A kind of thermoplastic polyurethane hot melt adhesive and preparation method

Abstract

The present invention discloses a polyurethane hot melt adhesive and a preparation method thereof. The thermoplastic polyurethane hot melt adhesive is prepared by synthesizing raw materials including polymer diols, diisocyanates, and a chain extender containing furanamide groups. The present invention introduces a furanamide group having both a rigid structure and hydrogen bond interaction into the hard segment of the polyurethane. The hot melt adhesive can form a variety of non-covalent bond interactions with metal atoms, ions and polar groups on the surface of the substrate through the amide group and the oxygen atoms on the furan ring. The hot melt adhesive has excellent comprehensive bonding properties, including good initial bonding strength and final bonding strength, and repeatable bonding, and can be applied to bonding a variety of materials including metals, composite materials, and plastics.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane hot melt adhesives, and in particular relates to a thermoplastic polyurethane hot melt adhesive and a preparation method thereof. Background Art

[0002] Polyurethane hot melt adhesive is suitable for bonding various materials, and has comprehensive advantages such as high bonding strength, high adhesive layer toughness, excellent low temperature performance and impact resistance, solvent resistance, and non-toxicity. Polyurethane hot melt adhesive can be divided into reactive polyurethane hot melt adhesive and thermoplastic polyurethane hot melt adhesive. Reactive polyurethane HMA can react chemically with moisture, and usually has higher bonding strength after curing than thermoplastic polyurethane hot melt adhesive, and generally has higher final bonding strength and good chemical resistance. However, it usually takes a long time for -NCO to react with moisture during the curing process, so its initial bonding strength is poor, and it requires a long positioning time, which is not suitable for fast bonding scenarios. In addition, the permanent chemical cross-linked structure produced after the reaction brings technical difficulties to the debonding, disassembly and repair of the assembly, making it impossible to debond and reuse the lap joints as needed. In addition, due to the high reactivity and moisture sensitivity of -NCO, the shelf life of reactive polyurethane HMA is short and easy to deteriorate, and the storage, transportation and use conditions are more stringent. Thermoplastic polyurethane hot melt adhesive has high initial bonding strength and short positioning time, and is particularly suitable for rapid bonding. The linear structure and physical cross-linking of thermoplastic polyurethane hot melt adhesive give it thermoplastic properties, which allows it to be heated to debond and bond again, making it easy to remove glue and repair and other secondary processing. It can also be processed into various shapes, has a long shelf life, and is easy to transport, store and use. However, the linear structure also limits the final bonding strength of thermoplastic polyurethane hot melt adhesive. As more and more electronic and mechanical products emphasize rapid assembly and rapid positioning of joints during the production process to optimize the production cycle, and emphasize higher strength bonding to meet mechanical properties, it is urgent to explore new ways to improve the bonding strength of thermoplastic polyurethane hot melt adhesives and the reusability of hot melt adhesives.

[0003] At present, there are few research reports on the introduction of furanamide structure into thermoplastic polyurethane hot melt adhesive to improve performance. Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences reported a 2,5-furandicarboxamide diamine compound, its preparation method and application, and disclosed that furandicarboxamide diamine can be used for the synthesis of polyurethane [CN105985302A, 2016.10.05]. However, for the synthesis of thermoplastic polyurethane adhesives, the use of diamines makes the polymerization reaction process difficult to control. The repeated heating and melting process during preparation and application is prone to form cross-linked structures such as allophanate and biuret, which is not conducive to the repeated use and high adhesion of thermoplastic polyurethane hot melt adhesives. Patent [US20080182944A1, 2008.07.31] reported a method for preparing a prepolymer or a binder by reacting a polyol having a furanamide structure with a polyacid or with a polynitriles. However, the functionality of the polyol is greater than 3, and permanent chemical crosslinking is formed after the prepolymer or binder is prepared, which does not meet the requirement of reusability of thermoplastic polyurethane hot melt adhesive.

[0004] Many research results show that it is a very effective strategy to introduce dynamic covalent bonds or non-covalent interactions between polymer molecular chains and between polymer adhesive layer molecular chains and substrate surfaces to improve the bonding strength of adhesives. In polyurethane hot melt adhesive systems, the regulation of chain extenders can give polyurethanes unique soft and hard segment structures, microphase separation characteristics, dynamic bond groups, etc. In addition, chain extenders and soft segments also have an important influence on regulating the interactions between polyurethane adhesive molecular chains and between colloids and substrate surfaces. However, some current dynamic bond introduction strategies are often accompanied by complex dynamic bond module chemical synthesis [Acs Materials Letters, 2021, 3(7), 1003-1009], or require the addition of metal ions and special fillers [Science Advances, 2021, 7(42):eabk2451], which limits the industrial application of this type of adhesive. Summary of the invention

[0005] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a thermoplastic polyurethane hot melt adhesive based on furanamide chain extender and a preparation method thereof. The obtained thermoplastic polyurethane hot melt adhesive has good bonding strength to metal, epoxy resin, polycarbonate (PC), etc., and has thermoplasticity and can be heated again for debonding and bonding.

[0006] To achieve the above object, the present invention adopts the following technical solution:

[0007] A thermoplastic polyurethane hot melt adhesive is prepared by synthesizing raw materials including a polymer diol, a diisocyanate, and a chain extender containing a furanamide group, wherein the chain extender containing a furanamide group is one or more compounds shown in the following formula:

[0008]

[0009] The molar ratio of the polymer diol to the chain extender containing furanamide groups is 1:1 to 5, preferably 1:

[0010] 1-3; the ratio of the total amount of the polymer diol and the chain extender containing furanamide groups to the amount of diisocyanate is 1:1.

[0011] The number average molecular weight of the polymer diol is 1000 to 5000 g / mol, preferably 1000 to 2000 g / mol.

[0012] The polymer diol is selected from one or more of polyethylene oxide diol, polypropylene oxide diol, polyethylene oxide-propylene oxide diol, polytetramethylene oxide diol, polyneopentyl adipate diol (PNA), polybutylene adipate-1,4-diol (PBA), polyhexanediol adipate-1,6-diol, polyethylene adipate diol, polymethylpropylene adipate diol, polydiethylene adipate diol or polybutylene adipate methylpropylene glycol ester diol.

[0013] The diisocyanate is one or more of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and 4,4'-methylenebis(phenyl isocyanate) (MDI).

[0014] The furanamide group-containing chain extender can be mixed with a variety of chain extenders with different carbon chain length chemical formulas.

[0015] The present invention also provides a method for preparing the thermoplastic polyurethane hot melt adhesive, which comprises: adding a catalyst to polymer diol, diisocyanate, and a chain extender raw material containing a furanamide group to react to obtain the thermoplastic polyurethane hot melt adhesive; the catalyst is one or more of dibutyltin dilaurate, dibutyltin dilaurate, di-n-butyltin dilaurate, and dibutyltin dilaurate.

[0016] Preferably, the mass amount of the catalyst accounts for 0.01-0.1% of the total mass of the polymer diol, the diisocyanate, and the chain extender containing the furanamide group.

[0017] Furthermore, the preferred preparation method is as follows: under nitrogen protection, the polymer diol, diisocyanate and catalyst are reacted at a temperature of 70 to 90° C. for 2 to 4 hours to obtain a prepolymer mixture, which is heated to 90 to 120° C.; then a chain extender containing a furanamide group is added to the prepolymer mixture at 90 to 120° C., and a chain extension reaction is carried out for 18 to 30 hours to obtain a polyurethane hot melt adhesive.

[0018] Furthermore, the polymer diol is preferably first stirred under vacuum at 120-140° C. to remove water for 1-4 hours, then the temperature is lowered to 70-90° C., nitrogen is introduced to replace the vacuum, and under nitrogen protection, diisocyanate and catalyst are added to react.

[0019] The chain extender containing furanamide groups provided by the present invention can be prepared by the following method:

[0020] Dimethyl furan-2,5-dicarboxylate was dissolved in methanol solvent and HO-(CH 2 ) a -NH 2 The compound is stirred at 50-60° C. for 20-30 hours, and after the methanol solvent is evaporated, it is washed with acetone, filtered, and dried to obtain the chain extender containing the furanamide group; the furan-2,5-dicarboxylic acid dimethyl ester, HO-(CH 2 ) a -NH 2 The molar ratio of the compounds is 1:2 to 5. a=1, 2, 3, 4, or 5.

[0021] The thermoplastic polyurethane hot melt adhesive prepared by the invention has a viscosity-flow transition temperature of 70-120° C. measured by temperature rheological scanning and a number average molecular weight of 10000-45000 g / mol measured by gel permeation chromatography.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: the introduction of furanamide groups in the hard segment increases the rigidity of the polyurethane molecular chain, improves the degree of physical crosslinking of the polyurethane, and gives the polyurethane adhesive layer good mechanical properties, which is specifically manifested in the significant improvement of the modulus, strength and toughness of the adhesive layer. Good mechanical properties are the basis for achieving good adhesion between the adhesive layer and the substrate. In addition, the furanamide groups introduced by the chain extender and the oxygen atoms on the furan ring can form a variety of non-covalent bond interactions with the free groups and atoms on the surface of the substrate, such as hydrogen bonds or metal-ion coordination bonds, which help to improve the bonding strength. The thermoplastic polyurethane hot melt adhesive based on furanamide chain extender provided by the present invention is green and degradable, has excellent mechanical properties, and has excellent comprehensive bonding properties, including good initial bonding strength and final bonding strength, and repeatable bonding, and can achieve strong bonding of various materials such as metals, composite materials, and plastics. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a nuclear magnetic resonance spectrum of the furanamide group-containing chain extender N,N-bis(2-hydroxyethyl)-2,5-furandicarboxamide used in the embodiments of the present invention.

[0024] Figure 2 It is the nuclear magnetic resonance spectrum of the control chain extender used in Comparative Example 1 of the present invention.

[0025] Figure 3 It is the nuclear magnetic resonance spectrum of the polyurethane hot melt adhesive prepared based on furanamide chain extender in Examples 1-4 of the present invention.

[0026] Figure 4 It is the infrared spectrum line graph of the polyurethane hot melt adhesive in Examples 1-4 of the present invention and Comparative Example 1.

[0027] Figure 5 It is a stress-strain curve diagram of the polyurethane hot melt adhesive in Examples 1-4 of the present invention and Comparative Example 1.

[0028] Figure 6 It is a curve diagram of the storage modulus (G') and loss modulus (G") of the polyurethane hot melt adhesive in Examples 1-4 of the present invention and Comparative Example 1 as a function of temperature.

[0029] Figure 7 It is a bar graph of the lap shear test results of the polyurethane hot melt adhesive of Example 3 of the present invention and commercial hot melt adhesives 3M-2665, Loctite-3542, and TPU-Lubrizol-5713.

[0030] Figure 8 It is a schematic diagram of the polyurethane hot melt adhesive based on furanamide chain extender of the present invention forming non-covalent interactions with metal atoms, ions or polar groups on the surface of the substrate to enhance adhesion. DETAILED DESCRIPTION

[0031] In order to better illustrate the technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] The raw materials used in the experiments in the embodiments and comparative examples of the present invention are as follows, but are not limited to the following raw materials. The present invention only uses the following raw materials as specific examples to further illustrate the effect of the furanamide chain extender-based polyurethane hot melt adhesive described in the present invention.

[0033] Polytetrahydrofuran-ethylene oxide glycol: PTMG-1000, number average molecular weight of 1000, Shanghai McLean Biochemical Technology Co., Ltd.; Polytetrahydrofuran-ethylene oxide glycol: PTMG-2000, number average molecular weight of 2000, Shanghai McLean Biochemical Technology Co., Ltd.; Diisocyanate: isophorone diisocyanate IPDI, Aladdin Reagent Co., Ltd.; Catalyst: dibutyltin dilaurate DBTDL, Aladdin Reagent Co., Ltd.; Furan-2,5-dicarboxylic acid dimethyl ester (FDE), Aladdin Reagent Co., Ltd.; Ethanolamine, Aladdin Reagent Co., Ltd.

[0034] The 1H-NMR test was performed on a Bruker Avance DMX 400MHz spectrometer using deuterated DMSO as solvent and tetramethylsilane as internal standard. The infrared spectroscopy (FT-IR) test was performed on a Paragon 1000 spectrometer (PerkinElmer) at 4000 cm -1 -500cm -1 The wavenumber range is tested in total reflection mode.

[0035] The rheological behavior of the polymer was tested by an ARES-G2 rheometer. A temperature sweep test was performed using a 25 mm parallel plate fixture, a strain of 0.1%, an angular frequency of 1 rad / s, and a heating rate of 5 °C / min.

[0036] Mechanical properties test, the polyurethane sample was prepared into a film with a thickness of 1mm by hot pressing method, and the hot pressing temperature was 120℃. Dumbbell-shaped specimens were prepared by cutting, and the test specimens were 35mm long, 2mm wide, and 1mm thick. The tensile strength and elongation at break were tested on a universal tensile machine Suns Technology Stock Co. Ltd equipped with a 1000N sensor, and the tensile rate was 50mm / min. Each sample was tested at least 3 times, and the Young's modulus was calculated by the slope of the initial linear stage of the stress-strain curve.

[0037] For the single lap shear strength test, polyurethane hot melt adhesive and commercial TPU-Lubrizol-5713 hot melt adhesive were pressed into a film with a thickness of 0.2 mm at 120°C using a hot press. The hot melt adhesive film was cut into rectangles (25 mm × 12.5 mm) and placed between two substrates (100 mm × 25 mm × 1.5 mm) to form an overlap area of ​​25 mm × 12.5 mm. The substrate was fixed with two paper clips and placed in an oven at a set temperature for 10 minutes of heat treatment. Before testing, the sample needs to be cured at 25°C for 24 hours. The lap shear strength test was carried out on a Suns Technology Stock Co. Ltd universal tensile machine equipped with a 5000N sensor, and each sample was tested at least 3 times. For the commercial 3M-2665 and Loctite-3542 adhesives, they were preheated in an oven at 120°C for 20 minutes, then coated on the substrate, and finally cured at 25°C for 7 days.

[0038] The present invention sets embodiments 1-5.

[0039] First, a chain extender N,N-bis(2-hydroxyethyl)-2,5-furandicarboxamide containing a furanamide group was prepared according to the following steps: furan-2,5-dicarboxylic acid dimethyl ester (7.37 g, 40 mmol) was dissolved in 100 mL of methanol at 50° C., and then ethanolamine (9.77 g, 160 mmol) was added to the solution, and the mixed solution was stirred at 50° C. for 24 hours, and the solvent methanol was removed by a rotary evaporator, and then the product and the raw material were repeatedly washed and filtered with acetone by means of the difference in solubility in acetone, and dried in a vacuum oven to obtain a white solid product N,N-bis(2-hydroxyethyl)-2,5-furandicarboxamide (HO-FDAM-OH), and the nuclear magnetic resonance spectrum was as shown in FIG. Figure 1 The molecular formula is shown below:

[0040]

[0041] Then, furanamide chain extender polyurethane hot melt adhesive was prepared. The present invention sets Examples 1-5, and the equivalent weights of the materials are shown in Table 1. The molecular weight and viscosity-flow transition temperature information of the prepared polyurethane hot melt adhesive are also listed in Table 1:

[0042] Table 1:

[0043]

[0044] The preparation steps of the polyurethane hot melt adhesive of Examples 1-4 are as follows:

[0045] PTMG-1000 (10 g, 10 mmol) was added to a 250 mL three-necked flask with mechanical stirring, and the water was removed under vacuum at 120°C for 2 hours. Then the temperature was lowered to 70°C, and nitrogen was introduced to replace the vacuum. A corresponding amount of IPDI and 0.01 g of DBTDL were added to the flask, and the temperature was gradually raised, and the reaction was carried out at 70°C, 80°C, and 90°C for 1 hour each; then the temperature was continued to be raised to 110°C, and a corresponding amount of HO-FDAM-OH was added to the prepolymer mixture, and the reaction was carried out at 110°C for 24 hours to obtain a polyurethane hot melt adhesive PUFD-x (x is the molar ratio of the chain extender to PTMG-1000). The nuclear magnetic resonance spectrum of the polyurethane hot melt adhesive prepared in Examples 1-4 is shown in FIG. Figure 3 shown.

[0046] PTMG-2000 (20 g, 10 mmol) was added to a 250 mL three-necked flask with mechanical stirring, and the water was removed under vacuum at 120°C for 2 hours. Then the temperature was lowered to 70°C, and nitrogen was introduced to replace the vacuum. IPDI (8.89 g, 40 mmol) and 0.015 g of DBTDL were added to the flask, and the temperature was gradually raised, and the reaction was carried out at 70°C, 80°C, and 90°C for 1 hour each; then the temperature was continued to be raised to 110°C, HO-FDAM-OH (7.27 g, 30 mmol) was added to the prepolymer mixture, and the reaction was carried out at 110°C for 24 hours to obtain the polyurethane hot melt adhesive PUFD-2000-3.

[0047] Comparative Example 1

[0048] The synthesis of the terephthalamide diol chain extender (called the control chain extender) is similar to that of HO-FDAM-OH. Dimethyl furan-2,5-dicarboxylate is replaced with dimethyl terephthalate, and the rest of the synthesis steps are the same. The molecular formula of the control chain extender is shown below

[0049]

[0050] Comparative Example 1 Preparation of polyurethane. The molar ratio of the chain extender and PTMG-1000 was 1:1, and HO-

[0051] FDAM-OH was replaced with p-phenylamide diol chain extender to obtain polyurethane PUET-1, and the NMR spectrum is shown in Figure 2 shown.

[0052] The infrared spectra of the polyurethane hot melt adhesive in Examples 1-4 and Comparative Example 1 are as follows: Figure 4 The FT-

[0053] The IR spectrum does not show the region at 2276 cm -1The absorption peak of isocyanate group around 1658cm -1 The absorption peak of amide C=O at 3300cm-1 and the stretching vibration absorption peak of -NH at 3300cm-1 are enhanced, indicating that more hydrogen bonds are formed. PUET-1 uses a benzene ring to replace the furan ring, and the lack of oxygen heteroatoms as hydrogen bond formation sites weakens the hydrogen bonding effect. This shows that the chain extender with furanamide structure is effective in enhancing the molecular chain hydrogen bonding of polyurethane hot melt adhesives.

[0054] The stress-strain curves of the polyurethane hot melt adhesive in Examples 1-4 and Comparative Example 1 are shown in FIG. Figure 5 Among them, PUFD-1 has both very impressive elongation and breaking strength, with the breaking elongation reaching more than 2500% and the breaking strength reaching 37MPa. The high toughness of the adhesive layer is of great significance for achieving strong bonding.

[0055] The storage modulus (G') and loss modulus (G") of the polyurethane hot melt adhesive in Examples 1-4 and Comparative Example 1 vary with temperature. Figure 6 shown.

[0056] The performance of the polyurethane hot melt adhesives obtained in Examples 1-5 and Comparative Example 1 was tested, and the test results are shown in Table 2:

[0057] Table 2:

[0058]

[0059] The lap shear test results of the polyurethane hot melt adhesive PUFD-1.5 of Example 3 and the commercial hot melt adhesives 3M-2665, Loctite-3542, and TPU-Lubrizol-5713 are shown in the columnar comparison chart as follows: Figure 7 shown.

[0060] From Table 2 and Figure 7 It can be seen from the comprehensive performance evaluation that Examples 2-4 exhibit excellent bonding performance to aluminum, copper, epoxy resin, and PC, and that Example 3 has better bonding performance to each material than the existing commercial hot melt adhesive. However, the bonding performance and mechanical properties of Comparative Example 1 are not as good as those of Examples 2-4.

[0061] The schematic diagram of the polyurethane hot melt adhesive based on furanamide chain extender forming non-covalent interactions with metal atoms, ions or polar groups on the surface of the substrate to enhance adhesion is shown in Figure 8 As shown, the furanamide groups can form hydrogen bonds or metal-ion coordination bonds with free groups and atoms on the surface of the substrate, which helps to improve the bonding strength.

[0062] The benzene ring in the molecular chain structure of the chain extender of Comparative Example 1 does not participate in the non-covalent interaction between the adhesive layer and the substrate like the furan ring, and the mechanical properties of the PUET-1 adhesive layer are obviously inferior to those of PUFD-1. The above results fully demonstrate that the furan ring is crucial to improving the bonding performance.

Claims

1. A thermoplastic polyurethane hot melt adhesive, characterized in that: The thermoplastic polyurethane hot melt adhesive is synthesized from raw materials including polymer diol, diisocyanate, and a chain extender containing a furanamide group. The chain extender containing a furanamide group is one or more compounds shown in the following formula: The molar ratio of the polymer diol to the chain extender containing furanamide groups is 1:1-5, and the molar ratio of the total molar sum of the polymer diol and the chain extender containing furanamide groups to the molar ratio of the diisocyanate is 1:

1.

2. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The number average molecular weight of the polymer diol is 1000 to 5000 g / mol.

3. The thermoplastic polyurethane hot melt adhesive according to claim 2, characterized in that: The polymer diol is selected from one or more of polyethylene oxide glycol, polypropylene oxide glycol, polyethylene oxide-propylene oxide glycol, polytetrahydrofuran-ethylene oxide glycol, polyneopentyl adipate glycol, poly1,4-butylene adipate glycol, poly1,6-hexane adipate glycol, polyethylene adipate glycol, polymethylpropylene adipate glycol, polydiethylene adipate glycol or polymethylpropylene adipate glycol.

4. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that: The diisocyanate is one or more of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and 4,4'-methylenebis(phenyl isocyanate).

5. The thermoplastic polyurethane hot melt adhesive according to claim 1, characterized in that The viscosity-flow transition temperature of the thermoplastic polyurethane hot melt adhesive is 70-120° C., and the number average molecular weight is 10000-45000 g / mol.

6. The method for preparing a thermoplastic polyurethane hot melt adhesive according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: adding a catalyst to polymer diol, diisocyanate and a chain extender containing a furanamide group to react and obtain the thermoplastic polyurethane hot melt adhesive; the catalyst is dibutyltin dilaurate.

7. The method for preparing a thermoplastic polyurethane hot melt adhesive according to claim 6, characterized in that: The mass dosage of the catalyst accounts for 0.01-0.1% of the total mass of the polymer diol, the diisocyanate and the chain extender containing the furanamide group.

8. The method for preparing a thermoplastic polyurethane hot melt adhesive according to claim 6 or 7, characterized in that: The preparation method is as follows: under nitrogen protection, polymer diol, diisocyanate and catalyst are reacted at 70-90°C for 2-4 hours to obtain a prepolymer mixture, which is heated to 90-120°C; then a chain extender containing furanamide groups is added to the prepolymer mixture at 90-120°C, and a chain extension reaction is carried out for 18-30 hours to obtain a polyurethane hot melt adhesive.

9. The method for preparing the thermoplastic polyurethane hot melt adhesive according to claim 8, characterized in that The polymer diol is first stirred under vacuum at 120-140° C. to remove water for 1-4 hours, then the temperature is lowered to 70-90° C., nitrogen is introduced to replace the vacuum, and under nitrogen protection, diisocyanate and a catalyst are added to react.

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