Electrical insulating paper

Abstract

An electrical insulating paper having 40-80 wt % of aramid fibrid, 10-50 wt % of aramid pulp, and 10-50 wt % of aramid short-cut. The aramid pulp is para-aramid pulp with a length of 0.5-6 mm and has a Schopper Riegler value of 15-85; the aramid fibrid is para-aramid fibrid; and the aramid short-cut is para-aramid short-cut. The paper shows a high dielectric strength and tensile index. A method for manufacturing the paper and an insulated conductor that includes the paper.

Claims

1. An electrical insulating paper comprising: 40-80 wt % of aramid fibrid, 10-50 wt % of aramid pulp, and 10-50 wt % of aramid short-cut, wherein the aramid of the aramid pulp consists of para-aramid and wherein the aramid pulp has a length of 0.5-6 mm and has a Schopper Riegler (SR) value of 15-85, and wherein the aramid fibrid has a SR value of 50-90, and/or a specific surface area (SSA) of less than 10 m.sup.2/g.

2. The electrical insulating paper according to claim 1, wherein the aramid fibrid is para-aramid fibrid, and/or the aramid short-cut is para-aramid short-cut.

3. The electrical insulating paper according to claim 1, wherein the paper comprises at most 70 wt % of the aramid fibrid.

4. The electrical insulating paper according to claim 1, wherein the paper contains at least 15 wt % of the aramid short-cut.

5. The electrical insulating paper according to claim 1, wherein the paper contains at least 15 wt % of the aramid pulp.

6. The electrical insulating paper according to claim 1, wherein the paper has a bulk density of at least 0.7 g/cm.sup.3.

7. The electrical insulating paper according to claim 1, wherein the paper has an electric resistance of at least 10.sup.13 ?cm according to the volume resistivity method of ASTM D-257.

8. A method for manufacturing the electrical insulating paper according to claim 1, comprising: preparing a suspension comprising the aramid fibrid, the aramid pulp, and the aramid shortcut, applying the suspension onto a porous screen, so as to lay down a mat of randomly interwoven material onto the porous screen, removing water from the mat by pressing and/or application of a vacuum, and subjecting the mat from which water is removed to a drying step.

9. The method according to claim 8, further comprising subjecting the dried paper to a calendering step.

10. The method according to claim 9, wherein the calendering step is performed at 100? C. or higher.

11. An insulated conductor comprising the paper according to claim 1.

12. A transformer, generator, or electric motor comprising the insulated conductor of claim 11.

Description

EXAMPLES

(1) Papers were made according to the method of ISO 5269-2 and thereafter calendered according to the general procedure, unless indicated differently. The ingredients for making paper amounted to 1.6 g of material (based on dry weight), resulting in sheets of 50 g/m.sup.2. The compositions, grammage, and thickness of the various papers are presented in table 1 below. Ex 1 is a paper according to the invention. Papers A through E are comparative.

(2) TABLE-US-00001 TABLE 1 Composition Fibrids Short Cut Pulp Grammage Thickness Ex [%] [%] [%] [g/m.sup.2] [um] Ex 1 50 30 20 50 49.5 A 20 30 50 50 52.3 B 50 50 50 55.0 C 100 50 48.7 D 50 50 50 49.0 E 50 50 50 55.6

(3) Various properties of these papers were determined, and the results thereof are presented in Table 2 below.

(4) TABLE-US-00002 TABLE 2 Results Dielectric Strength TI EAB Gurley Ex [kV/mm] [Nm/g] [%] [Gs] TI*DiS Ex 1 36.2 50.6 1.5 91400 1832 A 19.6 37.8 1.1 1230 741 B 23.4 54.4 1.9 7150 1273 C 67.1 69.5 3.2 1986096 4663 D 44.3 31.2 2.2 30000 1382 E 12.0 6.5 0.7 12 78

(5) From the results in Table 2 it can be seen that the paper of Example 1, which is according to the invention, shows a high value for the product of the tensile index and the dielectric strength, which makes it suitable for use in various applications. The paper containing fibrids only has a very high value for this parameter, but water removal during manufacture was difficult, and tear strength was low.