DD141881A1 - METHOD AND DEVICE FOR POLARIZING POLYMERFORMKOERPERN - Google Patents

Abstract

The invention relates to a method and a device which in the polarization front. Polymer moldings of importance are the after this. inventive method polarized polymer molding found in electroacoustic transducers and in the detection of I-beam radiation effective / use 'According to the invention' Method bzvz. the device according to the invention makes it possible Polymer moldings with above-average piezoelectric and / or ■ to obtain pyroelectric coefficients «The described Device or the method described are by the use a high voltage resistant variable series capacitor characterized during the polarization with the. Polymer moldings is connected in series.

Description

Prof. Dr. Christian Ruscher

Tite l the invention

Method and device for polarizing polymer moldings

Field of application of the invention

The invention relates to a method and a device which allow optimum polarization of polymer moldings. Polymer moldings containing polar molecular groups in their primary structure, e.g. Polyvinylidene fluoride, polyvinyl fluoride, polyvinyl chloride, polyamide-11, -7 »-55 or polyesters, polyurethanes, polyureas, polyacrylonitrile, polycarbonates, are characterized by a polariization in the electric field by piezoelectric and / or pyroelectric properties and therefore find as electro-acoustic batches Transducers and Temperaturmeßelemente an ever wider application. They are e.g. used successfully in microphones, loudspeakers, ultrasonic transducers and in the detection of laser radiation.

Characteristic of the known technical solutions

The polarization of polymer moldings has been a.

large number of invention descriptions and publications. DE-OS 26 57 536, DE-OS 2, 38 220, DB-OS 27 42 977, DE-OS .27 43 016, R _e G, Kepler ₉ JU A ₄ Anderson's Ferroelectricity in polyvinylidene fluoride ₀ J _e Appl «Pbys · 49 (1978) 3, S ₀ 1232 | M ₆ H, Litt-, C, Hsu, 'P.-Baeu: Pyroelectricity and piezoelectricity in nylon 11 _e J ₅ , Apple? kys · i§ (1377) 6, -. S · 2208) "In the Polarization" of .Polymerformkörpern). does it matter _? Optimum polarization can be achieved with reasonable technical effort. In this context, it is important to allow strong electric fields (near the breakdown field strength) to act on the polymer moldings at elevated temperatures during the polarization process, without electric breakdown occurring. In the invention XMG en DE-OS 27 19 880 "and DE-OS 27 19 881 an apparatus and a process are described, with a pulse shape applied electrical-.see PEiD. Based on the combined-.Use a DC electric field sbeschreib" this method t> ACR the corresponding apparatus have the disadvantages _f that si © ( "ζ * B. consuming versor supply units sur generation of the voltage pulses." complicated polarization regime) have firstly a complicated technisehen structure and secondly generate only medium pyroelectric ^ "coefficients" In the device described in the invention DE-OS 27 19 881 for the polarization of polymer moldings in strong electrical Peldem wird.eine expensive device 'technology required to produce the Polarisierungsspann.-uiig three device systems are used ^ where z »B _6, the third device system from two high-voltage cuvettes and a complicated high-voltage resistant switchgear exists. In other methods (DE-OS 26 11 047 _? DB-AS 26 11 047) · it is in principle impossible to polarize with high field strengths without Dur chbrüchser appearance on 'and. in addition to a too low polarization, relatively large polarization times are disadvantageous * To the Kacliteile of bekaiinten

To overcome methods and devices, it is necessary to find a solution with which optimum polarization can be realized in short times using simple technical means.

Object of the invention

The invention has as its object to provide a method and an apparatus which allow an effective polarization of polymer moldings. Optimum polarization with high reliability and reproducibility should be ensured. The device according to the invention or the method according to the invention should be feasible with simple technical means.

Dar Legun g of the essence of the invention

- Task

According to the invention, the object is to develop a method and a device with which, using relatively large field strengths, an optimal polarization of the polymer moldings is achieved without electrical breakdowns occur. The inventive method should be characterized in that during the polarization process, the measurement of the polarization is possible and thus control and control of its sequence can be realized. The polymer moldings polarized by the method according to the invention or with the device according to the invention should have above-average piezoelectric and / or pyroelectric coefficients.

Features of the invention

According to the invention, the object is achieved by using a high-voltage-resistant series capacitor during polarization. The capacitance Cp of the series capacitor is chosen such that Cg "^. C .. (at least one power of ten), where Cj is the capacitance of the metallized metal on both sides.

Under this condition, at the beginning of the polarization, almost the entire polarization voltage U _13f whose initial value corresponds to a field strength of at least 4000 kVcm, is deposited on the polymer molding and effects an orientation of the polar molecular groups in the polymer molding in the direction of the applied electric field. In the course of the polarization takes place with optimal choice of the capacitance Co of the series capacitor, a redistribution of Polarisierungsspanmxng Up of the polymer molded body on ö.en .Rhehenkondensator instead, so that even with -extrem: large values for Up on the polymer molding no electrical breakdown can occur, The polarization is preferably "at temperatures " T ^, for the

2 χ

Tp> · ^»1 T (T - melting temperature of the corresponding polymer molding} applies performed, but U- ^ remains asserted until the polymer molded body 1 by means of Kühlung'8 on 'Zimmertemperatur- or at least 20 to 30 ⁰ C below The time for the polarization process is 10 to 300 s.

According to FIG. 1, the bilaterally metallised polymer mold body 1 is subjected to a stress. series capacitor 2 is connected in series and is polarized by a equalization regulator 3; β voltage Up powered «While metallization 4 with the hot pole. the metallization 5 is connected to the capacitor capacitor 2 ". For measuring the voltage I.sub.U dropping across the series capacitor 2, a high-impedance voltage measuring device 6 is used which, together with the series capacitor 2 .and the equalization regulator 3 one-sided on mass potential »

The polymer molding 1 is electrically insulated from the heating system 7 and the cooling 8 by a quartz or mica plate 9. For temperature measurement, a thermocouple 10 is arranged on the quartz plate 9.

Hachdem the polymer molding 1 with the help of the heating system 7 (radiant heating, high-frequency or resistance heating, heating by Temperierflüssigkeit) was brought to the, polarization temperature, one sets with the DC voltage regulator 3 'abruptly or linearly increasing the polarizing voltage Up to the system series capacitor - Polymer molding 1 on. As a result of the series connection of the polymer molded body 1 and the series capacitor 2, almost the entire voltage Up on the shaped polymer body 1 initially drops off, since in the initial state Cg 1 CL applies. Palls Up is sufficiently large (field strength at least 4OOO kVcm) and the PoIarisierungstemperatur Tp is chosen (above - ^ T) that a sufficiently large Dipolbeweglichkeit is ensured in the polymer molded body 1, orient the corresponding Dipolgruppen.in direction of the applied electric field. As a result of this dipole orientation in the polymer molding 1, the capacitance C-, depending on the polarization increase in the polymer molding 1 during the polarization sproz esses, increases sharply, and it applies in the course of polarization C ₂ - Cj, if C _{2 in} accordance with the expected capacity change in Polymer molding 1 was optimally chosen. That is, however, that the initially falling mainly on the polymer molded body 1 voltage Up passes in the course of polarization on the series capacitor 2 and on this vee iron the electrical load of the polymer molding 1 is greatly reduced. With the method according to the invention it is thus possible to run the polarization at field strengths which are at least twice as large as those in the previously known methods. For example, if the capacitance C- of the polymer molded body 1 has reached the capacitance C _{2 of} the series capacitor ₂ , then there is an equal distribution of the voltage Up, and the polymer shaped body 1 is only half of Up at. In order to ensure optimum matching between the capacitance C _{2 of} the series capacitor and the capacitance C of the polymer molding 1, it is advantageous to use a variable series capacitor

can be use "whose capacity Cp even during the polarizing ungsprο esses ζ to an optimal sequence of polarization set".

Due to the specificity of the method, it is possible to polarize even in the vicinity of T with above-average field strengths. Between the series capacitor 2 and the polymer molding 1, a cybernetic interaction takes place. The faster the polarization in the polymer · ». mold body 1 increases, the shorter is the time during which the entire voltage Up is applied to the polymer molding 1, when the polarization has reached its maximum value, the redistribution of the voltage to the series capacitor a is closed, and the polymer molding 1 is one Voltage at which no electrical breakdown can occur «It is therefore possible, even at temperatures Tp? in which so far certainly electric breakdowns occurred with application of relatively high voltages Up to polarize with large field strengths _? on the other hand, the series capacitor has a current-limiting effect if microscopic breakdowns should occur in the course of polarization on weak parts of the polymer molding body 1. For the case that breakdowns of this kind occur briefly, the series capacitor 2 catches the entire polarization voltage Up until the corresponding weak point is again fixed by annealing and thus prevents a macroscopic breakdown on the entire dom .: Bolymerformkör, p .ett? The "series capacitor" 2 has a different punctuation in connection with the voltage-sensitive line 6. From the voltage Uj / measured at the series capacitor 2, the polarization of the polymer molded article 1 can be determined with known capacitance C2 and voltage Up It is therefore possible to follow the polarization process and to control it in such a way that a predetermined polarization is achieved.

ren macroscopic short circuits that may occur in the polymer molding 1 due to material defects indicated by the fact that the polarization voltage Up in its entirety immediately applied to the series capacitor 2. The polarization process can then be interrupted immediately and continued with a new sample. In addition, a subsequent control of the polarized polymer moldings is not necessary since it is possible to deduce the piezoelectric and pyroelectricity of the polarized polymer molded body 1 directly from the indicated voltage value Ujt at the series capacitor 2. The measurement of Ujt is necessarily high impedance (at least in teraohm range) make to avoid discharge of the series capacitor 2 during the cooling process after polarization.

The erfindungßgemäße method and the device according to the invention have the advantage that it can be polarized with extremely large field strengths without breakdowns. The polarized polymer moldings 1 are distinguished by above-average values of the piezoelectric and / or pyroelectric coefficients. The method and the corresponding device can be realized with simple means »The polarization time is in the range of a few seconds to minutes. The method according to the invention or the device according to the invention are preferably effective in the polarization of polymer moldings 1 in the form of films or films which have polar molecular groups in their primary structure. Examples of such polymers include halogenated vinyl polymers, polyesters and polyamides, polyurethanes, polyureas and also polyacrylonitrile and polycarbonates.

Embodiment 1

Polarization of fluoropoly-y-mers:

A uniaxially oriented polyvinylidene fluoride film with a thickness of 0.01 mm, which is predominantly present in modification I, is coated on both sides by vapor deposition with aluminum.

2 tallisiert (1.0 cm circular area) and on a PoIa-

The series capacitor used in the polarization has a capacitance of 10 nFj, which is more than an order of magnitude greater than the capacitance of the x-treated polymer film. After switching on the 5 kV polarization chip, the voltage across the series capacitor rises to over 2.5 kV within one minute so that less than 2.5 kV are applied to the sample during the further tolarization test With a polarization time of five minutes, the sample is cooled to room temperature while maintaining the field, and the polyvinylidene fluoride-pilm has a piezoelectric coefficient of 8 "given the polarization process shown. 10 egs, eeiu and

    2

a pyroelectric coefficient of 8 nC / cai K, in the polarization of a biaxially oriented polyvinyl

Oxide fluoride pillows (metallized area 0.8 cm) of thickness 0 _sec. 006 mm, using the same series clamp, will have a polarization span of 2 _$ 5 kV at

Temperature of 130 C applied * Again, the polarization can be carried out without electrical breakdown γ / ground (piezoelectric! 'Coefficient 5 * 10 * "' cgs _o esu, pyroelectric

p shear coefficient 4 nC / cm'K) «,

The polarization of polyvinyl fluoride films of the thickness of 0 ^ 015 mm (metallized area Ί, cm) requires a series capacitor with a capacitance of 1 nF. The 3PoIarisierungstemperatur is 110 ⁰ C. Es'v / ill with a polarizing voltage of 6 kV worked As a result, polarization was carried out at this. Example a pyroelectric ^

2 coefficient of 2 nC / cm K,

Polarization of polyacrylonitrileϊ

In the polarization of polyacrylonitrile, highly oriented films (uiiiaxially oriented) are assumed to have the thickness of Oj01 mm (metallized area 1 ei.), Kapa

The capacity of the series capacitor in this case is 5, the polarization voltage 5 kV. The IPolarisierung is carried out at 120 C after the regime already described Runaway. The obtained pyroelectric coefficient is 4 nC / cm ² K.

Embodiment 3 Polarization of polyamides:

A uniaxial polyamide film based on polyamide-11 with a thickness of 0.010 mm is metallized on both sides with aluminum (metallized area 1 cm). The polarization temperature is 120 ⁰ C, and it is applied a polarizing voltage of 5 kV. The capacity of the series capacitor is 5 nF. The film is polarized for 5 minutes and then cooled in the electric field to room temperature.

The same polarization regime also polarized formic acid-preserved films (0.010 mm thick) based on polyamide-7 and polyamide-55 from a 2% solution. The films were stretched four times before polarization and then likewise metallized with aluminum (area 0.8 cm ² ).

2 The pyroelectric coefficients are 2 nC / cm K for polyamide-11 and 3 nC / cm K for polyamides-55 and -7.

Claims (2)

1 _β method for. Polarization of polymer moldings with high field strengths, characterized in that the PoIa 'risierraigs voltage corresponding to at least a field strength of 4000 kVcm, is applied to the series connection of polymer moldings with the capacitance C and high voltage resistant variable Reihenkonden capacitors Cp, wherein as initial state Co ^ C- and Cp is chosen in such a way that at the beginning of the polarization sproz esses almost the entire polarization voltage is applied to C,. in the course of the polarization, a redistribution of the polarization voltage from C to Cp occurs and after polarization at least half of the applied polarization voltage of C is redistributed to Cp » 2. The method according to item 1, characterized in that are used as the polymer molded body films based on polymers with polar Moleklilgruppen, preferably halogenated vinyl polymers, polyesters, polyamides, - polyurethanes, Polyharn- .. substances, Polyetcrylnitril and polycarbonates. 3e method according to item 1 and 2 _S characterized in that the voltage measured in parallel to the series capacitor is used to control the polarization * 4 "device for the polarization of polymer moldings by means of GleichspannungsqueHe, tempering and Meßeinrich-. tungj. characterized in that a hochspannungsfeeter variable series capacitor (2) with the double-metallized polymer molded body (1) is electrically connected by series connection » 5 · 'device - after point 4, -. characterized in that the measuring and control device is a high-resistance Spannuügsmesser (6) is used « To do this, 1 soap drawings