JPH04262317A - Electrical insulating press-board and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve physical properties such as impregnating ability, compressive strength, heat resistivity, etc., with low relative dielectric constant by constituting a wet paper for lamination which is dried and integrated from a wooden pulp and a meta aromatic polyamide fiber pulp spread in a film shape. CONSTITUTION:After suspending a meta aromatic polyamide fiber pulps into water at its concentration lower than that of a wooden pulp, respective pulps are dissociated and dispersed from each other with a pulper or the like. The obtained slurry is transferred to a refiner, a clearance between a stator and a roter is adjusted such that it gradually narrows from a normal value so as to crash the pulps to pieces and spread them in a film shape. This is mixed in a precrushed wooden pulp slurry by an amount of 35 to 90% of the total weight and is made to a wet paper by a conventional method. An oil impregnated or gas impregnated electrical insulating pressboard can be produced by heating and pressing so as to dry and integrate it after plural sheets of the wet paper are laminated.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrically insulating pressboard (hereinafter simply referred to as pressboard) and a method for manufacturing the same. In particular, the present invention relates to an oil-impregnated or gas-impregnated electrical insulating pressboard that has a low dielectric constant and excellent physical properties such as impregnability, compression resistance, and heat resistance, and a method for manufacturing the same.

0002

[Prior Art] Conventionally, oil-filled high voltage equipment such as power transformers and reactors have been manufactured by laminating wet paper made from wood pulp or cotton fibers and drying them as an insulating material. Pressboard is widely used. In recent years, in order to further lower the dielectric constant of these pressboards, synthetic fibers with low dielectric constants, such as polyolefin, poly4-methylpentene-1, polybutylene terephthalate, polyethylene terephthalate, polyphenylene sulfide, polysulfone, and A press board containing arylate, tetrafluoroethylene, and polycarbonate has been proposed (Japanese Patent Laid-Open No. 57-16841).
No. 8, No. 62-156386, No. 63-16011, No. 63-138606, etc.).

[0003] However, when these synthetic fibers are immersed in oil, which is usually at a temperature of 80 to 100°C or higher, many of them cause problems such as swelling or dissolution. In addition, these synthetic fibers themselves have a weak affinity for wood pulp and cotton fibers, and their shapes are cylindrical or strip-like, so their binding strength with wood pulp, etc. is weak, so they easily slip out of the pressboard. It was a problem. This has caused serious problems such as deterioration of physical properties such as voltage resistance of the pressboard.

[0004] On the other hand, the above-mentioned or other synthetic materials are selected and used as solid insulating materials for gas-insulated equipment, which has been rapidly developing in recent years, but fibers made of these synthetic materials themselves Since they do not have the ability to bond to each other like wood fibers, it is extremely difficult to manufacture boards using only these synthetic fibers, with the exception of some resins. Therefore, when using synthetic materials, it is necessary to use film laminates or thick plates of film, rather than those composed of intertwined fibers.
In that case, it is completely impossible to impregnate these solid synthetic materials with an insulating gas, and the voids existing inside the solid synthetic materials cannot be crushed, resulting in a problem of lack of reliability.

[0005]

[Problems to be Solved by the Invention] Therefore, the present invention has been developed by incorporating synthetic fibers that do not swell or elute with high-temperature oil and have excellent bonding properties with wood pulp.
It is an object of the present invention to provide an oil-impregnated or gas-impregnated pressboard for electric insulation that has a lower dielectric constant than conventional pressboards and has excellent physical properties such as impregnability, compression resistance, and heat resistance.

[0006]

[Means for Solving the Problems] As a result of intensive studies to achieve the above object, the present inventors have developed an electrical insulating pressboard made by drying and integrating laminated wet paper, combining the wet paper with wood pulp and film. The inventors have discovered that a pressboard having the above-mentioned characteristics can be produced by constructing it from a meta-aromatic polyamide fiber pulp expanded into a shape, and have arrived at the present invention.

That is, the present invention provides (1) an electrically insulating press board formed by drying and integrating laminated wet paper, in which the wet paper is made of wood pulp and meta-aromatic polyamide fiber pulp developed into a film; an oil-impregnated or gas-impregnated pressboard for electrical insulation, and (2)
Wet paper is made from a slurry of a mixture of beaten wood pulp and meta-aromatic polyamide fiber pulp developed into a film, and after the wet paper is laminated, the laminate is dried and integrated by pressure and heating. The present invention relates to a method for producing an oil-impregnated or gas-impregnated electrically insulating pressboard.

The present invention will be explained in detail below. As shown in FIG. 1, the meta-aromatic polyamide fiber (aramid fiber) pulp used in the present invention is in a pulp-like state before being developed into a film. This type of meta-aromatic polyamide fiber pulp is easily available on the market. For example, meta-type meta-aromatic polyamide fiber (registered trademark CONEX pulp: polymetaphenylene isophthalamide fiber) commercially available from Teijin Ltd. can be mentioned.

[0009] Such meta-aromatic polyamide fiber pulp is produced by molding an optically isotropic solution of meta-aromatic polyamide at a draft ratio of 1.8 or more. It is obtained by adding and fibrillating, and has the property of bonding well to wood pulp. Meta-based aromatic polyamide fiber pulp has a morphology similar to that of wood pulp in appearance, but when observed microscopically in detail, it basically has a structure in which a thin aramid resin film is rolled into a cylindrical shape. There is. In order to develop meta-aromatic polyamide fiber pulp into a film, it is usually suspended in water to a lower concentration than wood pulp, and then processed using a pulper for as long as possible. Dissociates and disperses pulp. Next, this slurry is transferred to a refiner, the clearance between the stator and rotor is adjusted to the same level as in normal NUKP refining, and the slurry is expanded into a film by continuing beating and circulation until the extent of expansion is approximately 50 to 60%. At this point, the clearance of the refiner is further narrowed and so-called cutting beating is carried out, and the pulp is divided into small pieces.
Becomes fully expanded.

FIG. 2 is an enlarged photograph of a meta-aromatic polyamide fiber pulp that has been almost completely developed into a film. For reference, Figure 3 is shown. This drawing (photo) shows an enlarged view of fibers obtained by simply beating meta-aromatic polyamide fiber pulp in the same manner as wood pulp. In this case, the fibers are hardly developed and are only finely cut.

[0011] The size of the developed film is not particularly limited, but the vertical and horizontal dimensions are generally each 0.5 to 3.
．． It is about 0 mm. If both the vertical and horizontal dimensions are too large, the passage of water vapor in the thickness direction during the drying process when preparing a thick pressboard is hindered, and delamination is likely to occur in the pressboard. The size of the film is
For example, the desired value can be achieved by adjusting the concentration of the meta-aromatic polyamide fiber pulp slurry used in the above-mentioned expansion operation, the clearance between the stator and rotor of the refiner, the shape of the refiner blade, etc.

[0012] The slurry of meta-aromatic polyamide fiber pulp developed into a film is mixed with a slurry of wood pulp that has been beaten in advance, and the paper is formed by the same conventional method to produce wet paper. The freeness of wood pulp after beating is usually 200 to 500 ml/3 g of CSF. Further, the content of the meta-aromatic polyamide fiber pulp after being developed into a film is 90 to 200 ml/3 g.

The amount of the meta-aromatic polyamide fiber pulp is preferably 35 to 90% based on the total weight of the wood pulp and the meta-aromatic polyamide fiber pulp. If the amount of meta-aromatic polyamide fiber pulp is less than 35%, the oil immersion dielectric constant will be 3.5% even in relatively low density pressboards of about 1.0 g/cm2 or less.
If it becomes 8 or more, the practicality decreases. On the other hand, if it is more than 90%, the passage (escape path) for water vapor during heating and pressurization of the laminate becomes extremely small, delamination of the pressboard is likely to occur, and the time required for drying becomes extremely long.

[0014] A slurry consisting of wood pulp and meta-aromatic polyamide fiber pulp developed into a film is made into paper using a conventional method to obtain a wet paper, and after laminating a plurality of sheets of this wet paper, heating is performed. By applying pressure and drying and integrating, the oil-impregnated or gas-impregnated pressboard for electrical insulation of the present invention is manufactured. After vacuum drying, the board manufactured in this way is treated with insulating oil or sulfur hexafluoride gas (SF6).
), etc., and used as an electrical insulator.

[0015]

Effects of the Invention According to the present invention, an oil-impregnated or gas-impregnated electrical insulation press is provided which has a lower dielectric constant than conventional pressboards and also has excellent physical properties such as impregnability, compression resistance, and heat resistance. Board provided. In particular, since the board according to the present invention has an intertwined fiber structure of meta-aromatic polyamide fibers and wood fibers, there is no problem of poor impregnation with insulating oil or gas. Also, the dielectric constant of insulating gas such as SF6 gas is ε
s ~ 1.0, so even if it is impregnated with this, the dielectric constant of the pressboard is the same as when it is dry. As a result of the demand for solid materials with a lower dielectric constant than those for oil-immersed equipment, the board according to the present invention has excellent thermal stability and is suitable for gas-insulated equipment that has no choice but to use solid materials such as those mentioned above. Together, they can be used.

[0016]

[Examples] The present invention will be explained in more detail with reference to Examples below. Examples 1 to 4 Polymetaphenylene isophthalamide fiber pulp (Teijin Ltd.) was used as 1.5 kg of meta-aromatic polyamide fiber in a small conical refiner with a processing capacity of about 2 tons/day.
A slurry (pulp concentration: 1.0%) was prepared by adding water to make a total volume of 150 liters. In this refiner, the slurry was circulated for 30 minutes so that about 50% of the meta-aromatic polyamide fiber pulp was developed with a clearance between the rotor and the stator of 0.3 mm.

Next, the clearance between the stator and rotor of the refiner is gradually narrowed until it is finally 0.0
5mm, and the following table-
A meta-aromatic polyamide fiber pulp consisting of a film developed into the size shown in 1 was prepared. The meta-aromatic polyamide fiber pulp slurry prepared in this way was mixed with a wood pulp slurry that had been beaten to a freeness of 300 ml (the mixing ratio is as shown in Table 1), and thoroughly stirred. . From this mixed slurry, the basis weight of each leaf is 60
g/m2, and after laminating 22 sheets of wet paper, the laminated body was dried and integrated by real press treatment for 30 minutes under the conditions of 125 ° C. and 50 kg f/cm2, Manufactured pressboard. The thickness of the press board at this time is shown in Table 1. Examples 5 to 8 Slurry concentration of meta aromatic polyamide fiber pulp is 0
．． A pressboard was manufactured in the same manner as in Example 1 except that the clearance between the stator and rotor of the refiner was 0.5 to 0.3 mm. Comparative Examples 1 to 3 Pressboards were produced in the same manner as in Example 1, except that the meta-aromatic polyamide fiber pulp was used in the pulp state without being developed. Comparative Example 4 A pressboard was produced in the same manner as in Example 1 except that no meta-aromatic polyamide fiber pulp was used. Comparative Example 5 A cylindrical meta-type meta-aromatic polyamide fiber (2 to 3 denier, 3 mm cut) was used instead of the meta-aromatic polyamide fiber pulp, and the heating and pressing time was 15 minutes. A pressboard was produced in the same manner as in Example 1.

[0018] Regarding each of the press boards obtained in the above Examples and Comparative Examples, the density, dielectric constant, amount of compressive strain, amount of residual strain, and thermal stability were measured and observed. The results are shown in the same table.
Shown in 1. In addition, those impregnated with sulfur hexafluoride gas instead of JIS Type 1 oil also had excellent insulation properties. The measurement conditions are as follows. (1) Bulk density: Measured according to JIS C2305. (2) Relative permittivity: Using an insulating paper dielectric property measuring electrode (manufactured by Nissin Electric), after drying in vacuum, JIS type oil was vacuum injected, and the values before and after oiling were measured at 50°C. It was measured. Incidentally, the SF6 gas was impregnated at a pressure of 1.5 kg/cm2, but in this case, there was no difference in the dielectric constant before and after the impregnation. (3) Dielectric breakdown voltage Measured according to JIS C.2111.18.1.

Table 1 shows the strength per unit thickness (kV/m
m). (4) Tensile strength Measured according to JIS C.2111.7. Table-1
Indicates the strength per unit cross-sectional area (kgf/mm2). (5) Compressive properties and residual strain: Press boards cut into 40 mm x 40 mm dimensions were immersed in dry oil, then stacked at a height of about 50 mm at room temperature, and sampled at a displacement rate of 1 mm/min. The compressive strain rate was measured by applying pressure to 300 kg/cm2, and the residual strain rate was measured when the pressure was set to 0 at the same speed.

[0020] The compression properties and residual strain shown in Table 1 below are based on the values of Comparative Example 4 made of 100% wood pulp.
It was calculated as (6) Thermal stability A press board cut to a width of 15 mm and a length of 250 mm was dried, immersed in oil, sealed with oil in a sealed case, and heated at 140°C for 1 hour.
After heat treatment for 20 days, tensile strength was measured according to JIS C.2111.7.

Table 1 shows the ratio of the strength after heat treatment to the strength before heat treatment (remaining strength). (7) Fluff on the surface of the pressboard was visually observed.
Table 1────────────
──────────────────────────
Meta aromatic Meta aromatic
Insulation Tensile Polyamide Fiber Polyamide Fiber Bulk density Dry ratio Oil immersion ratio
Breaking strength Half amount (%)
film big deal
Voltage
(length x width mm) (g/cm3)
Dielectric constant Dielectric constant (kV/mm) (kgf/m
m2)──────────────────────
────────────── 1 35
1.0×1.0 1.10
2.26 3.79 16
11 2 50 〃
1.08 2.58 3.
60 16 8 fruit 3 8
0 〃 1.08
2.31 3.42 17
7 4 90 〃
1.00 2.36 3
．． 34 18 6 cases 5
35 3.0×2.0 1.09
2.65 3.76 16
11 6 50
〃 1.08 2.46
3.55 17 10 7
80 〃 1
．． 03 2.27 3.36
19 8 8 90
〃 1.00 2.24
3.32 19 7──
──────────────────────────
───────── 1 50
Undeveloped 1.08 3.03
4.05 15 8 ratio 2
60 〃 1
．． 06 2.87 3.85
15 6 3 70
〃 1.05 2.72
3.77 17 5 comparison
4 0 ─── 1
．． 14 3.22 4.35
15 12 (Wood half example 100%) 5 50 Cylindrical
1.09 2.96 3.97
15 5──────────────
────────────────────────
Table 1 (Continued)────────────
────────────────────────
pressure
shrink press
press board compression
residual heat
Fluff on the board surface
amount of distortion amount of distortion
Thickness Presence or absence (%) (%)
Stability (mm) ──────
──────────────────────────
───── 1 100
100 0.36
1.0-1.3 Same as Comparative Example 4 2
100 100
0.86 〃
〃Real 3 101
102 0.90
〃 〃し ４
103 104
0.94 〃
Example 5 100
100 0.38
〃 〃 6
100 100
0.87 〃
〃 7 101
103 0.94
〃 〃 8
103 104
0.97 〃
〃────────────────────
──────────────────── 1
101 105
0.38 〃
〃Ratio 2 101
105 0.47
〃 〃Comparison 3
110 116
0.66 〃
Example 4 100
100 0.20
〃 〃 5
100 100
0.20 〃
Many────────────────────
──────────────────From Table-1 above,
The pressboard obtained by the present invention has a lower dielectric constant than when using only wood pulp or unexpanded meta-aromatic polyamide fiber pulp, and moreover, the pressboard uses unexpanded meta-aromatic polyamide fiber pulp. It can be seen that the compression characteristics and the amount of residual strain are lower than in the case of use.

[Brief explanation of the drawing]

FIG. 1 is a photograph showing the shape of fine fibers of conventional meta-aromatic polyamide fiber pulp.

FIG. 2 is a photograph showing the fine shape of fibers when the meta-aromatic polyamide fiber pulp used in the present invention is expanded.

FIG. 3 is a photograph showing the fine shape of fibers obtained by conventional beating of meta-aromatic polyamide fiber pulp.

Claims (2)

[Claims] 1. An electrically insulating press board formed by drying and integrating laminated wet paper, wherein the wet paper is made of wood pulp;
An oil-impregnated or gas-impregnated pressboard for electrical insulation, characterized in that it is made of a meta-aromatic polyamide fiber pulp developed into a film. 2. Wet paper is made from a slurry of a mixture of beaten wood pulp and meta-aromatic polyamide fiber pulp developed into a film, and after the wet paper is laminated, the lamination is performed by applying pressure and heating. A method for producing an oil-impregnated or gas-impregnated pressboard for electrical insulation, characterized by drying and integrating the body.