JP2986632B2 - Aramid board with little hygroscopic deformation - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an aramid board obtained by laminating sheets containing m-aramid fibrids and integrating them by heating and pressurizing, especially having excellent dimensional stability when absorbing moisture and having good electric insulation. It relates to 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 sealed heat-generating equipment such as transformers, electric motors, and converters. Therefore, instead of the conventional cellulosic insulating board, aramid board having excellent heat resistance is widely used, and especially, poly (m-phenylene isophthalamide) which is easily available as a raw material
M-aramid boards, represented by, have come to be used in the largest quantities.

For example, pulp-like particles made of a wholly aromatic polymer such as m-aramid and short fibers made of the polymer and / or
Alternatively, an arbitrary number of wet paper webs mixed with inorganic short fibers are laminated and heated and pressurized to produce an oil immersion insulating board (see Japanese Patent Publication No. 57-46163), or an aromatic polyamide fibrid (for example, m.p. Aramid fibrid) and a high-density press board composed of high-temperature resistant floc (see JP-A-60-209100), or a low-density board having a relatively smooth surface using aramid fiber and fibrid. There has been proposed a proposal for using the same as a fire wall separating an automobile cabin and an engine compartment (see Japanese Patent Application Laid-Open No. 4-257400).

[0004]

However, as a result of recent economic development, it has been pointed out that an increase in electricity consumption and, consequently, an increase in the capacity of transformers and the like have led to an increase in the size of insulating boards used. In that case, the conventionally known m-aramid board is usually self-extended by absorbing equilibrium moisture when left at room temperature after being finally press-molded in an insulated state. The deformation amount often exceeds 10 mm.

Alternatively, a three-dimensionally formed part, 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. Therefore, if the pressed product is not dried again immediately before use, it cannot be stored in the predetermined transformer case, and if the desired dryer is not in the assembly plant, the pressed product must be stored in an insulated state and transported, etc. There are many difficulties in the process.

In connection with that solution, poly (p-phenylene terephthalamide) short fibers are optionally added to a system of pulp-like particles, ie m-aramid fibrids and short fibers, obtained from poly (m-phenylene isophthalamide). A combined impregnating sheet has been proposed (Japanese Unexamined Patent Publication No. Sho 62-62).
No. 41400), this sheet is composed of m-aramid fibrid and poly (p-phenylene terephthalamide)
Since the adhesiveness to short fibers is poor, the mechanical properties such as the strength and elongation of the board itself are insufficient.

As another means, a sheet-like structure comprising an entangled mixture of granular mica and substantially unmelted aramid (wholly aromatic polyamide) fibrids has been proposed (JP-B-43-20421 and JP 6
However, this is not preferable because mica having a low thermal conductivity is added and heat is stored in the aramid board.

In view of this situation, the inventors of the present invention have succeeded in suppressing the hygroscopic deformation without impairing the basic performance of an aramid board mainly composed of m-aramid fibrid and m-aramid fiber, and have excellent practicability. As a result of intensive studies to provide an aramid board, the present invention has been reached.

[0009]

That is, the present invention provides a novel aramid board which achieves the above-mentioned object,
-A plurality of sheets of the sheet (A) mainly composed of aramid fibrid and m-aramid fiber and a plurality of sheets of the p-aramid fiber cloth (B) are interposed between each layer of the cloth (B) by at least one layer.
The present invention relates to an aramid board with little hygroscopic deformation, wherein the sheets are laminated so that the sheets (A) of layers are interposed, and heated and pressed to form an integrated board.

The term “m-aramid fibrid” as used in the present invention means at least 80 mol% of the polymer repeating unit.
A solution of a wholly aromatic polyamide having m-phenylene isophthalamide as described above was fed into a stirring precipitant as described in, for example, Japanese Patent Publication No. 35-11851 and Japanese Patent Publication No. 3-39539, and sheared. Refers to pulp-like particles obtained by precipitating and precipitating 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, and is, for example, "CONEX" or "NOMEX". Such products are commercially available under registered trademarks such as. The fibers are usually used as short fibers having a fiber length of 0.3 to 30 mm.

The term "p-aramid fiber fabric" means a "fabric" mainly composed of "p-aramid fiber". Here, the “p-aramid fiber” means a fiber whose polymer repeating unit substantially consists of poly (p-phenylene terephthalamide) represented by the following formula (I) or a polymer whose repeating unit is substantially the following formula (II) And the following formula (III)
Copoly (p-phenylene / 3,3) which is a copolymer consisting of
4'-diphenyl ether / terephthalamide). These p-aramid fibers are commercially available under registered trade names such as "Kevlar", "Twaron" and "Technola".

[0013]

Embedded image

The "fabric" as used in the present invention means a woven fabric such as plain weave, twill weave and satin weave of long fibers or spun yarn, or a knitted fabric such as circular knit and warp knit. 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, since the adhesion to the sheet (A) is improved.

The sheet (A) constituting the aramid board of the present invention is mainly composed of m-aramid fibrids and m-aramid fibrids.
It is a sheet (web) made of aramid fibers, but may contain a small amount (for example, 20% by weight or less) of other components in addition to the above two components. The ratio (weight ratio) between m-aramid fibrids and m-aramid fibers in the sheet (A) is usually 90/10 to 10/90, preferably 70/90.
/ 30 to 30/70. If the amount of m-aramid fibrids is less than the lower limit, there is a problem in sheet adhesiveness,
Fiber amount is less than lower limit (fibrid amount exceeds upper limit)
In this case, it is not preferable because the effect of dimensional stability of moisture absorption of the board is insufficient.

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

For example, when a board is formed by laminating 10 layers, the odd-numbered or even-numbered layers are regarded as the fabric (B),
The remaining layers are combined as a sheet (A). On this occasion,
The sheet (A) may be overlapped so that two or more sheets are in contact with each other, but if the fabric (B) is successively overlapped with two or more layers so as to be in contact with each other, it is difficult to achieve the object of the present invention. The lamination order is such that one or more sheets (A) always exist between the fabrics (B).

In many cases, a sheet (A) is disposed on the uppermost layer (front surface) and the lowermost layer (bottom surface) of the laminate, and the fabric (B) is interposed between the sheets (A) and the layers separated from each other. It is preferable to form a sandwich sandwiched as much as possible.

The method for producing the sheet (A) used in the present invention is as follows.
Although not particularly limited, web formation by a known wet (papermaking) method is preferable since the aramid board of the present invention aims at high-density electrical insulation. As a wet method, it is possible to make a paper using a long net, a round net or a short net paper machine, and to perform defibration and beating as a preparation step if necessary. Also,
Various additives such as a glue and a resin can be added as long as the electrical insulation is not impaired. Since webs manufactured by the wet method usually show vertical / horizontal anisotropy because they are oriented in the flow direction of water, these webs are cut into a predetermined size (formed into sheets), and when laminated on a board. It is preferable to make the board alternately orthogonal because the resulting board has isotropic properties.

The fineness of the p-aramid fiber used for the fabric (B) is not particularly limited, but usually a 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 to 30 count is preferably used. Needless to say, the long fibers and spun yarns can be combined and twisted to be used as a substantially thicker fineness (count).

A known method can be used as a method for forming these knitted or knitted p-aramid fibers. However, it is not preferable that various oils applied at the time of fiber production and woven / knitted fabric processing are present at the time of board molding. Therefore, after woven / knitted, it is washed or scoured with warm water (including a detergent if necessary). 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 the board adhesion.

The aramid board of the present invention has a moisture absorption elongation percentage of
In many cases, it is affected by the moisture content of the laminated sheet (A). That is, in a conventionally known method (for example, see Japanese Patent Publication No. 57-46163) in which a board having a high moisture content is gradually dehydrated and dried under heat and pressure to integrate the resultant board, the resulting board does not have a small moisture absorption elongation. However, it is preferable that the sheet (A) is sufficiently dried in advance and quickly laminated and thermocompressed in consideration of industrial productivity. However, the presence of a small amount of water may be preferable in the case of thermocompression bonding because it promotes plasticization of the fibrid surface and improves the adhesive effect. Therefore, in the present invention, the moisture content of the sheet (A) at the time of lamination is less than 45 (weight)%, preferably 30 (weight).
%, Most preferably 0.5 to 5 (weight)%, from the viewpoint of productivity and the moisture absorption and extensibility of the obtained board. The cloth (B) also has a moisture content of less than 45 (weight)%. preferable.

At this time, a so-called "air release" operation is repeated in which the instantaneous pressure release is repeated several times during the pressing in order to release air or excessive moisture contained in the sheet (A) and the fabric (B). This is recommended from the standpoint of preventing blistering in the board.

The thermocompression bonding of each layer can be usually carried out by heating and pressing the laminate by a flat plate press or a roll press. Thermal pressure temperature is two hundred twenty-five to three hundred and thirty-five ° C., particularly preferably two hundred and seventy to three hundred and twenty ° C., the pressure is able to be changed according to the required density of the board, 20~1,000kg / cm ² in flat press roll 50-3 by press
About 00 kg / cm (linear pressure) is preferable.

Thus, the aramid board of the present invention has a good dimensional stability with a moisture absorption elongation of 0.5% or less as measured by the method described later, and also has a good thermal conductivity.
It does not cause local heat storage during use, and has excellent heat resistance, electrical insulation, and mechanical properties.

[0026]

According to the aramid board of the present invention having the above-described configuration, the change in elongation during moisture absorption can be effectively suppressed, so that inventory management after board production, transportation, and humidity management immediately before assembling electrical equipment are performed. There is no need to perform this, and the production process can be streamlined and costs can be reduced. Further, since the original properties of the m-aramid board are maintained, there is no restriction on material selection, and the same handling as that of the conventional m-aramid board is possible. Therefore, it can be widely used for various applications mainly for electric insulation.

[0027]

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 measurement methods. In the examples, “parts” simply means “parts by weight”. (A) Logarithmic viscosity: 0.5 g / 100 in 95% sulfuric acid
The logarithmic viscosity of the ml was measured at 30 ° C. (unit: dl / g). (B) Moisture absorption elongation: After measuring the vertical and horizontal dimensions (X ₁ , X ₂ ) of the board immediately after thermocompression bonding, the board was conditioned for 15 days in a room with a constant temperature and humidity of 20 ° C. and a relative humidity of 65%. The dimensions (Y ₁ , Y ₂ ) of the sample thus obtained in the vertical and horizontal directions were measured and calculated by the following equation.

[0028]

(Equation 1)

The length was measured using a two-dimensional coordinate measuring device (MA-1, BLTV) manufactured by Mutoh Kogyo KK (unit:%). (C) Dielectric breakdown voltage (BDV): based on 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 a usual method. A m-aramid fibrid (pulp particle) having a degree (CSF) of 105 ml and 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.

(A) Production of sheet 60 parts of m-aramid fibrids and 40 parts of m-aramid fiber prepared in the above (a) are dispersed in water about 200 times, and then a 25 cm × 25 cm field wire mesh is formed. It was made 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 moisture content of 2.
5% (weight). (This sheet is referred to as Sheet A-1.) (C) Fabric production Copoly (p-phenylene / 3,4'-diphenylether terephthalamide) fiber having a single yarn fineness of 1.5 denier and a total fineness of 55 denier is used. , 65 longitudinal directions / inch,
A woven fabric having a weave density of 65 / inch in the weft direction was prepared. The woven fabric is continuously scoured by a usual method (processing temperature: 60 ° C.,
After a processing time of 2 minutes), use a non-touch drier
Dry at 30 ° C. for 1 minute. The basis weight was 32 g / m ² . (The obtained cloth is referred to as cloth B-1.) After cutting the cloth B-1 to a size of 22 cm × 22 cm, the cloth was immersed in N-methyl-2-pyrrolidone at room temperature, dried, and then subjected to the following test. Used for (molding).

(D) Board molding Sheet A-1 and cloth B-1 cut into 22 cm × 22 cm
Of A-1 / B-1 / A-1 / B-1 / A-1 / A-1 / B-1 / A-1 / B-
1 / A-1 10 layers, 6 layers of sheet A-1, cloth B-1
Is placed on a flat plate press at 270 ° C., 50
After performing the “air release” operation at kg / cm ² , thermocompression bonding was performed for 5 minutes to prepare a board (Example 1).

For comparison, a board was prepared by laminating 10 sheets of the sheet A-1 alone and thermocompression-bonding them similarly (Comparative Example 1).

The moisture absorption elongation and BDV of each board are shown in Table 1 below.

[0035]

[Table 1]

[0036]

Examples 2-3, Comparative Example 2 (e) Fabric production Copoly (p-phenylene / 3,4'-diphenylether terephthalamide) fiber having a single yarn fineness of 1.5 denier and a total fineness of 1,500 denier was prepared. A woven fabric having a weave density of 17 threads / inch in the warp direction and 17 threads / inch in the weft direction was used (basis weight 220 g / m ² ). The 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) Board molding The sheet A-1 cut into 22 cm × 22 cm manufactured according to Example 1 (a) and the above cloth B-2 cut into the same dimensions
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 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 similarly prepared by laminating nine sheets A-1 alone (Comparative Example 2).

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

[0039]

[Table 2]

[0040]

Example 4, Comparative Example 3 (g) Fabric Production 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 woven density of 18 threads / inch in the warp direction and 18 threads / inch in the weft direction was prepared (having a basis weight of 162 g / m ² ). (This cloth is referred to as cloth B-3).

(H) Board molding The sheet A-1 cut into 22 cm × 22 cm manufactured according to Example 1 (a) and the above-mentioned cloth B-3 cut into the same dimensions
To 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, eleven sheets A-1 alone were stacked and pressed in the same manner to produce a board (Comparative Example 3).

Table 3 shows the moisture absorption elongation and BDV of each of the obtained boards.

[0044]

[Table 3]

From the results of Examples 1 to 4 and Comparative Examples 1 to 3 described above, the effects of the present invention became clear.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) B32B 1/00-35/00 H05K 1/03

Claims (7)

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