DD233443A1 - METHOD FOR PRODUCING POLYMER CAPACITORS HAVING A HIGH LOAD STABILITY - Google Patents

Abstract

The invention relates to a process for the preparation of polymer capacitors with a high charge stability, which remains constant over long periods of time and only slightly decreases even at relatively high temperatures. The process according to the invention is based on the fact that polymer film provided on both sides with firmly adhering electrode layers is aftertreated at high temperatures in the range of 100 to 300 ° C. and high electrical voltages which produce field strengths in the range of 10% to 90% of the breakdown field strength of the polymer film, and is subsequently cooled to room temperature , Capacitors produced in this way can be used everywhere where stored charge quantities have to be preserved for a long time, eg. As for data storage or as measuring capacitors in circuits for charge measurement.

Description

Dr. Wolfgang Stark

Dr. Rudi Danz

Dr. Manfred Pinnow

Title of the invention

Process for the preparation of polymer capacitors with high charge stability

Field of application of the invention

The invention relates to a process for the preparation of polymer capacitors with high charge stability. Such capacitors may be used where stored amounts of charge must not undergo change over long periods of time, e.g. for data storage or as measuring capacitors in circuits for charge measurement.

Characteristic of the known technical solutions

For the production of capacitors, a number of dielectric materials are used. Polymer films have a particularly wide spread because of their technologically favorable machinability, but also because of their

high dielectric strength and very good insulation properties found.

Most commonly used are polypropylene films, e.g. DE-OS 2619260, DE-OS 4367511 and polystyrene films, e.g. DE-OS 2649070, 2343857, used. In addition, the use of a range of other polymers for capacitor production is known. Thus, e.g. in DE-AS 2634389 also called films based on polytetrafluoroethylene, polycarbonate and polyethylene terephthalate.

The majority of the polymers used for capacitor production has a high insulation resistance from nature.

The typical values of the best insulating polymers are eg polypropylene - 10 ¹⁷ to 10 ¹⁸ μcm

Polystyrene - 10 ¹⁸ Sicm

1 8

Polytetrafluoroethylene - 10 .iicm

1 pi

Polychlorotrifluoroethylene - 10-Clem (see C. Rint, Handbook for High Frequency and Electrical Engineering). Purely the normal use of capacitors, these isolation properties are far enough. The long-term storage of cargoes, however, sets narrow limits. For example, with a specific conductivity of 10 "(item), the charge time constant is only about 50 hours. Each time the initial charge has dropped to about 1/3.

Aim of the invention;

The object of the invention is to develop a technologically simple process, with which it is possible to produce polymer capacitors with high charge stability, which is maintained over long periods.

Explanation of the essence of the invention

The invention is based on the task of treating the existing of a polymer dielectric so that the discharge time constant is increased by at least two orders of magnitude and decreases only slightly at higher temperatures.

The essence of the invention is to provide on both sides with adherent electrode layers capacitor films based on the polymers polytetrafluoroethylene (PTPE), polychlorotriloethylene (PCTPE) or the copolymer of hexafluoropropylene and tetrafluoroethylene (PEP) at high temperatures by applying high electrical voltages, the field strengths, which is up to 10% below the breakdown field strength of the respective film, to be post-treated. Cool down to room temperature after switching off the voltage. In the following, the method will be explained in detail.

There are PTFE, PCTFE or FEP films whose two-sided capacitor electrodes were realized by vapor deposition of a thin metal layer used.

The upper and lower electrodes are connected to a voltage source. Uachdem the film was heated to a temperature in the range 100 ⁰ C to 300 ⁰ C, is applied for a period of several minutes to hours such a high voltage that the internal field strength in the film reaches values of 10 to 90% of the breakdown electric field strength , After that, the voltage is regulated to Hull and. The condenser is cooled to room temperature over a period of 10 seconds to 30 minutes.

In order to make the capacitors in use independent of the voltage polarity , it is favorable to apply the high voltage during the after-treatment in a positive and in a negative direction over a same period of time.

The method according to the invention can be applied both to the unassembled capacitor foil already provided with electrodes and to the finished capacitor

become. However, the application to the starting film offers the advantage that no problems arise with regard to the heat resistance of the materials used for the assembly of the capacitor (eg sheaths, connecting wires, contacts).

It has been found that by using the method according to the invention, the discharge time constant increases by at least two orders of magnitude. Capacitors produced in this way, which were stored well encapsulated, in fact showed no measurable charge loss after 3000 hours. A further advantage of the applied method, is that even at elevated operating temperatures of the capacitor shows a significantly improved charge stability · At 70 to 80 ° G over 500 hours stored capacitors showed only a charge loss of about 5 %.

Exemplary embodiments Example 1

The starting material used was PTFE film, 20 μm thick, on which nickel-chromium electrodes were vapor-deposited on both sides. According to the method of the invention, the PTPE-Polie is heated in an oven at 250 ⁰ C and exposed for 30 min to a voltage of 1000 V. Thereafter, the electrodes are short-circuited and the film is cooled within 10 min to room temperature. The capacitor film is then provided with lead wires and encapsulated.

Capacitors produced in this way were charged to a voltage of 50 V for test purposes and stored in a shielded manner. Over a period of 3000 hours, even at 70 ⁰ G no decrease in the capacitor voltage could be measured.

Example 2

ΡστΙΈ-Polie the thickness of 25, to, which has both sides vapor-deposited electrodes, is heated on a hot plate to 150 ⁰ C and over a period of 60 min a voltage of

1300 7 suspended. Thereafter, the electrodes are short-circuited and the film is cooled to room temperature within 10 minutes. So treated capacitors were charged to 50 7 and stored shielded. They showed in the 7erlauf of 2400 hours at 70 ⁰ C no measurable decrease in the condensate οrspannung.

Example 3

FEP-3 oil of 12.7 μm thick with electrodes vapor-deposited on both sides is exposed to a voltage of 500 7 at 200 ^° C. The duration is 10 min. Thereafter, the voltage is set to full and the polie is cooled to room temperature within 60 s.

The treated capacitors showed no measurable decrease in the capacitor voltage at a boot to 50 7 and shielded storage over a period of 2400 hours at 70 ⁰ C.

Claims (3)

invention claim 1. A process for the preparation of polymer capacitors with high Laaungsstabilität based on fluoropolymers, characterized in that a fluoropolymer Konaensatorfolie at temperatures in the range of 100 ⁰ C to 300 ⁰ C of an electrical high-voltage after-treatment, the field strengths in the range of 10 % to 90 % of the breakdown field strength in the film, the exposure time of the voltage being in the range of 1 minute to 2 hours, and after switching off the voltage, the capacitor film is cooled to room temperature within 10 seconds to 30 minutes. 2. Method naah Punct 1, characterized in that after half the voltage exposure time, the polarity of the voltage is changed. 3. The method according to item 1, characterized in that is used as the fluoropolymer polytetrafluoroethylene, polychlorotrifluoroethylene or a copolymer of! Tetrafluoroethylene and hexafluoropropylene.