WO2017162165A1

WO2017162165A1 - Loudspeaker membrane and method of making same

Info

Publication number: WO2017162165A1
Application number: PCT/CN2017/077654
Authority: WO
Inventors: Christian Lembacher; Gustav Otto; Peter Thurner; Hong-Bidong NGUYEN
Original assignee: Sound Solutions International Co., Ltd.
Priority date: 2016-03-22
Filing date: 2017-03-22
Publication date: 2017-09-28

Abstract

A method of manufacturing a membrane for an electro-acoustic transducer through pad printing of a liquid plastics material is provided. The method includes providing a mold having a desired membrane geometry and depositing one or more layers of a liquid solution of a plastics material on the mold by means of pad printing. The liquid plastics material is allowed to cure, and the cured plastics material is removed off the mold in the shape of the membrane. The mold can be configured to hold other components of an electro-acoustic transducer that will be attached to the membrane after the curing step. Also provided is a membrane for an electro-acoustic transducer comprised of an plastics material and made by use of spray coating of a liquid plastics material solution.

Description

LOUDSPEAKER MEMBRANE AND METHOD OF MAKING SAME

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates, in general, to methods for manufacturing membranes for electro-acoustic transducers and membranes made by the disclosed methods. More particularly, the present invention relates to a method of manufacturing a membrane for an electro-acoustic transducer such as a micro speaker, miniature microphone or receiver, for use in mobile communication devices, such as a mobile phone, a tablet, a gaming device, a notebook or similar device.

Background Art

It is desirable for electro-acoustic transducers used in microelectronics to be as compact as possible. However, especially in the case of speakers, it is also desirable that the speaker should be able to output in a broad frequency range and at high sound pressure levels with low distortions.

A speaker comprises a membrane attached to a voice coil, which is positioned within a magnetic field defined by a permanent magnet and yoke arrangement. The performance of the speaker particularly depends on its resonant frequency. Above the resonant frequency, the output response is relatively flat. Therefore, a low resonant frequency gives rise to good wideband performance. The resonant frequency is a function of the stiffness and the mass of the moving parts. The stiffness inter alia depends on the stiffness of the membrane and the stiffness of the back volume.

The membrane in conventional micro speakers comprises a thermoplastic foil formed by deep drawing or stamping. The foil has a relatively high stiffness and, conversely, a relatively low compliance. Without additional measures, such a membrane causes a relatively high resonant frequency in a conventional micro speaker.

Recent improvements in membrane technology has seen membranes comprised of an elastomer having stiffness significantly less than conventional thermoplastic foils.

For example, one such improvement is detailed in U.S. Patent Application No. 13/380,428, filed June 23, 2010 (PCT date) , and published as U.S. Pat. Publ. No. 2012/0093353 A1 on April 19, 2012. (The entire disclosure of such application is herein incorporated by reference. ) The disclosed membrane is comprised of an elastomer, including silicone, and is made using injection molding.

While using injection molding to form elastomer membranes has many advantages over the use of deep drawing or stamping thermoplastic foil, it is not without its drawbacks. In particular, injection molding requires a two-part mold which adds to the complexity of the process and limits many aspects of the design, such as the minimum thickness obtainable for the membrane. The two-part mold also may not always be perfectly aligned, creating non-uniformity among multiple parts being produced. And even when near-perfect alignment can be achieved with new molds, during use, the mold pieces are susceptible to wear, which can cause alignment problems later.

Conventional membranes of thermoplastic foils are often constructed of multiple layers of different materials. The different layers of a multi-layer membrane can have different mechanical properties, allowing for adjustments for stability, damping or other performance characteristic. Examples of multi-layer membranes and the particular benefits of such are described in U.S. Patent Number 8,284,964 and U.S. Patent Serial No. 14/699,548, filed on April 19, 2015, the disclosures of each of which are herein incorporated by reference in their entirety.

However, multi-layer membranes comprised of an elastomer are not possible using injection molding. Further, while injection molding typically provides less variations in the thickness of a finished membrane than the deep drawn or stamping process, there is still a desire to improve the uniformity of the thickness of the membrane in order to lesson or eliminate tumbling of the membrane caused by asymmetries.

There is thus the need therefore to improve the process of manufacturing a membrane. In particular, membranes with desired mechanical properties and desired thickness shall be provided.

SUMMARY OF THE INVENTION

In order to address the issues above, there is provided, in one embodiment of the invention, a method of manufacturing a membrane for an electro-acoustic transducer, the method including the steps of providing a mold having a desired membrane geometry, depositing one or more layers of a liquid solution of a plastics material on the mold by means of pad printing, allowing the liquid plastics material to cure and removing the cured plastics material in the shape of the membrane off the mold. Accordingly, there is also provided a membrane for an electroacoustic transducer made by a method as disclosed above. Said membrane may be used in a mini speaker, a miniature microphone or a receiver for example.

By the measures of the presented method, advantageously the liquid plastics material can exactly be deposited on the mold. That means that the liquid plastics material is deposited in a nearly uniform thickness on the one hand and deposited only in desired areas on the other hand. Neither is possible with injections molding or spray coating to such an extent. Another particular advantage of the measures taken above is the avoidance of spray, which in case of spray coating little by little soils the machine, which fabricates the membranes. In contrast, such a machine is kept clean by use of pad printing.

To obtain a membrane having a desired thickness, the depositing step and the curing step may recursively be repeated until the membrane has said desired thickness.

In particular, the membrane has a (total) thickness of less than 100μm. In this way, good acoustic performance is achieved. In another embodiment, the membrane has a thickness of less than 80μm. In still another embodiment, the membrane has a thickness of less than 60μm.

In one embodiment, the liquid solution of a plastics material includes a liquid plastics material and a solvent. Accordingly, the depositing and curing steps comprise the deposition of at least one layer on the mold, allowing the layer to solidify by evaporation of the solvent, and thus curing of the liquid plastics material.

In particular, the depositing and curing steps comprise the deposition of multiple thin layers on the mold, allowing each layer to solidify by evaporation of the solvent, and thus curing of the liquid plastics material, before the next thin layer is deposited.

One should note that the curing step c) between the deposition of different layers does not necessarily include (but can include) the polymerization of the liquid plastics material. Curing in this context may mean the partial or complete evaporation of a solvent. Before taking the membrane off the mold in step d) , anyway the plastics material should be polymerized at least partial, for example by heat, radiation and/or a curing agent. According to an embodiment of the invention, the curing step c) may be caused or supported by actinic radiation. In this document actinic radiation means electromagnetic radiation, in particular UV-radiation.

Generally, masks may be used to selectively deposit plastics material onto the mold respectively onto transducer parts. The mask can be arranged between the printing pad and the mold /a membrane layer or between the printing pad and a surface, from which the printing pad takes up the plastics material to be deposited. In the latter case such a mask is termed "cliché" . A cliché basically comprises grooves in the shape, in which the plastics material shall be deposited onto the mold. In a first step, the grooves are filled with the liquid solution of the plastics material. Subsequently, superfluous material is taken away by moving a knife or a blade transversally over the cliché. Then the printing pad is pressed onto the cliché, from where it takes the liquid plastics material to be printed. The shape of the plastics material on the pad corresponds to the shape of the grooves in the cliché. Afterwards, the plastics material is transferred from the printing pad onto the mold respectively onto a membrane layer, which was already printed. In this way, the liquid plastics material can be deposited on the mold /a membrane layer in nearly any desired shape.

Further details and advantages of a method and a membrane of the disclosed kind will become apparent in the following description and the accompanying drawings.

In an advantageous embodiment of the disclosed method, different materials are deposited during at least two cycles of steps b) and c) . Accordingly, at least two layers differ in their characteristics. In particular different layers may have different mechanical (such as damping) and electrical properties when cured.

In a further advantageous embodiment of the disclosed method, the same material is deposited during all cycles of steps b) and c) . Accordingly, a membrane of a uniform material having a desired thickness may be produced.

Beneficially, an elastomer and/or a non-elastomer thermoplastic and/or a thermoset is used as plastics material. Accordingly, the membrane can comprise one or more pad printed layers of an elastomer and/or one or more pad printed layers of a non-elastomer thermoplastic and/or one or more pad printed layers of a thermoset. Generally, the membrane may be made of a uniform material or a nonuniform material as mentioned above. In particular, the outer layers may be made of a non-elastomer thermoplastics material and the inner layer or inner layers may be made of a elastomer. Of course, also non-elastomer thermoplastics layers may be arranged in-between elastomer layers.

If an elastomer is used as plastics material, the method of manufacturing a membrane for an electro-acoustic transducer particularly comprises the steps of:

- providing a mold having a desired membrane geometry,

- depositing one or more layers of a liquid elastomer solution on the mold by means of pad printing,

- allowing the liquid elastomer to cure and

- removing the cured elastomer in the shape of the membrane off the mold.

Beneficially, the mold is heated to a pre-determined temperature prior to the deposition step b) . Advantageously these measures allow the liquid plastics material to solidify almost immediately after deposition. Furthermore, polymerization of the plastics material may be caused or supported by heat.

In a particular advantageous embodiment of the presented method, the mold provided in step a) is configured with at least one recess/cavity, and one or more of a frame, a voice coil, a stiffening plate, a wire and/or an electrically conducting structure is put into the at least one recess/cavity before step b) . In this way, said parts may be adhered to the membrane, respectively may integrally be part of the manufacturing process of the membrane. Prior to the depositing step, the frame, the voice coil, the stiffening plate, the wire, the electrically conducting structure and/or other the part is placed into the cavity or recess in the mold, such that a surface of the part is in contact with the liquid solution of plastics material during the deposition step. When the cured membrane is removed from the mold, the frame, the voice coil, the stiffening plate, the wire, the electrically conducting structure and/or the other part is affixed to the membrane. In particular, one or more layers of a cured liquid plastics material is/are affixed to one or more of a frame, a voice coil, a stiffening plate, a wire and/or an electrically conducting structure without the use of an additional adhesive. Nevertheless, also an adhesive respectively a primer may be deposited onto the parts intended to be adhered to the membrane by means of pad printing before the deposition step b) . Masks and clichés may be used for the deposition of adhesives or primers in the same way as for the deposition of plastics material. Concretely, grooves in a cliché can be filled with an adhesive or a primer, from where the printing pad takes up the material to be printed. In this way, an adhesive or a primer can be deposited on the mold or on transducer parts in nearly any desired shape. For the sake of completeness, one should also note that different masks/clichés can be used for different layers/materials. Different materials can be deposited by the same printing pad or by different printing pads.

In yet another particular advantageous embodiment of the presented method, the mold provided in step a) is configured with at least one recess/cavity, and one or more of a frame, a voice coil, a stiffening plate, a wire and/or an electrically conducting structure is put into the at least one recess/cavity after step b) . In this way said parts are enclosed by the plastics material. That is why the bonding between the membrane material and the parts connected thereto is particularly good.

In an advantageous embodiment of the disclosed method, at least one layer is deposited by means of spray coating. Particularly, spray coating may be used for depositing the liquid solution of the plastics material into recesses/cavities of the mold. In one embodiment, spray-coating is done using an ultrasonic spray nozzle. In another aspect of the invention, the spray-coating is achieved using forced air, without the use of an ultrasonic spray nozzle.

At this point one should note that embodiments of the disclosed method and advantages resulting thereof equally apply to the disclosed membrane and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects, features, details, utilities, and advantages of the invention will become more fully apparent from the following detailed description, appended claims, and accompanying drawings, wherein the drawings illustrate features in accordance with exemplary embodiments of the invention, and wherein:

Figure 1 shows a schematic arrangement of a pad printing tool vis-a-vis of a mold for a membrane, wherein the a pad printing tool is in its retracted position and wherein the pad is wetted with a liquid solution of a plastics material；

Figure 2 shows the arrangement of Fig. 1 in a position, in which the pad respectively the material on it contacts the mold；

Figure 3 shows the arrangement of Fig. 1 in the retracted position of the pad printing tool position after the liquid solution of a plastics material has been transferred to the surface of the mold；

Figure 4 shows the arrangement of Fig. 1 in a state, in which the plastics material has been cured and the membrane has been taken off the mold；

Figure 5 shows a cross section of a membrane having three layers onto a mold；

Figure 6 shows a similar arrangement to that shown in Fig. 5, but with a frame, a coil and a center plate attached to the membrane；

Figure 7 shows a similar arrangement to that shown in Fig. 6, but with the first layer enclosing the frame, the coil and the center plate；

Figure 8 shows a cross section of a membrane having three layers, which are recessed in the region of a stiffening plate /center plate；

Figure 9 shows a perspective view of an exemplary membrane and in hand a perspective view of an exemplary surface of a mold； and

Figure 10 shows a cross sectional view of an exemplary speaker.

Like reference numbers refer to like or equivalent parts in the several views.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments are described herein to various apparatuses. Numerous specific details are set forth to provide a thorough understanding of the overall structure, function, manufacture, and use of the embodiments as described in the specification and illustrated in the accompanying drawings. It will be understood by those skilled in the art, however, that the embodiments may be practiced without such specific details. In other instances, well-known operations, components, and elements have not been described in detail so as not to obscure the embodiments described in the specification. Those of ordinary skill in the art will understand that the embodiments described and illustrated herein are non-limiting examples, and thus it can be appreciated that the specific structural and functional details disclosed herein may be representative and do not necessarily limit the scope of the embodiments, the scope of which is defined solely by the appended claims.

Reference throughout the specification to “various embodiments, ” “some embodiments, ” “one embodiment, ” or “an embodiment, ” or the like, means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, appearances of the phrases “in various embodiments, ” “in some embodiments, ” “in one embodiment, ” or “in an embodiment, ” or the like, in places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. Thus, the particular features, structures, or characteristics illustrated or described in connection with one embodiment may be combined, in whole or in part, with the features, structures, or characteristics of one or more other embodiments without limitation given that such combination is not illogical or non-functional.

It must be noted that, as used in this specification and the appended claims, the singular forms “a, ” “an” and “the” include plural referents unless the content clearly dictates otherwise.

The terms “first, ” “second, ” and the like in the description and in the claims, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms “include, ” “have, ” and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements is not necessarily limited to those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

All directional references (e.g., "plus" , "minus" , "upper″ , "lower" , "upward" , "downward" , "left" , "right" , "leftward" , "rightward" , "front" , "rear" , "top" , "bottom" , "over" , "under" , "above" , "below" , "vertical" , "horizontal" , "clockwise" , and "counterclockwise" ) are only used for identification purposes to aid the reader’s understanding of the present disclosure, and do not create limitations, particularly as to the position, orientation, or use of the any aspect of the disclosure. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein.

As used herein, the phrased “configured to, ” “configured for, ” and similar phrases indicate that the subject device, apparatus, or system is designed and/or constructed (e.g., through appropriate hardware, software, and/or components) to fulfill one or more specific object purposes, not that the subject device, apparatus, or system is merely capable of performing the object purpose.

Joinder references (e.g., "attached" , "coupled" , "connected" , and the like) are to be construed broadly and may include intermediate members between a connection of elements and relative movement between elements. As such, joinder references do not necessarily infer that two elements are directly connected and in fixed relation to each other. It is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative only and not limiting. Changes in detail or structure may be made without departing from the spirit of the invention as defined in the appended claims.

All numbers expressing measurements and so forth used in the specification and claims are to be understood as being modified in all instances by the term “about. ”

Figures 1 to 4 show a schematic arrangement of a mold 1 for a membrane and a pad printing tool being arranged vis-a-vis of the mold 1 in different states. The pad printing tool comprises a plunger 2 and a pad 3 in this example. Of course, the pad printing tool may be more complex as well. In this example, the pad 3 is arranged above the mold 1 and the moving direction of the plunger 2 is vertically oriented as indicated by arrows. Although this is a favorable arrangement, the pad 3 may also be arranged besides the mold 2 and the moving direction of the plunger 2 may be horizontal for example.

Figure 1 shows a state, in which the plunger 2 is in its retracted position and accordingly the pad 3 is lifted above the mold 1. Fig. 1 also shows, that the pad 3 is wetted with a liquid solution of a plastics material 4.

Figure 2 shows the arrangement of Fig. 1 in a next state, in which the plunger 2 moved downwards, and the pad 3 respectively the liquid plastics material 4 on it contacts the mold 1.

Figure 3 shows the arrangement of Fig. 1 in yet another state, in which the plunger 2 again is in its retracted position and the pad 3 is lifted above the mold 1.

Furthermore, the liquid solution of the plastics material 4 has been transferred to the surface of the mold 1 as shown in Fig. 3. For the sake of simplicity, all material 4 is transferred from the pad 3 to the mold 1 in this example. However, material 4 may be transferred from the pad 3 to the mold 1 also partly as the case may be.

Finally, Figure 4 shows the arrangement of Fig. 1 in a state, in which the plastics material 4 has been cured and forms the membrane 5, which is taken off the mold 1 in Fig. 4. Essentially, the plastics material 4 and the membrane 5 denote the same object in different states, meaning that the plastics material 4 becomes the membrane 5 after a curing step respectively after polymerization.

Accordingly, the method of manufacturing the membrane 5 for an electro-acoustic transducer, comprises the steps of:

a) providing a mold 1 having a desired membrane geometry,

b) depositing one or more layers of a liquid solution of a plastics material 4 on the mold 1 by means of pad printing,

c) allowing the liquid plastics material 4 to cure and

d) removing the cured plastics material 4 in the shape of the membrane 5 off the mold 1.

Steps b) and c) may be recursively repeated until the membrane 5 has a desired thickness. In this context, Fig. 5 shows a more detailed view of a membrane 5 having three

layers

6a, 6b and 6c. A membrane 5 having more than one layer 6a -6c may be produced if a desired thickness cannot be obtained in a single depositing step b) or, for example, if the different layers 6a -6c have different characteristics and different functions.

In this context, in one embodiment different materials are deposited during at least two cycles of steps b) and c) . Accordingly, at least two layers 6a -6c differ in their characteristics. In particular different layers 6a -6c may have different mechanical (such as damping) and electrical properties when cured. For example, different elastomers may be deposited, or an elastomer and/or a non-elastomer thermoplastic and/or a thermoset is used as plastics material 4 to form layers 6a -6c. In this way, the membrane 5 consists of nonuniform materials when cured. In particular, the

outer layers

6a and 6c may be made of a non-elastomer thermoplastics material and the inner layer 6b or inner layers may be made of an elastomer. Of course, also non-elastomer thermoplastics layers may be arranged in-between elastomer layers.

Generally, Ethere Ketone (PEEK) , Acrylate and/or Thermoplastic Elastomeric (TEP) , Polyetherimide (PEI) , and/or other materials may be used for the layers 6a -6c for example.

In another embodiment, the same material is deposited during all cycles of steps b) and c) . Accordingly, a membrane 5 of a uniform material having a desired thickness may be produced by the presented method.

Generally, the liquid solution of the plastics material 4 can include a liquid plastics material and a solvent. Accordingly, the depositing and curing steps b) and c) comprise the deposition of a first layer 6a on the mold 1, allowing the first layer 6a to solidify by evaporation of the solvent, and thus curing of the liquid plastics material 4. Optionally, a second layer 6b, a third layer 6c and also further layers may be deposited and cured in the same way. In particular, the depositing and curing steps b) and c) comprise the deposition of multiple thin layers 6a -6c on the mold 1, allowing each layer 6a -6c to solidify by evaporation of the solvent, and thus curing of the liquid plastics material 4, before the next thin layer 6a -6c is deposited. Although allowing curing of each layer 6a -6c is beneficial, nevertheless a next layer 6b may be deposited before a preceding layer 6a is fully cured. Layers 6a -6c may be deposited wet in wet or at least partly wet in wet accordingly.

To shorten the curing step c) , the mold 1 may be heated to a pre-determined temperature prior to the deposition step b) . Alternatively or in addition, the deposited material 4 may be irradiated by means of an ultraviolet lamp as the case may be. Advantageously these measures allowing the liquid plastics material 4 to solidify almost immediately after deposition on the mold 1.

One should also note that a curing step c) between the deposition of different layers 6a -6c does not necessarily include the polymerization of the liquid plastics material 4. Curing in this context may also mean the partial or complete evaporation of a solvent. Anyway, the curing step c) between the deposition of different layers 6a -6c may also include the partial or complete polymerization of the liquid plastics material. Before taking the membrane 5 off the mold 1 in step d) , the plastics material should be polymerized at least partial. Polymerization may caused or at least supported by heat and/or radiation for example. Polymerization may also be caused or supported by a curing agent in the plastics material 4.

A membrane 5 for a speaker, a microphone or a receiver usually is connected to one or more of a frame, a voice coil, a stiffening plate to provide the conversion of sound into electric signals and vice versa. For this reason, in a preferred variant of the manufacturing method, the mold 1 being provided in step a) and used in steps b) to d) is configured with at least one recess/cavity, and one or more of a frame, a voice coil, a stiffening plate and/or a wire is put into the at least one recess/cavity before step b) .

Fig. 6 shows an example of a mold 1, which receives a frame 7, a voice coil 8 and a stiffening plate 9 in particular recesses/cavities. Accordingly, the liquid plastics material 4 gets in contact with the above parts 7-9 when deposited onto the mold 1 in step b) .

In this way, said

parts

7, 8 and 9 may be adhered to the membrane 5, respectively may integrally be part of the manufacturing process of the membrane 5. When the liquid plastics material 4 is cured, the membrane 5 is removed from the mold 1 together with the frame 7, the voice coil 8 and the stiffening plate 9, which are all affixed to the membrane 5. In principle, said parts 7-9 may be connected to the membrane 5 without the use of adhesives. Anyway, an adhesive, a bonding agent or a primer may be deposited onto the parts 7-9, which ar intended to be adhered to the membrane 5, before depositing one or more layers 6a -6c of a liquid solution of a plastics material 4 on the mold 1 in step b) .

In the above example, the parts 7-9 are put into the recesses/cavities of the mold 1 before step b) . However, one or more of a frame 7, a voice coil 8, and/or a stiffening plate 9 may be put into the recesses/cavities of the mold 1 after step b) . In this way said parts 7-9 are enclosed by the plastics material 4 as is shown in Fig. 7. Concretely, a first layer 6a forms cavities to receive the frame 7, the voice coil 8, and/or the stiffening plate 9. The second layer 6b closes said cavities. That is why the bonding between the membrane 5 and the parts 7-9 connected thereto is particularly good.

Further layers

6c and 6d are deposited like in the above examples. To limit the deposition of the first layer 6a to the recesses/cavities of the mold 1, a mask respectively a cliché may be used.

One should note that the walls of the mold 1 may be inclined to ease taking the membrane 5 with the attached parts 7-9 out of the mold 1. The recess/cavity for the coil 8 may also be used to stabilize the coil 8 itself. In this case a comparably big amount of liquid plastics 4 can be put into the groove for the coil 8 (e.g. by spray coating or by depositing the liquid plastics 4 through needles) , and subsequently the coil 8 is pressed into the groove so that the liquid plastics 4 is pressed into the hollow spaces within the coil 8. In this way, a quite stable coil 8 is obtained during production of the membrane 5.

In the above examples, exclusively pad printing was used to deposit the liquid plastics material 4. Anyway, also other depositing methods may be used in combination. For example, at least one layer is deposited by means of spray coating in a preferred embodiment. In one embodiment, spray-coating is done using an ultrasonic spray nozzle. In another aspect of the invention, the spray-coating is achieved using forced air, without the use of an ultrasonic spray nozzle. With respect to the use of spray coating, reference is made to United States Provisional patent application titled Loudspeaker Membrane and Method of Making Same, having Serial No. 62/235,943, filed on October 1, 2015, the disclosure of which is herein incorporated by reference in its entirety.

Spray coating is particularly fine when concave areas or inner edges of the mold 1 or a layer 6a -6c have to coated as the spray easily reaches these areas. Pad printing may fail in these cases if the pad 3 does not reach said concave areas or inner edges. So, in the example shown in Fig. 7, for example, the first layer 6 may be deposited by means of spray coating, and the other layers 6a -6c may be deposited by means of pad printing.

Figure 8 shows a cross section of a membrane 5 having three layers 6a -6c, which are recessed in the region of a stiffening plate 9. In this example, the coil 8 is adhered to the stiffening plate 9, and the resulting arrangement is placed in the mold 1 before depositing the first layer 6a or at least before depositing the second layer 6b. In an alternative embodiment only the stiffening plate 9 is placed in the mold 1 and bonded to the membrane 5. In a subsequent step, the coil 8 is adhered to the stiffening plate 9.

Masks or clichés are used to form the recesses in layers 6a -6c shown in Fig. 8. A mask can be placed between the pad 3 of the pad printing tool and the mold 1 for example. Alternatively, the mask can also be placed between the pad 3 and a region to pick up the liquid plastics material 4. In the latter case such a mask is termed "cliché" . In a first step, the grooves of the cliché are filled with the liquid solution of a plastics material 4 (or with an adhesive or a primer) . Subsequently, superfluous material is taken away by moving a knife or a blade transversally over the cliché. Then the printing pad 3 is pressed onto the cliché, from where it takes the material 4 to be printed. The shape of material 4 on the pad 3 corresponds to the shape of the grooves in the cliché. Afterwards, the material 4 is transferred from the printing pad 3 onto the mold 1 respectively onto a membrane layer 6a -6c, which was already printed. In this way, the liquid plastics material 4 or an adhesive or a primer can be deposited on the mold 1 in nearly any desired shape.

When using a cliché, the steps mentioned above are part of the depositing step b) . So, the depositing step b) implicitly comprises transferring liquid solution of a plastics material 4 from a cliché to the pad 3 and from there to the mold 1 or to a membrane layer 6a -6c. Obviously, the transfer of a liquid solution of a plastics material 4 from a cliché to the pad 3 takes place before the state shown in Fig. 1.

One should also note for the example shown in Fig. 8 that the upper edge of the stiffening plate 9 is encompassed by the liquid plastics material 4 what improves bonding between the membrane 5 and the stiffening plate 9.

In the examples above, a frame 7, a voice coil 8 and a stiffening plate 9 is put into the mold 1 respectively bonded to the membrane 5. While these are favorable examples, the skilled in the art will easily perceive other or further examples of parts, which may be bonded to a membrane 5. Particularly, electrically conducting structures may be attached to the membrane 5, like a plate of a condenser, an antenna as well as wires (e.g. for connecting the coil) and so on.

By use of the method disclosed above, a membrane 5 for an electroacoustic transducer is obtained. Such a membrane may be used in a mini speaker, a miniature microphone or a receiver for example.

Generally, the membrane 5 may have a thickness of less than 100μm. In this way, good acoustic performance is achieved. In another embodiment, the membrane has a thickness of less than 80μm. In still another embodiment, the membrane has a thickness of less than 60μm.

Fig. 9 shows a perspective view of an exemplary membrane 5. The membrane comprises a flat border area 10, a flat center area 11, and a corrugated area 12 in-between. The frame 7 is connected to the border area 10 and the voice coil 8 and the stiffening plate 9 are connected to the center area 11.

Fig. 10 finally shows a cross-sectional view of an exemplary speaker 13, which comprises the membrane 5 with the frame 7, the voice coil 8 and the stiffening plate 9 and which is connected to a housing 14. Within the housing 14 there is a pot 15 connected to a permanent magnet 16 and a top plate 17. The top plate 17 focuses the magnetic field of the permanent magnet 16 into the a space between the top plate 17 and the pot 15. The voice coil 8 is positioned around the permanent magnet 16 respectively in the space between the permanent magnet 16 and the pot 15. The corrugated area 12 enables a vertical movement of the center area 11 in relation to the border area 10 so as to generate sound. In operation, an audio signal is fed into the coil 8 causing the coil 8 to oscillate within the magnetic field of the permanent magnet 16 and leading to a sound pressure produced by the movement of the membrane 5.

While the corrugated area 12 is shown as concave in relation to the top surface of membrane 5 in Figs. 9 and 10, in other embodiments the corrugated area 12 may be convex in relation to the surface of the membrane 5. Corrugations may also be omitted, and a smooth convex or concave torus area can be used instead. One should also note, that other configurations are applicable as well and the disclosed fabrication method is not limited to a membrane 5 as shown in Fig. 9 or a speaker 13 as shown in Fig. 10.

While embodiments of the membrane 5 and audio transducer 13 are shown and described as having a circular shape, it will be understood that in other embodiments, the membrane 5 and/or the audio transducer 13 may have a variety of shapes, including, but not limited to, ovular and rectangular. Accordingly, the invention is not limited to audio transducers having a circular shape.

Moreover, it should be noted that the invention is not limited to the above mentioned embodiments and exemplary working examples. Further developments, modifications and combinations are also within the scope of the patent claims and are placed in the possession of the person skilled in the art from the above disclosure. Accordingly, the techniques and structures described and illustrated herein should be understood to be illustrative and exemplary, and not limiting upon the scope of the present invention. The scope of the present invention is defined by the appended claims, including known equivalents and unforeseeable equivalents at the time of filing of this application. Although numerous embodiments of this invention have been described above with a certain degree of particularity, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of this disclosure.

In closing, it should be noted that any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated materials does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.

Claims

A method of manufacturing a membrane for an electro-acoustic transducer, the method comprising the steps of:

providing a mold having a desired membrane geometry；

depositing a layer of a liquid solution of a plastics material on the mold by means of pad printing；

allowing the layer of liquid solution of a liquid plastics material to cure； and

removing the cured plastics material in the shape of the membrane off the mold.
A method of manufacturing a membrane according to claim 1, wherein the depositing step and curing step are recursively repeated until the membrane has a desired thickness.
A method of manufacturing a membrane according claim 2, wherein different plastics materials are deposited during at least two cycles of the depositing step and curing step.
A method of manufacturing a membrane according to claim 2, wherein the same plastics material is deposited during all cycles of the depositing step and curing step.
A method of manufacturing a membrane according to claim 1, wherein the liquid solution of a plastics material includes a liquid plastics material and a solvent.
A method of manufacturing a membrane according claim 1, wherein the plastics material is one of an elastomer, a non-elastomer thermoplastic and a thermoset.
A method of manufacturing a membrane according to claim 1, wherein the mold is heated to a pre-determined temperature prior to the depositing step.
A method of manufacturing a membrane according to claim 1, wherein the mold is configured with at least one recess and wherein one or more of a frame, a voice coil, a stiffening plate, a wire and an electrically conducting structure is put into the at least one recess before the depositing step.
A method of manufacturing a membrane according to claim 1, wherein the mold provided is configured with at least one recess and wherein one or more of a frame, a voice coil, a stiffening plate, a wire and an electrically conducting structure is put into the at least one recess after the depositing step.
A method of manufacturing a membrane according to claim 1, further comprising the step of depositing a layer of a liquid solution of a plastics material on the mold by means of spray coating after curing step, and repeating the curing step.
A method of manufacturing a membrane according to claim 1, wherein the curing step comprises the use of actinic radiation.
A membrane for an electroacoustic transducer, the membrane made by a method comprising the steps of:

providing a mold having a desired membrane geometry；

depositing one or more layers of a liquid solution of a plastics material on the mold by means of pad printing；

allowing the layer of liquid solution of a plastics material to cure； and

removing the cured plastics material in the shape of the membrane off the mold.
The membrane according to claim 12, wherein the membrane has a thickness of less than 100μm.
The membrane according to claim 12, wherein the plastics material for each of the one or more layers is one of an elastomer, a non-elastomer thermoplastic and a thermoset.
The membrane according to claim 12, wherein the membrane is affixed to one or more of a frame, a voice coil, a stiffening plate, a wire and an electrically conducting structure without the use of an additional adhesive.