JP2012245728A - Composite sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrical insulation sheet that combines heat resistance, electrical characteristics, and chemical resistance, and is excellent in thermoformability, and especially deep drawing properties.SOLUTION: The composite sheet includes: a fiber sheet consisting of a synthetic fiber whose glass transition point is at most 200°C, and whose melting point is at least 250°C; and a silicone rubber.

Description

  The object of the present invention relates to a sheet that is not easily broken and excellent in thermoformability as an electrical insulating sheet for electrical equipment such as a motor, an alternator, and a transformer.

As a trend in recent years, new insulation systems have been developed along with the reduction in size, weight, and performance of electrical equipment. Among them, heat resistance, electrical characteristics, and chemical resistance are combined, but they are resistant to cracking and heat. There is a need for an electrical insulating sheet having excellent moldability.
Conventionally, as an electrical insulating sheet requiring heat resistance of heat class F or higher, 1) a film made of PPS or PI, 2) a laminate of the film and a fiber sheet, and 3) a polymetaphenylene isophthalamide fibrid It is known that papers composed of fibers and fibers, and 4) a laminate of the above paper and silicone rubber can be used (Patent Documents 1 to 4).
However, 1) films represented by the above lack impact resistance, and thus have problems such as being easily broken or easily torn during molding, and 2) films proposed for the purpose of improving the impact resistance of the film. The fiber sheet laminate has a problem that the interface between the film layer and the fiber sheet layer is peeled off during molding. 3) Further, since the paper composed of the polymetaphenylene isophthalamide fibrids and fibers does not soften or melt even at a high temperature of 200 ° C. or higher, the shape after deformation cannot be maintained by thermoforming. 4) Even if silicone rubber is laminated on the paper, thermoforming cannot be performed for the same reason as that of the paper alone.

  In addition, silicone rubber itself is too flexible and lacks self-holding ability, and therefore cannot be put into practical use unless the mechanical strength is improved by coating or impregnating the fiber sheet.

  In addition, as a method for improving the ease of tearing of silicone rubber, there is Patent Document 5 in which silicone rubber and a base material sheet are combined. Since thermosetting resin is used, it is unsuitable for thermoforming.

  As described above, an electrical insulating sheet that has both heat resistance, electrical characteristics, and chemical resistance but is resistant to cracking and excellent in thermoformability has not been developed so far.

JP 55-35459 A JP-A 63-237949 JP-A-4-228696 Japanese Patent Laid-Open No. 9-183187 JP-A-6-262694

  An object of the present invention is to provide an electrical insulating sheet excellent in thermoformability, particularly deep drawability, having heat resistance, electrical properties, and chemical resistance.

As a result of intensive studies to solve such problems, a fiber sheet made of a synthetic fiber having a glass transition point of 200 ° C. or lower and a melting point of 250 ° C. or higher is impregnated or coated with, for example, silicone rubber. It discovered that the said subject could be solved by setting it as the composite sheet which has a sheet | seat and silicone rubber.
In a preferred embodiment of the present invention, 20% to 100% by mass of the synthetic fiber having a glass transition point of 200 ° C. or lower and a melting point of 250 ° C. or higher is unstretched fiber.

  Furthermore, in a preferred embodiment of the present invention, the undrawn fiber is polyphenylene sulfide fiber (referred to as PPS fiber). Furthermore, in a preferred embodiment of the present invention, the composite sheet is for deep drawing. In a preferred embodiment of the present invention, the composite sheet is used for electrical insulation. Moreover, it can be set as an electrical insulation sheet by carrying out the deep drawing of the said composite sheet. In addition, the method for producing a composite sheet is to form a synthetic fiber having a glass transition point of 200 ° C. or less and a melting point of 250 ° C. or more into a sheet by a wet papermaking method, and then impregnate or coat with silicone rubber. It is a feature. Furthermore, the method for producing an electrical insulating material of the present invention is characterized in that the composite sheet is deep-drawn.

  According to the present invention, a composite sheet having high heat resistance and dielectric breakdown strength and excellent deep drawability is provided.

Perspective view of defective product obtained by deep drawing A perspective view of a cylindrical press die used for evaluating deep drawability in Examples

  The present inventors have intensively studied a composite sheet having both heat resistance and insulation performance and capable of deep drawing, and the fiber sheet alone is inferior in electrical insulation performance, and not only silicone rubber alone can be thermoformed. Since it is too flexible and lacks self-holding properties, it is a composite that includes a fiber sheet and silicone rubber, and the synthetic fiber constituting the fiber sheet has a glass transition point of 200 ° C. or lower and a melting point of 250 ° C. or higher. This is the first time that a composite sheet having desired performance has been conceived.

  Here, the deep drawing in the present invention includes general deep drawing in which a side wall is formed by inflow from the surroundings, and when forming a flat sheet three-dimensionally, It includes molding in which the part is stretched or compressed.

In general, since a fiber sheet has voids between fibers, the dielectric breakdown strength is poor, and the fiber sheet alone is not practical as an electrical insulating sheet. According to the present invention, silicone rubber fills the gaps between the fibers constituting the fiber sheet, or forms a silicone layer on the surface of the fiber sheet, so that the dielectric breakdown strength can be dramatically improved as compared with the fiber sheet alone. .
The fiber sheet in the present invention includes a synthetic fiber having a glass transition point of 200 ° C. or lower and a melting point of 250 ° C. or higher. The synthetic fiber having such a glass transition point and melting point is preferably 70% by mass or more, more preferably 80% by mass or more, and further 90% by mass or more in the fiber sheet.

  By including a synthetic fiber having a glass transition point in the above range, the fiber sheet of the present invention is easily deformed when a load is applied at a temperature of 200 ° C. or higher. Generally, the lower the glass transition point relative to the temperature during thermoforming, the softer the fiber sheet, so the glass transition temperature of the synthetic fiber having the glass transition point in the specific range is lower than 150 ° C. More preferably, it is 100 degrees C or less.

  The silicone rubber in the present invention is an elastic body in which silicone is crosslinked and cured, and has flexibility and easily deforms. Therefore, when laminated with a thermoformable sheet, it follows the deformation of the sheet. . Further, since silicone rubber is an elastic body, a repulsive force is generated against compressive stress. For this reason, conventionally, in the deep drawing of a cylindrical type, overlapping flaws of the flange and the side wall as shown in FIG. 1 are likely to occur. However, if the material can be easily deformed, the distortion generated in the circumferential direction is likely to occur. And the generation of wrinkles is suppressed. That is, the product of the present invention can be deep-drawn with less overlap wrinkles compared to a single fiber sheet.

  The fiber sheet in the present invention includes synthetic fibers having a glass transition point of 200 ° C. or lower and a melting point of 250 ° C. or higher. The synthetic fiber here refers to a synthetic resin in the form of a fiber. Among them, examples of fibers that can provide such a glass transition point and melting point include PPS fibers, PTFE fibers, wholly aromatic PET fibers, and PEN fibers. Among them, PPS fibers are preferable. The reason is that the PPS fiber is excellent in chemical resistance, hydrolysis resistance, hygroscopic dimensional stability, and fluidity at the time of heat softening, and therefore has excellent deep drawability.

  A fiber having a glass transition point exceeding 200 ° C. has a too high softening temperature, which makes deep drawing with a general-purpose facility difficult. In addition, as described above, generally, as the glass transition point is lower than the temperature at the time of thermoforming, the fiber sheet is softened. Therefore, the glass transition temperature of the synthetic fiber is more preferably 150 ° C. or less. Preferably, it is 100 degrees C or less more preferably.

Moreover, it is preferable that 20 mass%-100 mass% are unstretched fibers among the synthetic fibers which have the said glass transition point and melting | fusing point, More preferably, they are 25 mass%-100 mass%. By using 20% by mass or more of the synthetic fiber as unstretched fiber, the proportion of the amorphous component in the fiber constituting the fiber sheet increases. As a result, the softening start temperature is lowered, the fluidity at the time of softening is increased, and a deeper deep drawing process is possible.
Furthermore, among the heat resistant fibers, PPS fibers that are excellent in chemical resistance, hydrolysis resistance, moisture absorption dimensional stability, and fluidity during thermoforming can be particularly preferably used. For example, those commercially available from Toray Industries, Inc. under the trade name “Torcon” can be used.
PPS fiber is a fiber obtained by melt spinning PPS resin, and PPS resin is a polymer containing phenylene sulfide units such as p-phenylene sulfide units and m-phenylene sulfide units as repeating units. There may be a homopolymer of any of these units, or a copolymer having both units. Further, it may be a copolymer with another aromatic sulfide, but preferably 70 mol% or more of the repeating units are composed of p-phenylene sulfide.

  Moreover, as a weight average molecular weight of PPS resin used for a PPS fiber, 40000-60000 are preferable. By setting it to 40,000 or more, good mechanical properties as PPS fibers can be obtained. Moreover, it is preferable to set it to 60000 or less because the viscosity of the melt spinning solution can be suppressed and a special high pressure resistant spinning equipment is not required.

  In addition, after melt spinning through a die with an extruder-type spinning machine or the like, undrawn PPS fibers can be obtained by collecting without spinning.

  On the other hand, the stretched PPS fiber is the same as the unstretched PPS fiber, and after melt-spinning the PPS resin with an extruder spinning machine or the like, it is 3.0 times or more, preferably 5.5 times or less, more preferably It can be obtained by stretching in the range of 3.5 to 5.0 times. This stretching may be performed in one stage, but may be performed in two or more stages. In the case of using two-stage stretching, the first stage of stretching is preferably 70% or more of the total magnification, preferably 75 to 85%, and the rest is preferably performed by the second stage of stretching. The obtained unstretched PPS fiber and stretched PPS fiber may be cut without being crimped, or may be cut with crimp.

  In addition, as for the presence or absence of crimps, there are advantages to those having and not having crimps. The fibers having crimps are suitable for obtaining wet nonwoven fabrics having excellent strength by improving the entanglement between fibers in the production of wet nonwoven fabrics, for example. On the other hand, a fiber that does not have crimps is suitable for obtaining a uniform wet nonwoven fabric with little unevenness because it has good dispersibility in water.

  Although the short fiber and the long fiber are mentioned as a form of the fiber which comprises the fiber sheet in this invention, It can use properly by the form of the fiber sheet to manufacture.

  The fiber sheet of the present invention is a sheet-like molded body produced from the synthetic fiber, and for the purpose of improving heat resistance and insulation, minerals such as mica, titanium oxide, talc, kaolin, aluminum hydroxide, etc. Particles can be added. Examples of the form of the sheet include dry nonwoven fabrics, wet nonwoven fabrics, woven fabrics, and the like, but are not limited thereto, but wet nonwoven fabrics that can easily obtain uniform structures and thin sheets are particularly preferably used.

  Next, an example of a method for obtaining a wet nonwoven fabric that is particularly preferably used among the methods for producing a fiber sheet composed of fibers as described above will be described. However, the manufacturing method of the fiber sheet in this invention is not necessarily limited to this.

  The single fiber fineness of the fibers is preferably 0.05 dtex or more and 10 dtex or less. If it is thin, the fibers tend to be entangled with each other and it tends to be difficult to disperse them uniformly. When thicker, the fibers become thicker and harder, and the entanglement force between the fibers becomes weaker. Therefore, sufficient paper strength cannot be obtained, and the nonwoven fabric tends to be easily broken.

  Moreover, as a fiber length of the fiber used for a fiber sheet, all within the range of 1-20 mm are preferable. By setting it to 1 mm or more, the strength of the composite sheet can be increased by entanglement of fibers. Moreover, by setting it as 20 mm or less, it can prevent that a fiber etc. become lumps and unevenness etc. arise in a composite sheet.

The fiber sheet used in the present invention is preferably a paper-like material, and preferably has a basis weight of 5 g / m ² or more, more preferably 10 g / m ² or more, on the other hand 200 g / m ² or less, and further 120 g / m ² . Preferably there is. The thickness is preferably in the range of 5 μm or more, more preferably 10 μm or more, on the other hand, 500 μm or less, and further 300 μm.

  Next, a method for producing a non-woven fabric in a wet manner will be described.

  First, the fiber is dispersed in water to make a papermaking slurry. The total amount of fibers with respect to the entire papermaking slurry is preferably 0.005 to 5 mass%. By making the total amount 0.005% by mass or more, water can be efficiently used in the paper making process. Moreover, by making it 5 mass% or less, the dispersion state of a fiber improves and a uniform wet nonwoven fabric can be obtained.

  The papermaking slurry may be prepared by separately preparing a slurry of pre-stretched fibers and a slurry of unstretched fibers and then mixing them with a paper machine, or a slurry containing both directly. It is preferable to make the slurry of each fiber separately and then mix the two in terms of being able to control the stirring time according to the shape and characteristics of each fiber separately. It is preferable in terms of simplicity.

In order to improve the dispersion state, the papermaking slurry may be added with a dispersant or an oil agent composed of a cationic, anionic or nonionic surfactant, or an antifoaming agent that suppresses the generation of bubbles. Good.
The papermaking slurry prepared as described above is paper-made using a round-mesh type, long-mesh type, inclined net-type paper machine or hand-made paper machine, and dried with a Yankee dryer, a rotary dryer, etc. can do. Thereafter, calendering may be performed for surface smoothing, surface fluff suppression, densification and the like of the obtained wet nonwoven fabric.

  In the present invention, the deep drawability is improved by applying silicone rubber to the fiber sheet of the present invention. The silicone rubber in the present invention is an organopolysiloxane that has undergone a curing reaction in a three-dimensional structure, and examples of functional groups in the side chain include a methyl group, an ethyl group, a propyl group, a butyl group, an octyl group, and a cyclohexyl group. In addition to the alkyl group, it may have a halogenated alkyl group or an aryl group. Usually, there are many methyl groups, but the heat resistance of silicone can be improved by substituting a part of methyl groups with phenyl groups.

  Examples of the chemical reaction for obtaining a three-dimensional structure include a method of reacting a polysiloxane having a hydroxyl group at a terminal with a silicon compound having a plurality of hydrolyzable functional groups such as a carbonyloxy group and alkoxy. In this case, crosslinking can be performed by adding a large amount of a silicon compound having a plurality of functional groups to cause hydrolysis and condensation. There is also a method in which a polysiloxane in which hydrogen is directly bonded to a silicon atom and a polysiloxane having an unsaturated double bond such as a vinyl group are subjected to an addition reaction using a platinum catalyst or the like. Moreover, the method of mixing the polysiloxane which has a polymeric functional group in a side chain, and a radical generator, and bridge | crosslinking with a heat | fever is also illustrated.

  Silicone rubber can be used alone, or may be a mixture of two or more, and is a silicone rubber modified with an alkyd resin, acrylic resin, epoxy resin, polyester resin, phenol resin, acrylic resin, melamine resin. There may be. Examples of the curing reaction include peroxide curing, addition curing, condensation curing, dehydrogenation curing, UV curing, and the like, which may be one-pack type or two-pack type, but in the present invention, addition curing with excellent deep-curability is provided. Preferably, the catalyst used includes a platinum-based catalyst, a palladium-based catalyst, a rhodium-based catalyst, and the like.

  In addition, for the purpose of improving the thermal conductivity and mechanical strength of these silicone rubbers, there is no problem even if fillers such as silica, alumina, quartz, boron nitride, magnesium oxide, and calcium carbonate are mixed.

Such silicone rubber can be classified into a millable type and a liquid type. In the millable type, a silicone rubber composition can be obtained by uniformly mixing and heating using a rubber kneader such as a mixer. A composite sheet can be obtained by processing the obtained silicone rubber composition into a film by a molding method typified by extrusion molding or the like and supporting it on a fiber sheet. On the other hand, in the liquid type, the liquid silicone is directly coated on the fiber sheet and heated, or the fiber sheet is dipped in the liquid silicone and then heated, and then the silicone rubber is cured, and the composite sheet is formed. Obtainable. However, in the present invention, it is preferable to use a liquid type having excellent workability.
At this time, for the purpose of improving the interlayer adhesion between the fiber sheet and the silicone rubber, the fiber sheet surface or the silicone rubber surface may be subjected to surface modification such as corona treatment or plasma treatment, and the adhesion of the silicone rubber may be improved. The material to be improved may be applied to the fiber sheet in advance. On the other hand, an adhesion-imparting agent may be added to the silicone rubber composition.

  The tackiness of the silicone rubber side surface of the composite sheet is preferable for the application of attaching the sheet, but is not preferable when the sliding performance of the surface is required, such as the application of inserting the sheet. In this case, tackiness can be eliminated by adjusting the amount of catalyst and the curing atmosphere. Alternatively, after applying silicone on one side of the fiber sheet, another fiber sheet is laminated on the other side of the silicone layer, and the two-sided structure is made by having a silicone layer between the two fiber sheets. In both cases, a sheet excellent in slipperiness can be obtained.

  The composite sheet of the present invention includes a fiber sheet and silicone rubber, and the configuration is that the fiber constituting the fiber sheet is filled with silicone rubber, or the fiber sheet penetrates into the silicone rubber. And the fiber sheet and the silicone rubber are laminated and adhered as separate layers. Among them, it is preferable that at least a part of the silicone rubber layer penetrates into the fiber sheet from the viewpoint of enhancing the interlayer adhesion due to the anchor effect so that peeling does not occur during thermoforming.

  As described above, the method for obtaining the composite sheet of the present invention varies depending on the type of silicone used. For example, when millable type silicone is used, a silicone rubber composition obtained by uniformly mixing and heating using a rubber kneader such as a mixer is formed into a film by a molding method such as extrusion molding. After being processed into a composite sheet, the composite sheet can be obtained by supporting the fiber sheet. Here, as a method of supporting the silicone rubber composition in the form of a film on the fiber sheet, in addition to the method of bonding the silicone rubber composition and the fiber sheet via an adhesive, the fiber sheet is superimposed on the silicone rubber. Thus, a method of thermocompression bonding using a heat press, a heat calendar, or the like can be exemplified. In the case where liquid type silicone is used, the liquid silicone is directly coated on the fiber sheet and then heated to cure the silicone rubber to obtain a composite sheet. Alternatively, a method of obtaining a composite sheet by immersing a fiber sheet in liquid silicone and pulling it up and then heating to cure the silicone rubber can be exemplified. Among these methods, a method in which a liquid silicone is directly coated on a fiber sheet and then heated to cure the silicone rubber to obtain a composite sheet can be suitably employed from the viewpoint of workability and process simplification. .

In addition, for a multilayer laminate of a fiber sheet layer and a silicone rubber layer, a two-layer structure comprising one fiber sheet and one silicone rubber layer, a three-layer structure in which silicone rubber is sandwiched between fiber sheets, and a fiber sheet is sandwiched between silicone rubbers. Examples of such a three-layer structure and a multilayer structure in which the number of layers is further increased are also possible. The thickness of the composite sheet of the present invention can be preferably selected from 10 μm to 1000 μm depending on use conditions, but is not limited thereto. Also, the basis weight of the silicone rubber used is ^20g / ^{m 2 ~200g} / m 2 is preferred.

  Further, the composite sheet of the present invention can be formed into a desired shape by deep drawing to form an electrical insulating sheet.

  Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited thereto.

[Measurement and evaluation method]
(1) Basis weight According to JIS L 1906: 2000, one 25 cm × 25 cm test piece is collected, and each mass (g) in a standard state is measured, and the mass per 1 m ² (g / m ² ). expressed.

(2) Thickness According to JIS L 1906: 2000, which is applied mutatis mutandis according to JIS L 1906: 2000, thickness was measured under a pressure of 2 kPa with a 22 mm diameter pressurizer using a thickness measuring device at 10 different points of the sample. In order to calm the thickness, after waiting for 10 seconds, the thickness was measured, and an average value was calculated.

(3) Dielectric breakdown strength Measured according to JIS K 6911: 1995. Test specimens of about 10 cm × 10 cm are collected from five different specimens, and the specimens are sandwiched between disc-shaped electrodes with a diameter of 25 mm and a mass of 250 g, air is used as the test medium, and a voltage is applied at 0.25 kV / second. While increasing, an AC voltage having a frequency of 60 Hz was applied, and the voltage when dielectric breakdown was measured. A dielectric breakdown voltage tester (manufactured by Yasuda Seiki Seisakusho) was used for the measurement. The obtained dielectric breakdown voltage was divided by the thickness of the central portion measured in advance, and the dielectric breakdown strength was calculated.
(4) Deep Drawing Molding Test Using a cylindrical press mold with a drawing depth a = 9.3 mm and a drawing diameter b = 32 mm as shown in FIG. 2, a mold temperature: 220 ° C., a mold pressure: 5 kg / Under the condition of cm 2, deep drawing was performed while fixing the sample end with a clamp. The deep drawability was determined as follows.

  A: There is no overlap flaw on the side wall. Available.

  ○: Slight overlap flaws occur on the side wall (Long length is less than 4mm, Number of flaws is 3 or less). Available.

△: Overlapping occurs on the side wall part (over 4mm length, over 4 locations). Unavailable.
X: Fractured and could not be molded.

(5) Measurement of glass transition point of PPS fiber to be used Specific heat was measured with the following apparatus and conditions, and determined according to JIS K7121.
Measuring device: Temperature modulation DSC manufactured by TA Instrument
Measurement temperature range: about 0 to 350 ° C
Temperature calibration: Melting point of high purity indium and tin
Temperature increase rate: 2 ° C / min
Temperature modulation amplitude: ± 1 ° C
Temperature modulation period: 60 seconds
Sample weight: about 5 mg.

(6) Measurement of melting point of PPS fiber to be used Using a differential scanning calorimeter (manufactured by Shimadzu Corporation, DSC-60), about 2 mg of the sample was precisely weighed and heated at a heating rate of 10 ° C./min under nitrogen. . At that time, the peak temperature of the endothermic peak of melting observed was measured as the melting point (Tm).

[Example 1]
(1) Fiber sheet (stretched fiber)
As the drawn fiber, PPS fiber having a single fiber fineness of 1.0 dtex and a cut length of 6 mm, “Torcon” manufactured by Toray Industries, Inc., and product number S301 were used. Table 1 shows the results of measuring glass point transfer and melting point by the evaluation method. The glass transition point was 88.6 ° C. and the melting point was 283.2 ° C.

(Drawn fiber dispersion)
The stretched PPS fiber was prepared based on the configuration shown in Table 1 so that the finish was 100 g / m ^2, and 1 L of water was added to 1 g of the stretched PPS fiber together with a household juicer mixer. Stirring was repeated to obtain a dispersion. The stirring time was 10 seconds in order to prevent the fibers from getting tangled.
(Undrawn fiber)
As unstretched fibers, PPS fiber “Torcon” manufactured by Toray Industries, Inc., having a single fiber fineness of 3.0 dtex and a cut length of 6 mm, product number S111 was used. As a result of measuring the glass point transfer and melting point by the above evaluation method, the glass transition point was 89.5 ° C. and the melting point was 282.9 ° C. as shown in Table 1.

(Unstretched fiber dispersion)
Each of the unstretched PPS fibers is roughly divided into the numbers obtained by rounding up the first decimal place for the mass shown in Table 1, and each aliquot is taken into a domestic juicer mixer with 1 L of water and stirred. This was repeated to obtain a dispersion. The stirring time was 10 seconds in order to prevent the fibers from getting tangled.

(Manufacture of fiber sheets)
The fiber dispersion used in each Example / Comparative Example is finished on a handmade paper machine (manufactured by Kumagai Riki Kogyo Co., Ltd.) having a size of 25 cm × 25 cm and a height of 40 cm with a 140-mesh handmade paper net installed on the bottom. The mixture was added to 80 g / m ² , water was further added to make the total amount of the papermaking dispersion 20 L, and the mixture was sufficiently stirred with a stirrer.
Water from the handsheet machine was drained, and the wet paper remaining on the paper web was transferred to filter paper.

(Dry)
The wet paper is put into a rotary dryer together with the filter paper, and the process of drying at a temperature of 110 ° C., a process passing speed of 0.5 m / min, and a process length of 1.25 m (processing time 2.5 min) is repeated twice A dried fiber sheet was obtained.

(Heating / pressurizing treatment)
The dried fiber sheet was peeled from the filter paper and passed through a calendar processing machine (manufactured by Yuri Roll Co., Ltd.) consisting of a metal roll and a paper roll. The calender conditions were a temperature of 160 ° C., a pressure of 130 kgf / cm, and a roll rotation speed of 15 m / min.

(2) Silicone rubber An addition-type liquid silicone rubber manufactured by Shin-Etsu Chemical Co., Ltd. was used as the silicone rubber.

(3) Composite of fiber sheet and silicone rubber Dryer using a coater bar, after uniformly applying uncured silicone rubber on one side of the fiber sheet to an average thickness of 100 μm, and then adjusting the fiber sheet to 150 ° C. The mixture was allowed to stand for 5 minutes to cure the silicone rubber to obtain a composite sheet. At this time, the thickness of the cured silicone layer was an average of 100 μm, and the coating weight per unit area was 131 g / m ² .

[Example 2]
(1) Fiber sheet Based on the structure of Table 1, a fiber sheet was obtained in the same manner as in Example 1.
(2) Silicone rubber The same silicone rubber as in Example 1 was used.
(3) Composite of fiber sheet and silicone rubber A composite sheet was obtained in the same manner as in Example 1.

[Comparative Example 1]
After obtaining a fiber sheet by the same method as in Example 1, no silicone rubber was laminated.

[Comparative Example 2]
After obtaining the fiber sheet by the same method as in Example 2, no silicone rubber was laminated.
[Comparative Example 3]
(1) Preparation of fiber sheet Paper made of polymetaphenylene isophthalamide (trade name: Nomex # 410-4mil, manufactured by DuPont) was used.
(2) Silicone rubber The same silicone rubber as in Example 1 was used.
(3) Composite sheet and silicone rubber composite A composite sheet was obtained in the same manner as in Example 1.
(4) About glass transition point About the glass transition point of the material of the comparative example 2, the value described in the following literature was employ | adopted.

Reference 3rd edition Textbook H16.12.15 issued
P182 Table 1.70 Physical properties of aramid fibers
Meta-aramid Glass transition temperature 280-290 ° C

  As described above, a composite sheet having a dielectric breakdown strength that can be used as an electrical insulating sheet in Example 1 and excellent in deep drawability was obtained. On the other hand, Comparative Example 1 and Comparative Example 2 consisting only of a fiber sheet have poor dielectric breakdown strength, and overlapped wrinkles occurred in the side wall portion in the deep drawing test. In particular, in Comparative Example 2, overlapping wrinkles that could not be used as an electrical insulating sheet occurred. Moreover, although the comparative example 3 comprised with an aramid is excellent in dielectric breakdown strength, since a glass transition point is very high with 280 degreeC-290 degreeC, a material cannot follow a deformation | transformation in a deep drawing test. It fractured and a molded product could not be obtained. That is, the composite sheet lacked thermoformability.

  Further, in Example 2, where the amount of unstretched fibers is small compared to Example 1, it has a dielectric breakdown strength that can be used as an electrical insulating sheet. Since it was inferior, it was inferior to thermoformability.

  The laminate of the present invention can be used as an electrically insulating paper having good moldability, which can be used for motors, capacitors, transformers, cables, high voltage transmission transformers, etc. As a result, an electrically insulating material having a desired shape can be obtained. can get.

Claims (7)

A composite sheet having a fiber sheet made of synthetic fiber having a glass transition point of 200 ° C. or lower and a melting point of 250 ° C. or higher and silicone rubber. The composite sheet according to claim 1, wherein 20% by mass to 100% by mass of the total fibers constituting the fiber sheet is a synthetic fiber having the glass transition point and the melting point. The composite sheet according to claim 2, wherein the synthetic fiber having a glass transition point and a melting point is an unstretched fiber. The composite sheet according to claim 2, wherein the unstretched fibers are unstretched fibers of PPS fibers. The composite sheet according to any one of claims 1 to 3, which is for deep drawing. The composite sheet according to any one of claims 1 to 4, which is for electrical insulation. A method for producing an electrical insulating material, comprising deep-drawing the composite sheet according to claim 1.

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