected to low-pressure homogenizer treatment for 10 minutes in Niagara Beater to obtain a fibrid fiber slurry for aquatic plants.

[Comparative Example 2]

A test sheet was obtained in the same manner as in Comparative Example 1, except that the fibrin fiber slurry for aquatic plant and the flock fiber slurry for aquatic plant were mixed in order so that the weight ratio of the ready-to-

Table 1 shows the average fiber width, the blending ratio of fibers having a width of 10 m or less, and the test results of the properties of the test sheet by SEM observation of the obtained fibrid fiber.

As apparent from Table 1, it became possible to obtain a good sheet having high dielectric strength and non-heat resistance in the examples.

Claims (15)

An aramid flock having an average fiber diameter of 10 to 30 mu m, and
An aramid fibrid having an average width of 5 to 30 mu m,
An insulation strength of not less than 16 kV / mm and a non-insulation strength of not less than 30 mN · m2 / g. The method according to claim 1,
Wherein the fine aramid fibrids having a width of 15 탆 or less are contained in the aramid fibrids in a proportion of 30 fiber count% or more. 3. The method according to claim 1 or 2,
Wherein said fine aramid fibrids are homogenizer treated or refined. 4. The method according to any one of claims 1 to 3,
Wherein the aramid flock is made of meta-aramid. 5. The method according to any one of claims 1 to 4,
Wherein the aramid fibrids are made of meta-aramid. 6. The method according to any one of claims 1 to 5,
Wherein the aramid flock is contained in an amount of 20 to 80% by weight based on the total weight of the insulating paper. 7. The method according to any one of claims 1 to 6,
Wherein the aramid fibrid is contained in an amount of 20 to 80% by weight based on the total weight of the insulating paper. 8. The method according to any one of claims 1 to 7,
Wherein the weight ratio of the aramid flock to the aramid fibrid is 20:80 to 80:20. 9. The method according to any one of claims 1 to 8,
An insulating paper further comprising at least one binder made of a polymer other than aramid. 10. The method according to any one of claims 1 to 9,
An insulating paper further comprising at least one filler. 11. The method according to any one of claims 1 to 10,
And a part of the aramid flock and a part of the aramid fibrid are thermally bonded. 12. The method according to any one of claims 1 to 11,
An insulating paper having a basis weight of 20 to 500 g / m 2. An electrical insulator comprising an insulating paper according to any one of claims 1 to 12. An electrical device comprising the electrical insulator of claim 13. 15. The method of claim 14,
An electrical device that is a transformer, generator or motor.