Asymmetrical multi-layered membrane for electroacoustic transducers

Abstract

A multi-layered laminate for producing membranes for electroacoustic transducers, comprises a first layer of a polyether ether ketone film having a heat of crystallisation of at least 15 J/g, a second layer (of a thermoplastic plastic film having a heat of crystallisation of no more than 5 J/g, and an adhesive layer arranged between the first and second layers. Alternatively, the first and second layers are defined by their shrinkage properties after 15 minutes at 200° C.: the first layer has shrinkage of more than 10% in at least one direction, and the second layer has shrinkage of less than 10% in the longitudinal and transverse directions. A laminate constructed in this manner exhibits lower fold formation when processed using multi-cavity thermoforming. The laminates are useful for the production of membranes for electroacoustic transducers.

Claims

1. A multilayer laminate for the production of membranes for electroacoustic transducers, comprising a first layer (“first outer layer”) made of a polyetheretherketone foil (“PEEK foil”) with heat of crystallization of at least 15 J/g, determined in the first heating curve in differential scanning calorimetry, a second layer (“second outer layer”) made of a thermoplastic foil with a heat of crystallization of at most 5 J/g, determined in the first heating curve in differential scanning calorimetry, and an adhesive layer arranged between the first and second outer layer.

2. The multilayer laminate as claimed in claim 1, wherein the second outer layer is composed of an at least semicrystalline PEEK foil.

3. The multilayer laminate as claimed in claim 1, wherein the second outer layer is composed of a plastic of which the main constituent is selected from the group consisting of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetherimide, polyimide, polyarylate, polyphenyl sulfide, polyphenyl sulfone, polysulfone, and polyether sulfone.

4. The multilayer laminate as claimed in claim 1, wherein the thicknesses of the two outer layers are respectively from 1 μmm to 50 μm.

5. The multilayer laminate as claimed in claim 1, wherein the thickness of the adhesive layer is from 2 μm to 100 μm.

6. A process for the production of membranes for electroacoustic transducers made of a multilayer laminate as claimed in claim 1, said process comprising multicavity thermoforming.

7. An electroacoustic transducer comprising a multilayer laminates as claimed in claim 1.

8. An electronics device comprising an electroacoustic transducer according to claim 7.

9. A multilayer laminate for the production of membranes for electroacoustic transducers, comprising a first layer (“first outer layer”), the shrinkage of which in at least one direction after 15 minutes at 200° C. is greater than 10%, a second layer (“second outer layer”), the shrinkage of which in longitudinal and transverse direction respectively after 15 minutes at 200° C. is less than 10%, and an adhesive layer arranged between the first and second outer layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in greater detail with reference to the drawings, wherein:

(2) FIG. 1 is a schematic showing a 3-layer laminate according to the invention made of semicrystalline PEEK foil (1), adhesive (2), and amorphous PEEK foil (3; and

(3) FIG. 2 is a schematic showing an advantageous arrangement of the laminate of the invention in the thermoforming mold (4), which, after heating by compressed air (5), is forced into the depressions of the thermoforming mold.

(4) The multilayer laminate can be restricted to the three layers mentioned, but can also have further layers in the laminate structure.

(5) A 3-layer laminate made of semicrystalline PEEK foil (1), adhesive (2), and amorphous PEEK foil (3) is shown by way of example in FIG. 1.

(6) A material that has been found to be particularly suitable in the invention for the purposes of the second outer layer is a semicrystalline PEEK foil, i.e. a PEEK foil which has heat of crystallization of at most 5 J/g, determined in the first heating curve in differential scanning calorimetry.

(7) Other foils suitable for the purposes of the invention for use as second outer layer—i.e. as replacement for one of the two amorphous PEEK foils of conventional structures—are by way of example foils made of polyphenylene sulfide (PPS), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyarylate (PAR), polyimide (PI), polyetherimide (PEI), polyphenyl sulfone (PPSU), polyether sulfone (PES), or polysulfone (PSU).

(8) Foils used as second outer layer preferably have thicknesses in the range from 1 μm to 50 μm, preferably from 2 μm to 40 μm, particularly preferably from 5 μm to 15 μm.

(9) The amorphous PEEK foils for the first outer layer in the asymmetrical multilayer laminate likewise—independently of the thicknesses of the foils for the second outer layer—has thicknesses in the range from 1 μm to 50 μm, preferably from 2 μm to 40 μm, particularly preferably from 5 μm to 15 μm.

(10) It is possible here to select the same thickness for the amorphous first outer layer and the second outer layer that is the layer not capable of crystallization.

(11) When the properties of the abovementioned foils that can be used as second outer layer are compared with those of the amorphous PEEK foil obtainable commercially, it is found that the shrinkage of foils that are not capable of crystallization, in particular foils of the abovementioned materials with heat of crystallization of at most 5 J/g, is markedly smaller than the shrinkage of the amorphous PEEK foil. Comparative values are shown by way of example in table 1.

(12) TABLE-US-00001 TABLE 1 Shrinkage of various foils at 200° C. for 15 min. Shrinkage Shrinkage Morphology MD/% TD/% PEEK 6μ (Victrex, amorphous 19 4 Aptiv 2000-006GS) PEEK 9μ (Victrex, amorphous 12 4 Aptiv 2000-009GS) PEEK 8μ (Victrex, semi- 2 −2 Aptiv 1000-008GS) crystalline PPS 9μ (Toray, semi- 2 0.5 Torelina 3030) crystalline PPSU 9μ (Ajedium) amorphous 0.5 0 PAR 10μ (Lofo, amorphous 6 5 Aryphan N681 EM) PET 12μ (Toray, semi- 4 1 Lumirror 60.01) crystalline

(13) The invention therefore further provides a multilayer laminate for the production of membranes for electroacoustic transducers, comprising a first layer, the shrinkage of which in at least one direction after 15 minutes at 200° C. is greater than 10%, an adhesive layer arranged between the first and second outer layer, and a second outer layer, the shrinkage of which in longitudinal and transverse directions respectively after 15 minutes at 200° C. is less than 10%, preferably less than 5%. It is preferable to use, as foils for the first and the second outer layer, foils of the type described hereinafter; the statements made in relation to said foils apply correspondingly to said multilayer laminate.

(14) The shrinkage of the foils is determined by using a foil marker at room temperature to make two markings 10 cm apart on the foil, and suspending the foils freely for 15 minutes at 200° C. in a conventional oven. After cooling, the distance between the two markings is again measured, and the percentage change in the distance is determined. This measurement is made both in the longitudinal direction of the foil—also called machine direction or MD—and in the transverse direction of the foil—also called transverse direction or TD—in order to record the different shrinkage, depending on orientation.

(15) In the multilayer laminate of the invention, there is an intermediate layer made of an adhesive arranged between the amorphous PEEK foil and the semicrystalline PEEK foil. The function of this layer is stable bonding of the foils located above and below, and damping of the oscillation of the stiff external foils.

(16) Suitable adhesives are polyacrylates dissolved in solvents, or are aqueous polyacrylate dispersions, or else are rosin-modified natural and synthetic rubber. Polyacrylate adhesives in solution are particularly suitable here.

(17) It is preferable to apply the adhesive layer by coating from solvent or from water with the aid of a nozzle or of a doctor blade onto the first outer layer—in particular onto an amorphous PEEK foil of thickness from 6 μm to 12 μm, and then to dry the material for from 5 to 30 minutes at from 100 to 170° C. The second outer layer—in particular a semicrystalline PEEK foil of thickness from 6 μm to 12 μm, preferably 8 μm—is then laminated onto the dried adhesive.

(18) The thickness of the adhesive after drying is from 2 μm to 100 μm, preferably from 5 μm to 50 μm, particularly preferably from 10 μm to 30 μm.

(19) The multilayer laminates of the invention can be used with exceptional results in a process for the production of membranes for electroacoustic transducers, where they are subjected to the multicavity thermoforming process. In this process the multilayer laminate is placed onto the heatable thermoforming mold which comprises depressions which replicate, in negative form, the membrane that is to be formed. The multilayer laminate is then heated, for example via IR radiation, and thus softened, and then forced from above into the depressions by compressed air.

(20) Alternatively, it is also possible to use a ram made of silicone or of foamed silicone to force the softened multilayer laminate into the molds. The membranes of the invention, produced by this process, exhibited markedly less creasing than membranes made of two amorphous PEEK foils of thickness from 6 to 9 μm with adhesive layer located therebetween.

(21) FIG. 2 shows an advantageous arrangement of the laminate of the invention in the thermoforming mold. Reference signs 1 to 3 here describe the multilayer laminate as described for FIG. 1. This multilayer laminate is placed onto the preferably heated thermoforming mold 4 and, after heating by compressed air (5), is forced into the depressions of the thermoforming mold.

(22) Finally, the invention also provides the use of the multilayer laminates described for the purposes of this document for the production of membranes for electroacoustic transducers.

(23) The example below is intended to illustrate the invention, without any intention of restricting it.

EXAMPLE 1

(24) Aptiv 2000-006GS amorphous PEEK foil from Victrex, thickness 6 μm, is coated with a thickness of 20 μm of an acrylate adhesive, and is then dried at 120° C. for 5 minutes. Aptiv 1000-008GS semicrystalline PEEK foil, thickness 8 μm, is then applied onto the adhesive layer, and laminated thereto via application of pressure by a roller in the manner that excludes bubbles. An area of about 10 cm by 10 cm is cut out from this multilayer laminate, and is placed onto the thermoforming mold in such a way that the amorphous PEEK foil is in contact with the heated embossing mold and the semicrystalline foil faces upward. The laminate is then heated in the thermoforming mold and forced into the form of the finished membrane via application of pressure. In contrast to multilayer laminates made of two amorphous PEEK foils of thickness from 6 to 9 μm with adhesive layer located therebetween, the PEEK foil here facing upward and toward the compressed air is not affected by the creasing problem.