Diaphragm for micro sound production device and micro sound production device

Abstract

The present application relates to the technical field of acoustic products, and discloses a diaphragm for a micro sound generating device and the micro sound generating device. The diaphragm comprises a rubber film layer formed by cross-linking reaction of an acrylate polymer, wherein the acrylate polymer contains a carboxylic acid group, and the cross-linking agent is an amine cross-linking agent. By using the acrylate polymer containing the carboxylic acid group and the amine cross-linking agent, the cross-linking degree is effectively improved, so that the diaphragm has excellent rebound performance and temperature resistance; meanwhile, the forming mode of the diaphragm is not limited, and the preparation cost is reduced; and the low-frequency performance of the micro sound generating device is also improved, so that the micro sound generating device has full bass and comfortable listening experience.

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] Currently, the diaphragms of most micro-sound generating devices are made of acrylate rubber. However, in the process of realizing the embodiments of this application, the inventors of this application found that the existing diaphragm made of acrylate rubber can usually only be cross-linked with sulfur or peroxide and can only be molded. However, the molds used in the molding process are expensive, resulting in high cost of preparing rubber diaphragms. In addition, the temperature resistance of acrylate rubber needs to be further improved.

[0004] Therefore, there is a need to provide a diaphragm that has low manufacturing cost and excellent temperature resistance 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, which gives the diaphragm excellent resilience and excellent temperature resistance, while also making the diaphragm molding method unrestricted and reducing manufacturing costs.

[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 an acrylate polymer, wherein the acrylate polymer contains carboxylic acid groups and the crosslinking agent is an amine crosslinking agent.

[0008] Optionally, the monomers of the acrylate polymer include 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 acrylate polymer has a carboxylic acid group content of 0.1 wt% to 5 wt%.

[0012] Optionally, the amount of the amine crosslinking agent added is 0.5 wt% to 5 wt%, depending on the mass of the acrylate polymer.

[0013] Optionally, the amine crosslinking agent is one or more of hexamethylenediamine, hexamethylenediamine salt, hexamethylenediamine carbamate, triethylenetetramine, 2,2'-methylenediphenylamine, and di-o-tolueneguanidine.

[0014] Optionally, the glass transition temperature of the rubber film layer is -40℃ to -15℃.

[0015] Optionally, the rubber film layer has a recovery rate of more than 80% at 20% strain.

[0016] Optionally, the diaphragm is obtained by mixing the acrylate polymer with a crosslinking agent to obtain a compound, and then forming the compound into a film using a film-forming process and followed by molding treatment.

[0017] Optionally, the molding process is pneumatic molding.

[0018] Optionally, the hardness of the rubber is 45A to 85A. Preferably, the hardness of the rubber is 50A to 80A.

[0019] Optionally, the rubber, after being heat-aged in an oven at 175°C for 120 hours, exhibits a decrease in elongation at break of less than 55%.

[0020] Optionally, the rubber has a tensile strength of 6 MPa to 35 MPa and a tear strength of 10 N / mm to 100 N / mm.

[0021] Optionally, the thickness of the diaphragm is 20 μm to 200 μm.

[0022] 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.

[0023] Beneficial Effects: The diaphragm in this invention is used in miniature sound-generating devices. The diaphragm uses an acrylate polymer containing carboxylic acid groups as the raw rubber and an amine crosslinking agent as the crosslinking agent. By changing the crosslinking reaction mode, the degree of crosslinking is effectively improved, making the diaphragm molding method unrestricted. This results in the diaphragm having excellent temperature resistance and resilience, maintaining high resilience even after long-term use in harsh environments, reducing the risk of diaphragm collapse or rupture during long-term use. The miniature sound-generating device prepared using the above-mentioned diaphragm exhibits good low-frequency performance, with full bass and a comfortable listening experience. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] As described in the background section, the diaphragms of existing micro-sound generating devices are mostly made of acrylic rubber. However, the preparation of diaphragms using acrylic rubber typically relies on sulfur or peroxide crosslinking and is limited to compression molding. The molds used in compression molding are expensive, resulting in high costs for rubber diaphragm production. Research has revealed that acrylic rubber diaphragms are limited to sulfur or peroxide crosslinking due to their crosslinking mechanism. Sulfur or peroxides exhibit low or no crosslinking in the presence of oxygen (which absorbs free radicals and hinders the crosslinking reaction). This prevents ACM rubber from being molded in an aerobic environment, thus limiting the molding process to compression molding and preventing the use of cost-effective pneumatic molding. Based on this, the inventors, through further research and improvement, have used modified ACM and amine crosslinking agents to alter the crosslinking reaction mechanism, achieving sufficient chemical crosslinking even in an aerobic environment. This not only improves the diaphragm's temperature resistance and resilience but also eliminates limitations in the molding process, reducing manufacturing costs and providing strong support for future applications.

[0027] 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 an acrylate polymer, wherein the acrylate polymer contains carboxylic acid groups, and the crosslinking agent used in the crosslinking reaction is an amine crosslinking agent.

[0028] In an optional embodiment, the acrylate polymer comprises monomers including vinyl unsaturated monocarboxylic acids and / or vinyl unsaturated dicarboxylic acids. By employing the above-mentioned acrylate polymer, its reactivity is enhanced, allowing it to undergo a full crosslinking reaction with amine crosslinking agents to form a crosslinked structure, resulting in a rubber film layer with excellent temperature resistance and resilience.

[0029] Furthermore, the acrylate polymer may have the following structure:

[0030]

[0031] In the above structure, x, y, z, and m are natural numbers; R1 / R2 / R3 can be alkyl main monomers, such as ethyl main monomers, methyl main monomers, or n-butyl main monomers, and at least one of 2-methoxyethyl; the original polymerizing 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 fumaric acid, maleic acid, pentenic acid, allylmalonic acid, mesocarboxylic acid, tocanic acid, edaconic acid, and niconic acid. The above-structured acrylate polymer is obtained by polymerizing the main monomer with an ethylene unsaturated carboxylic acid monomer. By fully crosslinking the above-structured acrylate polymer with an amine crosslinking agent to form a cyclic imine structure, the temperature resistance of the diaphragm is significantly improved, giving the diaphragm excellent resilience performance, maintaining good resilience even after long-term use in harsh environments.

[0032] In an optional embodiment, the acrylate polymer contains 0.1 wt% to 8 wt% of carboxylic acid groups, for example, 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, etc. Preferably, the acrylate polymer contains 0.1 wt% to 5 wt% of carboxylic acid groups. In this embodiment, by reacting the acrylate polymer with an amine crosslinking agent to form a crosslinked structure and controlling the content of carboxylic acid groups in the acrylate polymer, the low-temperature operation requirements of the diaphragm are met, and the diaphragm still exhibits superior resilience performance in a low-temperature environment of -20°C.

[0033] The inventors of this application, through research on the influence of carboxylic acid group content on glass transition temperature and elongation at break, discovered that when the carboxylic acid group content in the acrylate polymer is 0.1wt% to 8wt%, the rubber formed by crosslinking the acrylate polymer containing carboxylic acid groups with an amine crosslinking agent has a glass transition temperature of -40℃ to -15℃ and an elongation at break of not less than 100%, which meets the requirements of the diaphragm for low-temperature use and gives the diaphragm good high elasticity at low temperatures. Moreover, it was also found that the glass transition temperature is highly correlated with the carboxylic acid group content in the acrylate polymer. The higher the carboxylic acid group content, the more crosslinking points there are, the greater the degree of crosslinking of the material, and the more restricted the molecular chain movement, resulting in an increase in glass transition temperature, an increase in damping factor, and a decrease in elongation at break and elastic recovery rate. Preferably, the carboxylic acid group content is between 0.1wt% and 5wt%. This preferred embodiment of the carboxylic acid group content range not only meets the requirements of the diaphragm for low-temperature use, but also enables the diaphragm to maintain a high elastic state in low-temperature environments, and will not experience membrane rupture due to low-temperature insufficiency during long-term low-temperature use.

[0034] In an optional embodiment, the amount of the amine crosslinking agent added is 0.5 wt% to 5 wt% of the acrylate polymer, for example, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, etc. This embodiment uses an acrylate 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 material with superior mechanical strength and resilience. This further reduces the risk of diaphragm deformation, collapse, and rupture during long-term use, improving the reliability of the diaphragm and providing good acoustic performance. When the polymer contains carboxyl groups, because its molecular chain also contains some unsaturated functional groups, it can also be crosslinked using sulfur and / or peroxides. However, sulfur and / or peroxides cannot undergo effective crosslinking reactions in the presence of oxygen, therefore, pressure molding cannot be used. To facilitate diaphragm molding, this application only uses amine crosslinking agents for crosslinking, which facilitates diaphragm coating and pressure molding.

[0035] In implementing the various embodiments of the present invention, the inventors of this application also discovered that when the amount of crosslinking agent added is low, such as <0.5wt%, 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 the diaphragm is prepared using this material, the diaphragm is 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 seriously 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 >5wt%, 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.

[0036] 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, a sufficient crosslinking reaction can be carried out with the carboxylic acid groups in the acrylate polymer to form a cyclic imine structure, thereby improving the material's temperature resistance and resilience, and further reducing the risk of diaphragm collapse and rupture during use.

[0037] Furthermore, although the acrylate 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 places strict requirements on the crosslinking molding process. Especially in the presence of oxygen, these crosslinking agents cannot undergo effective crosslinking reactions (or even fail to react), making it impossible to use the low-cost pneumatic molding process to prepare the diaphragm. Only compression molding can be used, which requires expensive molds, thus increasing the cost of diaphragm preparation. To better solve the above problems, this application uses an amine crosslinking agent to fully crosslink the carboxylic acid groups in the acrylate polymer, changing the crosslinking reaction mode. This not only improves the temperature resistance and resilience of the diaphragm, but also allows for a full chemical crosslinking reaction in an oxygen-rich environment. This enables the use of low-cost pneumatic molding to prepare the diaphragm, saving mold costs and effectively reducing the overall cost of diaphragm preparation, providing strong support for subsequent promotion and application.

[0038] In an optional embodiment, the diaphragm is obtained by mixing the acrylate polymer with a crosslinking agent to obtain a compound, then preparing a membrane using a film-forming process, and finally drying the membrane at low temperature followed by molding. This embodiment uses an acrylate 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, overcoming the limitations of existing diaphragm molding methods.

[0039] The molding process employs pneumatic molding, using an acrylate polymer containing carboxylic acid groups as the raw rubber and an amine crosslinking agent as the crosslinking agent. During pneumatic molding, chemical crosslinking can effectively occur to form a cyclic imine structure. This overcomes the limitations of existing technologies that rely solely on sulfur and / or peroxides for molding diaphragms using acrylate rubber materials. This improves the degree of crosslinking, enhances the material's mechanical properties, and results in a diaphragm with excellent temperature resistance and resilience. Simultaneously, it significantly reduces the diaphragm manufacturing cost, providing strong support for future applications. The pneumatic molding process uses only one 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 acrylate 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.

[0040] The diaphragm may be formed from a single rubber film layer; or it may be a multi-layer structure, such as two-layer or three-layer structures, wherein at least one layer in the multi-layer structure is the rubber film layer, and the other layers may be thermoplastic elastomers and / or engineering plastics. 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.

[0041] In a preferred embodiment, the rubber crosslinked with the acrylate polymer containing carboxylic acid groups and the amine crosslinking agent has a hardness of 45A to 85A, for example, 50A, 60A, 70A, 80A, etc. Preferably, the hardness is 50A to 80A. This embodiment uses the above-mentioned acrylate polymer containing carboxylic acid groups as raw rubber and the above-mentioned amine crosslinking agent as crosslinking agent. By improving and optimizing the hardness of the crosslinked rubber, the material has excellent elongation at break, which improves the temperature resistance of the diaphragm. This allows the diaphragm to maintain high resilience even after long-term use in harsh environments, and the resilience decreases slowly, thus improving the reliability of the diaphragm.

[0042] The inventors of this application, through research on the decrease rate of elongation at break of rubbers with different hardnesses after heat aging in an oven at 175°C for 120 hours, discovered that compared to conventional ACM rubber, the present invention, through crosslinking of acrylate polymers containing carboxylic acid groups with amine crosslinking agents to form a cyclic imine structure, significantly improves the temperature resistance of the material. Under the above hardness formulation, the decrease rate of elongation at break of the rubber after heat aging in an oven at 175°C for 120 hours is less than 55%, while the decrease rate of conventional ACM rubber is around 60%. Especially under the 50A to 80A hardness formulation, the decrease rate of elongation at break of the rubber is less than 53%. The degree of decrease in resilience of the diaphragm under long-term use is significantly reduced, making the diaphragm more reliable for long-term use in harsh environments, reducing acoustic distortion, and enabling the speaker to still have excellent sound performance under harsh environments.

[0043] Furthermore, the inventors of this application have discovered that, within the aforementioned hardness range, the rubber diaphragm layer still exhibits a recovery rate of over 80% at 20% strain. This recovery rate enhances the diaphragm's deformation recovery capability, significantly reducing the risk of diaphragm collapse or rupture during use, while simultaneously providing the loudspeaker with superior acoustic performance.

[0044] Preferably, the rubber after crosslinking the acrylate polymer with the amine crosslinking agent has a tensile strength of 6MPa to 35MPa and a tear strength of 10N / mm to 100N / mm. Under the above-mentioned suitable mechanical properties, the diaphragm prepared by the rubber is less likely to break during module use, which further improves the reliability of the diaphragm.

[0045] In a preferred embodiment, the hardness of the rubber after crosslinking the acrylate polymer with the amine crosslinking agent in this invention is 45A to 85A, and the thickness of the diaphragm is 20μm to 200μm, for example, 50μm, 100μm, 150μm, 180μm, etc. By comprehensively controlling the hardness of the rubber and the thickness of the diaphragm, the inventors of this application control the modulus and thickness of the sound-generating device, such as a loudspeaker, so that the loudspeaker has a low F0 while the diaphragm has sufficient stiffness and damping. More preferably, the inventors have found that when the hardness of the rubber is 50A to 80A and the diaphragm thickness is 20μm to 200μm, the diaphragm has excellent resilience, allowing the loudspeaker's F0 to reach 150Hz to 1500Hz, resulting in excellent low-frequency performance, full bass, and a comfortable listening experience.

[0046] 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. The mixing is achieved through the shearing action of a mixer or open mill, ensuring that each compounding agent is uniformly dispersed in the acrylate polymer, resulting in a uniformly dispersed compound. This mixing process ensures the compounding agents are uniformly dispersed in the continuous raw rubber, facilitating subsequent crosslinking reactions and the formation of a crosslinked structure. Specifically, adding reinforcing agents enhances the strength of the diaphragm; for example, adding reinforcing agents allows the crosslinked rubber to achieve the aforementioned hardness, thereby reducing the rate of decrease in diaphragm resilience under long-term use. 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, antioxidant 445. Adding vulcanization accelerators promotes vulcanization; for example, vulcanization accelerators TMTD and D can be used. The aforementioned compounding agents are not limited to these and may also be other reinforcing agents, antioxidants, vulcanization accelerators, or other compounding agents not listed in this embodiment but well known to those skilled in the art. The amount of crosslinking agent added is 0.5 wt% to 5 wt% of the acrylate polymer, and the amount of other compounding agents added is not particularly limited. For example, based on 100 parts of hydrogenated butadiene-acrylonitrile polymer, carbon black is 40 to 60 parts, antioxidant is 2 to 5 parts, vulcanization accelerator is 1 to 3 parts, and crosslinking agent is 0.5 to 5 parts.

[0047] 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 can 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.

[0048] 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. Optionally, the risk of cross-linking reaction of the rubber compound is reduced by controlling the temperature and time in the film-forming process to ensure the performance of the diaphragm. More specifically, 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, the compound compound is at risk of vulcanization reaction during the dissolution process, which can easily lead to curing of the rubber solution. Preferably, the dissolution temperature is controlled between 20°C and 70°C. This preferred temperature range not only achieves effective and uniform dispersion of the rubber compound but also avoids the risk of cross-linking. 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 strip 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 molding and cross-linking preparation of the diaphragm, and reducing the risk of cross-linking reaction of the adhesive, thus ensuring the performance of the diaphragm and the acoustic performance of the sound-generating device.

[0049] In a preferred embodiment, the compounded rubber is dissolved to obtain a liquid adhesive, and the solid content concentration of the liquid adhesive is controlled to be 10% to 45%, and the viscosity is 700 mPa·s to 85000 mPa·s, wherein the solid content = (mass of compounded rubber / mass of liquid adhesive) × 100%. By controlling the solid content and viscosity of the liquid adhesive, the uniformity of the coated strip is improved. The inventors of this application have found that the solid content of the liquid adhesive should not be too high or too low. When the solid content is too low, the liquid adhesive 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 and 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.

[0050] 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.

[0051] To better understand the above technical solutions of the present invention, the following detailed description is provided in conjunction with specific embodiments. The specific embodiments described below are merely preferred embodiments of the present invention and are not intended to limit the present invention.

[0052] Example 1

[0053] Formula: 100 parts of acrylate polymer raw rubber; 45 parts of carbon black N990; 3 parts of antioxidant 445; 2.1 parts of crosslinking agent hexamethylenediamine; and 2.3 parts of thiuram vulcanization accelerator. The original monomer of R4 in the structure of the acrylate polymer is acrylic acid, and the content of carboxylic acid groups in the acrylate polymer is 2 wt%.

[0054] 1) Mix the above 63A formula into a compound ACM-63.

[0055] 2) The ACM-63 compound was placed in a solvent of methyl ethyl ketone (MEK) and butyl acetate to obtain an ACM-63 solution; wherein the ratio of MEK to toluene was 10:1, the solid content of the solution was 25wt%, and the solution was stirred and dispersed at room temperature for 36 hours, filtered, allowed to stand to defoam, and the viscosity was 7250 mPa·s.

[0056] 3) Apply ACM-63 adhesive solution evenly and continuously to the surface of the release film from the coating head position. The continuously coated material is then placed into the drying tunnel along with the release film for drying. The drying tunnel temperature is 70℃~110℃, and the drying time in the drying tunnel is 7 minutes to prepare a material tape with a thickness of 120μm.

[0057] 4) Using air compression molding, the material strip is prepared into a single-layer ACM rubber diaphragm with a thickness of 120μm. This diaphragm has good temperature resistance and good resilience, meeting the requirements for low-temperature use. Moreover, the loudspeaker made from this diaphragm has excellent low-frequency performance, with full bass and a comfortable listening experience.

[0058] Comparative Example 1

[0059] The formula is as follows: 100 parts of conventional unmodified acrylate raw rubber; 45 parts of carbon black N990; 3 parts of antioxidant 445; 1 part of sulfur vulcanizing agent; and 1.5 parts of tetramethylthiuram disulfide vulcanization accelerator.

[0060] The method for preparing the tape is similar to that of Example 1, except that the viscosity of the adhesive solution in step 2) is 5960 mPa·s. However, the tape prepared in Comparative Example 1 cannot be fully vulcanized and cross-linked during air pressure molding, resulting in poor resilience of the prepared diaphragm, which cannot meet the usage conditions.

[0061] Examples 2-6

[0062] The preparation method is similar to that in Example 1, except that the crosslinking agent used in the formulation is 2,2'-methylenediphenylamine, with an addition amount of 5 wt%, and the mass percentage of carboxylic acid groups in the acrylate polymer is 0.1 wt%, 0.5 wt%, 1 wt%, 5 wt%, and 8 wt%, respectively.

[0063] The diaphragms in the above embodiments were all prepared by air compression molding. The diaphragms obtained in Examples 2-5 have excellent resilience and good temperature resistance, which meet the requirements for use. The loudspeakers prepared by these diaphragms have excellent low-frequency performance. Compared with Examples 2-5, the resilience of Example 6 is reduced when the temperature is below 30°C.

[0064] Meanwhile, the inventors tested the glass transition temperature and elongation at break of the above-described carboxylic acid group content formulations. Specifically, rubber samples were prepared by molding and crosslinking of the above-described compound rubbers with different carboxylic acid group contents, and the glass transition temperature and elongation at break of the rubber were tested. The test results are shown in Table 2.

[0065] The testing standards were as follows: Elongation at break was determined according to ASTM D412-2016, with dumbbell-shaped specimens and a tensile rate of 500 mm / min. Each group of samples was tested five times, and the average value was taken. The glass transition temperature was determined according to ISO 6721-4, with a heating rate of 20 °C / min. Each group of samples was tested three times, and the average value was taken.

[0066] Table 2. Test results of glass transition temperature and elongation at break.

[0067] Carboxylic acid group mass percentage (wt%) 0.1 0.5 1 5 8 Glass transition temperature (°C) -35.5 -34.9 -33.2 -29.6 -23.1 Elongation at break (%) 368.1 369.4 353.7 298.5 273.9

[0068] Through the above embodiments and their test results, it can be seen that by reacting carboxylic acid groups with amine crosslinking agents to form a crosslinked structure, and with the content of carboxylic acid groups within a certain range, the glass transition temperature of the rubber is between -40℃ and -15℃, and the elongation at break is not less than 100%, which meets the requirements of the diaphragm for low-temperature use. As shown in Table 2, the inventors of this application found that as the content of carboxylic acid groups increases, the number of crosslinking points increases, the degree of crosslinking of the material increases, the movement of molecular chains is restricted, resulting in an increase in the glass transition temperature, an increase in the damping factor, and a decrease in the elongation at break, leading to a decrease in the elastic recovery rate of the diaphragm. As shown in Example 6, its glass transition temperature increases, the elongation at break decreases slightly, and the elasticity of the diaphragm decreases below 30℃. However, Examples 2-5 still have high elasticity in environments below 30℃. Therefore, as a preferred option, the content of carboxylic acid groups is 0.1wt% to 5wt%. This range not only meets the requirements of the diaphragm for low-temperature use but also ensures that the diaphragm has good elasticity during long-term low-temperature use, preventing diaphragm rupture due to low-temperature intolerance, improving reliability and acoustic performance.

[0069] Examples 7-10

[0070] The preparation method is similar to that in Example 1, except that the crosslinking agent used is triethylenetetramine, with an addition amount of 2wt%, and the hardness formulations are 50A, 60A, 70A, and 80A, respectively.

[0071] The diaphragms in the above embodiments are all prepared by air compression molding, and the diaphragms have good temperature resistance and good resilience, which meet the requirements for use. Furthermore, the loudspeakers prepared by these diaphragms have excellent low-frequency performance.

[0072] Meanwhile, the inventors compared the reduction rate of elongation at break of the rubber with the above hardness formulation. Specifically, the rubber sample was prepared by molding and cross-linking of the compound with the above hardness formulation. After heat aging of the rubber sample in an oven at 175℃ for 120h, the reduction rate of its elongation at break was measured and compared with conventional ACM rubber. The specific test results are shown in Table 1.

[0073] Testing standard: The elongation at break is measured according to ASTM D412-2016 standard. The sample shape is dumbbell-shaped, the tensile rate is 500 mm / min, and each group of samples is tested 5 times and the average value is taken.

[0074] Table 1. Detection results of the decrease in elongation at break of rubber samples and conventional ACM rubber.

[0075] Conventional ACM rubber 56.1％ 57.8％ 63.4％ 67.3％ Examples 7-10 Rubber Samples 43.2％ 45.3％ 48.3％ 52.9％

[0076] As can be seen from the above embodiments and test results, compared with conventional ACM rubber, the hardness formulation of the present invention forms a cyclic imine structure by crosslinking an acrylate polymer containing carboxylic acid groups with an amine crosslinking agent, which greatly improves the temperature resistance of the material. After heat aging in an oven at 175°C for 120 hours, the elongation at break of the rubber is less than 55%, which is much lower than that of conventional ACM rubber. This allows the diaphragm to still have high resilience under long-term harsh environments, and the rate of decline in resilience is slow, which improves the reliability of the diaphragm and reduces the risk of diaphragm breakage, resulting in excellent acoustic performance.

[0077] 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 miniature sound-generating device, characterized in that, The diaphragm is manufactured by air compression molding. The diaphragm includes a rubber film layer formed by crosslinking an acrylate polymer. The acrylate polymer contains carboxylic acid groups, with a carboxylic acid group content of 0.1 wt% to 8 wt%. The crosslinking agent is an amine crosslinking agent, and the amount of the amine crosslinking agent added is 0.5 wt% to 5 wt% based on the mass of the acrylate polymer. The acrylate polymer comprises monomers including vinyl unsaturated monocarboxylic acids and / or vinyl unsaturated dicarboxylic acids; the acrylate polymer has the following structure: Where x, y, z, and m are natural numbers; R1 / R2 / R3 are at least one of ethyl, methyl, n-butyl, and 2-methoxyethyl; and the original monomer of R4 is an vinyl unsaturated monocarboxylic acid or an vinyl unsaturated dicarboxylic acid. 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, medaconic acid, tocanic acid, edaconic acid, and niconic acid.

2. The diaphragm for a miniature sound-generating device according to claim 1, characterized in that, The acrylate polymer has a carboxylic acid group content of 0.1wt% to 5wt%.

3. The diaphragm for a miniature sound-generating device according to claim 1, characterized in that, The amine crosslinking agent is one or more of hexamethylenediamine, hexamethylenediamine salt, hexamethylenediamine carbamate, triethylenetetramine, 2,2'-methylenediphenylamine, and di-o-tolueneguanidine.

4. The diaphragm for a miniature sound-generating device according to claim 1, characterized in that, The glass transition temperature of the rubber film is -40℃ to -15℃.

5. The diaphragm for a miniature sound-generating device according to claim 1, characterized in that, The rubber membrane layer has a recovery rate of over 80% at 20% strain.

6. The diaphragm for a miniature sound-generating device according to claim 1, characterized in that, The diaphragm is obtained by mixing the acrylate polymer with the crosslinking agent to obtain a compound, and then forming the compound into a film using a film-forming process and then performing a molding process; wherein, the molding process is air pressure molding.

7. The diaphragm for a miniature sound-generating device according to claim 6, characterized in that, The hardness of the rubber is 45A to 85A.

8. The diaphragm for a miniature sound-generating device according to claim 7, characterized in that, The thickness of the diaphragm is 20μm to 200μm.

9. A miniature sound-generating device, characterized in that, 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 1-8.

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