Ultraviolet curing adhesive composition as well as preparation method and application thereof

Abstract

The invention discloses an ultraviolet curing adhesive composition as well as a preparation method and application thereof. The ultraviolet curing adhesive composition is prepared from the following raw materials in parts by weight: 30 to 45 parts of self-made ultraviolet curing polyfunctional polyurethane acrylate oligomer, 35 to 50 parts of self-made ultraviolet curing bifunctional polyurethane acrylate oligomer, 20 to 40 parts of acrylic reactive diluent, 3 to 8 parts of photoinitiator and 1 to 3 parts of thickening agent. 0.5 to 2 parts of a silane coupling agent; the adhesive prepared from the self-made oligomer has the following beneficial effects that the adhesive can be quickly polymerized and crosslinked under the irradiation of an LED light source, the curing energy consumption is remarkably reduced, and the adhesive is adaptive to an automatic continuous production process; the adhesive layer shows excellent flexibility, stretch rate and temperature resistance; in a constant-temperature and constant-humidity test, the adhesive layer does not have the defects of adhesive overflow, bubbles and the like, and is low in volume shrinkage and excellent in dimensional stability; and the interface bonding strength of the loudspeaker voice coil and the diaphragm is high.

Description

Technical Field

[0001] This invention relates to the field of adhesive preparation technology, and in particular to a UV-curable adhesive composition, its preparation method, and its application. Background Technology

[0002] With the upgrading of the consumer electronics industry and the diversification of audio application scenarios, the global loudspeaker market demand continues to grow. As a major producer of electroacoustic devices, my country's loudspeaker industry reached a total market size of RMB 155.75 billion in 2024, a year-on-year increase of approximately 8.3% compared to 2023, demonstrating a steady development trend. Loudspeakers, as core electroacoustic transducers that convert electrical signals into sound signals, are widely used in consumer electronics (such as smart terminals and home theaters), professional audio (stage sound systems and broadcasting equipment), and public facilities (conference systems and security alarms). Their acoustic performance directly determines the user experience of end products. The loudspeaker structure typically includes a vibration system (diaphragm, voice coil, suspension), a magnetic circuit system (magnet, magnetic plate), and auxiliary support components. The rigid connection between the diaphragm and voice coil is crucial for ensuring efficient transmission of vibration energy.

[0003] In existing technologies, the assembly of voice coils and diaphragms mostly uses solvent-based adhesives. While these adhesives offer cost advantages, they also have the following technical drawbacks: 1. Environmental and occupational health risks: Relying on the volatilization of organic solvents (such as toluene and ethyl acetate) for curing results in high VOC emissions, failing to meet environmental standards such as GB 30981-2020. Long-term exposure can easily lead to respiratory damage in operators. 2. Production safety hazards: Solvents generally have flash points below 23°C, classifying them as Class A flammable hazardous materials. There is a risk of electrostatic ignition during processes such as stirring and coating, and storage must comply with the hazardous materials isolation requirements of GB 15603-1995, increasing management costs. 3. Low resource utilization efficiency: The actual effective solid content of solvent-based adhesives is only 30%~40%. Solvent volatilization during curing leads to low material utilization, and waste adhesive disposal must comply with the HJ1263-2022 hazardous waste treatment standard, further increasing overall costs.

[0004] To address the aforementioned issues, UV-curable adhesives have become the mainstream technology for bonding speaker voice coils and diaphragms due to their characteristics such as rapid curing (second-level curing), solvent-free curing, low curing energy consumption, and excellent adhesion to various substrates. For example, Chinese patent CN112521870A discloses a UV-curable adhesive composition and its uses. The patent describes a method for preparing this UV-curable adhesive, which features rapid curing, low shrinkage, and high bond strength. It also exhibits good flexibility, elasticity, and low hardness, making it particularly suitable for bonding TPEE diaphragms and other structural components in high-power, ultra-linear miniature speakers. However, this patent does not disclose specific criteria for determining "rapid curing" or provide data on the adhesive's bond strength.

[0005] Currently, the supply of this UV-curable adhesive is still mainly imported, such as those from foreign brands like 3M, Henkel, and Tesa. While these adhesives offer advantages in performance stability, they suffer from high procurement costs and long supply chain response times, making it difficult to meet the cost and rapid delivery demands of downstream manufacturing industries. Although several domestic UV adhesive manufacturers have emerged, and their products can achieve comparable basic curing performance, they still have shortcomings in key performance aspects, mainly manifested in the following ways: 1. Insufficient curing efficiency: slow curing speed and low double bond conversion rate under low-energy LED light sources (365nm), making it impossible to achieve surface drying and deep curing within 5 seconds; 2. Poor flexibility and unsatisfactory mechanical properties: making it difficult for the adhesive film to withstand high-frequency alternating stress, easily leading to cohesive failure or interfacial peeling; 3. Poor temperature resistance: prone to delamination and cracking under temperature cycling / thermal shock; 4. Insufficient interfacial adhesion: the peel strength of the speaker voice coil and diaphragm after bonding and curing is substandard, easily leading to interfacial failure and debonding under vibration or thermal cycling loads.

[0006] In summary, current technologies, whether imported high-performance products or domestically produced basic alternatives, fail to fully meet the comprehensive demands of high-end electroacoustic device manufacturing for high performance, low cost, and rapid delivery. There is an urgent need to develop a novel UV-curable adhesive composition to overcome these technical deficiencies, achieve breakthroughs in key performance indicators, and meet the pressing needs of downstream industries. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the first objective of the present invention is to provide a UV-curable adhesive composition that can be rapidly cured under low-energy LED light, and the cured adhesive layer has excellent flexibility, temperature resistance, elongation and other properties.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0009] A UV-curable adhesive composition comprising the following raw materials in parts by weight:

[0010] Prepare 30-45 parts of a self-made UV-curable multifunctional polyurethane acrylate oligomer;

[0011] 35-50 parts of a self-made UV-curable difunctional polyurethane acrylate oligomer;

[0012] 20-40 parts of acrylic reactive diluent;

[0013] 3-8 parts of photoinitiator;

[0014] Thickener 1-3 parts;

[0015] 0.5–2.0 parts of silane coupling agent;

[0016] Polymerization inhibitor 0.05–0.2 parts;

[0017] The structural formula of the self-made UV-curable multifunctional polyurethane acrylate oligomer is shown in Formula I:

[0018] Formula I

[0019] The structural formula of the self-made UV-curable difunctional polyurethane acrylate oligomer is shown in Formula II:

[0020] Formula II

[0021] In Formulas I and II, R2 represents a neopentyl glycol alkyl segment; R3 represents a 1,4-butanediol alkyl segment; R4 represents an alkyl group with 5 to 7 carbon atoms; R5 represents a specially modified acid alkyl segment; R6 represents a specially modified diol alkyl segment; R7 represents a 1,6-adiponic acid alkyl segment; and R1 represents any of the following structural formulas:

[0022] OR .

[0023] As a preferred technical solution, the self-made UV-curable multifunctional polyurethane acrylate oligomer comprises the following raw materials in parts by weight: 11-26 parts isocyanate dimer, 3-8 parts isocyanate trimer, 52-80 parts polyester polyol, 1.2-3.0 parts chain extender, 3-15 parts (meth)acrylate hydroxy ester, catalyst, and polymerization inhibitor; the amount of catalyst is 0.05%-0.2% of the total mass of isocyanate dimer and polyester polyol; the amount of polymerization inhibitor is 0.02%-0.08% of the mass of (meth)acrylate hydroxy ester. The above raw materials, in the above proportions, can be used to synthesize oligomers with the structure of Formula I.

[0024] As a preferred technical solution, the preparation process of the self-made UV-curable multifunctional polyurethane acrylate oligomer includes the following steps:

[0025] (1) Isocyanate dimer, isocyanate trimer, polyester polyol and catalyst are added to the reactor and reacted at 75-85℃ for 2-3 hours. Under the action of the catalyst, a stepwise polymerization reaction of -NCO groups and -OH occurs to generate urethane bonds. The temperature is controlled at 75-85℃ to ensure the reaction activity and avoid the reaction rate being too slow or incomplete due to the temperature being too low; it also prevents the side reactions caused by the temperature being too high. Nitrogen gas is passed through and stirred during the reaction to isolate oxygen and avoid oxidation.

[0026] (2) Cool down to 50-60℃, then add the chain extender dropwise. The main chain polymerization reaction in step 1 is highly reactive, and cooling down can reduce the system's reactivity, preventing the chain extender from reacting rapidly with the remaining -NCO groups. After adding the chain extender, raise the temperature to 68-72℃ to increase the reactivity of the -NCO groups with the -OH groups of the chain extender. React for 0.5-1 h to obtain the prepolymer. During the chain extension reaction, the increase in main chain length will lead to an increase in system viscosity, which may cause problems such as difficulty in stirring and uneven mixing of raw materials. Adding acetone can reduce the system viscosity, improve fluidity, and ensure that the chain extension reaction proceeds uniformly.

[0027] (3) While stirring, add (meth)acrylate hydroxyl ester containing a polymerization inhibitor dropwise to the prepolymer. The addition should be completed within 1 hour. After the addition is complete, raise the temperature to 65-75°C and react for 2-3 hours to obtain a self-made UV-curable multifunctional polyurethane acrylate oligomer. Measure the NCO value of the reaction system at regular intervals throughout the reaction. The reaction is complete when the NCO value reaches the theoretically calculated value.

[0028] As a preferred technical solution, in the raw materials of the self-made UV-curable multifunctional polyurethane acrylate oligomer, the isocyanate dimer is one or a mixture of two of isophorone diisocyanate (IPDI) and 4,4'-dicyclohexylmethane diisocyanate (HMDI). The isocyanate dimer can provide urethane bonds (-NH-COO-) to the oligomer, and the urethane bonds can endow the oligomer with excellent mechanical properties, wear resistance, and flexibility.

[0029] As a preferred technical solution, the isocyanate trimer is an HDI trimer; it can introduce structurally stable isocyanurate rings into the oligomer, and has advantages such as good thermal stability, good wear resistance, and good corrosion resistance. Furthermore, the isocyanate trimer can introduce branched structures into the oligomer molecular chain, increasing the reaction sites with reactive diluents and photoinitiators, significantly improving the curing rate under LED light sources, and facilitating the formation of a three-dimensional network structure.

[0030] As a preferred technical solution, the HDI trimer is more preferably Asahi Kasei's TPA-100.

[0031] As a preferred technical solution, the polyester polyol has a molecular weight of 1000-2000 and a hydroxyl value of 108-116 mg KOH / g, meaning that each mole of polyester polyol contains a moderate number of hydroxyl groups and a uniform distribution. When reacting with isocyanate dimers / trimers, it can achieve a precise match between the molar ratio of -NCO groups and -OH groups, avoiding the risk of gelation caused by excessively high hydroxyl values ​​leading to excessively fast reaction rates and a sudden increase in system viscosity. It also prevents incomplete reactions and excessive residual -NCO groups caused by excessively low hydroxyl values, ensuring the smooth progress of prepolymer preparation and subsequent grafting reactions with (meth)acrylate hydroxyl esters. The polyester polyol is mainly prepared by reacting 1,6-adipic acid, 1,4-butanediol, and neopentyl glycol, resulting in oligomers with multiple linear alkane segments of 1,6-adipic acid and 1,4-butanediol. These linear alkane segments have multiple single bonds with high rotational freedom, thereby improving the flexibility of the oligomers. The branched structure of neopentyl glycol alkyl groups can increase steric hindrance, ensuring that the oligomer has a certain degree of rigidity and preventing it from being too soft. In some embodiments, the polyester polyols are HDPOL-705 (molecular weight 1000, hydroxyl value 108-116 mgKOH / g) and HDPOL-5643 (molecular weight 2000, hydroxyl value 53-59 mgKOH / g) from Huide Technology.

[0032] As a preferred technical solution, the chain extender is 1,4-butanediol (BDO), whose -OH groups at both ends can react with the -NCO groups of isocyanate dimers / trimers to increase the oligomer molecular chains and improve the tensile strength and elongation at break of the adhesive layer.

[0033] As a preferred technical solution, the (meth)acrylate hydroxy ester is one or a mixture of hydroxyethyl acrylate (HEA), hydroxyethyl methacrylate (HEMA), hydroxypropyl acrylate (HPA), and hydroxypropyl methacrylate (HPMA). The (meth)acrylate hydroxy ester introduces photocurable active groups (carbon-carbon double bonds) into the oligomer, making it a core functional component for achieving UV curing.

[0034] As a preferred technical solution, the catalyst is an organotin catalyst or / and an organobismuth catalyst.

[0035] As a preferred technical solution, the polymerization inhibitor is one or more of p-hydroxyanisole, hydroquinone, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, and 2,2,6,6-tetramethylpiperidine-1-oxy radical, which can prevent the self-polymerization reaction of (meth)acrylate hydroxy esters during the synthesis process.

[0036] As a preferred technical solution, the self-made UV-curable difunctional polyurethane acrylate oligomer comprises the following raw materials in parts by weight: 15-20 parts isocyanate dimer, 72-79 parts polyester polyol, 1.4-2.0 parts chain extender, 3.5-8.0 parts (meth)acrylate hydroxy ester, catalyst, and polymerization inhibitor; the amount of catalyst is 0.05%-0.2% of the total mass of isocyanate dimer and polyester polyol; the amount of polymerization inhibitor is 0.02%-0.08% of the mass of (meth)acrylate hydroxy ester. The above raw materials, in the above proportions, can be used to synthesize oligomers with the structure of Formula II.

[0037] As a preferred technical solution, the preparation process of the self-made UV-curable dienergetic polyurethane acrylate oligomer includes the following steps:

[0038] (1) Isocyanate dimer, polyester polyol and catalyst are added to the reactor and reacted at 75-85℃ for 2-3 hours. Nitrogen gas is introduced during the reaction and the mixture is stirred while nitrogen gas is introduced.

[0039] (2) After cooling to 50-60℃, start adding chain extender dropwise. After the dropwise addition is complete, raise the temperature to 68-72℃ and react for 0.5-1h to obtain prepolymer. During the reaction, acetone is added to adjust the viscosity of the reaction system.

[0040] (3) While stirring, add (meth)acrylate hydroxy ester containing polymerization inhibitor dropwise to the prepolymer. The addition is completed within 1 hour. After the addition is completed, the temperature is raised to 65~75℃ and the reaction is carried out for 2~3 hours to obtain the self-made UV-curable di-energy polyurethane acrylate oligomer. The NCO value of the reaction system is measured at regular intervals throughout the reaction. The reaction is complete when the NCO value of the system reaches the theoretical calculation value.

[0041] As a preferred technical solution, in the raw materials of the self-made UV-curable difunctional polyurethane acrylate oligomer, the isocyanate dimer includes one or a mixture of two of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate; the polyester polyol has a molecular weight of 2000~2500 and a hydroxyl value of 45~53 mg KOH / g, selected from Baiyuan Chemical's BY-3037, which is obtained by reacting a specially modified acid and a glycol. It has excellent softness, resilience, good initial tack, high adhesion, and good adhesion to plastics such as leather, PET, PVC, ABS, and PC, as well as aluminum foil, glass, metal, and PMMA. It also has excellent hydrolysis resistance, acid and alkali resistance, low temperature resistance, and bending resistance, and has high comprehensive performance. The chain extender is 1,4-butanediol; the (meth)acrylate hydroxy ester is one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate; the catalyst is an organotin catalyst and / or an organozinc catalyst; the polymerization inhibitor is one or more of p-hydroxyanisole, hydroquinone, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxy radical, and 2,2,6,6-tetramethylpiperidine-1-oxy radical.

[0042] As a preferred technical solution, the acrylic reactive diluent comprises the following raw materials in the indicated mass fractions: 18%–51% tetrahydrofuran acrylate, 12%–41% dicyclopentenyl acrylate, 12%–41% isobornyl acrylate, and 8%–35% N,N-dimethacrylamide. Tetrahydrofuran acrylate, with its cyclic ether structure, exhibits excellent wetting and penetration capabilities to commonly used speaker substrates such as metal, glass, PI, PET, and PMMA. It can form hydrogen bonds or van der Waals forces with polar groups on the substrate surface, significantly improving the bonding strength of the adhesive interface. Dicyclopentenyl acrylate contains a rigid alicyclic structure, which significantly improves the density and chemical stability of the crosslinked network after curing. Isobornyl acrylate has high carbon-carbon double bond reactivity, which can increase the curing rate; simultaneously, the saturated alicyclic structure of isobornyl acrylate can improve the anti-aging properties of the adhesive film. The amide groups of N,N-dimethacrylamide are highly polar, exhibiting a micro-etching and interlocking effect on non-polar or weakly polar plastic substrates such as PC, PVC, ABS, PP, and PE. It can penetrate into the tiny pores on the substrate surface to form a mechanical interlock, significantly improving interfacial adhesion and ensuring a strong bond between the diaphragm and the voice coil, making it difficult to tear. Acrylic reactive diluents are low in volatility, environmentally friendly, and have higher flowability than oligomers. They can adjust the overall flowability of the adhesive and react with oligomers to form a cured film, imparting better physicochemical properties to the film.

[0043] As a preferred technical solution, the thickener is hydrophilic silica, more preferably Cabot's silica M5.

[0044] As a preferred technical solution, the photoinitiator is one or both of ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0045] As a preferred technical solution, the silane coupling agent is one or more of KH570, KH560, and KH172. The polymerization inhibitor is one or more of p-hydroxyanisole, p-benzoquinone, hydroquinone, and naphthoquinone.

[0046] To address the shortcomings of existing technologies, a second objective of this invention is to provide a preparation method for preparing the aforementioned UV-curable adhesive composition.

[0047] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0048] A method for preparing a UV-curable adhesive composition includes the following steps:

[0049] (1) Add the self-made UV-curable multifunctional polyurethane acrylate oligomer, the self-made UV-curable difunctional polyurethane acrylate oligomer, and the thickener into the mixer in the proportion of parts, and stir evenly at 800-1000 rpm at 20-30℃ in the dark.

[0050] (2) Add acrylic reactive diluent, polymerization inhibitor, silane coupling agent and photoinitiator into a mixer, protect from light, stir evenly, stir at 20-30℃, vacuum conditions of -0.1 to -0.09 MPa, at 600-1000 rpm until evenly mixed, and then depressurize with nitrogen to obtain the UV-curable adhesive composition.

[0051] To address the shortcomings of existing technologies, a third objective of this invention is to provide an application of a UV-curable adhesive composition:

[0052] The UV-curable adhesive composition is applied to the diaphragm of the speaker, the voice coil is then attached to the diaphragm, and finally cured by LED light, thus achieving the bonding between the speaker diaphragm and the voice coil.

[0053] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0054] (1) In the process of synthesizing UV-curable multifunctional polyurethane acrylate oligomers, this invention uses isocyanate trimers, which have advantages such as high reactivity and fast surface drying, thus improving the curing speed under LED lights and saving curing energy. The polyester polyol used in the synthesis of this oligomer is prepared by reacting small-molecule 1,6-adipic acid, 1,4-butanediol and neopentyl glycol, and has advantages such as excellent flexibility, heat resistance, and hydrolysis resistance. In addition, the polyester polyol used in the synthesis of the UV-curable difunctional polyurethane acrylate oligomers prepared in this invention has excellent softness, resilience, good initial tack, and high adhesion. It has good adhesion to leather, plastics, aluminum foil, glass, metal, PMMA, etc., and also has excellent water resistance, acid and alkali resistance, and high comprehensive performance. This invention uses the compounding of two oligomers as resins for bonding speaker voice coils, giving the adhesive composition excellent flexibility, heat resistance, resilience, good adhesion, and fast curing. By combining special functional acrylic monomers, coupling agents, etc., a UV-curable adhesive composition for bonding speaker voice coils with excellent overall performance is prepared.

[0055] (2) This invention combines self-made UV-curable polyurethane acrylate oligomers with highly active acrylic diluents and special photoinitiators. Under low-energy LED light source (200~300mW / cm²) irradiation, it can complete surface drying and deep curing within 3~5 seconds, fully meeting the high-speed requirements of high-efficiency speaker production lines. It solves the problems of slow curing speed and low double bond conversion rate in traditional domestic UV-curable adhesive compositions.

[0056] (3) The UV-curable adhesive composition of the present invention has excellent flexibility, tensile strength and shear strength after curing; it does not overflow or bubble under constant temperature and humidity; and it has outstanding interfacial bonding performance, so as to achieve a firm bond between the diaphragm and the voice coil of the loudspeaker. Attached Figure Description

[0057] Figure 1 This is a schematic diagram of the UV-curable adhesive composition of the present invention applied to a loudspeaker. Detailed Implementation

[0058] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below.

[0059] An example of a self-made UV-curable multifunctional polyurethane acrylate oligomer (PUA-1):

[0060] First, 75g of isophorone diisocyanate (IPDI), 24.35g of isocyanate trimer (TPA-100), 221.15g of polyester polyol (HDPOL-705), and 0.32g of dibutyltin dilaurate were placed in a four-necked flask equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser tube. The mixture was reacted at 75–85°C for 2–3 hours, with nitrogen purging during the reaction. Then, the temperature was lowered to 50–60°C, and 9.12g of 1,4-butanediol (BDO) was added dropwise to initiate a chain extension reaction. After the addition was complete, the temperature was raised to 68–72°C, and the reaction was continued for 0.5–1 hour. During this reaction, a small amount of acetone was added to control the viscosity of the reaction system. Then, while stirring, 19g of hydroxyethyl acrylate (HEA) containing a polymerization inhibitor (0.011g of p-hydroxyanisole) was added dropwise to the prepolymer over a period of 1 hour. After the addition is complete, the temperature is raised to 65-75℃ and reacted for 2-3 hours to obtain a self-made multifunctional polyurethane acrylate oligomer that can be cured by ultraviolet light.

[0061] An example of a self-made UV-curable difunctional polyurethane acrylate oligomer (PUA-2):

[0062] 50 g of isophorone diisocyanate (IPDI), 253.1 g of BY-3037, and 0.3 g of dibutyltin dilaurate were placed in a four-necked flask equipped with a mechanical stirrer, a dropping funnel, and a reflux condenser. The reaction was carried out at 75–85 °C for 2–3 h, with nitrogen gas purging during the reaction. Then, the temperature was lowered to 50–60 °C, and 5.07 g of 1,4-butanediol (BDO) was added dropwise to initiate a chain extension reaction. After the addition was complete, the temperature was raised to 68–72 °C and the reaction was carried out for 0.5–1 h. During this reaction, a small amount of acetone was added to control the viscosity of the reaction system. While stirring, 16.27g of hydroxypropyl methacrylate containing a polymerization inhibitor (0.011g p-hydroxyanisole) was added dropwise to the prepolymer over 1 hour. After the addition was complete, the temperature was raised to 65-75℃ and reacted for 2-3 hours to obtain a self-made difunctional polyurethane acrylate oligomer that can be cured by ultraviolet light.

[0063] Example 1

[0064] Accurately weigh each material according to the formula proportions in Table 1. Add 30 parts of the self-made UV-curable multifunctional polyurethane acrylate oligomer (PUA-1), 35 parts of the self-made UV-curable dual-functional polyurethane acrylate oligomer (PUA-2), and 2 parts of silica (M5) into the mixer in sequence. Protect from light, control the temperature at 20-30℃, and stir at 800-1000 rpm for 1 hour until the mixture is uniform.

[0065] Next, add 10 parts of tetrahydrofuran acrylate (THFA), 8 parts of dicyclopentenyl acrylate (DCPA), 8 parts of isobornyl acrylate (IBOA), 4 parts of N,N-dimethacrylamide (DMAA), 0.1 parts of polymerization inhibitor p-hydroxyanisole (MEHQ), 1 part of silane coupling agent (KH560), and 5 parts of photoinitiator TPO to a mixer, protect from light, and stir until homogeneous. Maintain the temperature at 20–30°C, and the vacuum conditions at -0.1 to -0.09 MPa, stirring at 600–1000 rpm for 1 hour until homogeneous. Then, release the nitrogen pressure to obtain the UV-curable adhesive composition.

[0066] like Figure 1 As shown, the adhesive 3 of Example 1 is applied to the diaphragm 1 of the speaker using a dispensing machine, and the voice coil 2 is used to adhere it. Then, an LED light with a light intensity of 200~300mW / cm2 is used to illuminate the diaphragm for 3~20s to cure the adhesive and bond the diaphragm and voice coil of the speaker.

[0067] Examples 2-12 and Comparative Examples 1-18 were prepared according to the formulations in Tables 1-4, following the same preparation method as in Example 1. The mass units of the components in Tables 1-4 are in grams.

[0068] Table 1 Adhesive formulations for Examples 1-12

[0069]

[0070] Table 2 Adhesive formulations for Examples 13-18

[0071] Table 3 Adhesive formulations for Comparative Examples 1-12

[0072] Table 4 Adhesive formulations for Comparative Examples 13-18

[0073] The adhesives for bonding loudspeaker voice coils provided in Examples 1-18 and Comparative Examples 1-18 were subjected to performance tests, and the test results are shown in Table 5. The test standards and methods are as follows:

[0074] 1. Curing speed test: Irradiate with an LED light (light intensity 200~300mW / cm2) and use a stopwatch to time the curing time.

[0075] 2. Hardness test: Measure the hardness of the cured dry adhesive using a Shore hardness tester.

[0076] 3. Flexibility Test: The cured dry adhesive was tested according to GB / T 1731-2020, with an axial bending of 3mm. For adhesives without cracks or peeling, the flexibility was rated as excellent; for adhesives with cracks or peeling, the flexibility was rated as poor.

[0077] 4. Temperature resistance test: Place the cured dry adhesive in a thermal shock test chamber at -40~120℃ for 500 cycles, with each cycle lasting 1 hour. If there is no overflow or bubbling, the temperature resistance is rated as excellent; if there is peeling, cracking, or bubbling, the temperature resistance is rated as poor.

[0078] 5. Constant Temperature and Humidity Test: Following the test standard GB / T10586-1989, place the bonded speaker diaphragm and voice coil in a constant temperature and humidity test chamber set at 85℃ and 85%RH for 20 days. If there is no peeling, cracking, or bubbling of the adhesive, the result is recorded as excellent; if there is peeling, cracking, or bubbling of the adhesive, the result is recorded as poor.

[0079] 6. Elongation: Tested according to ASTM D897-2008.

[0080] 7. Shear strength: Tested according to GB / T 7124-2008 at a rate of 15 mm / min.

[0081] 8. Adhesion Performance Evaluation: Apply adhesive to the speaker diaphragm using a dispensing machine, attach the voice coil, and then cure under LED light. Referring to the ASTM D3330 peel strength test method, if the speaker diaphragm and voice coil can be easily torn apart, it indicates poor adhesion, recorded as ○; if the speaker diaphragm and voice coil are difficult to tear apart, it indicates average adhesion, recorded as £; if the speaker diaphragm and voice coil are firmly bonded and difficult to tear apart, it indicates good adhesion, recorded as △.

[0082] Table 5 Performance test results of Examples 1-18 and Comparative Examples 1-18

[0083]

[0084] As shown in Table 5, (1) by comparing the test results of Example 1 and Comparative Example 1, it can be seen that if the amount of polyurethane acrylate oligomer PUA-1 added is lower than the dosage range in this invention, the flexibility, temperature resistance and LED curing time of the film will not meet the requirements. When the amount of PUA-1 added is within the range of this invention, all properties can meet the requirements. Moreover, as the amount of PUA-1 added increases, the hardness of the film also increases, and the LED curing time, tensile strength and shear strength also decrease. The flexibility, temperature resistance and constant temperature and humidity test of the film can all meet the requirements. This is because PUA-1 has more 1,6-adiponic acid alkyl and 1,4-butanediol alkyl chain segments, which can increase the chain length of the molecular chain. As the chain length increases, the number of chain segments increases, and the degree of freedom of rotation within the single bond increases, thereby improving the flexibility of the film. At the same time, PUA-1 has more branches. The carbon-carbon double bonds on each branch can crosslink with other oligomers and acrylate reactive diluents to form a three-dimensional network structure. The film with this structure has excellent temperature resistance. Furthermore, the multifunctional polyurethane acrylate oligomer incorporates isocyanate trimers, which possess high reactivity and can accelerate the curing rate. Comparative results from Example 6 and Comparative Example 2 show that when the amount of multifunctional polyurethane acrylate oligomer added to the formulation exceeds the amount specified in this invention, an imbalance occurs between PUA-1 and other components of the adhesive, leading to insufficient tensile strength of the adhesive film and poor adhesion between the speaker diaphragm and voice coil.

[0085] (2) By comparing the test results of Example 2 and Comparative Example 3, it can be seen that if the amount of difunctional polyurethane acrylate oligomer PUA-2 added is lower than the amount range in this invention, the diaphragm and voice coil of the speaker will not bond well, and the tensile strength and shear strength of the adhesive film will be insufficient. When the amount of PUA-2 added is within the range of this invention, all performance requirements can be met. As the amount of PUA-2 resin added increases, the curing time of the LED adhesive film, tensile strength and shear strength also increase, while the hardness decreases. However, the flexibility, temperature resistance and constant temperature and humidity test of the adhesive film can meet the requirements. This is because PUA-2 has polar bonds such as urethane bonds and ester bonds that can interact with the surfaces of materials such as leather, plastic, aluminum foil, glass, metal, and PMMA, increasing the interfacial bonding force and thus improving the adhesive strength of the adhesive film. The carbon-carbon double bonds at both ends of PUA-2 can form a three-dimensional network structure with the multifunctional polyurethane acrylate oligomer, so that the adhesive layer has good tensile strength. Moreover, the polyester polyol used in the synthesis of PUA-2 has excellent softness and resilience. By comparing the test results of Example 7 and Comparative Example 4, it was found that when the amount of PUA-2 added to the formulation exceeded the amount required by the present invention, it would lead to an imbalance between PUA-1 and PUA-2, resulting in a loose crosslinking network and reduced flexibility and temperature resistance of the film.

[0086] (3) By comparing the test results of Example 3, Example 8, and Comparative Example 5, it can be seen that if the amount of THFA added in the acrylic reactive diluent is lower than the dosage range in this invention, the diaphragm and voice coil of the speaker will not adhere well, and the shear strength, flexibility, and adhesion will be affected. When the amount of THFA added is within the range of this invention, all performance requirements can be met. Moreover, with the increase of the amount of THFA added, the curing time of the LED film decreases slightly, the hardness decreases, the elongation increases, and the shear strength increases slightly. This is mainly because compared with oligomers, THFA has low viscosity, which can reduce the overall viscosity of the adhesive curing system and improve the light transmission efficiency to accelerate LED curing. The tetrahydrofuran flexible heterocycle reduces the hardness of the cured film and increases the elongation by reducing the rigid stacking of the molecular chain. The ether oxygen polar group forms hydrogen bonds with the substrate surface to enhance the interfacial bonding, thereby improving the overall adhesion and bonding strength of the adhesive. The rigid-flexible balance of the THFA molecular structure endows the cured product with excellent flexibility, temperature resistance, shear strength, and hygrothermal stability. By comparing the test results of Example 17 and Comparative Example 6, it can be seen that when the amount of THFA added in the adhesive exceeds the amount of the present invention, the cured film will be excessively softened, the heat resistance will be reduced, and the crosslinking density of the system will be decreased.

[0087] (4) By comparing the test results of Examples 4, 9, 7, 8, and 17, it can be seen that when the amount of DCPA added decreases, the tensile strength, shear strength, temperature resistance, constant temperature and humidity test, and adhesion of the adhesive film are poor. When the amount of DCPA added is appropriate, all properties can meet the requirements. As the amount of DCPA added increases, the LED curing time of the adhesive film decreases slightly, while the hardness, tensile strength, and shear strength increase. This is mainly because in the DCPA molecular structure, the bicyclic rigid skeleton significantly improves the hardness and heat resistance of the cured material by enhancing the molecular chain segment packing density and thermal stability. Its monofunctional acrylate groups give the cured material excellent flexibility and tensile properties by regulating the crosslinking network density. At the same time, the low polarity of the bicyclic structure improves the hydrophobicity and resistance to humid heat aging of the material. In addition, DCPA has good adhesion to metal, plastic and other substrates. When the amount of DCPA increases, the tensile strength and flexibility of the adhesive film will decrease. This is mainly because DCPA contains a bicyclopentene rigid alicyclic structure, which leads to an increase in the hardness of the crosslinked adhesive film.

[0088] (5) By comparing the test results of Examples 5, 10, 18, 9, and 10, it was found that due to the high reactivity of IBOA, reducing the amount of IBOA added would result in slower LED curing speed, reduced elongation, and decreased shear strength. This phenomenon is mainly attributed to the highly active double bonds, rigid bicyclic skeleton, and hydrophobic characteristics in the IBOA monomer molecular structure, which synergistically achieve the technical effects of improved curing efficiency, optimized mechanical properties, and enhanced weather resistance. Therefore, insufficient IBOA addition will lead to the above situation. As the amount of IBOA gradually increases, the hardness of the colloid will increase, leading to a decrease in elongation. If excessive IBOA is added to the adhesive, the flexibility of the adhesive film will decrease, affecting the mechanical properties of the adhesive film. At the same time, excessive IBOA may dilute other key components in the formulation, such as photoinitiators and crosslinking agents, thereby affecting the curing effect of the colloid and the final bonding performance. Furthermore, excessive IBOA requires more energy to cure, which cannot meet the requirements for rapid LED curing.

[0089] (6) By comparing the test results of Examples 11, 12, 11, and 12, when the amount of DMAA added is too low, the tensile strength, shear strength, flexibility, temperature resistance, and adhesion of the adhesive film will deteriorate. This is because DMAA molecules have polar amide groups, which can crosslink with hydrogen bonds, thereby improving the bonding strength of the interface region between different phase materials. Moreover, DMAA has carbon-carbon double bonds, which can improve the physical properties of the adhesive film by crosslinking with oligomers. The crosslinking network regulates flexibility and environmental resistance, giving it advantages such as high reactivity and excellent adhesion. Furthermore, it has a micro-etching and interlocking effect on various plastic substrates such as PC, PVC, ABS, PMMA, PP, and PE, which can better promote adhesion. Therefore, insufficient DMAA addition will lead to the above situation. On the other hand, excessive addition of DMAA to the adhesive will dilute the over-curing system, resulting in a slower LED light curing speed of the coating and incomplete curing of the inner layer, which in turn leads to a decrease in crosslinking density, adhesion performance, and heat resistance of the adhesive layer. In summary, the amount of DMAA added, as specified in this invention, enables the adhesive to have excellent curing speed and the adhesive film to have suitable physical properties.

[0090] (7) By comparing the test results of Example 1, Example 13, Example 14, Comparative Example 13, and Comparative Example 14, it can be seen that when the amount of photoinitiator TPO added is lower than the amount used in this invention, the curing time, tensile strength, shear strength, flexibility, temperature resistance, constant temperature and humidity test results and adhesion of the adhesive film LED will not meet the requirements. The reason is that the number of free radicals generated by photoinitiator TPO under light is insufficient, which cannot quickly initiate the polymerization reaction of monomers and prepolymers, resulting in incomplete curing and the above phenomena. When the amount of photoinitiator TPO added exceeds the amount specified in this invention, the LED curing time, tensile strength, shear strength, flexibility, temperature resistance, constant temperature and humidity test, and adhesion of the adhesive film will not meet the requirements. This is because excessive TPO will cause the adhesive to rapidly absorb too much ultraviolet light, resulting in excessively fast surface curing. However, surface curing will limit the internal curing reaction, causing the coating surface to be over-cured while the interior is not fully cross-linked. When the amount of TPO added is controlled within the range specified in this invention, the LED curing time of the adhesive film decreases with the increase of the amount of TPO added, and the tensile strength, hardness, and shear strength of the adhesive film increase with the increase of the amount of TPO added. This is because the increase of the amount of TPO added increases the free radical generation rate, accelerates the cross-linking reaction, thereby increasing the cross-linking density, optimizing the mechanical properties, and ultimately achieving a simultaneous increase in tensile strength, hardness, and shear strength while shortening the curing time.

[0091] (8) By comparing the test results of Examples 2, 15, 16, and Comparative Examples 15 and 16, it can be seen that when the amount of coupling agent KH560 added is lower than that of the present invention, the tensile strength, shear strength, and adhesion of the adhesive film will not meet the requirements. This is because if the amount added is too low, the adhesive film cannot form a complete interfacial bonding network, resulting in insufficient mechanical properties and adhesion. When the amount of coupling agent KH560 added is higher than that of the present invention, the tensile strength, shear strength, temperature resistance, constant temperature and humidity test results, and adhesion of the adhesive will also deteriorate. When the amount of coupling agent KH560 added is controlled within the range specified in this invention, the LED curing time of the adhesive film does not change significantly with the increase of the amount of coupling agent KH560 added. However, the tensile strength, hardness, and shear strength of the adhesive film increase with the increase of the amount of coupling agent KH560 added. This is because, within the specified addition amount, the addition of coupling agent KH560 does not affect photocuring; it only strengthens the adhesion between the diaphragm and voice coil of the speaker. Its core function is not to directly participate in the curing reaction, but to strengthen the interfacial bonding through molecular bridging and to fine-tune the uniformity of the crosslinking network. Therefore, it exhibits the phenomenon of "basically unchanged curing time and increasing mechanical properties." The core role of coupling agent KH560 in this invention is to connect the adhesive film and the substrate surface. Through chemical modification, it simultaneously improves the adhesive strength, mechanical properties, and environmental stability. It is a key additive for solving the compatibility of inorganic-organic interfaces.

[0092] Obviously, the above embodiments of the present invention are merely examples to clearly illustrate the technical solutions of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A UV-curable adhesive composition, characterized in that, Including the following parts by weight of raw materials: Prepare 30-45 parts of a self-made UV-curable multifunctional polyurethane acrylate oligomer; 35-50 parts of a self-made UV-curable difunctional polyurethane acrylate oligomer; 20-40 parts of acrylic reactive diluent; 3-8 parts of photoinitiator; Thickener 1-3 parts; 0.5–2.0 parts of silane coupling agent; Polymerization inhibitor 0.05–0.2 parts; The structural formula of the self-made UV-curable multifunctional polyurethane acrylate oligomer is shown in Formula I: Formula I The structural formula of the self-made UV-curable difunctional polyurethane acrylate oligomer is shown in Formula II: Formula II In Formula I and Formula II, R2 represents a neopentyl glycol alkyl segment; R3 represents a 1,4-butanediol alkyl segment; R4 represents an alkyl group with 5 to 7 carbon atoms; R5 represents a specially modified acid alkyl segment; R6 represents a specially modified diol alkyl segment; and R7 represents a 1,6-adiponic acid alkyl segment. R1 represents any of the following structural formulas: OR 。 2. The UV-curable adhesive composition according to claim 1, characterized in that: The self-made UV-curable multifunctional polyurethane acrylate oligomer comprises the following raw materials in parts by weight: 11-26 parts isocyanate dimer, 3-8 parts isocyanate trimer, 52-80 parts polyester polyol, 1.2-3.0 parts chain extender, 3-15 parts (meth)acrylate hydroxy ester, catalyst, and polymerization inhibitor; the amount of catalyst is 0.05%-0.2% of the total mass of isocyanate dimer, isocyanate trimer, and polyester polyol; the amount of polymerization inhibitor is 0.02%-0.08% of the mass of (meth)acrylate hydroxy ester.

3. The UV-curable adhesive composition according to claim 2, characterized in that, The preparation process of the self-made UV-curable multifunctional polyurethane acrylate oligomer includes the following steps: (1) Isocyanate dimer, isocyanate trimer, polyester polyol and catalyst are added to the reactor and reacted at 75-85℃ for 2-3 hours. Nitrogen gas is passed through the reactor while stirring. (2) Cool down to 50-60℃, then add chain extender dropwise. After the dropwise addition is complete, raise the temperature to 68-72℃ and react for 0.5-1h to obtain the prepolymer. During this reaction, acetone is added to adjust the viscosity of the reaction system. (3) While stirring, add (meth)acrylate hydroxy ester containing polymerization inhibitor dropwise to the prepolymer, and complete the addition within 1 h. After the addition is complete, raise the temperature to 65~75℃ and react for 2~3 h to obtain the self-made UV-curable multifunctional polyurethane acrylate oligomer.

4. The UV-curable adhesive composition according to claim 1, characterized in that: The self-made UV-curable difunctional polyurethane acrylate oligomer is synthesized by reacting the following raw materials in parts by weight: 15-20 parts isocyanate dimer, 72-79 parts polyester polyol, 1.4-2.0 parts chain extender, 3.5-8.0 parts (meth)acrylate hydroxy ester, catalyst, and polymerization inhibitor; the amount of catalyst is 0.05%-0.2% of the total mass of isocyanate dimer and polyester polyol; the amount of polymerization inhibitor is 0.02%-0.08% of the mass of (meth)acrylate hydroxy ester.

5. The UV-curable adhesive composition according to claim 4, characterized in that, The preparation process of the self-made UV-curable dienergetic polyurethane acrylate oligomer includes the following steps: (1) Isocyanate dimer, polyester polyol and catalyst are added to the reactor and reacted at 75-85℃ for 2-3 hours. Nitrogen gas is passed through the reactor while stirring. (2) After cooling to 50-60℃, start adding chain extender dropwise. After the dropwise addition is complete, raise the temperature to 68-72℃ and react for 0.5-1h to obtain prepolymer. During the reaction, acetone is added to adjust the viscosity of the reaction system. (3) While stirring, add (meth)acrylate hydroxy ester containing polymerization inhibitor dropwise to the prepolymer. The addition is completed within 1 h. After the addition is completed, the temperature is raised to 65~75℃ and the reaction is carried out for 2~3 h to obtain the self-made UV-curable di-energy polyurethane acrylate oligomer.

6. A UV-curable adhesive composition according to claim 2 or 3, characterized in that: In the raw materials of the self-made UV-curable multifunctional polyurethane acrylate oligomer, the isocyanate dimer is one or a mixture of two of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate; the isocyanate trimer is an HDI trimer; the polyester polyol has a molecular weight of 1000-2000 and a hydroxyl value of 108-116 mgKOH / g, and is prepared by reacting 1,6-adipic acid, 1,4-butanediol and neopentyl glycol; the chain extender is 1,4-butanediol; the (meth)acrylate hydroxy ester is one or a mixture of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate; the catalyst is an organotin catalyst and / or an organobismuth catalyst; the polymerization inhibitor is p-hydroxyanisole, hydroquinone, 4-hydroxy-2,2,6-hydroxypropyl methacrylate. One or more of 6-tetramethylpiperidine-1-ox free radical and 2,2,6,6-tetramethylpiperidine-1-ox free radical.

7. The UV-curable adhesive composition according to claim 4 or 5, characterized in that: In the raw materials of the self-made UV-curable difunctional polyurethane acrylate oligomer, the isocyanate dimer includes one or a mixture of two of isophorone diisocyanate and 4,4'-dicyclohexylmethane diisocyanate; the polyester polyol has a molecular weight of 2000-2500 and a hydroxyl value of 45-53 mg KOH / g; the chain extender is 1,4-butanediol; the (meth)acrylate hydroxy ester is one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate; the catalyst is an organotin catalyst and / or an organozinc catalyst; and the polymerization inhibitor is one or more of p-hydroxyanisole, hydroquinone, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxo radical, and 2,2,6,6-tetramethylpiperidine-1-oxo radical.

8. The UV-curable adhesive composition according to claim 1, characterized in that: The acrylic reactive diluent comprises the following raw materials by mass fraction: 18%–51% tetrahydrofuran acrylate, 12%–41% dicyclopentenyl acrylate, 12%–41% isobornyl acrylate, and 8%–35% N,N-dimethylacrylamide; the thickener is hydrophilic silica; the photoinitiator is one or both of ethyl 2,4,6-trimethylbenzoylphenylphosphonate and 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; the silane coupling agent is one or more of KH570, KH560, and KH172; and the polymerization inhibitor is one or more of p-hydroxyanisole, p-benzoquinone, hydroquinone, and naphthoquinone.

9. A method for preparing a UV-curable adhesive composition according to any one of claims 1-8, comprising the following steps: (1) Add the self-made UV-curable multifunctional polyurethane acrylate oligomer, the self-made UV-curable difunctional polyurethane acrylate oligomer, and the thickener into the mixer in the proportion of parts, and stir evenly at 800-1000 rpm at 20-30℃ in the dark. (2) Add acrylic reactive diluent, polymerization inhibitor, silane coupling agent and photoinitiator into a mixer, protect from light, stir evenly, stir at 600 to 1000 rpm under vacuum conditions of -0.1 to -0.09 MPa at 20 to 30°C until evenly mixed, and then depressurize with nitrogen to obtain the UV-curable adhesive composition.

10. An application of a UV-curable adhesive composition as described in any one of claims 1 to 9, characterized in that, The UV-curable adhesive composition is applied to the diaphragm of the speaker, the voice coil is then attached to the diaphragm, and finally cured by LED light, thus achieving the bonding between the speaker diaphragm and the voice coil.

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