Polyethylene membrane and acoustic devices comprising a polyethylene membrane

Abstract

A polyethylene membrane which is air permeable, has a surface area per volume of less than 38 x 106 / m and has a thickness of from 0.5 μm to 5 μm is disclosed. The polyethylene membrane may be an acoustic cover, and may be used in an acoustic device. Also disclosed is an acoustic device comprising the polyethylene membrane and a method of making such an acoustic device.

Description

[0001] POLYETHYLENE MEMBRANE AND ACOUSTIC DEVICES COMPRISING A POLYETHYLENE MEMBRANE

[0002] FIELD

[0003] [1] This disclosure relates generally to polyethylene membranes, their use as acoustic covers and in acoustic devices, and processes for the preparation of the polyethylene membranes. This disclosure also relates to acoustic devices including the polyethylene membrane and methods for the manufacture of such acoustic devices.

[0004] BACKGROUND

[0005] [2] Acoustic membranes in acoustic devices can allow sound to propagate through and past the membrane and to and from an acoustic device. Acoustic membranes can also prevent ingress of water, dust, and other contaminants.

[0006] [3] US Patent No. 10 911 847 discloses a pressure equalizing assembly with a non- porous membrane traversing an acoustic pathway defined by an opening in a housing. The pressure equalizing assembly may have an insertion loss peak of not greater than 30 dB. Whilst the assembly may have a favorable insertion loss, their lack of air permeability of the non-porous membrane means that a breathable layer connected to at least a portion of the non-porous membrane is required to provide venting of the acoustic cavity.

[0007] [4] US 2014 / 0048351 discloses an acoustic protective cover assembly comprising a cover material such as porous membrane, and an acoustic gasket. The porous membrane is bonded to the acoustic gasket at a peripheral region. The porous membrane may be porous expanded polytetrafluoroethylene. Whilst the cover assembly had an acoustic insertion loss of less than 6 dB at 50% gasket compression, there is a desire to provide alternative porous membranes which are not-perfluoroalkyls or polyfluoroalkyl substances (PF AS).

[0008] [5] Thus, there is a need for improved membranes for acoustic devices, particularly those which are suitable for venting applications, prevent the ingress of contaminants, and exhibit good performance characteristics. In particular, a membrane which is air permeable for venting applications, prevents ingress of water and dust (including fine dust), is strong to withstand external pressure, exhibits low acoustic insertion loss, and is not fluorinated is desirable. SUMMARY

[0009] [6] In a first aspect, there is provided a polyethylene membrane. The polyethylene membrane may be air permeable, have a surface area per volume of less than 38 x 106 / m, and have a thickness of from 0.5 pm to 5 pm. In some embodiments, the polyethylene membrane may be an acoustic cover.

[0010] [7] In some embodiments, the polyethylene membrane has an air permeability as measured by the ATEQ airflow test described herein of 0.15 L / hr or more. In some embodiments, the polyethylene membrane has an air permeability as measured by the ATEQ airflow test described herein of from 0.15 L / hr to 500 L / hr.

[0011] [8] In some embodiments, the polyethylene membrane has a porosity of at least 5%. In some embodiments, the polyethylene membrane has a porosity of from 7% to 85%. In some embodiments, the polyethylene membrane has a porosity of from 7% to 60%.

[0012] [9] In some embodiments, the polyethylene membrane comprises polyethylene or modified polyethylene having an average molecular weight from 500,000 g / mol to 10,000,000 g / mol.

[0013]

[0010] In some embodiments, the polyethylene membrane has a mean mass per area of 2 gm'2or less.

[0014]

[0011] In some embodiments, the polyethylene membrane has a basis weight of from 0.7 gm'2to 1.8 gm'2.

[0015]

[0012] In some embodiments, the polyethylene membrane has an extended Water Entry Pressure of at least 30 minutes at 1 m. In some embodiments, the polyethylene membrane has an extended Water Entry Pressure of at least 30 minutes at 10 m. In some embodiments, the polyethylene membrane has an extended Water Entry Pressure pass rate of greater than 90%. In some embodiments, the polyethylene membrane has an extended Water Entry pass rate of 100%.

[0016]

[0013] In some embodiments, the polyethylene membrane has a surface area per volume in a range of from 4 x 105to 38 x 106 / m.

[0017]

[0014] In some embodiments, the polyethylene membrane has a mean acoustic insertion loss at 1 kHz of less than or equal to 1.9 dB. In some embodiments, the polyethylene membrane has a mean acoustic insertion loss at 1 kHz in a range of from 0.2 to 1.9 dB.

[0018]

[0015] In some embodiments, the polyethylene membrane has a bulk density in the range of from 0.30 to 0.87 g / cm3.

[0019]

[0016] In some embodiments, the polyethylene membrane has one or more of the following properties: a mean acoustic insertion loss at 1 kHz in a range of from 0.5 to 1.6 dB; an extended Water Entry Pressure (eWEP) of greater than or equal to 30 min at 10 m; a thickness in the range of from 0.7 pm to 4.0 pm; a basis weight of from 0.75 gm'2to 1.75 gm'2; an air permeability as measured by the ATEQ airflow test described herein of from 0.35 L / hr to 25 L / hr; a bubble point pressure in the range of from 25 psi to 150 psi; a surface area per volume in a range of from 5 x 106to 35 x 106 / m; a porosity in the range of from 7% to 60%; a bulk density in the range of from 0.35 cm3to 0.87 cm3; a Darcy permeability in the range of from 6 x 10'18to 9 x 10'16m2; a machine direction matrix tensile strength in the range of from 100 to 475 MPa; and a transverse direction matrix tensile strength in the range of from 170 to 350 MPa.

[0020]

[0017] In some embodiments, the polyethylene membrane comprises a coating. In some embodiments, the coating comprises an oleophobic coating.

[0021]

[0018] In some embodiments, the polyethylene membrane comprises an adhesive portion.

[0022]

[0019] In some embodiments, the polyethylene membrane is an acoustic cover.

[0023]

[0020] In a second aspect, the polyethylene membrane of the first aspect may be prepared by the following process: dissolving a polyethylene polymer in a solvent to form a solution; shaping the solution into a tape at a temperature above the solution temperature of the polyethylene polymer; cooling the tape to a temperature below the solution temperature to achieve gelation of the tape; removing the solvent from the gelled tape; and biaxially stretching the gelled tape at a temperature above the melting temperature of the polyethylene polymer to form the polyethylene membrane.

[0024]

[0021] In some embodiments of the second aspect, the process further comprises the step of compressing the gelled tape above the melting temperature of the polyethylene polymer before, during or after the biaxial stretching. For instance, after stretching the gelled tape in the machine direction, it may be subjected to a step of compressing at a temperature above the melting point of the polyethylene polymer. Alternatively, the step of compressing the gelled tape may be carried out after the step of biaxially stretching the gelled tape, e.g. after stretching in both the machine direction and transverse direction.

[0025]

[0022] In a third aspect, the polyethylene membrane of the first aspect may be prepared by the following process: providing a paste comprising polyethylene polymer and a lubricant; shaping the paste into a tape; removing the lubricant from the tape to form a dry polyethylene tape; compressing the dry polyethylene tape at a temperature below the melting temperature of the polyethylene polymer; and biaxially stretching the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer and / or compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer to form the polyethylene membrane.

[0026]

[0023] In some embodiments of the third aspect, the polyethylene tape is biaxially stretched at a temperature above the melting temperature of the polyethylene polymer without the step of compressing of the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer. In some embodiments, the polyethylene tape is compressed at a temperature above the melting temperature of the polyethylene polymer without the step of biaxial stretching the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer.

[0027]

[0024] In some embodiments of the third aspect, both of the steps of biaxial stretching of the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer and compression of the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer are carried out. In some embodiments of the third aspect, the step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer is carried out before, during or after the biaxial stretching. For instance, after stretching the polyethylene tape in a machine direction, it may be subjected to a step of compressing the polyethylene tape at a temperature above the melting point of the polyethylene polymer before stretching the polyethylene tape in the transverse direction. Alternatively, the step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out after the step of biaxially stretching the polyethylene tape, e.g. after stretching in both the machine direction and transverse direction.

[0028]

[0025] In some embodiments of the second and third aspects, the biaxial stretching may comprise stretching in the machine direction and the transverse direction. In some embodiments of the second and third aspects, one or both of the stretching in the machine direction and the transverse direction may be repeated under different conditions. For instance, stretching in the transverse direction may be carried out twice i.e. a first transverse stretching and a second transverse stretching. The second transverse stretching may be carried out at a lower expansion ratio and / or run speed than the first transverse stretching.

[0029]

[0026] In some embodiments of the second and third aspects, the stretching in a machine direction may be carried out at a temperature in the range of from 115 to 135 °C. In some embodiments, the stretching in a machine direction may be carried out at an expansion ratio in the range of from 1.4:1 to 8: 1. In some embodiments, the stretching in a machine direction may be carried out at a strain rate in the range of from 2 to 17% / s. In some embodiments, the stretching in a machine direction may be carried out at a run speed in the range of from 0.75 to 6 m / min.

[0030]

[0027] In some embodiments of the second and third aspects, the stretching in a transverse direction may be carried out at a temperature in the range of from 120 to 146 °C. In some embodiments, the stretching in a transverse direction may be carried out at an expansion ratio in the range of from 3:1 to 12: 1. In some embodiments, the stretching in a transverse direction may be carried out at a strain rate in the range of from 1.5 to 17% / s. In some embodiments, the stretching in a transverse direction may be carried out at a run speed in the range of from 1 to 21 m / min.

[0031]

[0028] In some embodiments of the second and third aspects, the step of compressing the gelled tape or the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out at a temperature in the range of from 115 to 135 °C. In some embodiments, the step of compressing the gelled tape or the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out at a line force in the range of from 150 to 450 N / mm. The step of compressing the gelled tape or the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out at a run speed in the range of from 1 to 6 m / min.

[0032]

[0029] In a fourth aspect, the polyethylene membrane of the first aspect may be prepared by the following process: dissolving a polyethylene polymer in a solvent to form a solution; shaping the solution into a tape at a temperature above the solution temperature of the polyethylene polymer; cooling the tape to a temperature below the solution temperature to achieve gelation of the tape; removing the solvent from the gelled tape; and biaxially stretching the gelled tape at a stretching temperature from 115°C to 170°C to form the polyethylene membrane.

[0033]

[0030] In some embodiments of the fourth aspect, the process further comprises the step of compressing the gelled tape at a compressing temperature from 115 to 135 °C before, during or after the biaxial stretching. For instance, after stretching the gelled tape in the machine direction, it may be subjected to a step of compressing at a compressing temperature from 115 to 135 °C. Alternatively, the step of compressing the gelled tape may be carried out after the step of biaxially stretching the gelled tape, e.g. after stretching in both the machine direction and transverse direction. In some embodiments, the compressing temperature is from 120 to 135 °C.

[0031] In a fifth aspect, the polyethylene membrane of the first aspect may be prepared by the following process: providing a paste comprising polyethylene polymer and a lubricant; shaping the paste into a tape; removing the lubricant from the tape to form a dry polyethylene tape; compressing the dry polyethylene tape at a compressing temperature below 115°C; and biaxially stretching the polyethylene tape at a stretching temperature from 115°C to 170°C and / or compressing the polyethylene tape at a compressing temperature from 115 to 135 °C to form the polyethylene membrane.

[0034]

[0032] In some embodiments of the fifth aspect, the compressing of the polyethylene tape may be carried out at a compressing temperature from 120°C to 135°C.

[0035]

[0033] In some embodiments of the fifth aspect, the polyethylene tape is biaxially stretched at a stretching temperature from 115°C to 170°C without the step of compressing of the polyethylene tape at a compressing temperature from 115 to 135 °C. In some embodiments, the polyethylene tape is compressed at a compressing temperature from 115 to 135 °C without the step of biaxial stretching the polyethylene tape at a stretching temperature from 115°C to 170°C.

[0036]

[0034] In some embodiments of the fifth aspect, both of the steps of biaxial stretching of the polyethylene tape a stretching temperature from 115°C to 170°C and compression of the polyethylene tape at a compressing temperature from 115 to 135 °C are carried out. In some embodiments of the third aspect, the step of compressing the polyethylene tape at a compressing temperature from 115 to 135 °C is carried out before, during or after the biaxial stretching. For instance, after stretching the polyethylene tape in a machine direction, it may be subjected to a step of compressing the polyethylene tape at a compressing temperature from 115 to 135 °C before stretching the polyethylene tape in the transverse direction. Alternatively, the step of compressing the polyethylene tape at a compressing temperature from 115 to 135 °C may be carried out after the step of biaxially stretching the polyethylene tape, e.g. after stretching in both the machine direction and transverse direction.

[0035] In some embodiments of the fourth and fifth aspects, the biaxial stretching may be carried out at a stretching temperature from 115°C to 150°C.

[0037]

[0036] In some embodiments of the fourth and fifth aspects, the biaxial stretching may comprise stretching in the machine direction and the transverse direction. In some embodiments of the fourth and fifth aspects, one or both of the stretching in the machine direction and the transverse direction may be repeated under different conditions. For instance, stretching in the transverse direction may be carried out twice i.e. a first transverse stretching and a second transverse stretching. The second transverse stretching may be carried out at a lower expansion ratio and / or run speed than the first transverse stretching.

[0038]

[0037] In some embodiments of the fourth and fifth aspects, the stretching in a machine direction may be carried out at a temperature in the range of from 115 to 135 °C. In some embodiments, the stretching in a machine direction may be carried out at an expansion ratio in the range of from 1.4:1 to 8: 1. In some embodiments, the stretching in a machine direction may be carried out at a strain rate in the range of from 2 to 17% / s. In some embodiments, the stretching in a machine direction may be carried out at a run speed in the range of from 0.75 to 6 m / min.

[0039]

[0038] In some embodiments of the fourth and fifth aspects, the stretching in a transverse direction may be carried out at a temperature in the range of from 120 to 146 °C. In some embodiments, the stretching in a transverse direction may be carried out at an expansion ratio in the range of from 3:1 to 12: 1. In some embodiments, the stretching in a transverse direction may be carried out at a strain rate in the range of from 1.5 to 17% / s. In some embodiments, the stretching in a transverse direction may be carried out at a run speed in the range of from 1 to 21 m / min.

[0040]

[0039] In some embodiments of the fourth and fifth aspects, the step of compressing the gelled tape or the polyethylene tape at a compressing temperature from 115 to 135 °C may be carried out at a line force in the range of from 150 to 450 N / mm. The step of compressing the gelled tape or the polyethylene tape at a compressing temperature from 115 to 135 °C may be carried out at a run speed in the range of from 1 to 6 m / min.

[0041]

[0040] In a sixth aspect, the use of the polyethylene membrane described herein as an acoustic cover is provided.

[0041] In a seventh aspect, the use of the polyethylene membrane described herein in an acoustic device is provided.

[0042]

[0042] In some embodiments of the use of the seventh aspect, the acoustic device comprises a housing defining an interior and exterior of the acoustic device, the housing comprising at least one opening in communication with the exterior of the acoustic device and a sound transducer, the sound transducer being positioned within the housing, and wherein the polyethylene membrane is used to cover the at least one opening of the housing to prevent ingress of water, dust and / or other contaminants.

[0043]

[0043] In an eighth aspect, an acoustic device comprising the polyethylene membrane described herein is provided.

[0044]

[0044] In some embodiments, the acoustic device is one of a speaker, a microphone, or any combination thereof.

[0045]

[0045] In some embodiments, the acoustic device comprises a housing defining an interior and exterior of the acoustic device. In some embodiments, the acoustic device comprises a sound transducer positioned within the housing. In some embodiments, the housing comprises at least one opening in communication with the exterior of the acoustic device and the polyethylene membrane covers the at least one opening. In some embodiments, the polyethylene membrane is affixed to the housing with an adhesive. In some embodiments, a stiffener plate covers the at least one opening of the housing, thereby providing support to the polyethylene membrane.

[0046]

[0046] In a ninth aspect, a method of making an acoustic device is provided, the method comprising the steps of:

[0047] (i) providing a housing, a sound transducer and a polyethylene membrane, wherein the housing comprises at least one opening in communication with an exterior of the acoustic device;

[0048] (ii) positioning the sound transducer within the housing; and

[0049] (iii) covering the at least one opening of the housing in communication with the exterior of the acoustic device with the polyethylene membrane.

[0050]

[0047] In some embodiments, the method further comprises the step of fixing the polyethylene membrane to the housing with an adhesive.

[0048] In some embodiments, the method further comprises the step of providing a stiffener plate and positioning the stiffener plate to cover the at least one opening of the housing, thereby providing support to the polyethylene membrane.

[0051] BRIEF DESCRIPTION OF THE DRAWINGS

[0052]

[0049] References are made to the accompanying drawings that form a part of this disclosure and that illustrate embodiments in which the systems and methods described in this Specification can be practiced.

[0053]

[0050] Figure 1 (FIG. 1) illustrates a schematic representation of an acoustic device according to an embodiment of the present disclosure.

[0054]

[0051] Figure 2 (FIG. 2) shows a schematic representation of the acoustic device of Figure 1, additionally comprising a perforated stiffener plate, according to an embodiment of the present disclosure.

[0055]

[0052] Figure 3 (FIG. 3) shows a schematic representation of the acoustic device of Figure 1, additionally comprising an anti-static layer, according to an embodiment of the present disclosure.

[0056]

[0053] Like reference numbers represent the same or similar parts throughout.

[0057] DETAILED DESCRIPTION

[0058]

[0054] There is an ongoing need for improved acoustic membranes. Some embodiments described herein can advantageously achieve appreciable acoustic performance as exhibited by a low mean insertion loss while providing air permeability and mechanical protection in immersion applications.

[0059]

[0055] [Polyethylene membrane]

[0060]

[0056] The present disclosure provides a polyethylene membrane. The polyethylene membrane is air permeable, has a surface area per volume of less than 38 x 106 / m, and has a thickness of from 0.5 pm to 5 pm.

[0061]

[0057] As used herein, the term “membrane” refers to an article, such as a sheet-like article, having three dimensions defined by three mutually perpendicular axes or directions in which two of the dimensions are typically larger than the third. For instance, the two larger dimensions are at least an order of magnitude greater than the smallest, third, dimension. Thus, the smallest, third dimension may represent the thickness of the membrane. This thickness can be measured along the third axis or direction, referred to herein as the thickness direction of the membrane.

[0062]

[0058] The membrane may have opposing first and second surfaces, in which the surfaces are separated by the thickness of the membrane i.e. the shortest distance between opposing first and second surfaces of the membrane. This distance may be defined by a line orthogonal to the planes of both of the first and second surfaces. Thus, the thickness direction may be a direction parallel to a line defining the thickness of the membrane.

[0063]

[0059] The first and second axes or directions are both orthogonal to the thickness direction of the membrane. The first and second directions therefore define a plane perpendicular to the thickness direction of the membrane. The plane defined by the first and second directions is therefore parallel to or overlaps with the planar sheet of the membrane.

[0064]

[0060] In some embodiments, the first direction is selected from one of the longitudinal (machine) direction and transverse direction of the membrane and the second direction is selected from the other of the longitudinal direction and transverse direction of the membrane. In some embodiments, the first direction is selected from one of the machine direction and transverse direction of the membrane and the second direction is selected from the other of the machine direction and transverse direction of the membrane.

[0065]

[0061] The polyethylene membrane has a thickness of from about 0.5 pm to about 5.0 pm, wherein the first and second directions are each orthogonal to the thickness direction. A membrane thickness of from about 0.5 pm to about 5.0 pm is beneficial for sound transmission, because generally the thinner the membrane, the better the sound transmission through the membrane. For example, a given membrane having a thickness of >5 pm would generally have more sound transmission loss relative to an identical membrane differing only in that it has a thickness of less than about <5.0 pm.

[0066]

[0062] The polyethylene membrane has a thickness of at least 0.5 pm. An excessively thin membrane may have poor mechanical and strength properties.

[0067]

[0063] In some embodiments, the polyethylene membrane may have a thickness of from about 0.6 pm to about 4.5 pm, or from about 0.7 pm to about 4.0 pm. Such a membrane thickness results in excellent sound transmission properties.

[0064] The polyethylene membrane thickness is measured as indicated in the test methods described herein as a mean thickness. The membrane thickness may be the non-contact thickness when the membrane is translucent or semi-translucent. This is because the measurement of non-contact thickness is carried out by an optical technique using the laser system described below. When the polyethylene membrane is opaque, such as in a more dense membrane, an optical technique for the measurement of membrane thickness is not appropriate and so contact thickness is measured by a motorised height gage as described below.

[0068]

[0065] As used herein, the term “air permeable” means that the polyethylene membrane has an airflow of at least 0.15 L / hr when evaluated based on the ATEQ test described herein. In some embodiments, air permeability is defined by an airflow in the range of from 0.15 L / hr to 500 L / hr, when evaluated based on the ATEQ test described herein. In some embodiments, air permeability is defined by an airflow in the range of from 0.20 L / hr to 400 L / hr, or from 0.25 L / hr to 300 L / hr, or from 0.30 L / hr to 200 L / hr, or from 0.35 L / hr to 25 L / hr when evaluated based on the ATEQ test described herein.

[0069]

[0066] Such flow rates are beneficial when the polyethylene membrane is used as a vent, particularly for membrane applications meeting the ingress protection (IP) standards. The polyethylene membrane prevents contaminants crossing the membrane and thereby contaminating any acoustic device protected by the membrane, for instance by meeting the IP6 standard for the prevention of the ingress of dust. The polyethylene membrane may also resist water entry, for instance meeting the IP68 standard for the prevention of ingress of water when immersed at a depth of at least 1 meter, as measured by extended Water Entry Pressure (eWEP). In some embodiments, the polyethylene membrane may resist water entry at pressures of at least 0.1 bar, such as in the range of from 10 to 60 MPa. In some embodiments, the polyethylene membrane may also resist liquid water entry, for instance by exhibiting a 100% pass rate, when immersed at a depth of at least 1 meter or at least 2 meters for at least 30 minutes, as measured by extended Water Entry Pressure (eWEP). In some embodiments, the polyethylene membrane may also resist liquid water entry, for instance by exhibiting at least a 90% pass rate, preferably a 100% pass rate, when immersed at a depth of at least 10 meters for at least 30 minutes, as measured by extended Water Entry Pressure (eWEP). Such immersion resistance performances provide a polyethylene membrane suitable for use as an acoustic cover in smartwatches.

[0067] The polyethylene membrane may also prevent water vapor entering an acoustic device where it may condense and cause the device to malfunction. The polyethylene membrane also has sufficient air permeability to allow for pressure equilibration between the two sides of the membrane, for instance between the external environment and the inside of an acoustic device through the membrane. This air permeability is represented by an airflow of at least 0.15 L / hr when evaluated based on the ATEQ test described herein.

[0070]

[0068] Some embodiments of the present disclosure are directed to a predominantly reactive acoustic membrane. In a predominantly reactive mode, sound transmits through a combination of the vibration of the membrane in the active area and within the gas phase in open porosity of the membrane.

[0071]

[0069] The polyethylene membrane has a surface area per volume of less than 38 x 106 / m. The surface area per volume may be calculated from the surface area per unit mass (SSA) as described below. The polyethylene membrane may have a surface area per volume of greater than or equal to 4 x 105 / m. In embodiments, the polyethylene membrane has a surface area per volume in a range of from 4 x 105 / m to 38 x 106 / m, or in a range of from 1 x 106 / m to 36 x 106 / m or in a range of from 5 x l06 / m to 35 x 106 / m.

[0072]

[0070] The polyethylene membrane may further comprise an oleophobic coating. The oleophobic coating may be present on one or both of the opposed external surfaces of the membrane. The oleophobic coating may also cover at least a portion of the internal surface of the polyethylene membrane, such as a portion of internal pores of the polyethylene membrane. The oleophobic coating may be selected from the group consisting of: perfluoroalkyls and polymers and copolymers of perfluoroalkyls such as Fluoropel 800 supplied by Cytonix, LL. and Fluorinert FC-84 supplied by 3M.

[0073]

[0071] The polyethylene membrane may further comprise one or more adhesive regions. The one or more adhesive regions may be present on one or both of the opposed external surfaces of the membrane. An adhesive region may be arranged around the perimeter of one or both of the external surfaces of the membrane. The adhesive region may comprise an adhesive, such as a pressure sensitive adhesive, a heat activated adhesive or a UV activated adhesive. The adhesive may be (i) an acrylic pressure sensitive adhesive such as Tesa® 75720 reinforced acrylic adhesive foam tape, Tesa® 4972 acrylic double-sided reinforced tape, an acrylic / silicone adhesive such as Tesa® 61532, a monolithic acrylic adhesive such as Tesa® 63305 or a bio-acrylic such as Tesa® 68875 supplied by Tesa SE or (ii) a phenolic resin / nitrile rubber heat activated film adhesive such as Tesa® 58469 supplied by Tesa SE or (iii) a UV activated acrylic adhesive such as AC-99005DT supplied by Advanced Adhesive Technology.

[0074]

[0072] Also significant to sound transmission loss is the mean mass per area of the membrane. The polyethylene membrane may have a mean mass per area of < 2.0 g / m2. The polyethylene membrane may have a mean mass per area of > 0.7 g / m2. The polyethylene membrane may have a mean mass per area of from about 0.7 g / m2to about 2.0 g / m2. A membrane mean mass per area of from about 0.7 g / m2to about 2.0 g / m2is beneficial for sound transmission, because generally the lower the mean mass per area of a membrane, the lower the sound transmission loss. For example, a membrane having a mean mass per area of 5 g / m2would generally have more sound transmission loss relative to an identical membrane differing only in that it has a mean mass per area of less than or equal to 2 g / m2.

[0075]

[0073] In some embodiments, the polyethylene membrane may have a mean mass per area of from about 0.6 g / m2to about 1.9 g / m2, or from about 0.7 g / m2to about 1.8 g / m2, or from about 0.75 g / m2to about 1.75 g / m2. Such a membrane mean mass per area results in excellent sound transmission properties.

[0076]

[0074] The mean mass per area of a membrane is measured as indicated in the test methods described herein. For a given polyethylene bulk density, the mean mass per area is related to the thickness of the membrane.

[0077]

[0075] In some embodiments, the polyethylene membrane may have a bubble point pressure of at least 25 psi. For example, the bubble point pressure may be in a range of from 25 psi to 150 psi.

[0078]

[0076] The polyethylene membrane has a geometric mean 5-point modulus of at least about 750 MPa. This ensures that the membrane has suitable strength properties to function effectively as an acoustic cover. A geometric mean 5-point modulus of at least about 750 MPa ensures that the membrane does not deform excessively under external pressure. Specifically, the membrane is strong enough to withstand external pressure. A membrane having an excessively low geometric mean 5-point modulus would have poor mechanical and strength properties.

[0079]

[0077] Moreover, the membrane should be elastic so that when the external pressure is released, the membrane may deform back to its original position or close to its original position, without being permanently stretched.

[0080]

[0078] In some embodiments, the polyethylene membrane may have a geometric mean 5-point modulus of at least about 800 MPa, or at least about 900 MPa, or at least about 1000 MPa, or at least about 1400 MPa. The polyethylene membrane may have a geometric mean 5 point-modulus of from about 800 MPa to about 5000 MPa, or from about 900 MPa to about 4000 MPa, or from about 1000 MPa to about 3000 MPa.

[0081]

[0079] The geometric mean 5-point modulus is defined as the square root of the product of the mean 5-point modulus in the first direction and the mean 5-point modulus in the second direction.

[0082] 5-point modulus g,e,o,— mean

[0083] = I / mean 5- p r*oint modulus f,i.rst . d .i.rect .i.on X mean 5- point modulus second . d.i.rection

[0084]

[0080] Thus, the mean 5-point modulus in the first direction and the mean 5-point modulus in the second direction are related to the geometric mean 5-point modulus.

[0085]

[0081] In some embodiments, the polyethylene membrane may have a mean 5-point modulus in the machine direction of at least about 700 MPa, or at least about 750 MPa, or at least about 800 MPa. The polyethylene membrane may have a mean 5-point modulus in the machine direction of from about 700 MPa to about 9000 MPa, or from about 750 MPa to about 8000 MPa, or from about 800 MPa to about 6500 MPa.

[0086]

[0082] In some embodiments, the polyethylene membrane may have a mean 5-point modulus in the transverse direction of at least about 400 MPa, or at least about 500 MPa, or at least about 600 MPa, or at least about 650 MPa. The polyethylene membrane may have a mean 5-point modulus in the transverse direction of from about 400 MPa to about 4000 MPa, or from about 500 MPa to about 3000 MPa, or from about 650 MPa to about 2750 MPa

[0087]

[0083] The mean 5-point modulus for each direction is calculated as indicated in the test methods described herein.

[0084] The polyethylene membrane may be formed from a polyethylene polymer comprising high and ultrahigh molecular weight polyethylene. In the context of the present disclosure, high and ultrahigh molecular weight polyethylene refers to polyethylene having an average molecular weight of about 500,000 g / mol to about 10,000,000 g / mol. The average molecular weight may refer to the weight average molecular weight, such as the weight viscosity-average molecular weight. The weight viscosity-average molecular weight may be calculated from the intrinsic viscosity, as discussed in for example Pure Appl. Chem. 2020; 92(9): 1469-1483. In some embodiments, the high and ultrahigh molecular weight polyethylene polymer has an average molecular weight of about 1,000,000 to about 10,000,000 g / mol, or about 2,000,000 g / mol to about 10,000,000 g / mol, or about 4,000,000 g / mol to about 8,000,000 g / mol.

[0088]

[0085] As used herein, the terms “melting point” and “melting temperature” are used interchangeably.

[0089]

[0086] In some embodiments, the polyethylene membrane may have a mean matrix tensile strength (MTS) in the machine direction of at least about 75 MPa, or of at least about 100 MPa. The polyethylene membrane may have a mean matrix tensile strength (MTS) in the machine direction in a range of from about 75 MPa to about 500 MPa, or from about 100 MPa to about 475 MPa.

[0090]

[0087] In some embodiments, the polyethylene membrane may have a mean matrix tensile strength (MTS) in the transverse direction of at least about 150 MPa, or of at least about 170 MPa. The polyethylene membrane may have a mean matrix tensile strength (MTS) in the transverse direction in a range of from about 150 MPa to about 375 MPa, or from about 170 MPa to about 350 MPa.

[0091]

[0088] In some embodiments, the polyethylene membrane may have a geometric mean matrix tensile strength (MTS) of at least about 100 MPa, or of at least about 150 MPa, or of at least about 180 MPa. The polyethylene membrane may have a geometric mean matrix tensile strength (MTS) in a range of from about 100 MPa to about 600 MPa, or from about 150 MPa to about 400 MPa, or from about 180 MPa to about 375 MPa.

[0092]

[0089] The geometric mean matrix tensile strength (MTS) = square root of the product of the mean MTS in the machine direction and the mean MTS in the transverse direction. irection mean MTSjranspersedirection

[0093]

[0090] The mean matrix tensile strength for each direction is calculated as indicated in the test methods described herein.

[0094]

[0091] In some embodiments, the polyethylene membrane may have a bulk density of at least about 0.30 g / cm3, or at least about 0.35 g / cm3. The polyethylene membrane may have a bulk density of less than or equal to about 0.87 g / cm3, or less than or equal to about 0.80 g / cm3. In some embodiments, the polyethylene membrane may have a bulk density of from about 0.30 g / cm3to about 0.87 g / cm3, or from about 0.35 g / cm3to about 0.87 g / cm3. In some embodiments, the polyethylene membrane may have a porosity of at least about 5%, or of least about 7%. The polyethylene membrane may have a porosity of less than or equal to about 85% or of less than or equal to about 80%, or of less than or equal to about 70%, or of less than or equal to about 60%. The polyethylene membrane may have a porosity in the range of from about 5% to about 85%, or from about 5% to about 80%, or from about 7% to about 80% or from about 7% to about 70%, or from about 7% to about 60%.

[0095]

[0092] In some embodiments, the polyethylene membrane may have a Darcy permeability of at least about 6 x 10'18m2, or of at least about 7 x 10'18m2. The polyethylene membrane may have a Darcy permeability of less than or equal to about 0.9 x 10’15m2. The polyethylene membrane may have a Darcy permeability in the range of from about 6 x 10'18m2to about 0.9 x 10'15m2.

[0096]

[0093] In some embodiments, the polyethylene membrane may have an extended Water Entry Pressure (eWEP) of greater than or equal to 30 min at 1 m. The polyethylene membrane may have an extended Water Entry Pressure (eWEP) of greater than or equal to 30 min at 10 m. The polyethylene membrane may have an eWEP pass of at least 90%, or 100%.

[0097]

[0094] In some embodiments, the polyethylene membrane may have mean insertion loss at 1 kHz of less than or equal to about 1.9 dB, or of less than or equal to about 1.8 dB, or of less than or equal to about 1.7 dB, or of less than or equal to about 1.6 dB. The polyethylene membrane may have a mean insertion loss at 1 kHz of at least about 0.2 dB, or of at least about 0.3 dB, or of at least about 0.4 dB, or of at least about 0.5 dB. The polyethylene membrane may have a mean insertion loss at 1 kHz of from about 0.2 to about 1.9 dB, or of from about 0.3 to about 1.8 dB, or of from about 0.4 to about 1.7 dB, or of from about 0.5 to about 1.6 dB, or from about 0.55 to about 1.55 dB.

[0098]

[0095] In some embodiments, the polyethylene membrane may have mean insertion loss at 3.15 kHz of less than or equal to about 2.1 dB, or of less than or equal to about 1.9 dB, or of less than or equal to about 1.7 dB, or of less than or equal to about 1.5 dB. The polyethylene membrane may have a mean insertion loss at 3.15 kHz of at least about 0.2 dB, or of at least about 0.3 dB, or of at least about 0.4 dB, or of at least about 0.5 dB. The polyethylene membrane may have a mean insertion loss at 3.15 kHz of from about 0.2 to about 2.1 dB, or of from about 0.3 to about 1.9 dB, or of from about 0.4 to about 1.7 dB, or of from about 0.5 to about 1.5 dB.

[0099]

[0096] In some embodiments, the polyethylene membrane may have mean insertion loss at 10 kHz of less than or equal to about 2.1 dB, or of less than or equal to about 1.9 dB, or of less than or equal to about 1.7 dB, or of less than or equal to about 1.4 dB. The polyethylene membrane may have a mean insertion loss at 10 kHz of at least about 0.2 dB, or of at least about 0.3 dB, or of at least about 0.35 dB. The polyethylene membrane may have a mean insertion loss at 10 kHz of from about 0.2 to about 2.1 dB, or of from about 0.3 to about 1.7 dB, or of from about 0.35 to about 1.4 dB.

[0100]

[0097] The mean insertion loss (dB) is measured as indicated in the test methods described herein.

[0101]

[0098] [Method of making the polyethylene membrane]

[0102]

[0099] The method of making the polyethylene membrane is not particularly limited and any method known in the art may be used, as long as the membrane has the required properties.

[0103]

[0100] The polyethylene membrane is formed from a polyethylene polymer comprising high or ultrahigh molecular weight polyethylene. As discussed above, in the context of the present disclosure, high or ultrahigh molecular weight polyethylene refers to polyethylene having an average molecular weight of about 500,000 g / mol to about 10,000,000 g / mol. In some embodiments, the ultrahigh molecular weight polyethylene polymer has an average molecular weight of about 1,500,000 to about 10,000,000 g / mol, or about 2,000,000 g / mol to about 10,000,000 g / mol, or about 4,000,000 g / mol to about 8,000,000 g / mol.

[0101] The high or ultrahigh molecular weight polyethylene polymer may be a homopolymer of ethylene or a copolymer of ethylene and at least one comonomer. Suitable copolymers include an alpha-olefin or a cyclic olefin having 3 to 20 carbon atoms, such as 1 -butene, 1 -pentene, 1 -hexene, 1 -heptene, 1 -octene, cyclohexene, and dienes with up to 20 carbon atoms. The comonomer may be present in the polyethylene copolymer in an amount of from 0.001 mol% to 10 mol%, or from 0.01 mol% to 5 mol%, or from 0.1 mol% to 1 mol%.

[0104]

[0102] The polyethylene polymer may also comprise a blend of high or ultrahigh molecular weight polyethylene and polyethylene having a relatively lower molecular weight, such as polyethylene having an average molecular weight of below about 500,000 g / mol.

[0105]

[0103] One method known in the art to produce porous polyethylene membranes is through a wet or gel process. In this process, polyethylene is mixed with a hydrocarbon liquid and other additives. This mixture is heated over the polymer melt and extruded into a sheet. This sheet can then be orientated biaxially before and / or after the hydrocarbon liquid is extracted, producing a microporous membrane. Various process details are known, such as those disclosed in US 4,873,034; US 5,051,183; 5,248,461; 5,643,511; US 6,566,012; and US 8,465,565 each of which are hereby incorporated- by-reference in their entirety. Additional discussion includes Casting and stretching of filled and unfilled UHMW-polyethylene films, Ir.F.H. Assinck, Centre for polymers and composites, Eindhoven University of Technology, Nov 1995 and Porous Biaxially, drawn UHMWPE Films, H.M. Fortuin, DSM Research BV, Department of Materials Technology - Fifth Int. Conf, of Environmental Ergonomics.

[0106]

[0104] The polyethylene membrane of the present disclosure may be made by a “gel process” for producing a polyethylene film, which is described in numerous documents such as US 4,948,544. The polyethylene membrane may be prepared by the following process: (i) dissolving a polyethylene polymer in a solvent to form a solution; (ii) shaping the solution into a tape at a temperature above the solution temperature of the polyethylene polymer; (iii) cooling the tape to a temperature below the solution temperature to achieve gelation of the tape; (iv) removing the solvent from the gelled tape; and (v) biaxially stretching the gelled tape at a stretching temperature from 115°C to 170°C to form the polyethylene membrane. In embodiments, the stretching temperature may be from 115°C to 150°C.

[0105] For example, the polyethylene membrane may be formed by dissolving a polyethylene polymer in a solvent to form a solution, shaping the solution into a tape or sheet at a temperature above the solution temperature of the polyethylene polymer, cooling the tape or sheet to a temperature below the solution temperature to achieve gelation of the tape or sheet, removing the solvent from the gelled tape or sheet and uniaxially or biaxially stretching the gelled tape or sheet above the melting temperature to form the polyethylene membrane, heated compression or a combination thereof and in any order, including repeats or omissions of process steps detailed in the examples below.

[0107]

[0106] Alternatively, the polyethylene membrane may be formed via a “paste-process”, which involves processing of polyethylene polymers to make tapes or membranes that are subsequently subjected to processing conditions suitable for the formation of a membrane. Such processing conditions may include heated compression and / or uniaxial or biaxial stretching of the tape or membrane in any order, including repeats or omissions of process steps detailed in the examples below. The polyethylene membrane may be prepared by the following process: (i) providing a paste comprising polyethylene polymer and a lubricant; (ii) shaping the paste into a tape; (iii) removing the lubricant from the tape to form a dry polyethylene tape; (iv) compressing the dry polyethylene tape at a compressing temperature below 115°C; and (v) biaxially stretching the polyethylene tape at a stretching temperature from 115°C to 170°C and / or compressing the polyethylene tape at a compressing temperature from 115 to 135 °C to form the polyethylene membrane. In embodiments, the stretching temperature may be from 115°C to 150°C and / or the compressing temperature of step (v) may be from 120°C to 135°C.

[0108]

[0107] The polyethylene membrane may be formed by (i) forming a polyethylene tape from a polyethylene polymer; (ii) compressing the polyethylene tape at a temperature below the melting temperature of the polyethylene polymer; and (iii) biaxially stretching the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer and / or compressing the polyethylene tape at a temperature above the melting point of the polyethylene polymer to form a polyethylene membrane. The polyethylene polymer may have an average molecular weight of about 500,000 g / mol to about 10,000,000 g / mol, the compression temperature may be from 115 to 135 °C or from 120°C to 135°C, the compression pressure may be at least 1 MPa, and the stretching temperature may be from 115°C to 170°C or from 115°C to 150°C.

[0109]

[0108] The polyethylene tape is formed by providing a paste comprising polyethylene polymer and a lubricant, shaping the paste into a tape, and removing the lubricant to form a dry polyethylene tape. For instance, polyethylene polymer particles may be initially mixed with a suitable lubricant (such as an isoparaffinic hydrocarbon) following the general process described in US 9,926,416 B2. The lubricated polymer particles may then be formed into a tape, which is then dried (to remove lubricant) prior to forming the polyethylene membrane using heated compression, uniaxial or biaxial stretching, or a combination thereof and in any order, including repeats or omissions of process steps detailed in the examples below. The tape may be referred to as a sheet.

[0110]

[0109] The polyethylene tape may be biaxially stretched at a temperature above the melting temperature of the polyethylene polymer without the step of compressing of the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer. Alternatively, the polyethylene tape may be compressed at a temperature above the melting temperature of the polyethylene polymer without the step of biaxial stretching the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer.

[0111]

[0110] Additionally, both of the steps of biaxial stretching of the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer and compression of the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer are carried out. For example, the step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out before, during or after the biaxial stretching. For instance, after stretching the polyethylene tape in a machine direction, it may be subjected to a step of compressing the polyethylene tape at a temperature above the melting point of the polyethylene polymer before stretching the polyethylene tape in the transverse direction. Alternatively, the step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out after the step of biaxially stretching the polyethylene tape, e.g. after stretching in both the machine direction and transverse direction.

[0112] [Hl] The biaxial stretching may comprise stretching in the machine direction and the transverse direction. One or both of the stretching in the machine direction and the transverse direction may be repeated under different conditions. For instance, stretching in the transverse direction may be carried out twice i.e. a first transverse stretching and a second transverse stretching. The second transverse stretching may be carried out at a lower expansion ratio and / or run speed than the first transverse stretching.

[0113]

[0112] The stretching in a machine direction may be preferably carried out at a temperature in the range of from 115 to 135 °C. In some embodiments, the stretching in a machine direction may be carried out at an expansion ratio in the range of from 1.4:1 to 8: 1. The stretching in a machine direction may be carried out at a strain rate in the range of from 2 to 17% / s. The stretching in a machine direction may be carried out at a run speed in the range of from 0.75 to 6 m / min.

[0114]

[0113] The stretching in a transverse direction may be carried out at a temperature in the range of from 120 to 146 °C. The stretching in a transverse direction may be carried out at an expansion ratio in the range of from 3 : 1 to 12: 1. The stretching in a transverse direction may be carried out at a strain rate in the range of from 1.5 to 17% / s. The stretching in a transverse direction may be carried out at a run speed in the range of from 1 to 21 m / min.

[0115]

[0114] In embodiments, the polyethylene membrane can be formed with a step of compressing the polyethylene tape in a heated compression step. The temperature at which the heated compression step is carried out above the melting point of the polyethylene polymer. The line force at which the heated compression step may be carried out is in the range of from 3 to 500 N / mm.

[0116]

[0115] The step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out at a temperature in the range of from 115 to 135 °C or 120 to 135 °C. The step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be preferably carried out at a line force in the range of from 150 to 450 N / mm. The step of compressing the polyethylene tape at a temperature above the melting temperature of the polyethylene polymer may be carried out at a run speed in the range of from 1 to 6 m / min.

[0117]

[0116] The skilled person will appreciate that the exact conditions, process steps and amounts of each component will depend on the nature of the polyethylene polymer and the desired properties of the resulting polyethylene membrane.

[0117] The polyethylene membrane may also be treated, for example to provide a coating thereon. For the avoidance of doubt, the membrane thickness, mean mass per area and geometric moduli, and the other properties described herein, refer to properties of the polyethylene membrane without the treatment or coating. It should be noted that the mechanical properties of the resultant membrane after application of a coating or surface treatment is expected to be substantially dominated by the base polyethylene membrane itself.

[0118]

[0118] [Acoustic device]

[0119]

[0119] The present disclosure also relates to an acoustic device comprising the polyethylene membrane described herein. The acoustic device may be one or both of a speaker and a microphone.

[0120]

[0120] The acoustic device may further comprise a housing defining an interior and an exterior of the acoustic device. The housing may comprise at least one opening in communication with the exterior of the acoustic device and the polyethylene membrane may cover at least one of the at least one opening. The acoustic device may further comprise a sound transducer positioned within the housing. The polyethylene membrane may be affixed to the housing with an adhesive.

[0121]

[0121] The acoustic device may further comprise a stiffener plate which covers the at least one opening of the housing, thereby providing support to the polyethylene membrane covering the at least one opening.

[0122]

[0122] As mentioned above, it has been surprisingly discovered that such a polyethylene membrane has an ideal balance of properties for use in an acoustic device. Specifically, the use of the polyethylene membrane for covering an opening in an acoustic device successfully prevents ingress of water, dust (including fine dust) and other contaminants into the acoustic device. Moreover, the polyethylene membrane is strong and therefore withstands external pressure without damage and / or rupture. Also, the polyethylene membrane does not result in significant sound insertion loss.

[0123]

[0123] [The components of the acoustic device]

[0124]

[0124] The acoustic device comprises a housing, a sound transducer and the polyethylene membrane described herein.

[0125] The housing is hollow and comprises an acoustic cavity, and the housing accommodates a sound transducer. The housing also has at least one opening in communication with the exterior of the acoustic device, through which sound passes and is received by the sound transducer. The sound passes through an acoustic cavity in the housing to reach the sound transducer.

[0125]

[0126] The material the housing is made from is not particularly limited, and may be any suitable material known in the art such as a resin, a polymer, a metal or the like. The housing provides protection for the sound transducer from contaminants. Any suitable housing known in the art may be used in the present disclosure.

[0126]

[0127] The sound transducer is not particularly limited, and its function may be to convert sound into electrical signals. Any suitable sound transducer known in the art may be used in the present disclosure.

[0127]

[0128] At least one of the at least one opening of the housing in communication with the exterior of the acoustic device is covered by the polyethylene membrane. In one embodiment, the polyethylene membrane fully covers the at least one opening so as to prevent ingress of contaminants. The polyethylene membrane, in combination with the housing, therefore protects the sound transducer from contaminants. This helps to improve the performance of the acoustic device, as contaminants affect the performance of the sound transducer.

[0128]

[0129] The polyethylene membrane may be fixed to the housing so as to cover the at least one opening. The membrane may form a hermetic seal with the housing so as to cover the at least one opening. A hermetic seal ensures water and other contaminants cannot enter the acoustic device via the seal. The seal between the housing and the polyethylene membrane may be formed by a layer of adhesive. The adhesive is not particularly limited and any suitable adhesive known in the art may be used.

[0129]

[0130] Figure 1 (FIG.l) depicts an example of an acoustic device (100) comprising a housing (110) having an opening (112) in communication with the exterior of the device (101), a sound transducer (120) and a polyethylene membrane (130) covering the opening. The polyethylene membrane fully covers the opening and is fixed by an adhesive (140) to the housing. The sound transducer (120) is positioned within the housing (114). In the embodiment depicted, the sound transducer (120) is supported on a device body (116) which is positioned within the housing.

[0131] The acoustic device may further comprise a stiffener plate to provide support for the polyethylene membrane. The stiffener plate may be selected from a perforated metal plate, a woven fabric, a nonwoven fabric, a mesh, a net, a sponge, a foam and a porous body made of a metal or a resin. The stiffener plate may be a perforated metal plate.

[0130]

[0132] The function of the stiffener plate is to act as a support for the polyethylene membrane when an external pressure is applied to the acoustic device, which pushes the membrane towards the inside of the acoustic device or housing. Typically, the polyethylene membrane is positioned between the opening of the housing and the stiffener plate, such that when an external pressure is applied to the acoustic device, the polyethylene membrane deforms towards the inside of the housing and pushes against the stiffener plate. The stiffener plate therefore provides mechanical support for the membrane and prevents further deformation. The stiffener plate is not in contact with the polyethylene membrane in the absence of external pressure on the acoustic device. The stiffener plate may be separated from the polyethylene membrane by a distance being at least about 30 pm. For example, the distance may be from about 30 pm to about 100 pm, or about 30 pm to 70 pm, or about 50 pm.

[0131]

[0133] The stiffener plate may be porous, or may contain holes or openings running through the thickness of the plate, such that the stiffener plate does not significantly affect sound transmission. In one embodiment, there is little to no sound transmission loss caused by the stiffener plate.

[0132]

[0134] An example of a stiffener plate in an acoustic device is provided in Figure 2 (FIG. 2). In Figure 2, the stiffener plate (210) is a perforated metal plate. As an external pressure is applied, the polyethylene membrane deforms towards the inside of the acoustic device and pushes against the stiffener plate. The stiffener plate therefore provides mechanical support to the polyethylene membrane.

[0133]

[0135] A coating may be provided on a surface of the polyethylene membrane. The coating may be present as a coating layer. The coating may comprise an oleophobic coating.

[0134]

[0136] The coating layer may improve the oil repellency of the membrane. Such layers may have a thickness in the range of from 10 to 150 nanometers, preferably in the range of from 20 to 100 nanometers, such as a thickness of 20 nanometers or 35 nanometers.

[0137] The coating may be on the external surface of the polyethylene membrane, such that the polyethylene membrane may be located between the coating and the sound transducer. This orientation situates the coating facing the exterior of the device, with the polyethylene membrane facing the interior of the device. The coating may promote adhesion of the polyethylene membrane to the housing by the adhesive.

[0135]

[0138] An additive may be incorporated into the polyethylene membrane e.g. into the bulk of the polyethylene membrane. The additive may be one or more of the group consisting of metal, carbon and electronically conductive polymer. The additive may be an anti-static component, such as an electrically conductive component. Thus, the polyethylene membrane may comprise polyethylene and an anti-static component. Thus, the polyethylene membrane may be a static dissipative membrane. The anti-static component may be selected from one or more of the group consisting of a metal, carbon and an electronically conductive polymer. Preferred metal, carbon and electronically conductive polymer may be of the types discussed above for the coating layer. The anti-static component may be present in an amount of less than or equal to 35 wt.%, by total weight of the polyethylene membrane e.g. anti-static component and polyethylene, such as in a range of from 1 to 35 wt.% by total weight of the polyethylene membrane or in a range of from 5 to 25 wt.% by total weight of the polyethylene membrane.

[0136]

[0139] Figure 3 (FIG. 3) illustrates an acoustic device (100) comprising a coating layer (150) on a surface of the polyethylene membrane (130). The polyethylene membrane (130) may be located between the coating layer (150) and the sound transducer (120). The polyethylene membrane may have opposing first and second surfaces. The coating layer may be disposed on the first surface of the polyethylene membrane, which may face towards the exterior of the housing (114) and is thus an exterior surface of the polyethylene membrane. The second surface of the polyethylene membrane may be disposed on the stiffener plate (210), if present, and may face the sound transducer (120). The coating layer (150) may be fixed to the housing (114) by adhesive (140) as discussed in the embodiment of Figure 1.

[0137]

[0140] In some embodiments, the acoustic device is a microphone or a speaker. In one embodiment, the acoustic device is a microphone.

[0138]

[0141] [Method of making the acoustic device]

[0142] The present disclosure provides a method of making the acoustic device described herein, the method comprising the steps of: providing the housing, the sound transducer and the polyethylene membrane, wherein the housing comprises at least one opening in communication with the exterior of the acoustic device; positioning the sound transducer within the housing; and covering the at least one opening of the housing in communication with the exterior of the acoustic device with the polyethylene membrane.

[0139]

[0143] The method may further comprise the steps of forming the polyethylene membrane by the above described “gel process” or “paste process”.

[0140]

[0144] In some embodiments, the method may further comprise the step of fixing the polyethylene membrane to the housing, for example by using an adhesive. In some embodiments, the method may further comprise the step of hermetically sealing the polyethylene membrane to the housing to provide a waterproof seal between the housing and the polyethylene membrane. In this way, the perimeter of the polyethylene membrane is sealed to the housing and covers the opening.

[0141]

[0145] In some embodiments, the method may further comprise the step of providing a stiffener plate and positioning the stiffener plate to cover the opening of the housing, such that the stiffener plate provides support to the polyethylene membrane when an external pressure is applied to the acoustic device. The stiffener plate may be the same as those described above. In one embodiment, the polyethylene membrane is positioned between the opening of the housing and the stiffener plate.

[0142]

[0146] [Use of the polyethylene membrane in an acoustic device]

[0143]

[0147] The present disclosure provides a use of the polyethylene membrane described herein as an acoustic cover, such as in an acoustic device. The present disclosure also provides a use of the polyethylene membrane described herein in an acoustic device. The polyethylene membrane is used to prevent ingress of water, dust (including fine dust) and other contaminants into the acoustic device by covering the opening of the housing, thereby providing a barrier to said contaminants. This protects the sound transducer and, in combination with the strength and acoustic properties of the polyethylene membrane, therefore ensures excellent performance of the acoustic device.

[0148] In one embodiment, the polyethylene membrane may be used as a cover for a microphone or speaker. In another embodiment, the polyethylene membrane may be used as a cover for a microphone.

[0144]

[0149] [Electronic devices containing the acoustic device]

[0145]

[0150] An electronic device may comprise the acoustic device of the present disclosure. The electronic device is not particularly limited and may include a smartwatch, mobile phone, digital camera, headphones, earphones, a voice recorder and the like. In one embodiment, the electronic device is a smartwatch.

[0146]

[0151] [Test methods]

[0147]

[0152] These tests methods relate to the above description and the examples section below.

[0148]

[0153] Mass per area: samples were die cut to form circular sections of 5.64 cm radius (area = 100 cm2). Each sample was weighed using a Mettler Toledo ME104TE Analytical balance and the average of six samples was divided by the test area of 100 cm2and multiplied by 100 to calculate the mass per area in units of g / m2.

[0149]

[0154] Bulk density: using the thickness measured using the KEYENCE LS-7600 laser or Mitutoyo Litematic thickness gage (see explanation below), the bulk density of the samples was calculated using the following formula: where: m = mass (g) r = circle cut radius (5.64 cm) t = thickness (cm).

[0150]

[0155] The bulk density therefore includes the pore spaces within the sample in the volume measurement.

[0151]

[0156] Skeletal density: is the ratio of the mass of solid material to the sum of the volumes of the solid material and closed (or blind) pores within the material as per the definition in ASTM D3766. Thus, the skeletal density of a solid is calculated by excluding all open pores but including internal (or blind) pore volume. The skeletal density can never be lower than the true bulk density calculated by the measurement of mass and volume directly if the thickness and mass of the polyethylene film are accurately known. The skeletal density of polyethylene was assumed to be p (polymer) = 0.94 g / cc. The skeletal density of polyethylene may change with the ratio of amorphous to crystalline regions in the polyethylene, which can be a result of the process of preparing such polymers. The skeletal density of polyethylene films, including polyethylene membranes, may be measured by gas pycnometry. A gas pycnometry instrument such as Micrometrics AccuPyc II 1340 can measure the skeletal volume of a material by He gas displacement using the volume-pressure relationship of Boyle’s Law.

[0152]

[0157] Porosity: samples were die cut to form circular sections of 5.64 cm radius (area = 100 cm2). Each sample was weighed using a Mettler Toledo Analytical balance. Using the thickness calculated by the KEYENCE laser (see explanation below), the bulk density of the samples was calculated as discussed previously.

[0153]

[0158] The skeletal density is the density of a solid calculated by excluding all open pores, but including internal (or blind) pore volume. The density of polyethylene was assumed to be p (polymer) = 0.94 g / cc.

[0154]

[0159] Thus, the membrane porosity or total porosity within the substrate is simply the void volume of the sample divided by the total volume of the sample. The membrane porosity can be calculated by the following formula:

[0155]

[0160] % Porosity = 100% * { 1- p(bulk) / p(skeleton)}

[0156]

[0161] Airflow (air permeability): the ATEQ airflow test typically measures laminar volumetric flow rates of air through membrane and film samples. Each film sample was clamped between two plates in a manner that seals an area of 2.99 cm2across the flow pathway. An ATEQ® (ATEQ Corp., Livonia, MI) Premier D Compact Flow Tester was used to measure airflow rate (L / hr) through each membrane sample by challenging it with a differential air pressure of 1.2 kPa (12 mbar) through the membrane. The instrument was operated with calibrated 5, 30 and 150 L flow tubes for making airflow measurements within the ranges of 0.15 to 0.5 L / hr, 0.5 to 30 L / hr and 3.8 to 500 L / hr, respectively, representing low-, mid- and high-flow regimes.

[0157]

[0162] The Darcy permeability of air at room temperature can be calculated as following for ATEQ measured values at 12 mbar:

[0158] Permeability (m2) = 2.073 x 10'17* ATEQ * t where:

[0159] ATEQ [@ 12 mbar] (L / h) t = thickness (pm).

[0160]

[0163] Contact Thickness: the contact thickness of the membranes was measured using a Mitutoyo Litematic VL-50S motorized height gage (commercially available from Mitutoyo Corporation, Kawasaki, Japan). The measurement is made by gently placing the sample membrane on a polished flat granite block and lowering the contact probe to apply a 1 gram force. The average of the twelve measurements was utilized to provide a mean contact thickness. Contact thickness is an appropriate technique for measuring the thickness of for polyethylene membranes which are opaque, and are therefore unsuitable for the measurement of non-contact thickness.

[0161]

[0164] Non-contact Thickness: the non-contact thickness of the membranes was measured using a KEYENCE LS-7600 laser system (commercially available from KEYENCE America). The optical measurement is made by gently placing the sample membrane against a polished stainless cylinder having a 2.54 cm diameter and smoothing it down with minimal applied tension. The thickness of the sample is determined by measurement of the shadow created in the parallel light path of within the two ends of the Keyence laser micrometer. The average of the three measurements was utilized to provide a mean non-contact thickness. Non-contact thickness is an appropriate technique for measuring the thickness of polyethylene membranes which are translucent or semi-translucent.

[0162]

[0165] Acoustic insertion loss: the general method used to measure insertion loss was as per the apparatus and method as described below and in Example 1 of WO 2018 / 140705 (or US 2018 / 0213340 Al) in the name of W. L. Gore & Associates, Inc., which is incorporated herein by reference in its entirety.

[0163]

[0166] An acoustic testing apparatus was configured with a testing system in an "open" condition, wherein the 28 available sample locations (and four reference ports) were left uncovered. The testing apparatus was closed to seal the acoustic chamber, and the system was operated through a frequency range of 100 Hz to 20 kHz at amplitude of 94 dB SPL (referenced to 20 Pa). The acoustic insertion loss across the acoustic cavity and respective ports in the sample holders was measured across the frequency range.

[0164] Insertion loss, IL = [dB SPL of Open Condition (no vent assembly present)] - [dB SPL of Vent Assembly (vent assembly present)] where SPL = Sound Pressure Level

[0165]

[0167] Bubble Point: liquids with surface free energies less than that of stretched porous polyethylene can be forced out of the structure with the application of a differential pressure. This clearing will occur from the largest passageways first. A passageway is then created through which bulk nitrogen flow can take place. The nitrogen flow appears as a steady stream of small bubbles through the liquid layer on top of the sample. The pressure at which the first bulk air flow takes place is called the bubble point and is dependent on the surface tension of the test fluid and the size of the largest opening. The bubble point can be used as a relative measure of the structure of a membrane and is often correlated with some other type of performance criteria, such as filtration efficiency.

[0166]

[0168] The bubble point was measured according to the general teachings of ASTM F316-03 using a Capillary Flow Porometer (Model 3G zh from Quantachrome Instruments). The sample holder comprised a porous metal plate (Part Number: 196450, Anton Paar), 25.4 mm in diameter and a plastic mask (Part Number ABF-300, Professional Plastics), 18mm inner diameter x 24.5 mm outer diameter. The sample was placed in between the metal plate and the plastic mask. The sample was then clamped down and sealed using an O-ring (Part Number: 193798, Anton Paar). The sample was wet with the test fluid (Silicone fluid, 10 cSt, having a surface tension of 19.75 dynes / cm).

[0167]

[0169] Mean Surface Area per unit mass and Mean Surface Area per Volume: The surface area per unit mass (SSA), expressed in units of m2 / g, of the polyethylene membrane was first measured using the Brunauer-Emmett-Teller (BET) method on a Quantachrome NOVAtouch LX4 Gas Sorption System (Quantachrome Instruments - Anton Paar - Boynton Beach, FL). A sample was cut from the center of the polyethylene membrane sheet and placed into a Type B long cell, 9 mm LG bulb (reference number 193885). The mass of the polyethylene membrane sample was approximately 0.1 to 0.2 grams. The tube was placed into the Coulter SA-Prep Surface Area Outgasser, (Model SA-PREP, P / N 5102014) from Beckman Coulter Inc., Fullerton, CA and purged at room temperature for 2 hours with helium. The sample tube was then removed from the SA-Prep Outgasser and weighed. A glass filler rod (reference number 193900) was placed in the cell and the assembly was then placed into the NOVAtouch LX4 Gas Sorption System and the BET surface area analysis was run in accordance with the instrument instructions using helium to calculate the free space and nitrogen as the adsorbate gas. A single BET surface area (m2 / g) measurement was recorded for each sample.

[0168]

[0170] Specific surface area (SSA) can be converted to surface area per volume (Sv) using the following calculation:

[0169] Sv = p (polymer) * SSA [106 / m] where: p (polymer) = 0.94 g / cc

[0170] SSA = specific surface area [m2 / g]

[0171]

[0171] Matrix tensile strength: to determine the matrix tensile strength (MTS), a sample polyethylene membrane was cut in the longitudinal and transverse directions using either an ASTM D638 Type V Die (D638) or an ASTM D412 Type F Die (D412F). Tensile load as a function of displacement was measured using an INSTRON® 5565 (Illinois Tool Works Inc., Norwood, MA) tensile test machine equipped with flat-faced grips and a 100 N load cell. The grip separation distance for ASTM D638V tests was set to 3.18 cm and using an ASTM defined gage length of 0.76 cm, a strain rate of 0.127 cm / s or 16.7 % / s was used. The grip separation distance for ASTM D412F tests was set to 8.26 cm and using an ASTM defined gage length of 5.89 cm, a strain rate of 0.847 cm / s or 14.4 % / s was used. After placing the sample in the grips, the sample was retracted 1.27 cm to obtain a baseline followed by a tensile test at the aforementioned strain rate. Three samples for each condition were tested individually samples in each orthogonal (e.g., longitudinal (machine) and transverse) direction and their respective averages were reported.

[0172]

[0172] The ultimate tensile strength was measured by the Instron load cell and is defined as the maximum load reached during each test run divided by the cross-section area at the center of the die cut dogbone. Data was exported into a data analysis program. Three samples in each orthogonal (e.g. longitudinal and transverse) direction were tested and their respective averages were reported. The larger of the two average maximum tensile moduli determined for the two orthogonal directions was assigned that of the first direction. The smaller of the two average maximum tensile moduli determined for the two orthogonal directions was assigned that of the second direction.

[0173] The matrix tensile strength (MTS) is used to communicate the tensile strength of a polymer making up a porous or non-porous article, and is calculated using the following formula:

[0173] MTS = TS * p polymer / P bulk. where TS = ultimate tensile strength from the uniaxial tensile testing;

[0174] Pbuik = sample bulk density;

[0175] Ppoiymer = theoretical skeletal density of PE, taken as 0.94 g / cm3.

[0176]

[0174] Sample assemblies and comparative sample assemblies described herein were prepared as follows:

[0177]

[0175] Procedure for the manufacture of Vent Assemblies

[0178]

[0176] Acoustic vent assemblies disclosed in the comparative and inventive examples were prepared as follows. First, a reinforced acrylic adhesive foam tape (tesa® 75720) and S5006L-38B Polyethylene Terephthalate (PET) release liner (obtained commercially from Tailun Electronic Materials (Suzhou) Co, Ltd.) were laminated and die-cut to form a 1.6 mm ID circular aperture. Secondly, to this assembly the bottom of the ePE acoustic membrane was attached by lamination to the adhesive foam tape along with a temporary second release liner on the topside of the ePE membrane. These layers are known as assembly one. In a parallel operation, a second acrylic doublesided reinforced tape (tesa® 4972) sandwiched by lamination to a Lumirror T60 PET film (obtained commercially from Toray Industries) and S7520L-25B PET release liner (obtained commercially from Tailun Electronic Materials (Suzhou) Co, Ltd. ) and then die-cut to match the identical 1.6 mm ID circular aperture cut of assembly one. These two assemblies were brought together, and heat pressed (as needed at 100 °C and 4 bar at a line speed of 1 m / min) while joining the free surface of the ePE membrane to the free adhesive side of the tesa® 4972 acrylic tape of the second assembly.

[0179]

[0177] A S5012L pull tab (obtained commercially from Tailun Electronic Materials (Suzhou) Co., Ltd.) was added to the assembly above and die cut to produce individual acoustic vent parts, each with a 3.2 mm OD circular geometry, on the base release liner. This assembly was then cut into individual sheets each containing multiple parts and given a 10 to 30 min heat treatment in the range of 70 to 110 °C in an oven. Prior to testing each vent assembly, the pull tab and the base liner were removed, and individual acoustic vent assemblies were installed on the testing apparatus as described in the test method section above.

[0180]

[0178] [Examples]

[0181]

[0179] The present disclosure will be described in more detail with reference to Examples. The present disclosure is not limited to the following Examples.

[0182]

[0180] Precursor membrane 1 manufactured by gel method 1

[0183]

[0181] A gel-processed ultrahigh molecular weight polyethylene membrane (“Precursor membrane 1”) prepared from a polyethylene resin of average molecular weight of 4,300,000 g / mol was obtained and used as a precursor for subsequent examples that were further processed to create the illustrative membrane examples presented herein. The UHMWPE membrane has a mass / area of 4.1 g / m2, a bubble point of 139 psi, an airflow of 3.5 L / hr at 12 mbar and 2.99 cm2, a thickness of 11.5 micrometers, a porosity of 62.0%, a specific surface area 45.7 m2 / g, a MD MTS of 228 MPa, a TD MTS of 174 MPa, and a TD modulus of 419 MPa.

[0184]

[0182] Precursor membranes manufactured by gel method 2

[0185]

[0183] Porous polyethylene membranes were prepared according to the following general method. A solution of UHMWPE and HMWPE with an overall average molecular weight in the approximate range of 1,000,000 to 5,000,000 g / mole in a solvent was extruded at a temperature of about 180° C.

[0186]

[0184] Examples of usable solvents of non- or low-polar solvents such as decaline or mixtures of solvents comprising decaline and / or other aliphatic or aromatic solvents, paraffin (oil) and / or other oils, or alcohols or ethers with long chains.

[0187]

[0185] The extruder head was fitted with a die with a 1 mm opening. The extruded film was cooled in a quench bath. The solvent was removed from the gel film by evaporation in an oven. The film from which solvent had been removed was simultaneously stretched in machine direction (MD) and transverse direction (TD), at a temperature in a range of about 120 to 140 ° C.

[0188]

[0186] Precursor tapes manufactured by paste method 1

[0189]

[0187] Powder preparation: 300 g of ultrahigh molecular weight polyethylene powder having an average molecular weight of approximately 7,000,000 g / mol (Mitsui Chemicals Inc., made as described in WO2012053261) was placed in a 2-liter screw cap jar. 180 mL of an isoparaffinic hydrocarbon lubricant (ISOPAR™ V; ExxonMobil Chemical Company, Spring, Texas) was added and mixed at room temperature for 15 minutes at 30 rpm using a tumbler. The mixture was preheated to 60°C prior to calendering.

[0190]

[0188] Tape calender process: Calender rolls with a diameter of 20.3 cm were preheated to 121°C with the gap between the rolls set at 0.2 mm. The lubricated polymer was introduced into the gap with a feeder to produce a 15.2 cm wide continuous tape at a line speed of 2.0 m / min. The tape was opaque, flexible, and approximately 0.21 mm thick.

[0191]

[0189] Lubricant removal: The tape was run roll-to-roll through a large bath containing a low aromatic hydrocarbon solvent (ISOPAR™ G; ExxonMobil Chemical Company, Spring, Texas) to displace the Isopar V™ with Isopar™ G and subsequently dried at 50°C.

[0192]

[0190] [Comparative Example Cl]

[0193]

[0191] An UHMWPE “precursor membrane 1” prepared according to gel method 1 was treated as follows.

[0194]

[0192] The above-described membrane was drawn in the longitudinal / machine direction between banks of rolls in an oven set to a temperature of 125°C at a run speed of 3.0 m / min. The speed ratio between the second bank of rolls and the first bank of rolls, and hence the expansion ratio was 1.5: 1 with a strain rate of 1.0 % / s.

[0195]

[0193] The longitudinally drawn membrane was then heated in a transverse expansion oven held at a temperature of approximately 125°C at a run speed of 5.0 m / min for a 1.0 min preheat and drawn transversely to a ratio of 6: 1 at a strain rate of 4.8 % / s. Then, the membrane is held approximately at 125°C for an additional 0.7 min while allowing to retract in the transverse direction by 15% of width and cooling to approximately room temperature for an additional 1.2 min.

[0196]

[0194] The properties of the resultant membrane Cl are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0197]

[0195] [Comparative Example C2]

[0196] A starting UHMW polyethylene resin having an average molecular weight of 3,000,000 g / mol, was used in “Gel method 2” to manufacture a precursor film as a tape.

[0198]

[0197] The approximate tape width and thickness was 0.3 m and 0.3 mm, respectively. The dried film was drawn in the longitudinal / machine direction between multiple sets of banks of rolls in an oven set at an approximate temperature of 130 °C. The speed ratio was set between each successive bank of rolls relative to the first bank resulting in a total machine direction expansion ratio of 7:1 with an average strain rate of 2.5% / s.

[0199]

[0198] The longitudinally drawn membrane was then heated in a transverse expansion oven set at an approximate temperature of 140°C and drawn transversely to a ratio of 12: 1 at a strain rate of 1.6% / s. Then, the membrane is allowed to relax approximately 1% in the transverse direction while clamped before exiting the oven.

[0200]

[0199] The properties of the resultant membrane C2 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0201]

[0200] [Comparative Example C3]

[0202]

[0201] A starting resin polyethylene having an average molecular weight of 3,000,000 g / mol, was used in “Gel method 2” to manufacture a precursor film as a tape.

[0203]

[0202] The approximate tape width and thickness was 0.3 m and 0.3 mm, respectively. The dried film was drawn in the longitudinal / machine direction between multiple sets of banks of rolls in an oven set at an approximate temperature of 130 °C. The speed ratio was set between each successive bank of rolls relative to the first bank resulting in a total machine direction expansion ratio of 7.3: 1 with an average strain rate of 2.5% / s.

[0204]

[0203] The longitudinally drawn membrane was then heated in a transverse expansion oven set at an approximate temperature of 140°C and drawn transversely to a ratio of 12: 1 at a strain rate of 1.7% / s. Then, the membrane is allowed to relax approximately 1% in the transverse direction while clamped before exiting the oven.

[0205]

[0204] The properties of the resultant membrane C3 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0206]

[0205] [Comparative Example C4]

[0206] A starting resin having an average molecular weight of 1,900,000 g / mol, was used in “Gel method 2” to manufacture a precursor film as a tape.

[0207]

[0207] The approximate tape width and thickness was 0.3 m and 0.3 mm, respectively. The dried film was drawn in the longitudinal / machine direction between multiple sets of banks of rolls in an oven set at an approximate temperature of 130 °C. The speed ratio was set between each successive bank of rolls relative to the first bank resulting in a total machine direction expansion ratio of 9: 1 with an average strain rate of 3.2% / s.

[0208]

[0208] The longitudinally drawn membrane was then heated in a transverse expansion oven set at an approximate temperature of 140°C and drawn transversely to a ratio of 11 : 1 at a strain rate of 2.1 % / s. Then, the membrane is allowed to relax approximately 1% in the transverse direction while clamped before exiting the oven.

[0209]

[0209] The properties of the resultant membrane C4 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0210]

[0210] [Comparative Example C5]

[0211]

[0211] A starting UHMW polyethylene resin having an average molecular weight of 7,000,000 g / mol, was used in “paste method 1” to manufacture a compressed precursor tape approximately 15.2 cm in width.

[0212]

[0212] The tape was then drawn in the longitudinal / machine direction between banks of rolls over a heated plate set to a temperature of 128 °C at a run speed of 1.0 m / min. The speed ratio between the second bank of rolls and the first bank of rolls, and hence the longitudinal expansion ratio was 3.5: 1 with a strain rate of 15.6 % / s.

[0213]

[0213] The longitudinally drawn membrane was then heated in a transverse expansion oven held at a temperature of approximately 135°C at a run speed of 5.0 m / min for a 0.6 min preheat and drawn transversely at an approximate temperature of 135°C to a ratio of 4.5: 1 at a strain rate of 2.6 % / s. Then, the membrane is held approximately at 135°C for an additional 0.3 min while pinned. This was transversely expanded Pass 1.

[0214]

[0214] The same transversely expanded Pass 1 membrane was then heated for a second time in the same transverse expansion oven at a continuous run speed of 2.0 m / min at a temperature of approximately 135°C for a 0.75 min preheat and then drawn transversely at a temperature of approximately 145°C to a ratio of 4.5: 1 at a strain rate of 2.6 % / s. Finally, the membrane is held approximately at 150°C for an additional 0.5 min while pinned.

[0215]

[0215] The properties of the resultant membrane C5 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0216]

[0216] [Exampl e E 1 ]

[0217]

[0217] An UHMWPE “precursor membrane 1” prepared according to gel method 1 was treated as follows. The membrane was drawn in the longitudinal / machine direction between banks of rolls over a heated plate set to a temperature of approximately 130°C at a run speed of 3.0 m / min. The speed ratio was set between the second bank of rolls and the first bank of rolls resulting in an expansion ratio of 1.5: 1 with a strain rate of 3.4 % / s.

[0218]

[0218] The longitudinally drawn membrane was then compressed at a run speed of 5.0 m / min between a heated chrome steel roller at a setpoint temperature of 120°C and a nylon roller held at a line force of 200N / mm. The resultant compressed membrane had no measurable airflow and was translucent and flexible.

[0219]

[0219] The partially densified membrane was then heated in a transverse expansion oven at a temperature of approximately 125°C at a run speed of 2.0 m / min for a 1.5 min preheat and drawn transversely to a ratio of 5.4: 1 at a strain rate of 4.9 % / s. Then, the membrane is held at 125°C for an additional 0.5 min while pinned.

[0220]

[0220] The properties of the resultant membrane El are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0221]

[0221] [Example E2]

[0222]

[0222] An UHMWPE “precursor membrane 1” prepared according to gel method 1 was treated as follows. The membrane was drawn in the longitudinal / machine direction between banks of rolls over a heated plate set to a temperature of approximately 130°C at a run speed of 3.0 m / min. The speed ratio was set between the second bank of rolls and the first bank of rolls resulting in an expansion ratio of 1.5: 1 with a strain rate of 3.4 % / s.

[0223] The longitudinally drawn membrane was then compressed at a run speed of 5.0 m / min between a heated chrome steel roller at a setpoint temperature of 120°C and a nylon roller held at a line force of 200N / mm. The resultant compressed membrane had no measurable airflow and was translucent and flexible.

[0223]

[0224] The partially densified membrane was then heated in a transverse expansion oven at a temperature of approximately 125°C at a run speed of 2.0 m / min for a 1.5 min preheat and drawn transversely to a ratio of 6.3 : 1 at a strain rate of 5.9 % / s. Then, the membrane is held at 125°C for an additional 0.5 min while pinned.

[0224]

[0225] The properties of the resultant membrane E2 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone.

[0225]

[0226] [Example E3]

[0226]

[0227] An UHMWPE “precursor membrane 1” prepared according to “gel method 1” was treated as follows.

[0227]

[0228] The “precursor membrane 1” was drawn in the longitudinal / machine direction between banks of rolls at a gap distance of 36.3 cm over a heated plate set to a temperature of 128°C at a run speed of 2.55 m / min. The speed ratio between the second bank of rolls and the first bank of rolls, and hence the expansion ratio was 2.8: 1.

[0228]

[0229] The longitudinally drawn membrane was then drawn transversely at a temperature of approximately 145°C to a ratio of 8.7: 1 at a run speed of 8 m / min at a strain rate of 8.4% / s for a residence time of 1.94 min. This was followed by a temperature treatment at 150°C for a residence time of 0.44 min while restrained.

[0229]

[0230] The properties of the resultant membrane E3 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D638-3 dog bone as described above.

[0230]

[0231] [Example E4]

[0231]

[0232] A starting UHMW polyethylene resin having an average molecular weight of 3,000,000 g / mol, was used in “gel method 2” in accordance with the method disclosed in US Patent No. 8,645,565 to manufacture a precursor film as a tape.

[0232]

[0233] The approximate tape width and thickness was 0.3 m and 0.3 mm, respectively. The dried film was drawn in the longitudinal / machine direction between multiple sets of banks of rolls in an oven set at an approximate temperature of 120 °C. The speed ratio was set between each successive bank of rolls relative to the first bank resulting in a total machine direction expansion ratio of 7.5: 1 with an average strain rate of 2.5% / s.

[0233]

[0234] The longitudinally drawn membrane was then heated in a transverse expansion oven set at an approximate temperature of 140°C and drawn transversely to a ratio of 11 : 1 at a strain rate of 1.7 % / s. Then, the membrane is allowed to relax approximately 1% in the transverse direction while clamped before exiting the oven.

[0234]

[0235] The properties of the resultant membrane E4 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone as described above.

[0235]

[0236] [Example E5]

[0236]

[0237] A starting UHMW polyethylene resin having an average molecular weight of 1,400,000 g / mol, was used in gel method 2 to manufacture a precursor film as a tape in accordance with the method disclosed in US Patent No. 8,645,565 to provide a gel- processed UHMWPE membrane and available as Solupor® from W. L. Gore & Associates, Inc.

[0237]

[0238] The resulting gel-processed UHMWPE membrane, Solupor®, had a mass / area of 5.4 g / m2, a bubble point of 12.6 psi, an airflow of 50.9 L / hr at 12 mbar and 2.99 cm2, a thickness of 59.7 microns, a porosity of 90.4%, a specific surface area 13.7 m2 / g, a MD MTS of 78 MPa, and a TD MTS of 163 MPa.

[0238]

[0239] The above-described membrane was then drawn in the longitudinal / machine direction between banks of rolls over a heated plate set to a temperature of 130°C at a run speed of 1.3 m / min. The speed ratio between the second bank of rolls and the first bank of rolls was set and hence the expansion ratio was 2.5: 1 with a strain rate of 6.0% / s.

[0239]

[0240] The longitudinally drawn membrane was then heated in a transverse expansion oven held at a temperature of approximately 145°C at a run speed of 1.5 m / min for a 1.0 min preheat and drawn transversely to a ratio of 6.5:1 at a strain rate of 3.1 % / s. Then, the membrane is held at approximately 145°C for an additional 0.67 min while pinned.

[0241] The transversely drawn membrane was then compressed at a line speed of 1.5 m / min between a set of double nip compression rollers consisting of a pair of heated chrome steel roller at an approximate temperature of 125°C and a nylon roller with a setpoint line force of 400N / mm in each nip.

[0240]

[0242] The properties of the resultant membrane E5 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone.

[0241]

[0243] [Example E6]

[0242]

[0244] The finished membrane as described above in comparative example C5, was further processed by the following steps through a double-nip heated compression machine. Run speed 2.0 m / min. Double nips, 130 °C and at a line force of 400 N / mm. The properties of the resultant membrane E6 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone.

[0243]

[0245] [Example E7]

[0244]

[0246] An approximately 15.2 cm wide calendered tape fabricated by paste method 1 from a starting UHMWPE resin of average molecular weight of approximately 7,000,000 g / mol was utilized. The tape was then drawn in the longitudinal / machine direction between banks of rolls over a heated plate set to a temperature of 128 °C at a run speed of 1.6 m / min. The speed ratio between the second bank of rolls and the first bank of rolls, and hence the longitudinal expansion ratio was 1.75: 1 with a strain rate of 10.0 % / s.

[0245]

[0247] The longitudinally drawn membrane was then heated in a transverse expansion oven held at a temperature of approximately 135°C at a run speed of 10.0 m / min for a 0.6 min preheat and drawn transversely at an approximate temperature of 135°C to a ratio of 5.0: 1 at a strain rate of 16.2 % / s. Then, the membrane is held approximately at 135°C for an additional 0.2 min while pinned. This was transversely expanded Pass 1.

[0246]

[0248] The same transversely expanded Pass 1 membrane was then heated for a second time in the same transverse expansion oven at a continuous run speed of 4.0 m / min at a temperature of approximately 135°C for a 0.88 min preheat and then drawn transversely at a temperature of approximately 145°C to a ratio of 4.8: 1 at a strain rate of 3.2 % / s. Finally, the membrane is held approximately at 150°C for an additional 1.25 min while pinned.

[0249] The membrane was then compressed using a double-nip heated compression machine. Run speed 2.0 m / min. Double nips, 130 °C and at a line force of 400 N / mm. The properties of the resultant membrane E7 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone.

[0247]

[0250] [Example E8]

[0248]

[0251] An approximately 15.2 cm wide calendered tape fabricated by paste method 1 from a starting UHMWPE resin of average molecular weight of approximately 7,000,000 g / mol was utilized. The tape was then drawn in the longitudinal / machine direction between banks of rolls over a heated plate set to a temperature of 129 °C at a run speed of 1.0 m / min. The speed ratio between the second bank of rolls and the first bank of rolls, and hence the longitudinal expansion ratio was 3.5: 1 with a strain rate of 15.6 % / s.

[0249]

[0252] The longitudinally drawn membrane was then heated in a transverse expansion oven held at a temperature of approximately 135°C at a run speed of 10.0 m / min for a 0.65 min preheat and drawn transversely at an approximate temperature of 135°C to a ratio of 5.0: 1 at a strain rate of 10.3 % / s. Then, the membrane is held approximately at 135°C for an additional 0.65 min while pinned. This was transversely expanded Pass 1.

[0250]

[0253] The same transversely expanded Pass 1 membrane was then heated for a second time in the same transverse expansion oven at a continuous run speed of 2.0 m / min at a temperature of approximately 135°C for a 0.75 min preheat and then drawn transversely at a temperature of approximately 145°C to a ratio of 4.0: 1 at a strain rate of 2.2 % / s. Finally, the membrane is held approximately at 150°C for an additional 0.5 min while pinned.

[0251]

[0254] The longitudinally drawn membrane was then compressed at a run speed of 5.0 m / min between single pair of compression nip rollers consisting of a heated chrome steel at a setpoint temperature of 130°C and a nylon roller at a line force of 350 N / mm. The properties of the resultant membrane E8 are detailed in Table 1. The matrix tensile strengths were calculated using an ASTM type D412F dog bone. Table 1

[0252] SHZ toneSHZ 10 m’MeanMean Mean Mean AOQC1AOQC 30 min NonMean Mean

[0253] Mean Mean Mean (ATEQ (BPP (BETBulkDarcy

[0254] ID eWEP contact or MD TD

[0255] IL @ 1 IL @ pass contact* MPA @ 12 Quanta- Sv) density Permeability MTS MTS kHz 10 kHz rate Thickness [g / m2] mbar) chrome) [106 / (g / em3) NCT [m2] [MPa] [MPa]

[0256] [dB] [dB] (%) [pm] [1 / h] [psi] m]

[0257] Cl 2.516 2.444 2.526 100 5.52 1.7 13.3 96 49.0 67.2% 0.31 1.52E-15 294 245

[0258] C2 2.563 2.24 2.506 0 12.9 1.7 32.5 29 24.8 86.0% 0.13 8.69E-15 190 260

[0259] C3 2.251 2.3 2.254 0 9.9 1.8 39.6 24.5 26.5 80.7% 0.18 8.13E-15 170 225

[0260] C4 2.276 2.24 2.231 100 8 1.3 14.9 33.6 25.2 82.7% 0.16 2.47E-15 227 172

[0261] C5 2.005 2.316 2.262 100 6.32 1.27 61 27.9 78.6% 0.20 7.99E-15 282 168

[0262] El 1.298 1.222 0.914 100 3.36 1.6 1.6 115 20.1 49.3% 0.48 1.11E-16 303 239

[0263] E2 1.185 1.125 0.84 100 2.7 1.5 0.7 148.5 34.0 40.9% 0.56 3.92E-17 306 309

[0264] E3 0.58 0.575 0.39 100 0.91* 0.79 0.39 112.9 13.9 7.6% 0.87 7.43E-18 421 230

[0265] E4 1.542 1.47 1.331 92.6 3.8 1.7 6.3 28.8 16.6 52.4% 0.45 4.96E-16 110 328

[0266] E5 0.964 0.926 0.719 100 1.61* 1.26 3.2 31.4 8.6 16.7% 0.78 1.07E-16 298 178

[0267] E6 0.997 0.965 0.6 100 2.88 1.73 1.7 81 15.8 36.1% 0.60 1.01E-16 466 191

[0268] E7 0.993 0.961 0.707 100 1.57 0.95 3.3 78.6 7.2 249

[0269] E8 0.567 0.536 0.422 100 2.07 0.8 20.6 62.3 25.2 58.9% 0.39 8.84E-16 366 338

[0270] *contact thickness measured, the remaining examples and the comparative examples measured non-contact thickness

[0271] IL = insertion loss

[0272] BPP = bubble point pressure

[0273] NCT = non-contact thickness

[0274] MTS = matrix tensile strength (MD = machine direction ; TD = transverse direction)

[0275]

[0255] All ranges described herein are exemplary in nature and include any and all values in between. The terms “substantially”, “approximately” and “about” used herein are interchangeable and refer to a measurement that includes the stated measurement and any measurements reasonably close to the stated measurement. Measurements that are reasonably close to the stated measurement deviate from the stated measurement by a reasonably small amount as understood and readily ascertained by individuals having ordinary skill in the relevant arts. Such deviations may be attributable to measurement error, differences in measurement and / or manufacturing equipment calibration, human error in reading and / or setting measurements, minor adjustments made to optimize performance and / or structural parameters in view of differences in measurements associated with other components, particular implementation scenarios, imprecise adjustment and / or manipulation of objects by a person or machine. In the event it is determined that individuals having ordinary skill in the relevant arts would not readily ascertain values for such reasonably small differences, the terms “about” and “approximately” can be understood to mean plus or minus 10% of the stated value.

[0276]

[0256] Throughout the description and claims, the terms take the meanings explicitly defined herein, unless the context clearly dictates otherwise.

[0277]

[0257] The phrases “in one embodiment”, “in an embodiment” and “in some embodiments” etc. as used herein do not necessarily refer to the same embodiment s), though they may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, though they may. All embodiments of the disclosure are intended to be combinable.

[0278]

[0258] The terms “comprises” and “comprising” mean to include but not limited to, such that further features may be present. The terms may also mean to consist of.

[0279]

[0259] All references and test methods cited herein are incorporated by reference in their entireties.

Claims

1. CLAIMSWhat is claimed is:

1. A polyethylene membrane, wherein the polyethylene membrane is air permeable, has a surface area per volume of less than 38 x 106 / m and has a thickness of from 0.5 pm to 5 pm.

2. The polyethylene membrane of claim 1, wherein the polyethylene membrane has an air permeability as measured by the ATEQ airflow test described herein of 0.15 L / hr or more.

3. The polyethylene membrane of claim 1 or claim 2, wherein the polyethylene membrane has an air permeability as measured by the ATEQ airflow test described herein of from 0.15 L / hr to 500 L / hr.

4. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a porosity of at least 5%.

5. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a porosity from 7% to 85%.

6. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a Darcy permeability of less than or equal to 0.9 x 10'15m2.

7. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a Darcy permeability from 6 x 10'18m2to 0.9 x 10'15m2.

8. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane comprises polyethylene or modified polyethylene having an average molecular weight from 500,000 g / mol to 10,000,000 g / mol.

9. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a mean mass per area of 2 gm'2or less.

10. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane having a basis weight of from 0.7 gm'2to 1.8 gm'2.

11. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has an extended Water Entry Pressure of at least 30 minutes at 1 m.

12. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has an extended Water Entry Pressure of at least 30 minutes at 10 m.

13. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has an extended Water Entry Pressure pass rate of greater than 90%.

14. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a surface area per volume in a range of from 4 x l05to 38 x l06 / m.

15. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a mean acoustic insertion loss at 1 kHz of less than or equal to 1.9 dB.

16. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a mean acoustic insertion loss at 1 kHz in a range of from 0.2 to 1.9 dB.

17. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane has a bulk density in the range of from 0.30 to 0.87 g / cm3.

18. The polyethylene membrane of any preceding claim, wherein the polyethylene membrane is an acoustic cover.

19. A polyethylene membrane according to any preceding claim, wherein the polyethylene membrane is prepared by the following process: dissolving a polyethylene polymer in a solvent to form a solution; shaping the solution into a tape at a temperature above the solution temperature of the polyethylene polymer; cooling the tape to a temperature below the solution temperature to achieve gelation of the tape; removing the solvent from the gelled tape; and biaxially stretching the gelled tape at a stretching temperature from 115°C to 170°C to form the polyethylene membrane.

20. A polyethylene membrane according to any of claims 1 to 18, wherein the polyethylene membrane is prepared by the following process: providing a paste comprising polyethylene polymer and a lubricant; shaping the paste into a tape; removing the lubricant from the tape to form a dry polyethylene tape; compressing the dry polyethylene tape at a compressing temperature below 115°C; and biaxially stretching the polyethylene tape at a stretching temperature from 115°C to 170°C and / or compressing the polyethylene tape at a compressing temperature from 115 to 135 °C to form the polyethylene membrane.

21. Use of a polyethylene membrane as an acoustic cover, wherein the polyethylene membrane is defined according to any one of claims 1 to 20.

22. Use of a polyethylene membrane in an acoustic device, wherein the polyethylene membrane is defined according to any one of claims 1 to 20.

23. The use according to Claim 22, wherein the acoustic device comprises a housing defining an interior and exterior of the acoustic device, the housing comprising at least one opening in communication with the exterior of the acoustic device and a sound transducer, the sound transducer being positioned within the housing, and wherein the polyethylene membrane is used to cover the at least one opening of the housing to prevent ingress of water, dust and / or other contaminants.

24. An acoustic device, wherein the acoustic device comprises: a polyethylene membrane as defined in any one of claims 1 to 20.

25. The acoustic device of claim 24, wherein the acoustic device is one of a speaker, a microphone, or any combination thereof.

26. The acoustic device of any one of claim 24 or claim 25, wherein the acoustic device comprises a housing defining an interior and exterior of the acoustic device.

27. The acoustic device of claim 26, wherein the acoustic device comprises a sound transducer positioned within the housing.

28. The acoustic device of claim 26 or claim 27, wherein the housing comprises at least one opening in communication with the exterior of the acoustic device and the polyethylene membrane covers the at least one opening.

29. The acoustic device of claim 28, wherein the polyethylene membrane is affixed to the housing with an adhesive.

30. The acoustic device of claim 28 or claim 29, wherein a stiffener plate covers the at least one opening of the housing, thereby providing support to the polyethylene membrane.

31. A method of making an acoustic device as defined in one of claim 28 to claim 30, the method comprising the steps of(i) providing a housing, a sound transducer and a polyethylene membrane, wherein the housing comprises at least one opening in communication with an exterior of the acoustic device;(ii) positioning the sound transducer within the housing; and(iii)covering the at least one opening of the housing in communication with the exterior of the acoustic device with the polyethylene membrane.

32. The method of claim 31, further comprising the step of fixing the polyethylene membrane to the housing with an adhesive.

33. The method according to claim 31 or claim 32, further comprising the step of providing a stiffener plate and positioning the stiffener plate to cover the at least one opening of the housing, thereby providing support to the polyethylene membrane.

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