COMPOSITE MATERIAL FOR PRODUCING AN ACOUSTIC MEMBRANE

Abstract

A composite material for producing an acoustic membrane, wherein the composite material comprises a silicone layer comprising an at least partially uncured silicone rubber and a support layer, wherein the support layer is adjacent to the silicone layer, as well as a method of preparing such a composite material and a process for producing an acoustic membrane from such a composite material.

Claims

1. A composite material for producing an acoustic membrane, wherein the composite material comprises at least: a silicone layer comprising an at least partially uncured silicone rubber; and a support layer, wherein the support layer is adjacent to the silicone layer.

2. A composite material according to claim 1, wherein the at least partially uncured silicone rubber is a high temperature vulcanizing addition-curing silicone rubber.

3. A composite material according to claim 2, wherein the silicone layer (2) comprises: a first silicone component with a Si—H substructure, a second silicone component with a Si-vinyl substructure, and a catalyst.

4. A composite material according to claim 3, wherein the catalyst is platinum.

5. A composite material according to claim 1, the silicone layer comprising an at least partially uncured silicone having a relative solvent resistance of below 80%, or below 50%.

6. A composite material according to claim 1, wherein the silicone layer further comprises an aprotic solvent.

7. A composite material according to claim 6, wherein the aprotic solvent is selected from the group consisting of toluene, cyclohexane, n-heptane, low boiling spirits fraction and mixtures thereof.

8. A composite material according to claim 1, wherein the silicone layer has a thickness of from 10 μm to 300 μm, or from 20 μm to 200 μm, or from 30 μm to 100 μm.

9. A composite material according to claim 1, wherein the composite material comprises one or two silicone layer(s), one or two support layer(s), and optionally one or more further layer(s), wherein the one or more further layer(s) is/are selected from the group consisting of damping layers and reinforcement layers.

10. A composite material according to claim 1, wherein the support layer is a release layer or a structure layer.

11. A composite material according to claim 10, wherein the composite material comprises two outer layers characterized in that at least one of the outer layers is a support layer and wherein the support layer is a release layer.

12. A composite material according to claim 11, wherein the release layer comprises a polyethylene terephthalate (PET) film or a paper, selected from the group consisting of PET film with one-sided siliconization, PET film with symmetric siliconization on both sides, PET film with differentiated siliconization on both sides, paper with one-sided olefin coating, paper with symmetric olefin coating on both sides, and paper with differentiated olefin coating on both sides.

13. A composite material according to claim 10, wherein the support layer is a structure layer.

14. A composite material according to claim 13, wherein the structure layer comprises: a thermoplastic material selected from the group consisting of PAEK (polyaryletherketone), e.g. PEEK (polyetheretherketone), PEI (polyether imide), PAR (polyarylate), modified PAR types, PC (polycarbonate), PA (polyamide), PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PPSU (polyphenylsulfone), PES (polyethersulfone), and PSU (polysulfone), or an elastomer selected from the group consisting of urethane elastomers, polyester elastomers, co-polyester elastomers, styrene block copolymers like SBS (styrene-butadiene block copolymer) or SEBS (styrene-ethylene-butylene-styrene block copolymer), elastic co-polyamides, elastomeric polyolefins, and acrylic elastomers, or a cured silicone.

15. A method for preparing a composite material according to claim 1 comprising: i) coating a support layer with a solution of an uncured silicone rubber in an aprotic solvent; and/or ii) laminating a support layer with a film of an at least partially uncured silicone rubber.

16. A method according to claim 15, wherein a method that includes item i) further comprises a step of essentially removing the aprotic solvent.

17. A method according to claim 15, wherein a method that includes item ii) comprises a step wherein the film of the at least partially uncured silicone rubber is shaped by calendering or extrusion before depositing the film on the support layer.

18. A process for producing an acoustic membrane from a composite material according to claim 1 comprising the steps of providing a precursor by cutting the composite material in a suitable two-dimensional extension, and shaping the precursor by using a forming tool and by exposing said precursor to conditions that allow the uncured silicone rubber to cure.

19. A process according to claim 18, wherein the precursor is derived from a composite material comprising two outer layers characterized in that at least one of the outer layers is a support layer and wherein the support layer is a release layer, and wherein the method comprises a step of: removing the release layer(s) before the step of shaping the precursor.

20. A process according to claim 18, wherein the conditions allowing the uncured silicone rubber to cure are achieved by raising the temperature of the silicone layer to a temperature of 100° C. or higher, or to a temperature of from 140° C. to 200° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0073] In the following aspects of the invention are described in figures and examples to illustrate embodiments of the invention. These embodiments should be understood as exemplary non-limiting examples.

[0074] FIG. 1 A to N show various preferred arrangements of a composite material according to the invention with a support layer 1 or 5 and a silicone layer 2, optionally comprising further layers (3, 4, 6).

[0075] FIG. 2 shows a schematic view of a solution coating process useful in method suitable for preparing a composite material.

[0076] FIG. 3 shows a schematic view of a calendering-based method suitable for preparing a composite material.

[0077] FIG. 4 shows a schematic view of an extrusion-based method suitable for preparing a composite material.

[0078] FIG. 5 shows alternative forming procedures suitable in a process of forming an acoustic membrane.

[0079] FIG. 6 shows results for a solvent resistance rub test performed with toluene for three comparable composite materials, wherein the materials were pretreated at the indicated temperature and the ordinate is labeled with the number of double rubs.

EXAMPLES

Different Arrangements for a Composite Material According to the Invention

[0080] FIGS. 1 A to N show different arrangements of composite materials according to the invention with at least one support layer 1 or 5 and a silicone layer 2. They may be composed for example as follows:

[0081] In the preferred arrangements of Fig. A to L a support layer is the bottom outer layer of the arrangement. Words such as “top” and “bottom” are not meant to indicate a certain orientation of the membrane, but are merely used to describe the figures in a pictorial way. Here, the support layer is a release layer 1 and said release layer 1 may be removed from the composite material. In the arrangements of Fig. H to L, the top outer layer is also a support layer being a release layer 1. Preferred materials for the release layer designated with 1 are for example PET film with one-sided siliconized surface, PET film with symmetric siliconized surfaces, PET film with differentiated siliconized surfaces, paper with one-sided olefin coating, paper with symmetrically olefin-coated surfaces, and paper with differentiated olefin coating on both sides. These layers preferably have a thickness in the range of 30 μm to 200 μm, for example around 100 μm.

[0082] Moreover, the preferred embodiments of FIG. 1 A to L share a first silicone layer 2 positioned directly adjacent to the release layer 1. Thus, the silicone layer 2 forms an outer layer after removal of the release layer 1, i.e. in a precursor for preparing an acoustic membrane. In embodiments of FIGS. 1 A, C, D, and F a second silicone layer 2 forms the top outer layer of the composite material. Thus, these silicone layers 2 are surfaced-exposed. In order to protect the fragile partially uncured silicone rubber in an outer layer, these embodiments should preferably be wound up to a roll for storage and transportation, wherein the support layer 1 is facing the outside of the roll. Consequently, also the top outer layer 2 is protected. In these cases an asymmetrically modified release layer 1 is preferred, i.e. with one-sided or differentiated modification, wherein the adhesion to the adjacent silicone layer should be considerably higher than the adhesion to the outside of the arrangement. This allows that the composite material can be unwound from the roll while maintaining its original arrangement.

[0083] The silicone layer in a composite material according to the invention preferably is a high-temperature vulcanizing silicone rubber, preferably a solid, two component material including a catalyst. Suitable silicone rubbers are commercially available. The silicone layer in the preferred embodiments has a thickness of below 100 μm, for example around 30 μm.

[0084] Furthermore, the multilayered arrangements with three or more layers may comprise a performance layer wherein the reference sign 3 indicates one or more damping layer(s) and the reference sign 4 indicates a reinforcement layer. Preferred materials for a damping layer 3 are soft materials. In the embodiments of FIGS. 1 A, B, D, E, H, I, K and L the damping layer consist of a material selected from the group consisting of an uncured silicone layer, a partially uncured silicone layer or a cured silicone layer, especially a silicone layer being softer than the silicone layer 2, a silicone gel or a pressure sensitive adhesive based on a silicone or acrylic material. A damping layer 3 preferably has a thickness in the range of 5 μm to 200 μm, for example 10 μm.

[0085] Preferred materials for the reinforcement layer 4 in embodiments of FIGS. 1 C, D, E, G, J, K and N may be PAEK, PEEK, e.g. perforated PEEK, PEI, PAR, PA, PET, PEN, PSU, PPSU, thermoplastic elastomers, silicones and also non-woven textile material such as fleece or also woven fabrics. The reinforcement layer preferably has a thickness in the range of below 20 μm or even below 10 μm, for example a 6 μm perforated PEEK layer.

[0086] In the embodiments of FIG. 1 M, the two support layers are structure layers 5. For example the layers 5 consist of cured silicone, e.g. thin silicone layers made out of the same starting materials as the adjacent silicone layer 2. However, the structure layers 5 are in the cured state. These embodiments allow for producing an acoustic material of a uniform silicone material. Additionally, this embodiment includes an optional layer 6, which may be formed by a material as described for the release layer and is removable.

[0087] FIG. 1 N shows an exemplary embodiment, wherein the support layer is a structure layer 5. This structure layer 5 is for example a cured silicone layer. Exemplarily, a structure layer being a cured silicone layer was investigated for mechanical properties and shown to have a Young's modulus above 3 MPa, e.g. around 4 MPa, and a tensile strength of 12 N/mm.sup.2 as measured for a strip of 20 mm and a thickness of 100 μm according to DIN EN ISO 527-1. In contrast, for a silicone layer comprising a partially uncured silicone rubber the deformation upon exposition of a tensile force is irreversible and therefore a Young's modulus can not be determined. The cured silicone as structure layer 5 protecting the underlying uncured silicone layer 2 was found to be extremely valuable for producing and handling of the composite material. For reasons of acoustic behavior and stability, it may be preferred that the composite material additionally comprises a further layer with higher mechanical stability. For example, in FIG. 1 N, the reinforcement layer 4 preferably is selected out of PAEK, PEEK, e.g. perforated PEEK, PEI, PAR, PA, PET, PEN, PSU, PPSU.

Preparation of a Composite Material According to the Invention by a Coating Procedure

[0088] FIG. 2 shows a schematic view of an in-line coating process, wherein the subsequent individual steps are operated from left to right as indicated by arrows. For production of a composite material according to the invention, first, a support layer, i.e. a rolled-up film or paper material, is provided from an unwind station K.

[0089] In the elongated state the support layer may be subjected to a surface treatment. For example the support layer may be exposed to plasma or corona treatment as indicated with L in FIG. 2. An advantage of these surface treatments may be a modified interaction of the support layer and the subsequently applied coating. However, the surface treatment is only optional in a method according to the invention.

[0090] Essential step of the coating process is the coating itself as indicated with C in FIG. 2. Here a solution of silicone rubber component(s) is applied on the support layer film. The inventors obtained a suitable solution for application in curtain coating with a solution of 20% by weight of a high-temperature vulcanizing Pt-catalyzed solid silicone material in toluene.

[0091] The large part of the solvent may be removed in a flotation dryer. In FIG. 2 a flotation dryer is visualized with multiple zones N1 to N5, wherein the temperature may be regulated individually in the zones. Removal of toluene for example was achieved with a temperature of below 80° C., for example with a maximum temperature of 70° C. These temperature ranges do not induce the curing of the silicone rubber and allow preparation of a composite material with an essentially uncured silicone rubber. Alternatively, temperatures above 80° C. may be shortly applied during drying, wherein partial curing is intended. Higher temperatures, e.g. above 100° C. may initiate the curing process. By use of different temperature zones the degree of curing may be controlled, e.g. by reducing the temperature in the subsequent zone. Thus, the coating process allows a person skilled in the art to vary the parameters in order to obtain an at least partially uncured silicone in the silicone layers with different degrees of pre-curing.

[0092] After flotation drying, schematically depicted with a second arrow in FIG. 2, a composite material according to an arrangement of FIG. 1 F is prepared. Optionally, further layers may be introduced. FIG. 2 shows an unwind station O, where another support layer, e.g. a release layer, may be provided to be placed on top of the silicone film before the composite material is rolled up. The resulting multi-layered composite material, for example in an arrangement according to FIG. 1 L, is rolled up on the rewind station P. The additional support layer provided on the unwind station O may also be a reinforcement layer yielding in an arrangement according to FIG. 1 G or the unwind station O may also provide a multi-layered film (e.g. another composite material according to the invention) to achieve more complex arrangements. The person skilled in the art may also easily concept an installation with an additional unwind stations to introduce further layers into the obtained composite material.

Preparation of a Composite Material by a Laminating Method

[0093] FIG. 3 shows a schematic view of an installation useful for an additional method for preparing a composite material according to the invention. Here, the components of an uncured silicone layer are provided directly in a feed 1, wherein the gear wheels symbolize a mean of mixing and displacing the solid or highly viscous silicone rubber material. The silicone mass is displaced by forced conveyance and fed forward to a calenderer visualized with two pressure rolls 2′ and 2″ rotating in opposite directions. Suitable parameters for calendering depend on the mechanical properties of the uncured silicone rubber.

[0094] After calendering, the uncured silicone rubber is deposited on a support layer. The support layer, e.g. a thermoplastic film or paper, is provided from an unwind station 3 and processed in the running direction as indicated by the arrow. Immediately, after depositing of the silicone on the support layer, the lamination process is continued by two calibrating rolls 4′ and 4″. Subsequently, the composite material 5 may be moved over several rolls along the running direction. Here, optionally different parameters may be selected for smoothening of the surface and controlling the thickness of the silicone layer. Also temperature gradients or irradiation may be applied to allow controlled pre-curing of the silicone rubber. Finally, the composite material is rolled up on the rewind station 6.

[0095] In a preferred variation, the method may be performed as indicated in FIG. 4. Here, the uncured silicone rubber is pre-processed in an extruder. The uncured silicone rubber is supplied to the barrel 7 of the extruder via the feed 1. Within the barrel 7 the silicone rubber is displaced by force conveyance, for example by a screw 8 which is moved by a motor 9. In order to prevent curing of the silicone rubber during processing in the extruder, the elements of the extruder being in contact with the silicone rubber mass are cooled. It is ensured that the temperature within the barrel 7 does not reach the critical temperature for vulcanizing the silicone rubber. The output of the extruder is subjected to a slot die 10 as indicated by the arrow. Especially, the die 10 should be cooled in order to prevent that the critical temperature for curing of the silicone is reached. Said die 10 may also be a multi-layer die allowing for generation of composite materials with more than two layers. The silicone rubber layer or multiple layers sorting from the slot die is/are deposited on a support layer. The subsequent processing of the laminate is conducted as described above.

Process for Producing an Acoustic Membrane

[0096] In a process of producing an acoustic membrane with a composite material according to the invention, the composite material first has to be prepared. The material should be cut into an appropriate size, said size being for example marginally larger than the intended dimension of the acoustic membrane for lateral allowance during forming. Additionally, the removal of one or more release layers may be a step in preparation of composite material. Thus, the precursor may preferably comprise the silicone layer as outer layer.

[0097] In a second step, curing of the silicone rubber is achieved to shape the precursor into the desired form of the acoustic membrane. Exemplary, suitable tools are schematically shown in FIG. 5. The flexible composite material or precursor 1 may be brought into the desired form by a shaping tool. The tools in FIG. 5 provide for example a shape that allows producing an acoustic membrane with a central recess. Generally the process of curing the silicone rubber in the silicone layer may be initiated by heat, if thermo-sensitive catalysts are comprised in the silicone rubber or alternatively by UV-light, if photo-initiators are present in the silicone rubber. Thermo-sensitive rubbers are preferred in composite materials according to the invention.

[0098] FIG. 5 A shows a thermoforming tool with a lower part 2 and an upper part 3, with the precursor being positioned between the two parts. The parts may be heated and by conduction the temperature in the silicone layer is raised to reach a temperature above the vulcanizing temperature. Thereby, curing of the high-temperature vulcanizing silicone is initiated or completed in case of partially cured silicone layer.

[0099] FIG. 5 B shows a variant of a thermoforming tool wherein the upper part 4 builds a pressure chamber. Vacuum or pressure may be applied to bring the precursor 1 into the desired shape, e.g. in this case by pressing the precursor 1 onto the lower part 2. For curing, the lower part of the thermoforming tool may be heated, or preferably forming in a pressure chamber may be combined with subsequent initiation of curing by radiation.

[0100] UV-radiation is the method of choice for curing UV-sensitive silicone rubbers. However, also thermo-sensitive silicone rubbers may be cured by radiation, e.g. by use of an infrared (IR) source. In FIG. 5 C, an IR source is indicated with the reference sign 5 to symbolize the initiation of curing by exposing the precursor 1 to thermal radiation. Heating via a radiation source is preferred because the onset and time of heating process can be controlled more accurately. Curing by radiation may be faster and more efficient than by heating the forming tool(s).

Solvent Resistance Rub Test

[0101] A solvent resistance rub test was performed in order to characterize the partially uncured silicone layer in composite materials according to the invention. The rub test is performed on basis of the standard ASTM D4752 and involves rubbing the surface of the silicone layer with cheesecloth soaked with toluene until failure or breakthrough of the film occurs. The type of cheesecloth, stroke distance, stroke rate, and approximately applied pressure of the rub should be identical for all tests. The higher the number of rubs, said rubs being counted as double rubs, the higher is the solvent resistance of the investigated layer. FIG. 6 shows the results for three composite materials, wherein all three have a silicone layer of 40 μm and they were heated to the indicated temperature for 5 min. The ordinate indicates the number of double rubs needed until failure or breakthrough of the respective material.

[0102] Heating to 140° C. results in a completely cured silicone layer, i.e. further curing for higher temperature or longer time did not result in increased solvent resistance. Thus, the composite material heated to 140° C. is a reference sample representing a cured state. The two embodiments heated to 100° C. or 120° C. are composite materials according to the invention with a partially uncured silicone rubber. The relative solvent resistance may be determined by dividing the achieved number of double rubs by the number of double rubs achieved with the completely cured reference material. The embodiment pre-treated at 100° C. has a relative solvent resistance of 9.8% and the embodiment pre-treated at 120° C. has a relative solvent resistance of 22.5%.