DE1544965B2 - ELECTRIC INSULATING COMPOUND - Google Patents

Description

The invention relates to an electrical insulating compound made of a plastic compound and a filler, which contains kaolin.

Electrical insulating compounds made from a plastic compound and a filler containing kaolin, are already known.

The object of the present invention is to improve the known electrical insulating masses in such a way that that they have the lowest possible loss factor and the lowest possible dielectric constant and generate as little abrasion as possible during manufacture.

This object is inventively achieved in that the kaolin annealed at 700 to 800 ⁰ C, then air-cooled and is processed without Aufschlämmungschemikalien. The kaolin should advantageously contain less than 10% montmorillonite.

Kaolin is an aluminum silicate of the formula

Al ₂ Si ₂ O ₅ (OH) ₄ .
As such, it is used to a lesser extent in special electrical grounds where dielectric properties are not of particular concern. Its main disadvantage is that it contains bound water of hydration, which gives it a high dielectric constant of about 2.5 and a high dissipation factor of about 0.16. This results in undesirable energy losses when such a material is used as a filler for high filling in a plastic insulator body.

ίο On the other hand, when the kaolin is heated to remove the bound water, its abrasive action increases, and this property causes increased wear and tear on ball mills and other processing equipment. When heated to around 1000 ° C., the kaolin recrystallizes and is converted into mullite, Al ₆ Si ₂ O ₁₃ . Powdered mullite is a very abrasive material. The abrasive properties of kaolin increase quite quickly when temperatures above 8 50 ⁹ C are used, as can be seen from the following values:

Calcination temperature
⁰ C Grinding index 25th 0 (approximate) 550 . 4th 650 8.5 750 12th 850 22.5 950 37.5 1050 (mullite) 42

The grinding index is based on the Valley Abrasion Meter (Kehl-Schleifmeßgerät), with the units in mg / hour Cu loss / 100 g clay can be read. The values given are averages of the determinations of two values.

According to the present invention, it is possible to produce an excellent filler from powdered kaolin, which is used for the production of electrical. · Insulator compounds with a low dielectric constant and a low loss factor, ie with values in the vicinity of approximately 1.25 to 1.30 or 0.005 to 0.02O _{5, is} valuable. This is achieved by the kaolin is subjected to a "tempering" -Erhitzen in the range of 700 to 800 ⁰ C. This temperature is well above the temperature range of the complete dehydration of kaolin, but is still in a heating range in which the abrasive action of the kaolin has not reached an excessively high value.

Contact with water, especially water containing slurry chemicals, the kaolin tempered in this way suffers deterioration. It is therefore important that water, in particular that containing slurry chemicals is kept away from this material.

Example 1

A sample of practically montmorillonite free Georgia kaolin with an average particle size of about 4 μ was a heating at different; Subject to temperatures, and the dielectric Properties of the obtained product were measured. In Table I are the results obtained listed. Although the breakdown voltage values are included in the table, this property is not binding criterion for the evaluation of the isolator mass.

T ⁰ C Table I. treatment Dielectric
constant Loss factor. Breakthrough
tension
kV / mm (V / mil) sample 25th (as implemented) 2.62 0.16 4.76 (121) A. 125 (at 125 ° C 2.46 0.15 2.76 (70) B. dried in the oven) 640 (calcined, air-cooled) 1.38 0.037 2.72 (69) C. 690 (calcined, air-cooled) 1.34 0.024 3.03 (77) D. 750 (calcined, air-cooled) 1.32 0.011 4.09 (104) E. 800- (calcined, air-cooled). 1.32 . 0.011 2.95 (75) F. 860 (calcined, air-cooled) . 1.30 0.010 3.98 (101) G 1000 (calcined, air-cooled) 1.31 0.070 3.23 (82) H

. From Table I it can be seen that although the complete dehydration is carried out of the kaolin at about 600 ⁰ C, however, the loss factor begins to fall at about 69O ⁰ C under about 0.025. At the mullite formation • temperature of 1000 ⁰ C, however, the loss factor increases considerably. Obviously, the recrystallization involved leads to a pronounced change in the surface properties and in the internal stress. Although the dissipation factor at 860 ° C (Sample G) is good, there is a significant increase in the abrasiveness of the product in this range.

The dielectric constant and the dissipation factor were determined according to ASTM method D150-59 T at 1000 Hz using the disk method. The results given are based on the average of two determinations. The breakdown voltage was (at 17 and 242 psi) at 60 Hz on a pressed disc of 34.9 mm (l _^3/8 ") diameter and g measured 25th The results presented are an average of five determinations. Since the relative humidity Having strongly influenced this test, all samples were measured at a relative humidity between 20 and 40%.

- Example2

A part of sample E from example 1 was removed (after cooling) and. a conventional slurry procedure subjected to transportation through a factory. This usual slurry procedure Mixing the kaolin with water containing sodium hexametaphosphate involves pumping to the filter device, flocculation with sulfuric acid up to a pH value of 3.7, filtering, washing and drying at 125 ° C. This dried sample was named Sample I. Were at the rehearsal the electrical tests carried out and compared with those of sample E in example 1; the results are given in Table II.

Table II

wash and dry at 125 ° C. All samples were air-cooled prior to measuring their electrical properties, which are given in Table III.

sample Dielectric
constant Loss factor Breakthrough
tension
kV / mm (V / mil) E.
I. 1.32
1.35 0.011
0.021 4.09 (104)
2.99 (76)

Example 3

5 sample T ⁰ C Tabel III Breakthrough
tension
kV / mm (V / mil) ¹⁰ y
K
L. 750
750
750 Dielectric
constant loss
factor 2.72 (69)
2.83 ^ (72)
3.11 (79) 1.28
1.32
1.32 0.006
0.008
0.020

Sample L in Table III is similar to Sample I in Table II. It can be seen that water has the electrical properties of the tempered kaolin is adversely affected, but its effect is also not almost as harmful as that of water plus

ao slurry chemicals, as can be seen from Table II results. .

Example4

A sample of kaolin having a smaller average particle size containing a naturally occurring small amount of montmorillonite (about 5%), wurde.auf an annealing temperature of 75O ⁰ C, similar to Sample E, heated and then divided into three fractions (samples M, N and O). The sample M was air cooled. Sample N was quenched in water, ^{dried at 125 °} C. and air-cooled, and sample O was air-cooled, acidified, filtered, washed and dried (like samples I and L) and air-cooled. The electrical tests were carried out on the samples. The results are given in Table IV.

40

45

From Table II it can be seen that the usual slurry of kaolin almost eliminates the loss factor doubled and makes the product unsuitable for high quality electrical insulator masses.

Table IV

sample Dielectric
constant Loss factor Breakthrough
tension
kV / mm (V / mil) M.
N
O 1.32
1.37
1.91 0.030
0.083
0.27 3.19 (81)
4.17 (106)
3.03 (77)

55

Another kaolin of similar composition as Sample A, but somewhat crude, was hitzegetempert at 750 ⁰ C and then divided into three fractions J, K, L, which were processed as follows:

Sample J was calcined at 75O ⁰ C and air cooled by cooling to room temperature.

Sample K was similar hitzegetempert and quenched with water (by inserting in tap water, which was free of added chemicals) and then at 125 ⁰ C dried.

Sample L was similarly heat annealed at 750 ° C, similarly quenched with water, and then with Sulfuric acid acidified to pH 3.7, filtered, ge-From Table IV it can be seen that if a small Amount of montmorillonite is present in the kaolin (e.g. about 1 to 10%), the small amount of the montmorillonite the damaging effect of quenching with water intensified, so that it is expedient to use the To keep montmorillonite content as low as possible, preferably below about 10 percent by weight or even 5 percent by weight. Although the water caused more damage to the electrical properties than in the case of practically montmorillonite-free kaolin, in this case it is very harmful Effect of slurry chemicals seen.

From the above it can be seen that kaolin with unusually good electrical properties and with minimal abrasive action can be achieved by heating the kaolin to a tempering temperature of 700 to 800 ^° C. and then air-cooling the clay and avoiding contact with liquid water, especially with aqueous slurry solutions, can be produced.

The kaolin tempered according to the invention can be used as a filler for plastic insulator compounds in amounts of about 1.0 to about 10% or 30 to 40% and even 50% or even up to 80% or more based on the weight, depending on the requirements of the recipe, may be added.

Examples of such recipes are the following:

Example 5

A phenolic insulator potting resin was made by mixing the following ingredients:

Parts by weight phenol-formaldehyde molding resin from electronic 105

Irish quality

• Denatured alcohol 200

Annealed kaolin 195

; The mixture is ground and then heated is evaporated to the alcohol, and then molded at about 230 ⁰ C (450 ° F) under high pressure. The above composition gives insulation properties which are at least as good as those which contain conventional insulating fillers in place of the tempered kaolin.

Example 6

IO The mixture is milled and hot extruded at 16O ⁰ C (32O ⁰ F). The electrical insulation behavior is at least as good as that obtained with similar compounds that contain conventional insulating fillers.

Example 7

Flexible butyl wire insulation was made by mixing the following ingredients:

Parts by weight

Butyl resin, wire insulation grade 100

N-methyl-N-4-dinitrosoaniline 1

Stearic acid 1

Annealed kaolin 60

Soot 40

Zinc oxide 5

Anti-stick wax. "\ 5 -, / *

NjN'-Bis-1-ethyl-S-methylpentyl-p-phe-. ^ /

nylenediamine 1,2 '

Sulfur 2

Benzothiazyl disulfide 1

Zinc dibenzyl dithiocarbamate 1.5

Zinc dibutyl dithiocarbamate 1 '

The mixture is ground and extruded at 160 ° C (320 ⁰ F). The electrical behavior of this mixture is the same as that of the usual electrical insulating masses.

Flexible vinyl insulation was made by mixing the following ingredients:

Parts by weight of polyvinyl chloride resin of electrical

Quality 60

_; Dioctyl phthalate plasticizer 40

Complex of basic lead silicate and

Silica gel, ....., ...., ... 5

Annealed kaolin 10

Claims (2)

Patent claims: 1. Electrical insulating compound made of a plastic compound and a filler containing kaolin, characterized in that the kaolin is ^{tempered at 700 to 800 0} C, then air-cooled and processed without slurry chemicals. 2. Electrical insulating compound according to claim 1, characterized in that the kaolin is less contains than 10% montmorillonite.