UV-thermal dual-curing adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of adhesives, and particularly relates to a UV-thermal dual-curing adhesive and a preparation method thereof, and the UV-thermal dual-curing adhesive comprises the following components: an acrylate monomer, epoxy resin, epoxy modified acrylic resin, a photoinitiator, a latent curing agent, ester-bond-free polymercaptan, a stabilizer, a silane coupling agent, a thixotropic agent and a filler. According to the preparation method of the ester-bond-free polythiol, the ester-bond-free polythiol is introduced into the adhesive, and the prepared UV-heat dual-curing adhesive has high toughness, high bonding strength and excellent heat and humidity resistance and has wide application prospects in bonding of 3C electronic products, wearable products and various camera modules.

Description

Technical Field

[0001] This invention specifically relates to a UV-thermal dual-curing adhesive and its preparation method, belonging to the field of adhesive technology. Background Technology

[0002] With the continuous upgrading and updating of various electronic and electrical products such as smartphones, smartwatches, and electric vehicles, the requirements for adhesives used in these products are also constantly increasing. Ultraviolet (UV) curing, due to its high efficiency, low production cost, and environmental friendliness, is widely used in 3C electronics and industrial production. However, UV curing technology itself also has certain drawbacks. For example, in some complex products with shadowed or opaque areas, thick adhesives, or colored coatings, UV light cannot completely penetrate the adhesive, limiting its application. To overcome these shortcomings, various dual-curing systems have emerged in recent years, such as UV-moisture curing and UV-thermal curing. Dual-curing technology combines UV curing with other curing methods, where the crosslinking and polymerization reactions are completed through two independent stages with different reaction principles.

[0003] Currently, the UV-thermal dual-curing system is the most studied. Its curing process is completed in two stages. The first stage is to achieve the purpose of initial positioning through ultraviolet light irradiation reaction. The second stage is to further complete the curing reaction through heating. On the one hand, it can cure the unirradiated parts, and on the other hand, it can further improve the bonding strength.

[0004] Patent application CN119463713A discloses a UV-thermal dual-curing adhesive and its preparation method. By introducing epoxy-modified N-substituted maleimide resin into the UV-thermal dual-curing adhesive, the adhesive's bonding strength is improved, while also exhibiting good flexibility and resistance to damp heat. Part of the research on UV-thermal dual-curing adhesives focuses on acrylates as the main component, with thiols being a crucial element. This system features fast curing speed, high hardness, and good adhesion. However, with increasingly demanding performance requirements for electronic products, the original performance is no longer sufficient. For example, in camera module structures, manufacturers require adhesives with high bonding strength to difficult-to-bond substrates such as LCP, and minimal strength degradation under high-reliability verification conditions such as high temperature and high humidity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a UV-thermal dual-curing adhesive and its preparation method. The preparation method uses the ester-free thiol provided by this invention to prepare a UV-thermal dual-curing adhesive with high toughness, high bonding strength, and excellent resistance to damp heat, which has broad application prospects in the bonding of 3C electronic products, wearable products, and various camera modules.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a UV-thermal dual-curing adhesive, wherein, by weight, the adhesive comprises:

[0007] 10-25 parts of acrylate monomer;

[0008] 5-10 parts epoxy resin;

[0009] 10-15 parts of epoxy-modified acrylic resin;

[0010] 2-4 parts of photoinitiator;

[0011] 10-20 parts of latent curing agent;

[0012] Stabilizer 0.2 to 1 part;

[0013] 15-40 parts of ester-free polythiol;

[0014] 1-2 parts of silane coupling agent;

[0015] Thixotropic agent 1-5 parts;

[0016] 15-30 parts of filler.

[0017] Furthermore, the mass ratio of acrylate monomer, epoxy-modified acrylic resin and ester-free polythiol is 1:(0.5-1):(1.5-3).

[0018] Furthermore, the acrylate monomer is at least one of monofunctional acrylate monomers and difunctional acrylate monomers; preferably at least one of isobornyl acrylate, tetrahydrofuran acrylate, lauryl acrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tricyclodecanediethanol diacrylate.

[0019] Furthermore, the epoxy resin is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin.

[0020] Furthermore, the epoxy-modified acrylic resin is at least one of a difunctional resin and a trifunctional resin; preferably at least one of Changxing DR-U084 and 6270.

[0021] Furthermore, the photoinitiator is at least one of photoinitiator 184, photoinitiator 651, and photoinitiator TPO-L;

[0022] Furthermore, the latent curing agent is at least one of imidazole curing agents, tertiary amine adducts, and modified amine curing agents; preferably at least one of Ajinomoto PN-23, PN-23J, MY-24, MY-25, Asahi Kasei HXA3922HP, HXA3932HP, and ADEKA EH-5011S, EH-5031S.

[0023] Furthermore, the silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane and γ-methacryloyloxypropyltrimethoxysilane.

[0024] Furthermore, the thixotropic agent is fumed silica.

[0025] Furthermore, the filler is spherical silica.

[0026] Furthermore, the preparation method of the ester-free polythiol includes the following steps:

[0027] S1. Under inert gas, N-(6-acetylthiohexyl)maleimide and 2,3-dithio(2-mercapto)-1-propanethiol undergo a click reaction in the presence of triethylamine to generate an intermediate, which is a polysulfide-crosslinked maleimide derivative.

[0028] S2. Slowly add concentrated hydrochloric acid to the intermediate, and after the reaction, the target product, ester-free polythiol, is obtained.

[0029] Furthermore, in step S1, the molar ratio of 2,3-dithio(2-mercapto)-1-propanethiol, N-(6-acetylthiohexyl)maleimide and triethylamine is 1:(2.5-2.8):(2-2.5).

[0030] Furthermore, in step S2, the molar ratio of the intermediate to concentrated hydrochloric acid is 1:(9-15), and the concentration of the concentrated hydrochloric acid is 12 mol / L.

[0031] Furthermore, in step S1, the reaction is carried out at room temperature for 6–12 hours.

[0032] Furthermore, in step S2, the reaction is carried out at 55-65°C for 6-12 hours.

[0033] This invention also discloses a method for preparing a UV-thermal dual-curing adhesive, the preparation method comprising the following steps:

[0034] (1) Under yellow light throughout the process, acrylate monomers, photoinitiators and epoxy-modified acrylic resins are added to a stirrer and stirred until the photoinitiator is completely dissolved.

[0035] (2) Under yellow light throughout the process, add epoxy resin, stabilizer, ester-free polythiol and silane coupling agent and mix evenly.

[0036] (3) Add filler and thixotropic agent under yellow light throughout the process and mix them evenly;

[0037] (4) Add latent curing agent under yellow light throughout the process and mix evenly to obtain UV-thermal dual-curing adhesive.

[0038] Furthermore, during the preparation of the adhesive, all materials are mixed evenly in a high-speed planetary mixer. In step (1), the rotation speed is set to 400 r / min and the mixture is stirred for 1 hour.

[0039] Furthermore, in step (2), the rotation speed is set to 400 r / min, and the stirring time is 1 h.

[0040] Furthermore, in step (3), the rotation speed is set to 400 r / min, and the vacuum degree is kept not lower than -0.08 MPa for 1 hour.

[0041] Furthermore, in step (4), the rotation speed is set to 400 r / min, the stirring time is 1 h, and the system temperature is controlled to not exceed 30℃.

[0042] The beneficial effects of this invention are:

[0043] (1) This invention provides a UV-thermal dual-curing adhesive and its preparation method. The ester-free polythiol prepared in this invention is introduced into the UV-thermal dual-curing adhesive. Since there are no ester bonds in the polythiol structure, the adhesive can avoid the strength reduction problem caused by the hydrolysis and breakage of ester bonds under high temperature and high humidity conditions. The introduction of maleimide structure in the ester-free polythiol improves the adhesion strength of the adhesive to difficult-to-bond substrates such as LCP. The introduction of long alkyl chain segments in the ester-free polythiol improves the flexibility of the adhesive.

[0044] (2) This invention provides a UV-thermal dual-curing adhesive and its preparation method. Through the addition reaction of double bonds and mercapto groups and the ring-opening reaction of epoxy groups and thiols, acrylate monomers, epoxy-modified acrylic resins and ester-free polythiols react to form a cross-linking network to produce a synergistic effect, thereby improving the overall performance of the adhesive and giving it high toughness, high bonding strength and excellent resistance to damp heat. Detailed Implementation

[0045] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0047] A UV-thermal dual-curing adhesive, comprising, by weight:

[0048] Acrylic ester monomer 10-25 parts; epoxy resin 5-10 parts; epoxy-modified acrylic resin 10-15 parts; photoinitiator 2-4 parts; latent curing agent 10-20 parts; stabilizer 0.2-1 part; ester-free polythiol 15-40 parts; silane coupling agent 1-2 parts; thixotropic agent 1-5 parts; filler 15-30 parts.

[0049] Specifically, the mass ratio of acrylate monomer, epoxy-modified acrylic resin and ester-free polythiol is 1:(0.5-1):(1.5-3).

[0050] Specifically, the acrylate monomer is at least one of monofunctional acrylate monomers and difunctional acrylate monomers; preferably at least one of isobornyl acrylate, tetrahydrofuran acrylate, lauryl acrylate, 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and tricyclodecanediethanol diacrylate.

[0051] Specifically, the epoxy resin is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin.

[0052] Specifically, the epoxy-modified acrylic resin is at least one of a difunctional resin and a trifunctional resin; preferably, it is at least one of Changxing DR-U084 and 6270.

[0053] Specifically, the photoinitiator is at least one of photoinitiator 184, photoinitiator 651, and photoinitiator TPO-L.

[0054] Specifically, the latent curing agent is at least one of imidazole curing agents, tertiary amine adducts, and modified amine curing agents; preferably at least one of Ajinomoto PN-23, PN-23J, MY-24, MY-25, Asahi Kasei HXA3922HP, HXA3932HP, ADEKAEH-5011S, and EH-5031S.

[0055] Specifically, the silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.

[0056] Specifically, the thixotropic agent is fumed silica.

[0057] Specifically, the filler is spherical silica.

[0058] Specifically, the preparation method of the ester-free polythiol, in this embodiment of the invention, includes the following steps:

[0059] S1, maleimide reacts with furan to form intermediate 1, which is 7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide;

[0060] Under S2 and inert gas conditions, intermediate 1 undergoes an alkylation reaction with 1,6-dibromohexane to generate intermediate 2, which is N-(6-bromohexyl)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide;

[0061] S3 and intermediate 2 undergo an affinity substitution reaction with potassium thioacetate to generate intermediate 3, which is N-(6-acetylthiohexyl)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide;

[0062] S4 and intermediate 3 react under reflux in toluene solution to generate intermediate 4, which is N-(6-acetylthiohexyl)maleimide;

[0063] S5. Under inert gas, intermediate 4 reacts with 2,3-dithio(2-mercapto)-1-propanethiol in the presence of triethylamine to generate intermediate 5, which is a polysulfide-crosslinked maleimide derivative.

[0064] S6. Add concentrated hydrochloric acid slowly to intermediate 5. After the reaction, the target product, ester-free polythiol, is obtained.

[0065] Synthesis of S1,7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide:

[0066] Specifically, in step S1, the molar ratio of maleimide to furan is 1:(2-2.5); the reaction is carried out at 90-110°C for 6-12 hours.

[0067] Specifically, in step S1, the solvent is at least one of toluene and ethyl acetate.

[0068] More specifically, in this embodiment of the invention, toluene is used as the solvent in step S1.

[0069] Specifically, the post-reaction processing procedure in step S1 of this embodiment of the invention is as follows:

[0070] After the reaction was completed, the reaction system was cooled to room temperature and filtered to obtain a white powder, which is intermediate 1.

[0071] Synthesis of S2, N-(6-bromohexyl)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide:

[0072] Specifically, in step S2, the molar ratio of intermediate 1: base: 1,6-dibromohexane is 1:(1.5~2):(1.5~2); the reaction is carried out at 50~60℃ for 12~24h; the solvent is a polar aprotic solvent, preferably at least one of DMF and acetonitrile.

[0073] More specifically, in this embodiment of the invention, DMF is selected as the solvent in step S2.

[0074] Specifically, in step S2, the alkaline condition is provided by K2CO3.

[0075] Specifically, in this embodiment of the invention, the post-reaction processing procedure of step S2 is as follows:

[0076] After the reaction was completed, the reaction system was cooled to room temperature, ethyl acetate was added to dilute the reaction solution, the mixture was filtered, the filtrate was collected, and the solution was washed three times with deionized water. The organic layer was collected, dried with anhydrous sodium sulfate, filtered, and the filtrate was concentrated and filtered to obtain the filter cake, which is intermediate 2.

[0077] Synthesis of S3, N-(6-acetylthiohexyl)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide:

[0078] Specifically, in step S3, the molar ratio of intermediate 2 to potassium thioacetate is 1:(1-1.5); the reaction is carried out at 40-60°C for 6-12 hours.

[0079] Specifically, in step S3, the solvent is at least one of acetone, DMF, acetonitrile, and tetrahydrofuran, preferably acetone.

[0080] Specifically, in this embodiment of the invention, the post-reaction processing procedure in step S3 is as follows:

[0081] After the reaction was completed, the reaction system was cooled to room temperature, the reaction solution was concentrated by rotary evaporation, dissolved in chloroform, washed three times with deionized water, the organic layer was collected and dried with anhydrous sodium sulfate, then filtered, the filtrate was concentrated and filtered to obtain the filter cake, which is intermediate 3.

[0082] Synthesis of S4, N-(6-acetylthiohexyl)maleimide:

[0083] Specifically, in step S4, the reaction is carried out at 100–120°C for 6–12 hours.

[0084] Specifically, in this embodiment of the invention, the post-reaction processing in step S4 is as follows:

[0085] After the reaction was completed, the reaction system was cooled to room temperature, and the solvent toluene was removed by rotary evaporation to obtain intermediate 4.

[0086] S5. Synthesis of polysulfide-crosslinked maleimide derivatives:

[0087] Specifically, in step S5, the molar ratio of 2,3-dithio(2-mercapto)-1-propanethiol: intermediate 4: triethylamine is 1:(2.5-2.8):(2-2.5); the reaction is carried out at room temperature for 6-12 hours.

[0088] Specifically, in this embodiment of the invention, the post-reaction processing in step S5 is as follows:

[0089] After the reaction is complete, the reaction solution is washed three times with saturated sodium bicarbonate aqueous solution and distilled water, respectively. The organic layer is collected and dried with anhydrous sodium sulfate. Then, it is filtered and the filtrate is concentrated to obtain a viscous oily substance, which is intermediate 5.

[0090] S6. Synthesis of ester-free polythiols:

[0091] Specifically, in step S6, the solvent selected in this embodiment of the invention is anhydrous methanol.

[0092] Specifically, in step S6, the molar ratio of intermediate 5 to concentrated hydrochloric acid is 1:(9-15), and the concentration of the concentrated hydrochloric acid is 12 mol / L.

[0093] Specifically, in step S6, the reaction is carried out at 55-65℃ for 6-12 hours.

[0094] Specifically, in this embodiment of the invention, the post-reaction processing in step S6 is as follows:

[0095] After the reaction was completed, the reaction system was cooled to room temperature, diluted with chloroform, washed three times with saturated sodium bicarbonate solution and distilled water respectively, the organic layer was collected and dried with anhydrous sodium sulfate, then filtered, and the filtrate was concentrated to obtain a viscous oily substance, which is ester-free polythiol.

[0096] The principles involved in the preparation process of ester-free polythiols described in the embodiments of the present invention are as follows, but these principles are not limitations of the preparation principle of ester-free polythiols in the present invention.

[0097]

[0098] A method for preparing a UV-thermal dual-curing adhesive, the method comprising the following steps:

[0099] (1) Under yellow light throughout the process, weigh the acrylate monomer, photoinitiator and epoxy modified acrylic resin, put them into a high-speed planetary stirrer, set the speed to 400 r / min, stir for 1 h, and stir until the photoinitiator is completely dissolved.

[0100] (2) Under yellow light throughout the process, weigh epoxy resin, stabilizer, ester-free polythiol and silane coupling agent, put them into a high-speed planetary stirrer, set the speed to 400 r / min, stir for 1 h, and mix evenly.

[0101] (3) Under yellow light throughout the process, weigh the filler and thixotropic agent, put them into a high-speed planetary mixer, set the speed to 400 r / min, and stir for 1 hour under the condition of maintaining a vacuum degree not lower than -0.08 MPa until they are evenly mixed.

[0102] (4) Under yellow light throughout the process, weigh the latent curing agent, put it into a high-speed planetary mixer, set the speed to 400 r / min, stir for 1 hour, control the system temperature to not exceed 30℃, and mix evenly to obtain UV-thermal dual-curing adhesive.

[0103] Example 1

[0104] The preparation steps for an ester-free polythiol are as follows:

[0105] Synthesis of S1,7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide:

[0106] Add 25g of maleimide to a 500mL round-bottom flask, dissolve it in 350mL of toluene, add 38mL of furan, and stir the reaction at 95℃ for 12h. After the reaction is complete, cool the reaction system to room temperature and filter it to obtain a white powder, which is intermediate 1.

[0107] Synthesis of S2, N-(6-bromohexyl)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide:

[0108] Add 50g of intermediate 1 to a 500mL round-bottom flask and dissolve it in 250mL of DMF. Then add 83g of potassium carbonate and protect with argon gas. Under 60℃, add 18.5mL of 1,6-dibromohexane and stir for 12h. After the reaction is complete, cool to room temperature and add 250mL of ethyl acetate to dilute the reaction solution. After filtration, collect the filtrate and wash it three times with 250mL of deionized water. Collect the organic layer, dry it with anhydrous sodium sulfate, filter, concentrate the filtrate and filter to obtain the filter cake, which is intermediate 2.

[0109] Synthesis of S3, N-(6-acetylthiohexyl)-7-oxabicyclo[2.2.1]hept-5-ene-2,3-dicarboximide:

[0110] Add 29g of intermediate 2 to a 500mL round-bottom flask, add 300mL of acetone to dissolve and disperse it, and react at 50℃ for 12h. After the reaction is complete, cool the reaction system to room temperature, concentrate the reaction solution by rotary evaporation, dissolve it with 200mL of chloroform, wash it three times with 200mL of deionized water, collect the organic layer and dry it with anhydrous sodium sulfate, then filter it, concentrate the filtrate and filter it to obtain the filter cake, which is intermediate 3.

[0111] Synthesis of S4, N-(6-acetylthiohexyl)maleimide:

[0112] Add 50g of intermediate 3 to a 500mL round-bottom flask, add 200mL of toluene to dissolve it completely, and react at 110℃ for 12h. After the reaction is complete, cool the reaction system to room temperature and remove the solvent toluene by rotary evaporation to obtain intermediate 4.

[0113] S5. Synthesis of polysulfide-crosslinked maleimide derivatives:

[0114] Under inert gas, 25 g of 2,3-dithio(2-mercapto)-1-propanethiol and 66.3 g of intermediate 4 were added to a 500 mL three-necked flask. 150 mL of chloroform was added to completely dissolve the intermediate. 25.2 g of triethylamine was slowly added dropwise at room temperature, and the reaction was allowed to proceed for 12 h at room temperature. The reaction solution was washed three times with 100 mL of saturated sodium bicarbonate aqueous solution and 100 mL of distilled water, respectively. The organic layer was collected and dried with anhydrous sodium sulfate. The solution was then filtered, and the filtrate was concentrated to obtain a viscous oily substance, which was intermediate 5.

[0115] S6. Synthesis of ester-free polythiols:

[0116] Add 50g of intermediate 5 to a 500mL three-necked flask, add 200mL of anhydrous methanol to dissolve it completely, then slowly add 55mL of concentrated hydrochloric acid, and react at 65℃ for 8h. After the reaction is complete, cool the reaction system to room temperature, add 200mL of chloroform to dilute, wash three times with 200mL of saturated sodium bicarbonate solution and 200mL of distilled water respectively, collect the organic layer and dry it with anhydrous sodium sulfate, then filter it, concentrate the filtrate to obtain a viscous oily substance, and dry it to obtain the target product, ester-free polythiol.

[0117] The preparation steps of a UV-thermal dual-curing adhesive are as follows:

[0118] Under yellow light throughout the process, (1) weigh 10g of isoborneol acrylate, 10g of tricyclodecanedimethylethanol diacrylate, 1g of photoinitiator 184, 1.5g of photoinitiator 651, and 10g of epoxy-modified acrylic resin Changxing 6270, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until the photoinitiator is completely dissolved; (2) weigh 10g of bisphenol A epoxy resin, 1g of stabilizer, 20g of ester-free polythiol, and 1.5g of γ-glycidyl etheroxypropyltrimethoxysilane, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are mixed evenly; (3) weigh 20g of filler spherical silica and 4g of thixotropic agent fumed silica, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are mixed evenly under the condition that the vacuum degree is not lower than -0.08Mpa; (4) weigh the latent curing agent ADEKA. Add 18g of EH-5011S to a high-speed planetary mixer, control the system temperature to not exceed 30℃, and stir at 400r / min for 1 hour to mix evenly. The UV-thermal dual-curing adhesive is obtained after mixing evenly.

[0119] Example 2

[0120] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0121] The preparation steps of a UV-thermal dual-curing adhesive are as follows:

[0122] Under yellow light throughout the process, (1) weigh 10g of isoborneol acrylate, 10g of tricyclodecanedimethylethanol diacrylate, 1g of photoinitiator 184, 1.5g of photoinitiator 651, and 10g of epoxy-modified acrylic resin Changxing 6270, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until the photoinitiator is completely dissolved; (2) weigh 10g of bisphenol A epoxy resin, 1g of stabilizer, 30g of ester-free polythiol, and 1.5g of γ-glycidyl etheroxypropyltrimethoxysilane, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are mixed evenly; (3) weigh 20g of filler spherical silica and 4g of thixotropic agent fumed silica, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are mixed evenly under the condition of maintaining a vacuum degree not lower than -0.08Mpa; (4) weigh the latent curing agent ADEKA. Add 18g of EH-5011S to a high-speed planetary mixer, control the system temperature to not exceed 30℃, and stir at 400r / min for 1 hour to mix evenly. The UV-thermal dual-curing adhesive is obtained after mixing evenly.

[0123] Example 3

[0124] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0125] The preparation steps of a UV-thermal dual-curing adhesive are as follows:

[0126] Under yellow light throughout the process, (1) weigh 10g of isoborneol acrylate, 10g of tricyclodecanedimethylethanol diacrylate, 1g of photoinitiator 184, 1.5g of photoinitiator 651, and 10g of epoxy-modified acrylic resin Changxing 6270, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until the photoinitiator is completely dissolved; (2) weigh 10g of bisphenol A epoxy resin, 1g of stabilizer, 40g of ester-free polythiol, and 1.5g of γ-glycidyl etheroxypropyltrimethoxysilane, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are mixed evenly; (3) weigh 20g of filler spherical silica and 4g of thixotropic agent fumed silica, and put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are mixed evenly under the condition of maintaining a vacuum degree not lower than -0.08Mpa; (4) weigh the latent curing agent ADEKA. Add 18g of EH-5011S to a high-speed planetary mixer, control the system temperature to not exceed 30℃, and stir at 400r / min for 1 hour to mix evenly. The UV-thermal dual-curing adhesive is obtained after mixing evenly.

[0127] Example 4

[0128] Preparation of an ester-free polythiol: In this Example 4, the ester-free polythiol was prepared in the same manner as in Example 1, except that: in step S5, 61.2 g of N-(6-acetylthiohexyl)maleimide was added and reacted at room temperature for 8 h; in step S6, 37.5 mL of concentrated hydrochloric acid was slowly added and the reaction temperature was controlled at 55 °C for 12 h.

[0129] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0130] Example 5

[0131] The preparation of an ester-free polythiol: Example 5 uses the same method as Example 1 to prepare an ester-free polythiol, and Example 3 uses the same method as Example 1 to prepare an ester-free polythiol. The difference is that in step S5, 68.6 g of N-(6-acetylthiohexyl)maleimide is added and reacted at room temperature for 6 h; in step S6, 62.5 mL of concentrated hydrochloric acid is slowly added and the reaction temperature is controlled at 65 °C for 6 h.

[0132] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0133] Example 6

[0134] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0135] The preparation steps of a UV-thermal dual-curing adhesive are as follows:

[0136] Under yellow light throughout the process, (1) weigh 5g of isoborneol acrylate, 5g of tricyclodecanedimethylethanol diacrylate, 1g of photoinitiator 184, 1g of photoinitiator 651, and 10g of epoxy-modified acrylic resin Changxing 6270, and put them into a high-speed planetary stirrer and stir at 400r / min for 1h until the photoinitiator is completely dissolved; (2) weigh 5g of bisphenol A epoxy resin, 0.2g of stabilizer, 15g of ester-free polythiol, and 1g of γ-glycidyl etheroxypropyltrimethoxysilane, and put them into a high-speed planetary stirrer and stir at 400r / min for 1h until they are mixed evenly; (3) weigh 15g of filler spherical silica and 1g of thixotropic agent fumed silica, and put them into a high-speed planetary stirrer and stir at 400r / min for 1h until they are mixed evenly; (4) weigh the latent curing agent ADEKA. Add 18g of EH-5011S to a high-speed planetary mixer, control the system temperature to not exceed 30℃, and stir at 400r / min for 1 hour to mix evenly. The UV-thermal dual-curing adhesive is obtained after mixing evenly.

[0137] Example 7

[0138] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0139] The preparation steps of a UV-thermal dual-curing adhesive are as follows:

[0140] Under yellow light throughout the process, (1) weigh 15g of tetrahydrofuran acrylate, 10g of dipropylene glycol diacrylate, 2g of photoinitiator 184, 2g of photoinitiator TPO-L, and 15g of epoxy-modified acrylic resin Changxing DR-U084, and put them into a high-speed planetary stirrer and stir at 400r / min for 1h until the photoinitiator is completely dissolved; (2) weigh 10g of bisphenol F type epoxy resin, 1g of stabilizer, 40g of ester-free polythiol, and 2g of γ-methacryloyloxypropyltrimethoxysilane, and put them into a high-speed planetary stirrer and stir at 400r / min for 1h until they are mixed evenly; (3) weigh 30g of filler spherical silica and 5g of thixotropic agent fumed silica, and put them into a high-speed planetary stirrer and stir at 400r / min for 1h until they are mixed evenly; (4) weigh the latent curing agent ADEKA. Add 18g of EH-5011S to a high-speed planetary mixer, control the system temperature to not exceed 30℃, and stir at 400r / min for 1 hour to mix evenly. The UV-thermal dual-curing adhesive is obtained after mixing evenly.

[0141] Example 8

[0142] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0143] The preparation steps of a UV-thermal dual-curing adhesive are as follows:

[0144] Under yellow light throughout the process, (1) weigh 10g of lauryl acrylate, 10g of 1,6-hexanediol diacrylate, 1g of photoinitiator 184, 1.4g of photoinitiator TPO-L, and epoxy-modified acrylic resin Changxing 6270. 12g, put it into a high-speed planetary mixer and stir at 400r / min for 1h until the photoinitiator is completely dissolved; (2) weigh 8g of phenolic epoxy resin, 0.5g of stabilizer, 20g of ester-free polythiol and 1.5g of γ-glycidyl etheroxypropyltrimethoxysilane, put them into a high-speed planetary mixer and stir at 400r / min for 1h until they are evenly mixed; (3) weigh 20g of filler spherical silica and 3g of thixotropic fumed silica, put them into a high-speed planetary mixer, and stir at 400r / min for 1h until they are evenly mixed; (4) weigh 18g of latent curing agent ADEKA EH-5011S, put it into a high-speed planetary mixer, control the system temperature to not exceed 30℃, put it into a high-speed planetary mixer, and stir at 400r / min for 1h until they are evenly mixed. The UV-thermal dual-curing adhesive is obtained when they are evenly mixed.

[0145] Comparative Example 1

[0146] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0147] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1. The difference is that Comparative Example 1 does not add the ester-free polythiol prepared in this invention, but instead adds 10g of 2,3-dithio(2-mercapto)-1-propanethiol.

[0148] Comparative Example 2

[0149] The preparation of an ester-free polythiol follows the same steps as in Example 1.

[0150] The preparation steps of a UV-thermal dual-curing adhesive are the same as in Example 1. The difference is that Comparative Example 2 does not add the ester-free polythiol prepared in this invention, but instead adds 20g of pentaerythritol tetra-3-mercaptopropionate.

[0151] Comparative Example 3

[0152] The preparation of an ester-free polythiol: Comparative Example 3 was prepared in the same manner as in Example 1, except that 50g of N-(6-acetylthiohexyl)maleimide was added in step S5 of Comparative Example 3.

[0153] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0154] Comparative Example 4

[0155] The preparation of an ester-free polythiol: Comparative Example 3 was prepared in the same manner as in Example 1, except that 78g of N-(6-acetylthiohexyl)maleimide was added in step S5 of Comparative Example 3.

[0156] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0157] Comparative Example 5

[0158] The preparation of an ester-free polythiol: Comparative Example 5 uses the same method as Example 1 to prepare an ester-free polythiol, except that in step S6 of Comparative Example 5, 30 mL of concentrated hydrochloric acid is slowly added.

[0159] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0160] Comparative Example 6

[0161] The preparation of an ester-free polythiol: Comparative Example 6 uses the same method as Example 1 to prepare an ester-free polythiol, except that in step S6, 75 mL of concentrated hydrochloric acid is slowly added.

[0162] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0163] Comparative Example 7

[0164] Preparation of an ester-free polythiol: Comparative Example 7 prepared an ester-free polythiol using the same method as in Example 1.

[0165] The preparation steps of a UV-thermal dual-curing adhesive are the same as those in Example 1.

[0166] The difference is that in this comparative example 7, 6g of isobornyl acrylate, 6g of tricyclodecanediethanol diacrylate, 15g of epoxy-modified acrylic resin Changxing 6270, and 36g of ester-free polythiol were added; at this time, the mass ratio of acrylic monomer, epoxy-modified acrylic resin and ester-free polythiol was 1:1.25:3, which is not within the range of 1:(0.5~1):(1.5~3).

[0167] The adhesives prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods involved are as follows.

[0168] The adhesives prepared in Examples 1-8 and Comparative Examples 1-7 were applied to dumbbell-shaped molds made according to GB / T 1040, cured for 3 seconds with a 1000mw UV lamp at 365nm, and then cured in an oven at 80℃ for 60 minutes. After cooling to room temperature, the molds were tested according to GB / T 1040. For tensile shear strength testing, samples were prepared by curing with a 1000mw UV lamp at 365nm for 3 seconds, followed by curing in an oven at 80℃ for 60 minutes. Mechanical properties were tested according to standard (GB / T 2792-2014). The high-temperature and high-humidity aging conditions were 85℃ and 85%RH for 500 hours. Test data are shown in Table 1 below:

[0169] Table 1. Performance test data of the adhesives prepared in the examples and comparative examples.

[0170]

[0171] As can be seen from Table 1, the UV-thermal dual-curing adhesives prepared by the preparation method of the present invention in Examples 1-8 have excellent strength and flexibility properties, and the tensile shear strength decays little after high temperature and high humidity. In Examples 1-3, as the content of ester-free polythiol gradually increases, the content of long alkyl chains and maleimide increases, the elongation at break after curing of the adhesive increases, the tensile strength gradually increases, the tensile shear strength gradually increases, and the decay of tensile shear strength after high temperature and high humidity gradually decreases.

[0172] A comparison of the data results from Comparative Example 1 and Example 1 shows that: Comparative Example 1 directly used 2,3-dithio(2-mercapto)-1-propanethiol. Due to its small molecular weight and high thiol content, the amount added was relatively small. The elongation at break of the adhesive prepared by Comparative Example 1 was significantly reduced, reaching a very low value; both tensile strength and shear tensile strength were lower than those of the adhesive prepared in Example 1, and the shear strength decayed less after high-temperature and high-humidity aging. This is because: in Comparative Example 1, due to its shorter molecular chain and lack of maleimide structure, the prepared sample exhibited poor flexibility and shear strength, but due to the absence of ester bonds, the shear strength decayed less after aging.

[0173] A comparison of the data results from Comparative Example 2 and Example 1 shows that: Comparative Example 2 used commercially available conventional tetrafunctional thiol pentaerythritol tetra-3-mercaptopropionate, which had a good elongation at break, but its tensile strength and tensile shear strength were both low, and it also showed a significant decrease after high-temperature and high-humidity aging. This is because: each molecule of pentaerythritol tetra-3-mercaptopropionate contains four thiol functional groups, giving it a high degree of cross-linking, which prevents a significant decrease in tensile strength and tensile shear strength; however, after high-temperature and high-humidity aging, its ester bond structure causes a significant decrease in tensile shear strength.

[0174] A comparison of the data results from Comparative Example 3 and Example 1 shows that in Comparative Example 3, when the amount of N-(6-acetylthiohexyl)maleimide added in step S5 during the preparation of ester-free polythiol was low, the molar ratio of 2,3-dithio(2-mercapto)-1-propanethiol, N-(6-acetylthiohexyl)maleimide, and triethylamine was outside the range set by this invention. Consequently, the resulting UV-thermal dual-curing adhesive exhibited lower elongation at break, lower tensile strength, and reduced tensile shear strength, although the decrease in tensile shear strength after high temperature and humidity was not significant. This is because insufficient N-(6-acetylthiohexyl)maleimide leads to incomplete thiol reaction in step S4, resulting in a reduced number of maleimide rings in the final product, thus causing lower elongation at break, tensile strength, and tensile shear strength.

[0175] A comparison of the data results from Comparative Example 4 and Example 1 shows that in Comparative Example 4, when an excess of N-(6-acetylthiohexyl)maleimide was added in step S5 during the preparation of ester-free polythiol, the resulting UV-thermal dual-curing adhesive exhibited a lower elongation at break, higher tensile strength, and lower tensile shear strength. This is because when N-(6-acetylthiohexyl)maleimide is in excess compared to 2,3-dithio(2-mercapto)-1-propanethiol, the purity of the prepared ester-free polythiol decreases, introducing independent maleimide rings into the product. Since the UV-thermal dual-curing adhesive in Comparative Example 4 contains more maleimide rings than that in Example 1, the tensile strength is higher and the elongation at break is lower.

[0176] A comparison of the data from Comparative Example 5 and Example 1 shows that in Comparative Example 5, when less concentrated hydrochloric acid was added in step S6 during the preparation of ester-free polythiol, the elongation at break was higher, but the tensile strength and tensile shear strength decreased, and the high-temperature and high-humidity aging degradation of the tensile shear strength did not change significantly. This is because the less concentrated hydrochloric acid resulted in incomplete deprotection in the final step of the preparation of ester-free polythiol, leading to a decrease in the thiol content and the degree of crosslinking, but the number of maleimide rings did not decrease.

[0177] A comparison of the data results from Comparative Example 6 and Example 1 shows that in Comparative Example 5, when a larger amount of concentrated hydrochloric acid was added in step S6 during the preparation of ester-free polythiol, the tensile strength and tensile shear strength decreased. This is because the larger amount of concentrated hydrochloric acid caused some maleimide rings to open in the final step of the preparation of ester-free polythiol, thus affecting the strength properties of the UV-thermal dual-curing adhesive.

[0178] A comparison of the data results from Comparative Example 7 and Example 1 shows that the adhesive prepared by the components in Comparative Example 8 according to the mass proportions of the present invention exhibits less degradation after high-temperature and high-humidity aging. However, compared to Example 1, its elongation at break, tensile strength, and tensile shear strength all show a significant decrease. This indicates that when the mass ratio of acrylate monomer, epoxy-modified acrylic resin, and ester-free polythiol is 1:1.25:3, the ratio is not within the range of 1:(0.5-1):(1.5-3). Excessive addition of thiol leads to incomplete reaction. While the resulting adhesive shows good resistance to humid heat aging under high-temperature and high-humidity conditions, other properties decline, and the overall performance of the material is inferior to the adhesive obtained when the mass ratio of acrylate monomer, epoxy-modified acrylic resin, and ester-free polythiol is controlled within the range of 1:(0.5-1):(1.5-3).

[0179] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0180] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A UV-thermal dual-curing adhesive, characterized in that, The adhesive comprises, by weight parts: 10-25 parts of acrylate monomer; 5-10 parts epoxy resin; 10-15 parts of epoxy-modified acrylic resin; 2-4 parts of photoinitiator; 10-20 parts of latent curing agent; Stabilizer 0.2 to 1 part; 15-40 parts of ester-free polythiol; 1-2 parts of silane coupling agent; Thixotropic agent 1-5 parts; 15-30 parts of filler.

2. The UV-thermal dual-curing adhesive according to claim 1, characterized in that, The mass ratio of acrylate monomer, epoxy-modified acrylic resin and ester-free polythiol is 1:(0.5-1):(1.5-3).

3. The UV-thermal dual-curing adhesive according to claim 1, characterized in that, The acrylate monomer is at least one of monofunctional acrylate monomer and difunctional acrylate monomer; The epoxy resin is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and phenolic epoxy resin.

4. The UV-thermal dual-curing adhesive according to claim 1, characterized in that, The epoxy-modified acrylic resin is at least one of a difunctional resin and a trifunctional resin; The photoinitiator is at least one of photoinitiator 184, photoinitiator 651, and photoinitiator TPO-L; The latent curing agent is at least one of imidazole curing agents, tertiary amine adducts, and modified amine curing agents.

5. The UV-thermal dual-curing adhesive according to claim 1, characterized in that, The silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane; The thixotropic agent is fumed silica; The filler is spherical silica.

6. The UV-thermal dual-curing adhesive according to any one of claims 1-5, characterized in that, The preparation method of the ester-free polythiol includes the following steps: S1. Under inert gas, N-(6-acetylthiohexyl)maleimide and 2,3-dithio(2-mercapto)-1-propanethiol undergo a click reaction in the presence of triethylamine to generate an intermediate, which is a polysulfide-crosslinked maleimide derivative. S2. Slowly add concentrated hydrochloric acid to the intermediate, and after the reaction, the target product, ester-free polythiol, is obtained.

7. The UV-thermal dual-curing adhesive according to claim 6, characterized in that, In step S1, the molar ratio of 2,3-dithio(2-mercapto)-1-propanethiol, N-(6-acetylthiohexyl)maleimide and triethylamine is 1:(2.5-2.8):(2-2.5).

8. The UV-thermal dual-curing adhesive according to claim 6, characterized in that, In step S2, the molar ratio of the intermediate to concentrated hydrochloric acid is 1:(9-15).

9. The UV-thermal dual-curing adhesive according to claim 6, characterized in that, In step S1, the reaction is carried out at room temperature for 6–12 hours; in step S2, the reaction is carried out at 55–65°C for 6–12 hours.

10. A method for preparing a UV-thermal dual-curing adhesive according to any one of claims 1-9, characterized in that, The preparation method includes the following steps: (1) Under yellow light throughout the process, acrylate monomers, photoinitiators and epoxy-modified acrylic resins are added to a stirrer and stirred until the photoinitiator is completely dissolved. (2) Under yellow light throughout the process, add epoxy resin, stabilizer, ester-free polythiol and silane coupling agent and mix evenly. (3) Add filler and thixotropic agent under yellow light throughout the process and mix them evenly; (4) Add latent curing agent under yellow light throughout the process and mix evenly to obtain UV-thermal dual-curing adhesive.

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