Low free monomer solvent-free polyurethane adhesive for aluminum-plastic compounding

Abstract

The invention discloses a low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic compounding, which belongs to the technical field of chemical building materials, and is characterized in that the number of isocyanate groups contained in a prepolymer is reduced by improving a formula, so that the viscosity of the prepolymer is reduced, the adhesive is easier to spread and level on the aspect of a base material, and the service life of the adhesive is prolonged. Aromatic polyester polyol and modified polyether polyol with a core-shell structure are introduced, so that the high temperature resistance of the adhesive can be effectively improved, the adhesive is suitable for compounding of various plastic films and aluminum foils, the core-shell structure can increase the strength of the polyurethane adhesive, slippage is generated through the core-shell structure, stress is dispersed, and the adhesive has good adhesion. The adhesive is prevented from losing efficacy under pressure, so that the adhesive is suitable for compounding various plastic films and aluminum foils, and the bonding strength of the adhesive is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical building materials, and in particular relates to a low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites. Background Art

[0002] Flexible packaging composite films are typically made by laminating multiple layers of films made from different materials. The key to composite quality lies in the adhesive used. Polyurethane adhesives dominate the adhesive landscape for composite flexible packaging due to their strong bonding strength, excellent safety, heat resistance, acid and alkali resistance, and rapid curing. Polyurethane adhesives are primarily classified into three categories: solvent-based, solvent-free, and water-based. In the current flexible packaging market, water-based polyurethane adhesives hold a relatively small market share due to their low bond strength, low initial tack, and poor wetting properties on non-polar substrates. In contrast, solvent-based polyurethane adhesives hold a higher market share, primarily in two-component systems. However, solvent-based adhesives emit large amounts of organic solvents during use, which poses a risk to the environment and can also cause health risks to workers. Solvent-free polyurethane adhesives contain no solvents, preventing environmental pollution from solvent volatilization during handling and use, nor do they contaminate food due to residual solvents after lamination. With the continuous improvement of people's environmental awareness and safety awareness, solvent-free composite technology has been rapidly promoted and developed.

[0003] In the composite process of soft packaging, films of different materials are laminated. Usually, CPP, PE, and EVA are used as the inner layer of the composite film, and PET, PA, BOPP, aluminum foil and other materials are used as the outer layer of the composite film. Materials such as PVC and PET have considerable polar groups. During the bonding process, the polar groups form hydrogen bonds with groups such as urethane bonds, ester bonds, and ether bonds in the adhesive, thereby strengthening the adhesion between the polyurethane adhesive and the substrate and increasing the bonding strength. However, most of the adhesives that currently meet the requirements of PET / VMPET composite films are solvent-based adhesives, and have low peel strength. For soft food packaging, solvent volatilization may cause food safety issues. Non-polar plastics, such as PP and PE, have low surface energy and may have difficulties in bonding with polar polyurethane adhesives due to low bonding strength. At the same time, the polyurethane adhesive synthesized by traditional methods has a high level of residual monomers. The free monomers will react in the adhesive layer to produce polyurea, which may migrate to the inner layer of PE. The presence of polyurea may also have a significant impact on the friction coefficient of the polyethylene film. Therefore, it is of great significance to develop a low-free monomer polyurethane adhesive for soft packaging composites with PET / VMPET / PE as the composite material. Summary of the Invention

[0004] The purpose of the present invention is to provide a low-free monomer solvent-free polyurethane adhesive for aluminum-plastic composites. By improving the formula, the number of isocyanate groups contained in the prepolymer is reduced, thereby reducing the viscosity of the prepolymer, making it easier for the glue to spread and level on the substrate. The introduction of aromatic polyester polyols and modified polyether polyols with a core-shell structure can effectively improve the high-temperature resistance of the adhesive, making it suitable for the composite of various plastic films and aluminum foils. The core-shell structure can increase the strength of the polyurethane adhesive, generate slip through the core-shell structure, thereby dispersing stress and avoiding the adhesive from failing under pressure. Therefore, the adhesive is suitable for the composite of various plastic films and aluminum foils, and the bonding strength of the adhesive is improved.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite is prepared by the following steps:

[0007] A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite is obtained by mixing a two-component polyurethane adhesive terminal isocyanate component A and a homemade aromatic polyester polyol component B according to a functional group molar ratio of 1.35:1 and curing at 40-50°C for 2-3 days.

[0008] Furthermore, the specific preparation steps of the isocyanate-terminated component A of the two-component polyurethane adhesive are as follows:

[0009] 15-60% of homemade aromatic polyester polyol and 0-20% of modified polyether polyol are added to a dry and clean four-necked flask, and vacuum dehydrated at 100-120°C for 2-3 hours to a water content of 500-520 ppm. The mixture is then cooled to 50-55°C, and 60-80% of aromatic / aliphatic / alicyclic diisocyanate is added. The mixture is heated to 75-85°C, reacted under nitrogen protection for 2-3 hours, naturally cooled to room temperature, and sealed and stored with nitrogen to obtain a two-component polyurethane adhesive terminal isocyanate component A.

[0010] Furthermore, the aromatic / aliphatic / alicyclic diisocyanate in component A is selected from a mixture of one or more of TDI, HDI, MDI, liquefied MDI, IPDI, and XDI.

[0011] Furthermore, the specific preparation steps of the homemade aromatic polyester polyol component B are as follows:

[0012] The dibasic acid and diol were added according to an alcohol-acid ratio of 1.2-1.4, 0.1-0.2% tetra-n-butyl titanate and 0.05-0.08% antioxidant 168 were added, the esterification temperature was 220-230°C, and the reaction was stirred at 220-230°C and 500-600r / min for 15-17h, and vacuum polycondensation was carried out at 230-240°C for 2h-3h, and the reaction was stopped to obtain the homemade aromatic polyester polyol component B.

[0013] Furthermore, the dibasic acid is composed of a mixture of one or more of terephthalic acid, phthalic acid, isophthalic acid, adipic acid, sebacic acid, and azelaic acid; the diol is composed of a mixture of one or more of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, trimethylolpropane, and triethylene glycol.

[0014] Furthermore, the specific preparation steps of the modified polyether polyol are as follows:

[0015] MOF / polyether polyol, octaepoxy POSS and DMF were added to a reactor, stirred at 20-25°C and 400-500 r / min for 20-30 min, and then benzyltriethylammonium chloride as a catalyst was added. The mixture was heated to 115-120°C and the reaction was continued for 2 h. The reaction was filtered and the unreacted epichlorohydrin was removed by rotary evaporation to obtain a modified polyether polyol.

[0016] Furthermore, the usage ratio of MOF / polyether polyol, octaepoxy POSS, DMF and benzyltriethylammonium chloride is 200-250 g: 200-220 g: 2-3 L: 12-15 mL.

[0017] Furthermore, the specific preparation steps of MOF / polyether polyol are as follows:

[0018] Add amino polyether polyol and deionized water into a polytetrafluoroethylene reactor, stir for 20-30 minutes at 20-25°C and 500-600 r / min, then add a mixed solution of sodium hexadecyl sulfate and 50-60wt% ethanol solution, heat to 120-130°C, continue stirring for 20-30 minutes, then add ferric chloride, continue stirring for 24 hours, filter, wash the filter cake with deionized water and anhydrous ethanol for 2-4 times, respectively, and vacuum dry at 60-70°C for 1-2 hours to obtain MOF / polyether polyol.

[0019] Furthermore, the usage ratio of amino polyether polyol, deionized water, sodium cetyl sulfate, ethanol solution and ferric chloride is 250-300 g: 2-3 L: 12-15 g: 120-220 mL: 100-120 g.

[0020] Furthermore, the specific preparation steps of amino polyether polyol are as follows:

[0021] Add 2,5-dihydroxyterephthalic acid and triethanolamine into the reactor, stir at 20-25℃ and 500-600r / min for 20-30min, introduce nitrogen for replacement 5-6 times, evacuate to the lowest vacuum degree of -0.095MPa, heat to 90-95℃, then add propylene oxide for ring-opening polymerization, and control the reaction temperature at 105℃ and the pressure within 0.4MPa. Continue the reaction for 30-40min, then add 50-60% by mass of hydrogen peroxide. Aqueous solution of potassium hydroxide was prepared, propylene oxide was added and the reaction was continued for 2-3 hours. The reaction temperature was controlled at 120-130°C and the pressure was controlled at 0.4-0.6 MPa. The mixture was aged for 1-2 hours and vacuumed. A 25-30% by mass phosphoric acid aqueous solution was added at 85-90°C and the reaction was continued for 30-40 minutes. Magnesium aluminum silicate adsorbent was added and the mixture was stirred for 20-30 minutes before dehydration and filtration. The filter cake was washed with deionized water and anhydrous ethanol for 2-4 times respectively and dried in vacuum at 60-70°C for 1-2 hours to obtain an aminated polyether polyol.

[0022] Furthermore, the usage ratio of 2,5-dihydroxyterephthalic acid, triethanolamine, propylene oxide, potassium hydroxide, phosphoric acid aqueous solution and magnesium aluminum silicate adsorbent is 300-400 g: 1.2-1.27 kg: 25-30 g: 4.8-5.2 g.

[0023] Beneficial effects of the present invention:

[0024] 1. The low-free-monomer solvent-free polyurethane adhesive prepared by the present invention solves the problems of low heat sealing strength and high friction coefficient existing in the current solvent-free two-component polyurethane adhesive products for lamination by developing and designing a low-free-monomer solvent-free polyurethane adhesive. It has good opening after lamination and has little effect on the friction coefficient of the film.

[0025] 2. By introducing aromatic polyester polyols, the adhesive's high-temperature resistance is significantly enhanced, resulting in excellent weather resistance and strong anti-fading properties. It is suitable for laminating various plastic films and aluminum foils. The raw material synthesis does not contain castor oil, palm oil, soybean oil, or other vegetable oils, resulting in a low odor and ease of use. This resulted in the development of a solvent-free two-component polyurethane adhesive suitable for both PET / VMPET and VMPET / PE laminations. The adhesive used for the outer layer is primarily a solvent-based polyurethane adhesive. This self-developed solvent-free two-component polyurethane adhesive achieves peel strengths exceeding 3.5N / 15mm for PET / VMPET laminations and over 4.1N / 15mm for inner VMPET / PE laminations. The adhesive reacts gently after mixing, enabling PET / PE lamination at machine speeds up to 415m / min. The adhesive exhibits excellent ink compatibility, with no ink dissolution, achieving a bond strength of 220g / 15mm on printed inks, minimizing the effects of solvents on the printing ink.

[0026] 3. The low-free-monomer solvent-free polyurethane adhesive of the present invention is composed of a two-component polyurethane adhesive terminal isocyanate component A and a homemade aromatic polyester polyol component B, wherein the two-component polyurethane adhesive terminal isocyanate component A contains a modified polyether polyol, and the modified polyether polyol can increase the bonding strength of the low-free-monomer solvent-free polyurethane adhesive as an adhesive by introducing a relatively stable benzene ring structure and a core-shell structure into the structure, and the core-shell structure is obtained by coordinating the 2,5-dihydroxyterephthalic acid monomer contained in the aminated polyether polyol with metal iron ions under hydrothermal conditions to obtain MOF / polyether polyol, and using this as the core, the surface uses the amino group as a site to catalyze the ring opening of the epoxy group in the octa-epoxy POSS to obtain a core-shell modified polyether polyol with POSS as the shell layer, which can effectively improve the high-temperature resistance of the adhesive, thereby being suitable for the composite of various plastic films and aluminum foils. The core-shell structure can increase the strength of the polyurethane adhesive adhesive, and the core-shell structure generates slippage, thereby dispersing stress and avoiding the adhesive from failing under pressure. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0028] Example 1: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0029] S1: Add 40% polyester polyol B-1 to a dry and clean four-necked flask, vacuum dehydrate at 110°C for 2.5 hours to a water content of 510 ppm, then cool to 52°C, add 65% MDI diisocyanate and 6% TDI diisocyanate, heat to 80°C, react under nitrogen protection for 2.5 hours, naturally cool to room temperature, and seal and store with nitrogen to obtain A-1.

[0030] S2: 4 parts of diethylene glycol, 8 parts of 1,4-butanediol, 3 parts of adipic acid, and 8 parts of azelaic acid were added at an alcohol-acid ratio of 1.4, and 0.15% of tetra-n-butyl titanate and 0.06% of antioxidant 168 were added. The mixture was stirred and reacted at 225°C and 550 r / min for 16 hours. The mixture was vacuum polycondensed at 235°C for 2.5 hours, and the reaction was stopped to obtain polyester polyol B-1.

[0031] S3: A-1 and B-1 were mixed at an R value of 1.35, and aged at 40°C for 2 days to obtain PU-1.

[0032] Example 2: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0033] S1: 350g 2,5-dihydroxyterephthalic acid and 125g triethanolamine were added to the reactor, stirred at 23°C and 550r / min for 25min, nitrogen was introduced for replacement 5 times, evacuated to the lowest vacuum degree of -0.095MPa, heated to 92°C, and then 365g propylene oxide was added to carry out ring-opening polymerization reaction, and the reaction temperature was controlled at 105°C and the pressure was controlled within 0.4MPa. The reaction was continued for 35min, and then 7g of 55% by mass of propylene oxide was added. To a potassium hydroxide aqueous solution, 870 g of propylene oxide was added and the reaction was continued for 2.5 h. The reaction temperature was controlled at 125 ° C, the pressure was controlled at 0.5 MPa, and the mixture was aged for 1.5 h. The mixture was vacuumed and 28 g of a 28% mass fraction of phosphoric acid aqueous solution was added at 88 ° C. The reaction was continued for 35 min. 5 g of magnesium aluminum silicate adsorbent was added and the mixture was stirred for 25 min. After dehydration, the mixture was filtered and the filter cake was washed with deionized water and anhydrous ethanol three times respectively, and dried in vacuo at 65 ° C for 1.5 h to obtain an amino polyether polyol.

[0034] S2: Add 280g of amino polyether polyol and 2.5L of deionized water into a polytetrafluoroethylene reactor, stir at 23°C and 550r / min for 25min, then add a mixed solution of 14g of sodium hexadecyl sulfate and 170mL of 55wt% ethanol solution, heat to 125°C, continue stirring for 25min, then add 110g of ferric chloride, continue stirring for 24h, filter, wash the filter cake with deionized water and anhydrous ethanol three times respectively, and dry in vacuo at 65°C for 1.5h to obtain MOF / polyether polyol.

[0035] S3: 230 g of MOF / polyether polyol, 210 g of octa-epoxy POSS, and 2.5 L of DMF were added to a reactor and stirred at 23°C and 450 rpm for 25 min. Then, 14 mL of benzyltriethylammonium chloride as a catalyst was added and the mixture was heated to 118°C. The reaction was continued for 2 h, filtered, and the unreacted epichlorohydrin was removed by rotary evaporation to obtain a modified polyether polyol.

[0036] S4: Add polyester polyol B-1 and 15% modified polyether polyol into a dry and clean four-necked flask, vacuum dehydrate at 110°C for 2.5 hours to a water content of 510 ppm, then cool to 52°C, add 65% MDI diisocyanate and 6% TDI diisocyanate, heat to 80°C, react under nitrogen protection for 2.5 hours, naturally cool to room temperature, and seal and store with nitrogen to obtain A-2.

[0037] S5: A-2 and B-1 were mixed at an R value of 1.35, and aged at 40°C for 2 days to obtain PU-2.

[0038] Example 3: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0039] 30% polyester polyol B-3 and 10% modified polyether polyol were added to a dry and clean four-necked flask, and vacuum dehydrated at 110°C for 2.5 hours to a water content of 510 ppm. The temperature was then lowered to 52°C, and 65% MDI diisocyanate and liquefied MDI diisocyanate were added. The mixture was heated to 80°C and reacted under nitrogen for 2.5 hours. The mixture was naturally cooled to room temperature and sealed and stored with nitrogen to obtain A-4.

[0040] A-4 and B-1 were mixed at an R value of 1.35 and aged at 40°C for 2 days to obtain PU-3;

[0041] Example 4: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0042] 4 parts of neopentyl glycol, 8 parts of 1,4-butanediol, 4.5 parts of adipic acid and 8 parts of isophthalic acid were added at an alcohol-acid ratio of 1.3, 0.15% of tetra-n-butyl titanate and 0.06% of antioxidant 168 were added, and the mixture was stirred and reacted at 225°C and 550 r / min for 16 hours. The mixture was vacuum polycondensed at 235°C for 2.5 hours, and the reaction was stopped to obtain polyester polyol B-2.

[0043] A-2 and B-2 were mixed at an R value of 1.35 and aged at 40°C for 2 days to obtain PU-4.

[0044] Example 5: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0045] 30% polyester polyol B-2 and 15% modified polyether polyol were added to a dry and clean four-necked flask, vacuum dehydrated at 110°C for 2.5 hours to a water content of 510 ppm, then cooled to 52°C, 65% MDI diisocyanate and liquefied MDI diisocyanate were added, heated to 80°C, reacted under nitrogen protection for 2.5 hours, naturally cooled to room temperature, and sealed and stored with nitrogen to obtain A-3.

[0046] A-3 and B-1 were mixed at an R value of 1.35 and aged at 40°C for 2 days to obtain PU-5;

[0047] Example 6: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0048] A-3 and B-2 were mixed at an R value of 1.35 and aged at 40°C for 2 days to obtain PU-6;

[0049] Example 7: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composites is prepared by the following steps:

[0050] 4 parts of diethylene glycol, 8 parts of 1,4-butanediol, 3 parts of adipic acid, and 8 parts of azelaic acid were added at an alcohol-acid ratio of 1.4, and 0.15% of tetra-n-butyl titanate and 0.06% of antioxidant 168 were added. The reaction was stirred at 225°C and 550 r / min for 16 hours, and vacuum polycondensed at 235°C for 2.5 hours. The reaction was stopped to obtain polyester polyol B-3.

[0051] A-3 and B-3 were mixed at an R value of 1.35 and aged at 40°C for 2 days to obtain PU-7.

[0052] Comparative Example 1: Based on Example 2, the aminated polyether polyol in step S2 was replaced by polyether polyol.

[0053] Comparative Example 2: Based on Example 2, the MOF / polyether polyol in step S3 was replaced with aminated polyether polyol.

[0054] Comparative Example 3: Based on Example 2, the modified polyether polyol in step S4 was replaced with commercially available polyether polyol.

[0055] The performance test of the low free monomer solvent-free polyurethane adhesive obtained in Examples 1 to 3 and Comparative Examples 1 to 3 is performed, and the results are shown in Table 1: The two-component solvent-free polyurethane adhesive A (NCO) and B (OH) components are mixed and stirred uniformly according to the formula design ratio A / B (1.2-1.8), and coated on a professional solvent-free laminating machine within 45 minutes to form a composite outer layer of PET (polyethylene terephthalate) / VMPET (polyethylene terephthalate aluminized film) and an inner layer of VMPET (polyethylene terephthalate aluminized film) / PE film, and the glue amount is controlled at 1.7 g / m 2 The films used were all corona treated. The composite samples were placed in a 48°C oven for reaction curing and were used for subsequent testing and evaluation of properties such as peel strength and friction coefficient.

[0056] Table 1

[0057]

[0058]

[0059] As can be seen from Table 1, the synthesized solvent-free two-component polyurethane adhesive has a low NCO free monomer content and the introduction of aromatic polyester polyols in combination with PPG400 as component B greatly improves the performance of the adhesive. In the PET / VMPET / PE structure, the prepared adhesive achieves significant results in reducing the friction coefficient and increasing the peel strength, greatly improving work efficiency.

[0060] In Comparative Example 1, the aminated polyether polyol in step S2 is replaced by polyether polyol, the MOF structure is missing, and the ordinary polyether polyol cannot coordinate with ferric chloride to form a metal organic framework, resulting in the inability to construct a core-shell structure. The stress dispersion ability of the adhesive is significantly reduced, the performance deteriorates, the peel strength is reduced, the friction coefficient is increased, and the machine speed is reduced. Due to the lack of a benzene ring stable structure and a core-shell slip effect, the high temperature resistance and bonding strength are weakened, the free monomers increase, and the lack of an amino group leads to a decrease in the reaction activity with isocyanate, and more free monomers may remain.

[0061] In comparative example 2, the MOF / polyether polyol in step S3 is replaced by an aminated polyether polyol. The core-shell structure is incomplete, and only the core of the aminated polyether polyol is retained, but the rigid support of MOF and the shell protection of POSS are lacking, resulting in limited modification effect, reduced peel strength, and a slightly higher friction coefficient. Due to the partial retention of the amino catalytic effect, the machine speed can still be maintained at 385m / min, but the reaction activity is low, the temperature resistance is limited, and the high temperature resistant skeleton of MOF is lacking, and thermal decay may occur after long-term use.

[0062] In comparative example 3, the modified polyether polyol in step S4 is replaced by a commercially available polyether polyol, which completely loses the core-shell properties. The commercially available polyether polyol has no benzene ring, MOF or POSS structure, and the adhesive becomes a conventional polyurethane system with the worst overall performance, the lowest peel strength, high friction coefficient, and low machine speed. Due to the lack of special structural design, the weather resistance and anti-attenuation ability are significantly reduced. The commercially available polyether may have poor compatibility with MDI / TDI, resulting in a decrease in the uniformity of the adhesive layer and affecting the appearance of the composite film.

[0063] While the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations can be made to the embodiments without departing from the principles and spirit of the invention.

Claims

1. A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite, characterized in that: Prepared by the following steps: A low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite is obtained by mixing a two-component polyurethane adhesive terminal isocyanate component A and a homemade aromatic polyester polyol component B according to a functional group molar ratio of 1.35:1 and curing at 40-50°C for 2-3 days.

2. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 1, characterized in that: The specific preparation steps of the two-component polyurethane adhesive terminal isocyanate component A are as follows: 15-60% of homemade polyester polyol and 0-20% of modified polyether polyol are added to a dry and clean four-necked flask, and vacuum dehydrated at 100-120°C for 2-3 hours to a water content of 500-520 ppm. The temperature is then lowered to 50-55°C, and 60-80% of aromatic / aliphatic / alicyclic diisocyanate is added. The mixture is heated to 75-85°C and reacted under nitrogen protection for 2-3 hours. The mixture is naturally cooled to room temperature and sealed and stored with nitrogen to obtain a two-component polyurethane adhesive terminal isocyanate component A.

3. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 2, characterized in that: The aromatic / aliphatic / alicyclic diisocyanate is selected from a mixture of one or more of TDI, HDI, MDI, liquefied MDI, IPDI, and XDI.

4. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 1, characterized in that: The specific preparation steps of the homemade aromatic polyester polyol component B are as follows: The dibasic acid and diol are added according to an alcohol-acid ratio of 1.2-1.4, 0.1-0.2% tetra-n-butyl titanate and 0.05-0.08% antioxidant 168 are added, the esterification temperature is 220℃-230℃, and the reaction is stirred at 220℃-230℃ and 500-600r / min for 15-17h, and vacuum polycondensation is carried out at 230℃-240℃ for 2h-3h. The reaction is stopped to obtain a homemade aromatic polyester polyol component B.

5. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 4, characterized in that: The dibasic acid is composed of a mixture of one or more of terephthalic acid, phthalic acid, isophthalic acid, adipic acid, sebacic acid, and azelaic acid; the diol is composed of a mixture of one or more of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, neopentyl glycol, trimethylolpropane, and triethylene glycol.

6. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 2, characterized in that: The specific preparation steps of the modified polyether polyol are as follows: MOF / polyether polyol, octaepoxy POSS and DMF were added to a reactor, stirred at 20-25°C and 400-500 r / min for 20-30 min, and then benzyltriethylammonium chloride as a catalyst was added. The mixture was heated to 115-120°C and the reaction was continued for 2 h. The mixture was filtered and the unreacted epichlorohydrin was removed by rotary evaporation to obtain a modified polyether polyol. The usage ratio of the MOF / polyether polyol, octaepoxy POSS, DMF and benzyltriethylammonium chloride is 200-250 g: 200-220 g: 2-3 L: 12-15 mL.

7. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 6, characterized in that: The specific preparation steps of the MOF / polyether polyol are as follows: Add amino polyether polyol and deionized water into a polytetrafluoroethylene reactor, stir for 20-30 minutes at 20-25°C and 500-600 r / min, then add a mixed solution of sodium hexadecyl sulfate and 50-60wt% ethanol solution, heat to 120-130°C, continue stirring for 20-30 minutes, then add ferric chloride, continue stirring for 24 hours, filter, wash the filter cake with deionized water and anhydrous ethanol for 2-4 times, respectively, and vacuum dry at 60-70°C for 1-2 hours to obtain MOF / polyether polyol.

8. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 7, characterized in that: The usage ratio of the amino polyether polyol, deionized water, sodium cetyl sulfate, ethanol solution and ferric chloride is 250-300 g: 2-3 L: 12-15 g: 120-220 mL: 100-120 g.

9. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 7, characterized in that: The specific preparation steps of the amino polyether polyol are as follows: Add 2,5-dihydroxyterephthalic acid and triethanolamine into the reactor, stir at 20-25℃ and 500-600r / min for 20-30min, introduce nitrogen for replacement 5-6 times, evacuate to the lowest vacuum degree of -0.095MPa, heat to 90-95℃, then add propylene oxide for ring-opening polymerization, and control the reaction temperature at 105℃ and the pressure within 0.4MPa. Continue the reaction for 30-40min, then add 50-60% by mass of hydrogen peroxide. Aqueous solution of potassium hydroxide was prepared, propylene oxide was added and the reaction was continued for 2-3 hours. The reaction temperature was controlled at 120-130°C and the pressure was controlled at 0.4-0.6 MPa. The mixture was aged for 1-2 hours and vacuumed. A 25-30% by mass phosphoric acid aqueous solution was added at 85-90°C and the reaction was continued for 30-40 minutes. Magnesium aluminum silicate adsorbent was added and the mixture was stirred for 20-30 minutes before dehydration and filtration. The filter cake was washed with deionized water and anhydrous ethanol for 2-4 times respectively and dried in vacuum at 60-70°C for 1-2 hours to obtain an aminated polyether polyol.

10. The low-free-monomer solvent-free polyurethane adhesive for aluminum-plastic composite according to claim 9, characterized in that: The usage ratio of the 2,5-dihydroxyterephthalic acid, triethanolamine, propylene oxide, potassium hydroxide, phosphoric acid aqueous solution and magnesium aluminum silicate adsorbent is 300-400g:1.2-1.27kg:25-30g:4.8-5.2g.

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