Preparation method and application of high-strength polyurethane structural adhesive disassembled by ultraviolet light

Abstract

The application relates to the technical field of detachable adhesives, and discloses a preparation method and application of a high-strength polyurethane structural adhesive which can be detached under ultraviolet light. First, an NCO-terminated polyurethane resin containing an aromatic disulfide bond is synthesized as component A, a mixture of multifunctional polyols, a coupling agent and a water-removing agent is used as component B, the components A and B are mixed in a certain proportion, a polyaddition polymerization reaction occurs, and the polyurethane adhesive is obtained. The prepared polyurethane adhesive has excellent mechanical strength and bonding strength and can be induced to debond under ultraviolet light. In the application, the aromatic disulfide bond structure is introduced into the polyurethane molecular main chain, the characteristics that the aromatic disulfide bond can be activated to reversibly split and recombine under ultraviolet light are utilized, the adhesive is endowed with the light-induced debonding function, the contradiction that high bonding strength and mild and reversible detachment cannot be simultaneously achieved is solved, and the types of the light-induced debonding adhesive are enriched.

Description

Technical Field

[0001] This invention relates to the field of removable adhesives, specifically to a method for preparing a high-strength polyurethane structural adhesive that can be disassembled by ultraviolet light and its application. Background Technology

[0002] Structural adhesives are a class of high-performance adhesive materials used for bonding load-bearing structural components. They typically have an lap shear strength exceeding 7 MPa and are generally used to create strong and reliable bonds. To achieve high cohesive strength and high interfacial bond strength, structural adhesives are often highly covalently cross-linked thermosetting resins, such as polyurethane adhesives, epoxy resin adhesives, and acrylic adhesives. However, this also means that once the resin cures into a glue, the adhesive is difficult to break down or remove, resulting in an irreversible bond. Due to their difficulty in degradation or recycling at the end of their service life, irreversible structural adhesives contribute to over 237 million tons of material waste annually. Therefore, developing adhesives that combine high bond strength with on-demand disassembly is crucial for resource reuse and preventing environmental pollution.

[0003] In recent years, smart switchable adhesives with stimulus-responsive functions have gradually attracted the attention of researchers, capable of reversibly switching between adhesion and debonding under specific external stimuli (such as heat, light, electric fields, or magnetic fields). Among these, photo-induced debonding has advantages such as high conversion ratio, good spatial selectivity, and high controllability compared to other stimulation methods, and has been widely used in semiconductor manufacturing, optical displays, tissue engineering, and new energy battery processing. However, photo-induced removable adhesives rely heavily on specific photosensitive groups, such as the photoisomerization reaction of spiropyran groups and azophenyl groups, and the dimerization reaction of anthracene groups, which greatly reduces the designability and universality of the molecular structure. Furthermore, the preparation is complex and the synthesis is difficult, limiting the further application of photo-induced removable adhesives. Patent CN119101486A discloses a photodegradable room-temperature curing two-component polyurethane adhesive and its preparation method. The components contain photodegradable oxime units, which can be degraded by ultraviolet irradiation, thereby reducing the adhesive strength and ultimately achieving substrate debonding. Although this method improves the designability and versatility of the molecular structure of photo-adhesive release adhesives, its bond strength is too low (below 2.25 MPa) to be used as a structural adhesive.

[0004] Therefore, it is urgent to develop a novel photo-induced debonding structure that can be disassembled under ultraviolet light. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a method for preparing a high-strength polyurethane structural adhesive that can be delaminated by ultraviolet light and its application. The ultraviolet-light-delaminated polyurethane adhesive provided by this invention possesses both excellent mechanical and adhesive strength, and can be delaminated by ultraviolet light, making it applicable to the structural bonding and efficient disassembly of transparent substrates such as acrylic sheets and polycarbonate. This invention introduces aromatic disulfide bonds into the polyurethane molecular backbone, leveraging the property that these bonds can be activated by ultraviolet light to undergo reversible homolytic cleavage and recombination, thus endowing the adhesive with photo-induced delamination functionality. This solves the contradiction between high adhesive strength and gentle reversible delamination, and also enriches the variety of photo-induced delamination adhesives.

[0006] The specific technical solution of the present invention is as follows: A method for preparing a high-strength polyurethane structural adhesive that can be disassembled by ultraviolet light includes the following steps: (1) Synthesis of NCO-terminated polyurethane resin containing aromatic disulfide bonds, which is used as component A; (2) Mix polyols with a functionality of ≥3, coupling agents and dehydrating agents uniformly in an organic solvent and use them as component B for later use; (3) Mix components A and B in a certain proportion to obtain a polyurethane adhesive that can be disassembled by ultraviolet light.

[0007] Further, in step (1), the NCO-terminated polyurethane resin containing aromatic disulfide bonds is obtained by reacting diisocyanate, aromatic disulfide and hydroxyl-terminated polyol.

[0008] The diisocyanate is selected from at least one of hydrogenated diphenylmethane diisocyanate (HMDI), isophorone diisocyanate (IPDI), and hexamethylene diisocyanate (HDI).

[0009] The aromatic disulfide is selected from at least one of 4,4'-diaminodiphenyl disulfide, 2,2'-diaminodiphenyl disulfide, 4,4'-dihydroxydiphenyl disulfide, and 3,3'-dihydroxydiphenyl disulfide.

[0010] The hydroxyl-terminated polyol is selected from at least one of polyether polyol, polyester polyol, and polyolefin polyol, and has a number average molecular weight of 1000 to 10000 g / mol.

[0011] Furthermore, the polyether polyol is selected from at least one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran glycol; the polyester polyol is selected from at least one of polycaprolactone diol, polylactic acid diol, polyethylene adipate diol, and polybutylene adipate diol; and the polyolefin polyol is selected from at least one of hydroxyl-terminated polybutadiene diol and hydrogenated hydroxyl-terminated polybutadiene.

[0012] The preparation method of the NCO-terminated polyurethane resin containing aromatic disulfide bonds in step (1) is as follows: Under a nitrogen atmosphere, diisocyanate, aromatic disulfide, hydroxyl-terminated polyol and organic solvent are mixed, a catalyst is added, and a polyaddition polymerization reaction is carried out to obtain an NCO-terminated polyurethane solution containing aromatic disulfide bonds.

[0013] The catalyst is an organometallic or tertiary amine catalyst, and the amount of catalyst used is 200-600 ppm based on the total mass of the system (including solvent); further, the organometallic catalyst is selected from at least one of dibutyltin dilaurate, lead octanoate, bismuth neodecanoate, and bismuth isooctanoate, and the tertiary amine catalyst is selected from triethylenediamine.

[0014] The organic solvent is selected from at least one of dimethylformamide, acetone, dimethylacetamide, and tetrahydrofuran, and is added in an amount sufficient to dissolve each component.

[0015] The reaction temperature for the polyaddition polymerization reaction is 50–90°C, and the reaction time is 1–12 h.

[0016] The molar ratio of the diisocyanate, aromatic disulfide, and hydroxyl-terminated polyol is 1:(0.3-0.7):(0.2-0.5).

[0017] Further, in step (2), the polyol with a functionality of ≥3, the coupling agent, the dehydrating agent and the organic solvent are physically mixed, wherein the polyol with a functionality of ≥3 is selected from at least one of glycerol, trimethylolpropane and pentaerythritol.

[0018] The coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, 3-isocyanopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane.

[0019] The dehydrating agent is selected from at least one of p-toluenesulfonyl isocyanate, 3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine, and triethyl orthoformate.

[0020] The coupling agent and dehydrating agent are added at amounts of 0.5-2 wt% and 0.1-2 wt% of the total mass of component B, respectively.

[0021] The organic solvent is selected from at least one of dimethylformamide, acetone, dimethylacetamide, and tetrahydrofuran, and is added in an amount sufficient to dissolve each component.

[0022] The mixing process involves mechanical stirring at room temperature for 5-10 minutes.

[0023] Further, in step (3), the NCO / OH molar ratio of components A and B is 1:(0.9-1), wherein this NCO / OH molar ratio determines the amount of polyol with a functionality ≥3 added to component B; the mixing process is mechanical stirring at room temperature for 5-10 minutes.

[0024] The polyurethane structural adhesive prepared by the above method, which can be debonded by ultraviolet light, has excellent mechanical strength and adhesive strength (tensile strength can reach 23.9 MPa, elongation at break can reach 459%, and tensile shear strength (acrylic sheet to acrylic sheet) can reach 8.74 MPa). It can also achieve ultraviolet light-induced debonding (after irradiation under ultraviolet light (365 nm) for 10 minutes, the tensile shear strength drops to 0.96 MPa, the switching ratio can reach 9.1, and debonding can be completed).

[0025] The UV-removable polyurethane structural adhesive provided by this invention can be applied to the structural bonding and efficient disassembly of transparent substrates such as acrylic sheets and polycarbonate.

[0026] Compared with the prior art, the present invention has the following advantages: (1) By introducing a dynamic aromatic disulfide bond structure into the main chain of polyurethane molecules, the polyurethane adhesive prepared by the invention takes advantage of the characteristic that the aromatic disulfide bond can be activated by ultraviolet light to undergo reversible homolytic cleavage and recombination, and has both high bonding strength and ultraviolet light disassembly function, thus solving the contradiction that it is difficult to achieve both strong bonding and reversible disassembly. (2) A novel photo-induced de-adhesive is provided, which improves the flexibility and universality of the molecular structure design of the photo-induced de-adhesive and the preparation process is simple and easy, which can promote the application of the photo-induced de-adhesive in more fields. Attached Figure Description

[0027] Figure 1 The infrared spectrum of the NCO-terminated polyurethane resin containing aromatic disulfide bonds in Example 1 is shown. Figure 2 The 1H NMR spectrum of the NCO-terminated polyurethane resin containing aromatic disulfide bonds in Example 1 is shown. Figure 3 The tensile stress-strain curves are shown for the two-component polyurethane adhesives containing aromatic disulfide bonds in Examples 1, 2, and 3. Detailed Implementation

[0028] The present invention will be further illustrated below with reference to embodiments, which will help those skilled in the art to further understand the present invention, but will not limit the present invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the instruments and reagents used, unless otherwise specified, can be obtained through normal commercial channels.

[0029] Example 1: A method for preparing a high-strength polyurethane structural adhesive that can be disassembled by ultraviolet light, the specific steps of which are as follows: (1) In a 250 mL round-bottom flask equipped with a mechanical stirrer, a nitrogen inlet tube, a thermometer and a reflux condenser, add 11.1 g (50 mmol) of isophorone diisocyanate (IPDI), 7.44 g (30 mmol) of 4,4'-diaminodiphenyl disulfide, 11 g (11 mmol) of polytetrahydrofuran diol (molecular weight 1000 g / mol) and 25 mL of dimethylformamide. Then add 0.02 g (367 ppm) of dibutyltin dilaurate (DBTDL) catalyst to the system, keep the temperature inside the flask at 60 °C and continue the reaction for 6 h to obtain a polyurethane solution with NCO-terminated aromatic disulfide bonds, which is used as component A. (2) Add 0.804 g (6 mmol) of trimethylolpropane, 0.1 g of γ-aminopropyltriethoxysilane and 0.1 g of p-toluenesulfonyl isocyanate to 8 mL of dimethylformamide, stir mechanically for 10 min at room temperature, mix evenly, and use as component B for later use; (3) Finally, mix component A and component B at a mass ratio of 13:2 (i.e., the NCO / OH molar ratio of components A and B is 1.05) and mechanically stir for 10 min at room temperature to obtain a high-strength polyurethane structural adhesive that can be disassembled by ultraviolet light.

[0030] Example 2: A method for preparing a high-strength polyurethane structural adhesive that can be disassembled by ultraviolet light, the specific steps of which are as follows: (1) In a 250 mL round-bottom flask equipped with a mechanical stirrer, a nitrogen inlet tube, a thermometer and a reflux condenser, add 13.1 g (50 mmol) of hydrogenated diphenylmethane diisocyanate (HMDI), 8.68 g (35 mmol) of 2,2'-diaminodiphenyl disulfide, 10 g (10 mmol) of polycaprolactone diol (molecular weight 1000 g / mol) and 25 mL of acetone. Then add 0.02 g (352 ppm) of bismuth neodecanoate catalyst to the system, keep the temperature inside the flask at 60 °C and continue the reaction for 6 h to obtain a polyurethane solution with NCO-terminated aromatic disulfide bonds, which is used as component A. (2) Add 0.34 g (2.5 mmol) pentaerythritol, 0.05 g γ-aminopropyltrimethoxysilane and 0.05 g 3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine to 8 mL of acetone, stir mechanically for 10 min at room temperature, mix evenly, and use as component B for later use; (3) Finally, mix component A and component B at a mass ratio of 7:1 (i.e., the NCO / OH molar ratio of components A and B is 1.028) and mechanically stir for 10 min at room temperature to obtain a two-component polyurethane adhesive.

[0031] Example 3: A method for preparing a high-strength polyurethane structural adhesive that can be disassembled by ultraviolet light, the specific steps of which are as follows: (1) In a 250 mL round-bottom flask equipped with a mechanical stirrer, a nitrogen inlet tube, a thermometer and a reflux condenser, add 8.4 g (50 mmol) hexamethylene diisocyanate (HDI), 3.75 g (15 mmol) 4,4'-dihydroxydiphenyl disulfide, 25 g (25 mmol) polybutylene adipate diol (molecular weight 1000 g / mol) and 25 mL tetrahydrofuran. Then add 0.02 g (i.e. 322 ppm) bismuth isooctanoate catalyst to the system, keep the temperature inside the flask at 60 °C and continue the reaction for 6 h to obtain a polyurethane solution with NCO-terminated aromatic disulfide bonds, which is used as component A for later use. (2) Add 0.614 g (6.67 mmol) glycerol, 0.15 g 3-isocyanate-propyltrimethoxysilane and 0.15 g p-methylbenzenesulfonyl isocyanate to 8 mL tetrahydrofuran, stir mechanically for 10 min at room temperature, mix evenly, and use as component B for later use. (3) Finally, mix component A and component B at a mass ratio of 15:2 (i.e., the NCO / OH molar ratio of components A and B is 1.04) and mechanically stir for 10 min at room temperature to obtain a two-component polyurethane adhesive.

[0032] Comparative Example 1: A method for preparing a polyurethane adhesive without aromatic disulfide bonds, the specific steps of which are as follows: (1) In a 250 mL round-bottom flask equipped with a mechanical stirrer, a nitrogen inlet tube, a thermometer and a reflux condenser, add 11.1 g (50 mmol) isophorone diisocyanate (IPDI), 2.7 g (30 mmol) 1,4-butanediol, 11 g (11 mmol) polytetrahydrofurandiol (molecular weight 1000) and 25 mL dimethylformamide. Then add 0.02 g of catalyst dibutyltin dilaurate (DBTDL) to the system, keep the temperature inside the flask at 60 °C and continue the reaction for 2 h to obtain an NCO-terminated polyurethane solution without aromatic disulfide bonds, which is used as component A for later use. (2) Add 0.804 g (6 mmol) of trimethylolpropane, 0.1 g of γ-aminopropyltriethoxysilane and 0.1 g of p-toluenesulfonyl isocyanate to 8 mL of dimethylformamide, stir mechanically for 10 min at room temperature, mix evenly, and use as component B for later use; (3) Finally, mix component A and component B at a mass ratio of 7:1 and mechanically stir at room temperature for 10 min to obtain a polyurethane adhesive without aromatic disulfide bonds.

[0033] Figure 1 The image shown is the infrared spectrum of the NCO-terminated polyurethane resin containing aromatic disulfide bonds in Example 1 of this invention, where 2265 cm⁻¹... -1 The infrared characteristic absorption peak corresponding to the NCO group indicates the successful synthesis of the resin.

[0034] Figure 2 The image shows the 1H NMR spectrum of the NCO-terminated polyurethane resin containing aromatic disulfide bonds in Example 1 of this invention. The resonance absorption peaks of all hydrogen-containing groups can be found in the spectrum, indicating the successful synthesis of the resin.

[0035] Figure 3 The figures shown are tensile stress-strain curves of the two-component polyurethane adhesives containing aromatic disulfide bonds in Examples 1, 2, and 3 of this invention. The adhesive prepared in Example 1 has a tensile strength of 23.9 MPa and an elongation at break of 459%, exhibiting excellent tensile mechanical properties. Therefore, Example 1, with the best mechanical properties, was selected for further adhesive performance testing.

[0036] The performance of the polyurethane adhesives prepared in Example 1 and the comparative example of this invention was tested. The specific testing items and standards involved are as follows: Infrared spectroscopy: Sample preparation and testing were carried out in accordance with the requirements of GB / T 6040-2019.

[0037] 1H NMR: Sample preparation and testing were performed in accordance with JY / T 0578-2020, using deuterated DMSO as the deuteration reagent.

[0038] Tensile strength: Tensile strength is tested under standard conditions (25℃, 50%RH), and the specimens are prepared and tested in accordance with the requirements of GB / T 528-2009.

[0039] Tensile shear strength: Acrylic sheet was used as the bonding substrate, and the specimens were prepared and tested in accordance with GB / T 7124-2008. The switching ratio = initial shear strength / tensile shear strength after ultraviolet irradiation.

[0040] The tensile shear strength test data of the polyurethane adhesives prepared in Example 1 and Comparative Example 1 are shown in Table 1.

[0041] Table 1. Tensile shear strength test data of the polyurethane adhesives prepared in Example 1 and Comparative Example 1. .

[0042] As can be seen from the data in Table 1, after being irradiated with ultraviolet light (365 nm) for 10 min, the tensile shear strength of Example 1 containing aromatic disulfide bonds dropped significantly to 0.96 MPa, with a switching ratio as high as 9.1; while the tensile shear strength of Comparative Example 1 without aromatic disulfide bonds remained almost unchanged after being irradiated with ultraviolet light (365 nm) for 10 min. This comparison shows that aromatic disulfide bonds have excellent photo-triggered debonding function.

[0043] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above. Those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of the present invention.

Claims

1. A method for preparing a high-strength polyurethane structural adhesive that can be disassembled under ultraviolet light, characterized in that, Includes the following steps: (1) Synthesis of NCO-terminated polyurethane resin containing aromatic disulfide bonds, which is used as component A; (2) Mix polyols with a functionality of ≥3, coupling agents and dehydrating agents uniformly in an organic solvent and use them as component B for later use; (3) Mix components A and B in a certain proportion to obtain a polyurethane adhesive that can be disassembled by ultraviolet light.

2. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 1, characterized in that, The preparation method of the NCO-terminated polyurethane resin containing aromatic disulfide bonds in step (1) is as follows: Under a nitrogen atmosphere, diisocyanate, aromatic disulfide, hydroxyl-terminated polyol and organic solvent are mixed, a catalyst is added, and a polyaddition polymerization reaction is carried out to obtain an NCO-terminated polyurethane solution containing aromatic disulfide bonds.

3. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 2, characterized in that, The diisocyanate is selected from at least one of hydrogenated diphenylmethane diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; The aromatic disulfide is selected from at least one of 4,4'-diaminodiphenyl disulfide, 2,2'-diaminodiphenyl disulfide, 4,4'-dihydroxydiphenyl disulfide, and 3,3'-dihydroxydiphenyl disulfide. The hydroxyl-terminated polyol is selected from at least one of polyether polyol, polyester polyol, and polyolefin polyol, and has a number average molecular weight of 1000 to 10000 g / mol. The catalyst is an organometallic or tertiary amine catalyst, and the dosage is 200-600 ppm; the organometallic catalyst is selected from at least one of dibutyltin dilaurate, lead octanoate, bismuth neodecanoate, and bismuth isooctanoate, and the tertiary amine catalyst is selected from triethylenediamine; The organic solvent is selected from at least one of dimethylformamide, acetone, dimethylacetamide, and tetrahydrofuran.

4. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 3, characterized in that, The polyether polyol is selected from at least one of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran glycol; the polyester polyol is selected from at least one of polycaprolactone diol, polylactic acid diol, polyethylene adipate diol, and polybutylene adipate diol; and the polyolefin polyol is selected from at least one of hydroxyl-terminated polybutadiene diol and hydrogenated hydroxyl-terminated polybutadiene.

5. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 2, characterized in that, The reaction temperature for the polyaddition polymerization reaction is 50–90°C, and the reaction time is 1–12 h.

6. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 2, characterized in that, The molar ratio of the diisocyanate, aromatic disulfide, and hydroxyl-terminated polyol is 1:0.3-0.7:0.2-0.

5.

7. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 1, characterized in that, In step (2), the polyol with a functionality of ≥3 is selected from at least one of glycerol, trimethylolpropane, and pentaerythritol; The coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, 3-isocyanopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, and γ-mercaptopropyltriethoxysilane. The dehydrating agent is selected from at least one of p-toluenesulfonyl isocyanate, 3-ethyl-2-methyl-2-(3-methylbutyl)-1,3-oxazolidine, and triethyl orthoformate; The organic solvent is selected from at least one of dimethylformamide, acetone, dimethylacetamide, and tetrahydrofuran.

8. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 1, characterized in that, In step (2), the amount of coupling agent and dehydrating agent added is 0.5-2 wt% and 0.1-2 wt% of the total mass of component B, respectively; the mixing process is mechanical stirring at room temperature for 5-10 minutes.

9. The method for preparing the UV-removable high-strength polyurethane structural adhesive according to claim 1, characterized in that, In step (3), the NCO / OH molar ratio of components A and B is 1:0.9-1, wherein this NCO / OH molar ratio determines the amount of polyol with a functionality ≥3 added to component B; the mixing process is mechanical stirring at room temperature for 5-10 minutes.

10. The application of the UV-removable polyurethane structural adhesive prepared according to any one of claims 1-9, characterized in that, It is used for structural bonding and efficient disassembly of transparent substrates such as acrylic sheets and polycarbonate.

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