METHOD FOR VARIABLY ADJUSTING THE ELECTRICAL INSULATING PROPERTIES OF VARISTOR-CONTAINING MATERIALS

Abstract

The present invention relates to a process for the variable adjustment of the electrical insulation properties of varistor-containing composite materials with the aid of defined filler mixtures, to the use of such filler mixtures, and to composite materials having resistive and capacitive field-control properties comprising filler mixtures of this type.

Claims

1. Process for the variable adjustment of the electrical insulation properties of varistor-containing composite materials, characterised in that one or more mass unit(s) of a dielectric polymer material are provided and in each case a particulate microvaristor filler A and a further particulate filler B in a predefined total mass A+B are added to the mass units, where the particulate filler B either has a lower electrical conductivity than the particulate microvaristor filler A or where the particulate filler B is a semiconductive particulate material having a higher electrical conductivity than that of the particulate microvaristor filler A, and where a mass ratio A:B in the range from 1:99 to 99:1 is in each case set differently in different mass units of the polymer material in the total mass A+B.

2. Process according to claim 1, characterised in that the total mass A+B, expressed in % by weight, is identical in each of the mass units of the polymer material, in each case based on the total weight of a mass unit of the dielectric polymer material including the total mass A+B of the particulate fillers A and B.

3. Process according to claim 2, characterised in that the total mass A+B is in the range from 5 to 35% by weight, based on the total weight of a mass unit of the dielectric polymer material including the total mass A+B of the particulate fillers A and B.

4. Process according to claim 1, characterised in that each mass unit of the dielectric polymer material that comprises the particulate fillers A and B has an E/p characteristic line that lies spatially between an E/p characteristic line of a mass unit of the same polymer material which only comprises the particulate microvaristor filler A, and the E/p characteristic line of a mass unit of the same polymer material which only comprises the particulate filler B.

5. Process according to claim 1, characterised in that the dielectric polymer material comprises silicones, polyurethanes, polyethylenes, epoxides or phenolic resins or comprises EPDM.

6. Process according to claim 1, characterised in that the particulate microvaristor filler A is a filler which consists of support particles and a coating surrounding each of the support particles, where the support particles comprise or in each case consist of at least one aluminium compound or silicon compound, and where the coating comprises a titanium dioxide doped with niobium and at least one further element.

7. Process according to claim 6, characterised in that the support particles comprise or in each case consist of aluminium oxide, silicon dioxide or an aluminosilicate.

8. Process according to claim 6, characterised in that the support particles consist of aluminium oxide, silicon dioxide, mullite, fly ash, kaolinite, pumice stone or perlite.

9. Process according to claim 6, characterised in that the titanium dioxide is doped, besides niobium, with at least one further element selected from the group consisting of Mn, Cr, Ce, V, Co, Fe, Zn, Sn, Y, Zr, Ta, Ca, Sr and Ba.

10. Process according to claim 9, characterised in that the titanium dioxide is doped, besides niobium, with at least one further element selected from the group consisting of Mn, Cr and Ce.

11. Process according to claim 1, characterised in that the particulate microvaristor filler A has an average particle size in the range from 1 to 150 m.

12. Process according to claim 1, characterised in that the particulate filler B is a semiconductive particulate material which has a higher electrical conductivity than the particulate microvaristor filler A and has a specific powder resistance in the range from 10.sup.8 to 10.sup.12 ohm*cm.

13. Process according to claim 1, characterised in that the particulate filler B has a lower electrical conductivity than the particulate microvaristor filler A and has a specific powder resistance in the range 10.sup.14 ohm*cm.

14. A method for the variable adjustment of the electrical insulation properties of varistor-containing composite materials, characterised in that the filler mixture consists of a predefined total mass A+B comprising a particulate microvaristor filler A and a further particulate filler B, where the particulate filler B either has a lower electrical conductivity than the particulate microvaristor filler A or where the particulate filler B is a semiconductive particulate material having a higher electrical conductivity than the particulate microvaristor filler A, and where a mass ratio A:B in the range from 1:99 to 99:1 exists in the total mass A+B, the method comprising adding the filler mixture to one or more mass units of a dielectric polymer material and the mass ratio A:B is set identically or differently from one another in each of the mass units.

15. The method according to claim 14, characterised in that the particulate microvaristor filler A is a filler which consists of support particles and a coating surrounding each of the support particles, where the support particles comprise or in each case consist of at least one aluminium compound or silicon compound, and where the coating comprises a titanium dioxide doped with niobium and at least one further element.

16. The method according to claim 14, characterised in that the particulate filler B is a semiconductive particulate material which has a higher electrical conductivity than the particulate microvaristor filler A and has a specific powder resistance in the range from 10.sup.8 to 10.sup.12 ohm*cm.

17. The method according to claim 14, characterised in that the particulate filler B has a lower electrical conductivity than the particulate microvaristor filler A and has a specific powder resistance in the range 10.sup.14 ohm*cm.

18. Varistor-containing composite material having resistive and capacitive field-control properties, comprising mass units of a dielectric polymer material, and a particulate microvaristor filler A and a further particulate filler B in a predefined total mass A+B in each mass unit of the dielectric polymer material, where the particulate filler B has a lower electrical conductivity than the particulate microvaristor filler A or where the particulate filler B is a semiconductive particulate material having a higher conductivity than the particulate microvaristor filler A, and where the same mass ratio A:B exists in each of the mass units of the polymer material that comprise the particulate fillers A+B and the mass ratio A:B is in the range from 1:99 to 99:1.

19. Varistor-containing composite material according to claim 18, characterised in that the total mass A+B in each of the mass units is in the range from 5 to 35% by weight, based on the total weight of the mass unit of the dielectric polymer material including the total mass A+B of the particulate fillers A and B.

20. Varistor-containing composite material according to claim 18, characterised in that the dielectric polymer material comprises silicones, polyurethanes, polyethylenes, epoxides or phenolic resins or comprises EPDM.

Description

[0084] FIG. 1: shows the diagrammatic circuit of the measurement arrangement (1b, bottom) with voltage source (DC), integrated voltage measurement (U), pico-ammeter (A) and test specimen, and the cylindrical test specimen with the relevant dimensions (1a, top) for determination of the electrical measurement results for the establishment of an E/p characteristic line.

[0085] FIG. 2: shows the characteristic DC field strength-specific resistance characteristic line (E/p) of a filler in accordance with Examples 5-10 to 5-14 from WO 2021/105319 A1 in RTV-2 silicone with pigment mass concentrations of 15, 20, 25, 30 and 35% by weight. The ranges for the switching points are highlighted by hatching.

[0086] FIG. 3: shows the characteristic DC field strength-specific resistance characteristic line (E/ of a filler in accordance with Example 1 of the present invention in RTV-2 silicone with various ratios of the fillers A:B. The ranges for the switching points are highlighted by hatching.

[0087] FIG. 4: shows the characteristic DC field strength-specific resistance characteristic line (E/ of a filler in accordance with Example 2 of the present invention in RTV-2 silicone with various ratios of the fillers A:B.

[0088] The invention is intended to be described below with reference to examples, but is not intended to be restricted thereto.

EXAMPLES

[0089] Preparation of Particulate Fillers:

[0090] Preparation of a Particulate Microvaristor Filler A:

[0091] 100 g of spherical aluminosilicate particles (BET 0.50 m.sup.2/g density 2.45 g/cm.sup.3, particle size d.sub.5-d.sub.95=1.2 m-17 m) are suspended in about 2 l of deionised water. A solution of 599 g of titanium oxychloride (400 g/l), 0.38 g of niobium pentachloride and 0.24 g of potassium chromium sulfate dodecahydrate is added dropwise to the suspension at 75 C. with stirring in an acidic medium. The pH of 2 is kept constant by simultaneous regulated metered addition of sodium hydroxide solution. When the total amount of the solution has been added, the mixture is stirred at 75 C. for a further 15 min. The reaction mixture is subsequently called to room temperature with stirring and adjusted to a pH of 5. The pigment obtained is filtered off via a suction filter, washed with water, dried at 110 C. and calcined at 850 C. for 120 min., giving an ochre-coloured pigment powder. The pigment particles obtained have hollow aluminosilicate spheres (particle size <40 m) as support particles and a coating comprising niobium- and manganese-doped titanium dioxide adherently precipitated onto them.

[0092] Preparation of a Semiconductive Particulate Filler B Having Increased Electrical Conductivity Compared with the Microvaristor Filler A:

[0093] In a 5 l stirred reactor, 100 g of mica having a maximum particle size of <15 m are suspended in 2 l of deionised water. 590 g of a solution comprising 121 g of SnCl.sub.4 and 0.273 g of SbCl.sub.3 in hydrochloric acid are metered in at 75 C. with stirring over the course of 2 hours. The pH is kept constant at pH=1.6 by simultaneous metered addition of sodium hydroxide solution. When the addition is complete, a further 10.6 g of 40% by weight titanium oxychloride solution in hydrochloric acid are added at pH=2, and the mixture is stirred at 75 C. for a further half an hour. The pH is subsequently adjusted to 4 using sodium hydroxide solution, and the suspension is cooled to room temperature. The pigment is filtered off, washed with water until salt-free, dried and calcined at 750 C. for 30 minutes, giving 171 g of pigment as a white lustrous powder. The content of antimony in the tin oxide layer is 0.25 mol-%, based on the sum of Sn+Sb. The pigment has a specific powder resistance of about 10.sup.12 ohm*cm (measurement voltage 100 V).

Example 1

[0094] Production of Test Specimens with Room Temperature-Crosslinking Silicone as Polymer Component

[0095] In order to produce a test specimen having a pigment mass concentration of 25%, the particulate microvaristor filler A obtained as above is incorporated into a room temperature-crosslinking silicone resin. In addition, further test specimens, likewise having a total mass concentration of 25%, are produced which, besides the microvaristor filler A, comprise a further filler B which has a lower electrical conductivity than the microvaristor filler A (3M Ceramic Microspheres W-210 from 3M, particle size d.sub.10-d.sub.90 2-12 m). The percentage proportion of A is set to between 25 and 90% and the percentage proportion of B is set, conversely, to between 75 and 10%, in each case based on the total mass A+B.

[0096] The particulate fillers are roughly premixed in a can with the respective proportions of component 1 of a commercial room temperature-crosslinking silicone resin RTV-2 (manufacturer's material data: comp. 1:comp. 2=9:1, viscosity of the mixture 3500 mPa*s at 23 C., Shore A hardness 45) and homogenised in a vacuum SpeedMixer (Hauschild) for at least 2 minutes at a reduced pressure of 4 mbar and 1600 revolutions per minute. The respective amounts of component 2 of the same RTV2 silicone resin are subsequently added, the components are again roughly premixed and homogenised in the vacuum SpeedMixer for at least 1 minute at 4 mbar and 1600 revolutions per minute. The viscous mass is now poured rapidly, while observing the pot life, into a mould, which determines the geometrical dimensions of the test specimen. The silicone resin is cured in the mould at for at least 30 minutes. After the mould has cooled, the mould is opened and the test specimen is removed and stored under dust-free conditions. The layer thicknesses of the crosslinked test specimens are between 500 m and 600 m and are determined at various points for each of the test specimens (circular base area, diameter 60 mm) as the average of ten measurements using an eddy-current layer thickness measuring instrument (Fischer Dualscope FMP30 with FD10 sensor in accordance with DIN EN ISO 2360). [0097] (Note: The two components of commercial room temperature-crosslinking silicone resins RTV-2 are usually called A and B by the manufacturers. In order to avoid confusion with the particulate filler components according to the present invention, the silicone resin components are by contrast called component 1 and component 2 here).

[0098] The pigment mass concentration PMC is defined as follows (the volatile fractions are not included), but is indicated in percentage terms here:

[00001]$\mathrm{PMC}=\frac{m\left(\mathrm{filler}\right)}{m\left(\mathrm{filler}\right)+m\left(\mathrm{binder}\right)}$$M=\mathrm{mass}$

Example 2

[0099] Test specimens are produced as described in Example 1 from with room temperature-cross-linking silicone as polymer component, but which, besides the particulate microvaristor filler A, also comprise the semiconductive particulate filler B as indicated above in the preparation procedure. The pigment mass concentration is 25% in each case. The percentage proportion of A is set to between 25 and 75% and the percentage proportion of B is set, conversely, to between 75 and 25%, in each case based on the total mass A+B.

[0100] Measurement of the Test Specimens with Respect to their Electrical Properties:

[0101] The current/voltage characteristics of the varistor filler/polymer test specimens produced are measured using a Heinzinger 10 kV DC voltage source (PNChp 10000-20 ump) and a Kethley pico-ammeter (6514 system electrometer) on a ring electrode in accordance with DIN EN 61340-2-3.

[0102] The diagrammatic structure of the measurement apparatus and the test specimen dimensions to be observed are shown by FIG. 1.

[0103] In order to standardise the results, the electric field strength E and the current density J are calculated in accordance with formulae (2-4) with the sample and electrode dimensions given in FIG. 1:

E=V/h(2)

J=I/A(3)

A=(d.sub.1+g).sup.2*/4(4) [0104] V=voltage in volts (V) [0105] I=current strength in amperes (A) [0106] A=effective electrode area (m.sup.2) [0107] h=electrode separation (sample thickness): 0.5 mm [0108] d.sub.1-d.sub.4=electrode diameters (see FIG. 1) [0109] d.sub.1=diameter of central electrode: 25 mm [0110] g=separation of ring electrode from central electrode: 2.5 mm

[0111] The specific resistances p of the test specimens are given by the equation =E/J.

[0112] The measurements of the current are carried out using a step-shaped voltage ramp at room temperature and relative atmospheric humidity between 20% and 30%.

[0113] Corresponding diagrams of all E/p characteristic lines determined are shown in FIGS. 3 (Example 1) and 4 (Example 2).

[0114] For comparison, FIG. 2 shows the diagram of E/p characteristic lines of test specimens comprising silicone resins which only comprise a particulate microvaristor filler A in increasing pigment mass concentration (in accordance with Examples 5-10 to 5-14 from WO 2021/105319 A1).