JP2014043499A - Aramid-polytetrafluoroethylene complex sheet, manufacturing method of the same and high frequency apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low dielectric insulation sheet excellent in mechanical properties, electrical insulation properties, dielectric properties, liquid impregnation properties and the like, and preferably used as an insulation member of a high frequency apparatus which can be used or operate at high temperatures.SOLUTION: An aramid-polytetrafluoroethylene complex sheet contains a sheet containing an aramid hybrid and an aramid short fabric, and a layer of polytetrafluoroethylene formed in a layer shape in a surface direction of the sheet, is treated by firing, and has a porosity of 30% or more and a thickness of 150 μm or less.

Description

  The present invention is a novel aramid-polytetrafluoroethylene composite sheet that is excellent in mechanical properties, electrical insulation properties, dielectric properties, liquid impregnation properties, etc., and is suitably used as an insulation member for high-frequency equipment that can be used or operates at high temperatures. About.

In high-frequency devices such as inverters, printed circuit boards, and mobile wireless communications that handle high-frequency signals, in order to switch high-frequency signals, the dielectric member (heat loss) P expressed by the following equation is reduced in the insulating member. There is a need to. Therefore, an insulating member having a low dielectric constant and a low dielectric loss tangent is required.

P = E ² × tan δ × 2πf × ε ₀ × εr × S / d (W)

Where E is the voltage, tan δ is the dielectric tangent of the substance, f is the frequency, ε ₀ is the dielectric constant of the vacuum, εr is the dielectric constant of the substance (relative dielectric constant), S is the area of the electrode, and d is the electrode spacing. .
On the other hand, semiconductors are used for switching high-frequency signals, but in recent years, development of high-temperature operating power semiconductors such as silicon carbide and gallium nitride has become active, depending on the usage conditions of the semiconductor switch circuit, etc. Suitable change characteristics, levels, etc. are desired.
However, the insulating member cannot always cope with the increasing efficiency, capacity and compactness of recent high-frequency devices.
Insulating members for high-frequency equipment such as generators, motors, inverters, converters, and printed circuit boards that require high efficiency and large capacity,
1) Low dielectric constant and dielectric loss tangent (low dielectric property)
2) High withstand voltage,
It is necessary to simultaneously satisfy the four characteristics of 3) having mechanical strength and 4) sufficiently impregnating a lubricant such as automatic oil. In particular, satisfying the above four characteristics in a high temperature state is considered to be extremely important in terms of sufficiently exhibiting the characteristics of a power semiconductor that is effective in high temperature operation.

  An object of the present invention is to provide a low dielectric insulating sheet that can withstand high efficiency and large capacity of a high-frequency device that can be used or operates at a high temperature.

In view of such a situation, the present inventors have intensively studied to develop a low dielectric insulating sheet that can withstand high efficiency and large capacity of a high-frequency device, and have reached the present invention.
In the first aspect, the present invention provides an aramid-poly formed from a sheet containing aramid fibrids and short aramid fibers and a polytetrafluoroethylene layer that is layered in the surface direction of the sheet. Provided is an aramid-polytetrafluoroethylene composite sheet, which is a tetrafluoroethylene composite sheet having a porosity of 30% or more and a thickness of 150 μm or less.
In a second aspect, the present invention provides the aramid-polytetrafluoroethylene composite sheet according to the first aspect, wherein the dielectric constant and dielectric loss tangent at 200 ° C. show a decreasing tendency with respect to an increase in measurement frequency.
In the third aspect, the present invention is that the ratio of the dielectric constant of 100 ° C. to the dielectric constant of 25 ° C., or the ratio of the dielectric constant of 200 ° C. to the dielectric constant of 25 ° C. is 0.9 to 1.1. The aramid-polytetrafluoroethylene composite sheet according to the first aspect or the second aspect is provided.
In a fourth aspect, the present invention is a method in which a sheet coated with a fine particle dispersion of polytetrafluoroethylene is calendered on a sheet produced from aramid fibrid and aramid short fibers by a wet papermaking method, and then calcined. A method for producing an aramid-polytetrafluoroethylene composite sheet according to the first to third aspects is provided.
In a fifth aspect, the present invention provides a high-frequency device using the aramid-polytetrafluoroethylene composite sheet according to any one of the first to third aspects as an insulating member.
In a sixth aspect, the present invention provides a power generator using the aramid-polytetrafluoroethylene composite sheet according to any one of the first to third aspects as an insulating member.
In a seventh aspect, the present invention provides a motor using the aramid-polytetrafluoroethylene composite sheet according to any one of the first to third aspects as an insulating member.
In an eighth aspect, the present invention provides an inverter using the aramid-polytetrafluoroethylene composite sheet according to any one of the first to third aspects as an insulating member.
In a ninth aspect, the present invention provides a converter using the aramid-polytetrafluoroethylene composite sheet according to any one of the first to third aspects as an insulating member.
In a tenth aspect, the present invention provides a printed circuit board characterized by using the aramid-polytetrafluoroethylene composite sheet according to any one of the first to third aspects as an insulating member.

(Aramid)
In the present invention, aramid means a linear polymer compound (aromatic polyamide) in which 60% or more of amide bonds are directly bonded to an aromatic ring. Examples of such aramids include polymetaphenylene isophthalamide and copolymers thereof, polyparaphenylene terephthalamide and copolymers thereof, poly (paraphenylene) -copoly (3,4'-diphenyl ether) terephthalamide, and the like. Can be mentioned. These aramids are industrially produced by, for example, conventionally known interfacial polymerization methods, solution polymerization methods and the like using isophthalic acid chloride and metaphenylenediamine, and can be obtained as commercial products. Is not to be done. Among these aramids, polymetaphenylene isophthalamide is preferably used in that it has excellent molding processability, thermal adhesiveness, flame retardancy, heat resistance, and the like.

(Aramid Five Brid)
In the present invention, aramid fibrids are film-form aramid particles having paper-making properties and are also called aramid pulp (see Japanese Patent Publication No. 35-11851, Japanese Patent Publication No. 37-5732, etc.).
Aramid fibrids are widely known to be used as a papermaking raw material after being disaggregated and beaten in the same manner as ordinary wood pulp, and can be subjected to so-called beating treatment for the purpose of maintaining quality suitable for papermaking. This beating process can be performed by a paper refiner, a beater, or other papermaking raw material processing equipment that exerts a mechanical cutting action. In this operation, the shape change of the fibrid can be monitored by the freeness test method stipulated in Japanese Industrial Standard P8121. In the present invention, the freeness of the aramid fibrid after the beating treatment is preferably within the range of 10 cm ^{3 to} 300 cm ³ (Canadian Freeness (JISP8121)). For fibrids with a freeness greater than this range, the strength of the multi-thermal electrical insulation sheet material formed therefrom may be reduced. On the other hand, if it is desired to obtain a freeness smaller than 10 cm ³ , the utilization efficiency of the mechanical power to be input becomes small, the processing amount per unit time is often reduced, and further, the fibrid is miniaturized. Since it proceeds too much, the so-called binder function is likely to be lowered. Therefore, even when trying to obtain a freeness smaller than 10 cm ³ in this way, no particular advantage is recognized.

(Aramid short fiber)
The aramid short fiber is obtained by cutting a fiber made of aramid. Examples of such a fiber include “Teijin Conex (registered trademark)” by Teijin Limited and “Nomex (registered trademark)” by DuPont. However, the present invention is not limited to these.
The length of the aramid short fibers can be selected from the range of generally 1 mm or more and less than 50 mm, preferably 2 to 10 mm. When the length of the short fiber is smaller than 1 mm, the mechanical properties of the sheet material are deteriorated. On the other hand, when the length is 50 mm or more, “entanglement”, “binding”, etc. are likely to occur in the production of aramid paper by the wet method. Prone to defects.

(Aramid sheet)
In the present invention, the aramid sheet is a sheet-like material mainly composed of the aramid fibrids and the aramid short fibers, and preferably has a thickness in the range of 30 to 180 μm. Furthermore, aramid sheet is preferably in the range of ^{10g / m 2 ~140g / m 2} , in particular has a basis weight in the range of ^{10g / m 2 ~70g / m 2} . Here, the mixing ratio of the aramid fibrid and the aramid short fiber can be arbitrary, but the ratio (mass ratio) of the aramid fibrid / aramid short fiber is preferably 1/9 to 9/1, more Although it is preferably 2/8 to 8/2, it is not limited to this range.
The aramid sheet is generally produced by a method of mixing the above-mentioned aramid fibrid and aramid short fibers and then forming a sheet. Specifically, for example, after dry blending the aramid fibrid and the aramid short fiber, a method of forming a sheet using an air flow, after the aramid fibrid and the aramid short fiber are dispersed and mixed in a liquid medium, the liquid permeation is performed. For example, a so-called wet papermaking method using water as a medium is preferably selected. .
In the wet papermaking method, a single or mixed aqueous slurry containing at least aramid fibrids and short aramid fibers is fed to a paper machine and dispersed, and then dewatered, squeezed and dried to be wound up as a sheet. The method is common. As the paper machine, a long paper machine, a circular paper machine, a slanted paper machine, and a combination paper machine combining these are used. In the case of production with a combination paper machine, a composite sheet composed of a plurality of layers can be obtained by sheet-forming and combining slurry having different blending ratios. Additives such as a dispersibility improver, an antifoaming agent, and a paper strength enhancer are used as necessary during papermaking.

(Polytetrafluoroethylene)
In the present invention, polytetrafluoroethylene is a polymer of tetrafluoroethylene, which is a fluororesin (fluorinated carbon resin) consisting only of fluorine atoms and carbon atoms. In the present invention, it is preferable to use an aqueous dispersion of polytetrafluoroethylene fine particles as will be described later. Examples of such an aqueous dispersion include “PTFE31-JR” manufactured by Mitsui DuPont Fluorochemical Co., Ltd., Daikin. Although what can be obtained by brand names, such as "Polyflon (trademark) PTFED series" of Co., Ltd., is mentioned, It is not limited to these.

(Aramid-polytetrafluoroethylene composite sheet)
The aramid-polytetrafluoroethylene composite sheet of the present invention is obtained by calendering a sheet coated with a fine particle dispersion of polytetrafluoroethylene on an aramid sheet prepared by a wet papermaking method from aramid fibrids and aramid short fibers, for example. Thus, it is preferable to carry out baking processing. The thickness of the composite sheet before calendering is preferably 35 to 260 μm, but is not limited thereto.
As a method of coating a dispersion of polytetrafluoroethylene fine particles on an aramid sheet, various known methods can be used without limitation, but the dispersion of polytetrafluoroethylene fine particles on the aramid sheet is coated with a coater. It is preferable to form a polytetrafluoroethylene layer that is layered in the plane direction. The coater can be selected from the group consisting of a bar coater, a roll coater, a reverse coater, a gravure coater, a knife coater and an air knife coater. The above-described coating process can be performed a plurality of times in an arbitrary order.
The aramid-polytetrafluoroethylene composite sheet obtained as described above improves mechanical strength and controls porosity and thickness by carrying out so-called calendering, in which heat is pressed between a pair of rolls at high temperature and pressure. can do. For example, in the case of using a metal roll, the conditions of the hot pressure are preferably a temperature of 270 to 370 ° C. and a linear pressure of 50 to 200 kg / cm. Particularly preferably, the temperature is within a range of 280 to 330 ° C. and a linear pressure of 60 to 120 kg / cm. If the temperature is lower than 270 ° C., the strength does not increase sufficiently, and if it is higher than 370 ° C., the composite sheet may easily stick to the roll surface and break. The above calendar processing can be performed a plurality of times in an arbitrary order.

  The calendered composite sheet is fired at a high temperature to reduce the dielectric, producing a low dielectric insulating sheet that can withstand high efficiency and large capacity of high-frequency devices that can be used or operate at high temperatures. can do. The firing process in the present invention is preferably performed in a state where at least one surface of the composite sheet is in contact with the gas. When pressure is applied by suppressing with a heating body from both sides, when it reaches 370 ° C. or higher, it is stuck to the pressure body and is difficult to manufacture. Specific methods include, but are not limited to, a method of passing through a baking furnace, heating in an oven, and contacting one side of a heating roll. Moreover, in order to manufacture continuously efficiently, it is preferable to carry out a baking process continuously after the said calendar process. A calcination temperature becomes like this. Preferably it is 370-410 degreeC, More preferably, it is 395-405 degreeC. If the firing temperature is higher than 410 ° C., the aramid sheet may be deteriorated. Moreover, when the firing temperature is lower than 370 ° C., the dielectric constant and dielectric loss tangent of the composite sheet may be increased. The preferred firing time is 3 seconds or more and 15 minutes or less, particularly preferably 5 seconds or more and 10 minutes or less, but is not limited thereto. If the firing time is short, firing does not proceed sufficiently and the dielectric constant and dielectric loss tangent may be high. If the firing time is too long, the sheet may be deteriorated and the mechanical strength may be lowered. The porosity of the fired composite sheet is preferably 30% or more for improving the impregnation property of a liquid such as automatic oil. Further, the thickness is preferably 150 μm or less in order to reduce the size and weight of the high-frequency device.

The aramid-polytetrafluoroethylene composite sheet of the present invention is preferably a composite sheet in which the dielectric constant and dielectric loss tangent at 200 ° C. tend to decrease with increasing measurement frequency. The aramid-polytetrafluoroethylene composite sheet of the present invention preferably has a dielectric constant of 100 ° C. and a dielectric constant of 25 ° C., or a ratio of a dielectric constant of 200 ° C. and a dielectric constant of 25 ° C. of 0.9 to 1.1.
The aramid-polytetrafluoroethylene composite sheet of the present invention can be suitably used as an insulating member for high-frequency devices such as generators, motors, inverters, converters, and printed circuit boards.
Hereinafter, the present invention will be described with reference to examples. These examples are for explaining the contents of the present invention by way of examples, and are not intended to limit the contents of the present invention in any way.

(Measuring method)
(1) Length-weighted average fiber length
Using a Fiber Quality Analyzer manufactured by Op Test Equipment, the length weighted average fiber length of about 4000 fine particles was measured.
(2) Measurement of basic weight and thickness It implemented according to JIS C2300-2.
(3) Calculation of density It calculated by basic weight ÷ thickness.
(4) Calculation of porosity The true specific gravity of aramid and polytetrafluoroethylene was calculated as 1.38 and 2.17, respectively.
(5) Measurement of tensile strength A Tensilon tensile tester was carried out at a width of 15 mm, a chuck interval of 50 mm, and a tensile speed of 50 mm / min.
(6) Dielectric constant, dielectric loss tangent Implemented according to JIS K6911.
(7) Dielectric breakdown voltage According to ASTM D149, an electrode diameter was 51 mm, and an AC direct voltage boosting method was used.
(8) Gurley Air Permeability Using a Gurley air permeability measuring instrument defined in JIS P8117, a sheet sample (area 642 mm ² ) held by a clamping plate having a 28.6 mm outer diameter hole is 100 cc (0 .1 dm ³ ) air passage time (seconds) was measured.

(Examples 1-4)
(Raw material preparation)
A polymetaphenylene isophthalamide fibrid was manufactured using a pulp particle manufacturing apparatus (wet precipitator) composed of a combination of a stator and a rotor described in JP-A-52-15621. This was processed with a disaggregator and a beater to adjust the length weighted average fiber length to 0.9 mm. The freeness of the obtained aramid fibrid was 90 cm ³ .
Meanwhile, a DuPont meta-aramid fiber (Nomex (registered trademark), single yarn fineness 2 denier) was cut into a length of 6 mm (hereinafter referred to as “aramid short fiber”).
(Manufacture of aramid sheet)
The prepared aramid fibrids and aramid short fibers were each dispersed in water to form a slurry. These slurries are mixed so that the blend ratio (weight ratio) of fibrids and aramid short fibers is 1/1, and a sheet-like material is produced with a tappy type hand machine (cross-sectional area of 625 cm ² ). An aramid sheet having a thickness of about 144 μm was obtained.
(Production of aramid-polytetrafluoroethylene composite sheet)
“PTFE31-JR” (polytetrafluoroethylene) manufactured by Mitsui DuPont Fluorochemical Co., Ltd. was coated on the aramid sheet with a knife coater and dried in an oven at 120 ° C. for 1 hour. Furthermore, polytetrafluoroethylene was applied and dried in an oven at 120 ° C. for 1 hour. The total thickness of the composite sheet was about 147 μm. After calendering the composite sheet under the conditions shown in Table 1, firing was carried out by bringing one surface into contact with a high-temperature roll continuously to obtain a composite sheet. Tables 1 and 2 show main characteristic values of the aramid-polytetrafluoroethylene composite sheet thus obtained.
The aramid-polytetrafluoroethylene composite sheet of the example has a low dielectric constant and dielectric loss tangent, a small thickness, and a sufficiently high dielectric breakdown voltage, strength, porosity, and air permeability. Therefore, it is used as an insulating member for high-frequency equipment. It is useful as an insulating sheet. Further, since the dielectric constant and the dielectric loss tangent tend to be further lowered as the frequency is increased at 200 ° C., the high frequency such as a motor operated by a high frequency inverter that can be used or operates at a high temperature is used. It is particularly useful as an insulating sheet for equipment.

(Comparative Examples 1-3)
(Production of aramid-polytetrafluoroethylene composite sheet)
In the same manner as in the Examples, “PTFE31-JR” manufactured by Mitsui DuPont Fluorochemical Co., Ltd. was applied on an aramid sheet with a knife coater and dried in an oven at 120 ° C. for 1 hour. Furthermore, polytetrafluoroethylene was applied and dried in an oven at 120 ° C. for 1 hour. The composite sheet was calendered, hot pressed and pressed under the conditions shown in Table 3. Table 3 shows the main characteristic values of the aramid-polytetrafluoroethylene composite sheet thus obtained.
The composite sheets of Comparative Examples 1 and 2 have high dielectric loss tangents, particularly high dielectric loss tangents of 25 Hz and 100 ° C. at 60 Hz and 1 kHz. In addition, the composite sheet of Comparative Example 3 has a large thickness, low strength, and dielectric breakdown. Since the voltage is low, it is considered insufficient as a low dielectric insulating sheet that can withstand high efficiency and large capacity of high frequency equipment.

Claims (10)

  An aramid-polytetrafluoroethylene composite sheet formed from a sheet containing aramid fibrids and aramid short fibers, and a polytetrafluoroethylene layer that is layered in the surface direction of the sheet, and having a void An aramid-polytetrafluoroethylene composite sheet characterized by having a rate of 30% or more and a thickness of 150 μm or less.   The aramid-polytetrafluoroethylene composite sheet according to claim 1, wherein the dielectric constant and dielectric loss tangent at 200 ° C. show a decreasing tendency as the measurement frequency increases.   The ratio of the dielectric constant of 100 ° C to the dielectric constant of 25 ° C, or the ratio of the dielectric constant of 200 ° C to the dielectric constant of 25 ° C is 0.9 to 1.1. The aramid-polytetrafluoroethylene composite sheet described.   4. A sheet coated with a fine particle dispersion of polytetrafluoroethylene is calendered on a sheet prepared from an aramid fibrid and an aramid short fiber by a wet papermaking method, and then calcined. The manufacturing method of the aramid polytetrafluoroethylene composite sheet of description.   A high-frequency apparatus using the aramid-polytetrafluoroethylene composite sheet according to any one of claims 1 to 3 as an insulating member.   A generator using the aramid-polytetrafluoroethylene composite sheet according to any one of claims 1 to 3 as an insulating member.   A motor using the aramid-polytetrafluoroethylene composite sheet according to any one of claims 1 to 3 as an insulating member.   An inverter using the aramid-polytetrafluoroethylene composite sheet according to any one of claims 1 to 3 as an insulating member.   A converter using the aramid-polytetrafluoroethylene composite sheet according to any one of claims 1 to 3 as an insulating member.   A printed circuit board comprising the aramid-polytetrafluoroethylene composite sheet according to claim 1 as an insulating member.