JPH06166146A - Aramide board of little hygroscopic deformation - Google Patents

Abstract

PURPOSE:To provide a heat-resistant aramide board excellent in dimensional stability at the time of moisture absorption and showing good electric insulating properties. CONSTITUTION:A plurality of sheets each formed from a mixture of a m- aramide fibrid and a m-aramide fiber by a papermaking process and a plurality of fabrics (B) composed of a p-aramide fiber are laminated so that at least one sheet (A) is interposed between the fabrics (B) and integrally heated and pressed to obtain a board.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aramid board in which sheets containing m-aramid fibrid are laminated and heated and pressed to be integrated, and particularly, the aramid board has excellent dimensional stability when absorbing moisture and has good electric insulation. It concerns a new aramid board.

[0002]

2. Description of the Related Art In recent years, there has been a demand for higher capacity and smaller size of electric equipment, and in particular, it has become unavoidable to raise the temperature of hermetically sealed heat generating equipment such as transformers, electric motors and converters. Therefore, aramid board with excellent heat resistance is widely used instead of the conventional cellulose-based insulation board, and poly (m-phenylene isophthalamide) is especially easy to obtain as a raw material.
The board of m-aramid represented by is becoming the most used.

For example, pulp-like particles made of wholly aromatic polymer such as m-aramid and short fibers made of the polymer, and / or
Alternatively, a method for producing an oil-immersed insulating board in which an arbitrary number of wet paper sheets mixed with inorganic short fibers are laminated and heated and pressed (see Japanese Patent Publication No. 57-46163), or an aromatic polyamide fibrid (for example, m -Aramid fibrid) and a high-temperature resistant floc (see Japanese Patent Application Laid-Open No. 60-209100) or a low-density board having a relatively smooth surface using aramid fibers and fibrids. A proposal (see Japanese Patent Laid-Open No. 4-257400) for utilizing it as a fire wall for separating an automobile cabin and an engine compartment is known.

[0004]

However, as a result of recent economic development, it has been pointed out that as a result of the recent economic development, the amount of electricity consumed has increased and the capacity of transformers and the like has increased, and the size of the insulating board used has increased. In that case, the conventionally known m-aramid board normally absorbs equilibrium moisture and self-expands when left at room temperature after finally being press-molded in an insulating state. It is not unusual for the deformation to exceed 10 mm.

Alternatively, a three-dimensionally molded component such as an insulating board for a railway vehicle transformer causes not only a change in length but also a change in shape due to subsequent moisture absorption. For this reason, the pressed product cannot be stored in the specified transformer case unless it is dried again immediately before use.If the desired dryer is not available at the assembly plant, the pressed product must be stored in an insulated state and transported. There are many process difficulties.

In connection with that solution, pulp-like particles derived from poly (m-phenylene isophthalamide), ie m-aramid fibrids, and optionally short poly (p-phenylene terephthalamide) fibers in the system of short fibers. A combination impregnating sheet has been proposed (Japanese Patent Laid-Open No. 62-
No. 41400), this sheet is made of m-aramid fibrids and poly (p-phenylene terephthalamide).
Since the adhesiveness to short fibers is poor, the mechanical properties such as strength and elongation of the board itself are insufficient.

As another means, a sheet-like structure composed of an entangled mixture of granular mica and aramid (wholly aromatic polyamide) fibrids which has not been substantially melted has been proposed (Japanese Patent Publication No. 43-20421 and Japanese Patent Publication No. 20421/43). JP-A-6
This is not preferable because it causes the accumulation of heat in the aramid board due to the addition of mica having a low thermal conductivity.

In view of the above situation, the inventors of the present invention have suppressed the hygroscopic deformation without impairing the basic performance of the aramid board mainly composed of m-aramid fibrid and m-aramid fiber, and have excellent practicability. As a result of earnest research to provide an aramid board, the present invention has been reached.

[0009]

That is, the present invention is a novel aramid board that achieves the above-mentioned object.
-A plurality of sheets (A) mainly composed of aramid fibrids and m-aramid fibers and a plurality of sheets of p-aramid fiber cloth (B) are provided at least 1 layer between each layer of cloth (B).
The present invention relates to an aramid board having a small hygroscopic deformation, which is obtained by laminating sheets (A) of layers and heating and pressurizing them to form an integrated board.

The "m-aramid fibrids" referred to in the present invention means at least 80 mol% of the polymer repeating units.
The above-mentioned solution of wholly aromatic polyamide which is m-phenylene isophthalamide is fed into a precipitating agent under stirring and sheared as described in, for example, Japanese Patent Publication No. 35-11851 and Japanese Patent Publication No. 3-39539. It refers to pulp-like particles obtained by precipitation / precipitation while applying force. The fibrid may contain a small amount of additives such as a modifier and a filler.

On the other hand, "m-aramid fiber" refers to a wholly aromatic polyamide fiber in which at least 80 mol% or more of the polymer repeating unit is m-phenylene isophthalamide, for example, "Conex" or "NOMEX". Those sold under the registered trademarks such as this correspond to this. The fibers are usually used as short fibers having a fiber length of 0.3 to 30 mm.

The term "p-aramid fiber cloth" means a "cloth" mainly composed of "p-aramid fiber". The term "p-aramid fiber" as used herein means a fiber whose polymer repeating unit is substantially composed of poly (p-phenylene terephthalamide) represented by the following formula (I) or a polymer repeating unit which is substantially represented by the following formula (II). And the following formula (III)
A copolymer consisting of copoly (p-phenylene / 3,3
Fibers composed of 4'-diphenyl ether / terephthalamide) are collectively referred to. These p-aramid fibers are commercially available under registered trade names such as "Kevlar", "Twaron" and "Technora".

[0013]

[Chemical 1]

The "fabric" referred to in the present invention means a woven fabric such as plain weave, twill weave, satin weave, or knitted fabric such as circular knitting and warp knitting of long fibers or spun yarn. These woven or knitted fabrics can be used as they are, but it is more preferable to remove various processing agents remaining on the fiber surface by scouring or the like because the adhesiveness with the sheet (A) is improved.

The above-mentioned sheet (A) constituting the aramid board of the present invention is mainly m-aramid fibrid and m-aramid fibrid.
Although it is a sheet (web) made of aramid fibers, it may be possible to include a small amount (for example, 20% by weight or less) of other components in addition to the above two components. The ratio (weight ratio) of m-aramid fibrids to m-aramid fibers in the sheet (A) is usually 90/10 to 10/90, preferably 70.
/ 30 to 30/70. If the amount of m-aramid fibrids is less than the lower limit, there is a problem with the adhesiveness of the sheet,
The amount of fiber is less than the lower limit (the amount of fibrid exceeds the upper limit)
In this case, the effect of dimensional stability of moisture absorption of the board is insufficiently expressed, which is not preferable.

The aramid board of the present invention is obtained by heating and pressing a laminate of the above-mentioned sheet (A) and p-aramid fiber cloth (B), but the order (arrangement) of lamination is important and It is necessary that at least one sheet (A) is laminated between the respective cloths (B) to be laminated.

For example, when a board is formed by stacking 10 layers, the odd-numbered or even-numbered layers are the cloth (B),
The remaining layer is a combination of the sheet (A). On this occasion,
The sheets (A) may be superposed so that two or more sheets are in contact with each other, but when two or more layers are continuously superposed so that the cloths (B) are in contact with each other, the object of the present invention is difficult to achieve. The stacking order is such that at least one sheet (A) is always present between the cloth (B).

In many cases, the sheet (A) is disposed on the uppermost layer (front surface) and the lowermost layer (bottom surface) of the laminate, and the cloth (B) is separated from the sheet (A) by a layer separated from each other. It is preferable that the sandwich is sandwiched as described above.

The method for producing the sheet (A) used in the present invention is as follows:
Although not particularly limited, since the aramid board of the present invention is intended for high-density electrical insulation, web formation by a known wet (papermaking) method is preferable. As a wet method, it is also possible to perform papermaking using a Fourdrinier, a cylinder or a shortdrinier paper machine, and if necessary, disintegrate or beaten as a preparatory step. Also,
It is also possible to add various additives such as a sizing agent and a resin as long as the electrical insulating property is not impaired. Webs produced by the wet method usually show vertical / horizontal anisotropy because they are oriented in the direction of water flow. Therefore, when these webs are cut into a predetermined size (sheeted) and laminated on a board, It is preferable to make them orthogonal to each other because the obtained board becomes isotropic in properties.

The fineness of the p-aramid fiber used in the fabric (B) is not particularly limited, but usually, the single fiber (single yarn) having a fineness of 0.5 to 3.0 denier is preferably used. The total fineness is 30 to 2,000 denier for long fibers,
In the case of spun yarn, 5-30 count is preferably used. Of course, it is also possible to combine and twist the above-mentioned long fibers and spun yarns and use them as a substantially thicker fineness (count).

As a method for woven or knitted these p-aramid fibers, a known method can be adopted. However, it is not preferable that various oils added during fiber production and woven / knit processing are present during board molding. Is desirable. Furthermore, if necessary, N-
It is also preferable to activate the fiber surface by treating the woven or knitted fabric with a solvent having a high affinity for aramid fibers such as methyl-2-pyrrolidone and N, N'-dimethylacetamide, from the viewpoint of improving board adhesion.

The moisture absorption elongation rate of the aramid board of the present invention is
In many cases, it is affected by the moisture content of the laminated sheet (A). That is, the conventionally known method of gradually dehydrating and drying under heat and pressure using a board having a high water content (see, for example, Japanese Patent Publication No. 57-46163) does not reduce the hygroscopic elongation of the obtained board. Although it is another matter if the sheets are laminated without limitation for a long time, it is desirable that the sheet (A) is sufficiently dried in advance, laminated and thermocompressed quickly in consideration of industrial productivity. However, the presence of a small amount of water is preferable in the case of thermocompression bonding because it promotes plasticization of the surface of the fibrids and improves the adhesive effect. Therefore, in the present invention, the moisture content of the sheet (A) when laminated is less than 45 (wt)%, preferably 30 (wt).
%, Most preferably 0.5 to 5 (wt)% is desirable in view of productivity and hygroscopic extensibility of the obtained board, and the cloth (B) also has a moisture content of less than 45 (wt)%. preferable.

At this time, in order to escape the air or excess water contained in the sheet (A) and the cloth (B), a so-called "air bleeding" operation is repeated in which a momentary pressure release is repeated several times during the pressing. Is recommended from the standpoint of preventing air blister formation in the board.

The thermocompression bonding of each layer can usually be carried out by heating and pressing the laminate with a flat plate press or a roll press. The hot pressing temperature is 225 to 335 ° C., particularly preferably 270 to 320 ° C., and the pressure can be changed according to the required density of the board, but it is 20 to 1,000 kg / cm ² with a flat plate press and rolls. 50-3 by press
It is preferably about 00 kg / cm (linear pressure).

Thus, the aramid board of the present invention has a hygroscopic elongation of 0.5% or less, which is measured by the method described below, and has good dimensional stability and good thermal conductivity.
It does not locally accumulate heat during use, and has excellent heat resistance, electrical insulation, and mechanical properties.

[0026]

EFFECTS OF THE INVENTION The aramid board of the present invention, by having the above-mentioned constitution, can effectively suppress the change in elongation upon absorption of moisture. Therefore, inventory control after board production, transportation and humidity control immediately before assembly of electric equipment can be performed. There is no need to do it, which makes it possible to streamline the production process and reduce costs. Furthermore, since the original properties of the m-aramid board are maintained, there is no restriction on material selection, and handling similar to that of the conventional m-aramid board is possible. Therefore, it can be widely used in various applications mainly for electrical insulation.

[0027]

EXAMPLES Next, the present invention will be described in detail with reference to examples. The characteristic values shown in the following examples are values obtained by the following measuring method. In the examples, "part" means "part by weight". (A) Logarithmic viscosity: concentration of 0.5 g / 100 in 95% sulfuric acid
The logarithmic viscosity of ml was measured at 30 ° C. (unit: dl / g). (B) Moisture absorption elongation rate: After measuring the vertical and horizontal dimensions (X ₁ , X ₂ ) of the board immediately after thermocompression bonding, the humidity is controlled for 15 days in a room at a constant temperature and humidity of 20 ° C and 65% relative humidity. The dimensions (Y ₁ , Y ₂ ) in the vertical and horizontal directions of the sample thus obtained were measured and calculated by the following formula.

[0028]

[Equation 1]

A two-dimensional coordinate measuring device (MA-1, BLTV) manufactured by Muto Kogyo Co., Ltd. was used to measure the length (unit:%). (C) Dielectric breakdown voltage (BDV): According to JIS-C2111. It was measured with an AC voltage (unit: KV / mm).

[0030]

Example 1, Comparative Example 1 (a) Preparation of fibrids and fibers From a poly (m-phenylene isophthalamide) polymer (logarithmic viscosity 1.6) prepared by interfacial polycondensation, Canadian standard drainage was carried out by an ordinary method. A m-aramid fibrid (pulp particles) having a degree (CSF) of 105 ml and a m-aramid fiber having a fineness of 2.0 denier, a length of 6 mm, a strength of 5.8 g / d and an elongation of 40% were produced.

(B) Manufacture of sheet 60 parts of m-aramid fibrid and 40 parts of m-aramid fiber prepared in (a) were dispersed in about 200 times of water, and then a 25 cm × 25 cm field wire mesh was prepared. Papermaking was carried out with a square paper machine. The obtained sheet was dried at 140 ° C. for 100 seconds by a drum type rotary dryer. The obtained sheet has a basis weight of 80 g / m ² , a thickness of 0.205 mm, and a water content of 2.
It was 5% (by weight). (This sheet is referred to as Sheet A-1.) (C) Fabrication of fabric Using copoly (p-phenylene / 3,4'-diphenyl ether terephthalamide) fiber having a single yarn fineness of 1.5 denier and a total fineness of 55 denier. , 65 lines / inch in the longitudinal direction,
A woven fabric having a weaving density of 65 yarns / inch in the weft direction was prepared. The fabric is continuously scoured by a usual method (treatment temperature 60 ° C.,
After processing for 2 minutes), use a non-touch dryer 1
It was dried at 30 ° C. for 1 minute. The basis weight was 32 g / m ² . (The obtained cloth is referred to as cloth B-1.) Incidentally, after cutting the cloth B-1 into a size of 22 cm × 22 cm, it is immersed in N-methyl-2-pyrrolidone at room temperature and dried, and the next test is conducted. Used for (molding).

(D) Molding of board Sheet A-1 and cloth B-1 cut into 22 cm × 22 cm
A-1 / B-1 / A-1 / B-1 / A-1 / A-1 / B-1 / A-1 / B-
10 sheets are laminated in the order of 1 / A-1, 6 layers of sheet A-1 and cloth B-1
The four-layer laminate is placed on a flat plate press at 270 ° C. and 50
After “air bleeding” operation at kg / cm ² , thermocompression bonding was performed for 5 minutes to prepare a board (Example 1).

For comparison, a board was also prepared by laminating only 10 sheets A-1 and thermocompression bonding (Comparative Example 1).

The hygroscopic elongation and BDV of each board thus obtained are shown in Table 1 below.

[0035]

[Table 1]

[0036]

Examples 2-3, Comparative Example 2 (e) Manufacture of Fabric Copoly (p-phenylene / 3,4'-diphenyl ether terephthalamide) fiber having a single yarn fineness of 1.5 denier and a total fineness of 1,500 denier was used. A woven fabric having a weaving density of 17 warps / inch and weft direction 17 / inch was prepared by using the fabric (area weight 220 g / m ² ). This woven fabric was scoured in the same manner as in Example 1 (c), immersed in N-methyl-2-pyrrolidone, and dried. (This cloth is referred to as cloth B-2) (f) Molding of board Sheet A-1 cut into 22 cm × 22 cm produced according to Example 1 (a) and the above cloth B-2 cut into the same size
To A-1 / B-2 / A-1 / B-2 / A-1 / A-1 / B-2 / A-1 / B-
2 / A-1 (Example 2) A-1 / A-1 / B-2 / A-1 / B-2 / A-1 / B-2 / A-1 / A-
10 sheets or 9 sheets were superposed in the order of 1 (Example 3) and pressed by the method of Example 1 (d).

For comparison, a board was prepared in the same manner by stacking only 9 sheets of sheet A-1 (Comparative Example 2).

The moisture absorption elongation rate and BDV of each obtained board are shown in Table 2 below.

[0039]

[Table 2]

[0040]

Example 4, Comparative Example 3 (g) Fabrication of Fabric Using poly (p-phenylene terephthalamide) fiber having a single yarn fineness of 1.5 denier and a total fineness of 1,000 denier,
A woven fabric having a weaving density of 18 yarns / inch in the warp direction and 18 yarns / inch in the weft direction was prepared (unit weight: 162 g / m ² ), and subjected to scouring treatment and N, N′-dimethylacetamide dipping treatment by the above-mentioned method. (This fabric is referred to as Fabric B-3).

(H) Molding of board Sheet A-1 cut into 22 cm × 22 cm produced according to Example 1 (a) and the above cloth B-3 cut into the same size.
A-1 / B-3 / A-1 / B-3 / A-1 / B-3 / A-1 / B-3 / A-
Eleven sheets were stacked in the order of 1 / B-3 / A-1 and pressed in the same manner as in Example 1 (d) (Example 4).

For comparison, 11 sheets A-1 alone were laminated and pressed in the same manner to prepare a board (Comparative Example 3).

The moisture absorption elongation rate and BDV of each obtained board are shown in Table 3 below.

[0044]

[Table 3]

From the results of Examples 1 to 4 and Comparative Examples 1 to 3 shown above, the function and effect of the present invention became clear.

Claims (7)

[Claims] 1. A plurality of sheets (A) mainly composed of m-aramid fibrids and m-aramid fibers and p-
A plurality of aramid fiber cloths (B) are laminated so that at least one layer of the sheet (A) is interposed between the respective layers of the cloth (B), and they are heated and pressed to form an integrated board. Aramid board with little moisture deformation. 2. The aramid board having a small hygroscopic deformation according to claim 1, wherein the m-aramid fibrid is a fibrid substantially composed of poly (m-phenylene isophthalamide). 3. The m-aramid fiber is substantially poly (m).
-A phenylamide isophthalamide) -containing short fiber, wherein the aramid board with less moisture absorption deformation according to claim 1. 4. The ratio (weight ratio) of the m-aramid fibrids and the m-aramid fibers in the sheet (A) is 9
The aramid board according to claim 1, 2 or 3, which is in the range of 0/10 to 10/90 and has a low moisture absorption deformation. 5. The p-aramid fiber fabric is a woven or knitted fabric substantially composed of poly (p-phenylene terephthalamide) fibers or copoly (p-phenylene / 3,4′-diphenyl ether terephthalamide) fibers. Item 1. An aramid board having a low moisture absorption deformation. 6. The laminated sheet is heated and pressed to obtain the sheet (A).
The aramid board according to any one of claims 1 to 5, which has a moisture content of less than 45% and is performed in a temperature range of 225 to 335 ° C. 7. The aramid board according to claim 1, which has a hygroscopic elongation of 0.5% or less.