JP2994156B2 - Low deformation aramid board - 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 pressing, and in particular, aramid having excellent dimensional stability when absorbing moisture and having good electric insulation. The board is about.

[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.

[0003] For example, an arbitrary number of wet papers obtained by mixing pulp-like particles made of an aromatic polymer such as m-aramid and short fibers made of the polymer and / or inorganic short fibers are laminated and heated and pressed. A method of manufacturing an oil immersion insulating board (see Japanese Patent Publication No. 57-46163), or a high-density press board comprising an aromatic polyamide fibrid (for example, m-aramid fibrid) and a high-temperature resistant floc Japanese Patent Application Laid-Open No. 4-257400), or a proposal to manufacture a low-density board having a relatively smooth surface using aramid fiber and use it for a fire wall separating an automobile cabin and an engine compartment.
And the like are known.

[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 this case, the conventionally known m-aramid board is normally stretched by absorbing equilibrium moisture when left at room temperature after being press-molded in an absolutely dry state. In the case of a large board, the deformation amount is 10 mm. It is not rare to exceed.

[0005] Alternatively, a three-dimensionally formed part such as an insulating board for a railway vehicle transformer causes a change in shape as well as a change in length due to subsequent moisture absorption. Therefore, if the pressed product cannot be stored in the predetermined transformer case unless it is dried again immediately before use, or if the desired dryer is not in the assembly plant, the pressed product must be stored in an absolutely dry state and transported. There are many difficulties in the process, such as no longer.

In connection with that solution, pulp-like particles obtained from poly (m-phenylene isophthalamide), namely m-aramid fibrids and p-type obtained from poly (p-phenylene terephthalamide) in a system of short fibers.
A sheet for impregnation in which aramide short fibers are arbitrarily combined has been proposed (see Japanese Patent Application Laid-Open No. 62-41400), but this sheet is composed of m-aramid fibrids and poly (p-phenylene terephthalamide) short fibers. Due to poor adhesion, the mechanical properties such as the strength and elongation of the board are insufficient.

As another means, a sheet-like structure comprising an entangled mixture of granular mica and substantially unmelted aramid (aromatic polyamide) fibrids has been proposed (JP-B-43-20421 and JP-B-43-20421). Kaisho 64
However, this method is not preferable because heat is stored in the aramid board because mica having a low thermal conductivity is added.

[0008] In view of this situation, the present inventors have proposed that m
-Achieved the present invention as a result of intensive research to provide highly practical aramid boards that suppress moisture absorption deformation without impairing the basic performance of aramid boards mainly composed of aramid fibrids and m-aramid fibers did.

[0009]

That is, the present invention provides a novel aramid board which achieves the above-mentioned object, comprising a plurality of sheets (A) mainly comprising m-aramid fibrids and m-aramid fibers, and m. At least one selected from a sheet (b-1) mainly composed of aramid fibrid and p-aramid fiber and / or glass fiber or a sheet (b-2) mainly composed of m-aramid fibrid and granular mica And a plurality of sheets (B)
Each of the sheets (B) is laminated so that at least one layer of the sheet (A) is interposed between the respective layers of the sheet (B) in a state of a water content of less than 45%, and heated and pressed to form an integrated board. It concerns low deformation aramid boards.

The term "m-aramid fibrid" as used in the present invention refers to a solution of a wholly aromatic polyamide in which at least 80 mol% or more of polymer repeating units are m-phenylene isophthalamide, for example, Japanese Patent Publication No. 35-11851. And pulp-like particles obtained by feeding into a precipitant with stirring and precipitating and precipitating while applying a shearing force, as described in Japanese Patent Publication No. 3-39539, and a small amount in the fibrid. 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.

On the other hand, “p-aramid fiber” refers to a poly (p-aramid fiber) having a polymer repeating unit substantially represented by the following formula (I):
-Phenylene terephthalamide) fiber,

[0013]

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A fiber comprising poly (p-phenylene / 3,4'-diphenyl ether terephthalamide), wherein the polymer repeating unit is substantially a copolymer represented by the following formula (II) and the following formula (III):

[0015]

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Are collectively referred to as These p-aramid fibers are commercially available under registered trade names such as "Kevlar", "Twaron", and "Acknola".

"Glass fiber" is a fiber substantially made of glass. Two or more of these p-aramid fibers and glass fibers can be used in combination. These fibers are also usually used in the form of short fibers like m-aramid fibers.

The term "granular mica" refers to granules of various types of mica, and among them, hard fired mica having a particle size of about 10 to 80 mesh is preferable.

The aramid board of the present invention essentially comprises m-
A total of four or more sheets containing aramid fibrids, preferably eight or more sheets, more preferably ten to several tens of sheets, laminated and heated and pressed to form an integrated board,
at least two sheets (A) mainly composed of m-aramid fibrid and m-aramid fiber, and a sheet (b-1) mainly composed of m-aramid fibrid and p-aramid fiber or / and glass fiber or A first feature is that at least two sheets of at least one sheet (B) selected from a sheet (b-2) mainly composed of m-aramid fibrids and granular mica are laminated in combination. .

The sheet (A) is a sheet (web) mainly composed of m-aramid fibrids and m-aramid fibers, but may contain a small amount of other components (for example, 20% by weight or less) in addition to the above two components. No problem. The ratio (weight ratio) of m-aramid fibrids and m-aramid fibers in the sheet (A) is usually 90/10 to 10/9.
0, preferably 70/30 to 30/70. When the amount of m-aramid fibrids is less than the lower limit, there is a problem in the adhesiveness of the sheet, and when the amount of fibers is less than the lower limit (the fibrid amount exceeds the upper limit), the effect of the moisture absorption dimensional stability of the board is insufficient. Not preferred.

On the other hand, the sheet (B) mainly comprises m-
Sheets (b-1) composed of aramid fibrids and p-aramid fibers, and sheets (b-2) composed mainly of m-aramid fibrid granular mica,
In the present invention, as the sheet (B), the above (b-1),
Either one or both of (b-2) can be used. The ratio (weight ratio) between m-aramid fibrids and p-aramid fibers or glass fibers in the sheet (b-1) is also usually 90/90 as in the case of the sheet (A).
10-10 / 90, preferably 70 / 30-30 / 70
And

In the mica mixed sheet (b-2), m
-It is preferable to contain a small amount of aramid fiber in addition to aramid fibrid and granular mica, and in this case, 30 to 70
(Weight)% m-aramid fibrids and 70-30
It is preferred to be composed of (weight)% granular mica and 20% by weight or less of aramid fiber.

When the content of mica in the mica mixed sheet (b-2) is less than 30% by weight of the total amount of the sheet,
The board does not contribute sufficiently to the suppression of moisture absorption and elongation.
Exceeding 0% by weight is not preferable because the electrical insulation of the sheet and thus the board is impaired.

The mica-mixed sheet (b-2) contains 20
The coexistence of aramid fibers up to the weight% is preferable because the mechanical properties of the sheet and thus the board are improved.

Here, as the aromatic polyamide constituting the aramid fiber, m-aramid and p-aramid, for example, poly (m-phenyleneisophthalamide),
Poly (p-phenyleneterephthalamide), poly (p-
Phenylene / 3,4'-diphenyl ether / terephthalamide).

In the aramid board of the present invention, the lamination order (arrangement) of the sheets (A) and (B) is important, and at least one sheet (B) is provided between the laminated sheets (B).
It is necessary that the sheets (A) are laminated so as to be interposed. For example, when laminating 10 sheets to form a board, odd-numbered or even-numbered sheets are referred to as sheet (B), and the remaining sheets are referred to as sheet (A). At this time, the sheet (A) may be overlapped so that two or more sheets are in contact with each other, but the object of the present invention is achieved when two or more sheets (B) are successively overlapped so as to be in contact with each other. Because it is difficult to do, sheet (B)
The stacking order is such that one or more sheets (A) always exist between them.

In many cases, the sheet (A) is disposed on the uppermost layer (top surface) and the lowermost layer (bottom surface) of the laminate, and the sheet (A)
It is preferable to form a sandwich in which the sheets (B) are sandwiched so as to form layers separated from each other.

The method for producing the sheets (A) and (B) to be laminated is not particularly limited. However, since the aramid board of the present invention is used for high-density electrical insulation, a web by a known wet (papermaking) method is used. Is preferred. 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 if necessary, dissociate or beat as a preparation step. Further, various additives such as a sizing agent and a resin can be added as long as the electrical insulation is not impaired.

[0029] Webs produced by the wet method usually show vertical / horizontal anisotropy because the fibers are oriented in the flow direction. Therefore, these webs are cut into a predetermined size (sheet formation).
However, it is preferable that the layers are alternately crossed at the time of lamination on the board, since the properties of the obtained board become isotropic.

When a sheet (web) containing p-aramid fibers is used as the sheet (B), the purpose is to improve the adhesiveness between adjacent m-aramid fibrids and a sheet (web) comprising m-aramid fibers. , A small amount of N-
The surface can be washed with an organic solvent such as methyl-2-pyrrolidone, N, N-dimethylformamide, N, N-dimethylacetamide, dimethylsulfoxide, hexamethylphosphoramide, and tetramethylurea.

In the aramid board of the present invention, the moisture content of each sheet to be laminated is important, and the moisture content of the sheet (web) at the time of lamination is 1% based on the sheet weight.
It is necessary to pre-dry and adjust so as to fall within the range of ~ 45 (weight)%. The pre-drying temperature is 10 at normal pressure.
0-180 ° C is suitable, preferably 130-150 ° C.
° C.

As will be described later, the moisture content of the paper is 50 to 50%.
In a conventionally known method (for example, Japanese Patent Publication No. 57-46163), a 95% (by weight) wet paper web is laminated, then gradually dehydrated and dried under heat and pressure to integrate. Does not get smaller. Therefore, in the present invention, it is necessary to sufficiently dry the wet paper in advance, to quickly laminate and thermocompress the wet paper. 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 at the time of lamination is less than 45 (weight)%, preferably less than 30 (weight)%, and most preferably 0.5 to 0.5%.
5% by weight. At that time, in order to escape the air or excessive moisture contained in the sheet, so-called “air bleeding” operation, which repeats instantaneous pressure release several times during the pressing, causes air swelling (blister) in the board. Recommended from the point of view of prevention.

When an organic solvent for aramid, for example, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, dimethylsulfoxide or the like is coexisted in a part of the water, the adhesiveness of the sheet may be improved. The preferred amount of the organic solvent is 3% by weight or less based on the sheet.

The thermocompression bonding can be usually carried out by heating and pressing a flat plate or roll press laminate. The thermocompression bonding temperature is preferably from 225 to 335 ° C.
70-320 ° C. and the pressure can be varied according to the required density of the board,
0~1,000kg / cm ^2, 50~300 a roll press
It is preferably about kg / cm (linear pressure).

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.

[0036]

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.

[0038]

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" means "parts by weight". (A) Logarithmic viscosity: 0.5 g / 10 in 95% sulfuric acid
The logarithmic viscosity of 0 ml was measured at 30 ° C. (Unit dl / g) (b) Moisture absorption elongation: After measuring the vertical and horizontal dimensions (L ₁ , L ₂ ) of the board immediately after thermocompression bonding, it was measured in a room at 20 ° C. and 65% relative humidity and constant temperature and humidity. The dimensions (l ₁ , l ₂ ) of the sample conditioned for one day in the vertical and horizontal directions were measured and calculated by the following formula.

For the measurement of the length, a two-dimensional coordinate measuring device (MA-1 BLTV) manufactured by Mutoh Kogyo Co., Ltd. was used.
(unit%)

[0040]

(Equation 1)

(C) Breakdown voltage (BDV): JIS
-Conforms to C2111. Measured with AC voltage. (Unit: KV / mm) (d) Thermal conductivity: Measured with "Thermolab I" (manufactured by Kato Tech). The temperature difference (Δt) between the upper and lower surfaces of the sample was set to 10 ° C. (Unit cal / cm · sec ℃)

[0042]

Examples 1-4, Comparative Example 1 (a) Preparation of Pulp and Fiber Canadian standard filtration from poly (m-phenylene isophthalamide) polymer (logarithmic viscosity 1.6) prepared by interfacial polycondensation by a usual method. An m-aramid fibrid (pulp-like particles) having a water content (CSF) of 105 ml and m-aramid fibers 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 obtained.

(A) Production of Sheet 60 parts of m-aramid fibrid and 40 parts of m-aramid fiber prepared in (a) above are dispersed in about 200 times the amount of water, and then a 25 cm × 25 cm wire mesh is provided. Paper 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 basis weight of the obtained sheet was 80 g / m ² , the thickness was 0.205 mm, and the moisture content was 2.5.
%Met. (This sheet is referred to as sheet A)

The above m-aramid fibrids (60 parts) and poly (p-phenylene terephthalamide) fiber (fineness: 1.
5 denier, length 3mm, strength 22g / d, elongation 4.0
%) Was dispersed in about 200 times the amount of water, and then formed and dried by the same method. The basis weight of the obtained sheet was 80 g / m ² , the thickness was 0.198 mm, and the water content was 1.8%. (This sheet is called sheet B)

Instead of the poly (p-phenylene terephthalamide) fiber of sheet B, poly (p-phenylene / 3,3)
A sheet was prepared in the same manner as sheet B except using 4'-diphenyl ether terephthalamide) fineness (fineness 1.5 denier, length 3 mm, strength 25 g / d, elongation 4.4%). The basis weight of the obtained sheet is 81 g /
m ² ), thickness 0.196 mm, and moisture content 1.1%.
(This sheet is referred to as sheet C)

Similarly, 40 parts of glass fiber [6 μm in diameter]
m, length 3 mm, manufactured by Nippon Electric Glass Co., Ltd.]. The obtained sheet had a basis weight of 78 g / m ² , a thickness of 0.240 mm, and a water content of 0.9%. (This sheet is referred to as sheet D.) Similarly, a sheet using 40 parts of hard-fired laminated mica [particle size 32-60 mesh Nippon Mica Seisakusho] was prepared. Sheet basis weight 77 g / m ² , thickness 0.188 mm,
The water content was 0.8%. (This sheet is called sheet E)

(C) Molding of board After the shapes of the above-mentioned sheets A and B were adjusted to 22 cm × 22 cm, 10 sheets were formed in the order of A / B / A / B / A / A / B / A / B / A. The laminate of the sheet A and the sheet B was placed on a flat plate press at 270 ° C. and 50 kg / cm ^2.
For 5 minutes to prepare a board (Example 1).

Boards using sheets C, D and E instead of sheet B were also prepared in the same manner (Examples 2 to 4), and for comparison, 10 sheets A alone were laminated. Similarly, a board which was thermocompression-bonded was prepared (Comparative Example 1).

The moisture absorption elongation, BDV,
The thermal conductivity is shown in Table 1 below.

[0050]

[Table 1]

As shown in Table 1, Examples 1 to 4 according to the present invention were used.
It was confirmed that the aramid board No. 4 was improved only in the moisture absorption elongation rate without impairing the BDV and thermal conductivity.

[0052]

Example 5, Comparative Example 2 (d) Production of sheet 40 parts of m-aramid fibrid and 10 parts of m-aramid fiber prepared in (a) of Examples 1 to 4 and Examples 1 to 4
(A) 50 parts of the hard-fired laminated mica used in the sheet E of (A) was dispersed in about 200-fold water and formed into a sheet by the method described in (A) above. The basis weight was 76 g / m ² , and the thickness was 0.1 mm. 1
A sheet having a size of 88 mm and a moisture content of 1.2% was obtained (sheet F).

(E) Board molding Six sheets (A) and five sheets (F) were laminated as described below and thermocompressed in the same manner as in (C) of Examples 1 to 4 to prepare a boat. Example 5). A / F / A / F / A / F / A / F / A / F / A

For comparison, a laminate composed of 11 sheets F was similarly thermocompression-bonded to prepare a board (Comparative Example 2).

Table 2 below shows the characteristic values of each board.

[0056]

[Table 2]

Although the heat conductivity of the board consisting of only the sheet F was inferior, it was confirmed that the board of the present invention showed almost no difference in heat conductivity from the board of the sheet A alone.

[0058]

Example 6, Comparative Example 3 (f) Production of Sheet In the same manner as in (d) of Example 5, except that the dewatering is adjusted to keep the moisture content of the sheet at 90%,
A sheet having a fiber / mica ratio of 40/10/50 (basis weight 77 g / m ² ) was obtained (sheet Y).

Similarly, dehydration of sheet A was adjusted to prepare a sheet having a water content of 90%. (Sheet X).

(G) Forming a board The above sheet X (three sheets) and sheet Y (two sheets) are laminated as follows, and dehydration is facilitated by X / Y / X / Y / X. An 80-mesh twill stainless steel (SUS304) wire mesh was sandwiched, and the temperature was increased from 140 ° C. to 270 ° C. in 10 minutes under a pressure of 50 kg / cm ² (constant) to obtain a five-layer board (Comparative Example 3). On the other hand, Example 5
A total of 5 sheets A (3 sheets) and F (2 sheets) were laminated in the order of A / F / A / F / A, and the above-mentioned wire mesh was inserted above and below the sheets, and 50 kg / cm ² and 270 ° C. For 10 minutes to obtain a board (Example 6). Table 3 shows the measurement results of each of these boards.

[0061]

[Table 3]

From Table 3, it is understood that when the moisture content of each laminated sheet is high, the moisture absorption elongation exceeds 0.5% and the dimensional stability is poor.

Claims (10)

(57) [Claims] 1. A plurality of sheets (A) mainly comprising m-aramid fibrid and m-aramid fiber,
At least one sheet selected from a sheet (b-1) mainly composed of aramid fibrid and p-aramid fiber and / or glass fiber or a sheet (b-2) mainly composed of m-aramid fibrid and granular mica A plurality of sheets (B) are laminated so that at least one layer of the sheet (A) is interposed between the respective layers of the sheet (B) in a state of a water content of less than 45%, and are heated and pressed to be integrated. Low-deformable aramid board characterized by having a board shape of 2. The low-deformable 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
2. The low-deformable aramid board according to claim 1, which is a short fiber composed of (phenyleneisophthalamide). 3. 4. The ratio (weight ratio) between m-aramid fibrids and m-aramid fibers in the sheet (A) is 90.
The low-deformable aramid board according to claim 1, wherein the ratio is / 10 to 10/90. 5. The p-aramid fiber is substantially poly (p
The low-deformable aramid board according to claim 1, which is a short fiber composed of -phenylene terephthalamide) or poly (p-phenylene / 3,4'-diphenylether terephthalamide). 6. The ratio (weight ratio) of m-aramid fibrids to the total amount of p-aramid fibers and glass fibers in the sheet (b-1) is 90/10 to 10/90. The low deformation aramid board as described. 7. The low-deformable aramid board according to claim 1, wherein the sheet (b-2) contains a small amount of m-aramid fibers in addition to the m-aramid fibrids and granular mica. 8. The sheet (b-2) is composed of 30 to 70% by weight of m-aramid fibrids, 70 to 30% by weight of granular mica, and 20% by weight or less of m-aramid fibers. The low-deformable aramid board according to claim 1 or 7, which is obtained. 9. The heating and pressurizing of the laminated sheet is performed in the range of 225 to 33.
The low-deformation aramid board according to any one of claims 1 to 8, which is performed at 5 ° C. 10. The low-deformable aramid board according to claim 1, having a water absorption elongation of 0.5% or less.