JPWO2019093305A1 - Insulating sheet - Google Patents

Abstract

The present invention is a sheet substrate composed of aramid flocs having an average fiber width of 10 to 30 μm and aramid fibrids having an average fiber width of 5 to 40 μm; average fibers of less than 5 μm present on at least the surface of the sheet substrate. It relates to fine binder fibers having a width; and an insulating sheet containing at least one kind of filler present on at least the surface of the sheet substrate. The insulating sheet of the present invention can suppress oxidative deterioration even when it comes into contact with a metal under high temperature conditions, and has excellent electrical insulation and excellent strength.

Description

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

With the expansion of applications for electronic parts and electrical equipment, the usage patterns of insulating sheets such as insulating paper are also diversifying. Paper made of cellulose fibers is often used as an inexpensive electrical insulating material because of its excellent electrical insulating properties, and is used for capacitors, transformers, electric wire covering materials, and the like. However, insulating paper containing cellulose fibers as the main component is made using deionized water for the purpose of removing residual ions in the insulating paper, so in addition to the need for dedicated equipment, a high humidity environment Underneath, since the cellulose fibers absorb moisture, the equilibrium water content in the insulating paper increases, and there is a problem that the electrical insulating property decreases.

Therefore, an electrically insulating paper made of aromatic polyamide, which is obtained by mixing flocs and fibrids of aromatic polyamide and then heat-pressure calendering, has been proposed (see Patent Document 1).

Further, an insulating paper has been proposed in which the fiber widths of the flocs and fibrids of the aromatic polyamide are within a predetermined range, and relatively fine fibers having a predetermined width or less are blended in the fibrids in a predetermined ratio (Patent Document). 2).

By the way, chlorine may be unavoidably mixed in the aramid-based insulating paper due to contact with a chlorine-containing medium in the manufacturing process, but it is difficult to completely remove the chlorine contained in the insulating paper. When the aramid-based insulating paper comes into contact with a member made of a metal such as iron or copper under high temperature conditions, the oxidation reaction is promoted due to the presence of chlorine, and the insulating paper and / or the metal member may be deteriorated. .. Therefore, in producing aramid-based insulating paper from aramid fibrid and fibers, it has been proposed to add hydrosaltite in the process of producing the insulating paper (see Patent Document 3).

Special Table 2014-501859 International Publication No. 2016/10396 Japanese Patent No. 3253794

According to Patent Document 3, by blending hydrotalcite in the papermaking process of aramid-based insulating paper, deterioration of the insulating paper when it comes into contact with a metal such as iron or copper under high temperature conditions can be suppressed. ..

When hydrotalcite is compounded in the papermaking process of insulating paper, hydrotalcite will be predominantly present in the insulating paper in the form of particles that intervene between the fibers. However, if a large amount of hydrotalcite particles are present inside the insulating paper in such a form, the entanglement of the fibers is hindered and the strength of the insulating paper is reduced, or due to the presence of hydrotalcite between the fibers. Problems such as a decrease in insulation due to an increase in voids (increase in air permeability) may occur. In addition, there is a concern that particles may fall off when the insulating paper is processed by heat pressure or the like.

An object of the present invention is to provide an insulating sheet which can suppress deterioration even when in contact with a metal under high temperature conditions, does not cause particles to fall off, and has excellent electrical insulation and excellent strength. To do.

The present invention
A sheet substrate consisting of aramid flocs with an average fiber width of 10-30 μm and aramid fibrids with an average fiber width of 5-40 μm,
Fine binder fibers having an average fiber width of less than 5 μm present on at least the surface of the sheet substrate, and
The present invention relates to an insulating sheet containing at least one kind of filler present on at least the surface of the sheet base material.

The insulating sheet of the present invention preferably has a dielectric strength of 15 kV / mm or more and a specific tear strength of 25 mN · m ² / g or more.

The fine binder fiber is preferably one that has undergone homogenizer treatment or refiner treatment.

The insulating sheet of the present invention may include a layer composed of the fine binder fiber and the filler on the sheet base material.

It is preferred that at least one of the aramid flocs, the aramid fibrids and the fine binder fibers consists of meta-aramid.

The amount of aramid flocs in the sheet substrate can be 80 to 20% by weight based on the weight of the sheet substrate.

The amount of aramid fibrid in the sheet base material can be 20 to 80% by weight based on the weight of the sheet base material.

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

The filler is preferably inorganic particles.

The inorganic particles preferably contain a bismuth compound.

In the insulating sheet of the present invention, it is preferable that at least a part of the aramid floc and at least a part of the aramid fibrid are heat-bonded.

The insulating sheet of the present invention preferably has a basis weight of 20 to 1000 g / m ² .

The present invention also relates to an electrical insulator with the insulating sheet and an electrical device with the electrical insulator, such as a transformer, a generator or an electric motor.

The insulating sheet of the present invention can suppress deterioration even when it comes into contact with a metal under high temperature conditions, and has excellent electrical insulation and excellent strength. Further, the insulating sheet of the present invention has less filler (particles) falling off from the sheet surface, and does not impair workability when the insulating sheet is thermally processed or processed and molded as an insulating member.

As a result of diligent studies, the present inventors
A sheet substrate consisting of aramid flocs with an average fiber width of 10-30 μm and aramid fibrids with an average fiber width of 5-40 μm,
Fine binder fibers having an average fiber width of less than 5 μm present on at least the surface of the sheet substrate, and
An insulating sheet containing at least one kind of filler existing on at least the surface of the sheet base material can suppress deterioration even if it comes into contact with a metal under high temperature conditions, the filler does not fall off, and excellent electricity is obtained. The present invention has been completed by finding that it has insulating properties and excellent strength.

In particular, the present inventors have allowed a filler, which is preferably an inorganic particle, more preferably an inorganic particle containing a bismuth compound, to be present on at least the surface of a sheet substrate composed of aramid fibrid and aramid floc, together with fine binder fibers. The insulating sheet of the present invention in the above form can suppress the removal of the filler from the sheet surface, and can suppress the deterioration of the insulating sheet and / or the metal even if it comes into contact with a metal under high temperature conditions, and , Has been found to have excellent electrical insulation and excellent strength.

The filler may be present on at least a part (preferably all) of the surface of the sheet base material, and can be present in the sheet base material as long as it is present on the surface of the sheet base material. .. However, it is preferable that the amount of the filler present in the sheet base material is small. Therefore, in the present invention, it is preferable that the filler is not blended in the sheet base material manufacturing process.

The fine binder fiber has an action of allowing the filler to be present on at least the surface of the sheet base material.

Further, by coating at least a part (preferably all) of the surface of the sheet base material with fine binder fibers, the insulating sheet of the present invention can also have excellent electrical insulating properties. Further, when the fine binder fibers are present (preferably filled) in the fine voids in the sheet base material, the discharge in the voids can be reduced or prevented, and the electrical insulation property can be further improved. it can. Further, since the insulating sheet of the present invention is not produced only by fine binder fibers, the production efficiency does not decrease and the strength does not decrease.

When the fine binder fiber is made of the same material as the sheet base material, it has an advantage that it has high adhesion to the sheet base material and does not impair performance such as insulation and heat resistance.

In the insulating sheet of the present invention, it is not essential that the fine binder fibers and the filler form a layer on the sheet base material, but when the sheet base material is provided with a layer composed of the fine binder fibers and the filler, the present invention is concerned. Since the thickness of the layer is sufficiently smaller than the thickness of the sheet base material, even if the insulating sheet of the present invention is heat-treated, it is possible to suppress a decrease in strength due to crystallization of aramid. Therefore, the insulating sheet of the present invention preferably includes a layer composed of the fine binder fiber and the filler on the sheet base material.

The sheet base material in the insulating sheet of the present invention is "consisting of aramid flocs and aramid fibrids" when the sheet base material is composed of only the aramid flocs and the aramid fibrids, and the aramid flocs and the aramid fibrids. It is meant to include both of the above-mentioned aramid fibrids when they contain components other than these.

Further, the "layer made of fine binder fibers and filler" in the insulating sheet of the present invention means a layer made of only the fine binder fiber and the filler, and a component other than the fine binder fiber and the filler. Includes both layers containing.

Hereinafter, the insulating sheet of the present invention will be described in detail.

[Aramid]
In the present invention, "aramid" means aromatic polyamide. In the present invention, the "aromatic polyamide" is chemically structurally 60 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more of the amide bond. It means a linear polymer compound directly bonded to a ring.

Aramids are classified into para-aramids, meta-aramids and copolymers thereof according to the position of the amide group substituted on the benzene ring. Paraaramides include polyparaphenylene terephthalamides and their copolymers, poly (paraphenylene) -copoly (3,4'-diphenyl ether) terephthalamide (poly (paraphenylene) -copoly (3,4'-diphenyl ether) terephthalamide. ) Etc. are exemplified. Examples of metaalamide include polymethaphenylene isophthalamide and a copolymer thereof. These aramids are industrially produced by, for example, conventionally known interfacial polymerization methods, solution polymerization methods, etc., and can be obtained as commercial products, but the present invention is not limited thereto. In the present invention, metaalamide is preferably selected. Metaaramid is soluble in general-purpose amide solvents, can be wet-molded using a polymer solution as a starting material, has excellent heat-sealing properties, and has good heat resistance and flame retardancy. .. Among the meta-aramids, polymetaphenylene isophthalamide is preferably used because it has good molding processability, heat adhesion, flame retardancy, heat resistance and the like.

In the insulating sheet of the present invention, it is preferable that at least one of aramid flocs, aramid fibrids and fine binder fibers is composed of meta-aramid.

[Aramid Flock]
"Aramid flocs" are short fibers made of aramid. The (number) average fiber length of aramid flocs in the present invention is preferably in the range of 1 to 50 mm, more preferably in the range of 2 to 40 mm, and even more preferably in the range of 3 to 30 mm. If the average fiber length is smaller than 1 mm, the strength of the insulating sheet may decrease. If the average fiber length exceeds 50 mm, "entanglement" and "binding" between the flocs are likely to occur in the insulating sheet, which may cause defects, which is not preferable.

The average fiber length of aramid flocs can be obtained, for example, by averaging the lengths of a predetermined number of aramid flocs (for example, 100 fibers). Specifically, the length of the aramid flocs existing in a predetermined area range (for example, 55 mm ² ) on the surface of the sheet base material may be measured by observation with a stereomicroscope or the like and averaged.

The sheet base material of the insulating sheet of the present invention contains aramid flocs. The aramid flocs in the present invention have a (number) average fiber width of 10 to 30 μm. The average fiber width of the aramid flocs is preferably 12 to 28 μm, more preferably 14 to 26 μm, and even more preferably 16 to 24 μm. The average fiber width of aramid flocs can be obtained, for example, by averaging the widths of a predetermined number of aramid flocs (for example, 100 fibers). Specifically, the width of the aramid flocs existing in a predetermined area range (for example, 60,000 μm ² ) on the surface of the sheet base material may be measured by SEM observation or the like and averaged.

The fineness of the aramid floc 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 9000 m of fiber. If the fineness is less than 0.1 denier, the entanglement in water becomes large and the performance of the insulating sheet may deteriorate. On the other hand, if the fineness exceeds 10 denier, the diameter of the flocs becomes too large, which may lead to a decrease in the aspect ratio, a decrease in the mechanical reinforcement effect, and poor uniformity of the insulating sheet, which is not preferable.

The aramid flocs used in the present invention preferably consist of meta-aramid. As the metaalamide, polymethaphenylene isophthalamide and a copolymer thereof are preferable, and for example, it can be produced by copolymerizing m-phenylenediamine and isophthalic acid chloride. Metaaramid flocs are commercially available, and for example, "Conex (registered trademark)" of Teijin Limited can be used, but the present invention is not limited thereto.

[Aramid Fibrid]
The sheet base material of the insulating sheet of the present invention contains aramid fibrid. "Aramid fibrid" is a film-like or fibrous fine particle made of aramid, and is sometimes called aramid pulp (for aramid fibrid, Tokukousho 35-11851, Tokukousho 37-5752). Etc.). Since fibrid has paper-making properties like ordinary wood (cellulose) pulp, it can be formed into a sheet by a paper machine after being dispersed in water.

The aramid fibrid used in the present invention preferably consists of meta-aramid. As the metaalamide, polymethaphenylene isophthalamide and a copolymer thereof are preferable, and for example, it can be produced by copolymerizing m-phenylenediamine and isophthalic acid chloride. The meta-aramid fibrid can be produced by a wet precipitation method, for example, according to the method described in Japanese Patent Publication No. 35-11851.

Aramid fibrid can be subjected to so-called beating treatment for the purpose of maintaining quality suitable for papermaking, similar to ordinary wood pulp. This beating process can be performed by a papermaking raw material processing device such as a disc refiner or a beater that exerts a mechanical cutting action.

The aramid fibrid in the present invention has a (number) average fiber width of 5-40 μm. The average fiber width of the aramid fibrid is preferably 5 to 35 μm, more preferably 6 to 30 μm, and even more preferably 6 to 19 μm. The average fiber width of the aramid fibrid can be obtained, for example, by averaging the widths of a predetermined number (for example, 100) of the aramid fibrid. Specifically, the width of the aramid fibrid existing in a predetermined area range (for example, 60,000 μm ² ) on the surface of the sheet base material may be measured by SEM observation or the like and averaged.

The length of the aramid fibrid in the present invention is not particularly limited. The range of 100 to 2000 μm is preferable, the range of 200 to 1500 μm is more preferable, and the range of 300 to 1000 μm is even more preferable.

[Sheet base material]
The sheet base material of the insulating paper of the present invention is a porous sheet-like material mainly composed of aramid flocs and aramid fibrids, and has a large number of voids. The form of the sheet-like material is not particularly limited, and various forms such as woven fabric, non-woven fabric, and paper can be mentioned, but the form of paper is preferable.

The size of the void, particularly when the void can be approximated to a sphere, the diameter (hole diameter) of the sphere is preferably 0.1 to 10 μm, more preferably 1 to 8 μm, and even more preferably 2 to 6 μm.

The thickness of the sheet base material is preferably 10 to 1000 μm, more preferably 20 to 800 μm, and even more preferably 30 to 500 μm. The basis weight of the sheet substrate is preferably from 10 to 1000 g / ^{m 2,} more preferably 20 to 500 g / ^{m 2,} even more preferably 30~300g / ^{m 2.}

The sheet base material preferably contains 20 to 80% by weight of aramid flocs, more preferably 30 to 70% by weight, and 40 to 60% by weight, based on the total weight (total mass) of the sheet base material. Is even more preferable.

The sheet substrate preferably contains 20 to 80% by weight of aramid fibrid, more preferably 30 to 70% by weight, and even more preferably 40 to 60% by weight, based on the total weight of the sheet substrate. preferable.

The mixing ratio of aramid floc and aramid fibrid in the sheet base material can be arbitrary, but the mixing ratio (weight ratio) of aramid floc / aramid fibrid is preferably 20:80 to 80:20, preferably 30:70 to 70:30 is more preferable, and 40:60 to 60:40 is even more preferable.

The sheet base material can be produced, for example, by a method in which aramid flocs and aramid fibrids are mixed and then made into a sheet. Specifically, for example, after dry mixing aramid flocs and aramid fibrids, a method of forming a sheet using an air flow; aramid flocs and aramid fibrids are dispersed and mixed in a liquid medium such as water to obtain a slurry. After that, a method can be used in which the slurry is discharged onto a support such as a liquid permeable net or a belt to form a sheet, and the liquid medium is removed and dried. The latter is preferable, and water is used among them. A so-called wet fabrication method used as a liquid medium is preferable.

In the wet papermaking method, a method of supplying an aqueous slurry containing at least aramid floc and aramid fibrid to a paper machine, dispersing it, dehydrating it, squeezing it, and drying it to wind it up as a sheet (wet papermaking method) is common. is there. As the paper machine, a long net paper machine, a circular net paper machine, an inclined paper machine, a combination paper machine combining these, and the like can be used. In the case of production with a combination paper machine, a composite sheet composed of a plurality of paper layers can be obtained by forming a sheet of slurries having different mixing ratios and combining them. Additives such as dispersibility improvers, defoamers, and paper strength enhancers are used during papermaking as needed.

The sheet base material obtained as described above can be improved in density, crystallinity, heat resistance, dimensional stability, mechanical strength, etc. by, for example, heat-pressing between a pair of rolls at a high temperature and high pressure. it can. As a result, it is preferable that at least a part of the aramid flocs and at least a part of the aramid fibrids are heat-sealed. The thermal pressure conditions can be exemplified in the range of a temperature of 100 to 350 ° C. (preferably 200 to 350 ° C.) and a linear pressure of 50 to 400 kg / cm when a metal roll is used, but are limited thereto. It is not something that is done. It is also possible to stack a plurality of sheet base materials at the time of heat pressure. Further, the above-mentioned thermal pressure processing can be performed a plurality of times in any order.

[Fine binder fiber]
The insulating sheet of the present invention contains fine binder fibers having an average fiber width of less than 5 μm, which are present on at least the surface of the sheet base material.

The fine binder fiber may be present only on the surface of the sheet base material, but may be present in the sheet base material. Specifically, the fine binder fiber may be present in the fine voids in the sheet base material. The existence form of the fine binder fibers when they are present in the fine voids of the sheet base material is not particularly limited, and for example, the voids may be filled with at least one fine binder fiber. The entire length of the fine binder fiber does not have to be included in the voids, and a part thereof may be present in the voids. Further, the voids may not be completely filled.

The average fiber width of the fine binder fibers in the present invention is preferably less than 4.5 μm, more preferably less than 4.0 μm, even more preferably less than 3.5 μm, even more preferably less than 3.0 μm, further less than 2.5 μm. More preferred. The average fiber width of the fine binder fibers is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.3 μm or more, even more preferably 0.4 μm or more, still more preferably 0.5 μm or more. preferable. Therefore, the average fiber width of the fine binder fibers is preferably less than 0.1 to 4.5 μm, more preferably less than 0.2 to 4 μm, even more preferably less than 0.3 to 3.5 μm, and 0.4 to less than. Less than 3.0 μm is even more preferable, and 0.5 to less than 2.5 μm is even more preferable. The average fiber width can be obtained, for example, by averaging the widths of a predetermined number of fine binder fibers (for example, 100 fibers). Specifically, the width of the fine binder fibers existing in a predetermined area range (for example, 60,000 μm ² ) on the surface of the insulating sheet of the present invention may be measured by SEM observation or the like and averaged.

The length of the fine binder fiber in the present invention is not particularly limited. The range of 100 to 2000 μm is preferable, the range of 200 to 1500 μm is more preferable, and the range of 300 to 1000 μm is even more preferable.

The fine binder fiber is preferably an organic fine fiber, more preferably a fine fiber made of an organic polymer, and further has high heat resistance (for example, a melting point of 150 ° C. or higher, preferably a melting point of 200 ° C. or higher). More preferably, the melting point is 250 ° C. or higher).

As the fine binder fiber, the same polymetaphenylene isophthalamide and its copolymer as aramid floc or aramid fibrid, other aramid (for example, para-aramid), polyethylene terephthalate and its copolymer, polybutylene terephthalate and its copolymer weight. Examples thereof include coalescence, cellulose such as microfibril cellulose or cellulose nanofibers. Among them, fibers of polymethaphenylene isophthalamide are preferable. In the present invention, one type of fiber may be used, or two or more types may be used in combination (so-called mixed extraction).

As the fine binder fiber, fine aramid fiber made of the same aramid as aramid floc and / or aramid fibrid is preferable.

The fine aramid fiber can be produced, for example, by refining the aramid fibrid. The type of the miniaturization treatment is not particularly limited, and may be a non-mechanical miniaturization treatment such as ultrasonic treatment, but a homogenizer treatment or a refiner treatment is preferable. Double disc refiner or conical refiner treatment is more preferred. Therefore, it is particularly preferable that the fine aramid fiber has undergone a double disc refiner or conical refiner treatment.

The insulating sheet of the present invention preferably includes a layer composed of fine binder fibers and a filler described later. When the insulating sheet of the present invention includes a layer composed of fine binder fibers and a filler described later, the amount of the binder fibers in the layer can be 5 to 80% by weight based on the weight of the layer, and further. It can be 10 to 60% by weight and 15 to 40% by weight.

The weight ratio of the fine binder fiber to the filler described below in the layer can be 5: 90 to 90: 5.

The amount of the fine binder fiber in the insulating sheet of the present invention is not particularly limited, but can be, for example, 0.01 to 30% by weight with respect to the total weight (total mass) of the insulating sheet. , 0.1 to 20% by weight, more preferably 0.5 to 10% by weight, and even more preferably 1 to 5% by weight.

[Filler]
The insulating sheet of the present invention contains at least one kind of filler (filler) present on at least the surface of the sheet base material. The filler has a particle shape.

The type of filler is not particularly limited, but inorganic particles are preferable, and for example, clay such as talc, silica, mica (mica), graphite, cericite, kaolin, bentonite, hydrotalcite, etc., carbon nanotubes, aluminum nitride, etc. , Aluminum oxide, boron nitride, calcium carbonate, magnesium hydrogen carbonate, barium sulfate, magnesium oxide, zinc oxide and other inorganic fillers. In the present invention, it is preferable that the filler is not blended in the papermaking process of the sheet base material. The filler may be hydrotalcite unless it is compounded in the sheet substrate papermaking process, but if the filler is compounded in the sheet substrate papermaking process, it is preferable that the filler is not hydrotalcite.

The filler is preferably a compound of manganese, zinc, bismuth, and aluminum, and more preferably contains a bismuth compound. It is even more preferable that the filler is a bismuth compound.

The bismuth compound is not particularly limited, and examples thereof include bismuth oxides, hydrated oxides, hydroxides, and bismuth salts such as nitrates, subnitrates, carbonates, and subcarbonates. Can be done. Specific examples thereof include bismuth oxide, bismuth hydroxide, bismuth subnitrate, bismuth subcarbonate, and other compounds of bismuth capable of producing bismuth oxide by thermal decomposition.

The insulating sheet of the present invention preferably includes a layer made of fine binder fibers and a filler. The filler may be contained in the sheet base material, but the amount thereof is preferably small. More preferably, the filler is present only on the surface of the sheet substrate.

The amount of the filler in the layer composed of the fine binder fibers and the filler can be 20 to 95% by weight based on the weight of the layer, and further 40 to 90% by weight and 60 to 85% by weight. There can be.

The weight ratio of the filler to the fine binder fibers in the layer can be 20:80-80:20.

The insulating sheet of the present invention may include a layer composed of only a filler. In this case, it is preferable to provide a layer made of only the fine binder fibers on the surface of the layer made of only the filler. In this case as well, the filler may be contained in the sheet base material, but the amount thereof is preferably small. More preferably, the filler is present only on the surface of the sheet substrate.

The amount of the filler in the insulating sheet of the present invention is not particularly limited, but can be, for example, less than 0.01 to 30% by weight with respect to the total weight (total mass) of the insulating sheet. It is preferably 0.1 to less than 20% by weight, more preferably less than 0.5 to 10% by weight, and even more preferably less than 1 to 5% by weight.

[Insulating sheet]
The insulating sheet of the present invention can be produced, for example, by coating one side or both sides of a sheet base material with fine binder fibers and fillers.

Specifically, for example, a method of dry-spraying the fine binder fiber and the filler on the surface of the sheet base material as they are, or a method of dispersing the fine binder fiber and the filler in a liquid medium such as water to prepare a coating liquid, and the coating liquid. Is applied onto the sheet base material, and the fine binder fibers and the filler are wet-sprayed on the sheet base material. In the case of wet spraying, the coating liquid is dried and the liquid medium is removed. A layer composed of fine binder fibers and a filler can be formed on one side or both sides of the sheet base material by either dry spraying or wet spraying. In particular, wet spraying can easily form a layer of fine binder fibers and fillers.

In the case of wet spraying, for example, the liquid medium may be sucked and removed through the voids of the sheet base material. However, in this case, the fine binder fibers and the filler are easily sucked into the voids of the sheet base material, and it becomes difficult for the fine binder fibers and the filler to be present on the surface of the sheet base material, which is not preferable.

It is not essential that the fine binder fibers and the filler form a layer on the sheet base material, but when the sheet base material is provided with a layer composed of the fine binder fibers and the filler, the thickness of the layer is the thickness of the sheet base material. Smaller than The thickness of the layer made of fine binder fibers is, for example, preferably 1 to 300 μm, more preferably 2 to 200 μm, and even more preferably 3 to 100 μm.

Further, the layer composed of the fine binder fiber and the filler may be present in at least a part of the sheet base material, but is preferably present in at least 50% of the surface of the sheet base material, and more preferably in at least 80%. It is preferably present in at least 90%, even more preferably.

The insulating sheet obtained as described above can be improved in density, crystallinity, heat resistance, dimensional stability, mechanical strength and the like by, for example, heat-pressing between a pair of rolls at a high temperature and high pressure. .. The heat pressure conditions can be exemplified in the range of a temperature of 100 to 350 ° C. (preferably 200 to 350 ° C.) and a linear pressure of 50 to 400 kg / cm when using a metal roll, for example. The pressure machining can be performed a plurality of times in any order.

In the insulating sheet of the present invention, the fine binder fibers are present on the surface of the sheet base material mainly composed of the aramid flocs and the aramid fibrids and / or in the voids in the sheet base material, and the sheet The presence of the filler on at least the surface of the base material can provide excellent electrical insulation. For example, the insulating sheet of the present invention can have a dielectric strength of 15 kV / mm or more and a specific tear strength of 25 mN · m ² / g or more. The dielectric strength of the insulating sheet of the present invention is preferably 16 kV / mm or more, and even more preferably 17 kV / mm or more. The specific tear strength of the insulating sheet of the present invention is preferably 30 mN · m ² / g or more, more preferably 35 mN · m ² / g or more.

Dielectric strength and specific tear strength are usually in a trade-off relationship. Therefore, for example, if the blending ratio of aramid fibrid is increased to increase the dielectric strength, the specific tear strength is lowered, while if the blending ratio of aramid floc is increased to increase the dielectric strength, the dielectric strength is lowered. However, in the insulating sheet of the present invention, the fine binder fibers cover the surface of the sheet base material and / or fill the voids in the sheet base material to improve the dielectric strength by using the aramid fibrid. In addition, the dielectric strength can be further increased, while the specific tear strength can be increased by using an appropriate amount of aramid flocs as needed. Therefore, the insulating sheet of the present invention can achieve both high dielectric strength and high specific tear strength.

The thickness of the insulating sheet of the present invention is preferably 10 to 1200 μm, more preferably 20 to 1000 μm, and even more preferably 30 to 800 μm. The basis weight of the insulating sheet of the present invention is preferably 10~1500g / ^{m 2,} more preferably 20~1000g / ^{m 2,} still more preferably 30 to 500 g / ^{m 2.}

[Other binders]
The insulating sheet of the present invention may further contain at least one other binder other than the fine binder fiber, if necessary. Examples of other binders include amorphous resins. The resin used as the other binder may be in the form of a water-soluble or dispersible polymer that is added directly to the sheet-based papermaking dispersion, or may be dried or further compressed and / or heat-treated. It may be in the form of a powder of a thermoplastic resin material mixed with aramid fibers so that it is activated as a binder by the heat applied between the two. Examples of the water-soluble or dispersible polymer include water-soluble or water-dispersible thermosetting such as polyamide resin, epoxy resin, phenol resin, urea resin, urethane resin, melamine formaldehyde resin, thermosetting polyester resin, and alkyd resin. Resin can be mentioned. Particularly useful is a water-soluble polyamide resin. An aqueous solution or an aqueous dispersion of a thermoplastic resin such as poly (vinyl alcohol), polypropylene, polyester, or poly (vinyl acetate) can also be used in the same manner. In addition, these thermoplastic resins can also be used as the powder of the above-mentioned thermoplastic resin material.

The other binder may be contained in the sheet base material, and when the insulating sheet of the present invention includes a layer made of fine binder fibers and a filler, it may be contained in the layer. However, especially when the other binder is film-forming, if the abundance ratio of the other binder is too high, the air permeability of the insulating sheet may decrease and blisters may occur during heat processing. Therefore, the other binder may occur. It is preferable that the blending amount of is small. The blending amount of the other binder can be, for example, 0.001 to 10% by weight, preferably 0.005 to 7% by weight, and 0.01 to 0.01% by weight, based on the total weight (total mass) of the insulating sheet. 3% by weight is more preferable, and 0.05 to 1% by weight is even more preferable. It is particularly preferable that the insulating sheet of the present invention does not contain the other binder.

[Other ingredients]
The insulating sheet of the present invention may contain other fibers made of a material other than aramid, if necessary. Examples of other fibers include heat-resistant fibers such as aromatic polyester fibers, aromatic polyetherketone fibers, and paraaramid fibers.

The paraaramid fiber is obtained by condensate of a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide, and the amide bond is at the para position of the aromatic ring or an orientation position similar thereto (for example, 4,4'-. It consists substantially of repeating units that are coupled in opposite directions (orientations extending coaxially or in parallel in opposite directions) such as biphenylene, 1,5-naphthalene, 2,6-naphthalene, etc., for example poly (paraphenylene terephthalamide). ), Poly (4,4'-benzanilide terephthalamide), poly (paraphenylene-4,4'-biphenylenedicarboxylic acid amide), poly (paraphenylene-2,6-naphthalenedicarboxylic acid amide), etc. Alternatively, an aromatic polyamide having a structure close to the para-oriented type can be specifically mentioned. These aromatic polyamides are produced by polymerizing a para-oriented aromatic diamine and a para-oriented aromatic dicarboxylic acid halide.

Examples of the para-oriented aromatic diamine are para-phenylenediamine (hereinafter, may be referred to as PPD), 4,4'-diaminobiphenyl, 2-methyl-para-phenylenediamine, 2-chloro-para-phenylenediamine, 2,6. -Naphthalenediamine, 1,5-naphthalenediamine, 4,4'-diaminobenzanilide and the like can be mentioned.

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

The other fibers may be contained in the sheet base material, and when the insulating sheet of the present invention includes a layer composed of fine binder fibers and fillers, the other fibers may be contained in the layer. The insulating sheet of the present invention does not have to contain the other fibers.

The insulating sheet of the present invention can function as an electrically insulating sheet. The insulating sheet of the present invention can have an electrical resistance of at least 10 ¹³ Ωcm, preferably at least 10 ¹⁵ Ωcm, according to the method of volume resistivity of ASTM D-257.

The insulating sheet of the present invention has excellent properties as an electrical insulating sheet, and in particular, has excellent electrical insulating properties and strength, and is therefore useful as a component of an electrical insulator. For example, the insulating sheet of the present invention or a laminate thereof can be used as a component of an electric insulator constituting an electric device such as a transformer, a generator, or a motor. The insulating sheet of the present invention or a laminate thereof may be impregnated with a resin such as phenol resin, epoxy, or polyimide, but even if it is not impregnated with the resin, excellent electrical insulation can be exhibited.

Therefore, the present invention
A sheet substrate consisting of aramid flocs with an average fiber width of 10-30 μm and aramid fibrids with an average fiber width of 5-40 μm,
Fine binder fibers having an average fiber width of less than 5 μm present on at least the surface of the sheet substrate An electrical insulation method using an insulating sheet containing at least one filler present on at least the surface of the sheet substrate, particularly How to improve electrical insulation,
Or,
A sheet substrate consisting of aramid flocs with an average fiber width of 10-30 μm and aramid fibrids with an average fiber width of 5-40 μm,
Fine binder fibers present on at least the surface of the sheet substrate and having an average fiber width of less than 5 μm Use for electrical insulation of insulating sheets containing at least one filler present on at least the surface of the sheet substrate, in particular. Has the aspect of, use for improving electrical insulation. The above description applies to the above aramid flocs and the above aramid fibrids.

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.

[Evaluation method]
(Average fiber width)
Each fiber slurry obtained from the following Examples and Comparative Examples is diluted, dropped onto a slide to form a uniform thin film, dried, and magnified 100 to 400 times with a scanning electron microscope to randomly form three fields of view. The fiber width of 30 fibers was randomly measured from each field of view, and the number average fiber width was calculated.

(Dielectric strength)
Measured according to ASTM D-149.

(Specific tear strength)
Measured according to JIS P8116: 2000.

(Heat deterioration test)
Two insulating sheets obtained from the following examples and comparative examples cut into 5 cm × 5 cm were prepared, a copper piece was sandwiched between them, and the entire sheet was sandwiched between stainless steel plates and heated in an oven at 280 ° C. for 120 hours. After that, the state of the insulating sheet was visually evaluated according to the following criteria.
-There are no holes in the copper piece contact part and its surroundings, and there is no difference in discoloration from the non-contact part.
-There is no hole in the copper piece contact part and its surroundings, but there is a difference in discoloration from the non-contact part.
× There is a hole of the same size as a piece of copper.

(Evaluation of filler dropout)
The insulating sheets before the heat and pressure treatment obtained from the following examples and comparative examples were cut into 23 cm × 23 cm, and 10 sheets were passed through a thermal calender having a temperature of 300 ° C. and a linear pressure of 60 kg / cm. The degree of contamination due to the transfer of the filler to the roll was visually evaluated according to the following criteria.
・ The roll is dirty.
× There is no dirt on the roll.

[Examples 1 to 5]
Aramid flocs were disaggregated using a standard disintegrator at an absolute dry weight concentration of 0.3% for 15 minutes to obtain a fiber slurry having an average fiber width of 20 μm. Next, the metaaramid fibrid was dissociated using a standard disintegrator at an absolute dry weight concentration of 1% for 15 minutes, and then refiner treatment was performed to obtain a fiber slurry having an average fiber width of 6.5 to 18.5 μm. The obtained aramid floc and meta-aramid fibrid are mixed at an absolute dry weight ratio of 45:65 or 50:50 to prepare a wet sheet with a square hand-making machine using a 120-mesh wire, and a press machine is used. It was dehydrated and dried by heating in a dryer to obtain a sheet substrate of 42 g / m ² . Next, the metaaramid fibrid was dissociated using a standard dissociator at an absolute dry weight concentration of 1% for 15 minutes, and then a high-pressure homogenizer was used to obtain fine binder fibers having an average fiber width of 3 to 4.8 μm. It was. The obtained fine binder fiber and a bismuth compound (manufactured by Nacalai Tesque, bismuth hydroxide (III)) are mixed at a solid content ratio of 1: 4 so that the solid content adhesion amount per side is 2.5 g / m ^2. , Both sides of the sheet substrate were coated using a wire bar. This was heat-pressurized with a metal roll heated to 300 ° C. to prepare an insulating sheet.

[Example 6]
Hydrotalcite (manufactured by Kyowa Chemical Industry Co., Ltd., trade name: Alchemizer) was used instead of the bismuth compound, and the solid content of the fine binder fiber per side was 1.0 g / m ² , and the fine binder fiber and hydrotalcite were used. Was mixed at a solid content ratio of 2:10 and applied to both sides of the sheet base material using a wire bar so that the amount of solid content adhered to one side was 6.0 g / m ^2. An insulating sheet was produced in the same manner as in 1.

[Example 7]
Adjust the refiner treatment and homogenizer treatment so that the average fiber width of the meta-aramid fibrid is 12.2 μm and the average fiber width of the fine binder fiber is 3.3 μm, and the aramid flocs and the meta-aramid fibrid are added to the absolute dry weight ratio of 50. It was prepared in the same manner as in Example 6 except that it was mixed at a ratio of 50 to 50.

[Comparative Example 1]
An insulating sheet was produced in the same manner as in Example 1 except that only fine binder fibers were applied without using a bismuth compound.

[Comparative Example 2]
An insulating sheet was produced in the same manner as in Example 1 except that the homogenizer treatment was adjusted so that the average fiber width of the fine binder fibers was 15 μm.

Average fiber width of various fibers constituting Examples 1 to 7 and Comparative Examples 1 and 2, type of filler, dielectric strength of the obtained insulating sheet, specific tensile strength, thermal deterioration test result, filler dropout evaluation result Is shown in Table 1.

As is clear from Table 1, in the examples, a good insulating sheet having high dielectric strength and specific tensile strength, good thermal deterioration test results, and no problem of filler falling off was obtained. On the other hand, the sheet of Comparative Example 1 could not suppress thermal deterioration because it did not use a filler. Further, since the sheet of Comparative Example 2 has a large fiber width of 15 μm (much larger than 5 μm), the dielectric strength and the specific tear strength are inferior to those of the sheet of Example, and the filler falls off. Could not be suppressed.

Claims (15)

A sheet substrate consisting of aramid flocs with an average fiber width of 10-30 μm and aramid fibrids with an average fiber width of 5-40 μm,
Fine binder fibers having an average fiber width of less than 5 μm present on at least the surface of the sheet substrate, and
An insulating sheet containing at least one kind of filler present on at least the surface of the sheet base material. The insulating sheet according to claim 1, wherein the dielectric strength is 15 kV / mm or more, and the specific tear strength is 25 mN · m ² / g or more. The insulating sheet according to claim 1 or 2, wherein the fine binder fiber has been subjected to a homogenizer treatment or a refiner treatment. The insulating sheet according to any one of claims 1 to 3, further comprising a layer composed of the fine binder fiber and the filler on the sheet base material. The insulating sheet according to any one of claims 1 to 4, wherein at least one of the aramid floc, the aramid fibrid, and the fine binder fiber is meta-aramid. The insulating sheet according to any one of claims 1 to 5, wherein the amount of the aramid flocs in the sheet base material is 80 to 20% by weight based on the weight of the sheet base material. The insulating sheet according to any one of claims 1 to 6, wherein the amount of the aramid fibrid in the sheet base material is 20 to 80% by weight based on the weight of the sheet base material. The insulating sheet according to any one of claims 1 to 7, wherein the weight ratio of the aramid floc to the aramid fibrid is 20:80 to 80:20. The insulating sheet according to any one of claims 1 to 8, wherein the filler is inorganic particles. The insulating sheet according to claim 9, wherein the inorganic particles contain a bismuth compound. The insulating sheet according to any one of claims 1 to 10, wherein at least a part of the aramid floc and at least a part of the aramid fibrid are heat-bonded. The insulating sheet according to any one of claims 1 to 11, which has a basis weight of ^{20 to} 1000 g / m ² . An electrical insulator comprising the insulating sheet according to any one of claims 1 to 12. An electrical device comprising the electrical insulator according to claim 13. The electrical device according to claim 14, which is a transformer, a generator, or an electric motor.