Preparation method of silicon-based hot melt adhesive

Abstract

The invention provides a preparation method of a silicon-based hot melt adhesive, which comprises the following steps: reacting dihydroxyl-terminated polyether A, polysiloxane B and isophorone diisocyanate under the protection of inert gas, and then adding a carboxyl chain extender C for chain extension to prepare a silicon-based block polymer of which the main chain contains a polysiloxane-polyether chain segment and the side chain contains carboxyl. The polymer does not need a tackifier or a plasticizer, can be directly used as a hot melt adhesive, and has potential application value in the fields of artificial intelligence, electronic sensing and the like.

Description

Technical Field

[0001] The invention provides a silicon-based hot melt adhesive and a preparation method thereof. The hot melt adhesive is a polysiloxane-polyether block copolymer, and the side chain is modified with a carboxyl group. Background Art

[0002] Due to its unique Si-O-Si main chain structure and adjustable side chain groups (such as methyl, phenyl, amino, epoxy, etc.), silicone materials give hot melt adhesives excellent high and low temperature resistance, flexibility, weather resistance, hydrophobicity and biocompatibility, becoming an important direction for high-end hot melt adhesive modification.

[0003] Silicone-modified hot melt adhesive has the following advantages: (1) Temperature resistance. The Si-O bond energy (452 ​​kJ / mol) is higher than the CC bond (348 kJ / mol), which enables the hot melt adhesive to maintain bonding performance in a wide temperature range of -50 to 250 °C, making it suitable for high-temperature packaging (such as LEDs, electronic components) and low-temperature environments (such as aerospace). (2) Flexibility. The low modulus (0.1 to 5 MPa) can buffer thermal stress and avoid cracking of the rigid adhesive layer, making it suitable for flexible electronics (wearable devices, folding screens). (3) Interface bonding. Through side chain polar groups (such as carboxyl and epoxy groups), chemical bonds are formed with metals, plastics, ceramics and other substrates to improve peel strength (30% to 100% higher than traditional EVA hot melt adhesive). (4) Aging resistance. The Si-O-Si main chain is UV-resistant and oxidation-resistant, and its outdoor service life can reach more than 10 years (such as photovoltaic module sealant). (5) Biosafety. It is suitable for medical patches, transdermal drug delivery systems, etc. Chinese invention patent CN114716959B discloses a polyurethane hot melt adhesive for automobile spare tire cover and its preparation method, the raw materials of which include hydroxyl polymer, crystalline alcohol modified copolymer polyester, hydroxyl and alkoxy polymer, aromatic isocyanate compound, amine and its derivative, organotin compound, random copolymer polyolefin, acrylic tackifier, defoamer and silicone wetting agent, and the prepared polyurethane hot melt adhesive has excellent peel strength. Chinese invention patent CN115725259B discloses a reactive polyurethane hot melt adhesive and its preparation method, the raw materials of which include polysiloxane modified polyether polyol, polyester polyol, tackifier resin, thermoplastic resin, polyisocyanate, adhesion promoter and catalyst, and the prepared reactive polyurethane hot melt adhesive has excellent fatigue resistance, high and low temperature resistance and resistance to hot and humid environment.

[0004] This patent prepares a silicon-based block polymer whose main chain is composed of polysiloxane and polyether segments - polysiloxane gives the material high temperature resistance and flexibility, while the polyether segment improves compatibility with polar substrates. Carboxyl groups are introduced into the side chain to enhance the bonding strength with the substrate through hydrogen bonding or coordination. The polymer can be directly used as a high-performance hot melt adhesive without the need for additional tackifiers or plasticizers. Summary of the invention

[0005] The present invention provides a method for preparing a silicon-based hot melt adhesive. The method has a simple process, and the obtained hot melt adhesive has excellent temperature resistance and high bonding strength, and does not require the addition of a tackifier or a plasticizer, and is suitable for high-end fields such as wearable electronics and flexible electrodes.

[0006] To achieve this purpose, the hot melt adhesive of the present invention is a silicon-based block polymer, the main chain of which contains polysiloxane and polyether segments, and the side chain has carboxyl groups. The polysiloxane segments impart high temperature resistance and flexibility, the polyether segments enhance compatibility with polar substrates, and the carboxyl groups enhance bonding strength through coordination bonds or hydrogen bonds. The present invention comprises the following steps:

[0007] (1) Preparation of isocyanate-terminated polyether precursor A: Heat the dihydroxy-terminated polyether A under vacuum conditions at 100-120° C. for 0.5-2 h to remove moisture, cool to 65-85° C., add isophorone diisocyanate and catalyst dibutyltin dilaurate, and react under the protection of an inert gas (such as nitrogen) for 1-2 h to obtain isocyanate-terminated polyether precursor A.

[0008] (2) Preparation of silicon-based precursor B: Heat polysiloxane B under vacuum conditions at 100-120° C. for 0.5-3 h to remove moisture, then dissolve it in solvent A, add it dropwise to the isocyanate-terminated polyether precursor A obtained in step (1), and carry out chain extension reaction at 65-85° C. for 1-2 hours under the protection of an inert gas (such as nitrogen) to obtain silicon-based precursor B.

[0009] (3) Preparation of silicon-based hot melt adhesive: dissolve the carboxyl chain extender C in solvent A, add dropwise to the silicon-based precursor B prepared in step (2), and heat at 65-85° C. under the protection of an inert gas (such as nitrogen).

[0010] The reaction was continued for 15-30 hours, and then the solvent A was removed by vacuuming at the same temperature for 1-3 hours. The obtained product was dissolved with solvent B and poured into a polytetrafluoroethylene mold, and dried in an oven at 60°C for 24-36 hours.

[0011] The silicon-based hot melt adhesive is obtained.

[0012] Preferably, in the step (1), the polyether A is selected from any one of polypropylene glycol and polytetramethylene glycol, the molar ratio of polyether A to isophorone diisocyanate is 1:2, the number average molecular weight of polyether A is 2000-4000 g / mol, and the amount of the catalyst dibutyltin dilaurate is 0.5wt%-3.0wt% of the mass of polyether A;

[0013] Preferably, the polysiloxane B in step (2) is selected from any one of bis(3-aminopropyl)-terminated poly(dimethylsiloxane) or bis(hydroxyalkyl)-terminated poly(dimethylsiloxane), the number average molecular weight of polysiloxane B is 2000-5000 g / mol, and the amount of polysiloxane B used is one-half of the molar number of the polyether A in step (1);

[0014] Preferably, the solvent A in steps (2) and (3) is selected from any one of N,N-dimethylacetamide and N,N-dimethylformamide, and the amount of solvent A is 2 to 4 times the mass of polysiloxane B;

[0015] Preferably, the carboxyl chain extender C in step (3) is selected from any one of 2,2-dihydroxymethylbutyric acid or 2,3-diaminopropionic acid, the amount of the carboxyl chain extender C is one quarter of the molar number of isophorone diisocyanate, and the amount of the solvent A is 2 to 4 times the mass of the carboxyl chain extender C;

[0016] Preferably, the solvent B in step (3) is selected from methanol or tetrahydrofuran, and the amount of solvent B is 10 to 30 times the mass of silicon-based precursor B.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention uses silicon-based block polymer as hot melt adhesive, which solves the compatibility problem between polysiloxane and polyether, and does not contain small molecule components, thus avoiding the decrease in bonding performance caused by the precipitation of small molecules.

[0019] (2) The hot melt adhesive of the present invention has a simple preparation process, has excellent bonding performance and high temperature resistance, and can be recycled and reprocessed, meets green environmental protection requirements, and is suitable for artificial intelligence, electronic sensing and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The bonding strength of the silicone-based hot melt adhesive obtained in Example 1-2.

[0021] Figure 2 This is a load-bearing photograph of the stainless steel sheet bonded with the silicon-based hot melt adhesive in Example 2-3. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described in detail below, but the embodiments of the present invention are not limited thereto. The raw materials, reagents, etc. used in the following embodiments can be obtained from commercial sources unless otherwise specified.

[0023] Example 1

[0024] (1) Preparation of isocyanate-terminated polyether precursor A: 1.0 g (0.5 mmol) of polypropylene glycol with a number average molecular weight of 2000 g / mol was heated at 100 °C under vacuum for 1 h to remove moisture, then cooled to 75 °C, 22.2 mg (1.0 mmol) of isophorone diisocyanate and 5.0 mg of catalyst dibutyltin dilaurate were added, and the mixture was stirred at room temperature for 1 h. 2 The reaction was carried out under protection for 1.5 h to obtain an isocyanate-terminated polyether precursor A.

[0025] (2) Preparation of silicon-based precursor B: 0.75 g (0.25 mmol) of bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a number average molecular weight of 3000 g / mol was heated at 120° C. under vacuum for 1 h to remove moisture, then dissolved in 1 mL of N,N-dimethylacetamide and added dropwise to the isocyanate-terminated polyether precursor A prepared in step (1). 2 The reaction was carried out at 75°C for 1.5 h under protection to obtain a silicon-based precursor B.

[0026] (3) Preparation of silicon-based hot melt adhesive: 37.8 mg (0.25 mmol) of 2,2-dihydroxymethylbutyric acid was dissolved in 1.2 mL of N,N-dimethylacetamide, and added dropwise to the silicon-based precursor B obtained in step (2). The mixture was reacted at 75°C for 15 h under nitrogen protection, and then vacuumed at the same temperature for 2 h to remove N,N-dimethylacetamide. The obtained product was dissolved in 20 mL of tetrahydrofuran and poured into a polytetrafluoroethylene mold. The mixture was dried in an oven at 60°C for 30 h to obtain a silicon-based hot melt adhesive.

[0027] Example 2

[0028] (1) Preparation of isocyanate-terminated polyether precursor A: 1.0 g (0.5 mmol) of polytetramethylene glycol with a number average molecular weight of 2000 g / mol was heated at 120° C. under vacuum for 0.5 h to remove moisture, then cooled to 70° C., 22.2 mg (1.0 mmol) of isophorone diisocyanate and 5.0 mg of catalyst dibutyltin dilaurate were added, and the mixture was stirred at room temperature for 2 hours. 2 The reaction was carried out under protection for 2 hours to obtain an isocyanate-terminated polyether precursor A.

[0029] (2) Preparation of silicon-based precursor B: 1.25 g (0.25 mmol) of bis(hydroxyalkyl)-terminated poly(dimethylsiloxane) with a number average molecular weight of 5000 g / mol was heated at 120° C. under vacuum for 0.5 h to remove moisture, then dissolved in 1 mL of N,N-dimethylformamide and added dropwise to the isocyanate-terminated polyether precursor A prepared in step (1). 2 The reaction was carried out at 70°C for 2 h under protection to obtain a silicon-based precursor B.

[0030] (3) Preparation of silicon-based hot melt adhesive: 26.0 mg (0.25 mmol) of 2,3-diaminopropionic acid was dissolved in 1.2 mL of N,N-dimethylformamide, and added dropwise to the silicon-based precursor B obtained in step (2). The mixture was reacted at 70°C for 20 h under nitrogen protection, and then vacuumed for 1 h at the same temperature to remove N,N-dimethylformamide. The obtained product was dissolved in 15 mL of tetrahydrofuran and poured into a polytetrafluoroethylene mold. The mixture was dried in an oven at 60°C for 24 h to obtain a silicon-based hot melt adhesive.

[0031] Example 3

[0032] (1) Preparation of isocyanate-terminated polyether precursor A: 1.5 g (0.5 mmol) of polypropylene glycol with a number average molecular weight of 3000 g / mol was heated at 100 °C under vacuum for 1.5 h to remove moisture, then cooled to 80 °C, 22.2 mg (1.0 mmol) of isophorone diisocyanate and 5.0 mg of catalyst dibutyltin dilaurate were added, and the mixture was stirred at room temperature for 2 hours. 2 The reaction was carried out under protection for 1 hour to obtain an isocyanate-terminated polyether precursor A.

[0033] (2) Preparation of silicon-based precursor B: 0.75 g (0.25 mmol) of bis(3-aminopropyl)-terminated poly(dimethylsiloxane) with a number average molecular weight of 2000 g / mol was heated at 120° C. under vacuum for 1 h to remove moisture, then dissolved in 1 mL of N,N-dimethylacetamide and added dropwise to the isocyanate-terminated polyether precursor A prepared in step (1). 2 The reaction was carried out at 80°C under protection for 1 h to obtain a silicon-based precursor B.

[0034] (3) Preparation of silicon-based hot melt adhesive: 37.8 mg (0.25 mmol) of 2,2-dihydroxymethylbutyric acid was dissolved in 1.2 mL of N,N-dimethylacetamide, and added dropwise to the silicon-based precursor B obtained in step (2). The mixture was reacted at 80°C for 15 h under nitrogen protection, and then vacuumed at the same temperature for 2 h to remove N,N-dimethylacetamide. The obtained product was dissolved in 20 mL of tetrahydrofuran and poured into a polytetrafluoroethylene mold. The mixture was dried in an oven at 60°C for 36 h to obtain a silicon-based hot melt adhesive.

Claims

1. A method for preparing a silicone-based hot melt adhesive, characterized in that: The hot melt adhesive is a silicon-based block polymer, the main chain of which includes polysiloxane and polyether segments, and the side chain contains a carboxyl group, wherein the polysiloxane segment provides high temperature resistance and flexibility, the polyether segment can enhance the compatibility with the polar substrate, and the presence of the carboxyl group can form a coordination bond or hydrogen bond with the substrate to improve the bonding strength of the material, without adding a tackifier or plasticizer, and can be directly used as a hot melt adhesive. The preparation method comprises the following steps: (1) Preparation of isocyanate-terminated polyether precursor A: heating dihydroxy-terminated polyether A under vacuum at 100-120° C. for 0.5-2 hours to remove moisture, cooling to 65-85° C., adding isophorone diisocyanate and catalyst dibutyltin dilaurate, and reacting under the protection of an inert gas (such as nitrogen) for 1-2 hours to obtain isocyanate-terminated polyether precursor A; (2) Preparation of silicon-based precursor B: heating polysiloxane B under vacuum conditions at 100-120° C. for 0.5-3 hours to remove moisture, then dissolving it in solvent A, adding it dropwise to the isocyanate-terminated polyether precursor A obtained in step (1), and carrying out a chain extension reaction at 65-85° C. for 1-2 hours under the protection of an inert gas (such as nitrogen) to obtain silicon-based precursor B; (3) Preparation of silicon-based hot melt adhesive: dissolve the carboxyl chain extender C in solvent A, add the solution dropwise to the silicon-based precursor B obtained in step (2), react at 65-85° C. for 15-30 hours under the protection of an inert gas (such as nitrogen), then evacuate the solution at the same temperature for 1-3 hours to remove solvent A, dissolve the obtained product in solvent B and pour it into a polytetrafluoroethylene mold, and dry it in an oven at 60° C. for 24-36 hours to obtain the silicon-based hot melt adhesive.

2. A method for preparing a silicone-based hot melt adhesive as claimed in claim 1, characterized in that: The polyether A in the step (1) is selected from any one of polypropylene glycol and polytetramethylene glycol, the molar ratio of polyether A to isophorone diisocyanate is 1:2, the number average molecular weight of polyether A is 2000-4000 g / mol, and the amount of the catalyst dibutyltin dilaurate is 0.5wt%-3.0wt% of the mass of polyether A.

3. The method for preparing a silicone-based hot melt adhesive according to claim 1, characterized in that: In the step (2), the polysiloxane B is selected from any one of bis(3-aminopropyl)-terminated poly(dimethylsiloxane) or bis(hydroxyalkyl)-terminated poly(dimethylsiloxane), the number average molecular weight of the polysiloxane B is 2000 to 5000 g / mol, and the amount of the polysiloxane B used is one half of the molar number of the polyether A in the step (1).

4. The method for preparing a silicone-based hot melt adhesive according to claim 1, characterized in that: The solvent A in the steps (2) and (3) is selected from any one of N,N-dimethylacetamide and N,N-dimethylformamide, and the amount of solvent A is 2 to 4 times the mass of polysiloxane B.

5. The method for preparing a silicone-based hot melt adhesive according to claim 1, characterized in that: The carboxyl chain extender C in step (3) is selected from any one of 2,2-dihydroxymethylbutyric acid and 2,3-diaminopropionic acid, the amount of chain extender C is one quarter of the molar number of isophorone diisocyanate, and the amount of solvent A is 2 to 4 times the mass of chain extender C.

6. The method for preparing a silicone-based hot melt adhesive according to claim 1, characterized in that: The solvent B in step (3) is selected from methanol or tetrahydrofuran, and the amount of solvent B is 10 to 30 times the mass of silicon-based precursor B.

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