DE3013160C2 - Electrode plate electret of an electroacoustic transducer and method for its manufacture - Google Patents

Description

The invention relates to an electret according to the

The preamble of claim 1 and a method for its production. In particular, it is a Electrode plate with a polarized, high molecular film. The electret is used in an electroacoustic transducer due to the change the electrostatic capacity converts an electrical signal into an acoustic signal or vice versa.

An electrostatic speaker is known in which an electrode plate electret is connected to an electret on one side of the electrode plate of a membrane is arranged opposite, and in which the membrane is caused to vibrate by an electrical signal, so that the electrical signal is converted into an acoustic signal Convert signal. Furthermore, an electrostatic microphone is known in which an electrode plate Electret is arranged opposite a membrane and in which the membrane is made to vibrate by an acoustic signal and the acoustic signal by changing the electrostatic capacitance between the electrode plate electret and the Membrane is converted into an electrical signal. There are the following methods of making the Electrode plate electrets have been made for such electrostatic types of electroacoustic transducers. So was z. B. a polarized, high molecular weight film, commonly referred to as electret film, by means of an adhesive on the Electrode plate glued. However, this method has the disadvantage that the adhesive has the properties of the Electret film and thus the properties of the electret and thus the degree of conversion or gain of the converter is reduced. In addition, it is difficult to apply the electret film evenly to the whole Glue the surface of the electrode plate so that

there is a risk that the electret film will be mechanically pulled, as a result of which the electrification is hindered and the service life is reduced. The known method has the further disadvantage that the gluing of the electret film with the electrode plate is cumbersome and so the series production is impaired and no consistent quality can be guaranteed.

A method is also known in which the high molecular weight film is welded onto the electrode plate is, by fusing the film at a temperature; ia the melting point of the film and Conversion of the electret film on the electrode plate into an electret. This method has the disadvantage that the strength of the high molecular weight film when heated and fusion welded to the film Electrode plate becomes non-uniform, so that the electret film is physically unstable and thus only one has a short service life. In addition, the method has the disadvantage that the laminated bodies up to Near the melting point of the high molecular film must be heated, and that this method is a has too low productivity

The invention is therefore based on the object of providing an electrode plate electret, that can be produced easily and simply, is suitable for series production and that is physically stable and has a long service life

The object of the invention is also to provide a method for producing such an electret an electret film which does not have to be adhered to the electrode plate by means of an adhesive and wherein the electret film has a uniform thickness. The electrode plate electret should also be included the electret film of uniform thickness and long life and properties be able to be produced in series production. In addition, the electrode plate electrets should be without high-temperature treatment be producible in an economical process.

According to the invention, this object is achieved by the features of claims 1 and 3, respectively

In the electrode plate electret of the present invention, there is a high molecular film interlayer arranged between a polarized high molecular film and the electrode plate. The high molecular one Intermediate film layer has a lower melting point and strength than that polarized high molecular film. In the electrode plate electret of the present invention, there is a a suitable number of holes 80 are arranged to correspond to the holes or through-bores 34 and 56 in FIGS. 1 and 2 correspond.

This electrode plate electret is made as follows:

The polarizable high molecular weight film is welded to the electrode plate, i. H. with the intermediary high molecular weight film interlayer. The polarizable high molecular film is after Fusion welded to the electrode polarized. The high molecular film interlayer has a lower melting point than the polarizable high molecular one Film on, so the temperature for the fusion welding is maintained so that it is close the melting point of the intermediate film layer. Because the fusion weld at a relatively low Temperature is carried out, it is also easily carried out. The strength of the polymerizable high molecular weight The film is not changed during fusion welding and therefore remains uniform. Because of From these facts, the electrode plate electret of the present invention is physically stable, electrically excellent and has a long service life.

Preferably, the thickness of the high molecular film interlayer is less than that of the polymerizable high molecular weight film. The fusion welding, the heating and compressive stress of the Laminated bodies are performed at the same time.

ίο The polymerizable high molecular film can also be fusion-welded to the electrode plate via the high molecular film interlayer after the high molecular film has been polarized. In this case, too, there is no risk of the layer thickness of the polarized film changing, since the temperature for the fusion welding is below the melting point of the polarized high molecular weight film. The reduction in polarization is negligible. Since the temperature and time for fusion-welding the polarized high molecular film with the electrode plate via the high molecular film interposer. in substantially the temperature and time Fuei ^d: 6 hardening or aging corresponds to the polarized film, the Gesamtherstellzeit can be reduced by that one carries out the hardening simultaneously with the fusion welding.

The invention is explained in more detail with reference to the following drawings

Fig. 1 shows a cross section through an example of an electroacoustic! Converter for use in an electrostatic headphone,

Fig. 2 shows a cross section through an example of an electrostatic microphone,

3 shows a cross section through an example of an electrode plate electret according to the invention, FIG. 4 shows a cross section of a heating device

with a plurality of electret laminated bodies which are layered on top of one another and at the same time the Are exposed to fusion welding processes,

Fig. 5 shows a schematic of an apparatus for the continuous formation of an electret laminate and the continuous implementation of fusion welding,

Fig. 6 shows a scheme for a polarization method, as used in the present invention.

For a better understanding of the invention, an example of an electroacoustic transducer is first presented below

as explained using an electrode plate electret.

F i g. 1 shows a. Example of such an electroacoustic transducer for use in headphones. A cylindrical housing 11 has inwardly directed one-piece flanges 12 and 13 at both open ends. The electrode plate electrets 14 and 15 are arranged on the inside on the flanges 12 and 13 near the two openings of the housing 11. In the space between the electrode plate electrets 14 and 15, a membrane 16 with annular spacers 17 and 18 made of insulating material is arranged. The membrane 16 is made by applying conductive layers 21 and 22 on both sides of a polyester resin film or a similar high molecular weight film 19, e.g. B. 3 to 6 'in thick by vapor deposition of aluminum or a similar metal. The metal rings 23 and 24 are between the conductive layers 21

and 22 and the spacers 17 and 18 are arranged. The electrode plate electrets 14 and 15 are made of electrical conductors; H. Elcktrodenpl ,, itten 25 and 26 and electret films 27 and 28 bonded to the electrode plates. These electrode plate electrets are in contact with the flanges 12 and 13 of the housing 11 via the electrode plates 25 and 26, respectively.

The electrode plate electrets 14 and 15 of the present invention contain high molecular weight films 31 and 32, respectively. which are arranged between the electret films 27 and 28 and the electrode plates 25 and 26, respectively. By the electrode plate electrets 14 and 15 are passed through sound radiation holes 33 and 34, respectively. A An electrical signal from a signal source 35 is sent to the primary side of a transformer 36 brought up, the secondary side at both ends electrically with the electrode plates 25 and 26 and the Center tap is electrically connected to the metal rings 21 and 22. With this arrangement, the Membrane Ib in a Stoö-Zug-Weis «: in motion set, based on the electrical signal from the signal source 35. One of the conductive layers 21 or 22 of the membrane 16 can optionally also be omitted will.

Fig. 2 shows an example of an electrostatic microphone in which a microphone unit 42 and a Impedance converter unit 43 in a cylindrical housing 41 in the axial direction of the housing are arranged. A cylindrical capsule 44 is accommodated in the microphone unit 42, the Microphone unit 42 is in contact with the inner surface of the housing 41. The front panel 45 of the capsule 44 is equipped with a sound guide hole 46 which is covered with a dust cloth 47. On the On the inside of the front plate 45, a membrane 48 is attached close to the plate 45 but with a spacing d.iizu. The membrane 48 has been made by vacuum evaporation of a metal on one side a high molecular film 49 so as to form a conductive layer 51. On the membrane 48 is a Metal ring 52 glued to the side on which the conductive layer 51 is located; the Melallring 52 is up in contact with the inner surface of the front plate 45 of the capsule 44. In the vicinity of the membrane 48 is a Electrode plate electret 54 with an annular spacer 53 interposed therebetween. The electrode plate electret 54 is held by an electrode holder 55. The electrode holder 55 consists of a cylindrical part, closed at the bottom, made of a synthetic hani, which is attached to his The electrode plate electret 54 carries through the open end to form a rear space Electrode plate electret 54 therethrough is an air hole

56 arranged.

The electrode plate electret 54 includes an electrode plate 57 and one applied thereon Electret film 58 and one between the electrode plate

57 and the electret film 58 disposed high molecular film interlayer 59. In the impedance converting unit 43, a tube 61 is arranged below the capsule 44, the tube being essentially in contact stands with the inner peripheral surface of the housing 41, and on the rear side of the tube 61 is a printed circuit board 62 arranged so that the rear open end is closed. The two end parts of the housing 41 are with the front of the front panel 45 of the capsule 44 and the back of the printed circuit board 62, whereby the microphone unit 42 and the impedance converter unit 43 are mechanically interconnected. An impedance converter 63 is mounted on the printed circuit board 62 arranged in the tube 61. The impedance converter 63 is connected to the electrode plate 57 of the electrode plate electrical circuit 54 connected via the bottom plate of the electrode holder 55. If there is an acoustic signal in the Microphone enters via the front through the .Schallführungloch 46, the membrane 48 is in

ίο offset oscillation and thus changes the electrostatic Capacitance between membrane 48 and electrode plate electret 54; that way it becomes obtained electrical signal output from the impedance converter 63 with low impedance.

The invention relates to electrode plate electrets 14, 15 and 54 for use in electroacoustic Converters as shown in FIGS. The electrode plate electret according to the invention is shown in FIG Fig. 3 marked with the numeral 74. It contains a high molecular weight Finn 74, the polariser uai is üiiu the one on a ladder, d. H. on an electrode plate 71 with a high molecular film interlayer 72 is arranged.

The polarizable high molecular film 73 is made

z. B. from a 4-ethylene fluoride-6-pΓopylenfluoridcopolymerisat or perfluoroethylene propylene (FEP). Polycarbonate (PC), polyethylene (PE), polyvinylidene fluoride (PVF ₂ ) or polypropylene (PP). These high molecular films have a fusion welding temperature

jo in the range of 282-371 ° C. 204-22I ⁰ C. 121 -2O4 ° C. 204-218 ⁰ C or 140-204 ° C. When the electrode plate electret according to the invention is used in a headphone, the polarizable high molecular film 73 consists e.g. B. from a film with a diameter of 50-60 mm and a thickness of 75-125μπι. If desired, the adhesive strength of the film can be improved by conventional treatment methods, e.g. By treating one side of the film with a sodium naphthalene solution to roughen the film surface, or aluminum, nickel or a similar metal can be deposited on one side of the film by vacuum evaporation.

The interlayer high molecular weight film 72 is similarly formed and generally comprises one Diameter of 50-60 mm and a thickness of 10-30μΐη. The intermediate film layer is between of the electrode plate 71 and the polarizable high molecular film 73 in this case are the electrode plate 73, the interlayer high molecular film 72 and the polarizable high molecular Film 73 stacked in this order to form a laminated body 74, wherein the pretreated side of the film 73 adheres to the film 72. Then, the laminated body 74 is atmospheric Temperature in the fusion welding area of the high molecular film interlayer 72 heated and thereby the polarized high molecular film 73 with the electrode plate 71 via the high molecular film interlayer 72 connected.

A thermostat as shown in FIG. 4 can be used for the fusion treatment, in which a release agent 77, e.g. B. made of a polytetrafluoroethylene film (PTFE) between the support surface 76 and the electrode plate 71 of the high molecular film interlayer 72 and the polarizable high molecular film 73 in this arrangement on the release agent 77 is arranged and thus forms the laminated body 74. The release agent 77 has a heat resistance

above J (K) C and is therefore not mild Laminated body 74 welded.

My multitude of such laminates 74 (see Fig. 4) is heat-treated at the same time, the desired number of laminates 74 being arranged one above the other is iind the laminated body in each case by interposed Release films are separated from one another. On top of the stack the laminate is placed on top Trers. -Nittclfilm a weight of / .. B. approx. 2 kg applied.

The temperature in the thermostat 75 is approximately in the range of the .Schmclzsehwctstemperatiir of the used high molecular weight film interchangeability 72. If z. B. a poly carbonate film is used as the high molecular film intermediate layer 72, the temperature in the thermostat 75 to about 210-250 "C. for the case of the Use a polyethylene film to about 150 "C and in the case of using a polyvinylidene fluoride film set to about 220 ° C. and, in the case of a polypropylene film, to about 200 "C. The TherrT! Os! 2! 75 becomes at the set temperature held for about an hour and then allowed to cool the thermostat.

However, the melt treatment can also be carried out as in FIG. 5 can be performed. Here is a Aluminum plate or an electrode plate made of a similar metal 71 with a thickness of about 0.6 to Delivered 1 mm in the direction of arrow 79, the high molecular film intermediate layer 72 is from a supply reel 81 is pulled off and placed on the electrode plate 72 via guide rollers 82. At the same time, the for The high molecular weight film 73 provided for the polarization is pulled off from the feed spindle 83 and over the Guide rollers 84 placed on the high molecular weight film intermediate layer 72. The polarizable high molecular weight Film 73 is 75-125 μm thick, with the side of the Film that is in contact with the high molecular weight film interlayer 72 by treatment with a Sodium naphthalene solution can be roughened or coated with aluminum, nickel or a similar metal can be vacuum-deposited. The high molecular film intermediate layer 72 is about 20-30 μm thick. Of the Laminated body 74 composed of the electrode plate 71, the high molecular film interlayer 72 and the polarizable high molecular film 73 is in a heater 86 via guide rollers 85 with a predetermined feed speed introduced. The temperature in the heater 86 is at a predetermined temperature in the fusion welding area of the high molecular film interlayer 72 is set. In the heating device 86, not shown heat rollers are provided, which a predetermined Apply pressure to the laminate 74. The laminated body 74 is heated by the heater 86 passed through and heated and pressurized for a predetermined period of time. To this Way, the polarizable high molecular film 73 with the electrode plate 71 over the high molecular Intermediate film layer 72 bonded

Of the laminated body 74 composed of the polarizable high molecular film 73, the high molecular film interlayer 72 and the electrode plate 71 thus assembled by fusion welding then, the high molecular film 73 is polarized.

Before the polarization process, holes 80 (see FIG. 6), which correspond to holes 34 and 56 in the Devices according to FIGS. 1 and 2 correspond to the laminate 74 via conventional means, e.g. Legs Press incorporated. In the continuous process for producing the laminated body 74. as in FIG. 5 shown, the laminated body 74 can also be perforated at the same time in the form in which the Klektrodcnplattcn-F. finally leaks in the electro acoustic transducer is used.

F i g. b shows an example of the polarization process, the laminated body 74 being arranged on a base (not shown) after the fusion welding. The plus pole 87 of the power source is connected to the electrode plate 71, which is the bottom layer of the laminated body 74, and the needle electrode 88, which is connected to the minus side or the minus pole of the power source 87, is perpendicular and above the high molecular weight film 73. which forms the top layer of the laminated body 74, the distance from the center of the film 73 being approximately 50 mm. Then a direct voltage of about 25 kV is applied to the electrode plate 71 and the ,., 4 "!" I "i ....", 4., Au r ..- "ι ..,., In

to generate a corona discharge on the surface of the high molecular film 73. After The laminate 74 becomes polarized at a temperature of about 150 ° C. for about 1 hour j, exposed to the aging process in order to complete the process for producing the electrets according to the invention.

The invention is illustrated in more detail by the following example.

"' Example

A high molecular weight film for polarization is made from 4-ethylene fluoride-6-propylene fluoride copolymer with a melting point of 260-280 ° C and one

r. Thickness of 125 μπι used, with one side of the The film is slightly roughened by treatment with a sodium naphthalene solution. The high molecular film 73 is melted with a 1 mm thick aluminum electrode plate 71 at a temperature of 240 ° C.

4 (i welds, with as a high molecular film intermediate layer 72 a 20 μm thick polycarbonate film with a melting point of 220-230 ° C. is used. To of fusion welding, the high molecular film 73 is polarized at -25 kV using a 5 needle electrode and a corona discharge, as described above in connection with FIG. 6 is described. The film is then aged for about 1 hour at 150 ° C. As a result, the initial surface potential was about -850 V. The sample thus obtained was

-, ο subjected to an accelerated temperature test at 90 ° C and measured the time until the size of the surface potential had decreased by 1 dB. the The time until the value had dropped to 89.1% of its initial value was 1920 hours.

For comparison, the same polarizable high molecular film as above was used with the same Electrode plate as above welded at 280 ° C, but without the use of the high molecular weight Intermediate layer, and then the film was made under the same conditions as above indicated, polarized and then aged. The surface potential as in the case of the sample according to the invention, this sample was -850 V; the time until the The amount of surface potential decreased by 1 dB in the temperature acceleration test 150 h. The time is thus considerably shorter than that of the sample according to the invention using a high molecular weight film interlayer.

Since the electrode plate electret of the present invention contains a high molecular film intermediate layer and this with the electrode plate at the fusion welding temperature the intermediate film layer can be welded and the welding melting temperature is relatively low, the welding of the Layers can be done easily. Because the melting point of the polymerizable high molecular film is higher than the fusion welding temperature, the polarizable, high-molecular film, which is attached to the Electrode plate is welded, a uniform Thick and is physically stable and has a long service life. Compared to that known method in which club fabrics are used, the fusion welding is characterized by an improved processability of the polarizable, high molecular film and guarantees a Uniform fusion welding of the film over the entire surface of the electrode plate. Furthermore can the electrode plate according to the invention

ΓΜ-, ι ... ".": Il_ "r. ; _. ο ■ r

Liitivii tit vwiitiiiiaii in jci ic! CTügcn.

In the method described above, the polarizable high molecular film is made with the electrode plate weld fused and then converted into an electret. But it is also possible to use the polarize high molecular film beforehand and then polarize the polarized film with the electrode plate and the the high molecular film interlayer applied to it to be welded together. In this case the Fusion welding is carried out at a temperature below the melting point of the high molecular film. The polarization of the high molecular weight film is hardly affected. As the conditions for fusion welding, e.g. The temperature and the treatment time are essentially the same as the aging conditions for the conversion of the polarized film into an electret, the aging for the polarization can be carried out simultaneously with the heating for the fusion welding, so that the overall production time is significantly reduced.

The polarization of the high molecular film can not only by corona discharge polarization can be achieved, but also by thermal polarization, electron beam polarization, etc. The However, corona discharge method is preferred because it has polarization in air at room temperature and made possible with simple devices. In the case of corona discharge polarization, a number of

"ι laminated bodies one after the other of the polarization treatment are exposed by passing the laminated bodies 74 with the holes 80 through them on a conveyor belt through the corona discharge space (see Fig. 6). In this case it becomes a conductive

, Conveyor belt is used, which is electrically grounded, and the electrode plate 71 is in contact with the conductive conveyor belt.

Preferably, the side of the electrode plate that with the high molecular film interlayer welded and

Ii is fused, roughened, (e.g. by sandblasting nuillgiuuc ov / uia uuu /. In uicstiii ι äii ιϋιΊΓί uiC roughness of the surface to improve the adhesion of the high molecular film intermediate layer with the electrode plate, and so the possibility of

'■■ Difficult to peel off the film. In the case where the polarizable, high molecular film is first welded to the electrode plate and then welded is polarized, the roughness of the rough surface of the electrode plate increases the effective area

κι for the polarization. This will make the potential lines scattered and the number of potential lines of the polarized high molecular film per unit area increased and the dispersion of potential lines per unit area is suppressed, thereby creating a plurality of potential lines

ϊ is obtained. This way the used increases Voltage per unit area becomes the equivalence, and the polarization becomes sufficient and in more uniform Form carried out and is stable.

For this purpose 2 sheets of drawings

Claims (10)

Patent claims: 1. Electrode plate electret for the electrostatic type of electroacoustic transducer, Containing an electrode plate with a polarized high molecular film, characterized in that it is a high molecular Intermediate film layer (31, 32) with a lower melting point than the polarized high molecular weight Film (27, 28) between the polarized high molecular film and the electrode plate (25, 26) and the intermediate film layer is fusion-welded to the polarized high molecular film and the electrode plate 2. electrode plate electret according to claim 1, characterized in that the surface of the Electrode plate is roughened for contact with the high molecular weight film interlayer. 3. A method for producing an electrode plate electret according to one of claims 1 or 2, in which a polarizable, high molecular weight film is applied to an eggshell pial and then is polarized, characterized in that a laminate is formed by between the polarizable high molecular film and the electrode plate has an interlayer high molecular film having a lower melting point than that of the polarizable high molecular film and then the laminated body on a Temperature close to the melting point of the high molecular film interlayer is heated to the polarized ^: 2n high molecular weight film with the Fusion weld the electrode plate over the high molecular film interlayer. 4. The method according to claim 3, characterized in that the process step of Fusion welding is carried out in such a way that a large number of the laminated bodies are layered on top of one another, wherein the layered bodies placed on top of one another are each provided with a separating agent or a separating layer, which has a higher melting point than the high molecular film interlayer and which from the electrode plate and the polarizing strip: n High molecular weight film can be easily peeled off, the laminated bodies are separated from each other into one Introduces thermostat and thereby exposing the laminate to pressure from above and the thermostat set to a temperature suitable for fusion welding. 5. The method according to claim 3, characterized in that the laminate is produced in such a way that that the electrode plate is supplied continuously, the high-molecular film intermediate layer is continuously applied to the electrode plate, whereby the interlayer high molecular weight film is unwound from a spool, the feed speed which corresponds to the electrode plate, and one continuously the polarizable high molecular weight Film picks up from a supply spool and delivers it at the same speed as the Electrode plate is supplied. 6. The method according to claim 5, characterized in that the laminate from the continuously fed electrode plate, the high molecular weight intermediate film layer and the polarizable high molecular film for a predetermined time by a heated oven leads and thus carries out the fusion welding. 7. The method according to any one of claims 3 to 6, characterized in that the surface of the high molecular film for contact with the slightly roughened the high molecular film interlayer. 8. The method according to any one of claims 3 to 6, characterized in that the high molecular weight Film intermediate layer a thickness of 10 to 30 μm ίο has. 9. A method for producing an electrode plate electret according to one of claims 1 or 2 with an electrode plate with a polarized high molecular film, characterized in that a laminated body is formed by interposing the polarized high molecular film and the electrode plate has a high molecular film interlayer with a lower melting point than that of the polarized high molecular film introduces and then the laminate on a Temperature close to the melting point of the high molecular film interlayer is heated to the polarized, high molecular film with the electrode plate over the high molecular intermediate film layer to be fusion welded. 10. The method according to claim 9, characterized in that the fusion welding dienr the aging of the polarization of the polaririer'.en, high molecular weight film.