Dielectric polyurethane film

Abstract

The present invention relates to a process for producing a dielectric polyurethane film, in which at least the following steps are performed continuously: I) a mixture comprising: a) a compound containing isocyanate groups and having a content of isocyanate groups of >10% by weight and 50% by weight, b) a compound containing isocyanate-reactive groups and having an OH number of 20 and 150, at least one solvent having a vapor pressure at 20 C. of >0.1 mbar and <200 mbar, at least one wetting additive, is produced, where the sum of the number-average functionalities of isocyanate groups and of isocyanate-reactive groups in the compounds a) and b) is 2.6 and 6, II) immediately after production thereof, the mixture is applied to a carrier in the form of a wet film, III) the wet film is cured to form the polyurethane film and IV) the polyurethane film is separated from the carrier. The invention further provides a dielectric polyurethane film obtainable by the process according to the invention, a process for producing an electromechanical transducer, and an electromechanical transducer obtainable by this process.

Claims

1. A process for producing a dielectric polyurethane film, in which at least the following steps are performed continuously: I) producing a mixture comprising a) a compound containing isocyanate groups and having a content of isocyanate groups of >10% by weight and 50% by weight, b) a compound containing isocyanate-reactive groups and having an OH number of 20 and 150, c) at least one solvent having a vapour pressure at 20 C. of >0.1 mbar and <200 mbar, d) at least one wetting additive, where the sum of the number-average functionalities of the isocyanate groups and of the isocyanate-reactive groups in the compounds a) and b) is 2.6 and 6, II) immediately after production of the mixture, applying the mixture to a carrier in the form of a wet film, III) curing the wet film to form the polyurethane film and IV) separating the polyurethane film from the carrier, wherein the wet film is cured in step III) by conducting the wet film through a first drying section having a temperature of 40 C. and 120 C., wherein the total residence time of the wet film in the drying section is 10 seconds and 60 minutes, wherein the dielectric polyurethane film has an electrical resistivity >1.5E12 ohm m determined according to ASTM D 257 and wherein the creep at 10% deformation after 30 min to DIN 53 441 is <30%.

2. The process according to claim 1, wherein the mixture is applied to the carrier in step II) by means of a die.

3. The process according to claim 2, wherein the distance of the die from the carrier is less than three times the thickness of the wet film.

4. The process according to claim 1, wherein a wet film having a thickness of 10 to 300 M is produced in step II).

5. The process according to claim 1, wherein the wet film after the first drying section is additionally conducted through a second drying section having a temperature of 60 C. and 130 C.

6. The process according to claim 5, wherein the wet film after the second drying section is additionally conducted through a third drying section having a temperature of 110 C. and 180 C.

7. The process according to claim 1, wherein the solvent has a vapour pressure at 20 C. of >0.2 mbar and <150 mbar.

8. The process according to claim 1, wherein the compound a) has a number-average functionality of isocyanate groups of 2.0 and 4.

9. The process according to claim 1, wherein the compound a) comprises an aliphatic polyisocyanate.

10. The process according to claim 1, wherein the compound b) has a number-average functionality of isocyanate-reactive groups of 2.0 and 4.

11. The process according to claim 1, wherein the compound b) comprises a diol.

12. The process according to claim 1, wherein the carrier comprises plastic or paper.

13. The process according to claim 1, wherein the tensile strength of the dielectric polyurethane film is >2 MPa to DIN 53 504.

14. The process according to claim 1, wherein the dielectric strength of the dielectric polyurethane film is >40 V/m to ASTM D 149-97a.

15. A dielectric polyurethane film obtained by the process according to claim 1.

16. A process for producing an electromechanical transducer comprising producing a dielectric polyurethane film by a process according to claim 1 in a first step, and disposing an electrode on each of the opposite sides of the dielectric polyurethane film in a second step.

17. An electromechanical transducer obtained by the process according to claim 16.

Description

(1) The FIGURE shows the schematic structure of the coating system used. In the FIGURE, the individual components have the following reference numerals: 1 reservoir vessel 2 metering device 3 vacuum degassing device 4 filter static mixer 6 coating device 7 air circulation dryer 8 carrier 9 cover layer

(2) Component b) was introduced into one of the two reservoir vessels 1 of the coating system. Component a) was introduced into the second reservoir vessel 1. Each of the two components were then conveyed by the metering devices 2 to the vacuum degassing device 3, and degassed. From here, they were then each passed through the filters 4 into the static mixer 5, in which the components were mixed. The liquid material obtained was then fed to the coating device 6.

(3) The coating device 6 in the present case was a slot die. With the aid of the coating device 6, the mixture was applied as a wet film to a carrier 8 and then cured in the air circulation dryer 7. This gave a dielectric polyurethane film, which was then provided with a cover layer 9 and wound up.

(4) The present invention further provides a dielectric polyurethane film obtainable by the process according to the invention

(5) The invention still further provides a layer structure comprising a carrier substrate, an inventive dielectric polyurethane film applied thereto, and optionally a cover layer applied to the side of the film remote from the carrier substrate.

(6) The layer structure may especially have one or more cover layers on the film in order to protect it from soil and environmental influences. For this purpose, it is possible to use polymer films or film composite systems, or else clearcoats.

(7) The cover layers used are preferably film materials analogous to the materials used in the carrier, and these may have a thickness of typically 5 to 200 m, preferably 8 to 125 m, more preferably 20 to 50 m.

(8) Preference is given to cover layers having a very smooth surface. A measure used here is the roughness, determined to DIN EN ISO 4288 Geometrical Product Specifications (GPS)Surface texture . . . , test condition: R3z front and reverse sides. Preferred roughnesses are in the region of less than or equal to 2 m, preferably less than or equal to 0.5 m.

(9) The cover layers used are preferably PE or PET films of thickness 20 to 60 m. More preferably, a polyethylene film having a thickness of 40 m is used.

(10) It is likewise possible that, in the case of a layer structure on the carrier, a further cover layer is applied as a protective layer.

(11) The invention likewise provides a process for producing an electromechanical transducer, in which, in a first step, a process according to the invention is used to produce a dielectric polyurethane film and, in a second step, one electrode is applied to each of the opposite sides of the dielectric polyurethane film.

(12) The electrodes can be applied, for example, by means of a printing process, for instance inkjet, flexographic printing, screen printing, or by means of a coating bar, die or roller, or else by means of metallization under reduced pressure. Typical materials are based on carbon or on metals, for instance silver, copper, aluminium, gold, nickel, zinc or other conductive metals and materials. The metal may be applied as a salt or as a solution, as a dispersion or emulsion, or else as a precursor.

(13) The invention further provides an electromechanical transducer obtainable by this process.

(14) In the electromechanical transducer, the dielectric polyurethane film may especially be disposed between the electrodes in such a way that the dielectric polyurethane film contacts at least one of the electrodes.

(15) In one embodiment of the present invention, the dielectric polyurethane film may also be disposed between the electrodes in such a way that the electrodes adjoin it on opposite side of the dielectric polyurethane film.

(16) For construction of an inventive transducer, the inventive dielectric polyurethane films, as described, for example, in WO 01/06575, can be coated on both sides with electrodes.

(17) It is likewise possible in the context of the present invention to produce the electrodes and the dielectric polyurethane film in separate steps and to join them together subsequently. Typical methods would, for example, be adhesive bonding or lamination.

(18) The transducer can advantageously be used in a wide variety of different configurations for production of sensors, actuators and/or generators.

(19) The present invention therefore further provides an electronic and/or electric device, especially a module, automatic device, instrument or component, comprising an inventive electromechanical transducer.

(20) The present invention further relates to the use of an inventive electromechanical transducer in an electronic and/or electric device, especially in an actuator, sensor or generator. Advantageously, the invention can be implemented in a multitude of very different applications in the electromechanical and electroacoustic sector, especially in the sectors of energy harvesting from mechanical vibrations, acoustics, ultrasound, medical diagnostics, acoustic microscopy, mechanical sensing, especially pressure, force and/or expansion sensing, robotics and/or communications technology. Typical examples thereof are pressure sensors, electroacoustic transducers, microphones, loudspeakers, vibration transducers, light deflectors, membranes, modulators for glass fibre optics, pyroelectric detectors, capacitors and control systems and intelligent floors, and also systems for conversion of water wave energy, especially sea wave energy, to electrical energy.

EXAMPLES

(21) The invention is illustrated in detail hereinafter by examples.

(22) Unless indicated otherwise, all percentages are based on weight.

(23) Unless stated otherwise, all analytical measurements were conducted at temperatures of 23 C. under standard conditions.

(24) Methods:

(25) Unless explicitly mentioned otherwise, NCO contents were determined by volumetric means to DIN EN ISO 11909.

(26) The viscosities reported were determined by means of rotary viscometry to DIN 53019 at 23 C. with a rotary viscometer from Anton Paar Germany GmbH, Germany, Helmuth-Hirth-Str. 6, 73760 Ostfildern.

(27) Measurements of film layer thicknesses were conducted with a mechanical gauge from Dr. Johannes Heidenhain GmbH, Germany, Dr.-Johannes-Heidenhain-Str. 5, 83301 Traunreut. The specimens were analysed at three different sites and the mean was used as a representative measurement.

(28) The tensile tests were executed by means of a tensile tester from Zwick, model number 1455, equipped with a load cell of overall measurement range 1 kN to DIN 53 504 with a pulling speed of 50 mm/min. The specimens used were S2 tensile specimens. Each measurement was executed on three specimens prepared in the same way, and the mean of the data obtained was used for assessment. Specifically for this purpose, as well as the tensile strength in [MPa] and the elongation at break in [%], the stress in [MPa] at 100% and 200% elongation was determined.

(29) The permanent extension was determined by means of a Zwicki tensile tester from Zwick/Roell, equipped with a load cell of overall measurement range 50 N, on an S2 specimen of the sample to be examined. This measurement involved extending the sample at a rate of 50 mm/min up to n*50%, on attainment of this deformation releasing the strain on the sample to force=0 N, and measuring the extension still present. Directly thereafter, the next measurement cycle starts with n=n+1; the value of n is increased until the sample breaks. Here, only the value for 50% deformation is measured.

(30) The determination of stress relaxation was likewise executed using the Zwick tensile tester, the instrumentation corresponds to the experiment for determination of permanent extension. The specimen used here was a sample strip of dimensions 6010 mm.sup.2, which was clamped with a clamp separation of 50 mm. After very rapid deformation to 55 mm, this deformation was kept constant for a period of 30 min and the force profile was determined over this time. The stress relaxation after 30 min is the percentage decline in stress, based on the starting value directly after deformation to 55 mm.

(31) The measurements of dielectric constant to ASTM D 150-98 were executed with a test setup from Novocontrol Technologies GmbH & Co. KG, Obererbacher Strae 9, 56414 Hundsangen, Germany (measurement bridge: Alpha-A Analyzer, measurement head: ZGS Active Sample Cell Test Interface) with a specimen diameter of 20 mm. A frequency range from 10.sup.7 Hz to 10.sup.2 Hz was examined. The measure used for the dielectric constant of the material examined was the real part of the dielectric constant at 10-0.01 Hz.

(32) Electrical resistivity was measured by means of a laboratory setup from Keithley Instruments (Keithley Instruments GmbH, Landsberger Strae 65, D-82110 Germering, Germany) model No.: 6517 A and 8009 to ASTM D 257, a method for determining the insulation resistance of materials.

(33) The determination of dielectric strength to ASTM D 149-97a was conducted with a hypotMAX high-voltage source from Associated Research Inc, 13860 W Laurel Drive, Lake Forest, Ill. 600045-4546, USA, and a sample holder constructed in-house. The sample holder contacts the polymer samples of homogeneous thickness with only low mechanical pretension, and prevents the user from coming into contact with the voltage. The non-pretensioned polymer film in this setup is subjected to static load with rising voltage until electrical breakdown through the film occurs. The measurement result is the voltage attained at breakdown, based on the thickness of the polymer film in [V/m]. 5 measurements are executed per film and the average is reported.

(34) Substances and Abbreviations Used:

(35) Desmodur N100 biuret based on hexamethylene diisocyanate, NCO content 2200.3% (to DIN EN ISO 11 909), viscosity at 23 C. 100002000 mPa.Math.s, Bayer MaterialScience AG, Leverkusen, DE Desmodur N3300 isocyanurate based on hexamethylene diisocyanate, NCO content 21.80.3% (to DIN EN ISO 11 909), viscosity at 23 C. 3000750 mPa.Math.s, Bayer MaterialScience AG, Leverkusen, DE Desmodur XP 2599 aliphatic prepolymer containing ether groups and based on hexamethylene 1,6-diisocyanate (HDI), isocyanate content 60.5% (DIN EN ISO 11 909), viscosity at 23 C. 2500500 mPa.Math.s, Bayer MaterialScience AG, Leverkusen, DE Desmodur N75 BA 75% Desmodur N100 and 25% butyl acetate; 16050 mPas, Bayer MaterialScience AG, Leverkusen, DE Desmodur N75 MPA 75% Desmodur N100 and 25% methoxypropyl acetate, 25075 mPas, Bayer MaterialScience AG, Leverkusen, DE Arcol PPG 2000 DMC-catalysed polypropylene oxide of mean molar mass Mn=2000; product from Bayer MaterialScience AG P200H/DS polyester polyol based on 1,6-hexanediol and phthalic anhydride, molar mass 2000 g/mol, Bayer MaterialScience AG, Leverkusen, DE Desmophen C2201 polycarbonate polyol based on 1,6-hexanediol, prepared by reaction with dimethyl carbonate, molar mass 2000 g/mol, Bayer MaterialScience AG, Leverkusen, DE Desmophen C 2200 linear aliphatic polycarbonate diol having terminal hydroxyl groups and a molecular weight of approx. 2000 g/mol, Bayer MaterialScience AG, Leverkusen, DE. Irganox 1076 octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, Ciba Specialty Chemicals Inc., Basle, CH Terathane 650 INVISTA GmbH, D-65795 Hatterheim, poly-THF of molar mass Mn=650 g/mol PolyTHF 1000 BASF AG poly-THF of molar mass Mn=1000 g/mol Ketjenblack EC 300 J product from Akzo Nobel AG Tib Kat 220 butyltin tris(2-ethylhexanoate), from Tib Chemicals AG, Mannheim Metacure T-12 dibutyltin dilaurate from Air Products and Chemicals, Inc. DBTDL dibutyltin dilaurate from E. Merck KGaA, Frankfurter Str. 250, D-64293 Darmstadt, Germany BYK 310 solution of a polyester-modified polydimethylsiloxane, Altana BYK 3441 solution of an acrylate copolymer, Altana. Desmophen C 1200 linear aliphatic polycarbonate polyester, Bayer MaterialScience AG, Leverkusen, DE. Butyl acetate and methoxypropyl acetate from Sigma-Aldrich. Hostaphan RN 2SLK: release film from Mitsubishi based on polyethylene terephthalate with silicone coating. A film of width 300 mm was used. Release paper polymethylpentene-coated release paper.

(36) For the coating experiments of the inventive examples, a Coatema coating system with 7 dryers in a continuous roll-to-roll process was used. Application system: slot die from TSE Troller, Switzerland. Unless mentioned otherwise, the distance from the die to the carrier was set to 100 m. A two-component low-pressure casting machine with two gear pumps (heated), stirred and heatable vessels, heatable hoses and filters was used. In addition, a static heatable mixer was used. A first drying section was operated at 80 C. (air feed 2 m/s), a second drying section at 100 C. (air feed 3 m/s), a third drying section at 110 C. (air feed 8 m/s), a fourth drying section at 130 C. (air feed 7, 5, 2, 2 m/s). The web speed of the carrier was regulated at 1 m/min; the air feed blown into the drying sections was dry air. The layer thickness of the finished dielectric polyurethane film was 100 m.

(37) The inventive examples were producible continuously for more than 8 hours without blockage of the application system or occurrence of coating defects.

Example 1

(38) 21.39 parts by weight of Desmodur N100 were reacted with a polyol mixture of 0.0024 part by weight of Tib Kat 220 and 100 parts by weight of P200H/DS. The isocyanate (Desmodur N100) was used at 40 C., the polyol blend (P200H/DS with TIB Kat 220) at 80 C. The hoses for the respective components were heated to 40 C. and 80 C. respectively. The static mixer was heated to 65 C.; the die was at 60 C. The ratio of NCO to OH groups was 1.07. It was poured onto the Hostaphan film.

Example 2

(39) 21.39 parts by weight of Desmodur N100 were reacted with a polyol mixture of 0.0024 part by weight of Tib Kat 220 and 100 parts by weight of Desmophen C2201. The isocyanate (Desmodur N100) was used at 40 C., the polyol blend (Desmophen C2201 with TIB Kat 220) at 80 C. The hoses for the respective components were heated to 40 C. and 80 C. respectively. The static mixer was heated to 65 C.; the die was at 60 C. The ratio of NCO to OH groups was 1.07. It was poured onto the Hostaphan film.

Example 3

(40) 151.50 parts by weight of Desmodur N75 MPA were reacted with a polyol mixture of 0.02 part by weight of Tib Kat 220 and 536.84 parts by weight of P200H/DS, 3.24 parts by weight of Byk 310 and 308.41 parts by weight of methoxypropyl acetate. The isocyanate (Desmodur N75 MPA) was used at 23 C., the polyol blend (P200H/DS with TIB Kat 220) at 23 C. The hoses, the static mixer and the nozzle were each at 23 C. The ratio of NCO to OH groups was 1.07. It was poured onto the paper.

Example 4

(41) 113.62 parts by weight of Desmodur N75 BA were reacted with a polyol mixture of 0.01 part by weight of Tib Kat 220 and 459.30 parts by weight of P200H/DS, 2.77 parts by weight of Byk 3441 and 158.31 parts by weight of butyl acetate. The isocyanate (Desmodur N75 BA) was used at 23 C., the polyol blend (P200H/DS with TIB Kat 220) at 23 C. The hoses, the static mixer and the nozzle were each at 23 C. The ratio of NCO to OH groups was 1.07. It was poured onto the paper.

Comparative Example A-3/4

(42) The procedure was as in Examples 3 and 4, except that BYK 310 and Byk 3441 respectively were omitted. It was not possible to produce a film on the roller coating system used since the polyurethane did not lead to any wetting.

Comparative Example A-3/4

Die Distance

(43) The procedure was as in Examples 3 and 4, except that the distance of the die was increased to 400 m. It was not possible to produce a film on the roller coating system used since the wetting was very irregular.

Comparative Example B-9

(44) The raw materials used were not degassed separately. 50.0 g of Desmophen C2201 and 0.05 g of Irganox 1076 were weighed into a polypropylene cup, mixed in a Speedmixer at 3000 revolutions per minute for a period of 1 minute and then preheated to 60 C. After the Irganox 1076 stabilizer had dissolved completely, 0.01 g of DBTDL was added and this mixture was homogenized once again at 3000 revolutions per minute for a period of 1 min. 10.79 g of Desmodur N 3300 were weighed into this homogeneous mixture and this mixture was again mixed in a Speedmixer at 3000 revolutions per minute for a duration of 1 minute.

(45) The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were cured at 100 C. in a drying cabinet for a duration of 1 h. After curing, the films were easily removable by hand from the glass pane.

(46) At 1 minute, the pot life of the mixture was too short to be able to use the mixture in a roll-to-roll process. Nor is the one-component mode of operation suitable, since the mixture solidifies in the application system after a few minutes prior to application in the roll-to-roll process, and so continuous coating is impossible. The drying time of one hour was also much too long. A glass pane is an inflexible carrier unsuitable as a release film in a roll-to-roll process.

(47) In addition, the dielectric constant was only 4.6 and the elongation at break only 175%.

Comparative Example B-10

(48) The raw materials used were not degassed separately. 50.0 g of Desmophen C2200 and 0.05 g of Irganox 1076 were weighed into a polypropylene cup, mixed in a Speedmixer at 3000 revolutions per minute for a period of 1 minute and then preheated to 60 C. After the Irganox 1076 stabilizer had dissolved completely, 0.15 g of Desmorapid SO was added and this mixture was homogenized once again at 3000 revolutions per minute for a period of 1 min. 11.48 g of Desmodur N 100 were weighed into this homogeneous mixture and this mixture was again mixed in a Speedmixer at 3000 revolutions per minute for a duration of 1 minute.

(49) The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were cured at 100 C. in a drying cabinet for a duration of 1 h. After curing, the films were easily removable by hand from the glass pane.

(50) At 1 minute, the pot life of the mixture was too short to be able to use the mixture in a roll-to-roll process. Nor is the one-component mode of operation suitable, since the mixture solidifies in the application system after a few minutes prior to application in the roll-to-roll process, and so continuous coating is impossible. The drying time of one hour was also much too long. A glass pane is an inflexible carrier unsuitable as a release film in a roll-to-roll process.

(51) TABLE-US-00001 Dielectric Volume resistivity strength Modulus of Example [ohm cm] [V/m] elasticity [MPa] 9 1.435E+14 69.4 2.22 10 9.10E+13 72.4 1.99

Comparative Example C-5

(52) The raw materials used were not degassed separately. 29.412 g of Desmodur XP 2599 and 50.0 g of Desmophen C 2200 were mixed with an amount of 0.045 g of Desmorapid SO and 0.05 g of Irganox 1076 in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 1 minute. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(53) At 1 minute, the pot life of the mixture was too short to be able to use the mixture in a roll-to-roll process. Nor is the one-component mode of operation suitable, since the mixture solidifies in the application system after a few minutes prior to application in the roll-to-roll process, and so continuous coating is impossible. A glass pane is an inflexible carrier unsuitable as a release film in a roll-to-roll process.

(54) Electrical resistivity is too low.

Comparative Example C-6

(55) The raw materials used were not degassed separately. 50.0 g of Desmophen C 1200 were mixed with 0.05 g of Irganox 1076, 9.188 g of Desmodur N100 and an amount of 0.013 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 1 minute. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(56) At 1 minute, the pot life of the mixture was too short to be able to use the mixture in a roll-to-roll process. Nor is the one-component mode of operation suitable, since the mixture solidifies in the application system after a few minutes prior to application in the roll-to-roll process, and so continuous coating is impossible. A glass pane is an inflexible carrier unsuitable as a release film in a roll-to-roll process.

(57) Elongation at break is too low at 125%; resistivity is likewise too low.

Comparative Example C-7

(58) The raw materials used were not degassed separately. 309.5 g of the prepolymer from Example 1 were preheated to 60 C., weighed together with 10.0 g of TMP, 0.2 g of DBTDL and 0.01 g of Irganox 1076 into a polypropylene cup and mixed in a Speedmixer at 3000 revolutions per minute for a duration of 1 minute.

(59) The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were cured at 100 C. in a drying cabinet for a duration of 1 h. After curing, the films were easily removable by hand from the glass pane.

(60) At 1 minute, the pot life of the mixture was too short to be able to use the mixture in a roll-to-roll process. Nor is the one-component mode of operation suitable, since the mixture solidifies in the application system after a few minutes prior to application in the roll-to-roll process, and so continuous coating is impossible. The drying time of one hour was also much too long. A glass pane is an inflexible carrier unsuitable as a release film in a roll-to-roll process.

(61) Electrical resistivity is too low.

Comparative Example 1a

(62) Produced according to DE 10 2007 005 960, Example 1.

(63) All liquid raw materials were carefully degassed under argon in a three-stage process; the carbon black was sieved through a 125 m sieve. 10 g of Terathane 650 (INVISTA GmbH, D-65795 Hatterheim, poly-THF of molar mass Mn=650) are weighed together with 0.596 g of carbon black (Ketjenblack EC 300 J, product from Akzo Nobel AG) into a 60 ml disposable mixing vessel (APM-Technika AG, Cat. No. 1033152) and mixed in a Speedmixer (product from APM-Technika AG, CH-9435 Heerbrugg; distributor in Germany: Hauschild; model: DAC 150 FVZ) at 3000 rpm for 3 min to give a homogeneous paste. Subsequently, 0.005 g of dibutyltin dilaurate (Metacure T-12, Air Products and Chemicals, Inc.) and 6.06 g of the isocyanate N3300 (the isocyanurate trimer of HDI; product from Bayer MaterialScience AG) are weighed into this and the mixture is mixed at 3000 rpm for 1 min in a Speedmixer. The reaction paste was poured onto a glass pane and drawn out with a coating bar of wet film thickness 500 m to give a homogeneous film of solids content 2%. The film was subsequently heat-treated at 80 C. for 16 h.

(64) The dielectric strength was determined to be 5 V/m and the resistivity to be 2.00E03 ohm m. Both values are below requirements.

Comparative Example 1b

(65) Produced according to DE 10 2007 005 960, Example 2.

(66) All liquid raw materials were carefully degassed under argon in a three-stage process; the carbon black was sieved through a 125 m sieve. 10 g of Arcol PPG 2000 (DMC-catalysed polypropylene oxide of mean molar mass Mn=2000; product from Bayer MaterialScience AG) are weighed together with 0.636 g of carbon black (Ketjenblack EC 300) into a 60 ml disposable mixing vessel and mixed in a Speedmixer at 3000 rpm for 3 min to give a homogeneous paste. Subsequently, 0.005 g of dibutyltin dilaurate and 7.13 g of the isocyanate Desmodur XP 2599 (allophanate prepolymer of the formula I where n=30 to 38, again using Arcol PPG 2000 as the polyalkylene oxide; product from Bayer MaterialScience AG) are weighed into this mixture and mixed in at 3000 rpm for 1 min in a Speedmixer. The reaction paste was poured onto a glass pane and drawn out with a coating bar of wet film thickness 500 m to give a homogeneous film of solids content 2%. The film was subsequently heat-treated at 80 C. for 16 h.

(67) The dielectric strength was determined to be 30 V/m and the resistivity to be 1.67E08 ohm m. Both values are below requirements.

Comparative Example 2

(68) Produced according to WO 2010049079, Example 1.

(69) 200 g of PolyTHF 2000 and 50 g of PolyTHF 1000 were heated to 80 C. in a standard stirring apparatus. Subsequently, at 80 C., a mixture of 66.72 g of isophorone diisocyanate and 520 g of methyl ethyl ketone was added, and the mixture was stirred at reflux (about 8 hours) until the theoretical NCO value had been attained. The finished prepolymer was cooled to 20 C. and then a solution of 25.2 g of methylenebis(4-aminocyclohexane) and 519.5 g of isopropanol was metered in within 30 min. Then stirring was continued until IR spectroscopy was no longer able to detect any free isocyanate groups.

(70) The resulting clear solution had the following properties:

(71) Solids content: 25%

(72) Viscosity (viscometer, 23 C.): 4600 mPas

(73) The solution used to produce a polymer layer in each case was not degassed separately. The required amount of 100 g of the solution was weighed into a polypropylene cup (PP cup). The reaction mixture, which was still liquid, was used to manually coat layers of wet film thickness 1 mm onto glass panes using a coating bar. After production, all layers were dried at 30 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the layers were easily removable by hand as films from the glass pane.

(74) Creep was determined to be 42.5%. This is well above the requirements of <10%.

(75) All other examples in WO 2010049079 according to the reported data for the films are outside the requirements, or the material is not a polyurethane.

Comparative Example 3a

(76) Produced according to EP 2280034, Comparative Example 1.

(77) The raw materials used were not degassed separately. 10 g of Desmodur XP 2599 were mixed with 28.1 g of a trifunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 6000 g/mol and a proportion of ethylene oxide units of 0% by weight and with 0.028 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(78) Creep was determined to be 13.5%, electrical resistivity to be 3.54E08 ohm m and dielectric strength to be 20.4 V/m. This is outside the requirements.

Comparative Example 3b

(79) Produced according to EP 2 280 034, Comparative Example 2.

(80) The raw materials used were not degassed separately. 10 g of Desmodur XP 2599 were mixed with 28.06 g of a difunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 4000 g/mol and a proportion of ethylene oxide units of 0% by weight and with 0.028 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(81) Creep was determined to be 13.9%, electrical resistivity to be 1.91E08 ohm m and dielectric strength to be 21.3 V/m. This is outside the requirements.

Comparative Example 3c

(82) Produced according to EP 2 280 034, Comparative Example 3.

(83) The raw materials used were not degassed separately. 3.91 g of Desmodur N3300 were mixed with 39.88 g of a difunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 4000 g/mol and a proportion of ethylene oxide units of 0% by weight and with 0.12 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(84) Creep was determined to be 30.3%, electrical resistivity to be 4.77E08 ohm m and dielectric strength to be 25 V/m. This is outside the requirements.

Comparative Example 3d

(85) Produced according to EP 2 280 034, Comparative Example 4.

(86) The raw materials used were not degassed separately. 3.58 g of Desmodur XP2410 were mixed with 39.88 g of a trifunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 6000 g/mol and a proportion of ethylene oxide units of 0% by weight and with 0.12 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(87) Electrical resistivity was determined to be 5.08E08 ohm m and dielectric strength to be 25.4 V/m. This is outside the requirements.

Comparative Example 3e

(88) Produced according to EP 2 280 034, Comparative Example 5.

(89) The raw materials used were not degassed separately. 3.91 g of Desmodur N3300 were mixed with 39.88 g of a trifunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 6000 g/mol and a proportion of ethylene oxide units of 0% by weight and with 0.12 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(90) Electrical resistivity was determined to be 1.50E09 ohm m and dielectric strength to be 33.4 V/m. This is outside the requirements.

Comparative Example 3f

(91) Produced according to EP 2 280 034, Example 1.

(92) The raw materials used were not degassed separately. 3.0 g of Desmodur N 3300 (isocyanurate based on HDI) and 7.0 g of the prepolymer from Example 1 were weighed into a polypropylene cup and mixed together in a Speedmixer at 3000 revolutions per minute for 1 minute. This mixture was then mixed with 41.2 g of a difunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 4000 g/mol and a proportion of ethylene oxide units of 0% by weight and with an amount of 0.041 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(93) Creep was determined to be 21.3%, electrical resistivity to be 1.74E09 ohm m and dielectric strength to be 24.6 V/m. This is outside the requirements.

Comparative Example 3g

(94) Produced according to EP 2 280 034, Example 2.

(95) The raw materials used were not degassed separately. 3.0 g of Desmodur N 3300 (isocyanurate based on HDI) and 7.0 g of the prepolymer from Example 1 were weighed into a polypropylene cup and mixed together in a Speedmixer at 3000 revolutions per minute for 1 minute. This mixture was then mixed with 41.2 g of a trifunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 6000 g/mol and a proportion of ethylene oxide units of 0% by weight and with an amount of 0.041 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(96) Creep was determined to be 24.4%, electrical resistivity to be 1.42E09 ohm m and dielectric strength to be 18.2 V/m. This is outside the requirements.

Comparative Example 3h

(97) Produced according to EP 2 280 034, Example 3.

(98) The raw materials used were not degassed separately. 4.0 g of Desmodur N 3300 (isocyanurate based on HDI) and 16.0 g of the prepolymer from Example 1 were weighed into a polypropylene cup and mixed together in a Speedmixer at 3000 revolutions per minute for 1 minute. This mixture was then mixed with 66.16 g of a difunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 4000 g/mol and a proportion of ethylene oxide units of 20% by weight, based on the polyether, and with an amount of 0.132 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(99) Electrical resistivity was determined to be 5.10E08 ohm m and dielectric strength to be 35.5 V/m. This is outside the requirements.

Comparative Example 3i

(100) Produced according to EP 2 280 034, Example 4.

(101) 1300 g of hexamethylene 1,6-diisocyanate (HDI), 1.3 g of benzoyl chloride and 1.3 g of methyl para-toluenesulphonate were initially charged in a 4 liter four-neck flask while stirring. Within 3 hours, at 80 C., 1456 g of a difunctional polypropylene glycol polyether having a number-average molecular weight of 2000 g/mol were added thereto and the mixture was stirred at the same temperature for a further 1 hour. Subsequently, by thin film distillation at 130 C. and 0.1 Torr, the excess HDI was distilled off; 1 g of chloropropionic acid was present in the receiver flask. The resulting NCO prepolymer had an NCO content of 3.23% and a viscosity of 1650 mPas (25 C.).

(102) The raw materials used were not degassed separately. 9.0 g of the above-described prepolymer were weighed together with 1.0 g of Desmodur N 3300 into a polypropylene cup and mixed together in a Speedmixer at 3000 revolutions per minute for 1 minute. This mixture was then mixed with 24.22 g of a difunctional polypropylene glycol-polyethylene glycol polyether having a number-average molecular weight of 4000 g/mol and a proportion of ethylene oxide units of 20% by weight, based on the polyether, and with an amount of 0.048 g of DBTDL in a polypropylene cup in a Speedmixer at 3000 revolutions per minute for a duration of 3 minutes. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 80 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(103) Creep was determined to be 19.9%, electrical resistivity to be 9.93E08 ohm m and dielectric strength to be 38.6 V/m. This is outside the requirements.

Comparative Example 4a

(104) Produced according to DE 10 2007 059858, Example 4.

(105) 82.5 g of PolyTHF 1000, 308 g of PolyTHF 2000 and 10.0 g of 2-ethylhexanol were heated to 70 C. Subsequently, at 70 C., a mixture of 41.4 g of hexamethylene diisocyanate and 54.7 g of isophorone diisocyanate was added within 5 min, and the mixture was stirred at 110-125 C. until the NCO value had gone below the theoretical value. The finished prepolymer was dissolved with 880 g of acetone at 50 C. and then a solution of 3.8 g of ethylenediamine, 4.6 g of isophoronediamine, 26.3 g of diaminosulphonate and 138 g of water was metered in within 10 min. The mixture was stirred for a further 15 min. Thereafter, dispersion was effected by addition of 364 g of water within 10 min. Subsequently, the solvent was removed by distillation under reduced pressure, and a storage-stable dispersion was obtained.

(106) Particle size (LKS): 181 nm

(107) Viscosity: 1300 mPas

(108) The required amount of 100 g of the dispersion was weighed into a PP cup. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 30 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(109) Creep was determined to be 48.3% and dielectric strength to be 21 V/m, which are thus outside the requirements made.

Comparative Example 4b

(110) Produced according to DE 10 2007 059858, Example 5.

(111) 450 g of PolyTHF 1000 and 2100 g of PolyTHF 2000 were heated to 70 C. Subsequently, at 70 C., a mixture of 225.8 g of hexamethylene diisocyanate and 298.4 g of isophorone diisocyanate was added within 5 min, and the mixture was stirred at 100-115 C. until the NCO value had gone below the theoretical value. The finished prepolymer was dissolved with 5460 g of acetone at 50 C. and then a solution of 29.5 g of ethylenediamine, 143.2 g of diaminosulphonate and 610 g of water was metered in within 10 min. The mixture was stirred for a further 15 min. Thereafter, dispersion was effected by addition of 1880 g of water within 10 min. Subsequently, the solvent was removed by distillation under reduced pressure, and a storage-stable dispersion was obtained.

(112) Solids content: 56%

(113) Particle size (LKS): 276 nm

(114) Viscosity: 1000 mPas

(115) The required amount of 100 g of the dispersion was weighed into a PP cup. The reaction mixture, which was still liquid, was used to manually coat films of wet film thickness 1 mm onto glass panes using a coating bar. After production, all films were dried at 30 C. in a drying cabinet overnight and then subjected to further heat treatment at 120 C. for 5 min. After the heat treatment, the films were easily removable by hand from the glass pane.

(116) Creep was determined to be 48.3% and dielectric strength to be 23 V/m, which are thus outside the requirements made.

Assessment of the Examples and Comparative Examples

(117) The electrical resistivity and dielectric strength of the films were determined. The results are shown for the Comparative Examples and Inventive Examples in Table 1 below.

(118) TABLE-US-00002 Tensile Elongation strength at break PE 50% Creep DC DS Rb Example # [MPa] [%] [%] [%] 0.01 Hz [V/m] [m] 1 7.2 268 0.75 4.8 6.7 110.6 2.82E+12 2 6.5 266 0.65 1.36 7.8 83.4 2.08E+12 3 8.9 305 0.06 7.97 5.9 82.5 2.07E+12 4 8.5 278 1.04 5.8 8.5 99.1 2.41E+12 Comp. Ex.: 1a nd nd nd nd <4 5 2.00E+03 Comp. Ex.: 1b nd nd nd nd 700 30 1.67E+08 Comp. Ex.: 2 33.5 540 6.26 42.5 21.5 61.3 4.52E+10 Comp. Ex.: 3a 0.327 107 0.32 13.5 25.4 20.4 3.54E+08 Comp. Ex.: 3b 0.178 125 0.45 13.9 16.6 21.3 1.91E+08 Comp. Ex.: 3c 0.28 262 1.71 30.3 8.6 25 4.77E+08 Comp. Ex.: 3d 0.63 85 0.65 10.5 28.9 25.4 5.08E+08 Comp. Ex.: 3e 0.7 110 0.24 6.2 10.8 33.4 1.50E+09 Comp. Ex.: 3f 0.143 364 1.84 21.3 8.7 24.6 1.74E+09 Comp. Ex.: 3g 0.392 251 1.76 20.4 11.6 18.2 1.42E+09 Comp. Ex.: 3h 0.927 211 1.29 4.7 2800 35.5 5.10E+08 Comp. Ex.: 3i 1.085 516 2.48 19.9 1796 38.6 9.93E+08 Comp. Ex.: 4a 33.5 650 4.98 48.3 21.5 21 4.90E+11 Comp. Ex.: 4b 42.8 640 4.98 48.3 657 23 5.00E+11

(119) It has been found that the inventive films give distinct advantages over those of the prior art. The inventive films were also produced on an industrial scale in a roll-to-roll coating process. The comparative examples are laboratory batches.

(120) A particular advantage of the inventive films is the combination of very high electrical resistivity and high dielectric strength. The inventive films can especially be used for production of electromechanical transducers with particularly good efficiencies.