JPH1120083A - Composite sheet and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure adequate relaxation effects for an electric field and also the display of outstanding antistatic function and upgraded mechanical characteristics by specifying the volumetric intrinsic resistance value of an aramid sheet containing silicone rubber. SOLUTION: A silicone rubber layer and an aramid sheet material are laminated on each other. The aramid sheet material is composed of aramid fibrid and an aramid block, and further, contains carbon fiber. The volumetric intrinsic resistance value of the aramid sheet material is 10<-2> -10<7> Ωcm. Aramid which composes the aramid sheet is poly-m-phenyleneisophthalamide. The aramid fibrid is a film-like microparticle compound of aramid and is sometimes called aramid pulp. The aramid block is a short aramid fiber. The aramid sheet material is a sheet-like molding, such as woven fabric or unwoven fabric, manufactured by a dry or a wet process, from the aramid fibrid and/or the aramid block.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a rotating machine (generator,
The present invention relates to a composite sheet using an aramid-based sheet material as an electric insulating material in the field of electric motors, transformers, and electric and electronic devices, and a method for producing the same. In particular, the present invention relates to a composite sheet that can be suitably used as a material for preventing corona generation of a rotating machine, an antistatic component of an electronic / electric device, an auxiliary material for processing and assembling, and a method for producing the same.

[0002]

2. Description of the Related Art In a large rotating machine, a voltage of several kV to 10 kV is applied between a coil portion as a conductor and a slot insulating material as an insulator.
A large voltage of about several kV is almost always applied. When partial discharge occurs in this portion, insulation damage due to ionized molecules progresses, resulting in a significant reduction in the life of the rotating machine. In particular, with the recent miniaturization of equipment, the thickness of the insulating layer is reduced to increase the electric field strength, and thus the possibility of such partial discharge tends to increase. At the same time, an increase in the generated (output) voltage and current due to the increase in capacity is also considered to be a factor that causes the above problem. Therefore, the rotating machine,
In particular, in a large rotating machine, in order to secure the reliability of an insulation system capable of suppressing corona generation, a material capable of reducing an electric field generated between a coil and an insulating material is extremely important.

Conventionally, as a method of alleviating an electric field of a rotating machine to which a high voltage is applied, 1) a conductive paint is applied to the outermost surface of an insulating layer.
2) a method of winding or inserting a conductive thin material (for example, paper, film, tape, etc.) 3) a method of mounting a conductive composite material (for example, FRP laminate), 4) a conductive method 5) A method in which conductive silicone rubber is filled in a portion where a large discharge is detected by partial discharge monitoring or a conductive paint is applied to the coil surface to repair the portion is appropriately adopted. Among them, the method using a conductive elastomer is recognized to be effective in corona generation in combination with a secondary effect of suppressing (absorbing) vibration of a coil due to rotation.

[0004] However, the above method of applying a conductive paint does not always have good workability in the manufacturing process of equipment.
The impact on the working environment due to solvent evaporation cannot be ignored,
There is a problem in that it takes a long time for the operation, and in addition, the reproducibility of the conductivity (resistance value).

[0005] On the other hand, the method using a conductive silicone rubber is excellent in vibration absorption, heat resistance and corona generation suppressing effect. However, since the mechanical strength of the silicone rubber used is not sufficient, the method in the equipment manufacturing process is not sufficient. There are problems such as breakage due to tearing, and the need to handle the silicone rubber itself because it is too soft and lacks self-holding properties. Therefore, there is a strong demand for the development of a material (referred to as a corona-suppressing material) capable of suppressing electric field relaxation, that is, corona discharge, having both good properties, mechanical strength, and good handleability of the conductive silicone rubber. Was.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a composite having an electric field relaxation function and an antistatic function which can be favorably used as a corona suppressing material for a rotating machine, an antistatic component for an electronic / electric device, and an auxiliary material for processing and assembling them. A sheet and a method for producing the sheet are provided. The inventor of the present invention has made intensive studies to solve the above-mentioned problems. As a result, the aramid-based sheet material contains silicone-based rubber, and the composite sheet material has a volume resistivity of 10 ⁻² Ωcm or more and 10 ⁷ Ωcm. The inventors have found that the following effects can be sufficiently solved, and that the above-mentioned problems can be solved by having a good antistatic function and improved mechanical properties, thereby achieving the present invention.

[0007] That is, the composite sheet according to the first invention of the present application is an aramid-based sheet material containing silicone-based rubber, and has a volume resistivity of 10 ^-2 Ωcm or more.
It is characterized by being not more than 0 ⁷ Ωcm. The composite sheet according to the second invention of the present application is characterized in that the composite sheet according to the first invention has a layer structure of at least two or more layers in which a silicone rubber layer and an aramid sheet material are laminated. Features. A composite sheet according to a third invention of the present application is characterized in that, in the composite sheet according to the above first or second invention, the aramid-based sheet material comprises an aramid fibrid and an aramid floc.

[0008] The composite sheet according to the fourth invention of the present application comprises:
The composite sheet according to the third aspect described above, wherein the composite sheet is an aramid-based sheet material composed of aramid fibrid and aramid floc, further containing carbon fibers, and having a volume resistivity of 10 ⁻² Ωcm or more and 10 ⁷ Ωcm or less. There is a feature. The composite sheet according to the fifth invention of the present application is such that the silicone rubber contained in the aramid sheet material according to any one of the first to fourth inventions has a volume resistivity of 10 ⁻² Ωcm or more, It is characterized by being 10 ⁷ Ωcm or less. A composite sheet according to a sixth aspect of the present invention is characterized in that the aramid constituting the aramid-based sheet according to any one of the first to fifth aspects is polymetaphenylene isophthalamide.

A method of manufacturing a composite sheet according to a seventh aspect of the present invention is a method of manufacturing a composite sheet for manufacturing the composite sheet according to any one of the first to sixth aspects described above, wherein the method comprises the steps of: The layer and the aramid-based sheet material layer are integrally laminated. The method for producing a composite sheet according to the eighth invention of the present application is a method for producing a composite sheet for producing the composite sheet according to any of the first to sixth inventions, wherein the aramid-based sheet material layer and At least one or more silicone rubber layers are laminated. The method for producing a composite sheet according to the ninth invention of the present application is the method for producing a composite sheet for producing the composite sheet according to the seventh or eighth invention, wherein the aramid constituting the aramid-based sheet is a polyamide sheet. It is characterized by being metaphenylene isophthalamide.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the "volume resistivity" is a value obtained by dividing a potential gradient in a direction parallel to a direction of a current flowing inside a material by the current density (unit: Ωc).
m). In the present invention, “conductive” is defined as having a volume resistivity of 10 ⁷ Ωcm or less.

(A) Silicone Rubber The silicone rubber in the present invention is a crosslinked polymer compound having a rubber elasticity in which the main chain skeleton is mainly connected by siloxane bonds. A material containing polydimethylsiloxane as a main component can be exemplified as a typical silicone rubber, but is not limited thereto. Such silicone rubbers include millable rubber vulcanizates, liquid rubber cured products,
It can be classified as a rubber dispersion cured product. Silicone rubber itself has inherently large volume resistivity,
Rather, it is classified as an insulator. Therefore, to impart conductivity to the silicone rubber of the insulator, carbon black, graphite, metal powder, metal fiber, conductive polymer,
Ceramics and the like can be added. Also color tone,
Additives such as fillers and chemicals can be added for the purpose of improving properties such as mechanical strength, hardness, durability and oxidation resistance. In order to further improve the rubber properties, a plurality of types of silicone rubber may be blended. In the present invention, a silicone rubber containing such various additives and formed into a sheet is referred to as a silicone rubber sheet.

The volume resistivity of the silicone rubber sheet is not particularly limited, but is preferably 10 ^-2 Ωcm or more and 10 ⁷ Ωcm or less. With a volume resistivity value smaller than this range, the volume resistivity region of the metal, for example, the volume resistivity value of copper is 1.7 × 10 ⁻⁶ Ωcm, and the volume resistivity value of aluminum is 2.
It approaches 7 × 10 ⁻⁶ Ωcm (at 20 ° C.), and it is difficult to expect the original electric field relaxation effect. If the volume resistivity is larger than the above range, the voltage drop is small and the electric field relaxation effect is still insufficient. That is, it is essential that the corona suppressing material has a volume specific resistance value in an intermediate region between the volume specific resistance values of the insulating material and the conductor. In order to achieve such a resistance value in a silicone rubber-based sheet, as described above, carbon black,
A method of adding a conductive filler such as metal powder and metal fiber is simple, effective, and practical.

(B) Aramid Aramid means a wholly aromatic polyamide. In terms of chemical structure, it is defined as a linear synthetic polymer in which 60 mol% or more of the bonds connecting the benzene rings are amide groups. Aramids are classified into para-aramids, meta-aramids, and copolymers thereof, depending on the substitution position of the amide group on the benzene ring. Examples of the para-aramid include polyparaphenylene terephthalamide and a copolymer thereof, poly (paraphenylene) -copoly (3,4 diphenyl ether) terephthalamide, and the like. Examples of the meta-aramid include polymetaphenylene isophthalamide and a copolymer thereof. In the present invention, meta-aramid is preferably used. Meta-aramid has features such as being soluble in general-purpose amide solvents, being capable of being wet-molded using a polymer solution as a starting material, being excellent in heat-sealing properties, and having good heat resistance and flame retardancy. is there. Meta-aramid can be industrially produced generally by a solution polymerization method by a condensation reaction of meta-phenylenediamine and isophthalic acid dichloride, a two-stage interfacial polymerization method, and the like.
It should be noted that other components may be copolymerized as long as the properties of meta-aramid are not impaired.

(C) Aramid fibrid Aramid fibrid is a film-like fine particle made of aramid, and is sometimes called aramid pulp.
No. 11851, JP-B-37-5752, etc.). Since fibrids have papermaking properties like ordinary wood (cellulose) pulp, they can be dispersed in water and then formed into a sheet by a paper machine. In this case, to improve properties such as electrical insulation and mechanical properties, a disintegrator,
An operation of dispersing the fibrid mass using equipment such as a beater and reducing the twist of each fibrid can be applied. In this operation, the morphological change of the fibrid can be monitored by a freeness test method specified in Japanese Industrial Standards P8121. In the present invention, the degree of filtration is preferably in the range of 10 to 300 ml (Canadian freeness). In the case of a fibrid having a degree of filtration higher than 300 ml, the strength and the dielectric breakdown voltage of the sheet molded product are not sufficient. On the other hand, even if a filtration degree lower than 10 ml is to be obtained, there is no remarkable advantage because the utilization efficiency of the input mechanical power is small and the throughput per unit time is often impaired.

(D) Aramid floc Aramid floc is a short fiber made of aramid. Examples of such fibers are "Conex (registered trademark)" and "Technola (registered trademark)" of Teijin Limited, "Apier (registered trademark)" of Unitika Limited, and "Nomex (registered trademark)" of DuPont. , "Kevlar (registered trademark)" and "Twaron (registered trademark)" of Akzo Corporation, but are not limited thereto. The fineness of the floc is preferably in the range of 0.1 denier to 10 denier. Here, denier is a unit expressed in mass (gram) per 9000 m of fiber. If the fineness is smaller than 0.1 denier, the entanglement in water is increased and the sheet quality is deteriorated, which is not preferable. On the other hand, the fineness is 10
If the denier is exceeded, the diameter of the flock becomes too large, and disadvantages such as a decrease in the aspect ratio, a decrease in the mechanical reinforcing effect, and poor uniformity in the sheet occur. The length of the flock is suitably in the range of 1 to 50 mm. When the length is smaller than 1 mm, the reinforcing effect of the sheet is reduced, and when the length of the flock is more than 50 mm, "locking" and "binding" of the flock are likely to occur when forming the sheet, which causes defects. It is not preferable because it is easy. In order to improve convergence, antistatic properties, smoothness, dispersibility in water, and the like, a surface treatment agent can be applied to the floc in advance.

(E) Aramid-based sheet The aramid-based sheet material of the present invention refers to a woven fabric (cloth) which is a sheet-like molded product for producing the aramid fibrid and / or aramid floc by a dry method or a wet method. ), Non-woven fabrics (dry and wet), paper, film, etc., but are not limited thereto. Among them, an aramid paper containing at least an aramid fibrid and an aramid floc is preferably used.

(F) Method for Producing Aramid Paper In the present invention, for producing aramid paper, there is no particular limitation, and a conventionally known wet papermaking method can be preferably applied. In the wet papermaking method, a single or mixed slurry containing at least aramid fibrid, aramid floc or other stock is sent to a paper machine and dispersed, and then dewatered, water-squeezed and dried to form a sheet. How to take. As the paper machine, a fourdrinier paper machine, a round 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, papermaking comprising a plurality of paper layers may be used. In papermaking, additives such as a dispersibility improver, an antifoaming agent, and a paper strength enhancer can be used as needed.
In addition, other fibrous components can be added.

Aramid fibrids have excellent properties as a binder, so that aramid floc and other additional components can be efficiently captured, and the paper stock yield is good. The density and mechanical strength of the aramid paper obtained by the wet papermaking method can be improved by hot pressing at a high temperature and a high pressure between a pair of flat plates or a metal roll. The condition of the heat pressure is, for example, when a metal roll is used, a temperature of 100 to
350 degrees and a linear pressure of 50 to 300 kg / cm can be exemplified, but not limited to these. It is also possible to simply press at room temperature without adding a heating operation. A plurality of sheets can be stacked during hot pressing. In the present invention, an aramid-mixed paper containing carbon fibers in the aramid paper has a volume resistivity of 10 ⁻² Ωcm or more and 10 ⁷ Ωc.
When it is less than m, the volume resistivity value of the composite sheet according to the present invention is preferably reproduced stably.

(G) Carbon Fiber In the present invention, the carbon fiber contained in the aramid sheet material is obtained by firing a fibrous organic substance at a high temperature in an inert atmosphere and carbonizing it. In general, carbon fibers are roughly classified into those obtained by firing polyacrylonitrile (PAN) fibers and those obtained by spinning pitches and then firing. In addition, carbon fibers are produced by spinning resins such as phenolic resins and then firing. Some of them can be used in the present invention. It is also possible to perform an oxidative cross-linking treatment using oxygen or the like before baking to prevent the fiber from being melted during baking.

The fineness of the carbon fiber used in the present invention is 0.5.
A range from 10 to 10 denier is preferred. The fiber length is 1-3
It is selected from the range of 0 mm. The aramid-mixed paper containing the carbon fiber can be easily produced by adding the carbon fiber to the slurry, mixing and dispersing, and applying the same papermaking method in the wet papermaking of the aramid paper described above. The required amount of carbon fiber in the aramid-mixed paper can vary depending on the fiber fineness and fiber length, but is generally 1 to 90 by weight.
% Range. If the amount of carbon fiber is smaller than this, the volume resistivity increases, and if the amount of carbon fiber is larger than this, the strength of the aramid-mixed paper is not sufficient and the reinforcing effect of the silicone rubber becomes insufficient. .

As described above, hot pressing can be applied to aramid-mixed paper containing carbon fibers. By this heat pressure,
While the aramid floc, aramid fibrid and carbon fiber (and other components) are in increased spatial contact, the carbon fiber breaks. The volume resistivity of aramid blended paper is determined by the result of the cancellation of these phenomena. There is a clear correlation between the density and the volume resistivity of the aramid-mixed paper under a range of heat and pressure conditions.
The composite sheet according to the present invention is characterized by comprising at least the silicone-based rubber and the aramid-based sheet material as constituents, and has a volume resistivity value of 10 ⁻² Ωcm or more and 10 ⁷ Ωcm or less.

Here, there is no particular limitation on the structure of the composite sheet comprising the silicone rubber and the aramid sheet material of the present invention. The above-mentioned silicone rubber is filled in the aramid sheet, and the silicone rubber forms a three-dimensional network inside the aramid sheet, or the independent layers of the silicone rubber and the aramid sheet material are laminated. There is no problem even with a multilayered structure. The structure in which the aramid sheet is a porous structure and the silicone rubber substantially penetrates into the aramid sheet is also within the scope of the present invention. Specifically, a two-layer structure including one silicone rubber sheet and one aramid sheet, a three-layer structure in which an aramid sheet is sandwiched between silicone rubber sheets, and a three-layer structure in which a silicone rubber sheet is sandwiched between aramid sheets Examples include a layered structure or a structure having more layers. The thickness of the composite sheet of the present invention is preferably 0.05 mm to 1 mm depending on the form of use.
It can be selected from the range of 00 mm, but is not limited to this.

(H) Method for Producing Composite Sheet The composite sheet of the present invention is obtained by laminating the silicone rubber sheet and the aramid sheet, and applying or extruding a silicone rubber sheet precursor to the aramid sheet. It can be manufactured by a lamination method or the like. Even if the aramid sheet is not conductive, if the silicone rubber has a volume resistivity of 10 ^-2 Ωcm or more and the silicone rubber sufficiently penetrates into the aramid sheet to form a conductive path, electrolysis may occur. It is possible to realize a volume specific resistance value in a range necessary for the expression of the relaxation function. When laminating an aramid-based sheet and a silicone-based rubber, it is possible to apply a conductive adhesive, perform a primer treatment, or the like for the purpose of improving the adhesion between the layers. Further, as described above, a method of applying or impregnating the silicone-based rubber to the aramid-based sheet and permeating at least a part of the aramid-based sheet for integration can be applied.

When the aramid-based sheet is an aramid-mixed paper containing aramid fibrid, aramid floc and carbon fiber, the composite is stable in quality with little variation in volume resistivity due to lamination and penetration of silicone rubber. There is an advantage that a body sheet can be created.
The composite sheet thus obtained has a volume resistivity of 10 ⁻² Ωcm or more and 10 ⁷ Ωcm or less, has an effect as an electric field relaxation material, and has an effect of an antistatic function.

[0025]

As described above, the composite sheet obtained by the present invention is composed of an aramid-based sheet material having excellent heat resistance and a silicone-based rubber. It has the required durability in high temperature environments. Since the composite sheet according to the present invention has an intermediate volume resistivity value between a conductor and an insulator, the composite sheet can be mounted between the conductor and the insulator of a rotating machine to reduce the concentration of an electric field and to achieve partial discharge. The occurrence of corona due to this can be suppressed. Furthermore, while maintaining the cushioning properties derived from the silicone rubber, the conventional disadvantages such as tearability and difficulty in handling can be solved. Therefore, it is possible to achieve long-term stability and reliability of a rotating machine using the composite sheet according to the present invention as a corona generation suppressing material or an electronic appliance using an antistatic material.

[0026]

The present invention will be described in detail with reference to examples.
Note that these examples explain and supplement the spirit of the present invention and do not limit the present invention in any way. (Measurement method) The measured values were evaluated by the following methods. (1) Measurement of the basis weight and thickness of the sheet The measurement was performed according to JIS C2111. (2) Dielectric breakdown voltage It was carried out based on ASTM D-149. (3) Tensile strength and elongation The test was performed based on ASTM D-828. (4) Volume specific resistivity 9 volts DC was applied to a sample of the composite sheet according to the present invention having a size of 5 × 5 cm, and a resistance value R (Ω) was measured from a current value after 30 seconds with a tester. The volume specific resistance value r was calculated from the following equation. r = 25R / (sample thickness: cm) (5) Tear strength Measured according to ASTM D1004.

(Preparation of Raw Materials) (Reference Example) A polymetaphenylene isophthalamide fibrid was produced by a method using a wet precipitator comprising a combination of a stator and a rotor described in Japanese Patent Publication No. 52-151624. This was treated with a beater to adjust the Canadian Standard Freeness (CSF) to 105 ml. Separately, a meta-aramid fiber “NOMEX (registered trademark)” manufactured by DuPont was cut to a length of 6 mm to obtain a papermaking raw material (flock). The fineness (denier) of this floc was 2. In Reference Example 1, a sheet of aramid paper was produced from the fibrid and floc thus produced by a wet papermaking method.

In Reference Example 2, a mixed slurry was prepared by adding chopped fiber (fiber length: 6 mm, fineness: 2 denier) to the above-mentioned slurry of fibrids and flocs to the Toray Industries, Inc. carbon fiber "Treca (registered trademark)". A sheet of aramid-mixed paper was formed by wet papermaking. The sheets obtained in Reference Examples 1 and 2 were passed between a pair of heating rolls to apply heat pressure. Table 1 shows the main characteristic values of the aramid paper and the aramid-mixed paper thus obtained.

[0029]

[Table 1]

(Example) On the surfaces of the aramid sheet samples of Reference Examples 1 and 2, "Silascon (registered trademark)" XA-2869 primer manufactured by Dow Corning Co., Ltd. was applied. Further, after forming conductive silicone rubber (uncrosslinked) to which carbon black has been added into a sheet shape (thickness 0.3 mm),
Combined from one side of the aramid paper, 120 ° C, 0.98G
Pressing was performed under a pressure of Pa (10 kgf / cm ² ) to prepare a composite sheet having a two-layer structure. In this case, in Example 1, the silicone rubber was impregnated and penetrated into the aramid paper. On the other hand, in Example 2, a two-layer structure of a silicone rubber layer and an aramid sheet layer made of the above-described aramid-mixed paper was formed. Table 2 shows the main characteristics of these composite sheets.

Comparative Example Table 2 shows the characteristics of a single conductive silicone rubber sheet material applied to a coil surface for the purpose of electric field relaxation in a conventional rotating machine to which a high voltage is applied. .

[0032]

[Table 2]

In any of Examples 1 and 2,
It has been shown that by combining a silicone rubber sheet material and an aramid sheet made of aramid paper or aramid mixed paper, the tear strength is improved, and further, the volume resistivity value of the composite sheet is It was shown to be maintained in the middle range between conductors and insulators, and thus proved to be suitable as an electric field relaxation material.

Claims (9)

[Claims] 1. A composite sheet comprising an aramid-based sheet material containing a silicone-based rubber, wherein the composite sheet has a volume resistivity value of 10 ⁻² Ωcm or more and 10 ⁷ Ωcm or less. 2. The composite sheet according to claim 1, wherein the composite sheet has a layer structure of at least two or more layers in which a silicone rubber layer and an aramid sheet material layer are laminated. 3. The composite sheet according to claim 1, wherein the aramid-based sheet material comprises aramid fibrid and aramid floc. 4. An aramid sheet material comprising aramid fibrid and aramid floc, further containing carbon fibers, and having a volume resistivity of 10 ⁻² Ωcm or more and 10 ⁷ Ωc.
The composite sheet according to claim 3, wherein m is equal to or less than m. 5. The silicone rubber contained in the aramid sheet material has a volume resistivity value of 10 ⁻² Ωcm or more and 10 ⁷ or more.
The composite sheet according to any one of claims 1 to 4, wherein the composite sheet has an Ωcm or less. 6. The composite sheet according to claim 1, wherein the aramid constituting the aramid-based sheet material is polymetaphenylene isophthalamide. 7. The method for constructing a composite sheet according to claim 1, wherein the silicone rubber layer and the aramid sheet material layer are integrally laminated. A method for producing a composite sheet. 8. The method for producing a composite sheet according to claim 1, wherein at least one or more of each of an aramid-based sheet material layer and a silicone-based rubber layer is laminated. Of producing a composite sheet. 9. The method for producing a composite sheet according to claim 7, wherein the aramid constituting the aramid-based sheet material is polymetaphenylene isophthalamide.