Preparation method of vibrating diaphragm, vibrating diaphragm and sound production device

Abstract

The invention relates to a preparation method of a vibrating diaphragm, the vibrating diaphragm and a sound production device, and the preparation method comprises the following steps: firstly, providing raw materials which at least comprise ethylene-acrylate raw rubber and a vulcanizing agent; the raw materials are mixed, the ethylene-acrylate raw rubber and the vulcanizing agent are subjected to a pre-crosslinking reaction, a target pre-crosslinked rubber compound is obtained, and the crosslinking degree of the target pre-crosslinked rubber compound ranges from 10% to 30%; the target pre-crosslinked rubber compound is dissolved in a solvent, target pre-crosslinked gel paste is obtained, the content of gel in the target pre-crosslinked gel paste ranges from 5% to 25%, and the viscosity ranges from 5000 CPS to 40000 CPS; and finally, performing coating, drying and air pressure forming processes on the target pre-crosslinked gel paste to obtain the vibrating diaphragm. According to the method provided by the invention, the vulcanizing agent / auxiliary agent can be prevented from being separated out during dissolution, and the strength and acoustic performance of the vibrating diaphragm are ensured; meanwhile, the prepared vibrating diaphragm has a smoother and more compact surface, and also has higher tensile strength.

Description

Technical Field

[0001] This disclosure relates to the field of sound-generating devices, and more particularly to a method for preparing a diaphragm and the diaphragm itself. Background Technology

[0002] With the rapid development of industries such as mobile phones, computers, new energy vehicles and smart wearables, consumers have increasingly higher requirements for the sound quality of electronic products. As the core component for realizing audio interaction, the performance of sound-producing devices (such as speakers) directly affects the user experience.

[0003] The diaphragm is a key component of a sound-generating device. CN116208902A discloses a diaphragm formation process. This process involves first uniformly mixing ethylene-acrylate raw rubber with a reinforcing agent and an antioxidant to obtain uncrosslinked ethylene-acrylate rubber. Then, this uncrosslinked ethylene-acrylate rubber is dissolved in a solvent, followed by coating and drying steps to obtain the diaphragm. However, this process is prone to causing the vulcanizing agent / auxiliary agent to precipitate in the solvent, leading to the loss of necessary components during coating and filtration, thus affecting the performance of the final product. Furthermore, the surface of the diaphragm obtained by this process is uneven, with depressions in some areas, affecting the diaphragm's appearance and acoustic performance.

[0004] Therefore, how to improve the diaphragm manufacturing process to obtain diaphragms with better flatness and superior performance is a problem that those skilled in the art want to solve. Summary of the Invention

[0005] According to a first aspect of this disclosure, a method for preparing a diaphragm is provided, the method comprising the following steps: providing raw materials, said raw materials comprising at least ethylene-acrylate raw rubber and a vulcanizing agent; The raw materials are mixed and the ethylene-acrylate raw rubber and the vulcanizing agent undergo a pre-crosslinking reaction to obtain a target pre-crosslinked compound, wherein the degree of crosslinking of the target pre-crosslinked compound is between 10% and 30%. The target pre-crosslinked compound is dissolved in a solvent to obtain a target pre-crosslinked gel paste, wherein the gel content in the target pre-crosslinked gel paste is between 5% and 25%, and the viscosity is between 5000 CPS and 40000 CPS. The target pre-crosslinked gel paste is coated and dried to obtain the target rubber film; The target rubber diaphragm is subjected to a pneumatic molding process to obtain the diaphragm.

[0006] In one exemplary embodiment, mixing the raw materials and causing the ethylene-acrylate raw rubber and the vulcanizing agent to undergo a pre-crosslinking reaction includes: adding the raw materials to a mixing device for mixing, and controlling the maximum temperature inside the mixing device to be between 80°C and 140°C, causing the ethylene-acrylate raw rubber and the vulcanizing agent to undergo a pre-crosslinking reaction to obtain a pre-crosslinked compound; removing the pre-crosslinked compound from the mixing device and detecting the degree of crosslinking of the pre-crosslinked compound; if the degree of crosslinking of the pre-crosslinked compound is between 10% and 30%, determining the pre-crosslinked compound as the target pre-crosslinked compound.

[0007] In one exemplary embodiment, mixing the raw materials and causing the ethylene-acrylate raw rubber and the vulcanizing agent to undergo a pre-crosslinking reaction further includes: if the degree of crosslinking of the pre-crosslinked compound is less than 10%, then placing the pre-crosslinked compound in an environment with a temperature of 15°C to 50°C to allow the ethylene-acrylate raw rubber and the vulcanizing agent to undergo a further pre-crosslinking reaction until the degree of crosslinking of the pre-crosslinked compound reaches more than 10% and less than 30%, thereby obtaining the target pre-crosslinked compound.

[0008] In an exemplary embodiment, when performing a pneumatic molding process on the target rubber diaphragm, the molding time T of the pneumatic molding process and the degree of crosslinking X of the target pre-crosslinked compound satisfy the relationship (1), and the molding pressure P of the pneumatic molding process and the degree of crosslinking X of the target pre-crosslinked compound satisfy the relationship (2): T=205-550X (1) P=9X-0.8 (2) Where 10%≤X≤30%, the molding time T is in seconds, and the molding air pressure P is in megapascals.

[0009] In an exemplary embodiment, if the thickness of the target rubber film is less than or equal to 110 micrometers, the target pre-crosslinked gel paste is coated and dried to obtain the target rubber film, including: coating the target pre-crosslinked gel paste on a release substrate and drying it to obtain the target rubber film. If the thickness of the target rubber film is greater than 110 micrometers, the target pre-crosslinked gel paste is coated and dried to obtain the target rubber film, including: coating the target pre-crosslinked gel paste on a release substrate and drying it to obtain a rubber sub-film, the thickness of the rubber sub-film being less than or equal to 110 micrometers; and stacking at least two of the rubber sub-films to obtain the target rubber film.

[0010] In one exemplary embodiment, the ethylene-acrylate raw rubber includes a first type of ethylene-acrylate raw rubber and a second type of ethylene-acrylate raw rubber. The first type of ethylene-acrylate raw rubber has a glass transition temperature of less than or equal to -40°C and a Mooney viscosity of less than 15 MU. The second type of ethylene-acrylate raw rubber has a glass transition temperature of greater than -40°C and less than or equal to -30°C and a Mooney viscosity of greater than 20 MU. The mass of the first type of ethylene-acrylate raw rubber accounts for 1% to 30% of the total mass of the second type of ethylene-acrylate raw rubber and the first type of ethylene-acrylate raw rubber.

[0011] In one exemplary embodiment, the raw material further includes one or more of antioxidants, reinforcing agents, accelerators, and processing aids.

[0012] In one exemplary embodiment, the raw materials, by weight, comprise: 100 parts of a first type of ethylene-acrylate raw rubber and a second type of ethylene-acrylate raw rubber; 95-160 parts of reinforcing agent; 0.1-8 parts of antioxidant; 0.1-5 parts of vulcanizing agent; 0.1-8 parts of accelerator; and 1-10 parts of processing aid.

[0013] According to a second aspect of this disclosure, a diaphragm is provided, which is prepared according to the method described in any of the above embodiments.

[0014] According to a third aspect of this disclosure, a sound-generating device is provided, which includes the diaphragm described in the above embodiments.

[0015] The method for preparing the diaphragm provided in this embodiment includes the following steps: First, raw materials are provided, which include at least ethylene-acrylate raw rubber and a vulcanizing agent; then, the raw materials are mixed, and the ethylene-acrylate raw rubber and the vulcanizing agent undergo a pre-crosslinking reaction to obtain a target pre-crosslinked compound, wherein the crosslinking of the target pre-crosslinked compound is between 10% and 30%; then, the target pre-crosslinked compound is dissolved in a solvent to obtain a target pre-crosslinked gel paste, wherein the gel content in the target pre-crosslinked gel paste is between 5% and 25%, and the viscosity is between 5000 CPS and 40000 CPS; finally, the target pre-crosslinked gel paste is subjected to coating, drying, and air-pressure molding processes to obtain the diaphragm. Compared to existing technologies, the method provided in this disclosure involves a pre-crosslinking reaction between the ethylene-acrylate raw rubber and the vulcanizing agent during the raw material mixing step, before the target pre-crosslinked gel paste is dissolved in the solvent to form the target pre-crosslinked gel paste. This results in a final target pre-crosslinked gel paste with a gel content of 5%-25% and a viscosity of 5000 CPS-40000 CPS. During the coating and drying process, the microgel network contained within the target pre-crosslinked gel paste effectively suppresses the Bénard eddy and coffee ring effects of the solvent, ensuring uniform solvent evaporation and consistent shrinkage throughout. This results in a smooth, dense, and defect-free target rubber film, thereby producing a smooth, defect-free diaphragm. Simultaneously, through the pre-crosslinking reaction, the vulcanizing agent / auxiliary agent molecules are "locked" in the initially formed crosslinked network through chemical bonding, making them less likely to precipitate out during subsequent dissolution steps. Furthermore, the three-dimensional crosslinked network formed by the pre-crosslinking... As a physical barrier, it significantly reduces the migration rate and diffusion ability of residual free vulcanizing agents / auxiliaries, thereby solving the precipitation problem of vulcanizing agents / auxiliaries in the dissolution step and ensuring the strength and acoustic performance of the diaphragm. It is important to note that the degree of crosslinking of the target pre-crosslinked compound should not be too high or too low, and is more suitable between 10% and 30%. When the degree of pre-crosslinking is low, the weak crosslinking points formed in the target pre-crosslinked compound are easily destroyed by shear force during the subsequent dissolution process. However, the degree of pre-crosslinking should not be too high either, as this will cause the target pre-crosslinked compound to fail to dissolve in the solvent within the specified time, or require extremely high shear force to disperse it. This process will damage the molecular chains, leading to a decrease in the acoustic performance of the diaphragm. In addition, the micro-crosslinking points generated by the pre-crosslinking reaction can serve as "crosslinking seeds" to generate a more uniform and dense crosslinking network in the subsequent air compression molding process, resulting in a diaphragm with higher tensile strength. Detailed Implementation

[0016] Embodiments of this disclosure will now be described in more detail. It should be understood that the steps described in the method embodiments of this disclosure may be performed in different orders and / or in parallel. Furthermore, method embodiments may include additional steps and / or omit the steps shown. The scope of this disclosure is not limited in this respect.

[0017] The term "comprising" and its variations as used herein are open-ended, meaning "including but not limited to". The term "based on" means "at least partially based on". The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one additional embodiment"; the term "some embodiments" means "at least some embodiments". Definitions of other terms will be given in the description below. It should be noted that the concepts of "first", "second", etc., used in this disclosure are only used to distinguish different devices, modules, or units, and are not intended to limit the order of functions performed by these devices, modules, or units or their interdependencies.

[0018] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0019] The equipment and raw materials used in this disclosure are all commercially available, including but not limited to the following: Vamac® Ultra LT, AEM raw rubber, DuPont, USA.

[0020] Vamac® Ultra XF, AEM raw rubber, DuPont, USA.

[0021] HYT-05C, talc powder, Suzhou Youkuang Plastic New Material Co., Ltd.

[0022] Anti-aging agent 246, Flectol TMQ, AkzoNobel.

[0023] HMDC, hexamethylenediamine carbamate, vulcanizing agent, DuPont Diak No. 1.

[0024] ACT55, a guanidine / amine complex derivative, is an accelerator manufactured by Safic Alken, France.

[0025] Licowax PE520, polyethylene wax, Clariant.

[0026] Struktol A50P, a fatty acid ester processing aid, from Struktol Corporation.

[0027] TP-95, a polyester plasticizer, manufactured by Rohm and Haas (USA).

[0028] This disclosure provides a method for preparing a diaphragm, the method comprising the following steps: S101. Provide raw materials, wherein the raw materials include at least ethylene-acrylate raw rubber and vulcanizing agent.

[0029] In this step, the raw materials required for diaphragm preparation are provided, which include at least ethylene-acrylate raw rubber and a vulcanizing agent. In some embodiments, the raw materials may also include at least one or more of antioxidants, reinforcing agents, accelerators, and processing aids.

[0030] In some embodiments, the aforementioned ethylene-acrylate raw rubber includes a first type of ethylene-acrylate raw rubber and a second type of ethylene-acrylate raw rubber. The first type of ethylene-acrylate raw rubber has a glass transition temperature less than or equal to -40°C and a Mooney viscosity less than 15 MU; the second type of ethylene-acrylate raw rubber has a glass transition temperature greater than -40°C and less than or equal to -30°C and a Mooney viscosity greater than 20 MU. The mass of the first type of ethylene-acrylate raw rubber accounts for 1% to 30% of the total mass of the second type of ethylene-acrylate raw rubber and the first type of ethylene-acrylate raw rubber. In this embodiment, the first type of ethylene-acrylate raw rubber has a lower glass transition temperature and a lower Mooney viscosity, thus exhibiting excellent low-temperature resistance. The second type of ethylene-acrylate raw rubber has a higher glass transition temperature and Mooney viscosity, thus exhibiting better processability. Mixing the first type of ethylene-acrylate raw rubber and the second type of ethylene-acrylate raw rubber in a specific ratio makes the diaphragm processing smooth and efficient, and the resulting diaphragm has better low-temperature resistance.

[0031] In some embodiments, the above raw materials, by weight, include: 100 parts of type I ethylene-acrylate raw rubber and type II ethylene-acrylate raw rubber; 95-160 parts of reinforcing agent; 0.1-8 parts of antioxidant; 0.1-5 parts of vulcanizing agent; 0.1-8 parts of accelerator; and 1-10 parts of processing aid.

[0032] In some embodiments, the raw materials, by weight, include 95 parts, 100 parts, 105 parts, 110 parts, 115 parts, 120 parts, 125 parts, 130 parts, 135 parts, 140 parts, 145 parts, 150 parts, 155 parts, 160 parts of reinforcing agent or any value between any two of the above ranges.

[0033] In some embodiments, the above-mentioned raw materials include, by weight, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts of antioxidant, or any value between any two of the above ranges.

[0034] In some embodiments, the raw materials include, by weight, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts of vulcanizing agent, or any value between any two of the above ranges.

[0035] In some embodiments, the above-mentioned raw materials include, by weight, 0.1 parts, 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts, 5 parts, 5.5 parts, 6 parts, 6.5 parts, 7 parts, 7.5 parts, 8 parts of accelerator or any value between any two of the above ranges.

[0036] In some embodiments, the raw materials, by weight, include 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts, 10 parts of processing aids or any value between any two of the above ranges.

[0037] In some embodiments, the above raw materials, by weight, include: 90 parts of type I ethylene-acrylate raw rubber; 10 parts of type II ethylene-acrylate raw rubber; 125 parts of reinforcing agent; 5 parts of antioxidant; 1.5 parts of vulcanizing agent; 0.4 parts of accelerator; and 9 parts of processing aid.

[0038] In some embodiments, the above raw materials, by weight, include: 99 parts of type I ethylene-acrylate raw rubber, 1 part of type II ethylene-acrylate raw rubber; 125 parts of reinforcing agent; 5 parts of antioxidant; 1.5 parts of vulcanizing agent; 0.4 parts of accelerator; and 9 parts of processing aid.

[0039] In some embodiments, the above raw materials, by weight, include: 80 parts of type I ethylene-acrylate raw rubber; 20 parts of type II ethylene-acrylate raw rubber; 125 parts of reinforcing agent; 5 parts of antioxidant; 1.5 parts of vulcanizing agent; 0.4 parts of accelerator; and 9 parts of processing aid.

[0040] In some embodiments, the above raw materials, by weight, include: 70 parts of type I ethylene-acrylate raw rubber; 30 parts of type II ethylene-acrylate raw rubber; 125 parts of reinforcing agent; 5 parts of antioxidant; 1.5 parts of vulcanizing agent; 0.4 parts of accelerator; and 9 parts of processing aid.

[0041] In some specific embodiments, the first type of ethylene-acrylate raw rubber is Vamac® Ultra LT.

[0042] In some specific embodiments, the second type of ethylene-acrylate raw rubber is selected from one or more of Vamac® UltraHVG, Vamac® Ultra XF, Vamac® Ultra IP, and Vamac® Ultra HT.

[0043] In some embodiments, the mass of the second type of ethylene-acrylate raw rubber accounts for 1%, 5%, 10%, 15%, 20%, 25%, 30% of the total mass of the first type of ethylene-acrylate raw rubber and the second type of ethylene-acrylate raw rubber, or any value between any two of the above ranges.

[0044] In some embodiments, the vulcanizing agent includes amine vulcanizing agents and / or peroxide vulcanizing agents.

[0045] In some more specific embodiments, the vulcanizing agent is selected from one or more of hexamethylenediamine carbamate, hexamethylenediamine carbamate, N,N'-dicinnamaldehyde hexamethylenediamine, dicumyl peroxide, and bis-2,5-(2,5-dimethyl-2,5-ditert-butylperoxy)hexane.

[0046] In some embodiments, the antioxidants mentioned above include one or more of amine antioxidants, phenolic antioxidants, and quinoline antioxidants.

[0047] In some more specific embodiments, the antioxidant is selected from one or more of 6PPD (N-1,3-dimethylbutyl-N'-phenyl-p-phenylenediamine), IPPD (N-isopropyl-N'-phenyl-p-phenylenediamine), antioxidant 445 (4,4'-bis(α,α-dimethylbenzyl)diphenylamine), antioxidant BLE (acetone-diphenylamine condensate), and antioxidant 246 (TMQ polymer).

[0048] In some embodiments, the reinforcing agent includes one or more of talc, silica, carbon black, quartz powder, calcium carbonate, and montmorillonite.

[0049] In some embodiments, the aforementioned accelerator includes one or more of amine vulcanization system accelerators, peroxide vulcanization system accelerators, and sulfur vulcanization system accelerators.

[0050] In some more specific embodiments, the aforementioned promoters include one or more of guanidine / amine complex derivatives, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), tetramethylguanidine (TMG), magnesium oxide (MgO), and triallyl isocyanurate (TAIC).

[0051] In some embodiments, the aforementioned promoter is a guanidine / amine complex derivative, ACT55.

[0052] In some embodiments, the above-mentioned processing aids include one or more of flow aids, dispersants, release agents, and plasticizers.

[0053] In some more specific embodiments, the above-mentioned processing aids are selected from one or more of stearic acid, zinc stearate, polyethylene wax (PE wax), fatty acid G-78, fatty acid ester Struktol A50P, organosilicon Dow Corning MB50-001, and polyester plasticizer TP-95.

[0054] In some embodiments, the processing aids are Licowax PE520, fatty acid ester Struktol A50P, and polyester plasticizer TP-95.

[0055] S102. Mix the above raw materials and allow the ethylene-acrylate raw rubber and vulcanizing agent to undergo a pre-crosslinking reaction to obtain the target pre-crosslinked compound, wherein the degree of crosslinking of the target pre-crosslinked compound is between 10% and 30%.

[0056] In this step, the raw materials provided in step S101 are mixed and subjected to a pre-crosslinking reaction to obtain a target pre-crosslinked compound, and the degree of crosslinking of the target pre-crosslinked compound is controlled between 10% and 30%. In some embodiments, the degree of crosslinking of the target pre-crosslinked compound is 10%, 15%, 20%, 25%, 30%, or any value between any two of the above values.

[0057] It should be noted that the degree of crosslinking in this embodiment is calculated using the following formula: Current degree of crosslinking = [(current torque - ML0) / (MH - ML0)] * 100% Among them, the current degree of crosslinking is the current degree of crosslinking of the material, the current torque refers to the current torque of the material (ML value in the vulcanization curve), ML0 is the lowest torque of the material before significant crosslinking reaction has occurred, and MH refers to the highest torque of the material at a specified vulcanization temperature and time.

[0058] Taking the target pre-crosslinked compound as an example, the calculation of the degree of crosslinking in the embodiments of this disclosure is further explained: In the embodiments of this disclosure, the degree of crosslinking of the target pre-crosslinked compound = [(torque of the target pre-crosslinked compound - minimum torque of the mixed raw materials before significant crosslinking occurs) / (maximum torque reached by the mixed raw materials at a vulcanization temperature of 180°C and a vulcanization time of 30 min - minimum torque of the mixed raw materials before significant crosslinking occurs)] * 100%.

[0059] In some embodiments, mixing the above raw materials and subjecting the ethylene-acrylate raw rubber and vulcanizing agent to a pre-crosslinking reaction includes the following steps: The above-mentioned raw materials are added to a mixing equipment for mixing, and the maximum temperature inside the mixing equipment is controlled between 80°C and 140°C. The above-mentioned ethylene-acrylate raw rubber and the vulcanizing agent undergo a pre-crosslinking reaction to obtain a pre-crosslinked compound. Optionally, the mixing equipment can be an internal mixer. It should be noted that the degree of crosslinking of the target pre-crosslinked compound is highly correlated with the maximum temperature inside the mixing equipment. That is, the maximum temperature inside the mixing equipment affects the degree of crosslinking of the target pre-crosslinked compound. In order to ensure that the degree of crosslinking of the target pre-crosslinked compound is between 10% and 30%, the maximum temperature inside the mixing equipment should be controlled as much as possible between 80°C and 140°C. In some embodiments, the maximum temperature inside the mixing equipment is 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, or any value between any two of the above values.

[0060] The pre-crosslinked compound is removed from the mixing equipment, and its degree of crosslinking is tested. The purpose of this step is to determine the degree of crosslinking of the pre-crosslinked compound, as this affects the degree of crosslinking during diaphragm molding, molding state, and tensile strength.

[0061] If the degree of crosslinking of the pre-crosslinked compound is between 10% and 30%, it is determined to be the target pre-crosslinked compound. It is important to note that the degree of crosslinking of the target pre-crosslinked compound should not be too high or too low; a range of 10% to 30% is ideal. When the degree of pre-crosslinking is low, the weak crosslinking points formed in the target pre-crosslinked compound are easily destroyed by shear force during subsequent dissolution. However, the degree of pre-crosslinking should not be too high either. Excessive pre-crosslinking will prevent the target pre-crosslinked compound from dissolving in the solvent within the specified time, or require extremely high shear force to disperse it. This process will damage the molecular chains, leading to a decrease in the acoustic performance of the diaphragm. In some embodiments, if the degree of crosslinking of the pre-crosslinked compound is determined to be less than 10%, the pre-crosslinked compound is placed in an environment with a temperature of 15°C to 50°C to allow the ethylene-acrylate raw rubber and vulcanizing agent to undergo further pre-crosslinking reaction until the degree of crosslinking of the pre-crosslinked compound reaches more than 10% and less than 30%, thus obtaining the target pre-crosslinked compound. In actual processes, many factors affect the degree of crosslinking, such as the proportions of the raw material components and the temperature of the mixing equipment. Therefore, the degree of crosslinking of the pre-crosslinked compound may be affected by different factors and may be less than 10%. In this case, to ensure the effect of pre-crosslinking, the pre-crosslinked compound can be placed in an environment with a predetermined temperature to allow further pre-crosslinking reaction to occur internally. In some embodiments, the temperature at which it is placed can be 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, or any value between any two of the above ranges.

[0062] S103. The above-mentioned target pre-crosslinked compound is dissolved in a solvent to obtain a target pre-crosslinked gel paste. The gel content in the target pre-crosslinked gel paste is between 5% and 25%, and the viscosity is between 5000 CPS and 40000 CPS. It should be noted that the gel content in the target pre-crosslinked gel paste in this embodiment is detected by a thermal flow field separation method, and the viscosity is detected under the condition of a solid content of 25% and measured using a rotational viscometer.

[0063] The purpose of this step is to dissolve the target pre-crosslinked compound in a solvent to obtain the target pre-crosslinked gel paste. Optionally, a high-shear device can be used to assist in the dissolution. Optionally, the solvent can be at least one of a weakly polar and a non-polar solvent. For example, a weakly polar solvent can be ethyl acetate and / or butyl acetate, and a non-polar solvent can be toluene and / or cyclohexane. It should be noted that strongly polar materials, such as methyl ethyl ketone (MEK) or DMF, should not be used during dissolution because these strongly polar solvents will react with the components in the compound, affecting the diaphragm's performance. In some embodiments, the gel content in the target pre-crosslinked gel paste is 5%, 10%, 15%, 20%, 25%, or any two of the above values. In some embodiments, the viscosity of the target pre-crosslinked gel paste is 5000 CPS, 10000 CPS, 15000 CPS, 20000 CPS, 30000 CPS, 40000 CPS, or any two of the above values.

[0064] After the target pre-crosslinked compound is dissolved in a solvent to form a target pre-crosslinked gel paste, it contains many air bubbles and cannot be directly coated into a film. Therefore, it needs to stand for a period of time to defoam. In the prior art, because crosslinking is not performed, the vulcanizing agent / auxiliary agent precipitates during the standing process. The precipitated vulcanizing agent / auxiliary agent is filtered out in subsequent steps, making the final diaphragm prone to low crosslinking degree and poor performance due to the lack of vulcanizing agent / auxiliary agent. In the embodiments of this disclosure, because of pre-crosslinking, the vulcanizing agent / auxiliary agent is bonded to other components through chemical bonds, and the gel network formed by pre-crosslinking can also act as a physical barrier to solve the problem of vulcanizing agent / auxiliary agent precipitation during defoaming and standing. Understandably, after the target pre-crosslinked gel paste is defoamed and stood, it is necessary to filter out substances with larger particle sizes in the gel paste. This ensures that the subsequently formed rubber film is smoother. Preferably, the maximum particle size in the target pre-crosslinked gel paste is less than or equal to 25 micrometers. In this way, the coated and formed diaphragm can have a more uniform thickness and a smaller surface roughness.

[0065] S104. Perform coating and drying processes on the target pre-crosslinked gel paste to obtain the target rubber film.

[0066] The purpose of this step is to form a film, that is, to obtain the target pre-crosslinked gel paste after dissolution, and to obtain the target rubber film through processes such as coating and drying.

[0067] In some embodiments, if the thickness of the target rubber film is less than or equal to 110 micrometers, the target pre-crosslinked gel paste is coated and dried to obtain the target rubber film, including: coating the target pre-crosslinked gel paste onto a release substrate and drying it to obtain the target rubber film. If the thickness of the target rubber diaphragm is greater than 110 micrometers, the target pre-crosslinked gel paste is coated and dried to obtain the target rubber diaphragm, including: coating the target pre-crosslinked gel paste onto a release substrate and drying it to obtain a rubber sub-diaphragm, the thickness of which is less than or equal to 110 micrometers; and stacking at least two rubber sub-diaphragms to obtain the aforementioned target rubber diaphragm. In actual process, the applicant discovered that when the target rubber diaphragm to be prepared is relatively thick, the target rubber diaphragm obtained by a single coating and drying process contains a large number of pores, affecting the diaphragm's performance. To solve this problem, the applicant conducted in-depth research and found that when the thickness of the target rubber diaphragm to be prepared is less than or equal to 110 micrometers, the number of pores in the target rubber diaphragm prepared by a single coating and drying process does not affect the diaphragm's performance; however, when the thickness of the target rubber diaphragm to be prepared is greater than 110 micrometers, the number of pores in the target rubber diaphragm prepared by a single coating and drying process does affect the diaphragm's performance. Therefore, for thicker rubber membranes, the applicant uses stacked composite rubber sub-membranes to prepare them. The thickness of these sub-membranes is controlled to be below 110 micrometers, which solves the problem of excessive pores caused by thicker target rubber membranes.

[0068] S105. Perform a pneumatic molding process on the above-mentioned target rubber diaphragm to obtain a diaphragm.

[0069] In this step, the target rubber diaphragm obtained after coating and drying is subjected to a pneumatic molding process to obtain a diaphragm. During the pneumatic molding process, the target rubber diaphragm is heated and pressurized. During this process, further cross-linking, i.e., vulcanization, will occur inside the target rubber diaphragm. In the actual process, the applicant found that for target pre-crosslinked compound rubbers with different pre-crosslinking degrees, if the same pneumatic molding process parameters are used, the quality of the final diaphragm is very unstable, and problems such as insufficient vulcanization, over-vulcanization, poor molding state, and difficulty in demolding will occur. In order to solve this problem, the applicant conducted a large number of experiments, focusing on the relationship between molding pressure P and the cross-linking degree X of the target pre-crosslinked compound rubber at 190℃, and the relationship between molding time T and the cross-linking degree X of the target pre-crosslinked compound rubber. Finally, the experimental results were fitted to obtain the following relationship (1) and relationship (2): T=205-550X (1) P=9X-0.8 (2) Where 10%≤X≤30%, the molding time T is in seconds, and the molding air pressure P is in megapascals.

[0070] Therefore, before performing the air compression molding process, the degree of crosslinking of the target pre-crosslinked compound corresponding to the target rubber diaphragm should be determined first. Different process parameters or conditions should be adopted according to different degrees of crosslinking. In this way, situations such as insufficient vulcanization, over-vulcanization, poor molding state, and difficulty in demolding can be avoided, thereby improving the yield of diaphragm products.

[0071] In addition, the molding temperature can be selected between 180℃ and 200℃, specifically 180℃, 185℃, 190℃, 195℃, 200℃ or any value between any two of the above values.

[0072] In one specific embodiment, the molding temperature of the above-mentioned pneumatic molding process is 190°C.

[0073] Compared to existing technologies, the method provided in this disclosure involves a pre-crosslinking reaction between the ethylene-acrylate raw rubber and the vulcanizing agent during the raw material mixing step, before the target pre-crosslinked gel paste is dissolved in the solvent to form the target pre-crosslinked gel paste. This results in a final target pre-crosslinked gel paste with a gel content of 5%-25% and a viscosity of 5000 CPS-40000 CPS. During the coating and drying process, the microgel network contained within the target pre-crosslinked gel paste effectively suppresses the Bénard eddy and coffee ring effects of the solvent, ensuring uniform solvent evaporation and consistent shrinkage throughout. This results in a smooth, dense, and defect-free target rubber film, thereby producing a smooth, defect-free diaphragm. Simultaneously, through the pre-crosslinking reaction, the vulcanizing agent / auxiliary agent molecules are "locked" in the initially formed crosslinked network through chemical bonding, making them less likely to precipitate out during subsequent dissolution steps. Furthermore, the three-dimensional crosslinked network formed by the pre-crosslinking... As a physical barrier, it significantly reduces the migration rate and diffusion ability of residual free vulcanizing agents / auxiliaries, thereby solving the precipitation problem of vulcanizing agents / auxiliaries in the dissolution step and ensuring the strength and acoustic performance of the diaphragm. It is important to note that the degree of crosslinking of the target pre-crosslinked compound should not be too high or too low, and is more suitable between 10% and 30%. When the degree of pre-crosslinking is low, the weak crosslinking points formed in the target pre-crosslinked compound are easily destroyed by shear force during the subsequent dissolution process. However, the degree of pre-crosslinking should not be too high either, as this will cause the target pre-crosslinked compound to fail to dissolve in the solvent within the specified time, or require extremely high shear force to disperse it. This process will damage the molecular chains, leading to a decrease in the acoustic performance of the diaphragm. In addition, the micro-crosslinking points generated by the pre-crosslinking reaction can serve as "crosslinking seeds" to generate a more uniform and dense crosslinking network in the subsequent air compression molding process, resulting in a diaphragm with higher tensile strength.

[0074] This disclosure also provides a diaphragm, which is prepared by the method provided in any of the above embodiments / implementations.

[0075] This disclosure also provides a sound-generating device, which includes the diaphragm provided in any of the above embodiments / implementations.

[0076] The technical solutions of this disclosure will be further described below with reference to several embodiments and comparative examples. Example 1

[0077] The raw materials provided include 90 parts of Type I ethylene-acrylate raw rubber, 10 parts of Type II ethylene-acrylate raw rubber, 1.5 parts of vulcanizing agent, 5 parts of antioxidant, 125 parts of reinforcing agent, 0.4 parts of accelerator, and 9 parts of processing aid; specifically, the Type I ethylene-acrylate raw rubber is selected from Vamac® Ultra LT, the Type II ethylene-acrylate raw rubber is selected from Vamac® Ultra XF, the vulcanizing agent is selected from HMDC, the antioxidant is selected from antioxidant 246, the reinforcing agent is selected from HYT-05C, the accelerator is selected from ACT55, and the processing aids are selected from Licowax PE520 (2 parts), Struktol A50P (2 parts), and TP95 (5 parts). The above raw materials are added to a mixer and mixed to obtain the target pre-crosslinked compound. The process parameters involved in the mixing are shown in Table 1. The target pre-crosslinked compound obtained in step 2 was dissolved in ethyl acetate to obtain the target pre-crosslinked gel paste. The gel content and viscosity of the target pre-crosslinked gel paste are shown in Table 1. The gel content in the target pre-crosslinked gel paste was detected by the thermal flow field separation method. The viscosity was detected under the condition of 25% solid content and measured by a rotational viscometer.

[0078] The target pre-crosslinked gel paste obtained in step 3 is coated onto the release film and dried to obtain the target rubber film. The target rubber diaphragm obtained in step 3 is subjected to a pneumatic molding process. The process parameters for pneumatic molding are shown in Table 1. Example 2

[0079] The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. Therefore, the crosslinking degree, gel content and viscosity of the target pre-crosslinked compound are different from those in Example 1. In addition, the air pressure and time in the air pressure molding process parameters in step (5) are different from those in Example 1. See Table 1 for details. Example 3

[0080] The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. Therefore, the crosslinking degree, gel content and viscosity of the target pre-crosslinked compound are different from those in Example 1. In addition, the air pressure and time in the air pressure molding process parameters in step (5) are different from those in Example 1. See Table 1 for details. Example 4

[0081] The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. Therefore, the crosslinking degree, gel content and viscosity of the target pre-crosslinked compound are different from those in Example 1. In addition, the air pressure and time in the air pressure molding process parameters in step (5) are different from those in Example 1. See Table 1 for details.

[0082] Comparative Example 1 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the maximum temperature of the internal mixer is controlled at 10°C during the mixing process in step 2, so that the compound does not undergo cross-linking. Therefore, a compound without pre-cross-linking is obtained, and its degree of cross-linking, gel content and viscosity are different from those of Example 1. See Table 1 for details.

[0083] Comparative Example 2 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. Therefore, the crosslinking degree, gel content and viscosity of the target pre-crosslinked compound are different from those in Example 1. In addition, the time in the air pressure molding process parameters in step (5) is different from that in Example 1. See Table 1 for details.

[0084] Comparative Example 3 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. Therefore, the crosslinking degree, gel content and viscosity of the target pre-crosslinked compound are different from those in Example 1. In addition, the air pressure in the air pressure molding process parameters in step (5) is different from that in Example 1. See Table 1 for details.

[0085] Comparative Example 4 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the air pressure in the air pressure forming process parameters in step (5) is different from that in Example 1. See Table 1 for details.

[0086] Comparative Example 5 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. See Table 1 for details.

[0087] Comparative Example 6 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the mixing time in step (2) is different from that in Example 1. Therefore, the crosslinking degree, gel content and viscosity of the target pre-crosslinked compound are different from those in Example 1. In addition, the air pressure and time in the air pressure molding process parameters in step (5) are different from those in Example 1. See Table 1 for details.

[0088] Comparative Example 7 The raw materials and preparation process are as shown in Example 1. The difference from Example 1 is that the time in the air pressure forming process parameters in step (5) is different from that in Example 1. See Table 1 for details.

[0089] Table 1: Parameters involved in Examples 1-4 and Comparative Examples 1-7

[0090] The performance of the diaphragms prepared in Examples 1-4 and Comparative Examples 1-7 was tested, and the test results are shown in Table 2.

[0091] The degree of cross-linking in molding refers to the degree of cross-linking of the diaphragm after air pressure molding. Based on actual production and application experience, the degree of cross-linking in molding of the diaphragm is preferably between 92% and 98%, and more preferably between 94% and 96%. If it is less than 92%, the stability of the diaphragm is insufficient, which affects the acoustic performance of the diaphragm. If it is greater than 98%, there is a risk of over-vulcanization, which reduces the toughness of the diaphragm and significantly shortens its service life.

[0092] The process of dissolving and precipitating refers to the process where the compound is dissolved in a solvent (i.e., step 2), filtered using a 25µm filter, and allowed to stand at room temperature (25°C) for 6 hours. The result is then observed whether a white precipitate is formed. This white precipitate is identified as a vulcanizing agent.

[0093] The coating condition refers to the condition of the rubber surface after the rubber solution is coated onto the release film and then dried. It is divided into two categories: ○ indicates a good coating condition with a smooth surface and no defects such as bubbles, pits, or orange peel; × indicates a poor coating condition with defects such as bubbles, pits, or orange peel on the rubber surface.

[0094] The molding state refers to the state of the diaphragm after air pressure molding, including three types: ○ indicates a good molding state, with clear texture and easy demolding; △ indicates a slightly poor molding state, with defects in the molding or difficulty in demolding; × indicates a very poor molding state, with unclear texture and unusable.

[0095] Tensile strength was tested according to ASTM D412-2016 standard.

[0096] Table 2: Diaphragm performance of diaphragms prepared in Examples 1-4 and Comparative Examples 1-7

[0097] The performance test results of Examples 1-4 and Comparative Example 1 show that the pre-crosslinked diaphragm has a crosslinking degree between 94% and 96%, which is preferred, while the non-pre-crosslinked diaphragm has a crosslinking degree of only 70.07%. In the dissolution step, the pre-crosslinked diaphragm does not precipitate vulcanizing agent after filtration and precipitation, while the non-pre-crosslinked diaphragm does precipitate vulcanizing agent after precipitation. During coating, the pre-crosslinked diaphragm has a smooth surface without bubbles, pits, orange peel, or other defects, while the non-pre-crosslinked diaphragm has bubbles, pits, orange peel, or other defects on the coated surface. After molding, the pre-crosslinked diaphragm has a good molding state, clear texture, and high tensile strength, while the non-pre-crosslinked diaphragm has significantly lower tensile strength than the pre-crosslinked diaphragm.

[0098] As can be seen from the performance test results of Example 2 and Comparative Example 6, when the crosslinking degree of the target pre-crosslinked compound is less than 10%, the gel content in the target pre-crosslinked gel paste obtained by dissolving in the solvent is low (4.59%, see Table 1). After filtration and precipitation, a small amount of vulcanizing agent will precipitate out. Due to the precipitation of vulcanizing agent, the crosslinking degree after molding is low (88.53%), which is not within the preferred range of 92%-98%. At the same time, its molding state and tensile strength are not ideal.

[0099] As can be seen from the performance test results of Example 4 and Comparative Example 5, after dissolving for 72 hours at a solid content of 25% and a rotation speed of 800 rpm / min, the target pre-crosslinked compound with a crosslinking degree of more than 30% cannot be completely dissolved in the solvent.

[0100] The target pre-crosslinked compound rubbers in Examples 3, 2, and 3 all have the same degree of crosslinking, which is 24.79%. However, the process parameters used in the air compression molding process are different. The molding pressure and molding time of Example 3 were calculated according to the above-mentioned formulas (1) and (2). From the performance test results, it can be seen that the degree of crosslinking is within the preferred range, there is no dissolution, and it has a good coating state and molding state with high tensile strength. Compared with Example 3, Comparative Example 2 has the same molding time, but the pressure is lower. From the performance test results, the molding state is poor due to insufficient pressure. Compared with Example 3, Comparative Example 3 has the same molding pressure, but the molding time is too long, which leads to over-vulcanization of the product, so the tensile strength is significantly reduced. The target pre-crosslinked compound rubbers in Examples 1, 4, and 7 all have the same degree of crosslinking, which is 15.41%. However, the process parameters used in the air compression molding process are different. The molding pressure and molding time of Example 1 were calculated based on the above-mentioned relationships (1) and (2). The performance test results show that the degree of crosslinking is within the preferred range, with no dissolution or exudation, indicating good coating and molding conditions, and high tensile strength. Comparative Example 4, compared to Example 1, has the same molding time but a higher molding pressure. During molding, the rubber material is pressed into the microstructure of the molding die, leading to difficulty in demolding. Comparative Example 7, compared to Example 1, has the same molding pressure but a shorter molding time, resulting in a lower degree of crosslinking, which is not within the preferred range. Simultaneously, the molding condition is poor, and the tensile strength is low.

[0101] In summary, it can be seen that by introducing pre-crosslinking to form a target pre-crosslinked compound in the diaphragm preparation process, and keeping the degree of crosslinking of the target pre-crosslinked compound between 10% and 30%, the precipitation of vulcanizing agent in the dissolution step can be reduced, while improving the unevenness of the surface during the coating process. Finally, a diaphragm with a smooth, dense, and defect-free surface and good tensile strength is obtained.

[0102] The above description is merely an embodiment of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features disclosed in this disclosure that have similar functions.

[0103] While specific embodiments of this disclosure have been described in detail by way of example, those skilled in the art should understand that the examples are for illustrative purposes only and not intended to limit the scope of this disclosure. Those skilled in the art should understand that modifications can be made to the above embodiments without departing from the scope and spirit of this disclosure. The scope of this disclosure is defined by the appended claims.

Claims

1. A method for preparing a diaphragm, characterized in that, The method includes the following steps: Provide raw materials, which include at least ethylene-acrylate raw rubber and vulcanizing agents; The raw materials are mixed and the ethylene-acrylate raw rubber and the vulcanizing agent undergo a pre-crosslinking reaction to obtain a target pre-crosslinked compound, wherein the degree of crosslinking of the target pre-crosslinked compound is between 10% and 30%. The target pre-crosslinked compound is dissolved in a solvent to obtain a target pre-crosslinked gel paste, wherein the gel content in the target pre-crosslinked gel paste is between 5% and 25%, and the viscosity is between 5000 CPS and 40000 CPS. The target pre-crosslinked gel paste is coated and dried to obtain the target rubber film; The target rubber diaphragm is subjected to a pneumatic molding process to obtain the diaphragm.

2. The method according to claim 1, characterized in that, Mixing the raw materials and subjecting the ethylene-acrylate raw rubber and the vulcanizing agent to a pre-crosslinking reaction includes: The raw materials are added to a mixing equipment for mixing, and the maximum temperature inside the mixing equipment is controlled between 80°C and 140°C. The ethylene-acrylate raw rubber and the vulcanizing agent undergo a pre-crosslinking reaction to obtain a pre-crosslinked compound. The pre-crosslinked compound is removed from the mixing equipment, and the degree of crosslinking of the pre-crosslinked compound is tested. If the degree of crosslinking of the pre-crosslinked compound is between 10% and 30%, the pre-crosslinked compound is determined to be the target pre-crosslinked compound.

3. The method according to claim 2, characterized in that, The process of mixing the raw materials and subjecting the ethylene-acrylate raw rubber and the vulcanizing agent to a pre-crosslinking reaction further includes: If the degree of crosslinking of the pre-crosslinked compound is less than 10%, the pre-crosslinked compound is placed in an environment with a temperature of 15°C to 50°C to allow the ethylene-acrylate raw rubber and the vulcanizing agent to undergo further pre-crosslinking reaction until the degree of crosslinking of the pre-crosslinked compound reaches more than 10% and less than 30%, thus obtaining the target pre-crosslinked compound.

4. The method according to claim 1, characterized in that, When performing a pneumatic molding process on the target rubber diaphragm, the molding time T of the pneumatic molding process and the degree of crosslinking X of the target pre-crosslinked compound satisfy the relationship (1), and the molding pressure P of the pneumatic molding process and the degree of crosslinking X of the target pre-crosslinked compound satisfy the relationship (2): T=205-550X (1) P=9X-0.8 (2) Where 10%≤X≤30%, the molding time T is in seconds, and the molding air pressure P is in megapascals.

5. The method according to claim 1, characterized in that, If the thickness of the target rubber film is less than or equal to 110 micrometers, the target pre-crosslinked gel paste is coated and dried to obtain the target rubber film, including: coating the target pre-crosslinked gel paste on a release substrate and drying it to obtain the target rubber film. If the thickness of the target rubber film is greater than 110 micrometers, the target pre-crosslinked gel paste is coated and dried to obtain the target rubber film, including: coating the target pre-crosslinked gel paste on a release substrate and drying it to obtain a rubber sub-film, the thickness of the rubber sub-film being less than or equal to 110 micrometers; and stacking at least two of the rubber sub-films to obtain the target rubber film.

6. The method according to claim 1, characterized in that, The ethylene-acrylate raw rubber includes a first type of ethylene-acrylate raw rubber and a second type of ethylene-acrylate raw rubber. The first type of ethylene-acrylate raw rubber has a glass transition temperature of less than or equal to -40°C and a Mooney viscosity of less than 15 MU. The second type of ethylene-acrylate raw rubber has a glass transition temperature of greater than -40°C and less than or equal to -30°C and a Mooney viscosity of greater than 20 MU. The mass of the first type of ethylene-acrylate raw rubber accounts for 1% to 30% of the total mass of the second type of ethylene-acrylate raw rubber and the first type of ethylene-acrylate raw rubber.

7. The method according to claim 6, characterized in that, The raw materials also include one or more of antioxidants, reinforcing agents, accelerators, and processing aids.

8. The method according to claim 7, characterized in that, The raw materials comprise, by weight, 100 parts of a total of Type I ethylene-acrylate raw rubber and Type II ethylene-acrylate raw rubber; 95-160 parts of reinforcing agent; Anti-aging agent: 0.1-8 parts; Vulcanizing agent 0.1~5 parts; Accelerator 0.1~8 parts; Processing aids: 1-10 parts.

9. A diaphragm, characterized in that, The diaphragm is prepared by the method described in any one of claims 1-8.

10. A sound-generating device, characterized in that, The sound-generating device includes the diaphragm as described in claim 9.

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