UV-moisture dual-curing organosilicon sealant and preparation method thereof

Abstract

The invention provides a UV-moisture dual-curing organosilicon sealant and a preparation method thereof, and belongs to the technical field of adhesives. The UV-moisture dual-curing organosilicon sealant is prepared from the following components in parts by mass: 30 to 80 parts of vinyl alkoxy polysiloxane, 6 to 50 parts of vinyl-terminated polydimethylsiloxane, 4 to 10 parts of sulfydryl polydimethylsiloxane, 3.8 to 7 parts of a thixotropic agent, 3 to 6 parts of a cross-linking agent, 0.5 to 2 parts of a photoinitiator and 0.1 to 5 parts of a moisture curing catalyst. According to the UV-moisture dual-curing organosilicon sealant provided by the invention, on the premise that excellent electrical insulation, weather resistance, chemical resistance and the like of organosilicon are maintained, the purposes that the surface of the sealant after UV curing is dry in touch, low in volume shrinkage rate and free of yellowing can be achieved.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a UV-moisture dual-curing silicone sealant and its preparation method. Background Technology

[0002] Silicone rubber molecules have a -Si-O-Si- main chain, exhibiting outstanding electrical insulation, radiation resistance, high and low temperature resistance, and hydrophobic properties. Therefore, silicone-based sealants are widely used in the electronics and electrical industries, including mobile phones, displays, and photovoltaics. Generally, liquid silicone rubber sealants can be cross-linked into solid materials through moisture curing or heat curing. However, moisture curing of silicone typically requires 24 hours or longer to achieve initial strength, impacting production efficiency. Meanwhile, heat curing methods require heating equipment and incur higher energy costs, making them difficult to apply to precision components that cannot be heated.

[0003] Ultraviolet (UV) curing technology is a highly efficient and low-cost curing technique that uses UV excitation to harden liquid adhesives into solid polymers in a short time. Applying this technology to the curing of silicone sealants combines UV and moisture curing methods. Initial UV curing is achieved in the light-transmitting adhesive layer, while the opaque, shaded areas are further cured in the next process using moisture, shortening process waiting time and thus improving production efficiency on the production line.

[0004] Most current UV-moisture dual-curing sealants are compositions of isocyanate-modified acrylates or silicone grafted with acryloyl groups. For example, patent application CN111040726A discloses an acrylic monomer-modified silicone resin with double bonds and hydroxyl structures at the polymer chain ends. The prepared silicone coating can be UV cured at room temperature or cured in moisture. However, UV curing of acrylate groups in air can cause oxygen inhibition, resulting in a non-drying surface to the touch. At the same time, acrylate polymers have a potential corrosive effect on electronic devices and PCBs (Printed Circuit Boards). The cured adhesive is prone to yellowing, and the high shrinkage rate during acrylic monomer polymerization can generate significant stress in the filling application of mobile phone frames, reducing waterproof and dustproof performance. Furthermore, the increased adhesion is not conducive to product maintenance and repair. Patent CN114774066B discloses a fast-positioning, low-shrinkage UV-curable polyurethane hot melt adhesive. It involves preparing a flexible polyurethane-modified diol with acrylate double bonds, introducing these double bonds, capable of free radical photopolymerization, into the polyurethane prepolymer. Upon UV irradiation, the prepolymer side chains with double bonds undergo free radical photopolymerization, forming a certain degree of crosslinking, rapidly increasing the cohesive strength of the adhesive and achieving rapid positioning. The main chain segments reach their final strength through subsequent moisture curing. This method uses a relatively large amount of isocyanate, raising concerns about toxicity and the potential for bubbling during moisture curing. Summary of the Invention

[0005] To address the aforementioned technical issues, this invention provides a UV-moisture dual-curing silicone sealant. After UV curing, this silicone sealant exhibits a touch-dry surface, low volume shrinkage, moderate hardness, mechanical strength, and adhesive properties, making it particularly suitable for filling micropores in mobile phones or wearable electronic products.

[0006] Specifically, in order to achieve the above objectives, the present invention adopts the following technical solution: A UV-moisture dual-curing silicone sealant comprises the following components in parts by weight: 30-80 parts vinylalkoxy polysiloxane, 6-50 parts vinyl-terminated polydimethylsiloxane, 4-10 parts mercapto polydimethylsiloxane, 3.8-7 parts thixotropic agent, 3-6 parts crosslinking agent, 0.5-2 parts photoinitiator, and 0.1-5 parts moisture-curing catalyst.

[0007] In a preferred embodiment, the vinylalkoxy polysiloxane has the structural formula shown in formula (1): Formula (1), wherein R1 and R4 are independently selected from methoxy, ethoxy, propoxy, and vinyl, respectively; R2 is vinyl; R3 is selected from methoxy, ethoxy, and propoxy; the sum of a, b, and c is an integer from 220 to 1500, where a is an integer from 210 to 1300, b is an integer from 4 to 20, and c is an integer from 6 to 180.

[0008] In a further preferred embodiment, the vinyl group in the vinyl alkoxy polysiloxane has a vinyl group mass fraction of 0.10% to 0.30%.

[0009] In a preferred embodiment, the vinylalkoxy polysiloxane has a viscosity of 500~65000 mPa·s at 25°C.

[0010] In a preferred embodiment, the structure of the terminal vinyl polydimethylsiloxane is shown in formula (2): Equation (2), where m is an integer from 350 to 1000.

[0011] In a further preferred embodiment, the vinyl content in the vinyl-terminated polydimethylsiloxane is 0.08% to 0.20% by mass.

[0012] In a preferred embodiment, the viscosity of the end-vinyl polydimethylsiloxane at 25°C is 1000~20000 mPa·s.

[0013] In a preferred embodiment, the structure of the mercaptopolydimethylsiloxane is shown in formula (3): Equation (3), where d is an integer from 15 to 32 and e is an integer from 100 to 365.

[0014] In a further preferred embodiment, the mass fraction of thiol groups in the thiol-based polydimethylsiloxane is 2% to 5.2%.

[0015] In a preferred embodiment, the viscosity of the mercaptopolydimethylsiloxane at 25°C is 200~1000 mPa·s.

[0016] In a preferred embodiment, the thixotropic agent is any one or a combination of several of the following: hydrophilic fumed silica V15, hydrophilic fumed silica T30, hydrophilic fumed silica N20, hydrophobic fumed silica AEROSIL R812S, hydrophobic fumed silica R974, and hydrophobic fumed silica R972.

[0017] In a preferred embodiment, the crosslinking agent is at least one selected from methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, dimethyldiethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

[0018] In a further preferred embodiment, based on the requirements for curing performance and sealing adhesion, the crosslinking agent is at least one of methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane (KH-570), and 3-aminopropyltrimethoxysilane (KH-540).

[0019] In a preferred embodiment, the photoinitiator is at least one of 2-hydroxy-2-methylphenylacetone (photoinitiator 1173), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and ethyl 2,4,6-trimethylbenzoylphenylphosphonate (TPO-L).

[0020] In a preferred embodiment, the moisture-curing catalyst is selected from organotin catalysts and titanium compound catalysts.

[0021] In a further preferred embodiment, the organotin catalyst is at least one of dibutyltin dilaurate (DBTDL), dibutyltin di(acetylacetonyl)ditin, dibutyltin diacetate, and dimethoxydibutyltin.

[0022] In a further preferred embodiment, the titanium compound catalyst is at least one of tetraisopropoxy titanate, tetrabutyl titanate, and diisopropoxy-di(acetylacetonyl)titanium.

[0023] This invention also provides a method for preparing the UV-moisture dual-curing silicone sealant according to any of the above embodiments, comprising the following steps: S1. Add the vinylalkoxy polysiloxane, terminal vinyl polydimethylsiloxane and thixotropic agent to the reaction vessel, mix evenly, and degas under vacuum. S2. Cool the material obtained in step S1 to a temperature <40°C, add the mercaptopolydimethylsiloxane, crosslinking agent, photoinitiator and moisture curing catalyst, and degas under vacuum to obtain the UV-moisture dual-curing silicone sealant.

[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The UV-moisture dual-curing silicone sealant provided by the present invention, while maintaining the superior electrical insulation, weather resistance and chemical resistance of silicone itself, can achieve the purpose of finger-touch dryness of the colloid surface after UV curing, low volume shrinkage, no yellowing and certain adhesion through mercapto-ene click addition.

[0025] (2) It can achieve rapid positioning during the application process and moisture curing in the next step to achieve final strength, which can improve the production efficiency of the production line. Its hardness and mechanical strength are moderate, making it suitable for potting, sealing and bonding of internal microstructures of electronic products, further broadening the selection of electronic sealant materials. Detailed Implementation

[0026] The following description, in conjunction with embodiments, clearly and completely describes the technical solutions of this application, so that those skilled in the art can fully understand this application. Obviously, the described embodiments are merely some preferred embodiments of this application, and not all embodiments. Any equivalent modifications or substitutions made by those skilled in the art to the following embodiments without creative effort are within the protection scope of this application.

[0027] The structure of the vinylalkoxy polysiloxane used in this application is shown in formula (1): Formula (1), in which R1 and R4 are independently selected from methoxy, ethoxy, propoxy, and vinyl, respectively; R2 is vinyl; R3 is selected from methoxy, ethoxy, and propoxy; the sum of a, b, and c is an integer from 220 to 1500, a is an integer from 210 to 1300, b is an integer from 4 to 20, and c is an integer from 6 to 180; the viscosity of vinylalkoxy polysiloxane at 25°C is 500 to 65000 mPa·s, and the mass fraction of vinyl is 0.10% to 0.30%.

[0028] The structure of the vinyl-terminated polysiloxane is shown in formula (2): Formula (2), where m is an integer from 350 to 1000; the viscosity of the vinyl-terminated polysiloxane at 25°C is 1000 to 20000 mPa·s, and the vinyl mass fraction is 0.08% to 0.20%. The structural formula of mercaptopolydimethylsiloxane is shown in Formula (3): Equation (3), where d is an integer from 15 to 32 and e is an integer from 100 to 365. The viscosity of mercaptopolydimethylsiloxane at 25°C is 200–1000 mPa·s, and the mass fraction of mercapto is 2%–5.2%. Hydrophilic fumed silica V15, T30, and N20 are all products of Wacker Chemie AG, Germany. Hydrophobic fumed silica AEROSIL R812S, R974, and R972 are all purchased from Evonik Degussa (China) Investment Co., Ltd.

[0029] Example 1 A UV-moisture dual-curing silicone sealant, comprising the following components by weight:

[0030] In the structure of vinylalkoxy polysiloxane (Formula (1)), a is 620~640, b is 6~10, c is 10~20, the viscosity at 25℃ is 5000mPa·s, and the vinyl content is 0.14wt%. In the structure of terminal vinyl polydimethylsiloxane (Formula (2)), m is 840~860, the viscosity at 25℃ is 10000mPa·s, and the vinyl content is 0.14wt%. In the structure of mercapto polydimethylsiloxane (Formula (3)), d is 15~20, e is 345~365, the viscosity at 25℃ is 1000mPa·s, and the mercapto content is 2.1wt%. The thixotropic agent is Wacker hydrophilic fumed silica V15. The crosslinking agent is a mixture of methyltrimethoxysilane, dimethyldimethoxysilane, and KH-570 in a mass ratio of 3:1:2. The photoinitiator is a mixture of photoinitiator 1173 and TPO in a 1:1 mass ratio. The moisture curing catalyst is diisopropoxy-di(acetylacetonyl)titanium.

[0031] The preparation method of this UV-moisture dual-curing silicone sealant includes the following steps: S1. According to the mass fraction of the raw materials, add vinylalkoxy polysiloxane, terminal vinyl polydimethylsiloxane and thixotropic agent to the mixing tank. After manually stirring evenly, place it in a planetary vacuum mixer and run it for vacuum degassing for 180s at a revolution speed of 1800 rpm and a rotation speed of 600 rpm.

[0032] S2. Cool the material obtained in step S1 to a temperature <40℃, add mercaptopolydimethylsiloxane, crosslinking agent, photoinitiator and moisture curing catalyst to the mixing tank, set the revolution speed to 1500rpm and the rotation speed to 500rpm, run the vacuum degassing for 120s, mix evenly and pour into a light-proof sealing tube for storage to obtain the UV-moisture dual-curing silicone sealant.

[0033] Example 2 A UV-moisture dual-curing silicone sealant, comprising the following components by weight:

[0034] In the structure of vinylalkoxy polysiloxane (Formula (1)), a is 210~220, b is 4~6, c is 6~10, the viscosity at 25℃ is 500 mPa·s, and the vinyl content is 0.10 wt%. In the structure of terminal vinyl polydimethylsiloxane (Formula (2)), m is 960~1000, the viscosity at 25℃ is 20000 mPa·s, and the vinyl content is 0.08 wt%. In the structure of mercapto polydimethylsiloxane (Formula (3)), d is 20~25, e is 100~125, the viscosity at 25℃ is 200 mPa·s, and the mercapto content is 5.0 wt%. The thixotropic agent is hydrophobic fumed silica AEROSIL R812S. The crosslinking agent is a mixture of dimethyldimethoxysilane, vinyltrimethoxysilane, and KH-540 in a mass ratio of 2:1:2. The photoinitiator is photoinitiator 1173. The moisture curing catalyst is dibutyltin dilaurate (DBTDL).

[0035] The preparation method of this UV-moisture dual-curing silicone sealant is the same as that of Example 1, except that the types and amounts of raw materials are different.

[0036] Example 3 A UV-moisture dual-curing silicone sealant, comprising the following components by weight:

[0037] In the structure of vinylalkoxy polysiloxane (Formula (1)), a is 1250~1300, b is 15~20, c is 160~180, the viscosity at 25℃ is 65000mPa·s, and the vinyl content is 0.30wt%. In the structure of vinyl-terminated polydimethylsiloxane (Formula (2)), m is 350~380, the viscosity at 25℃ is 1000mPa·s, and the vinyl content is 0.20wt%. In the structure of mercapto polydimethylsiloxane (Formula (3)), d is 25~30, e is 280~320, the viscosity at 25℃ is 800mPa·s, and the mercapto content is 2.3wt%. The thixotropic agent is a mixture of hydrophilic fumed silica N20 and hydrophobic fumed silica R974 in a mass ratio of 1:1. The crosslinking agent is a mixture of dimethyldiethoxysilane, dimethyldimethoxysilane, and KH-570 in a mass ratio of 3:2:1. The photoinitiator is a mixture of photoinitiator 1173 and TPO-L in a mass ratio of 1:4. The moisture curing catalyst is a mixture of tetraisopropoxytitanate and DBTDL in a mass ratio of 3:1.

[0038] The preparation method of this UV-moisture dual-curing silicone sealant is the same as that of Example 1, except that the types and amounts of raw materials are different.

[0039] Example 4 A UV-moisture dual-curing silicone sealant, comprising the following components by weight:

[0040] In the structure of vinylalkoxy polysiloxane (Formula (1)), a is 900~950, b is 10~15, c is 60~80, the viscosity at 25℃ is 20000mPa·s, and the vinyl content is 0.25wt%. In the structure of terminal vinyl polydimethylsiloxane (Formula (2)), m is 880~920, the viscosity at 25℃ is 15000mPa·s, and the vinyl content is 0.12wt%. In the structure of mercapto polydimethylsiloxane (Formula (3)), d is 26-32, e is 200~230, the viscosity at 25℃ is 500mPa·s, and the mercapto content is 3.0wt%. The thixotropic agent is a mixture of hydrophilic fumed silica T30 and hydrophobic fumed silica R974 in a mass ratio of 1:1. The crosslinking agent is a mixture of methyltrimethoxysilane and vinyltriethoxysilane in a mass ratio of 1:2. The photoinitiator is a mixture of photoinitiator 1173 and TPO-L in a mass ratio of 1:4. The moisture-curing catalyst is tetrabutyl titanate.

[0041] The preparation method of this UV-moisture dual-curing silicone sealant is the same as that of Example 1, except that the types and amounts of raw materials are different.

[0042] Comparative Example 1 This comparative example provides a UV-moisture dual-curing silicone sealant, the composition of which differs from that of Example 1 in that it does not contain mercaptopolydimethylsiloxane, and the amount of vinylalkoxypolysiloxane is 66.5 parts. The preparation method of this UV-moisture dual-curing silicone sealant is the same as that of Example 1, except for the aforementioned difference in raw materials.

[0043] Comparative Example 2 This comparative example provides a UV-moisture dual-curing silicone sealant, the composition of which differs from that of Example 1 in that the amount of vinylalkoxy polysiloxane is 6 parts and the amount of terminal vinyl polydimethylsiloxane is 80 parts. The preparation method of this UV-moisture dual-curing silicone sealant is the same as that of Example 1, except that the amounts of the aforementioned raw materials differ from those in Example 1.

[0044] Comparative Example 3 This comparative example provides a UV-moisture dual-curing silicone sealant, the composition of which differs from that of Example 1 in that it does not contain terminal vinyl polydimethylsiloxane, the amount of mercapto polydimethylsiloxane is 22.5 parts, and the amount of vinylalkoxy polysiloxane is 60 parts. The preparation method of this UV-moisture dual-curing silicone sealant is the same as that of Example 1, except for the aforementioned difference in raw materials.

[0045] Product performance testing The performance of the silicone sealants in the above embodiments and comparative examples was tested. The test methods are as follows, and the test results are shown in Table 1.

[0046] (1) Surface drying time test: The test was conducted in accordance with the method in GB / T 13477.5-2002 "Test methods for building sealing materials - Part 5: Determination of surface drying time" to characterize the moisture curing performance.

[0047] (2) Viscosity and thixotropic value test: Anton Paar rheometer, PP25 rotor, test plate spacing is 0.5mm, the viscosity value is taken at 1 rpm, and the thixotropic value is the ratio of the viscosity value at 1 rpm to the viscosity value at 10 rpm.

[0048] (3) Hardness test: Select a 6mm thick cured adhesive block and use a Shore A hardness tester for testing.

[0049] (4) Mechanical property test: The test shall be conducted in accordance with the method in GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber".

[0050] (5) Adhesion performance: The test was conducted in accordance with the method in GB / T 7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)" and the test substrates were aluminum and glass.

[0051] (6) UV curing: UV curing is performed by irradiating the surface with 3500MJ energy using a 365~395nm LED lamp, and the surface is judged by touch to see if it is completely cured.

[0052] (7) Shrinkage rate: Test the density of a certain mass of adhesive before curing and calculate the liquid volume; then test the volume of the same mass of adhesive block after complete curing by UV and moisture. Shrinkage rate = (liquid volume - adhesive block volume) / liquid volume × 100%. The liquid volume and adhesive block volume use the same unit.

[0053] Table 1 Performance test results of the silicone sealants in the examples and comparative examples

[0054] As shown in Table 1, without the addition of mercaptopolydimethylsiloxane, the silicone sealant in Comparative Example 1 could not cure. This indicates that mercaptopolydimethylsiloxane acts as a UV crosslinking agent in this system, ensuring normal UV curing, increasing crosslinking density, and further enhancing tensile strength. In Comparative Example 2, the dosage of vinylalkoxypolysiloxane and mercaptopolysiloxane exceeded the specified range, resulting in neither UV curing nor moisture curing, making it impossible to measure performance data such as shrinkage rate and hardness. This indicates that the dosage of vinylalkoxypolysiloxane and mercaptopolysiloxane in this application should be within the given range; otherwise, incomplete functional group reactions will occur, leading to incomplete curing or even no curing of the adhesive. With similar viscosities, Comparative Example 3, without the addition of terminal vinylpolydimethylsiloxane, showed a shrinkage rate at least 50% higher than that in Example 3, indicating that terminal vinylpolysiloxane plays a greater role in improving the overall elongation in the formulation. Data from Examples 1-4 show that this UV moisture dual-curing sealant has a low shrinkage rate, ensuring flexibility while maintaining certain strength and adhesion performance. Different performance matching can be selected according to different application points, and it has the characteristic of being repairable. It is suitable for potting and bonding of internal microstructures in electronic products.

[0055] The embodiments described above are merely preferred embodiments of this application and are not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by anyone skilled in the art. Any simple equivalent changes and modifications made based on the scope of protection of this application and the content of the specification should be included within the scope of protection of this application.

Claims

1. A UV-moisture dual-curing silicone sealant, characterized in that, It includes the following components in parts by weight: 30-80 parts vinylalkoxy polysiloxane, 6-50 parts vinyl-terminated polydimethylsiloxane, 4-10 parts mercapto polydimethylsiloxane, 3.8-7 parts thixotropic agent, 3-6 parts crosslinking agent, 0.5-2 parts photoinitiator, and 0.1-5 parts moisture-curing catalyst.

2. The UV-moisture dual-curing silicone sealant according to claim 1, characterized in that, The structural formula of the vinylalkoxy polysiloxane is shown in formula (1): Formula (1), wherein R1 and R4 are independently selected from methoxy, ethoxy, propoxy, and vinyl, respectively; R2 is vinyl; R3 is selected from methoxy, ethoxy, and propoxy; the sum of a, b, and c is an integer from 220 to 1500, where a is an integer from 210 to 1300, b is an integer from 4 to 20, and c is an integer from 6 to 180.

3. The UV-moisture dual-curing silicone sealant according to claim 2, characterized in that, The vinyl alkoxy polysiloxane has a vinyl content of 0.10% to 0.30% by mass.

4. The UV-moisture dual-curing silicone sealant according to claim 1, characterized in that, The structural formula of the terminal vinyl polydimethylsiloxane is shown in formula (2): Equation (2), where m is an integer from 350 to 1000.

5. The UV-moisture dual-curing silicone sealant according to claim 4, characterized in that, The vinyl content in the terminal vinyl polydimethylsiloxane is 0.08% to 0.20% by mass.

6. The UV-moisture dual-curing silicone sealant according to claim 1, characterized in that, The structural formula of the mercaptopolydimethylsiloxane is shown in formula (3): Equation (3), where d is an integer from 15 to 32 and e is an integer from 100 to 365.

7. The UV-moisture dual-curing silicone sealant according to claim 6, characterized in that, The mass fraction of thiol groups in the thiol-based polydimethylsiloxane is 2% to 5.2%.

8. The UV-moisture dual-curing silicone sealant according to claim 1, characterized in that, The thixotropic agent is any one or a combination of several of the following: hydrophilic fumed silica V15, hydrophilic fumed silica T30, hydrophilic fumed silica N20, hydrophobic fumed silica AEROSIL R812S, hydrophobic fumed silica R974, and hydrophobic fumed silica R972. Or / and, the crosslinking agent is at least one selected from methyltrimethoxysilane, dimethyldimethoxysilane, vinyltrimethoxysilane, dimethyldiethoxysilane, vinyltriethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and 3-aminopropyltrimethoxysilane.

9. The UV-moisture dual-curing silicone sealant according to claim 1, characterized in that, The photoinitiator is at least one of 2-hydroxy-2-methylphenylacetone, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, and ethyl 2,4,6-trimethylbenzoylphenylphosphonate. Or / and, the moisture curing catalyst is selected from organotin catalysts and titanium compound catalysts.

10. The method for preparing the UV-moisture dual-curing silicone sealant according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Add the vinylalkoxy polysiloxane, terminal vinyl polydimethylsiloxane and thixotropic agent to the reaction vessel, mix evenly, and degas under vacuum. S2. Cool the material obtained in step S1 to a temperature <40°C, add the mercaptopolydimethylsiloxane, crosslinking agent, photoinitiator and moisture curing catalyst, and degas under vacuum to obtain the UV-moisture dual-curing silicone sealant.

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