A high-strength polyurethane adhesive usable at low temperatures and a method for preparing the same

Abstract

The application discloses a high-strength polyurethane adhesive which can be used at low temperature and a preparation method thereof, relates to the technical field of high polymer compounds, and comprises the following steps: dissolving polyol A, isocyanate B and a catalyst C in a polar solvent E, reacting at 80 DEG C for 1 h, and preparing an isocyanate prepolymer; adding a chain extender D to the isocyanate prepolymer solution in step 1, and performing a polymerization reaction at 60 DEG C for 6 h to obtain a polyurethane solution; pouring the polyurethane solution in step 2 into a mold, volatilizing the solvent at 80 DEG C, and then further drying under vacuum at 80 DEG C to obtain the polyurethane adhesive. The polyurethane adhesive of the application can still maintain high adhesive strength (>30MPa) and stability (adhesive strength does not decrease in liquid nitrogen for 60 days) at low temperature (-60 DEG C) and ultralow temperature (-196 DEG C), the adhesion process is convenient (no heating is needed, and direct adhesion can be achieved at -20 DEG C), fast and environment-friendly, and thus meets the development trend of green adhesive materials.

Description

Technical Field

[0001] This invention relates to the field of polymer compound technology, specifically to a high-strength polyurethane adhesive that can be used at low temperatures and its preparation method. Background Technology

[0002] Polymer materials exhibiting high adhesive strength in extreme environments (such as low temperatures) have wide applications in various fields, including biomedicine, aerospace, and polar engineering equipment. In recent years, with the continuous development of various fields requiring low-temperature adhesives, general polymer materials with low-temperature adhesive properties can no longer meet the increasingly diverse application scenarios. Therefore, much work has been conducted both domestically and internationally in recent years to enhance the adhesive strength of polymer materials at low temperatures. Currently, nanofiller modification is the most widely used method with good low-temperature adhesive strength enhancement effects. However, due to compatibility issues between fillers and polymers, fillers tend to aggregate in the material, leading to stress concentration and ultimately hindering further increases in adhesive strength. Therefore, developing a simple and effective method for preparing polymer materials with high adhesive strength at low temperatures is essential. Summary of the Invention

[0003] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a high-strength polyurethane adhesive that can be used at low temperatures, comprising the following steps:

[0004] Step 1: Under gas protection, polyol A, isocyanate B and catalyst C are dissolved in polar solvent E and reacted at 80°C for 1 hour to obtain isocyanate prepolymer.

[0005] Step 2: Under gas protection, chain extender D is added to the isocyanate prepolymer solution in step 1, and polymerization reaction is carried out at 60°C for 6 hours to obtain polyurethane solution.

[0006] Step 3: Pour the polyurethane solution from Step 2 into a mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0007] The molar ratio of the above polyol A, isocyanate B and chain extender D is 1:2:1.

[0008] Preferably, polyol A is one or more of polyethylene glycol, polypropylene glycol, poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), polytetrahydrofuran, polydimethylsiloxane, and polycaprolactone diol.

[0009] Preferably, isocyanate B is one or more of hexamethylene diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, isophorone diisocyanate, and isophthalic diisocyanate.

[0010] Preferably, catalyst C is dibutyltin dilaurate; chain extender D is one or more of adipic dihydrazide, isophthalic dihydrazide, sebacate dihydrazide, carbamate dihydrazide, and 1,6-hexanediamine.

[0011] Preferably, the polar solvent E is one or a combination of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0012] Preferably, in step 1, the concentration of polyol A in the polar solvent E is 50–100 mg / mL.

[0013] Preferably, the mold is made of any one of glass, silicone, or polytetrafluoroethylene.

[0014] The present invention also provides a high-strength polyurethane adhesive that can be used at low temperatures, which is prepared by the preparation method described above.

[0015] The present invention has the following beneficial effects:

[0016] The polyurethane adhesive of the present invention can maintain high adhesive strength (>30MPa) and stability (adhesive strength does not decrease after 60 days in liquid nitrogen) at low temperature (-60℃) and ultra-low temperature (-196℃), which is far superior to several commercial adhesives used for comparison.

[0017] The adhesion process is convenient (no heating required, direct adhesion is possible even at -20℃), fast (curing is completed within 30 seconds), and environmentally friendly (solvent-free), meeting the development trend of green adhesive materials.

[0018] The synthesis process is simple and energy-saving (maximum heating temperature 80℃), meeting the development trend of energy conservation and environmental protection. Attached Figure Description

[0019] Figure 1 The infrared curve of the polyurethane adhesive prepared in Example 1 of this invention;

[0020] Figure 2 The TGA curve of the polyurethane adhesive prepared in Example 2 of this invention;

[0021] Figure 3 The DSC curve of the polyurethane adhesive prepared in Example 3 of this invention;

[0022] Figure 4This is a bar chart showing the adhesion strength of the polyurethane adhesive prepared in Example 4 of the present invention at -60°C on different substrates;

[0023] Figure 5 This is a photograph showing the iron sheet adhered to by the polyurethane adhesive prepared in Embodiment 5 of the present invention being immersed in liquid nitrogen and then lifted to lift a heavy object;

[0024] Figure 6 These are comparative photographs of the polyurethane adhesive prepared in Example 6 of this invention and a commercial adhesive after being immersed in liquid nitrogen;

[0025] Figure 7 The bar chart shows the adhesive strength of the polyurethane adhesive prepared in Example 7 of the present invention before immersion in liquid nitrogen and after immersion for 3 days, 30 days and 60 days.

[0026] Figure 8 This is a flowchart illustrating a method for preparing a high-strength polyurethane adhesive that can be used at low temperatures, according to the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0029] Example 1: As Figure 8 As shown, a method for preparing a high-strength polyurethane adhesive that can be used at low temperatures includes the following steps:

[0030] Step 1: Under gas protection, 5.32 mmol of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 10.64 mmol of isophorone diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer;

[0031] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0032] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0033] It should be noted that the adhesion method of the high-strength polyurethane adhesive prepared by this invention, which can be used at low temperatures, is as follows:

[0034] The high-strength polyurethane adhesive prepared according to this invention, which can be used at low temperatures, is uniformly coated onto the surface of a substrate (such as an iron sheet, copper sheet, aluminum sheet, ceramic sheet, or glass sheet), and then bonded and cured to an unbonded substrate at temperature G. After the adhesive has cured, the bonding strength is tested using the tensile mode of a universal testing machine at temperature H. Temperature G ranges from -20℃ to 25℃, and temperature H ranges from -196℃ to 25℃.

[0035] It should be noted that the performance testing method for the polyurethane adhesive obtained by this invention is as follows:

[0036] The performance of this adhesive was evaluated by testing its shear strength under uniaxial tensile strain using a UTM4103 Tension Instrument (Shenzhen SUNS Technology Co. LDT, China). The test method (taking a bonded iron sheet as an example): the iron sheet size was 60mm × 10mm, the bonding area A1 was 10mm × 10mm, and the tensile rate was 50mm / min. A certain force F1 was applied during the longitudinal tensile test; F1 is the shear force. The shear strength in the test was defined as: σ1 = F1 / A1. Note that the shear strength σ1 defined here is the shear force F1 divided by the bonding area A1.

[0037] Using the polyurethane adhesive prepared in this embodiment to bond iron sheets, the bonding strength was tested using a universal testing machine in an environmental chamber at -60°C, and the obtained bonding strength was 34.8 MPa. Figure 1 The image shows the infrared curve of the polyurethane adhesive prepared in Example 1 of this invention.

[0038] Example 2: This example differs from Example 1 in that the 10.64 mmol isophorone diisocyanate in step 1 is replaced with 10.64 mmol toluene-2,4-diisocyanate. Specifically:

[0039] Step 1: Under gas protection, 5.32 mmol of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 10.64 mmol of toluene-2,4-diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer;

[0040] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0041] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0042] The copper sheet bonded using the polyurethane adhesive prepared in this embodiment was tested using a universal testing machine in an environmental chamber at -60°C, and the resulting bond strength was 29.8 MPa. Figure 2 The figure shows the TGA curve of the polyurethane adhesive prepared in Example 2 of the present invention. There is no obvious weight loss step before 300°C, indicating that the adhesive does not contain solvent (DMAC).

[0043] Example 3: This example differs from Example 1 in that the 10.64 mmol isophorone diisocyanate in step 1 is replaced with 10.64 mmol hexamethylene diisocyanate, specifically:

[0044] Step 1: Under gas protection, 5.32 mmol of poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol), 10.64 mmol of hexamethylene diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer;

[0045] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0046] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0047] The aluminum sheet bonded using the polyurethane adhesive prepared in this embodiment was tested using a universal testing machine in an environmental chamber at -60°C, and the resulting bond strength was 28.7 MPa. Figure 3 The figure shows the DSC curve of the polyurethane adhesive prepared in Example 3 of the present invention, which shows that the glass transition temperature of the adhesive is -52.81℃.

[0048] Example 4: This example differs from Example 2 in that the 5.32 mmol poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) in step 1 is replaced with 5.32 mmol polyethylene glycol. Specifically:

[0049] Step 1: Under gas protection, 5.32 mmol polyethylene glycol, 10.64 mmol toluene-2,4-diisocyanate and 20 μl di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer.

[0050] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0051] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0052] The ceramic sheets bonded using the polyurethane adhesive prepared in this embodiment were tested using a universal testing machine in an environmental chamber at -60°C, and the resulting bond strength was 29.03 MPa. Figure 4 The figure shows a bar chart of the adhesion strength of the polyurethane adhesive prepared in Example 4 of the present invention at -60°C on different substrates. The adhesion strength of the adhesive on iron sheet, copper sheet, aluminum sheet, ceramic sheet and glass sheet at -60°C is 34.19MPa, 32.38MPa, 30.63MPa, 29.03MPa and 23.58MPa, respectively.

[0053] Example 5: This example differs from Example 2 in that the 5.32 mmol poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) in step 1 is replaced with 5.32 mmol polypropylene glycol. Specifically:

[0054] Step 1: Under gas protection, 5.32 mmol of polypropylene glycol, 10.64 mmol of toluene-2,4-diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer.

[0055] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0056] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0057] Using the polyurethane adhesive prepared in this embodiment to bond iron sheets, after immersion in liquid nitrogen (-196°C) and testing with a universal testing machine, the bond strength was found to be 32.8 MPa. Figure 5 The image shows a photograph of an iron sheet adhered to by the polyurethane adhesive prepared in Example 5 of the present invention after being immersed in liquid nitrogen and then lifted to remove a heavy object. This illustrates that the adhesive has extremely high bonding strength at extreme low temperatures (-196°C).

[0058] Example 6: This example differs from Example 2 in that the 5.32 mmol poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) in step 1 is replaced with 5.32 mmol polytetrahydrofuran, specifically:

[0059] Step 1: Under gas protection, 5.32 mmol of polytetrahydrofuran, 10.64 mmol of toluene-2,4-diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer.

[0060] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0061] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0062] The polyurethane adhesive prepared in this embodiment was used to bond iron sheets. After immersion in liquid nitrogen (-196°C), the bond strength was tested using a universal testing machine, and the obtained bond strength was 35.8 MPa. Figure 6 The image shows a comparison photograph of the polyurethane adhesive prepared in Example 6 of this invention and a commercial adhesive after immersion in liquid nitrogen. After immersion in liquid nitrogen for two hours, the commercial adhesives EP-AA, AA-AB, and EVA-HB all experienced brittle fracture, while the polyurethane adhesive PU prepared in Example 6... 1900 -IA remains intact.

[0063] Example 7: This example differs from Example 2 in that the 5.32 mmol poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) in step 1 is replaced with 5.32 mmol polycaprolactone diol. Specifically:

[0064] Step 1: Under gas protection, 5.32 mmol of polycaprolactone diol, 10.64 mmol of toluene-2,4-diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer.

[0065] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0066] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0067] The polyurethane adhesive prepared in this embodiment was used to bond iron sheets. After immersion in liquid nitrogen (-196°C), the bond strength was tested using a universal testing machine, and the obtained bond strength was 32.4 MPa. Figure 7 The figure shows a bar chart of the adhesive strength of the polyurethane adhesive prepared in Example 7 of the present invention before immersion in liquid nitrogen and after immersion for 3 days, 30 days and 60 days. The adhesive strength of the adhesive did not decrease significantly during the process.

[0068] Example 8: This example differs from Example 2 in that the 5.32 mmol poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) in step 1 is replaced with 5.32 mmol polydimethylsiloxane, specifically:

[0069] Step 1: Under gas protection, 5.32 mmol of polydimethylsiloxane, 10.64 mmol of toluene-2,4-diisocyanate and 20 μl of di-n-butyltin dilaurate were dissolved in 60 ml of ultra-dry N,N-dimethylacetamide (DMAC) and reacted at 80 °C for 1 h to obtain the isocyanate prepolymer.

[0070] Step 2: Under gas protection, 5.32 mmol of adipate dihydrazide was added to the isocyanate prepolymer solution in Step 1, and the polymerization reaction was carried out at 60°C for 6 hours to obtain a polyurethane solution.

[0071] Step 3: Pour the polyurethane solution from Step 2 into a silicone mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive.

[0072] The polyurethane adhesive prepared in this embodiment was used to bond iron sheets. After immersion in liquid nitrogen (-196°C), the bond strength was tested in a universal testing machine and found to be 32.7 MPa.

[0073] In summary, this invention introduces a synergistic strategy of "polyol + isocyanate + hydrazide" in molecular structure design to construct a multi-level cross-linked polyurethane structural network, which solves the problems of insufficient adhesive strength and stability faced by adhesives at low temperatures in the prior art, and exhibits superior performance.

[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength polyurethane adhesive that can be used at low temperatures, characterized in that, Includes the following steps: Step 1: Under gas protection, polyol A, isocyanate B and catalyst C are dissolved in polar solvent E and reacted at 80°C for 1 hour to obtain isocyanate prepolymer. Step 2: Under gas protection, chain extender D is added to the isocyanate prepolymer solution in step 1, and polymerization reaction is carried out at 60°C for 6 hours to obtain polyurethane solution. Step 3: Pour the polyurethane solution from Step 2 into a mold, evaporate the solvent at 80°C, and then further dry it under vacuum at 80°C to obtain the polyurethane adhesive. The molar ratio of the above polyol A, isocyanate B and chain extender D is 1:2:1; Polyol A is poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol). Chain extender D is adipic acid dihydrazide; Isocyanate B is one of hexamethylene diisocyanate, toluene-2,4-diisocyanate, and isophorone diisocyanate.

2. The method for preparing a high-strength polyurethane adhesive that can be used at low temperatures according to claim 1, characterized in that, Catalyst C is di-n-butyltin dilaurate.

3. The method for preparing a high-strength polyurethane adhesive usable at low temperatures according to claim 1, characterized in that, The polar solvent E is one or more of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide.

4. The method for preparing a high-strength polyurethane adhesive that can be used at low temperatures according to claim 3, characterized in that, In step 1, the concentration of polyol A in polar solvent E is 50–100 mg / mL.

5. The method for preparing a high-strength polyurethane adhesive usable at low temperatures according to claim 1, characterized in that, The mold can be made of any one of glass, silicone, or polytetrafluoroethylene.

6. A high-strength polyurethane adhesive that can be used at low temperatures, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 5.

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