Diaphragm for micro sound production device and micro sound production device

Abstract

This invention relates to the field of acoustic product technology, and discloses a diaphragm for a miniature sound-generating device and the miniature sound-generating device itself. The diaphragm comprises a rubber membrane layer formed by a crosslinking reaction of a hydrogenated butadiene-acrylonitrile polymer, wherein the hydrogenated butadiene-acrylonitrile polymer contains carboxylic acid groups, and the crosslinking agent is an amine crosslinking agent. This invention improves the diaphragm's temperature resistance, reduces the risk of diaphragm collapse and rupture, and enhances the low-frequency performance of the miniature sound-generating device, giving it a full bass and a comfortable listening experience. Simultaneously, it solves the problems of limited diaphragm molding methods and high manufacturing costs inherent in existing diaphragm manufacturing technologies.

Description

Technical Field

[0001] This invention relates to the field of acoustic product technology, and in particular to a diaphragm for a miniature sound-generating device and a miniature sound-generating device. Background Technology

[0002] Sound-generating devices are crucial acoustic components in consumer electronics, converting electrical signals into sound. In recent years, consumer electronics have developed rapidly, especially with the rapid growth of small electronic devices such as mobile phones and tablets. This has created a demand for smaller, higher-performance miniature sound-generating devices, requiring further improvements in their performance. Sound-generating devices typically use a diaphragm as the vibrating element, and the diaphragm plays a vital role in the device's sound production performance, determining the quality of the electrical-to-sound energy conversion.

[0003] With the increasing demand for high-fidelity sound, diaphragms made of rubber (e.g., nitrile rubber, butyl rubber, hydrogenated nitrile rubber, etc.) have been widely used in the field of sound-generating devices. However, in the process of realizing the embodiments of this application, the inventors of this application found that the temperature resistance and resilience of the diaphragms made of the above-mentioned hydrogenated nitrile rubber need to be further improved. Moreover, the prior art for making diaphragms using hydrogenated nitrile rubber usually only uses sulfur or peroxide crosslinking and can only be molded. The molds for molding are expensive, resulting in high costs for making the rubber diaphragms.

[0004] Therefore, there is a need to provide a diaphragm that has low manufacturing cost, excellent temperature resistance and resilience to solve the above problems. Summary of the Invention

[0005] Based on this, one embodiment of the present invention aims to provide a diaphragm and a micro-sound generating device for use in a micro-sound generating device, so as to improve the temperature resistance and resilience of the diaphragm, overcome the limitations of existing technology in diaphragm manufacturing, and reduce the cost of diaphragm manufacturing.

[0006] The above objective can be achieved through the following technical solutions:

[0007] According to one aspect of the present invention, a diaphragm for a miniature sound-generating device is provided, the diaphragm comprising a rubber film layer formed by a crosslinking reaction of a hydrogenated nitrile butadiene polymer, wherein the hydrogenated nitrile butadiene polymer contains carboxylic acid groups and the crosslinking agent is an amine crosslinking agent.

[0008] Optionally, the hydrogenated butadiene-acrylonitrile polymer has monomers comprising vinyl unsaturated monocarboxylic acids and / or vinyl unsaturated dicarboxylic acids.

[0009] Optionally, the vinyl unsaturated monocarboxylic acid is selected from one or more of acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, and cinnamic acid.

[0010] Optionally, the vinyl unsaturated dicarboxylic acid is selected from one or more of trans-butenedioic acid, maleic acid, pentenedioic acid, allylmalonic acid, mesocarboxylic acid, tocanic acid, edaconic acid, and niconic acid.

[0011] Optionally, the hydrogenated butyronitrile polymer has a carboxylic acid group content of 0.1 wt% to 5 wt%.

[0012] Optionally, the hydrogenated butadiene-acrylonitrile polymer contains an acrylonitrile block, wherein the acrylonitrile block content is 15 wt% to 50 wt%.

[0013] Optionally, the amount of the amine crosslinking agent added is 0.5 wt% to 5 wt%, based on the mass of the hydrogenated butyronitrile polymer.

[0014] Optionally, the amine crosslinking agent is one or more of hexamethylenediamine, hexamethylenediamine salt, hexamethylenediamine carbamate, triethylenetetramine, 2,2'-methylenediphenylamine, and di-o-tolueneguanidine.

[0015] Optionally, the rubber after crosslinking the hydrogenated butadiene-acrylonitrile polymer with the amine crosslinking agent has a glass transition temperature of -40℃ to -15℃.

[0016] Optionally, the rubber crosslinked with the hydrogenated nitrile butadiene polymer and the amine crosslinking agent has a hardness of 45A to 85A, and the diaphragm thickness is 20μm to 200μm. Preferably, the rubber has a hardness of 50A to 80A, a tensile strength of 6MPa to 35MPa, and a tear strength of 10N / mm to 100N / mm.

[0017] Optionally, the decrease in elongation at break of the rubber after heat aging in an oven at 175°C for 120 hours is less than 50%.

[0018] Optionally, the rubber film layer has a recovery rate of more than 80% at 20% strain.

[0019] Optionally, the diaphragm is obtained by mixing the hydrogenated butadiene-nitrile polymer with the crosslinking agent to obtain a compound, and then forming the compound into a film using a film-forming process and followed by molding treatment.

[0020] Optionally, the molding process is pneumatic molding.

[0021] According to another aspect of the present invention, a miniature sound-generating device is provided, comprising a vibration system and a magnetic circuit system cooperating with the vibration system; the vibration system includes a diaphragm and a voice coil coupled to one side of the diaphragm, the magnetic circuit system driving the voice coil to vibrate to drive the diaphragm to produce sound, the diaphragm being the diaphragm for the miniature sound-generating device of the present invention.

[0022] Beneficial effects: In this invention, the rubber membrane layer in the diaphragm is prepared by cross-linking a hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups with an amine cross-linking agent, which improves the temperature resistance of the diaphragm and makes the diaphragm have good resilience. Even in harsh environments with high and low temperatures, it can maintain high elasticity for a long time, reducing the risk of diaphragm collapse and rupture. At the same time, by using a hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups for cross-linking with an amine cross-linking agent, the molding method of the diaphragm is not limited. The miniature sound-generating device prepared by the diaphragm of this invention has excellent low-frequency performance, with full bass and a comfortable listening experience. Detailed Implementation

[0023] Unless otherwise specified, the raw materials and equipment used in this invention are commonly used in the art; the methods used in this invention, unless otherwise specified, are conventional methods in the art. Unless otherwise specified, the meanings of the terms in this specification are the same as those generally understood by those skilled in the art, but in case of conflict, the definitions in this specification shall prevail. The terms "comprising," "including," "containing," "having," or other variations thereof are intended to cover non-closed inclusion, and no distinction is made between these terms. The term "comprising" means that other steps and components may be added without affecting the final result. The term "comprising" also includes the terms "consisting of" and "substantially consisting of." The compositions and methods / processes of this invention comprise, consist of, and substantially consist of the essential elements and limitations described herein, as well as any additional or optional ingredients, components, steps, or limitations described herein.

[0024] All numerical values ​​or expressions relating to component amounts, process conditions, etc., used in the specification and claims are to be understood to be modified with “about” in all cases. All ranges relating to the same component or property include endpoints that can be independently combined. Because these ranges are continuous, they include every value between the minimum and maximum values. It should also be understood that any numerical range referenced in this application is intended to include all subranges within that range.

[0025] As described in the background section, the temperature resistance and resilience of diaphragms made from hydrogenated nitrile butadiene rubber (NBR) need further improvement. Furthermore, existing technologies for preparing NBR diaphragms typically only allow for sulfur or peroxide crosslinking and compression molding, resulting in high production costs. Research has revealed that NBR diaphragms are limited by their crosslinking mechanism, requiring only sulfur or peroxide crosslinking. However, sulfur or peroxides exhibit low or no crosslinking in the presence of oxygen (which absorbs free radicals and hinders the crosslinking reaction). This prevents NBR diaphragms from being molded in an aerobic environment, limiting molding to compression molding and preventing the use of lower-cost pneumatic molding processes. Based on this, the inventors, through further research and improvement, have used modified NBR and amine crosslinking agents to alter the crosslinking reaction mechanism. This allows for sufficient chemical crosslinking even in the presence of oxygen, improving the diaphragm's temperature resistance and resilience, unrestricting the molding process, significantly reducing production costs, and providing strong support for future widespread application.

[0026] An embodiment of the present invention provides a diaphragm for a miniature sound-generating device, the diaphragm comprising a rubber film layer formed by a crosslinking reaction of a hydrogenated nitrile butadiene polymer, wherein the hydrogenated nitrile butadiene polymer contains carboxylic acid groups, and the crosslinking agent used in the crosslinking reaction is an amine crosslinking agent.

[0027] The hydrogenated butadiene-acrylonitrile polymer comprises monomers including vinyl unsaturated monocarboxylic acids and / or vinyl unsaturated dicarboxylic acids. By employing the above-mentioned hydrogenated butadiene-acrylonitrile polymer and subjecting it to a full crosslinking reaction with an amine crosslinking agent to form a crosslinked structure, the mechanical properties of the material are improved, resulting in a rubber film layer with excellent temperature resistance and resilience. Further, the hydrogenated butadiene-acrylonitrile polymer may have the following structure:

[0028]

[0029] In the above structure, x, y, z, m, and n are natural numbers; the original monomer of R4 is an ethylene-unsaturated monocarboxylic acid or an ethylene-unsaturated dicarboxylic acid. Further, the ethylene-unsaturated monocarboxylic acid can be selected from one or more of acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, and cinnamic acid. The ethylene-unsaturated dicarboxylic acid can be selected from one or more of trans-butenedioic acid, maleic acid, pentenedioic acid, allylmalonic acid, mesocarboxylic acid, tocanic acid, edaconic acid, and niobaconic acid. The main monomer is polymerized with the ethylene-unsaturated carboxylic acid monomer to obtain the hydrogenated butadiene-acrylonitrile polymer with the above structure. By fully crosslinking this hydrogenated butadiene-acrylonitrile polymer with an amine crosslinking agent to form a cyclic imine structure, the temperature resistance and resilience of the diaphragm are significantly improved.

[0030] The hydrogenated butadiene-acrylonitrile polymer contains 0.1 wt% to 5 wt% of carboxylic acid groups, for example, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, etc. By reacting the hydrogenated butadiene-acrylonitrile polymer with an amine crosslinking agent to form a crosslinked structure and controlling the content of carboxylic acid groups in the hydrogenated butadiene-acrylonitrile polymer, the material has a glass transition temperature of -40℃ to -15℃ and an elongation at break of greater than or equal to 100%. This glass transition temperature and elongation at break give the diaphragm excellent low-temperature resilience, even at temperatures below -20℃, resulting in good acoustic performance for the sound-generating device.

[0031] The inventors of this application investigated the effect of carboxylic acid group content on the low-temperature performance of diaphragms. Table 1 shows the effect of carboxylic acid group content on glass transition temperature and elongation at break. Testing standards: Elongation at break was determined according to ASTM D412-2016 standard, with dumbbell-shaped specimens and a tensile rate of 500 mm / min. Each group of samples was tested 5 times, and the average value was taken. Glass transition temperature was determined according to ISO 6721-4 standard, with a heating rate of 20 °C / min. Each group of samples was tested 3 times, and the average value was taken. The specimens were rubber samples obtained by crosslinking a hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups with an amine crosslinking agent.

[0032] Table 1. Effect of carboxylic acid group content on glass transition temperature and elongation at break.

[0033] Carboxylic acid group mass percentage (wt%) 0.1 0.5 1 5 8 Glass transition temperature (°C) -27.1 -26.9 -26.8 -23.4 -20.2 Elongation at break (%) 372 361 348 296 254

[0034] As shown in Table 1, the content of carboxylic acid groups in the hydrogenated butadiene-acrylonitrile polymer is between 0.1wt% and 8wt%, the glass transition temperature of the rubber is between -30℃ and -20℃, the elongation at break is above 254%, the diaphragm can maintain good resilience when working at -20℃, the sound-generating device exhibits high sound quality, and the risk of diaphragm rupture during sound generation in low-temperature environments is reduced. As shown in Table 1, the inventors of this application have discovered a high correlation between the glass transition temperature and the content of carboxylic acid groups in the hydrogenated nitrile butadiene polymer. The higher the content of carboxylic acid groups, the more crosslinking points there are, the greater the degree of crosslinking of the material, and the more restricted the movement of molecular chains, leading to an increase in the glass transition temperature, an increase in the damping factor, and a decrease in the elongation at break. The higher the elongation at break, the better the resilience of the diaphragm. When the content of carboxylic acid groups is 8 wt%, the decrease in elongation at break is significant. Therefore, as a preferred embodiment, the content of carboxylic acid groups in the hydrogenated nitrile butadiene polymer is 0.1 wt% to 5 wt%. Within this range, the elongation at break of the diaphragm is above 290%, which not only meets the requirements of the diaphragm for use at temperatures below -23°C, but also enables the diaphragm to maintain high elasticity even after long-term use at low temperatures. During long-term use at low temperatures, there will be no diaphragm rupture due to low temperature intolerance, and the sound-generating device will also exhibit superior sound quality.

[0035] In a preferred embodiment, the hydrogenated butadiene-acrylonitrile polymer contains 0.1 wt% to 5 wt% carboxylic acid groups and 15 wt% to 50 wt% acrylonitrile blocks. The inventors have discovered a high correlation between the glass transition temperature and the content of carboxylic acid groups and acrylonitrile blocks in the hydrogenated butadiene-acrylonitrile polymer. Higher carboxylic acid group and acrylonitrile block content results in a higher glass transition temperature. Extensive synthetic experiments have verified that when the carboxylic acid group content is between 0.1 wt% and 5 wt% and the acrylonitrile block content is between 15 wt% and 50 wt%, the prepared diaphragm exhibits optimal mechanical properties, with a glass transition temperature between -40°C and -15°C, meeting the diaphragm's requirements for low-temperature use. If the content of either the carboxylic acid group or the acrylonitrile block is below the lower limit of the above range, there are too few crosslinking points, resulting in fewer crosslinked structures and poor diaphragm resilience, failing to meet usage requirements. If the content of either the carboxylic acid group or the acrylonitrile block exceeds the upper limit of the above range, the material is overly crosslinked, increasing brittleness and significantly reducing elongation at break, making the prepared diaphragm prone to breakage during prolonged use. This embodiment uses a hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups to crosslink with an amine crosslinking agent. By simultaneously controlling the content of carboxylic acid groups and acrylonitrile blocks in the hydrogenated butadiene-acrylonitrile polymer, the temperature resistance and resilience of the diaphragm are improved. This makes the diaphragm less prone to rupture during low-temperature use, and the sound-generating device has excellent acoustic performance, vibration effect and damping effect.

[0036] The amount of the amine crosslinking agent added is 0.5wt% to 5wt% of the hydrogenated butadiene-acrylonitrile polymer, for example, it can be 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, etc. This embodiment uses a hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups to react with an amine crosslinking agent to form a crosslinked structure, and controls the amount of amine crosslinking agent added to effectively control the crosslinking density and rate, resulting in superior mechanical strength of the material, high resilience of the diaphragm, and reduced risks of deformation, collapse, and rupture during long-term use. This gives the sound-generating device excellent acoustic performance. Furthermore, by using a hydrogenated butadiene-acrylonitrile polymer and an amine crosslinking agent for crosslinking, the diaphragm crosslinking molding method is unrestricted, and pneumatic molding can be used, thereby reducing manufacturing costs. Although the hydrogenated butadiene-acrylonitrile polymer of this invention contains unsaturated functional groups, and in principle, it can be crosslinked using sulfur and / or peroxide crosslinking agents, the use of sulfur and / or peroxide crosslinking agents requires strict crosslinking molding processes. In particular, these crosslinking agents cannot undergo effective crosslinking reactions in the presence of oxygen, thus preventing the use of pressure molding for diaphragm fabrication and necessitating compression molding, thereby increasing diaphragm fabrication costs. To better address these issues, this application uses amine crosslinking agents to fully crosslink the carboxylic acid groups in the hydrogenated butadiene-acrylonitrile polymer and controls the crosslinking density and rate. This not only improves the diaphragm's temperature resistance and resilience but also allows for sufficient chemical crosslinking reactions in an oxygen-rich environment, enabling pressure molding for diaphragm fabrication, saving mold costs, and effectively reducing diaphragm fabrication costs, providing strong support for subsequent promotion and application.

[0037] The inventors of this application have discovered that when the amount of crosslinking agent added is low, such as less than 0.5 wt%, the effective crosslinking density of the material formed by the crosslinking reaction is low, and the mechanical strength and resilience of the material are poor. When diaphragms are prepared using this material, the diaphragms are prone to deformation and collapse during long-term use, which leads to a drop in the acoustic Fr curve. In addition, the vulcanization rate of the material is slow, which severely limits the production efficiency of the diaphragm and increases the production cost of the diaphragm. On the other hand, when the amount of crosslinking agent added is too high, such as greater than 5 wt%, the effective crosslinking density formed by the material is too high, which leads to a serious decrease in its elongation at break and a decrease in damping. The prepared diaphragm is prone to polarization during vibration, which leads to an increase in its acoustic distortion. Furthermore, there is a risk of diaphragm breakage during repeated vibration.

[0038] The crosslinking agent preferred in this invention is an amine crosslinking agent, which can be one or more of hexamethylenediamine, hexamethylenediamine salt, hexamethylenediamine carbamate, triethylenetetramine, 2,2'-methylenediphenylamine, and di-o-tolueneguanidine. By using one or more of the above-mentioned amine crosslinking agents and allowing them to fully crosslink with the carboxylic acid groups in the hydrogenated butadiene-acrylonitrile polymer to form a cyclic imine structure, the temperature resistance and mechanical properties such as resilience of the diaphragm are improved, eliminating the risk of diaphragm collapse and rupture during use. Although sulfur and / or peroxides can be used for crosslinking when the polymer contains carboxyl groups because its molecular chain also contains some unsaturated functional groups, sulfur and / or peroxides cannot undergo an effective crosslinking reaction in the presence of oxygen, thus preventing the use of pressure molding. To facilitate diaphragm molding, this application only uses amine crosslinking agents for crosslinking, which facilitates diaphragm coating and pressure molding.

[0039] In an optional embodiment, the diaphragm of the present invention is obtained by mixing the hydrogenated butadiene-nitrile polymer with a crosslinking agent to obtain a compound, and then preparing a membrane by using a film-forming process on the compound. The membrane is then dried at low temperature and subjected to molding treatment. This embodiment uses a hydrogenated butadiene-nitrile polymer containing carboxylic acid groups as the raw rubber and an amine crosslinking agent as the crosslinking agent, changing the crosslinking mode to achieve sufficient chemical crosslinking reaction even in an aerobic environment. This overcomes the limitations of existing diaphragm molding methods and can reduce the cost of diaphragm manufacturing.

[0040] The molding process employs pneumatic molding. By using a hydrogenated nitrile butadiene polymer containing carboxylic acid groups as the raw rubber and an amine crosslinking agent as the crosslinking agent, the crosslinking method is altered. During pneumatic molding, effective chemical crosslinking forms a crosslinked structure, overcoming the limitation of existing technologies that rely solely on sulfur and / or peroxides for molding diaphragms from hydrogenated nitrile butadiene rubber. This improves the degree of crosslinking, enhances the material's mechanical properties and diaphragm resilience, and significantly reduces the diaphragm manufacturing cost, providing strong support for future applications. The pneumatic molding process uses a single mold. The composite film layer, formed by the rubber film layer and / or other film layers, is adhered to the mold. The mold is placed in a sealed cavity, and high-temperature, high-pressure molding is achieved by filling the cavity with gas (e.g., air) and heating it. This invention utilizes an amine crosslinking agent to crosslink with the hydrogenated nitrile butadiene polymer containing carboxylic acid groups. Even the presence of oxygen during the filling process does not affect the crosslinking reaction, effectively improving the degree of crosslinking and overcoming the limitations of existing technologies. This solves the problem of high costs associated with the current use of acrylic rubber to prepare diaphragms.

[0041] Optionally, the diaphragm may consist of only one rubber film layer; or it may be a multi-layer structure, such as two or three layers, wherein at least one of the multiple layers is the rubber film layer, and the other layers may be thermoplastic elastomers and / or engineering plastics to meet other performance requirements such as diaphragm waterproofing. The thermoplastic elastomer may be selected from at least one of thermoplastic polyester elastomers, thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, and silicone elastomers. The engineering plastic may be selected from at least one of polyetheretherketone, polyarylate, polyetherimide, polyimide, polyphenylene sulfide, polyethylene naphthalate, polyethylene terephthalate, and polybutylene terephthalate.

[0042] In a preferred embodiment, the rubber after crosslinking the hydrogenated butadiene-acrylonitrile polymer with an amine crosslinking agent has a hardness of 45A to 85A, for example, 50A, 60A, 70A, 80A, etc., preferably 45A to 85A. This embodiment significantly improves the temperature resistance by using the above-mentioned hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups and an amine crosslinking agent as crosslinking agents to form a cyclic imine structure. At the same time, by improving and optimizing the hardness of the rubber, the rubber in this hardness range, after heat aging in an oven at 175°C for 120 hours, has a reduction rate of less than 50% in elongation at break. This results in the rubber film layer having a recovery rate of more than 80% at 20% strain, and still exhibiting excellent resilience under long-term use at high temperatures, as well as excellent acoustic properties.

[0043] The inventors of this application tested the decrease rate of elongation at break after heat aging of rubber and compared it with conventional HNBR rubber. Table 2 compares the decrease rate of elongation at break of conventional HNBR rubber and the rubber sample of this invention after heat aging in an oven at 175℃ for 120 hours at different hardness levels. Testing standard: Elongation at break was measured according to ASTM D412-2016 standard. The sample shape was dumbbell-shaped. The rubber sample of this invention was obtained by crosslinking a hydrogenated butadiene-acrylonitrile polymer containing carboxylic acid groups with an amine crosslinking agent. The tensile rate was 500 mm / min, and each group of samples was tested 5 times and the average value was taken.

[0044] Table 2. Decrease in elongation at break of rubber after heat aging at different hardness levels.

[0045] hardness 50A 60A 70A 80A Conventional HNBR rubber 55.1％ 53.7％ 62.5％ 64.8％ Rubber sample of the present invention 38.6％ 41.3％ 45.8％ 47.9％

[0046] As shown in Table 2, the inventors of this application have discovered that, compared to conventional HNBR rubber, the present invention significantly improves the temperature resistance of the material by crosslinking a hydrogenated butadiene-nitrile polymer containing carboxylic acid groups with an amine crosslinking agent to form a cyclic imine structure. It still exhibits good resilience under long-term harsh environments. Furthermore, the rubber formulations with hardnesses of 50A to 80A, after heat aging in a 175°C oven for 120 hours, show a decrease in elongation at break of less than 50%. Compared to conventional HNBR rubber, the resilience of the rubber formulations in this application decreases more slowly, reducing the risk of diaphragm breakage and acoustic distortion, thus allowing the speaker to maintain excellent sound quality even under high-temperature, long-term use. Furthermore, the rubber film layer prepared using the above-mentioned hardness exhibits a recovery rate of over 80% at 20% strain, ensuring the diaphragm retains high resilience even after large strains, further reducing the risk of diaphragm breakage during vibration.

[0047] Furthermore, the inventors discovered that, based on the aforementioned hardness and the following mechanical properties, namely, the tensile strength of the rubber is 6MPa to 35MPa and the tear strength is 10N / mm to 100N / mm, the prepared diaphragm is less prone to breakage during module use, thereby further improving the reliability of the diaphragm and enhancing its acoustic performance.

[0048] In a preferred embodiment, the rubber crosslinked with the hydrogenated nitrile butadiene polymer and the amine crosslinking agent has a hardness of 45A to 85A and a diaphragm thickness of 20μm to 200μm, for example, 50μm, 100μm, 150μm, 180μm, etc. The inventors of this application have discovered that by comprehensively controlling the hardness of the rubber and the thickness of the diaphragm, the modulus and thickness of the sound-generating device, such as a loudspeaker, can be controlled, giving the diaphragm sufficient stiffness and damping while allowing the loudspeaker to have a low F0. More preferably, a rubber hardness of 50A to 80A allows the loudspeaker's F0 to reach 150Hz to 1500Hz, with excellent low-frequency performance, full bass, and a comfortable listening experience.

[0049] In the mixing process, in addition to adding crosslinking agents, other compounding agents, such as reinforcing agents, antioxidants, and vulcanization accelerators, can also be added. These are mixed using the shearing action of a mixer or open mill to ensure that each compounding agent is uniformly dispersed in the continuous phase of the hydrogenated nitrile butadiene polymer, resulting in a uniformly dispersed compound. Adding reinforcing agents enhances the strength of the diaphragm; for example, adding reinforcing agents to achieve the aforementioned hardness improves the resilience of the diaphragm under harsh conditions during production and reduces the rate of decline in resilience during long-term use in harsh environments. The reinforcing agent can be, for example, at least one of carbon black, carbonates, and metal oxides. Adding antioxidants delays or inhibits the polymer oxidation process, thereby preventing polymer aging and extending its service life. The antioxidant can be, for example, BHT antioxidant. Adding vulcanization accelerators promotes vulcanization; specifically, vulcanization accelerators such as TMTD and D can be used. The above-mentioned compounding agents are not limited to these and can also be other compounding agents not listed in this embodiment but well-known to those skilled in the art. The crosslinking agent is added at a rate of 0.5 wt% to 5 wt% of the hydrogenated nitrile butadiene polymer. There are no particular restrictions on the amount of other compounding agents added. An exemplary and non-limiting formulation example is given, based on 100 parts of hydrogenated nitrile butadiene polymer, with 40 to 60 parts of carbon black, 2 to 5 parts of antioxidant, 1 to 3 parts of vulcanization accelerator, and 0.5 to 5 parts of crosslinking agent.

[0050] The film-forming process can be either coating or calendering. Taking coating as an example, the film-forming process may include dissolving the compounded rubber in a polar solvent to obtain a rubber solution, coating the rubber solution onto the surface of a mold such as a release film or protective film to obtain a film, and sending the continuously coated film into an oven tunnel for low-temperature drying to obtain a tape. The polar solvent may be at least one of ethyl acetate, toluene, acetone, butanone, tetrahydrofuran, methyl formate, and butyl acetate. Further, the thickness of the tape is 10–300 μm; preferably 25–200 μm, and the tape thickness tolerance is ±5 μm, thereby ensuring the uniformity of the rubber film layer and making the diaphragm less prone to polarization.

[0051] During the film-forming process, the compound is controlled to prevent cross-linking, ensuring that the cross-linking reaction occurs only during the air-pressure molding process. Alternatively, the risk of cross-linking reaction can be reduced by controlling the temperature and time in the film-forming process to ensure the performance of the diaphragm.

[0052] Optionally, during dissolution, the temperature is controlled between 0 and 100°C, such as 10°C, 30°C, 50°C, and 90°C. The inventors of this application have found that if the dissolution temperature is below 0°C, the solvent's solubility is poor, and the compound cannot be effectively and uniformly dispersed. If the dissolution temperature is above 100°C, there is a risk of vulcanization reaction during the dissolution process, which can easily lead to curing of the adhesive. Preferably, the dissolution temperature is controlled between 20°C and 70°C. This preferred temperature range not only ensures effective and uniform dispersion of the adhesive but also avoids the risk of crosslinking. During low-temperature drying, the drying temperature is controlled between 30℃ and 140℃, such as 50℃, 70℃, 90℃, and 120℃, and the drying time is between 0.2min and 30min, such as 1min, 10min, and 20min. The inventors of this application have found that when the temperature inside the drying tunnel is below 30℃, the solvent evaporation time in the coated film is relatively long, severely affecting production efficiency, and the prepared material tape has a high solvent residue, which is detrimental to the subsequent preparation of the diaphragm. When the temperature is above 140℃, the coated film is at risk of premature cross-linking reaction, which is detrimental to the stability of the material. Preferably, the drying temperature is controlled between 50℃ and 120℃, and the drying time is between 0.5min and 20min, thereby improving production efficiency, facilitating subsequent diaphragm preparation, and reducing the risk of cross-linking reaction of the adhesive, thus ensuring the performance of the diaphragm.

[0053] Optionally, after dissolving the compounded rubber, a glue solution is obtained. The solid content concentration of the glue solution is controlled at 10% to 45%, and the viscosity is 700 mPa·s to 85000 mPa·s, wherein the solid content = (mass of compounded rubber / mass of glue solution) × 100%. By controlling the solid content and viscosity of the glue solution, the uniformity of the coated strip is improved. The inventors of this application have found that the solid content of the glue solution should not be too high or too low. When the solid content is too low, the glue solution on the release film will have high fluidity, resulting in poor uniformity of the surface thickness of the coated strip. On the other hand, when the solid content is too high, the viscosity is extremely high, the fluidity is poor, which will lead to problems such as excessively long defoaming process time, poor flowability on the release film, and slow solvent evaporation rate in the drying tunnel.

[0054] According to another aspect of the present invention, a miniature sound-generating device is provided, comprising a vibration system and a magnetic circuit system cooperating with the vibration system; the vibration system includes a diaphragm and a voice coil coupled to one side of the diaphragm. When the miniature sound-generating device is working, the voice coil is energized and driven by the magnetic field force of the magnetic circuit system, causing the voice coil to vibrate up and down, thereby driving the diaphragm to vibrate, and sound is generated when the diaphragm vibrates. Miniature sound-generating devices, such as loudspeakers, prepared using the diaphragm described in this invention have excellent low-frequency performance, possessing full bass and a comfortable listening experience, and exhibit less swaying vibration during vibration, resulting in more stable sound.

[0055] To better understand the above technical solutions of the present invention, the following detailed description is provided in conjunction with specific embodiments. These specific embodiments are merely preferred embodiments of the present invention and are not intended to limit the scope of the invention. In one embodiment, the raw rubber type 2510 was purchased from Zeon Corporation.

[0056] Example 1

[0057] Formula: 100 parts hydrogenated butadiene-acrylonitrile polymer raw rubber; 58 parts carbon black; 3 parts BHT antioxidant; 1.5 parts hexamethylenediamine vulcanizing agent; 1.8 parts vulcanization accelerator. The original R4 monomer in the structure of the hydrogenated butadiene-acrylonitrile polymer is acrylic acid, and the content of carboxylic acid groups is 1.5 wt%.

[0058] 1) The above 70A formula is intensively mixed to form compound HNBR-70;

[0059] 2) HNBR-70 was placed in a solvent of methyl ethyl ketone (MEK) and butyl acetate to obtain HNBR-70 adhesive solution; wherein the ratio of MEK to butyl acetate was 5:1, the solid content was 20wt%, the mixture was stirred and dispersed at room temperature for 50h, filtered, allowed to stand to defoam, and the viscosity was 6150mPa·s.

[0060] 3) Apply HNBR-70 adhesive solution evenly and continuously to the surface of the release film from the coating head. The continuously coated material enters the drying tunnel along with the release film for drying. The drying tunnel temperature is 85℃ and the drying time in the drying tunnel is 12min, to prepare a 100μm thick strip.

[0061] 4) A single-layer HNBR rubber diaphragm with a thickness of 100μm is prepared from the material strip using a pneumatic molding method. This diaphragm has good temperature resistance; even after long-term use at -20℃, it still maintains excellent resilience with minimal reduction in resilience. This results in excellent low-frequency performance for the speaker, providing full bass and a comfortable listening experience. Furthermore, the pneumatic molding method significantly reduces the diaphragm manufacturing cost, overcoming the limitations imposed by existing technologies using hydrogenated nitrile butadiene rubber for diaphragm fabrication due to constraints in crosslinking agents and molding processes.

[0062] The description of this invention is given for illustrative and descriptive purposes only and is not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A diaphragm for a micro acoustic device, characterized by, The diaphragm comprises a rubber film layer formed by crosslinking a hydrogenated nitrile butadiene polymer, wherein the hydrogenated nitrile butadiene polymer contains carboxylic acid groups and the crosslinking agent is an amine crosslinking agent; the rubber film layer has a recovery rate of more than 80% at 20% strain; the rubber exhibits a reduction in elongation at break of less than 50% after heat aging in an oven at 175°C for 120 hours; the diaphragm is obtained by mixing the hydrogenated nitrile butadiene polymer with the crosslinking agent to obtain a compound, forming the compound into a film using a film-forming process, and then performing a molding process; wherein the molding process is gas compression molding.

2. The diaphragm for a micro sound generating device according to claim 1, wherein The hydrogenated butadiene-nitrile polymer has monomers including vinyl unsaturated monocarboxylic acids and / or vinyl unsaturated dicarboxylic acids.

3. The diaphragm for a miniature sound-generating device according to claim 2, characterized in that, The vinyl unsaturated monocarboxylic acid is selected from one or more of acrylic acid, methacrylic acid, ethylacrylic acid, crotonic acid, and cinnamic acid; The vinyl unsaturated dicarboxylic acid is selected from one or more of trans-butenedioic acid, maleic acid, pentenedioic acid, allylmalonic acid, medoconic acid, tocanic acid, edoconic acid, and niconic acid.

4. The diaphragm for a micro sound generating device according to claim 3, wherein The hydrogenated butyronitrile polymer has a carboxylic acid group content of 0.1wt% to 5wt%.

5. The diaphragm for a micro sound generating device according to claim 4, wherein The hydrogenated butadiene-acrylonitrile polymer contains an acrylonitrile block, and the content of the acrylonitrile block is 15wt% to 50wt%.

6. The diaphragm for a micro sound generating device according to claim 4 or 5, wherein Based on the mass of the hydrogenated butadiene-acrylonitrile polymer, the amount of amine crosslinking agent added is 0.5wt% to 5wt%.

7. The diaphragm for a micro acoustic device according to claim 6, wherein The amine crosslinking agent is one or more of hexamethylenediamine, hexamethylenediamine salt, hexamethylenediamine carbamate, triethylenetetramine, 2,2'-methylenediphenylamine, and di-o-tolueneguanidine.

8. The diaphragm for a micro acoustic device of claim 6, wherein, The rubber obtained by crosslinking the hydrogenated butadiene-acrylonitrile polymer with the amine crosslinking agent has a glass transition temperature of -40℃ to -15℃.

9. The diaphragm for a micro acoustic device of claim 6, wherein, The rubber obtained by crosslinking the hydrogenated butadiene-acrylonitrile polymer with the amine crosslinking agent has a hardness of 45A to 85A, and the thickness of the diaphragm is 20μm to 200μm.

10. A micro acoustic device, comprising: The device includes a vibration system and a magnetic circuit system that cooperates with the vibration system; the vibration system includes a diaphragm and a voice coil coupled to one side of the diaphragm, the magnetic circuit system drives the voice coil to vibrate so as to drive the diaphragm to produce sound, and the diaphragm is the diaphragm for a micro sound-producing device as described in any one of claims 1-9.

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