Long-term vibration-resistant photocuring structural adhesive for repairing PC shell of unmanned aerial vehicle

Abstract

The invention discloses a long-term vibration-resistant light-cured structural adhesive for sealing and repairing a PC (polycarbonate) shell of an unmanned aerial vehicle and a preparation method of the long-term vibration-resistant light-cured structural adhesive. The long-term vibration-resistant light-cured structural adhesive is prepared from 2-functionality polyurethane acrylate, a TPO (thermoplastic polyolefin) initiator, an acrylic phosphate adhesion promoter, isobornyl acrylate, tetrahydrofuran acrylate, fumed silica and 0.5%-1% of a silane coupling agent. The light-cured structural adhesive prepared by the invention has the advantages of high curing speed, high transparency, high and low temperature resistance, water resistance and high bonding strength, and is particularly suitable for PC shells of unmanned aerial vehicles in application scenes requiring vibration resistance.

Description

Technical Field

[0001] This invention relates to the field of adhesives, specifically, to a simple-to-prepare, vibration-resistant, and weather-resistant UV structural adhesive and its preparation method. Background Technology

[0002] Structural adhesives are used to bond structural components of various materials, replacing riveting, welding, and bolting. They offer advantages such as light weight, smooth surface, low stress concentration, and good sealing. Structural adhesives require high bond strength, good durability, fast curing, ease of use, and good adhesion to a variety of materials. Traditional structural adhesives are mainly classified into epoxy, polyurethane, acrylic, silicone, and cyano-based types, and generally suffer from long curing cycles, VOC content, and insufficient vibration resistance.

[0003] As the core carrier of the low-altitude economy, drones face increasingly stringent requirements for lightweight and high reliability. Due to its excellent impact resistance, light transmittance, and lightweight properties, PC (polycarbonate) has become the mainstream material for drone shells. However, during use (especially in long-term vibration environments such as those caused by the drone's own wings, motors, wind, and crashes), these shells are prone to cracking, interface peeling, and shear strength attenuation, requiring timely repair.

[0004] Photocurable acrylic structural adhesives are composed of (meth)acrylate oligomers, reactive diluents, photoinitiators, stabilizers, and other additives. The oligomers are mainly epoxy (meth)acrylates, polyurethane (meth)acrylates, and polyester (meth)acrylates; the reactive diluents are (meth)acrylate monoesters, diesters, etc.

[0005] In response, through precise formulation design, the UV structural adhesive proposed in this invention can achieve various properties of traditional structural adhesives, and can reach its maximum strength within tens of seconds. Simultaneously, it can meet the usage requirements of automated dispensing production lines during finished product assembly, which is unmatched by other types of structural adhesives, and it also exhibits good long-term applicability after curing. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of all the above-mentioned technologies by providing a simple, efficient, and vibration-resistant UV structural adhesive and its preparation method.

[0007] The technical solution adopted by this invention to solve its technical problem A long-term vibration-resistant UV-cured structural adhesive (hereinafter referred to as UV structural adhesive) for sealing and repairing PC shells of drones comprises the following components calculated by the mass percentage of amines: 2. Functionality of polyurethane acrylate 50~80%; Reactive diluent 20-40%; Fumed silica 2-3%; Silane coupling agent 0.5~1%; Phosphate acrylate 0.1~0.2%; Photoinitiator 0.8~2%.

[0008] As a preferred embodiment, the UV structural adhesive described above contains a difunctional polyurethane acrylate with a molecular weight of 6500~7000 and a glass transition temperature of -30~0℃. The elongation at break was 298.77%; the tensile strength was 21.221 MPa.

[0009] As a preferred embodiment, the synthesis of this difunctional polyurethane acrylate resin in this invention comprises the following process flow: (1) Tricyclodecanediethanol, 16-hexanediol and 16-adipic acid were added to the reactor in a molar ratio of 8:16:23. The catalyst (tetrabutyl titanate) was added at 100 ppm of the total feed amount. The reactor was first dehydrated and impurity removed.

[0010] (2) Heat the reactor to 180~220℃ and carry out the esterification reaction under normal pressure to generate low molecular weight esters. At the same time, remove some of the water generated in the reaction. When the acid value drops to 50~100mgKOH / g, the normal pressure stage ends.

[0011] (3) Vacuum polycondensation: gradually increase the vacuum level to 5~50Pa, raise the temperature to 220~240℃ for deep polycondensation, and continuously monitor the acid value (≤0.1mgKOH / g) and hydroxyl value (≤19mgKOH / g) after 1 hour. After reaching the target index, proceed to the second step of reaction with IPDI (isophoretic diisocyanate).

[0012] (4) Add 2 moles of IPDI (isophora diketone diisocyanate), and use 5 g of dibutyltin dilaurate as a catalyst. React at 60~70℃ for 2 hours. When NCO < 1.35%, proceed to the third step of reaction with hydroxypropyl methacrylate.

[0013] (5) Finally, add 2 moles of HPMA (hydroxypropyl methacrylate). React at 80~90℃ for 3 hours. When NCO < 0.3%, stop the reaction to obtain difunctional polyurethane acrylate.

[0014] The molecular weight of the polyester diol mentioned above is 6500~7000; the alkyd-acid ratio of the polyester diol is 1.043:1.

[0015] As a preferred embodiment, the diisocyanate is IPDI (isophoretic diisocyanate) (Yantai Wanhua). As a preferred embodiment, the hydroxy methacrylate is HPMA (hydroxypropyl methacrylate) (Jiangsu Sanmu 97%). As a preferred option, the UV-active diluent is one or more of IBOA isobornyl acrylate (Wuxi Akoli) and THFA tetrahydrofuran acrylate (Jiangsu Sanmu Chemical Co., Ltd.).

[0016] As a preferred embodiment, the fumed silica is TS720 (Cabot, USA).

[0017] As a preferred embodiment, the silane coupling agent is vinyltrimethoxysilane (Shandong Silicon Science & Technology Co., Ltd. SICO-V171). As a preferred embodiment, the acrylate phosphate adhesion promoter is EM39 from Changxing Special Materials Co., Ltd.

[0018] As a preferred embodiment, the photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO) (Tianjin Jiuri Chemical).

[0019] This invention provides a method for preparing a UV structural adhesive, comprising the following steps: According to the formula, add the UV reactive diluent and photoinitiator to the high-speed dispersion vessel and stir. Then add the difunctional polyurethane acrylate, acrylate phosphate adhesion promoter and silane coupling agent and continue stirring. After uniform dispersion, add fumed silica and continue dispersion. Vacuum degassing is performed to obtain the UV structural adhesive.

[0020] As a more preferred embodiment, the present invention provides a method for preparing a UV structural adhesive, comprising the following steps; (1) First, put the UV active monomer and initiator into the dispersion tank, and stir and dissolve them evenly at 800~1200 rpm for 60 min; (2) Add the difunctional polyurethane acrylate, acrylate phosphate adhesion promoter and silane coupling agent into the dispersion tank of step 1 and disperse for 60 min. (3) Add the fumed silica to the dispersion tank of step 2 and disperse at high speed for 30 min; (4) Finally, the mixture obtained in step 3 is vacuum degassed, filtered through a 300-mesh filter, and packaged to obtain the UV structural adhesive.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects: 1. The UV structural adhesive provided by this invention uses difunctional polyurethane acrylate with a specific structure and molecular weight as the main body, which has high adhesion, high tear strength, high elongation at break and high weather resistance. Compared with existing traditional structural adhesives, it is more durable, can extend the service life of products, maintain performance for a long time and reduce the cost of use.

[0022] 2. The UV structural adhesive provided by the present invention incorporates fumed silica, which on the one hand improves thixotropy to facilitate construction, and on the other hand enhances the tear resistance and bonding strength of the adhesive.

[0023] 3. The UV structural adhesive provided by the present invention, due to the introduction of a specific vinyltrimethoxysilane, under the action of a photoinitiator, enables it to crosslink with the acryloyloxy group of the entire photocuring system, forming an island effect, which further improves the bonding strength and water resistance.

[0024] 4. The UV structural adhesive provided by this invention cures quickly (30 seconds), is highly efficient, and is environmentally friendly. Detailed Implementation

[0025] The present invention will be further described in detail below through embodiments. These embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0026] In the following examples, IBOA: isobornyl acrylate (Wuxi Akoli), THFA: tetrahydrofuran acrylate (Jiangsu Sanmu Chemical Co., Ltd.), fumed silica: TS720 (Cabot, USA), silane coupling agent: vinyltrimethoxysilane (Shandong Sikco SICO-V171), accelerator: EM39 from Changxing Special Materials Co., Ltd., and photoinitiator: 2,4,6-trimethylbenzoyldiphenylphosphine oxide TPO (Tianjin Jiuri Chemical).

[0027] In the following examples, the 2-functional polyurethane acrylate resin was prepared by the following steps: (1) Tricyclodecanediethanol, 16-hexanediol, and 16-adipic acid were added to the reactor in a molar ratio of 8:16:23. The catalyst (tetrabutyl titanate) was added at 100 ppm of the total feed amount. Dehydration and impurity removal were performed first. (2) The reactor was heated to 180~220℃ and esterification reaction was carried out under normal pressure to generate low molecular weight esters. At the same time, some of the water generated by the reaction was removed. When the acid value dropped to 50~100 mgKOH / g, the normal pressure stage was ended. (3) Vacuum polycondensation was carried out. The vacuum degree was gradually increased to 5~50 Pa and the temperature was raised to 220~240℃ for deep polycondensation. After 1 hour, the acid value (≤0.1 mgKOH / g) and hydroxyl value (≤19 mgKOH / g) were continuously monitored. After the target index was reached, the second step of reaction with IPDI (isophorone diisocyanate) was carried out. (4) Add 2 moles of IPDI (isophorone diisocyanate), using 5 g of dibutyltin dilaurate as a catalyst, and react at 60~70℃ for 2 hours. When NCO < 1.35%, proceed to the third step of reacting with hydroxypropyl methacrylate. (5) Finally, add 2 moles of HPMA (hydroxypropyl methacrylate), using 16 g of p-hydroxyanisole as a polymerization inhibitor, and react at 80~90℃ for 3 hours. When NCO < 0.3%, stop the reaction to obtain difunctional polyurethane acrylate.

[0028] Example 1 1. A UV structural adhesive, comprising the following components by weight: Raw material name Number of parts by weight 1 2-functionality polyurethane acrylate 80.4 copies 2 IBOA 15 copies 4 THFA 0 copies 5 TS720 fumed silicon 2 copies 6 Coupling agent SICO-V171 0.5 copies 7 Adhesion promoter EM39 0.1 copies 8 Initiator TPO 2 copies 2. The preparation method includes the following steps: (1) First, put the UV active monomer and initiator into the dispersion tank, and stir and dissolve them evenly at 800~1200 rpm for 60 min; (2) Add the difunctional polyurethane acrylate, acrylate phosphate adhesion promoter and silane coupling agent into the dispersion tank of step 1 and disperse for 60 min. (3) Add the fumed silica to the dispersion tank of step 2 and disperse at high speed for 30 min; (4) Finally, the mixture obtained in step 3 is vacuum degassed, filtered through a 300-mesh filter, and packaged to obtain the UV structural adhesive.

[0029] Example 2 1. A UV structural adhesive, comprising the following components by weight: Raw material name Number of parts by weight 1 2-functionality polyurethane acrylate 67.4 copies 2 IBOA 20 copies 4 THFA 8 copies 5 TS720 fumed silicon 2 copies 6 Coupling agent SICO-V171 0.5 copies 7 Adhesion promoter EM39 0.1 copies 8 Initiator TPO 2 copies 2. The preparation method is the same as in Example 1.

[0030] Example 3 1. A UV structural adhesive, comprising the following components by weight: Raw material name Number of parts by weight 1 2-functionality polyurethane acrylate 62.4 copies 2 IBOA 25 copies 4 THFA 8 copies 5 TS720 fumed silicon 2 copies 6 Coupling agent SICO-V171 0.5 copies 7 Adhesion promoter EM39 0.1 copies 8 Initiator TPO 2 copies 2. The preparation method is the same as in Example 1.

[0031] Comparative Example 1 1. A UV structural adhesive, comprising the following components by weight: Raw material name Number of parts by weight 1 2-functionality polyurethane acrylate 69.4 copies 2 IBOA 20 copies 4 THFA 8 copies 5 TS720 fumed silicon 0 copies 6 Coupling agent SICO-V171 0.5 copies 7 Adhesion promoter EM39 0.1 copies 8 Initiator TPO 2 copies 2. The preparation method is the same as in Example 1.

[0032] Comparative Example 2 1. A UV structural adhesive, comprising the following components by weight: Raw material name Number of parts by weight 1 2-functionality polyurethane acrylate 67.9 copies 2 IBOA 20 copies 4 THFA 8 copies 5 TS720 fumed silicon 2 copies 6 Coupling agent SICO-V171 0 copies 7 Adhesion promoter EM39 0.1 copies 8 Initiator TPO 2 copies 2. The preparation method is the same as in Example 1.

[0033] Comparative Example 3 1. A UV structural adhesive, comprising the following components by weight: Raw material name Number of parts by weight 1 2-functionality polyurethane acrylate 67.5 copies 2 IBOA 20 copies 4 THFA 8 copies 5 TS720 fumed silicon 2 copies 6 Coupling agent SICO-V171 0.5 copies 7 Adhesion promoter EM39 0 copies 8 Initiator TPO 2 copies 2. The preparation method is the same as in Example 1.

[0034] Examples 1-3 and Comparative Examples 1-3 were applied to a PC board (100mm*25mm*2mm) (Covestro Polymers China Co., Ltd.). Adhesive was applied to one end of the PC board, with a length of 12.5mm, a width of 25mm, and a thickness of 0.5mm. Another PC board of the same size was placed on top of the adhesive and precisely aligned (to avoid adhesive overflow). The excess adhesive squeezed out from the sides was cleaned off using a scraper. This process was repeated for LEDs (365nm) with power ≥80Mw / cm². 2 Under illumination by lamp, the curing time is 30 seconds.

[0035] All test samples were stabilized in a constant temperature and humidity chamber (temperature 21℃~25℃, humidity 45%~55%) for 24 hours before various performance tests were conducted on Examples 1~3 and Comparative Examples 1~3 (all results were measured in a constant temperature and humidity laboratory). The performance test methods are shown in Table 1. The test results are shown in Table 2.

[0036] Table 1 project index Test methods Remark Tensile shear strength ≥12MPa GB / T14074-2017 Guangzhou Biaogeda Universal Testing Machine Vibration resistance test intensity attenuation ≤10% GB / T38924.6-2020 5000 hours Strength retention rate during high and low temperature cycling tests ≥85% GB / T2423.2012 50 cycles (4 hours each at -40℃ to 60℃) Table 2 Performance indicators Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Thixotropic index 2.3 1.9 1.5 1 1.9 1.9 room temperature tensile shear strength 9.9 MPa 13.8 MPa 12.7 MPa 13.3 MPa 11.2 MPa 11.8 MPa Strength retention rate after high and low temperature cycling 72.1% 88.8% 84.9% 85.1% 82.4% 87.7% Intensity decay after 5000 hours 19.2% 5.3% 9.3% 11.6% 9.7% 8.5% The difunctional polyurethane acrylate of this invention, as the main resin, can impart strong tear strength, peel strength, and weather resistance (high and low temperatures, vibration) to the adhesive layer. IBOA homopolymer has a high glass transition temperature and, when used as an active monomer in a photocurable adhesive, can improve the strength of the system. As a monofunctional monomer, it also has considerable toughness, low internal stress, and improved shrinkage and adhesion. THFA has a saturated five-membered ring and low polarity, while PC (polycarbonate) has a relatively moderate overall polarity, which meets the principle of polarity matching. In addition, it has both the rigidity and flexibility of a cyclic structure, which can simultaneously meet the requirements of strength and vibration toughness as an adhesive. The reasonable compounding of the two active diluents improves the wetting and adhesion of the adhesive layer to the PC substrate, achieving a balance between the flexibility and rigidity of the adhesive layer.

[0037] The addition of coupling agent SICO-V171 silane coupling agent and EM39 phosphate ester adhesion promoter significantly improves the adhesion of the PC substrate interface, achieving high bonding strength without the need for a primer.

[0038] The addition of fumed silica can significantly improve the yield value and viscosity of the adhesive (represented in this paper by the thixotropic index: the ratio of low shear rate to high shear rate), effectively suppressing sagging and collapse of the adhesive during construction and curing, ensuring the accuracy and stability of bonding. At the same time, due to the large specific surface area of ​​fumed silica, the surface silanol groups interact with the polymer molecular chains to form physical cross-linking points, further improving the adhesion and reliability.

[0039] This invention, through optimizing the ratio of oligomers and reactive diluents and combining them with various functional materials, has successfully developed a long-term vibration-resistant light-curing structural adhesive for PC shells of drones. This adhesive requires no primer and no special treatment of the substrate. It can be rapidly cured by 30 seconds of UV irradiation. The room temperature shear strength of PC-PC bonding reaches 13.8 MPa. After 5000 hours of vibration resistance testing, the strength decay is only 5.3%, and the strength retention rate is 88.8% after high and low temperature cycling. All performance characteristics meet the requirements of drone use.

[0040] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A long-term vibration-resistant, light-curing structural adhesive for sealing and repairing PC shells of unmanned aerial vehicles (UAVs), characterized in that, It contains the following components by mass percentage: 50-80 parts of 2-functionality polyurethane acrylate; 20-40 parts of reactive diluent; 2-3 parts of fumed silica; 0.5 to 1 part of silane coupling agent; 0.1 to 0.2 parts of phosphate acrylate; Photoinitiator 0.8 to 2 parts.

2. The photocurable structural adhesive according to claim 1, characterized in that: The difunctional polyurethane acrylate is prepared by reacting tricyclodecanediethanol, 16-hexanediol and 16-adipic acid in a molar ratio of 8:16:23 to obtain a polyester diol with a specific molecular weight, then reacting it with 2 moles of diisocyanate to generate a prepolymer with isocyanate structures at both ends, and then end-capping it with 2 moles of (meth)acrylate hydroxy ester to obtain the difunctional polyurethane acrylate.

3. The polyester diol according to claim 2, characterized in that: The polyester diol has a molecular weight of 6000~6200; the alcohol-acid ratio of the polyester diol is 1.043:

1.

4. The diisocyanate according to claim 2, characterized in that: The preferred diisocyanate is IPDI (isophoretic diisocyanate).

5. The (meth)acrylate hydroxy ester according to claim 2, characterized in that: The preferred hydroxy methacrylate is hydroxypropyl methacrylate.

6. The photocurable structural adhesive according to claim 1, characterized in that: The difunctional polyurethane acrylate has a molecular weight of 6500~7000; the glass transition temperature of the difunctional polyurethane acrylate is -30~0℃.

7. The photocurable structural adhesive according to claim 1, characterized in that: The active diluent is one or more of isobornyl methacrylate and tetrahydrofuran methacrylate.

8. The UV structural adhesive according to claim 1, characterized in that: The silane coupling agent is vinyltrimethoxysilane; The photoinitiator is 2,4,6-trimethylbenzoyl diphenylphosphine oxide (TPO).

9. A method for preparing a UV structural adhesive, characterized in that: Includes the following steps; (1) Mix the reactive diluent and photoinitiator according to the mass ratio, control the temperature between 40 and 50°C, and stir to make the solution uniform; (2) After dissolving until clear and transparent, add difunctional polyurethane acrylate, phosphate acrylate and silane coupling agent into the mixing tank and stir evenly. (3) Finally, slowly add the fumed silica and stir. (4) The material after being stirred evenly is degassed under vacuum to obtain the product.

10. The method for preparing the UV structural adhesive according to claim 9, characterized in that: Includes the following steps; (1) Mix the reactive diluent and photoinitiator according to the mass ratio, control the temperature between 40 and 50°C, and stir for 60 minutes to ensure uniform dissolution; (2) After dissolving until clear and transparent, add difunctional polyurethane acrylate, phosphate acrylate and silane coupling agent into the stirred tank and stir for 60-90 min. (3) Finally, slowly add the fumed silica and stir for 30-60 minutes; (4) The material after being stirred evenly is degassed under vacuum to obtain the product.