WO2021186277A1

WO2021186277A1 - Diaphragm for microspeaker and manufacturing method thereof

Info

Publication number: WO2021186277A1
Application number: PCT/IB2021/051772
Authority: WO
Inventors: Chao Yang; Christopher B. Walker, Jr.
Original assignee: 3M Innovative Properties Company
Priority date: 2020-03-17
Filing date: 2021-03-03
Publication date: 2021-09-23
Also published as: CN113411738A; CN113411738B

Abstract

The invention provides a diaphragm for a microspeaker and a manufacturing method thereof. The diaphragm is a single-layer diaphragm or a multi-layer diaphragm and comprises at least one layer of a chemically cross-linked thermoplastic polyurethane elastomer, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25°C to 150°C, as measured by a rheological curve. The diaphragm for a microspeaker according to the technical solution of the present invention is easy to be prepared by thermoforming, and has appropriate modulus, good strength, elasticity, and thermal stability.

Description

DIAPHRAGM FOR MICROSPEAKER AND MANUFACTURING METHOD THEREOF

Technical Field

The present invention relates to the technical field of acoustic devices, and in particular to a diaphragm for a microspeaker and a method of manufacturing a diaphragm for a microspeaker.

Background

With the rapid development of the mobile phone industry, the customer’s demands for mobile multimedia applications is increasing, and the requirement for the quality of mobile phone sounds has been further increased. As a sound-producing part of the mobile phone, the quality of microspeaker directly determines the quality of the multimedia of the mobile phone. The principle of producing a sound by a microspeaker is that the voice coil drives a diaphragm to vibrate under the effect of an electromagnetic force, which then pushes air to produce sound. The role of the diaphragm is to push the air, provide damping, and maintain a fast response during vibration. The vibration stability of the diaphragm directly determines the sound quality of the microspeaker.

Firstly, the diaphragm for a microspeaker should have certain rigidity and strength to produce high sound pressure and wide frequency coverage. Secondly, the diaphragm for a microspeaker should be highly damped to have a smooth frequency response. Thirdly, the diaphragm for a microspeaker should have high resilience performance to have a large amplitude, so that the speaker has a high volume. However, it is difficult to find a material that has both high rigidity and good damping properties. It is generally necessary to compromise on the rigidity and damping properties of the membrane material, or to combine a rigid material with a highly damping material. In addition, it is difficult to find a material with high rigidity, high strength and high resilience at the same time.

The present diaphragms of microspeakers usually make use of a single-layer film of plastic materials, including, for example, a polypropylene (PP) film, a polyethylene terephthalate (PET) film, a polyimide (PI) film, a polyethylene naphthalate (PEN) film, a polyetheretherketone (PEEK) film or the like. These plastic materials have a high glass transition temperature Tg, which can maintain high rigidity and maintain the shape of the diaphragm at a higher operating temperature. They can also generate high sound pressures over a wide frequency range. However, if the glass transition temperature Tg of the diaphragm material is too high, it will increase the difficulty of the thermoforming process during the preparation of the diaphragm because the temperature of the thermoforming needs to be higher than the glass transition temperature Tg of the plastic material.

With the increase of the end user’s requirements for the sound quality and volume of microspeakers, a multi-layer composite fdm structure including a plastic fdm as described above has gradually appeared, including a three-layer film, a five-layer film and a seven-layer film or the like. In the design of the multilayer film structure, a damping adhesive layer is used, whose main functions are to improve the stability of the diaphragm, control fO of the diaphragm and reduce distortion, thereby improving the sound quality. The commonly used materials for the damping adhesive layer include an acrylic damping adhesive, a silicone damping pressure-sensitive adhesive, and the like. The multi-layer diaphragm with a damping layer can have a smoother frequency response. However, due to the rigidity of the plastic film in the diaphragm, the elasticity of the diaphragm is poor and the applicable amplitude (volume) thereof is small.

The application of elastomer materials in diaphragms can effectively solve the problems related to resilience. In fact, in the manufacture of large loudspeakers, rubber materials are widely used to make folding ring components. The folding ring components in diaphragms can effectively reduce the stretching of the diaphragms during vibration, thereby improving the stability of the diaphragms upon vibration. For the preparation of microspeakers, it is also reported about the related technologies using injection molding of liquid silicone rubbers. Due to the complicated manufacturing process, difficult processing, and high precision requirements for injection molds, the large-scale applications of these technologies have been limited.

At present, when a thermoplastic elastomer material is used to make a diaphragm, a diaphragm having a folding structure is still prepared according to the traditional hot press molding process. The thermoplastic elastic materials (especially, the thermoplastic polyurethane materials) have poor thermal stability, difficult thermoforming processes, and poor creep resistance. This material does not have the mechanical properties required to meet the long-term vibration of a diaphragm and is prone to failure during long-term work. When the working temperature of the diaphragm exceeds the thermoforming temperature of the thermoplastic elastomer material, the diaphragm will become soft and permanently deformed, causing damage to the structure of the diaphragm. In addition, the polyurethane film prepared by the chemical cross-linking method cannot be hot-pressed because it has a three-dimensional network structure, and it is not suitable for preparing a diaphragm by the hot-press molding process. At present, there is still a huge demand in the industry for a diaphragm for a microspeaker that may be manufactured by a simple manufacturing process, and has good resilience, high rigidity and high strength. Therefore, it is of great significance to develop a diaphragm for a microspeaker that is easy to be prepared by thermoforming, and has appropriate modulus, good strength, elasticity, and thermal stability.

Summary of the Invention

In view of the technical problem set forth above, an object of the present invention is to provide a diaphragm for a microspeaker and a manufacturing method thereof. The diaphragm for a microspeaker according to the technical solution of the present invention is easy to be prepared by thermoforming, and has appropriate modulus, good strength, elasticity, and thermal stability.

The present inventors have completed the present invention through intensive research.

According one aspect of the invention, there provides a diaphragm for a microspeaker, the diaphragm being a single-layer diaphragm or a multi-layer diaphragm and comprising at least one layer of a chemically cross-linked thermoplastic polyurethane elastomer, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25 °C to 150°C, as measured by a rheological curve.

According another aspect of the invention, there provides a method of manufacturing a diaphragm for a microspeaker, comprising subjecting a thermoplastic polyurethane elastomer fdm to a chemical crosslinking treatment, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25°C to 150°C, as measured by a rheological curve.

The advantages of the present invention over the prior art in the field are that the diaphragm for a microspeaker according to the technical solution of the present invention is easy to be prepared by thermoforming, and has appropriate modulus, good strength, elasticity, and thermal stability.

Brief Description of the Drawings

The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate exemplary embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain the features of the invention.

Fig. 1 shows a schematic cross-sectional view of a diaphragm for a microspeaker having a single-layer structure according to an embodiment of the present invention;

Fig. 2 shows a schematic cross-sectional view of a multi-layer diaphragm for a microspeaker having a three-layer structure according to another embodiment of the present invention;

Fig. 3 shows a schematic cross-sectional view of a multi-layer diaphragm for a microspeaker having a four-layer structure according to another embodiment of the present invention; and

Fig. 4 shows a schematic cross-sectional view of a multi-layer diaphragm for a microspeaker having a five-layer structure according to still another embodiment of the present invention.

Detailed Description of the Invention

The present invention will be further described in detail below in conjunction with the drawings and specific embodiments. It will be appreciated that other embodiments may be practiced without departing from the scope or spirit of the invention. Therefore, the following detailed description is non-limiting.

All numbers indicating the sizes, quantities, and physicochemical properties of a feature used in the specification and claims, unless otherwise indicated, are understood to be modified in all instances by the term “about”. Accordingly, the numerical parameters set forth in the above description and the appended claims are approximations unless otherwise indicated, and those skilled in the field are able to use the teachings disclosed herein. The range of values defined by endpoints includes all numbers in the range and any range within the range, for example, 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4, and 5, or the like.

The inventors of the present invention have found in research that some thermoplastic elastomeric materials can be used for the diaphragm for a microspeaker after being thermoformed. The thermoplastic elastomer materials can greatly improve the resilience and consistency of the diaphragm and can achieve high amplitude vibration. However, the thermoplastic elastomer materials generally have poor temperature resistance and cannot withstand larger power or higher working temperature. In addition, the thermoplastic elastomer materials have poor creep resistance (strength) and do not have the mechanical properties demanded by the long-term vibration of a diaphragm. According to the technical solution of the present invention, by subjecting a specific thermoplastic polyurethane elastomer material to a chemical crosslinking treatment (preferably, by using electron beam radiation), the thermoplastic polyurethane elastomer material may be cross linked. Therefore, the thermal stability and creep resistance of the diaphragm made of the material are greatly improved without substantially affecting its elastic property.

Specifically, according to an aspect of the invention, there provides a method of manufacturing a diaphragm for a microspeaker, comprising subjecting a thermoplastic polyurethane elastomer film to a chemical crosslinking treatment, wherein: the chemically cross- linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25 °C to 150°C, as measured by a rheological curve.

According to the technical solution of the present invention, the term “thermoplastic polyurethane elastomer (TPU)” refers to a thermoplastic elastomer obtained by polymerizing a diisocyanate and a dihydroxy compound. Preferably, the term “thermoplastic polyurethane elastomer (TPU)” refers to a thermoplastic block copolymer composed of a soft segment and a hard segment alternately connected, wherein the hard segment is an isocyanate segment (including an aliphatic isocyanate segment or an aromatic isocyanate segment), and the soft segment is a polyether polyol segment or a polyester polyol segment. In the thermoplastic polyurethane, in addition to the ratio of the hard segment and the soft segment, the types of the isocyanate, the polyether polyol, and the polyester polyol also affect the properties of the thermoplastic polyurethane.

The thermoplastic polyurethane elastomer can be plasticized by heating without chemical cross-linking or little cross-linking in the chemical structure, and its molecules are basically linear, but there is some physical cross-linking. The molecules of the thermoplastic polyurethane elastomer are substantially linear. The thermoplastic polyurethane elastomer has no or little cross- linking in the structure thereof and can be plasticized by heating. However, there is some physical cross-linking in the thermoplastic polyurethane elastomer. It should be noted that the thermoplastic polyurethane elastomer usually undergoes physical cross-linking through the interaction between urethane groups in the molecule thereof. However, the thermoplastic polyurethane elastomers containing only physical crosslinks are inferior in strength, elasticity, and thermal stability.

According to the technical solution of the present invention, the term “chemically cross- linked thermoplastic polyurethane elastomer” refers to a chemically cross-linked thermoplastic polyurethane elastomer formed by subjecting a thermoplastic polyurethane elastomer used for making a diaphragm to a chemical crosslinking treatment. The chemical crosslinking treatment forms a cross-linked network structure inside the thermoplastic polyurethane elastomer via chemical crosslinking points formed by chemical bonds, and because of this, the chemically cross- linked thermoplastic polyurethane elastomer does not have thermoplasticity. That is, the chemically cross-linked thermoplastic polyurethane elastomer is not a thermoplastic elastomer anymore.

Preferably, in the diaphragm, the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve.

Preferably, the chemically cross-linked thermoplastic polyurethane elastomer has appropriate mechanical properties (including strength and elasticity). The single-layer diaphragm comprising the chemically cross-linked thermoplastic polyurethane elastomer has a tensile modulus in a range of 1 MPa to 150 MPa and an elongation at break in a range of 180% to 500%. By controlling the tensile modulus and elongation at break of the diaphragm within the above range, the basic function of the diaphragm to drive air to generate sound can be achieved, and the stability and consistency of the device’s operation over a long time and a wide frequency range can be guaranteed.

The “rheological curve” according to the present invention is measured by using an Ares G2 Rotary Rheometer produced by the TA Company in USA, in which an 8-inch parallel plate clamp is used to hold a chemically cross-linked thermoplastic polyurethane elastomer sample have a thickness of 1 mm, and when the heating rate is 5°C/min, the testing frequency is 1 Hz, and the strain is less than or equal to 1%, rheological measurement is performed at different temperature points to obtain the storage modulus G’ and the loss modulus G”, and further according to the following formula, the loss factor value (that is, the damping value) tan d is calculated from the storage modulus G’ and the loss modulus G”. tan 5=G”/G’

According to the above formula, when the thermoplastic polyurethane elastomer is chemically cross-linked and when the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25 °C to 150°C, as measured by a rheological curve using a rotational rheological method, it may be indicated that the chemically cross-linked thermoplastic polyurethane elastomer has good thermal stability (that is, thermal damping stability).

Preferably, when the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve, the chemically cross-linked thermoplastic polyurethane elastomer has excellent thermal stability.

The diaphragm has a thickness in a range of 5 pm to 100 pm, preferably 10 to 75 pm and more preferably 15 to 50 pm.

There is no particular limitation on the specific type of thermoplastic polyurethane elastomer (TPU) which can be used in the present invention, as long as it has a crosslinkable structure in the molecule thereof (including a structure having a crosslinkable group or a structure that can be broken and cross-linked by electron beam irradiation).

There is no specific restriction on the thermoplastic polyurethane elastomer (TPU) that can be used in the present invention, which can be prepared by the known methods known in the art or can also be obtained commercially. The commercially available products of the thermoplastic polyurethane elastomer (TPU) that can be used in the present invention include: the TPU materials of EUASTOUUANE series produced by BASF Company; the TPU materials of DESMOPAN series produced by Covestro Company; and the TPU films produced by Shibata Company.

For the diaphragm to have further improved thermal stability while having good strength and elasticity, the thermoplastic polyurethane elastomer constituting the diaphragm must undergo a chemical crosslinking treatment. The method for chemically crosslinking the thermoplastic polyurethane elastomer is not particularly limited and the conventional physical and chemical methods can be used, such as electron beam radiation crosslinking, microwave radiation crosslinking, ultraviolet radiation crosslinking, chemical crosslinking, and the like.

Preferably, the thermoplastic polyurethane elastomer is cured by radiating electron beam. The electron beam radiation comprises radiating the thermoplastic polyurethane elastomer using an electron beam having electron beam energy of 100 to 300 KV for an electron beam dose of 1 to 12 Mrad, preferably 3 to 12 Mrad so as to destroy the weak portions of the thermoplastic polyurethane elastomer molecules and cause crosslinking through chemical bonds.

According to the technical solution of the invention, the multi-layer diaphragm further includes at least one plastic layer which has a tensile modulus of 1 MPa to 1000 MPa and a yield strain of 3% to 30%. The plastic layer is one or more selected from a group consisting of a polyethylene naphthalate (PEN) layer, a polyetheretherketone (PEEK) layer, a polyaryletherketone (PEAK) layer, a polyimide (PI) layer, and a thermoplastic polyester elastomer (TPEE) layer.

According to the technical solution of the present invention, in order to further improve the elasticity of the diaphragm to provide vibration with high sensitivity, consistency, and high amplitude according to the actual situation, preferably, the diaphragm has a folding structure.

There is no particular limitation on the folding structure that can be used in the present invention, and it may be one or a combination of the folding structures that the diaphragm in the field of microspeakers has.

According to a specific embodiment of the present invention, the diaphragm is a single layer diaphragm. Fig. 1 shows a schematic cross-sectional view of a diaphragm 1 for a microspeaker having a single-layer structure according to an embodiment of the present invention. The diaphragm 1 is composed of the chemically cross-linked thermoplastic polyurethane elastomer as described above.

According to another specific embodiment of the present invention, the diaphragm is a three-layer diaphragm. Fig. 2 shows a schematic cross-sectional view of a multi-layer diaphragm G for a microspeaker having a three-layer structure according to another embodiment of the present invention. The multi-layer diaphragm G includes an elastic layer 2’, a damping layer 3’, and an elastic layer 4’ in order. Both of the elastic layer 2’ and the elastic layer 4’ are composed of the chemically cross-linked thermoplastic polyurethane elastomer as described above. Preferably, the damping layer 3 ’ is one or more selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer. The specific types of the silicone damping adhesive, the acrylic damping adhesive and the polyolefin damping adhesive that can be used in the present invention are not particularly limited, and they can be selected by those skilled in the art based on their conventional knowledge. The three-layer diaphragm has a thickness in the range of 30 to 100 pm, preferably 36 to 80 pm, and more preferably 42 to 60 pm. Preferably, the elastic layer 2’ and the elastic layer 4’ each independently has a thickness in a range of 5-30 pm, preferably 7-20 pm and more preferably 10-15 pm, and the damping layer 3’ has a thickness in the range of 5-60 pm, preferably 10-40 pm and more preferably 12-30 pm. According to another specific embodiment of the present invention, the diaphragm is a four-layer diaphragm. Fig. 3 shows a schematic cross-sectional view of a multi-layer diaphragm 1” for a microspeaker having a four-layer structure according to another embodiment of the present invention. The multi-layer diaphragm 1” includes an elastic layer 2”, a plastic layer 3”, a damping layer 4”, and a plastic layer 5” in order. The elastic layer 2” is composed of the chemically cross- linked thermoplastic polyurethane elastomer as described above, which preferably has a tensile modulus in a range of 1 MPa to 150 MPa. The plastic layer 3” and the plastic layer 5” are the same or different, and are preferably selected from one or more selected from a group consisting of a polyethylene naphthalate (PEN) layer, a polyetheretherketone (PEEK) layer, a polyaryletherketone (PEAK) layer, a polyimide (PI) layer, and a thermoplastic polyester elastomer (TPEE) layer, more preferably a polyetheretherketone (PEEK) fdm, including a semi-crystalline polyetheretherketone (PEEK) fdm and an amorphous polyetheretherketone (PEEK) fdm. The plastic layer 3” and the plastic layer 5” have a tensile modulus of 1000-2000 MPa and a yield strain of 3% -8%. A thermoplastic polyester elastomer (TPEE) having a tensile modulus of 500- lOOOMPa and a yield strain of 8% ~ 30% may also be selected. The damping layer 4” may be selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer. The four-layer diaphragm has a thickness of 30-100 pm, and preferably 42-60 pm.

According to another specific embodiment of the present invention, the diaphragm is a five-layer diaphragm. Fig. 4 shows a schematic cross-sectional view of a multi-layer diaphragm 1 for a microspeaker having a five-layer structure according to still another embodiment of the present invention. The multilayer diaphragm 1 comprises a plastic layer 2’”, a damping layer 3’”, an elastic layer 4’”, a damping layer 5’”, and a plastic layer 6’” in order. The elastic layer 4’” is composed of the chemically cross-linked thermoplastic polyurethane elastomer as described above, which preferably has a tensile modulus in a range of 1 MPa to 150 MPa. The plastic layer 2’” and the plastic layer 6’” are the same or different, and are preferably selected from one or more selected from a group consisting of a polyethylene naphthalate (PEN) layer, a polyetheretherketone (PEEK) layer, a polyaryletherketone (PEAK) layer, a polyimide (PI) layer, and a thermoplastic polyester elastomer (TPEE) layer, more preferably a polyetheretherketone (PEEK) film, including a semi-crystalline polyetheretherketone (PEEK) film and an amorphous polyetheretherketone (PEEK) film. The plastic layer 2’” and the plastic layer 6’” have a tensile modulus of 1000-2000 MPa and a yield strain of 3% -8%. The damping layer 3’” and the damping layer 5’” may be selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer. The thickness of the five-layer structured diaphragm is 30 to 100 pm, preferably 42 to 60 pm. The plastic layer 2’” and the plastic layer 6’” each independently has athickness of 3-10 pm, preferably 5-9 pm; the damping layer 3’” and the damping layer 5’” each independently has athickness of 5-30 pm, preferably 10-20 pm; and the elastic layer 4’” has athickness of 5 to 30 pm, preferably 10-20 pm.

According to another aspect of the invention, there provides a method of manufacturing a diaphragm for a microspeaker, comprising subjecting a thermoplastic polyurethane elastomer film to a chemical crosslinking treatment, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25°C to 150°C, as measured by a rheological curve.

Preferably, the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve.

For the diaphragm to have further improved thermal stability while having good strength and elasticity, the thermoplastic polyurethane elastomer constituting the diaphragm has been chemical cross-linked. The chemical crosslinking treatment forms a cross-linked network structure inside the thermoplastic polyurethane elastomer via chemical crosslinking points formed by chemical bonds, and because of this, the chemically cross-linked thermoplastic polyurethane elastomer does not have thermoplasticity.

There is no particular limitation on the specific type of thermoplastic polyurethane elastomer which can be used in the present invention, as long as it meets the above requirements on the softening temperature range and has a crosslinkable structure in the molecule thereof (including a structure having a crosslinkable group or a structure that can be broken and cross- linked by electron beam irradiation).

There is no specific restriction on the thermoplastic polyurethane elastomer (TPU) that can be used in the present invention, which can be prepared by the known methods in the art or can also be obtained commercially. The commercially available products of the thermoplastic polyurethane elastomer (TPU) that can be used in the present invention include: the TPU materials of EUASTOUUANE series produced by BASF Company; the TPU materials of DESMOPAN series produced by Covestro Company; and the TPU fdms produced by Shibata Company.

The method for chemically crosslinking the thermoplastic polyurethane elastomer is not particularly limited and the conventional physical and chemical methods can be used, such as electron beam radiation crosslinking, microwave radiation crosslinking, ultraviolet radiation crosslinking, chemical crosslinking, and the like.

In order to make the diaphragm have a certain shape, the thermoplastic polyurethane elastomer constituting the diaphragm may also be subjected to a thermoforming treatment, which may be performed before the chemical crosslinking treatment or after the chemical crosslinking treatment.

The diaphragm may be a single-layer diaphragm or a multi-layer diaphragm. The multilayer film includes at least one chemically cross-linked thermoplastic polyurethane elastic film, at least one damping film, and at least three layers in total, and the modulus thereof is between 1 MPa and 1000 MPa, and the elongation at break thereof should be between 80% and 500%.

Preferably, the thickness of the chemically cross-linked thermoplastic polyurethane elastomer film is in a range of 5 to 100 pm.

According to a specific embodiment of the present invention, there provides a method for preparing a multi-layer diaphragm having a three-layer structure. First, a multi-layer diaphragm 1 ’ is prepared by a lamination method, wherein the multi-layer diaphragm 1 ’ includes an elastic layer 2’, a damping layer 3’, and an elastic layer 4’ in order. Both the elastic layer 2’ and the elastic layer 4’ are composed of the chemically cross-linked thermoplastic polyurethane elastomer as described above. Preferably, the damping layer 3’ is one or more selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer. The specific types of the silicone damping adhesive, the acrylic damping adhesive and the polyolefin damping adhesive that can be used in the present invention are not particularly limited, and they can be selected by those skilled in the art based on their conventional knowledge. The three-layer diaphragm has a thickness in the range of 30 to 100 pm, preferably 36 to 80 pm, and more preferably 42 to 60 pm. Preferably, the elastic layer 2’ and the elastic layer 4’ each independently has a thickness in a range of 5-30 pm, preferably 7-20 pm and more preferably 10- 15 pm, and the damping layer 3’ has a thickness in the range of 5-60 pm, preferably 10-40 pm and more preferably 12-30 pm.

According to a specific embodiment of the present invention, there provides a method for preparing a multi-layer diaphragm having a four-layer structure. First, a multi-layer diaphragm 1” is prepared by a lamination method, wherein the multi-layer diaphragm 1” includes an elastic layer 2”, a plastic layer 3”, a damping layer 4”, and a plastic layer 5” in order. The elastic layer 2” is composed of the chemically cross-linked thermoplastic polyurethane elastomer as described above, which preferably has a tensile modulus in a range of 1 MPa to 150 MPa. The plastic layer 3” and the plastic layer 5” are the same or different, and are preferably selected from one or more selected from a group consisting of a polyethylene naphthalate (PEN) layer, a polyetheretherketone (PEEK) layer, a polyaryletherketone (PEAK) layer, a polyimide (PI) layer, and a thermoplastic polyester elastomer (TPEE) layer, more preferably a polyetheretherketone (PEEK) film, including a semi-crystalline polyetheretherketone (PEEK) film and an amorphous polyetheretherketone (PEEK) film. The plastic layer 3” and the plastic layer 5” have a tensile modulus of 1000-2000 MPa and a yield strain of 3% -8%. A thermoplastic polyester elastomer (TPEE) having a tensile modulus of 500-1000MPa and a yield strain of 8% ~ 30% may also be selected. The damping layer 4” may be selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer. The four-layer diaphragm has a thickness of 30-100 pm, and preferably 42-60 pm.

According to a specific embodiment of the present invention, there provides a method for preparing a multi-layer diaphragm having a five-layer structure. First, a multi-layer diaphragm 1 is prepared by a lamination method, wherein the multilayer diaphragm G” includes a plastic layer 2’”, a damping layer 3’”, an elastic layer 4’”, a damping layer 5’”, and a plastic layer 6’” in this order. The elastic layer 4’” is composed of the chemically cross-linked thermoplastic polyurethane elastomer as described above, which preferably has a tensile modulus in a range of 1 MPa to 150 MPa. The plastic layer 2’” and the plastic layer 6’” are the same or different, and are preferably selected from one or more selected from a group consisting of a polyethylene naphthalate (PEN) layer, a polyetheretherketone (PEEK) layer, a polyaryletherketone (PEAK) layer, a polyimide (PI) layer, and a thermoplastic polyester elastomer (TPEE) layer, more preferably a polyetheretherketone (PEEK) film, including a semi-crystalline polyetheretherketone (PEEK) film and an amorphous polyetheretherketone (PEEK) film. The plastic layer 2’” and the plastic layer 6’” have a tensile modulus of 1000-2000 MPa and a yield strain of 3% -8%. The damping layer 3’” and the damping layer 5’” may be selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer. The thickness of the five-layer structured diaphragm is 30 to 100 pm, preferably 42 to 60 pm. The plastic layer 2’” and the plastic layer 6’” each independently has a thickness of 3-10 pm, preferably 5-9 pm; the damping layer 3’” and the damping layer 5’” each independently has a thickness of 5-30 pm, preferably 10-20 pm; and the elastic layer 4’” has a thickness of 5 to 30 pm, preferably 10-20 pm.

The various exemplary embodiments of the present invention are further illustrated by the following list of embodiments, which should not be construed as unduly limiting the present invention.

Embodiment 1 is a diaphragm for a microspeaker, the diaphragm being a single-layer diaphragm or a multi-layer diaphragm and comprising at least one layer of a chemically cross- linked thermoplastic polyurethane elastomer, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25°C to 150°C, as measured by a rheological curve.

Embodiment 2 is the diaphragm according to Embodiment 1, wherein the chemically cross- linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve.

Embodiment 3 is the diaphragm according to Embodiment 1 or 2, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a tensile modulus in a range of 1 MPa to 150 MPa and an elongation at break in a range of 180% to 500%.

Embodiment 4 is the diaphragm according to any one of Embodiments 1-3, wherein the diaphragm has a thickness in a range of 5 pm to 100 pm.

Embodiment 5 is the diaphragm according to any one of Embodiments 1-4, wherein the chemically cross-linked thermoplastic polyurethane elastomer is cross-linked by radiation.

Embodiment 6 is the diaphragm according to of Embodiment 5, wherein the chemically cross-linked thermoplastic polyurethane elastomer is cross-linked by radiating electron beam.

Embodiment 7 is the diaphragm according to any one of Embodiments 1-6, wherein the multi-layer diaphragm is a diaphragm having three layers.

Embodiment 8 is the diaphragm according to any one of Embodiments 1-7, wherein the multi-layer diaphragm further includes a damping layer.

Embodiment 9 is the diaphragm according to Embodiment 8, wherein the damping layer is one or more selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer.

Embodiment 10 is the diaphragm according to any one of Embodiments 8-9, the multi layer diaphragm further includes at least one plastic layer which has a tensile modulus of 1 MPa to 1000 MPa and a yield strain of 3% to 30%.

Embodiment 11 is the diaphragm according to Embodiment 10, wherein the plastic layer is one or more selected from a group consisting of a polyethylene naphthalate layer, a polyetheretherketone layer, a polyaryletherketone layer, a polyimide layer, and a thermoplastic polyester elastomer layer.

Embodiment 12 is the diaphragm according to any one of Embodiments 7-11, wherein the multi-layer diaphragm has a thickness in a range of 10 pm to 100 pm.

Embodiment 13 is the diaphragm according to any one of Embodiments 1-12, wherein the diaphragm has a tensile modulus in a range of 1 MPa to 1000 MPa.

Embodiment 14 is the diaphragm according to any one of Embodiments 1-12, wherein the diaphragm has an elongation at break in a range of 80% to 500%.

Embodiment 15 is a method of manufacturing a diaphragm for a microspeaker, comprising subjecting a thermoplastic polyurethane elastomer film to a chemical crosslinking treatment, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25°C to 150°C, as measured by a rheological curve.

Embodiment 16 is the method of manufacturing a diaphragm for a microspeaker according to Embodiment 13, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve.

Embodiment 17 is the method of manufacturing a diaphragm for a microspeaker according to any one of Embodiments 15-16, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a tensile modulus in a range of 1 MPa to 150 MPa and an elongation at break in a range of 180% to 500%.

Embodiment 18 is the method of manufacturing a diaphragm for a microspeaker according to any one of Embodiments 15-17, wherein the chemical crosslinking treatment comprises crosslinking the thermoplastic polyurethane elastomer film by radiation. Embodiment 19 is the method of manufacturing a diaphragm for a microspeaker according to Embodiment 18, wherein the chemical crosslinking treatment comprises crosslinking the thermoplastic polyurethane elastomer film by radiating electron beam.

Embodiment 20 is the method of manufacturing a diaphragm for a microspeaker according to any one of Embodiments 15-19, wherein the diaphragm is a single-layer diaphragm or a multi - layer diaphragm comprising at least one layer of a chemically cross-linked thermoplastic polyurethane elastomer.

Embodiment 21 is the method of manufacturing a diaphragm for a microspeaker according to Embodiment 20, wherein the multi-layer diaphragm is a diaphragm having three layers.

The invention will be described in greater detail with reference to the embodiments. It is to be understood that the description and examples are intended to be illustrative, and not restrictive. The scope of the invention is defined by the appended claims.

Examples

In the present invention, unless otherwise indicated, the reagents employed were all commercially available and used directly without further purification.

Table 1 List of raw materials

* The softening temperature of the thermoplastic polyurethane elastomer was obtained by measuring the rheological curve with a rotary rheometer.

Testing Methods

Tensile Modulus and Elongation at Break

A universal testing machine produced by Instron Company was used to measure the tensile modulus (unit: MPa) and elongation at break (unit: %) of respective diaphragm samples prepared in the following examples, wherein the fixture force of the universal testing machine was 100 N, the diaphragm samples were 50 mm ^c 25.4 Inch, and the testing speed was 50 mm/min.

According to the invention, when a diaphragm sample had a tensile modulus greater than or equal to 1 MPa and an elongation at break greater than 80%, the diaphragm sample is considered to meet the basic requirements.

Yield Strain

A universal testing machine produced by Instron Company was used to measure the tensile modulus (unit: MPa) and elongation at break (unit: %) of respective diaphragm samples prepared in the following examples, wherein the fixture force of the universal testing machine was 100N, the diaphragm samples were 50 mm ^c 25.4 Inch, and the testing speed was 50 mm/min.

A stress-strain curve obtained from the above process is achieved and observed to see whether there is yield in the stress-strain curve, if so, calculate the yield strain value (%).

Rheological Curve

The properties concerning rheological curves of the single-layer diaphragm samples prepared in the following examples 1-3 were measured according to the following method to investigate the changing degrees in the damping properties thereof.

Specifically, the rheological curve was measured by using an Ares G2 Rotary Rheometer produced by the TA Company from USA. First, each of respective diaphragm samples having a thickness of 1 mm was held by an 8-inch parallel plate clamp, and when the heating rate was 5°C/min, the testing frequency was 1 Hz, and the strain was less than or equal to 1%, rheological measurement was performed at different temperature points to obtain the storage modulus G’ and the loss modulus G”, and further according to the following formula, the loss factor value (that is, the damping value) tan d was calculated from the storage modulus G’ and the loss modulus G”. tan 5=G”/G’

The Highest Hot Pressing Temperature

Thermoplastic polyurethane elastomer materials can improve the resilience of the diaphragm. However, because the common thermoplastic polyurethane elastomer materials are easily softened by heat and cause heat shrinkage, the thermocompression molding temperature used is limited, and the pattern on the diaphragm is not clear.

According to the application, a hot pressing machine was used to heat press respective diaphragm samples into diaphragms with a folding structure (or patterns) at a pressure of 10 MPa. “Hot Pressing” comprised the steps of heating a mold to a preset temperature and performing hot pressing with a pressure of 10 MPa for 90 seconds, then opening the mold and releasing the mold after natural cooling. “The Highest Hot Pressing Temperature” refers to the lowest molding temperature (°C) when the diaphragm was damaged (including film breakage, heat shrinkage, or the diaphragm could not be released from the mold, or the like).

Thermal Stability

Each of the diaphragm samples obtained in the following examples was processed into a voice coil product having a pattern for a speaker. The voice coil product was then heated to a series of specific temperatures and allowed to operate for 1 min each. After the voice coil product was cooled to room temperature, it was observed to see whether the pattern on the diaphragm is clear.

If it was clear, the highest temperature in the series of specific temperatures at which the pattern remained clear was used to indicate the thermal stability of the diaphragm sample.

Example 1

The thermoplastic polyurethane elastomer TPU Film, which was a single-layer film having a thickness of 20 pm was selected. This single-layer film was divided into four parts: Film A, Film B, Film C and Film D. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad; Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser; and Film D was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 12 Mrad by using the same laser.

Then, the Film A, Film B, Film C and Film D were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the rheological curve (wherein the measurement for rheological curve was performed at 25°C to 150°C), the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 2 below.

Table 2

Example 2

The thermoplastic polyurethane elastomer ELASTOLLAN C 85 A 10 produced by BASF Company was hot extruded by an extruder into a single-layer fdm having a thickness of 30 pm. This single-layer film was divided into three parts: Film A, Film B, and Film C. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad. In addition, Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser. Then, the Film A, Film B, and Film C were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the rheological curve (wherein the measurement for rheological curve was performed at 25 °C to 220°C), the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 3 below. Table 3

Example 3

The thermoplastic polyurethane elastomer ELASTOLLAN C 65 A produced by BASF Company was hot extruded by an extruder into a single-layer fdm having a thickness of 30 pm. This single-layer film was divided into three parts: Film A, Film B, and Film C. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad. In addition, Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser.

Then, the Film A, Film B, and Film C were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the rheological curve (wherein the measurement for rheological curve was performed at 25 °C to 150°C), the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 4 below.

Table 4

In the above Examples 1-3, different thermoplastic polyurethane elastomers were used as base materials to prepare the diaphragm samples. From the results in Tables 2-4, it can be seen that when the diaphragm samples were cross-linked by an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad, 6 Mrad or 12 Mrad, the tensile modulus of the diaphragm samples did not change much, indicating that the strength of the diaphragm samples were basically maintained; additionally, the elongation at break of the diaphragm samples decreased, indicating that the elasticity of the diaphragm samples was reduced to a certain extent. But, the elongation at break was more than 180%, which met the requirement for a diaphragm product of a speaker. In addition, it should be noted that when the diaphragm samples were cross- linked with electron beam energy of 150 KV for 3 Mrad, 6 Mrad or 12 Mrad, the loss factor value tan d of the diaphragm samples at different time points remains basically unchanged, which proves that the diaphragm samples treated by electron beam crosslinking have excellent thermal stability. In addition, in Examples 1-3, since the thermoplastic polyurethane elastomer materials were chemically cross-linked by electron beam radiation, the highest hot pressing temperature and thermal stability thereof were greatly improved.

The following Examples 4-7 relate to the preparation and characterization of multi-layer diaphragms.

Example 4

A silicone damping adhesive (PSA 6574) and a thermoplastic polyurethane elastomer (TPU) (ELASTOLLAN C 65 A) were extruded into a three-layer diaphragm by an extruder. The three-layer diaphragm included a three-layer composite structure of TPU fdm (15 pm) / PSA 6574 silicone damping adhesive (10 pm) / TPU fdm (15 pm) (as shown in Figure 2). This diaphragm sample was divided into three parts: Film A, Film B, and Film C. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad. In addition, Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser.

Then, the Film A, Film B, and Film C were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 5 below. Table 5

Example 5

A polyolefin damping adhesive (ABSORTOMER EP1001) and a thermoplastic polyurethane elastomer (TPU) (ELASTOLLAN C 85 A 10) were extruded into a three-layer diaphragm by an extruder. The three-layer diaphragm included a three-layer composite structure of TPU film (25 pm) / ABSORTOMER EP1001 polyolefin damping adhesive (25 pm) / TPU film (25 pm) (as shown in Figure 2). This diaphragm sample was divided into three parts: Film A, Film B, and Film C. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad. In addition, Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser.

Then, the Film A, Film B, and Film C were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 6 below.

Table 6

Example 6

A APTIV 2000 PEEK film, an acrylic damping adhesive 3M 2567 ATT and a thermoplastic polyurethane elastomer EFASTOFFAN C 85 A 10 (TPU) were extruded into a four-layer diaphragm by an extruder. The four-layer diaphragm included a four-layer composite structure of TPU film (30 pm) / APTIV 2000 PEEK film (6 pm)/ acrylic damping adhesive 3M 2567 ATT (20 pm)/ APTIV 2000 PEEK film (6 pm) (as shown in Figure 3). This diaphragm sample was divided into three parts: Film A, Film B, and Film C. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad. In addition, Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser.

Then, the Film A, Film B, and Film C were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 7 below.

Table 7

Example 7

A APTIV 2000 PEEK film, an acrylic damping adhesive 3M 2567 ATT and a thermoplastic polyurethane elastomer ELASTOLLAN C 65 A (TPU) were extruded into a five-layer diaphragm by an extruder. The five-layer diaphragm included a five-layer composite structure of APTIV 1000 PEEK film (8 pm) / acrylic damping adhesive 3M 2567 ATT (10 pm) / TPU film (15 pm) / acrylic damping adhesive 3M 2567 ATT (10 pm) / APTIV 1000 PEEK film (8 pm) (as shown in Figure 4). This diaphragm sample was divided into three parts: Film A, Film B, and Film C. Then, Film B was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 3 Mrad. In addition, Film C was irradiated by using an electron beam having electron beam energy of 150 KV for an electron beam dose of 6 Mrad by using the same laser.

Then, the Film A, Film B, and Film C were measured according to the methods described above for measuring the tensile modulus, the elongation at break, the highest hot pressing temperature and the thermal stability, respectively. The test results are shown in Table 8 below. Table 8

It can be known from the above Examples 4-7 that the multi-layer diaphragms obtained according to the technical solution of the present invention had good modulus, elasticity and thermal stability.

Although the specific embodiments have been shown and described in the present invention, those skilled in the field will understand that the specific embodiments shown and described may be replaced with various alternative and/or equivalent embodiments without departing from the scope of the invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed in the present invention. Accordingly, the invention is limited only by the claims and the equivalents thereof.

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

Claims

WHAT IS CLAIMED IS:

1. A diaphragm for a microspeaker, the diaphragm being a single-layer diaphragm or a multi-layer diaphragm and comprising at least one layer of a chemically cross-linked thermoplastic polyurethane elastomer, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25 °C to 150°C, as measured by a rheological curve.

2. The diaphragm according to claim 1, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve.

3. The diaphragm according to claim 1 or 2, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a tensile modulus in a range of 1 MPa to 150 MPa and an elongation at break in a range of 180% to 500%.

4. The diaphragm according to claim 3, wherein the diaphragm has a thickness in a range of 5 pm to 100 pm.

5. The diaphragm according to claim 3, wherein the chemically cross-linked thermoplastic polyurethane elastomer is cross-linked by radiation.

6. The diaphragm according to claim 5, wherein the chemically cross-linked thermoplastic polyurethane elastomer is cross-linked by radiating electron beam.

7. The diaphragm according to claim 3, wherein the multi-layer diaphragm is a diaphragm having three layers.

8. The diaphragm according to claim 7, wherein the multi-layer diaphragm further includes a damping layer.

9. The diaphragm according to claim 8, wherein the damping layer is one or more selected from a group consisting of a silicone damping adhesive layer, an acrylic damping adhesive layer and a polyolefin damping adhesive layer.

10. The diaphragm according to claim 7, wherein the multi-layer diaphragm further includes at least one plastic layer which has a tensile modulus of 1 MPa to 1000 MPa and a yield strain of 3% to 30%.

11. The diaphragm according to claim 10, wherein the plastic layer is one or more selected from a group consisting of a polyethylene naphthalate layer, a polyetheretherketone layer, a polyaryletherketone layer, a polyimide layer, and a thermoplastic polyester elastomer layer.

12. The diaphragm according to claim 7, wherein the multi-layer diaphragm has a thickness in a range of 10 pm to 100 pm.

13. The diaphragm according to claim 7, wherein the diaphragm has a tensile modulus in a range of 1 MPa to 1000 MPa.

14. The diaphragm according to claim 7, wherein the diaphragm has an elongation at break in a range of 80% to 500%.

15. A method of manufacturing a diaphragm for a microspeaker, comprising subjecting a thermoplastic polyurethane elastomer fdm to a chemical crosslinking treatment, wherein: the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.4 in a temperature range from 25°C to 150°C, as measured by a rheological curve.

16. The method of manufacturing a diaphragm for a microspeaker according to claim 15, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a loss factor less than or equal to 0.2 in a temperature range from 50°C to 100°C, as measured by a rheological curve.

17. The method of manufacturing a diaphragm for a microspeaker according to claim 15, wherein the chemically cross-linked thermoplastic polyurethane elastomer has a tensile modulus in a range of 1 MPa to 150 MPa and an elongation at break in a range of 180% to 500%.

18. The method of manufacturing a diaphragm for a microspeaker according to claim

17, wherein the chemical crosslinking treatment comprises crosslinking the thermoplastic polyurethane elastomer fdm by radiation.

19. The method of manufacturing a diaphragm for a microspeaker according to claim

18, wherein the chemical crosslinking treatment comprises crosslinking the thermoplastic polyurethane elastomer fdm by radiating electron beam.

20. The method of manufacturing a diaphragm for a microspeaker according to any one of claims 15-19, wherein the diaphragm is a single-layer diaphragm or a multi-layer diaphragm comprising at least one layer of a chemically cross-linked thermoplastic polyurethane elastomer.

21. The method of manufacturing a diaphragm for a microspeaker according to claim 20, wherein the multi-layer diaphragm is a diaphragm having three layers.