Diaphragms for micro loudspeakers and related methods

Abstract

A diaphragm for a microspeaker has an organic polymer film layer in direct contact with one or both skin layers. The one or two skin layers independently include a block copolymer having a hard segment and a soft segment, wherein a portion of the hard segment is included in a crystalline physically crosslinked domain. The organic polymer film layer is not sticky at 25 DEG C. A method of making the diaphragm is also described. The method includes co-extruding the block copolymer and an organic polymer to provide a multilayer film comprising the one or two skin layers and the organic polymer film layer in direct contact with the one or two skin layers. A microspeaker including the diaphragm is also described.

Description

BACKGROUND OF THE INVENTION

[0001] Micro-speakers can be found in small electronic devices such as mobile phones, tablets, earbuds, headphones, and laptop computers. In a micro-speaker, a voice coil vibrates a diaphragm under the action of an electromagnetic force, and then pushes air to generate sound.

[0002] U.S. Patent No. 10,856,083 (Cheng et al.) and U.S. Patent Application Publications 20210120340, 20210258707, and 20210266672 (each belonging to Wang et al.) describe multi-layer diaphragms including a thermoplastic elastomer layer and an adhesive layer. The adhesive layer is required to have adhesive properties.

[0003] International Patent Application Publications WO 2021 / 186276 and WO 2021 / 186277 (each belonging to Yang et al.) describe single-layer or multi-layer diaphragms respectively containing chemically cross-linked thermoplastic polyester elastomers and chemically cross-linked thermoplastic polyurethane elastomers. For multi-layer diaphragms, the chemically cross-linked thermoplastic elastomer layers are separated by one or more damping adhesive layers. SUMMARY OF THE INVENTION

[0004] In one aspect, the present disclosure provides a diaphragm for a micro-speaker, the diaphragm having an organic polymer film layer in direct contact with one or two surface layers. The one or two surface layers independently include a block copolymer having hard segments and soft segments, wherein a part of the hard segments is included in a crystalline physical cross-linking domain. The organic polymer film layer is non-tacky at 25°C.

[0005] In another aspect, the present disclosure provides a diaphragm for a micro-speaker, the diaphragm having an organic polymer film layer in direct contact with and co-extruded with one or two surface layers. The one or two surface layers independently include a block copolymer having hard segments and soft segments, wherein a part of the hard segments is included in a crystalline physical cross-linking domain.

[0006] In another aspect, the present disclosure provides a diaphragm for a micro-speaker, the diaphragm having an organic polymer film layer in direct contact with one or two surface layers. The one or two surface layers independently include a block copolymer having hard segments and soft segments, wherein a part of the hard segments is included in a crystalline physical cross-linking domain. The organic polymer film layer contains a second block copolymer having a second hard segment and a second soft segment, wherein a part of the second hard segment is included in a crystalline physical cross-linking domain. The second soft segment is the same as the soft segment in the block copolymer in at least one of the one or two surface layers. The organic polymer film layer has a lower modulus than the one or two surface layers.

[0007] On the other hand, the present disclosure also provides a method for fabricating a diaphragm for any one of the above aspects. The method includes co-extruding a block copolymer and an organic polymer to provide a multilayer film, the multilayer film including one or two surface layers and an organic polymer film layer in direct contact with the one or two surface layers.

[0008] The two surface layers may be in direct contact with the organic polymer film layer on opposite sides of the organic polymer film layer.

[0009] On the other hand, the present disclosure provides a micro-speaker including a diaphragm.

[0010] In this application, terms such as "a", "an", and "the" are not intended to refer only to a single entity, but rather to include general categories of specific examples that can be used for illustration. The terms "a", "an", "the", and "said" can be used interchangeably with the term "at least one". The phrases "at least one of... " and "comprising at least one of... " followed by a list refer to any one of the items in the list and any combination of two or more items in the list. Unless otherwise indicated, all numerical ranges include their end values and non-integer values between the end values (e.g., 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.8, 4, and 5, etc.).

[0011] The terms "first" and "second" are used in the present disclosure only in their relative sense. It should be understood that these terms are used only for convenience in describing one or more embodiments of the embodiments unless otherwise specified.

[0012] As used herein, the term "acrylic" or "acrylate" includes compounds having at least one of an acrylic acid or methacrylic acid group.

[0013] The term "(meth)acrylic" with respect to a monomer, oligomer, or polymer means a vinyl-functional alkyl ester formed as a reaction product of an alcohol with acrylic acid or methacrylic acid.

[0014] The term "polymer" or "polymeric" includes homopolymers and copolymers, as well as homopolymers or copolymers that can be formed in miscible blends, for example, by co-extrusion or by reactions including, for example, transesterification reactions. The term "copolymer" includes random copolymers, block copolymers, graft copolymers, and star copolymers. The term "polymer" includes oligomers.

[0015] The term "crosslinking" refers to bonding polymer chains together via covalent chemical bonds (usually by crosslinking molecules or groups) to form a network polymer. Crosslinked polymers are generally characterized by insolubility, but can be swellable in the presence of a suitable solvent.

[0016] The "alkyl group" and the prefix "alk-" encompass straight-chain and branched-chain groups as well as cyclic groups. In some embodiments, unless otherwise specified, the alkyl group has up to 30 carbons (in some embodiments, up to 25, 20, 18, 16, or 15 carbons). The cyclic group can be monocyclic or polycyclic.

[0017] The foregoing summary of the disclosure is not intended to describe every disclosed embodiment or every implementation of the disclosure. The following description more specifically exemplifies illustrative embodiments. Accordingly, it should be understood that the figures and the following description are for illustrative purposes only and should not be construed as unduly limiting the scope of the disclosure. The figures are not drawn to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings incorporated herein and forming a part of this specification illustrate some embodiments of the disclosure.

[0019] Figure 1 A cross-sectional view of a multi-layer diaphragm for a micro-speaker having a three-layer structure according to an embodiment of the disclosure is shown. DETAILED DESCRIPTION

[0020] Certain known products that can be used as diaphragms for micro-speakers, including those described in the foregoing references, are made by laminating two surface layers with an adhesive film layer, where the adhesive layer serves as a damping core. We have found that the bond between the surface layer and the adhesive layer is generally weak, which can lead to a high rupture / failure rate due to delamination of the finished product during severe vibration. Lamination is typically carried out at room temperature, so an adhesive that is tacky at 25 °C is required. The diaphragm for a micro-speaker is generally cut from a multi-layer film having the above two surface layers and an adhesive core layer into a desired shape. When the adhesive core layer is tacky at 25 °C, it can adhere to the blade or die during cutting. Therefore, the tacky adhesive core results in the need to regularly clean the blade or die, thereby increasing the time, waste, and cost of the method. The diaphragm of the present disclosure can avoid these problems.

[0021] Figure 1 Embodiments of the diaphragm of the disclosure are shown in Figure 1As shown in the schematic cross-sectional view, one embodiment of the diaphragm 210 includes a first surface layer 240 (having two main surfaces, namely main surface 242 and main surface 244) and an optional second surface layer 260 (having two main surfaces, namely main surface 262 and main surface 264), wherein each of the first surface layer and the second surface layer is adjacent to opposite surfaces of the organic polymer film layer 250 (having two main surfaces, namely main surface 252 and main surface 254). More specifically, the first main surface 242 and the first main surface 262 form the outer surface of the diaphragm 210; the second main surface 244 of the first surface layer 240 is adjacent to the first main surface 252 of the organic polymer film layer 250; and the second main surface 264 of the second surface layer 260 is adjacent to the second main surface 254 of the organic polymer film layer 250. In some embodiments, the diaphragm further includes one or more additional layers, and in some embodiments, the one or more additional layers are attached to the first main surface 242 and the first main surface 262.

[0022] In some embodiments, the thickness of the diaphragm is in the range of 5 microns to 100 microns. In some embodiments, such as Figure 1 the thickness of the three-layer diaphragm of the diaphragm 210 shown is in the range of 30 microns (μm) to 100 μm, 36 μm to 80 μm, or 45 μm to 65 μm. In some embodiments, the first surface layer 240 and the second surface layer 260 each independently have a thickness in the range of 5 μm to 30 μm, 7 μm to 20 μm, or 10 μm to 15 μm, and the organic polymer film layer 250 has a thickness in the range of 5 μm to 60 μm, 10 μm to 40 μm, or 12 μm to 30 μm.

[0023] The diaphragm for a micro-speaker according to the present disclosure includes one or two surface layers independently containing a block copolymer. The block copolymer includes a hard segment and a soft segment. The soft segment and the uncrystallized hard segment form an amorphous phase, and a part of the hard segment crystallizes to form crystalline microdomains, which serve as physical crosslinking domains. Such block copolymers are generally referred to as thermoplastic elastomers at least before any chemical crosslinking is carried out as described below. In some embodiments, the block copolymer includes at least one of polyester, polyurethane, or polyamide. Thus, it can be at least one of a thermoplastic polyester elastomer, a thermoplastic polyurethane elastomer, or a thermoplastic polyamide elastomer at least before any chemical crosslinking is carried out as described below. In some embodiments, the diaphragm includes two surface layers (such as Figure 1 the diaphragm 210 shown) that are in direct contact with the organic polymer film layer on opposite sides of the organic polymer film layer. In these two surface layers, the block copolymers can be the same or different (i.e., they are independently selected). In some embodiments, the two surface layers contain different block copolymers or different combinations of block copolymers.

[0024] A variety of thermoplastic polyester elastomers (TPEEs) can be used to practice the present disclosure. They can be prepared by known methods or can be commercially available. The soft segments in the TPEE can include, for example, polyethers or aliphatic polyesters (such as aliphatic polyesters, polytetrahydrofuran ethers, polyphenylene ethers, polypropylene oxides, polyethylene oxides, and combinations thereof) with a relative molecular mass in the range of 600 grams per mole to 6000 grams per mole. The hard segments in the TPEE can include polymers of dibasic acids (such as terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, biphenyldicarboxylic acid, and combinations thereof) and diols (such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, and combinations thereof). Commercially available TPEEs that can be used for the diaphragm of the present disclosure include those purchased from Ticona under the trade name "RITEFLEX", from Du Pont De Nemours and Company, Wilmington, DE under the trade name "HYTREL", from Eastman, Kingsport, TN under the trade name "ECDEL", from DSM under the trade name "ARNITEL", and from Chenguang Kexin Company under the trade name "SUNPRENE".

[0025] In some embodiments, the TPEE is a block copolymer composed of polyester hard segments and polyether soft segments. In some embodiments, the thermoplastic polyester elastomer is a block copolymer composed of crystalline hard segments of polybutylene terephthalate (PBT) and polyether soft segments based on long-chain polytetrahydrofuran. Examples of suitable thermoplastic polyester elastomers including these structures include those purchased from Du Pont De Nemours and Company under the trade names "HYTREL 3078", "HYTREL 5556", "HYTREL 6356", "HYTREL 7246", and "HYTREL 8238". Other suitable thermoplastic polyester elastomers include those purchased from Shibata Company under the trade name "TPEE D63".

[0026] A variety of thermoplastic polyurethane elastomers (TPUs) can be used to practice the present disclosure. They can be prepared by known methods or can be commercially available. TPU is a thermoplastic block copolymer composed of alternately connected soft segments and hard segments, where the hard segments are isocyanate segments (e.g., including aliphatic isocyanate segments, aromatic isocyanate segments, or combinations thereof), and the soft segments are polyether polyol segments or polyester polyol segments. The polyether polyol segments and polyester polyol segments can be any of the segments described above for TPEE. In addition to the ratio of the hard segments and soft segments, the types of isocyanate, polyether polyol, and polyester polyol also affect the properties of TPU. TPU molecules are substantially linear, and TPU has some physical crosslinking, typically formed by the interaction between urethane groups in the molecule. Commercially available TPUs that can be used for the diaphragms of the present disclosure include those purchased from BASF Company, Ludwigshafen, Germany under the trade name "ELASTOLLANE", TPUs purchased from Covestro Company under the trade name "DESMOPAN", and TPU films produced by Shibata Company.

[0027] A variety of thermoplastic polyamide elastomers can be used to practice the present disclosure. They can be prepared by known methods or can be commercially available. In thermoplastic polyamide elastomers, the soft segments can be polyether polyol segments or polyester polyol segments, such as any of the segments described above for TPEE. Thermoplastic polyamides are commercially available, for example, from Avient, Avon Lake, OH under the trade name "PEBAX".

[0028] In some embodiments, one or both surface layers contain inorganic fillers. Any fillers commonly known to those skilled in the art can be used in the context of the present disclosure. Examples of suitable fillers that can be used include zeolites, clay fillers, glass beads, silica-based fillers, hydrophobic silica-based fillers, hydrophilic silica-based fillers, pyrogenic silica, fibers (especially glass fibers, carbon fibers, graphite fibers, silica fibers, ceramic fibers), hollow ceramic microspheres, nanoparticles (especially silica nanoparticles), and combinations thereof. Other additives can optionally be included in one or both surface layers to achieve any desired properties. Examples of such additives include pigments, toughening agents, reinforcing agents, flame retardants, antioxidants, and various stabilizers. The amount of additives added is sufficient to obtain the desired final properties. In some embodiments, the filler can be present in one or both surface layers in an amount of up to 10 wt%, 7.5 wt%, 5 wt%, or 2.5 wt% based on the total weight of the corresponding layer.

[0029] The diaphragm for a micro speaker according to some embodiments of the present disclosure includes an organic polymer film layer in direct contact with one or two surface layers containing a block copolymer, wherein, in some embodiments, the organic polymer film layer is not sticky at 25°C. "Direct contact" means that there is no adhesive between the first layer and the organic polymer film layer. For the purposes of the present disclosure, a ball rolling test can be used to determine the stereoregularity of a material. As described in the examples below, a non-sticky organic polymer film can be defined by the ball rolling off it in a ball rolling test conducted at 25°C.

[0030] A variety of organic polymer film layers can be used to practice the present disclosure. They can be prepared by known methods or can be commercially available. In some embodiments, the organic polymer film layer comprises at least one of an acrylic copolymer or a second block copolymer (in some embodiments, a triblock copolymer). The second block copolymer can have a hard segment and a soft segment, wherein a part of the hard segment is included in the crystalline physical crosslinking domain. Available block copolymers include block copolymers having polyester, polyurethane or polyamide hard segments and polyether or aliphatic polyester soft segments. The soft segment can include, for example, a polyether or aliphatic polyester having a relative molecular mass in the range of 600 g / mol to 6000 g / mol (e.g., aliphatic polyester, polytetrahydrofuran ether, polyphenylene ether, polypropylene oxide, polyethylene oxide, and combinations thereof). Further examples of available block copolymers include, for example, styrene block copolymers having isoprene, butadiene or ethylene-butene soft segments and acrylic block copolymers, such as poly(methyl methacrylate)-poly(n-butyl methacrylate)-poly(methyl methacrylate) triblock copolymer. In some embodiments, the organic polymer film layer comprises at least one of a polyamide-polyether-polyamide triblock copolymer, an acrylic copolymer or a styrene block copolymer. In some embodiments, the organic polymer film layer comprises a styrene block copolymer, and in some embodiments, a styrene-isoprene-styrene copolymer, a styrene-butadiene-styrene copolymer or a styrene-ethylene-butene-styrene copolymer. In some embodiments, the organic polymer film layer comprises an acrylic copolymer, and in some embodiments, a poly(methyl methacrylate)-poly(n-butyl methacrylate)-poly(methyl methacrylate) triblock copolymer.

[0031] In some embodiments, the organic polymer film layer comprises a second block copolymer having a second hard segment and a second soft segment, wherein a portion of the second hard segment is included in the crystalline physical crosslinking domain, and wherein the second soft segment is the same as the soft segment in the block copolymer in at least one of the one or two surface layers. The second block copolymer can be used in combination with any of the other materials that can be used in the organic polymer film layer in any of its embodiments described above. Examples of suitable second block copolymers include, for example, the copolymer commercially available under the trade name "HYTREL 3078" from Du Pont De Nemours and Company. Including the second block copolymer in the organic polymer film layer can improve the compatibility of the organic polymer film layer with the one or two surface layers.

[0032] Suitable commercially available materials that can be used in the organic polymer film layer include an acrylic copolymer commercially available under the trade name "ABC KURARITYLA2330" from Kuraray, Chiyoda City, Japan, a styrene-ethylene-butene-styrene copolymer commercially available under the trade name "KRATON G1645" from Kraton, Houston, TX, a blend of polyether and polyamide commercially available under the trade name "PEBAX 3533" from Avient, Avon Lake, OH, and a thermoplastic elastomer commercially available under the trade name "VERSAFLEX 4132" from Avient.

[0033] Other acrylic copolymers that can be used in the organic polymer film layer include various acrylic copolymers made from (meth)acrylic acid alkyl ester monomers. Examples of suitable (meth)acrylic acid alkyl esters for preparing acrylic polymers include those represented by Formula I:

[0034] CH2=C(R’)COOR(I)

[0035] wherein R’ is a hydrogen or methyl group, and R is an alkyl group having from 1 to 30, 4 to 30, 6 to 30, 8 to 30, 6 to 24, 6 to 20, 6 to 18, 8 to 24, 8 to 20 or 8 to 20 carbon atoms, and may be straight-chain or branched. Examples of suitable monomers represented by formula I include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, octyl (meth)acrylate, isooctyl (meth)acrylate, 2-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, isodecyl acrylate, undecyl (meth)acrylate, n-dodecyl acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, tetradecyl (meth)acrylate, pentadecyl (meth)acrylate, hexadecyl (meth)acrylate, heptadecyl (meth)acrylate, 2-propylheptyl (meth)acrylate, stearyl (meth)acrylate, n-nonyl (meth)acrylate, isononyl (meth)acrylate, isomyristyl (meth)acrylate, isostearyl (meth)acrylate, octadecyl (meth)acrylate and docosyl (meth)acrylate. Suitable (meth)acrylic acid alkyl ester monomers also include a mixture of at least two or at least three structural isomers of the secondary alkyl (meth)acrylate of formula II:

[0036]

[0037] wherein R 1 and R 2 are each independently a C1 to C 30 saturated linear alkyl group; the sum of the number of carbons in R 1 and R 2 is from 7 to 31, and R 3 is H or CH3. In some embodiments, the sum of the number of carbons in R 1 and R 2 can be from 7 to 27, 7 to 25, 7 to 21, 7 to 17, 7 to 11, 7, 11 to 27, 11 to 25, 11 to 21, 11 to 17 or 11. Methods for making and using such monomers and monomer mixtures are described in U.S. Patent No. 9,102,774 (Clapper et al.). In some embodiments, the (meth)acrylic acid alkyl ester monomer comprises at least one of 2-ethylhexyl (meth)acrylate, 2-propylheptyl (meth)acrylate or isooctyl (meth)acrylate.

[0038] In some embodiments, the acrylic copolymer useful for the organic polymer film layer comprises monomer units of “high T g ” monomers, and these high T g monomers provide a homopolymer having a glass transition temperature (T g ) of at least 50 °C, 60 °C or 70 °C upon polymerization (i.e., the homopolymer formed from this monomer has a T g ) of at least 50 °C, 60 °C or 70 °C. The acrylic polymer may comprise at least 5 wt% (in some embodiments, at least 7.5 wt%, 10 wt%, 12.5 wt% or 15 wt%) of monomer units of “high T g ” monomers. The T g of the homopolymer is measured by differential scanning calorimetry and many are reported in the “Polymer Property Database” found at polymerdatabase.com. Some suitable high T g monomers include methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, sec-butyl methacrylate, tert-butyl (meth)acrylate, cyclohexyl methacrylate, isobornyl (meth)acrylate, stearyl (meth)acrylate, phenyl acrylate, benzyl methacrylate, 3,3,5-trimethylcyclohexyl (meth)acrylate, tert-butylcyclohexyl methacrylate, 2-phenoxyethyl methacrylate, N-octyl (meth)acrylamide, tetrahydrofurfuryl methacrylate, and mixtures thereof. Other suitable high T g monomers have a single vinyl group that is not a (meth)acryloyl group, such as various vinyl ethers (e.g., vinyl methyl ether), vinyl esters (e.g., vinyl acetate and vinyl propionate), styrene, substituted styrenes (e.g., α-methylstyrene), vinyl halides, and mixtures thereof. In some embodiments, based on the total weight of the acrylic copolymer, the acrylic copolymer useful for the organic polymer film layer comprises 15 weight percent (wt%) to 50 wt% of high T g monomer units. In some embodiments, based on the total weight of the acrylic copolymer, the acrylic copolymer comprises 20 wt% to 50 wt%, 25 wt% to 50 wt%, 20 wt% to 45 wt% or 25 wt% to 45 wt%, 17 wt% to 23 wt% or 17 wt% to 20 wt% of high T g monomer units.

[0039] In some embodiments, the acrylic copolymer useful for the organic polymer film layer comprises acid monomer units or other polar monomer units. Examples of (meth)acrylic monomer units include those from acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, ethylacrylic acid, crotonic acid, citraconic acid, cinnamic acid, ethyl β-carboxyacrylate, and 2-methacryloyloxyethyl succinate. Other available acid monomer units include those from sulfonic acids (such as 2-sulfoethyl methacrylate, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid) and their salts, and phosphonic acids (such as vinylphosphonic acid) and their salts. In some embodiments, the (meth)acrylic monomer unit is an acrylic monomer unit or a methacrylic monomer unit. The (meth)acrylic monomer unit includes salts of these acids, such as alkali metal salts and ammonium salts. Other available polar monomer units include those from hydroxy- or amino-substituted acrylates (e.g., 2-hydroxyethyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, 6-hydroxyhexyl acrylate, 8-hydroxyoctyl acrylate, 10-hydroxydecyl acrylate, 12-hydroxylauryl acrylate, methyl (4-hydroxymethylcyclohexyl)acrylate, ethoxylated hydroxyethyl methacrylate (such as monomers commercially available from Sartomer under the trade names CD570, CD571, CD572), dimethylaminoethyl acrylate, tert-butylaminoethyl acrylate, aminoethyl acrylate, N,N-dimethylaminoethyl acrylate, N,N-dimethylaminopropyl acrylate, and the methacrylates of the foregoing acrylates), N-vinyl-2-pyrrolidone, N-vinylcaprolactam, (meth)acrylonitrile ethyl cyanoacrylate, maleic anhydride, and combinations thereof. In some embodiments, the polar monomer unit is present in an amount of up to 15 wt% based on the total weight of the acrylic copolymer. In some embodiments, the polar monomer unit is present in an amount of at least 0.1 wt%, at least 0.5 wt%, at least 1 wt%, at least 2 wt%, or even at least 3 wt% based on the total weight of the acrylic copolymer. Thus, in some embodiments, the polar monomer unit is present in an amount in the range of 0.1 wt% to 15 wt%, 0.5 wt% to 15 wt%, 1.0 wt% to 10 wt%, 2.0 wt% to 8.0 wt%, 2.5 wt% to 6.0 wt%, or 3.0 wt% to 6.0 wt% based on the total weight of the acrylic copolymer. In some embodiments, the amount of the polar monomer unit is up to 10 weight percent or up to 5 weight percent.

[0040] "High T g " monomer or at least one of the polar monomers, including any of those described in any of the embodiments above, can be used to increase the cohesive strength of the resulting acrylic polymer. Including "High T g"Monomer units of at least one of the monomers or polar monomers generally increase the modulus of the acrylic polymer and decrease the tackiness of the acrylic polymer. The amount of "high T g " monomer units, polar monomer units, or a combination thereof, including any one of the above amounts, is selected such that the acrylic polymer is non-tacky.

[0041] In some embodiments, the acrylic copolymer is prepared from 45 to 65 parts of 2-ethylhexyl acrylate, 2 to 8 parts of N-vinylpyrrolidone, 30 to 50 parts of isobornyl acrylate, 1 to 5 parts of acrylic acid, 0.05 to 0.3 part of 2,2-dimethoxy-1,2-diphenylethan-1-one, 0.05 to 1 part of an antioxidant (such as the antioxidant commercially available under the trade name “IRGANOX 1076” from BASF Corp., Ludwigshafen, Germany), and 0.005 to 0.04 part of isooctyl thioglycolate. In some embodiments, the acrylic polymer is prepared from 55 to 75 parts of an octyl acrylate isomer blend prepared as described in U.S. Patent No. 9,102,774 (Clapper et al.), 20 to 40 parts of isobornyl acrylate, 1 to 5 parts of acrylic acid, 0.05 to 0.3 part of 2,2-dimethoxy-1,2-diphenylethan-1-one, 0.05 to 1 part of an antioxidant (such as the antioxidant commercially available under the trade name “IRGANOX 1076” from BASF Corp.), and 0.005 to 0.04 part of isooctyl thioglycolate. In some embodiments, the acrylic polymer is prepared from 54 parts of 2-ethylhexyl acrylate, 5 parts of N-vinylpyrrolidone, 38 parts of isobornyl acrylate, 3 parts of acrylic acid, 0.15 part of 2,2-dimethoxy-1,2-diphenylethan-1-one, 0.4 part of an antioxidant (such as the antioxidant commercially available under the trade name “IRGANOX 1076” from BASF Corp., Ludwigshafen, Germany), and 0.02 part of isooctyl thioglycolate. In some embodiments, the acrylic polymer is prepared from 67 parts of an octyl acrylate isomer blend prepared as described in U.S. Patent No. 9,102,774 (Clapper et al.), 30 parts of isobornyl acrylate, 3 parts of acrylic acid, 0.15 part of 2,2-dimethoxy-1,2-diphenylethan-1-one, 0.4 part of an antioxidant (such as the antioxidant commercially available under the trade name “IRGANOX 1076” from BASF Corp.), and 0.02 part of isooctyl thioglycolate. The intrinsic viscosity of any of these polymers can be in the range of 0.6 to 0.8, 0.6 to 0.7, about 0.646, or about 0.682. The intrinsic viscosity can be obtained by measuring the flow time of a 10 mL polymer solution (0.3 g / dL polymer dissolved in ethyl acetate) using a Lauda viscometer in a water bath controlled at 27 °C, using the procedure described on pages 84 and 85 of the second edition (1971) of Textbook of Polymer Science by F.W. Billmeyer, published by Wiley-Interscience.

[0042] Acrylic polymers useful for organic polymer film layers can be prepared by any conventional free radical polymerization method, including solution, radiation, bulk, dispersion, emulsion, solventless, and suspension methods. Copolymers produced by such polymerization methods can be random or block copolymers. The degree of conversion (conversion of monomer to polymer) can be monitored during polymerization by measuring the refractive index of the polymerization mixture. In some embodiments, acrylic polymers are prepared using a substantially solventless free radical polymerization method.

[0043] The monomer mixture can contain a polymerization initiator, especially of the thermal or photoinitiator type, and in an amount effective to polymerize the comonomers. In a typical thermal polymerization process, the monomer mixture is subjected to thermal energy in the presence of a thermal polymerization initiator (i.e., a thermal initiator). Examples of suitable thermal initiators are those available from E.I. DuPont de Nemours Co. under the trade name "VAZO", including "VAZO 67" (2,2'-azobis(2-methylbutyronitrile)), "VAZO 64" (2,2'-azobis(isobutyronitrile)), and "VAZO 52" (2,2'-azobis(2,4-dimethylvaleronitrile)), as well as various peroxides such as benzoyl peroxide, cyclohexanone peroxide, lauroyl peroxide, and mixtures thereof.

[0044] Suitable photoinitiators include those purchased from IGM Resins, Waalwijk, The Netherlands under the trade name "OMNIRAD", and include 1-hydroxycyclohexyl phenyl ketone ("OMNIRAD 184"), 2,2-dimethoxy-1,2-diphenylethan-1-one ("OMNIRAD 651"), bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide ("OMNIRAD 819"), 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methylpropan-1-one ("OMNIRAD 2959"), 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone ("OMNIRAD 369"), 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one ("OMNIRAD 907"), and 2-hydroxy-2-methyl-1-phenylpropan-1-one ("OMNIRAD 1173"), oligo[2-hydroxy-2-methyl-1-[4-(1-methylethenyl)phenyl]propanone] purchased from IGM Resins under the trade name "ESACURE KIP 150", and bifunctional α-hydroxy ketones purchased from IGM Resins under the trade names "ESACURE ONE" and "ESACURE KIP 160" (2-hydroxy-1-[4-[4-(2-hydroxy-2-methylpropanoyl)phenoxy]phenyl]-2-methylpropanone). Bifunctional α-hydroxy ketones mean that the photoinitiator includes two α-hydroxy ketone groups. Polyfunctional α-hydroxy ketones mean that the photoinitiator includes two or more α-hydroxy ketone groups. Additional suitable photoinitiators include benzyl dimethyl ketal, 2-methyl-2-hydroxyacetophenone, benzoin methyl ether, benzoin isopropyl ether, anisoin methyl ether, aromatic sulfonyl chlorides, photoactive oximes, and combinations thereof.

[0045] If desired, a chain transfer agent can be added to the monomer mixture to control the molecular weight of the acrylic polymer. Examples of chain transfer agents that can be used include carbon tetrabromide, alcohols, thiols, and mixtures thereof. In some embodiments, the chain transfer agent comprises at least one of isooctyl thioglycolate or carbon tetrabromide.

[0046] In some embodiments, one or both of the skin layers and the organic polymer film layer are coextruded. For the purposes of this disclosure, coextrusion means the simultaneous melt processing of multiple melt streams and the combination of such melt streams, for example, into a single integrated structure or coextruded film from a single extrusion die. The multilayer film composed of at least one or both of the skin layers and the organic polymer film layer can be coextruded using any suitable type of coextrusion die and any suitable film-forming method (such as blown film extrusion or cast film extrusion). In some embodiments, the multilayer melt stream can be formed by a multilayer feedblock, such as the multilayer feedblock shown in U.S. Patent No. 4,839,131 (Cloeren) or other specialized feedblocks or dies, such as those made by Cloeren Co., Orange, TX. The feedblocks and dies used are typically heated to facilitate polymer flow and layer adhesion, where the temperature of the die depends on the polymer used. Coextrusion techniques can be found in many polymer processing references, including Progelhof, R.C. and Throne, J.L., "Polymer Engineering Principles", Hanser / Gardner Publications, Inc., Cincinnati, Ohio, 1993.

[0047] In some embodiments, additional layers are coextruded with one or both of the skin layers and the organic polymer film layer. Again referring to Figure 1 , in some embodiments, a polyolefin layer (e.g., LLDPE) can be coextruded as a support layer along the first major surfaces 242 and 262 of the skin layers during the coextrusion process. Such layers can be removed to fabricate the diaphragms of this disclosure.

[0048] In the available blown film method, block copolymers and organic polymers that can be used for one or both of the skin layers and the organic polymer film layer are simultaneously extruded through concentric annular holes provided in a blown film die, as described above in any of its embodiments. As the roll drags the tube upward, the coextruded polymer tube is inflated with pressurized air, thus causing the lateral and vertical stretching of the film. Then the extruded multilayer tube is continuously slit, and the opening is propagated to form a flat sheet and is guided through the nip rolls to produce a film including one or both of the skin layers and the organic polymer film layer.

[0049] It should be understood that solvent-based adhesives (e.g., "PSA 6574" silicone damping adhesive, a pressure-sensitive adhesive purchased from Momentive Company, and "3M 3567ATT" acrylic damping adhesive, a pressure-sensitive adhesive purchased from 3M Company, St. Paul, MN) are generally not used in co-extrusion processes. Additionally, certain polymers such as polyetheretherketone (PEEK) are not likely to be co-extruded with thermoplastic elastomers (e.g., any of the thermoplastic polyurethane elastomers such as those described above), because the extrusion temperature of PEEK exceeds 340 °C. Thus, the extrusion of such materials reported in WO2021 / 186277 (Yang et al.) refers to extruding individual layers and laminating them together.

[0050] Lamination and co-extrusion processes can result in different structures at the interfaces between layers. Compatible chemicals in co-extruded layers can lead to interfacial diffusion. Such interlayer diffusion is not observed in laminated layers. In embodiments where one or two surface layers and an organic polymer film layer are co-extruded, the polymer compositions used for each layer can be selected to have similar properties such as chemical structure and melt viscosity. The compatibility of the organic polymer film layer with one or two surface layers can increase the interlayer adhesion during co-extrusion.

[0051] The organic polymer film layer generally has a lower elastic modulus than one or two surface layers. In some embodiments, the elastic modulus of the organic polymer film layer is at least 10%, 15%, 20%, 25%, or 50% lower than the elastic modulus of one or two surface layers. On the other hand, in some embodiments, the elastic modulus of the organic polymer film layer is at least 1%, 2%, 5%, or 10% of the elastic modulus of one or two surface layers (i.e., it is within two orders of magnitude of the elastic modulus of one or two surface layers). As used herein, "elastic modulus" is synonymous with Young's modulus, elastic modulus, and DMT modulus.

[0052] For example, after embedding a sample of the diaphragm in a suitable resin (such as epoxy resin) and obtaining a cross-section by cryosectioning, the elastic modulus of the cross-section of the diaphragm having an organic polymer film layer and one or two surface layers, as well as the interfacial diffusion between the layers, can be determined by nanoindentation based on an atomic force microscope (AFM). In AFM, a small sharp probe tip attached to the end of a cantilever raster scans the surface. As the tip is scanned, the AFM cantilever bends; the cantilever bending force is described by Hooke's law: Fc = -kx, where k is the cantilever spring constant, Fc is the force on the cantilever, and x is the cantilever deflection. A method for determining the elastic modulus uses a dynamic AFM mode called Peak Force Tapping, in which the tip is modulated such that the tip and the surface intermittently come into contact. At each x-y position, the maximum force (peak force) between the tip and the sample is kept constant to generate a three-dimensional topographic map of the surface. In addition to topographic imaging, this mode also acquires the force-distance curve between the tip and the sample at each pixel of the image channel. The force-distance curve is obtained as the tip approaches the surface and retracts from the surface. The Peakforce Tapping mode used in the following examples calculates the modulus using the DMT model. To determine whether the organic polymer film layer has a lower elastic modulus than one or two surface layers, the material can be measured towards the central part of the layer, i.e., at points within 50% of the total thickness of the layer set around the central plane of the layer.

[0053] The interfacial diffusion between the layers of the diaphragm can be detected by AFM by measuring the elastic modulus towards the central part of the organic polymer film layer, the central part of one of the surface layers, and at the edge of the surface layer in interfacial contact with the organic polymer film layer. The elastic modulus at the interface can be different from both the central part of the organic polymer film layer and the central part of one of the surface layers. This interface cannot be detected in the laminated sample.

[0054] In some embodiments, the storage modulus of the organic polymer film layer is higher than that typically observed for a pressure-sensitive adhesive (PSA). In some embodiments, as measured by a rheometer, the storage modulus of the organic polymer film layer at 25 °C and a frequency of 1 Hz is at least 0.15 megapascals (MPa), at least 0.2 MPa, at least 0.25 MPa, at least 0.3 MPa, or greater than 0.3 MPa. Polymer compositions having a storage modulus equal to or greater than these values tend to lose tack. Once the modulus of the polymer layer exceeds 0.2 MPa at 1 rad / s at the application temperature, it is generally considered useless in a lamination process unless additional heat is introduced. Heat is detrimental to a typical diaphragm lamination process because it has a negative impact on the crystallization of the surface layer, which ultimately affects the acoustic performance. Therefore, in some embodiments, the storage modulus of the organic polymer film layer is too high for an organic polymer film layer that can be used in a lamination process.

[0055] In some embodiments, the storage modulus of the diaphragm is in the range of 50 MPa to 1000 MPa, 75 MPa to 900 MPa, or 85 MPa to 700 MPa. For example, an elastic modulus within the above ranges enables the diaphragm to effectively drive air to generate sound and provides the stability and consistency of the diaphragm during long-term operation. The storage modulus is measured across the entire diaphragm, including the organic polymer film layer and one or two surface layers. For the purposes of this disclosure, the modulus of the entire diaphragm is determined using dynamic mechanical analysis according to the test method described in the examples below.

[0056] In some embodiments, at least one of the one or two surface layers or the organic polymer film layer is chemically crosslinked. Chemical crosslinking refers to a crosslinked network structure that includes chemical bonds (such as covalent bonds) between polymer chains in addition to or instead of physical crosslinks that are typically present in thermoplastic elastomers. The chemical crosslinking treatment forms a crosslinked network structure within the block copolymer of one or two surface layers, within the organic polymer film layer, or between the organic polymer film layer and at least one of the surface layers through chemical crosslinking points formed by covalent bonds. After chemical crosslinking, the elastomers in the one or two surface layers and optionally the organic polymer film layer are no longer used as thermoplastic materials, even if they are formed from one or more thermoplastic elastomers. To determine whether the one or two surface layers and the organic polymer film layer are chemically crosslinked, a solubility assessment can be performed. For the purposes of this disclosure, if there is residue left in the sample that is immersed in a solvent and decanted according to the solubility test described below, then chemical crosslinking is present. A suitable solvent for the one or two surface layers is dimethyl sulfoxide. Suitable solvents for the organic polymer film layer include dimethyl sulfoxide or acetone for acrylic copolymers, and toluene for styrene block copolymers.

[0057] In some embodiments, at least one of the one or two surface layers or the organic polymer film layer is unchemically crosslinked. In some embodiments, both the one or two surface layers and the organic polymer film layer are unchemically crosslinked. In some embodiments, even after the diaphragm is exposed to electron beam radiation, both the one or two surface layers and the organic polymer film layer are unchemically crosslinked.

[0058] The method for chemically crosslinking at least one of the one or two surface layers or the organic polymer film layer is not particularly limited, and conventional methods such as electron beam radiation crosslinking, microwave radiation crosslinking, ultraviolet radiation crosslinking, and thermal crosslinking can be used. In some embodiments, at least one of the one or two surface layers or the organic polymer film layer is crosslinked by electron beam radiation. In some embodiments, at least one of the one or two surface layers or the organic polymer film layer has a crosslinkable structure in its molecule (including a structure having a crosslinkable group or a structure that can be broken and crosslinked by electron beam radiation). In some embodiments, the energy of the electron beam radiation is from 100 kV to 300 kV, and the diaphragm of the present disclosure is exposed to an electron beam dose of from 3 Mrad to 12 Mrad to form crosslinks through covalent bonds.

[0059] In some embodiments, as measured by rheometry, the loss factor of the organic polymer film layer in the range of 100 Hz to 10,000 Hz at 25 °C is at least 0.01, 0.015, 0.02, 0.03, 0.04, or 0.05. For the purposes of the present disclosure, the rheometer is an ARES-G2 rheometer (TA Instruments, New Castle, DE). The method described in the examples below can be used. The loss factor value tanδ is calculated from the storage modulus G' and the loss modulus G".

[0060] tanδ = G" / G'

[0061] When the loss factor of the organic polymer film layer has these values, the organic polymer film layer generally provides beneficial vibration damping performance.

[0062] In some embodiments, as measured by dynamic mechanical analysis using the method described in the examples below, the loss factor of the diaphragm at 25 °C and 1000 Hz is at least 0.01, 0.015, 0.02, 0.03, 0.04, 0.05, or 0.06. In some embodiments, as measured by dynamic mechanical analysis, the loss factor of the diaphragm at 25 °C and 1000 Hz is at most 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, or 0.5.

[0063] The diaphragm of the present disclosure can be prepared by molding one or two surface layers and an organic polymer film layer into a desired shape by any method known in the art. In some embodiments, the diaphragm is prepared by thermoforming. In embodiments where a chemical crosslinking treatment is performed, thermoforming can be carried out before or after the chemical crosslinking treatment. Compared with some engineering thermoplastics (such as PEEK) commonly used to make diaphragms, the thermoforming of the diaphragm of the present disclosure can be carried out more easily because the glass transition temperature of the material used in the diaphragm of the present disclosure is generally lower than that of such engineering thermoplastics.

[0064] In some embodiments, the diaphragm has a folded structure. One or more of any number of folded structures known to be usable for diaphragms can be used for the diaphragm of the present disclosure. In some embodiments, the folded structure can be beneficial to the sensitivity, consistency, and amplitude of the diaphragm.

[0065] The following list of embodiments describes some embodiments of the present disclosure.

[0066] In a first embodiment, the present disclosure provides a diaphragm for a micro speaker, the diaphragm comprising: one or two surface layers, the one or two surface layers independently comprising a block copolymer, the block copolymer comprising a hard segment and a soft segment, wherein a portion of the hard segment is included in a crystalline physical crosslinking domain; and an organic polymer film layer, the organic polymer film layer being in direct contact with the one or two surface layers, wherein the organic polymer film layer is non-tacky at 25 °C. In a second embodiment, the present disclosure provides the diaphragm according to the first embodiment, wherein the one or two surface layers and the organic polymer film layer are co-extruded. In a third embodiment, the present disclosure provides a diaphragm for a micro speaker, the diaphragm comprising one or two surface layers, the one or two surface layers independently comprising a block copolymer, the block copolymer comprising a hard segment and a soft segment, wherein a portion of the hard segment is included in a crystalline physical crosslinking domain co-extruded with an organic polymer film layer in direct contact with the one or two surface layers. In a fourth embodiment, the present disclosure provides the diaphragm according to any one of the first to third embodiments, wherein the organic polymer film layer comprises at least one of a second block copolymer or an acrylic copolymer, wherein the second block copolymer comprises a hard segment and a soft segment, wherein a portion of the hard segment is included in a crystalline physical crosslinking domain. In a fifth embodiment, the present disclosure provides the diaphragm according to any one of the first to fourth embodiments, wherein the organic polymer film layer comprises a second block copolymer having a second hard segment and a second soft segment, wherein a portion of the second hard segment is included in a crystalline physical crosslinking domain, and wherein the second soft segment is the same as the soft segment in the block copolymer in at least one of the one or two surface layers. In a sixth embodiment, the present disclosure provides the diaphragm according to any one of the first to fifth embodiments, wherein the organic polymer film layer has a lower modulus than the one or two surface layers. In a seventh embodiment, the present disclosure provides a diaphragm for a micro speaker, the diaphragm comprising: one or two surface layers, the one or two surface layers independently comprising a block copolymer, the block copolymer comprising a hard segment and a soft segment, wherein a portion of the hard segment is included in a crystalline physical crosslinking domain; and an organic polymer film layer, the organic polymer film layer being in direct contact with the one or two surface layers, wherein the organic polymer film layer comprises a second block copolymer having a second hard segment and a second soft segment, wherein a portion of the second hard segment is included in a crystalline physical crosslinking domain, and wherein the organic polymer film layer has a lower modulus than the one or two surface layers. In an eighth embodiment, the present disclosure provides the diaphragm according to the seventh embodiment, wherein the second soft segment is the same as the soft segment in the block copolymer in at least one of the one or two surface layers.In a ninth embodiment, the present disclosure provides a diaphragm according to any one of the first to eighth embodiments, wherein the diaphragm includes two surface layers in direct contact with the organic polymer film layer on opposite sides of the organic polymer film layer. In a tenth embodiment, the present disclosure provides a diaphragm according to any one of the first to ninth embodiments, and the diaphragm further includes one or more additional layers.

[0067] In an eleventh embodiment, the present disclosure provides a diaphragm according to any one of the first to tenth embodiments, wherein at least one of the one or two surface layers or the organic polymer film layer is chemically crosslinked. In a twelfth embodiment, the present disclosure provides a diaphragm according to any one of the first to tenth embodiments, wherein at least one of the one or two surface layers or the organic polymer film layer is not chemically crosslinked. In a thirteenth embodiment, the present disclosure provides a diaphragm according to any one of the first to twelfth embodiments, wherein the block copolymer includes at least one of polyester, polyurethane, or polyamide. In a fourteenth embodiment, the present disclosure provides a diaphragm according to any one of the first to thirteenth embodiments, wherein the block copolymer includes polyester. In a fifteenth embodiment, the present disclosure provides a diaphragm according to any one of the first to fourteenth embodiments, and as measured by dynamic mechanical analysis, the loss factor of the diaphragm is at least 0.05 at 25°C. In a sixteenth embodiment, the present disclosure provides a diaphragm according to any one of the first to fifteenth embodiments, wherein at least one of the one or two surface layers includes inorganic fillers. In a seventeenth embodiment, the present disclosure provides a diaphragm according to any one of the first to sixteenth embodiments, and the thickness of the diaphragm is in the range of 5 microns to 100 microns.

[0068] In an eighteenth embodiment, the present disclosure provides a diaphragm according to any one of the first to seventeenth embodiments, wherein the organic polymer film layer includes a second block copolymer, and the second block copolymer includes an acrylic triblock copolymer, a polyamide-polyether-polyamide triblock copolymer, a polyester-polyether-polyester triblock copolymer, or a styrene block copolymer. In a nineteenth embodiment, the present disclosure provides a diaphragm according to the eighteenth embodiment, wherein the styrene block copolymer is a styrene-isoprene-styrene copolymer, a styrene-butadiene-styrene copolymer, or a styrene-ethylene-butene-styrene copolymer. In a twentieth embodiment, the present disclosure provides a diaphragm according to any one of the first to nineteenth embodiments, wherein the organic polymer film layer includes an acrylic copolymer, and the acrylic copolymer includes monomer units of (meth)acrylic acid alkyl esters represented by the following formula:

[0069] CH2=C(R’)COOR

[0070] wherein R’ is a hydrogen or methyl group, and R is a monomer unit of at least one of a linear or branched alkyl group having 1 to 30 carbon atoms, N-vinylpyrrolidone, or acrylic acid, at least 20% by weight of the monomer units of at least one high T g monomer, and in some embodiments, is a monomer unit of at least one of isobornyl acrylate or isobornyl methacrylate at least 20% by weight.

[0071] In a twenty-first embodiment, the present disclosure provides a method for fabricating a diaphragm according to any one of the first to twentieth embodiments, the method comprising co-extruding the block copolymer and the organic polymer to provide a multilayer film, the multilayer film comprising the one or two surface layers and an organic polymer film layer in direct contact with the one or two surface layers. In a twenty-second embodiment, the present disclosure provides the method according to the twenty-first embodiment, the method further comprising irradiating the multilayer film. In a twenty-third embodiment, the present disclosure provides the method according to the twenty-first embodiment, the method further comprising electron beam irradiating the multilayer film. In a twenty-fourth embodiment, the present disclosure provides the method according to the twenty-third embodiment, wherein the electron beam irradiation has an electron beam energy of 100 kV to 300 kV and an electron beam dose of 3 Mrad to 12 Mrad.

[0072] In a twenty-fifth embodiment, the present disclosure provides a micro-speaker comprising a diaphragm according to any one of the first to twentieth embodiments or a diaphragm fabricated by the method according to any one of the twenty-first to twenty-fourth embodiments.

[0073] Although the objects and advantages of the present disclosure are further illustrated by the following examples, the specific materials and their amounts, as well as other conditions and details listed in these examples should not be construed as undue limitations on the present disclosure.

[0074] Example

[0075] Unless otherwise specified, all parts, percentages, ratios, etc. used in the examples and the rest of the specification are by weight, and all reagents used in the examples are obtained from or available from general chemical suppliers such as, for example, Sigma-Aldrich, St. Louis, MO, USA, or can be synthesized by conventional methods. The following abbreviations are used in this section: mm = millimeter, μm = micrometer, nm = nanometer, mL = milliliter, m = meter, kV = kilovolt, Mrad = megarad, in = inch, g = gram, min = minute, °C = degree Celsius, Hz = hertz, kHz = kilohertz, nN = nanonewton, N = newton, Pa = pascal, MPa = megapascal, and rpm = revolutions per minute. Unless otherwise stated, all parts, percentages, ratios, etc. in the examples and the rest of this specification are by weight. The raw materials used in the examples and comparative examples according to the present invention are shown in Table 1 below. Unless otherwise stated, the raw materials are used directly without further purification.

[0076] Table 1: Materials Used in Examples

[0077]

[0078]

[0079] Test Method

[0080] Rheology Measurement

[0081] All rheological data were collected using an ARES-G2 rheometer (TA Instruments, New Castle, DE) with an 8 mm parallel plate as the upper plate and a 25 mm parallel plate as the lower plate.

[0082] Samples of only the core layer were prepared by extrusion onto a liner using a Coperion ZSK (Coperion, Stuttgart, Germany). The samples were then exposed to electron beam radiation at a dose of 180 kV and 6 Mrad using a BroadBeam LE series electron beam system with a Comet AG emitter (PCT Engineered Systems, Davenport, IA). The film of the irradiated sample was then peeled from the liner and folded several times until it was approximately 1 mm thick. The folded sample was then placed in a hot press at 180 °C and maximum pressure for 5 minutes, at which point a solid sample was formed. An 8 mm disk was then punched out and the sample was mounted on the rheometer.

[0083] Then, under an inert atmosphere of nitrogen, rheological temperature sweep data was collected in the range of -50 °C to 200 °C at a heating rate of 3 °C / min, a strain of 1%, a frequency of 1 Hz, and a compressive force of 0 ± 1.0 N. The T g and storage modulus (G’) at 25 °C are shown in Table 2 below.

[0084] Table 2: Rheometer Results of Core Layer

[0085] Core Material Tg, °C Storage Modulus G’, Pa ABC KURARITY LA 2330 -34.4 195,027 ABC KURARITY LA 2330 / HYTREL 3078(75 / 25) -34.4 297,051 KRATON G1645 / HYTREL 3078(95 / 5) -34.33 435,860 VERSAFLEX 4132 0.1 144,437

[0086] Ball Rolling Test

[0087] The stereoregularity of the core layer was determined using the rolling ball method of ASTM D3121-17. Single-layer samples of only the core layer were prepared by extrusion on a Coperion ZSK (Coperion, Stuttgart, Germany). The samples were then exposed to electron beam radiation at a dose of 180 kV and 6 Mrad using a BroadBeam LE series electron beam system with a Comet AG emitter (PCT Engineered Systems, Davenport, IA). The films were then cut as specified in D3121-17 and the rolling ball test was conducted in accordance with the ASTM provisions. As demonstrated by the rolling ball rolling off the core film, none of the core materials shown in Table 2 above exhibited any stereoregularity.

[0088] Dynamic Mechanical Analysis (DMA) Test

[0089] The modulus and damping (loss tangent value) of the specified films were determined using a Q800 dynamic mechanical analysis (DMA) instrument (TA Instruments, New Castle, DE). Samples were prepared by cutting approximately 6 mm wide strips in the longitudinal and transverse film directions. The samples were mounted in tension clamps and the time-temperature superposition module was selected as the method. After closing the furnace, the temperature was lowered to -50 °C and held for 5 minutes. Then the temperature was raised from -50 °C to 50 °C at 10 °C intervals while maintaining the oscillatory strain at 0.05%. For the purposes of this disclosure, the storage modulus (G’), loss modulus (G”), and loss tangent value are the main relevant physical parameters.

[0090] Solubility Test

[0091] The solubility of the membrane samples was analyzed to evaluate the chemical bonds formed by electron beam crosslinking. Each time a sample analysis was performed, three samples of approximately 0.2 g to 0.3 g were prepared and then placed in a beaker with 20 mL of DMSO. The solution was heated with a hot plate set at 250 °C and then stirred at a speed of 600 rpm until the polymer coagulated on the magnetic stirrer. After 10 minutes, when the solution was still hot, the solvent was poured into a waste container. The beaker and the stir bar were rinsed several times with acetone. Another 20 mL of acetone was added to the beaker, and then it was placed on a cold plate while stirring to extract the remaining DMSO and other soluble substances. The process was repeated and then left to stand for 1 hour. At the end of 1 hour, the residue in the beaker was removed and then dried in an oven at 80 °C for 1 hour. For Example 4 and Example 5, the residue from the DMSO and acetone treatments was further immersed in toluene (20 mL) while stirring for 10 minutes. The filtered residue was rinsed with acetone and then dried at 80 °C for 1 hour. Then the dried sample was weighed. The surface composition of the dried sample was measured by a NicoletiS50 FTIR spectrometer (ThermoFisher Scientific, Waltham, MA).

[0092] Atomic Force Microscope (AFM) Test

[0093] Selected samples were imaged using a Bruker Dimension Icon AFM (Bruker, Billerica, MA). Peak force quantitative nanomechanics (QNM) tapping mode was used to study nanomechanical properties including modulus.

[0094] Samples were prepared by cross-sectioning at -60 °C using cryo-microscopy techniques. The AFM probe used to analyze the core layer was a ScanAsyst Air silicon tip with a silicon nitride cantilever, having a nominal radius of 2 nm, a spring constant = 0.4 N / m, and a resonant frequency of ~70 kHz. This tip is most suitable for softer materials with reference values in the range of approximately 10 MPa. The tip was optimized for imaging the core layer by calibration against a soft polydimethylsiloxane (PMDS) reference material with a modulus of approximately 10 Mpa, purchased as part of a calibration kit from Bruker. The AFM probe used to analyze the skin layer was an RTESPA-150 silicon tip with a silicon cantilever, having a nominal radius of 8 nm, a spring constant = 5 N / m, and a resonant frequency of ~150 kHz. This tip is most suitable for slightly harder materials compared to the ScanAsyst Air probe. The tip was optimized for imaging the skin layer by calibration against a PMDS reference material with a modulus of approximately 90 Mpa, purchased as part of a calibration kit from Bruker.

[0095] A 5 μm × 5 μm scan area was scanned at a rate of 0.9 Hz at the center of each layer and at the interface between the skin and core layers. A larger area scan was also performed over the entire skin / core / skin structure. Imaging parameters included a peak force set point of 1 nN, a peak force amplitude of 75 nm, a peak force frequency of 2 kHz, an integral gain of 1.5, and a proportional gain of 5.0. Images were processed to remove scan lines and / or tilt. Height data was processed with a 1 st st order plane fit.

[0096] Example 1

[0097] The film consists of a core of the "ABC KURARITY LA2330" acrylic block copolymer and a skin layer of "HYTREL 5556" thermoplastic polyester elastomer.

[0098] The multilayer film was produced on a Collin Lab Line 7 layer blown film production line (Collin Lab and Pilot Solutions GmbH, Maitenbeth, Germany). The air flow to the die was manually controlled to achieve a blow-up ratio of approximately 2:1. Subsequently, the bubble was collapsed approximately 2.2 meters above the die and wound onto a 7.6 cm (3 inch) paper core. The feed materials were provided by seven individual 25 mm diameter single screw extruders each with an L / D ratio of approximately 30:1. The screws feeding each layer had a compression ratio of 3:1.9 with the Maddock mixing section in layer 4. Layers 1 and 7 were LDPE 611A, layers 2 and 6 were LDPE 640i for the peelable surface layer to help achieve bubble stability. Layers 3 and 5 contained the surface layer material and layer 4 was the core material.

[0099] The processing temperatures were as follows: For layers (1, 2, 4, 6, 7) extruder temperatures: Zone 1: 120°F (49°C), Zone 2: 300°F (149°C), Zone 3: 330°F (165°C), Zone 4: 380°F (193°C), Zone 5: 380°F (193°C), Zone 6: 380°F (193°C). For layers 3 and 5 extruder temperatures: Zone 1: 120°F (49°C), Zone 2: 340°F (171°C), Zone 3: 360°F (182°C), Zone 4: 430°F (221°C), Zone 5: 430°F (221°C), Zone 6: 430°F (221°C). Adapter and die temperatures were as follows: Adapter 420°F (215°C), Die 420°F (215°C).

[0100] The film thickness after peeling the LDPE surface layer was 50 μm to 60 μm (2 mils to 2.3 mils).

[0101] A dynamic electron beam device (PCT Ebeam and Integration, Davenport, IA) was used on the production line to expose the film to electron beam radiation at a dose of 200 kV and 6 Mrad.

[0102] Example 2

[0103] The film consists of a core of a 75 / 25 blend of the "ABC KURARITY LA2330" acrylic block copolymer and a "HYTREL 3078" thermoplastic polyester elastomer with a surface layer of "HYTREL 5556" thermoplastic polyester elastomer. The preparation of Example 2 is the same as that of Example 1, except for the following processing temperatures: Layer (1, 2, 4, 6, 7) extruder temperatures: Zone 1: 120°F (49°C), Zone 2: 300°F (149°C), Zone 3: 330°F (165°C), Zone 4: 380°F (193°C), Zone 5: 380°F (193°C), Zone 6: 380°F (193°C). Layer 3 and Layer 5 extruder temperatures: Zone 1: 120°F (49°C), Zone 2: 340°F (171°C), Zone 3: 360°F (182°C), Zone 4: 430°F (221°C), Zone 5: 430°F (221°C), Zone 6: 430°F (221°C). Adapter and die temperatures are as follows: Adapter 420°F (215°C), Die 420°F (215°C).

[0104] Example 3

[0105] The film consists of a core of a 75 / 25 blend of the "ABC KURARITY LA2330" acrylic block copolymer and a "HYTREL 3078" thermoplastic polyester elastomer with a surface layer of "HYTREL 8238" thermoplastic polyester elastomer. The preparation of Example 3 is the same as that of Example 1, except that Layers 2 and 6 have 611A LDPE instead of 640i, and the processing temperatures are as follows: Layer (1, 2, 4, 6, 7) extruder temperatures: Zone 1: 120°F (49°C), Zone 2: 300°F (149°C), Zone 3: 330°F (165°C), Zone 4: 380°F (193°C), Zone 5: 380°F (193°C), Zone 6: 380°F (193°C). Layer 3 and Layer 5 extruder temperatures: Zone 1: 120°F (49°C), Zone 2: 340°F (171°C), Zone 3: 360°F (182°C), Zone 4: 450°F (232°C), Zone 5: 480°F (249°C), Zone 6: 480°F (249°C). Adapter and die temperatures are as follows: Adapter 470°F (243°C), Die 470°F (243°C).

[0106] Example 4

[0107] The film consists of a core of a 95 / 5 blend of the "KRATON G1645" styrene block copolymer and a skin layer of a 50 / 50 blend of the "HYTREL7246" thermoplastic polyester elastomer and the "TRITAN FX150" copolyester on the "HYTREL 3078" thermoplastic polyester elastomer. The preparation of Example 4 is the same as that of Example 1, except for the following processing temperatures: Layer (1, 2, 6, 7) extruder temperature: Zone 1: 120°F (49°C), Zone 2: 300°F (149°C), Zone 3: 330°F (165°C), Zone 4: 380°F (193°C), Zone 5: 380°F (193°C), Zone 6: 280°F (193°C). Layer 3 and Layer 5 extruder temperature: Zone 1: 120°F (49°C), Zone 2: 350°F (177°C), Zone 3: 390°F (199°C), Zone 4: 420°F (215°C), Zone 5: 470°F (243°C), Zone 6: 470°F (243°C). Layer 4 extruder temperature: 120°F (49°C), Zone 2: 300°F (149°C), Zone 3: 330°F (165°C), Zone 4: 380°F (193°C), Zone 5: 380°F (193°C), Zone 6: 390°F (199°C). Adapter and die temperatures are as follows: Adapter 450°F (232°C), Die 450°F (232°C).

[0108] Example 5

[0109] The film consists of a core of the "VERSAFLEX 4132" thermoplastic elastomer and a skin layer of the "HYTREL 5556" thermoplastic polyester elastomer. The preparation of Example 5 is the same as that of Example 1, except that Layers 2 and 6 have 640i LDPE instead of 611A, and the processing temperatures are as follows: Layer (1, 2, 4, 6, 7) extruder temperature: Zone 1: 120°F (49°C), Zone 2: 300°F (149°C), Zone 3: 330°F (165°C), Zone 4: 380°F (193°C), Zone 5: 380°F (193°C), Zone 6: 280°F (193°C). Layer 3 and Layer 5 extruder temperature: Layer 3 and Layer 5 extruder temperature: Zone 1: 120°F (49°C), Zone 2: 340°F (171°C), Zone 3: 360°F (182°C), Zone 4: 430°F (221°C), Zone 5: 430°F (221°C), Zone 6: 430°F (221°C). Adapter and die temperatures are as follows: Adapter 420°F (215°C), Die 420°F (215°C).

[0110] Examples 1 to 5 were evaluated using the above dynamic mechanical analysis (DMA) and solubility test methods. For DMA, a frequency of 1000 Hz and a strain of 0.5% were used. Data at 25 °C were recorded. Table 3 below gives the compositions of the core and the surface layer and the results of the evaluation.

[0111] Table 3: Compositions and Results of Examples 1 to 5

[0112]

[0113] Example 2 was evaluated by AFM using the above test method. The average modulus was measured at the center of the surface layer, the center of the core layer, and the edge of the surface layer at the interface with the core layer, and found to be 237 MPa, 18.5 MPa, and a value between the two, respectively.

[0114] Those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the present disclosure. Such modifications and changes are intended to fall within the scope of the invention as defined by the appended claims.

Claims

1. A diaphragm for a micro-speaker, the diaphragm comprising: One or two surface layers, the one or two surface layers independently comprising a block copolymer, the block copolymer comprising hard segments and soft segments, wherein a portion of the hard segments is included in crystalline physical crosslinking domains, and An organic polymer film layer, the organic polymer film layer being in direct contact with the one or two surface layers, wherein the organic polymer film layer is non-tacky at 25 °C.

2. The diaphragm according to claim 1, wherein the one or two surface layers and the organic polymer film layer are co-extruded.

3. The diaphragm according to claim 1 or 2, wherein at least one of the one or two surface layers or the organic polymer film layer is chemically crosslinked.

4. The diaphragm according to claim 1 or 2, wherein at least one of the one or two surface layers or the organic polymer film layer is not chemically crosslinked.

5. The diaphragm according to any one of claims 1 to 4, wherein the block copolymer comprises at least one of polyester, polyurethane or polyamide.

6. The diaphragm according to any one of claims 1 to 5, wherein the organic polymer film layer comprises at least one of a second block copolymer or an acrylic copolymer, the second block copolymer having second hard segments and second soft segments, wherein a portion of the second hard segments is included in crystalline physical crosslinking domains.

7. The diaphragm according to claim 6, wherein the organic polymer film layer comprises the second block copolymer having second hard segments and second soft segments, wherein the second soft segments are the same as the soft segments in the block copolymer in at least one of the one or two surface layers.

8. The diaphragm according to claim 6 or 7, wherein the organic polymer film layer comprises the second block copolymer having hard segments and soft segments, wherein the second block copolymer comprises an acrylic triblock copolymer, a polyamide-polyether-polyamide triblock copolymer, a polyester-polyether-polyester triblock copolymer or a styrene block copolymer.

9. The diaphragm according to any one of claims 6 to 8, wherein the organic polymer film layer comprises an acrylic copolymer, the acrylic copolymer comprising: Monomer units of an alkyl acrylate or an alkyl methacrylate represented by the following formula CH2=C(R’)COOR wherein R’ is a hydrogen or a methyl group, and R is a straight-chain or branched-chain alkyl group having 1 to 30 carbon atoms; Monomer units of at least one of N-vinylpyrrolidone or acrylic acid; and Monomer units of at least one of isobornyl acrylate or isobornyl methacrylate of at least 20% by weight.

10. The diaphragm according to any one of claims 1 to 9, as measured by dynamic mechanical analysis, the loss factor of the diaphragm being at least 0.05 at 25 °C.

11. The diaphragm according to any one of claims 1 to 10, wherein at least one of the one or two surface layers comprises an inorganic filler.

12. The diaphragm according to any one of claims 1 to 11, wherein the organic polymer film layer has a lower modulus than the one or two surface layers as measured by an atomic force microscope.

13. A method of fabricating a diaphragm according to any one of claims 1 to 12, the method comprising co - extruding the block copolymer and the organic polymer to provide a multilayer film, the multilayer film including the one or two surface layers and the organic polymer film layer in direct contact with the one or two surface layers.

14. The method according to claim 13, the method further comprising subjecting the multilayer film to electron beam radiation.

15. The method according to claim 14, wherein the electron beam radiation has an electron beam energy of 100 kV to 300 kV and an electron beam dose of 3 Mrad to 12 Mrad.

16. A micro - speaker, the micro - speaker including a diaphragm according to any one of claims 1 to 12.

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