Two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil and preparation method thereof

Abstract

The present invention relates to the technical field of preparation of two-component solvent-free polyurethane adhesive, and discloses a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil and a preparation method thereof; the present invention adopts homemade modified epoxy resin to prepare two-component solvent-free polyurethane adhesive, and the prepared solvent-free adhesive has the characteristics of low viscosity (25°C / 2000-3000mpa·s), low use temperature (40-45°C), long application period (40°C, ≥45 minutes), and high bonding strength to PET and Al, which can meet the composite requirements of high barrier material PET and aluminum foil, and its composite processability is good, which is very suitable for the solvent-free composite process of such high barrier materials. At the same time, it also solves the problems of environmental protection and high energy consumption of solvent-based adhesives currently used in the industry, as well as the problems of large viscosity, high use temperature and short application period of solvent-free adhesives used for composite films of this type on the market.

Description

Technical Field

[0001] The invention belongs to the field of preparation of two-component solvent-free polyurethane adhesive, and in particular relates to a two-component solvent-free polyurethane adhesive suitable for composite bonding of PET and aluminum foil and a preparation method thereof. Background Art

[0002] Since Henkel of the Federal Republic of Germany first used solvent-free polyurethane adhesive to make composite film materials more than 20 years ago, due to its obvious economical, safe and environmentally friendly advantages, it has made great progress in the Federal Republic of Germany, the United States, Japan and the world. In Europe and the United States, the amount of solvent-free composite processing only accounted for 10% of the total amount of composite film packaging materials in the past, but now it has accounted for more than 50% of the total processing volume.

[0003] At present, the market for soft packaging materials is developing rapidly, and the application of two-component solvent-free polyurethane adhesive in soft packaging lamination is becoming more and more extensive. In the film lamination of snacks, pre-prepared food, pet food, beverages, medicines, ordinary packaging bags, etc., the proportion of two-component solvent-free polyurethane is increasing, far exceeding solvent-based adhesives. Solvent-free PU adhesive has the advantage of "generation gap" compared to traditional solvent adhesives. It has a wide operating temperature range, high bonding strength, no solvent volatilization, 100% solid content, and is an energy-saving and emission-free technology. The reaction speed and ultra-low viscosity of the formula itself increase the product production speed, improve labor productivity and economic benefits.

[0004] At present, in the conventional multi-layer structure of PET and PE, RCPP, etc., two-component solvent-free polyurethane adhesive has been basically fully realized for compounding. However, in the compounding of high-barrier film materials, such as PET and aluminum foil (AL), due to the rigidity of the materials and the bonding strength of the composite, the mainstream in the market is still solvent-based polyurethane adhesive for compounding. The conventional two-component solvent-free polyurethane adhesive in the industry has low viscosity, too low initial adhesion, and insufficient bonding performance to aluminum foil, which limits its application in such high-barrier material films. Although some companies on the market have launched solvent-free polyurethane adhesives suitable for the compounding of such high-barrier materials, their basic principle is to increase the viscosity of the system, increase the molecular weight and cohesive strength, thereby improving the adhesion to PET and AL. They generally have problems such as high viscosity (25℃ / 6000-10000mpa·s), high use temperature (60-65℃), and short application period (60℃, ≤30 minutes), which affects their large-scale promotion and use. Summary of the invention

[0005] Based on the problems existing in the prior art, the primary purpose of the present invention is to provide a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, which has the characteristics of low viscosity (25℃ / 2000-3000mpa·s), low operating temperature (40-45℃), long application period (40℃, ≥45 minutes), and high bonding strength to PET and AL, which can meet the composite requirements of high barrier material PET and aluminum foil, and has good composite processability, and is very suitable for the solvent-free composite process of such high barrier materials.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, characterized in that it comprises two components A and B, which are calculated by mass.

[0009] The component A comprises: 25-26.5 parts of difunctional polyether polyol, 9-10 parts of multifunctional polyether polyol, and 64-65.5 parts of isocyanate;

[0010] The B component comprises: 60-69 parts of a 2-functionality polyester polyol, 20-25 parts of a multifunctionality polyether polyol, and 10-19 parts of a homemade modified epoxy resin;

[0011] The homemade modified epoxy resin comprises: 8-9 parts of isocyanate, 60-61 parts of polyether polyol, 30-31.8 parts of epoxy resin, and 0.1-0.2 parts of boron trifluoride ether;

[0012] The mass ratio of the A component to the B component is (90-110):80.

[0013] Preferably, in the homemade modified epoxy resin, the isocyanate is pure MDI, the polyether polyol is PPG400, and the epoxy resin is E44 epoxy resin.

[0014] Preferably, in component A, the difunctional polyether polyol is a PO-type polyether with a hydroxyl value of 54-115 mgKOH / g; the multifunctional polyether polyol is MN500 and / or MN350; and the isocyanate is MDI-50.

[0015] Preferably, in component B, the hydroxyl value of the difunctional polyester polyol is 53-225 mgKOH / g; and the multifunctional polyether polyol is MN500 and / or MN350.

[0016] The method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil of the present invention is characterized in that the homemade modified epoxy resin is prepared by the following method:

[0017] (1) Add 8-9 parts of pure MDI to the reactor, heat to 60-65°C, then dropwise add 4.9-5.5 parts of PPG400 within 20-25 minutes, and stir to react for 2-2.5 hours;

[0018] (2) Add 30-31.8 parts of E44 epoxy resin, raise the temperature to 80-85°C, and stir to react for 1.5-2 hours;

[0019] (3) Add 54-55.5 parts of PPG400, add 0.1-0.2 parts of boron trifluoride etherate dropwise at 80-85°C over 15-20 minutes, and continue stirring to react for 2-2.5 hours;

[0020] (4) Cooling to 60-65°C, adding toluene to dissolve, washing to remove boron trifluoride etherate, and distilling toluene to obtain a colorless, transparent, viscous liquid, which is the homemade modified epoxy resin.

[0021] Preferably, the preparation method of component A is as follows: add difunctional polyether polyol and multifunctional polyether polyol into a reaction kettle, heat to a first temperature, decompress and dehydrate, then release the pressure, cool to a second temperature, add isocyanate to react, cool to a third temperature, vacuum and degas, and obtain component A.

[0022] Preferably, in the preparation method of component A, the first temperature is 100-105°C, the vacuum degree of reduced pressure dehydration is less than 100 Pa, the time is 2-2.5h, and the pressure relief method is to introduce nitrogen; the second temperature is 80-90°C, the reaction time is 1.5-2h; the third temperature is 60-65°C, and the vacuum degassing time is 10-15 minutes.

[0023] Preferably, the preparation method of the B component is: add difunctional polyester polyol, multifunctional polyether polyol and homemade modified epoxy resin into a reaction kettle, heat to a first temperature, decompress and dehydrate, cool to a second temperature, vacuum and degas, to obtain the B component.

[0024] Preferably, in the preparation method of component B, the first temperature is 100-105°C, the vacuum degree of reduced pressure dehydration is less than 100 Pa, and the time is 2-2.5h; the second temperature is 60-65°C, and the vacuum degassing time is 10-15 minutes.

[0025] The inventive mechanism of the present invention:

[0026] At present, ordinary two-component solvent-free polyurethane adhesives are fully capable of laminating common soft-pack films such as PET, PA, PE, and RCPP in the industry. However, when laminating high-barrier materials such as PET and aluminum foil (AL), solvent-based polyurethane adhesives are still more commonly used in the industry due to the rigid stress of the materials and the adhesion to the aluminum foil. Although a few companies in the industry have launched two-component solvent-free polyurethane adhesives suitable for laminating such high-barrier PET and AL, the principle is generally to increase the molecular weight of the resin system, thereby increasing the cohesion and bonding strength, and achieving a good bonding and laminating effect on PET and AL. This brings about the problems of high viscosity (25℃ / 6000-10000mpa·s), high operating temperature (60-65℃), and short application period (60℃, ≤30 minutes). Due to the high operating temperature, the viscosity of the glue and the excessive load on the coating machine are likely to increase during use. Therefore, the gluing system generally needs to be cleaned every 6-12 hours. At the same time, the short applicability period will also lead to the downtime for reel change not being too long, otherwise the rubber roller needs to be cleaned again, affecting production efficiency.

[0027] In order to solve the composite problem of PET and AL in soft packaging materials, the present invention synthesizes a homemade modified epoxy resin through a special synthesis method, and then uses the modified epoxy resin to synthesize a two-component solvent-free polyurethane adhesive, and introduces the epoxy resin structure into the system, thereby achieving a good bonding effect on PET and aluminum foil. At the same time, due to the special modification of the epoxy resin, a network-like polyurethane epoxy block resin structure with high cohesion is introduced, so that the adhesive system itself has good cohesion, and can achieve good initial adhesion to rigid materials PET and AL at low viscosity, avoiding the problem of delamination after composite. Finally, the problems of this type of adhesive in the industry, such as high viscosity (25℃ / 6000-10000mpa·s), high use temperature (60-65℃), and short application period (60℃, ≤30 minutes), are solved.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention adopts a self-made modified epoxy resin to synthesize a two-component solvent-free polyurethane adhesive, which has the characteristics of low viscosity (25°C / 2000-3000mpa·s), low operating temperature (40-45°C), long application period (40°C, ≥45 minutes), and high bonding strength to PET and AL, which can meet the composite requirements of high barrier material PET and aluminum foil, and its composite processability is good, which is very suitable for the solvent-free composite process of such high barrier materials. The epoxy resin structure is introduced into the system through the self-made modified epoxy resin. At the same time, the epoxy resin is not simply physically mixed and added, but participates in the reaction in the system to form a block network structure, so as to achieve good bonding to PET film and aluminum foil (peel strength ≥8N / 15mm), and the bonding strength is higher than the same type of products on the market (about 7N / 15mm).

[0030] (2) The present invention adopts a self-made modified epoxy resin to synthesize a two-component solvent-free polyurethane adhesive. By adopting a method of multi-step modification of epoxy resin by polyether polyol and isocyanate, epoxy resin can be introduced to achieve good bonding performance to the material. At the same time, due to the introduction of a special block network structure, the characteristics of low viscosity and high cohesion can be achieved at the same time. Good initial adhesion to rigid materials PET and AL is achieved at low viscosity (25°C / 2000-3000mpa·s), and the stress stratification problem of rigid materials after composite is prevented. In addition, since polyether polyol is used to modify the epoxy resin in the self-made modified resin, the problem of brittle curing after adding epoxy resin is solved. Compared with the prior art, the final product has a lower viscosity, a lower use temperature, and a greatly improved application period. DETAILED DESCRIPTION

[0031] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments. However, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work belong to the protection scope of the present invention. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0032] The epoxy resin E44 used in the embodiments of the present invention was purchased from Jiangsu Sanmu Group Co., Ltd.

[0033] 2-functionality polyether polyols 1000LM and 2000LM were purchased from Dow Chemical Company;

[0034] Multifunctional polyether polyol MN500 (3 functionalities, hydroxyl value 331-341 mgKOH / g) and MN350 (3 functionalities, hydroxyl value 475-485 mgKOH / g) were purchased from Shandong Bluestar Dongda Co., Ltd.

[0035] Isocyanate MDI-50, purchased from Yantai Wanhua Group Co., Ltd.;

[0036] The difunctional polyester polyols 5505 (hydroxyl value 195-225 mgKOH / g), 5510 (hydroxyl value 106-118 mgKOH / g), and 5520 (hydroxyl value 53-59 mgKOH / g) were purchased from Shanghai Huide Technology Co., Ltd.

[0037] Example of homemade modified epoxy resin

[0038] Step 1: Add 8.24 parts of pure MDI to the reactor, heat to 60-65°C, then slowly drop 5.49 parts of PPG400, which takes about 20-25 minutes to complete. After the dropwise addition is completed, stir and react at 60-65°C for 2-2.5 hours.

[0039] Step 2: Add 31.32 parts of epoxy resin E44, raise the temperature to 80-85°C, and stir to react for 1.5-2 hours.

[0040] Step 3: Add 54.85 parts of PPG400, keep the reaction temperature at 80-85°C, slowly drop 0.1 parts of boron trifluoride etherate, and add it in about 15-20 minutes. After the addition is completed, continue to stir and react for 2-2.5 hours.

[0041] Step 4: Cool down to 60-65°C, add toluene to dissolve the resin prepared above, then wash with water 3 times to remove the residual boron trifluoride ether, then distill out the toluene, and finally obtain a colorless, transparent, viscous liquid, which is the homemade modified epoxy resin.

[0042] Example 1

[0043] A method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, comprising the following steps:

[0044] Component A:

[0045] Step 1: Add 25.5 parts of 1000LM and 9.5 parts of MN500 into the reactor, heat to 100-105°C, dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa, and then introduce nitrogen to release the pressure;

[0046] Step 2: Cool down to 80-90°C, add 65 parts of MDI-50, and stir to react for 1.5-2 hours;

[0047] Step 3: Cool down to 60-65℃ and perform vacuum degassing for 10-15 minutes, then unload and package to obtain the synthesized solvent-free adhesive component A.

[0048] Component B:

[0049] Step 1: Add 25 parts of 5505, 40 parts of 5520, 23 parts of MN350, and 12 parts of homemade modified epoxy resin into the reaction kettle, heat to 100-105°C, and dehydrate for 2-2.5h at a vacuum degree of less than 100Pa;

[0050] Step 2: Cool down to 60-65℃, vacuum and degas for 10-15 minutes, and pack the product to obtain the synthesized solvent-free adhesive component B.

[0051] Example 2

[0052] A method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, comprising the following steps:

[0053] Component A:

[0054] Step 1: Add 25.5 parts of 1000LM and 9.5 parts of MN500 into the reactor, heat to 100-105°C, dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa, and then introduce nitrogen to release the pressure;

[0055] Step 2: Cool down to 80-90°C, add 65 parts of MDI-50, and stir to react for 1.5-2 hours;

[0056] Step 3: Cool down to 60-65℃ and perform vacuum degassing for 10-15 minutes, then unload and package to obtain the synthesized solvent-free adhesive component A.

[0057] Component B:

[0058] Step 1: Add 22 parts of 5505, 40 parts of 5520, 21 parts of MN350, and 17 parts of homemade modified epoxy resin into the reaction kettle, heat to 100-105°C, and dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa;

[0059] Step 2: Cool down to 60-65℃, vacuum and degas for 10-15 minutes, and pack the product to obtain the synthesized solvent-free adhesive component B.

[0060] Example 3

[0061] A method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, comprising the following steps:

[0062] Component A:

[0063] Step 1: Add 25.9 parts of 2000LM and 9.3 parts of MN350 into the reactor, heat to 100-105°C, dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa, and then introduce nitrogen to release the pressure;

[0064] Step 2: Cool down to 80-90°C, add 64.8 parts of MDI-50, and stir to react for 1.5-2 hours;

[0065] Step 3: Cool down to 60-65℃ and perform vacuum degassing for 10-15 minutes, then unload and package to obtain the synthesized solvent-free adhesive component A.

[0066] Component B:

[0067] Step 1: Add 31 parts of 5505, 30 parts of 5510, 24 parts of MN500, and 15 parts of homemade modified epoxy resin into the reaction kettle, heat to 100-105°C, and dehydrate for 2-2.5h at a vacuum degree of less than 100Pa;

[0068] Step 2: Cool down to 60-65℃, vacuum and degas for 10-15 minutes, and pack the product to obtain the synthesized solvent-free adhesive component B.

[0069] Example 4

[0070] A method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, comprising the following steps:

[0071] Component A:

[0072] Step 1: Add 25.9 parts of 2000LM and 9.3 parts of MN350 into the reactor, heat to 100-105°C, dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa, and then introduce nitrogen to release the pressure;

[0073] Step 2: Cool down to 80-90°C, add 64.8 parts of MDI-50, and stir to react for 1.5-2 hours;

[0074] Step 3: Cool down to 60-65℃ and perform vacuum degassing for 10-15 minutes, then unload and package to obtain the synthesized solvent-free adhesive component A.

[0075] Component B:

[0076] Step 1: Add 60 parts of 5510, 22 parts of MN500, and 18 parts of homemade modified epoxy resin into the reaction kettle, heat to 100-105°C, and dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa;

[0077] Step 2: Cool down to 60-65℃, vacuum and degas for 10-15 minutes, and pack the product to obtain the synthesized solvent-free adhesive component B.

[0078] Comparative Example 1

[0079] In the comparative example 1, the self-made modified epoxy resin was not added to the component B, and the two-component solvent-free polyurethane adhesive was directly prepared.

[0080] Component A:

[0081] Step 1: Add 25.5 parts of 1000LM and 9.5 parts of MN500 into the reactor, heat to 100-105°C, dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa, and then introduce nitrogen to release the pressure;

[0082] Step 2: Cool down to 80-90°C, add 65 parts of MDI-50, and stir to react for 1.5-2 hours;

[0083] Step 3: Cool down to 60-65℃ and perform vacuum degassing for 10-15 minutes, then unload and package to obtain the synthesized solvent-free adhesive component A.

[0084] Component B:

[0085] Step 1: Add 10 parts of 5505, 60 parts of 5520, and 30 parts of MN350 to the reactor and heat to 100-105°C, and dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa;

[0086] Step 2: Cool down to 60-65℃, vacuum and degas for 10-15 minutes, and pack the product to obtain the synthesized solvent-free adhesive component B.

[0087] Comparative Example 2

[0088] Epoxy resin E44 was added to component B of comparative example 2 to prepare a two-component solvent-free polyurethane adhesive.

[0089] Component A:

[0090] Step 1: Add 25.5 parts of 1000LM and 9.5 parts of MN500 into the reactor, heat to 100-105°C, dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa, and then introduce nitrogen to release the pressure;

[0091] Step 2: Cool down to 80-90°C, add 65 parts of MDI-50, and stir to react for 1.5-2 hours;

[0092] Step 3: Cool down to 60-65℃ and perform vacuum degassing for 10-15 minutes, then unload and package to obtain the synthesized solvent-free adhesive component A.

[0093] Component B:

[0094] Step 1: Add 25 parts of 5505, 40 parts of 5520, 21 parts of MN350, and 17 parts of epoxy resin E44 into the reaction kettle, heat to 100-105°C, and dehydrate for 2-2.5 hours at a vacuum degree of less than 100Pa;

[0095] Step 2: Cool down to 60-65℃, vacuum and degas for 10-15 minutes, and pack the product to obtain the synthesized solvent-free adhesive component B.

[0096] Performance Testing

[0097] The examples 1 to 4 and comparative examples 1 to 2 were used in a ratio of 100:80, the commercially available product was used in a ratio of 100:95, the glue amount was controlled at 2-2.2 g / cm2, a small coating machine was used to composite the PET film and aluminum foil, the composite coil was rolled up and put into an oven at 45-50°C for 48 hours for slitting test.

[0098] Table 1 shows the performance test results of Examples 1 to 4, Comparative Examples 1-2, and competing products.

[0099] Table 1

[0100]

[0101] From the test results, it can be seen that the two-component solvent-free polyurethane adhesive synthesized after adding the homemade modified epoxy resin has the characteristics of low viscosity (25℃ / 2000-3000mpa·s), low operating temperature (40-45℃), long application period (40℃, ≥45 minutes), and high bonding strength to PET and AL, which can meet the composite requirements of high barrier materials PET and aluminum foil. From the comparative test, it can be seen that although the formula adhesive without the addition of homemade modified epoxy resin has a lower viscosity, the composite PET / AL film has blistering and low peel strength, which cannot meet the requirements. Although the peel strength of the formula with the addition of epoxy resin E44 is improved to a certain extent, the epoxy group of the added epoxy resin E44 cannot react and crosslink with the system and is free outside the system, so the peel strength is much lower than the formula with the addition of homemade modified epoxy resin. At the same time, due to insufficient cohesion and lack of initial adhesion, the composite film has the problem of curing and blistering.

[0102] Compared with commercially available products, commercially available products have significantly higher viscosity and higher operating temperatures (60-65°C). At the same time, due to the high operating temperature, this shortens its applicable period to less than 30 minutes, which is equivalent to the shutdown time for roll changing during production not exceeding 30 minutes, affecting the convenience of its process. In summary, the present invention provides a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, which has the characteristics of low viscosity (25°C / 2000-3000mpa·s), low operating temperature (40-45°C), long applicable period (40°C, ≥45 minutes), and high bonding strength to PET and AL. It can meet the composite requirements of high barrier material PET and aluminum foil, and its composite processability is good, which is very suitable for the solvent-free composite process of such high barrier materials.

[0103] The above descriptions are only some specific implementation methods of the present invention, and the protection scope of the present invention is not limited thereto. Any changes or substitutions made by any technician familiar with the technical field within the technical scope disclosed in the present invention without making any creative work shall fall within the protection scope of the present invention.

Claims

1. A two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil, characterized in that: Contains two components, A and B, by mass fraction, The component A comprises: 25-26.5 parts of difunctional polyether polyol, 9-10 parts of multifunctional polyether polyol, and 64-65.5 parts of isocyanate; The B component comprises: 60-69 parts of a 2-functionality polyester polyol, 20-25 parts of a multifunctionality polyether polyol, and 10-19 parts of a homemade modified epoxy resin; The homemade modified epoxy resin comprises: 8-9 parts of isocyanate, 60-61 parts of polyether polyol, 30-31.8 parts of epoxy resin, and 0.1-0.2 parts of boron trifluoride ether; In the homemade modified epoxy resin, the isocyanate is pure MDI, the polyether polyol is PPG400, and the epoxy resin is E44 epoxy resin; The homemade modified epoxy resin is prepared by the following method: (1) Add 8-9 parts of pure MDI to the reactor, heat it to 60-65°C, then drop 4.9-5.5 parts of PPG400 over 20-25 minutes, and stir to react for 2-2.5 hours; (2) Add 30-31.8 parts of E44 epoxy resin, raise the temperature to 80-85°C, and stir to react for 1.5-2 hours; (3) Add 54-55.5 parts of PPG400, add 0.1-0.2 parts of boron trifluoride etherate dropwise at 80-85°C within 15-20 minutes, and continue stirring and reacting for 2-2.5 hours; (4) Cooling to 60-65°C, adding toluene to dissolve, washing to remove boron trifluoride etherate, and distilling toluene to obtain a colorless, transparent, viscous liquid, which is the homemade modified epoxy resin; The mass ratio of component A to component B is (90-110):

80.

2. The two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil according to claim 1, characterized in that: In component A, the difunctional polyether polyol is a PO-type polyether with a hydroxyl value of 54-115 mgKOH / g; the multifunctional polyether polyol is MN500 and / or MN350; and the isocyanate is MDI-50.

3. The two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil according to claim 2, characterized in that: In component B, the hydroxyl value of the difunctional polyester polyol is 53-225 mgKOH / g; and the multifunctional polyether polyol is MN500 and / or MN350.

4. The method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil according to any one of claims 1 to 3, characterized in that: The preparation method of the component A is as follows: add a difunctional polyether polyol and a multifunctional polyether polyol into a reaction kettle, heat it to a first temperature, decompress and dehydrate, then release the pressure, cool it to a second temperature, add isocyanate to react, cool it to a third temperature, vacuum and degas, and obtain component A.

5. The method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil according to claim 4, characterized in that: In the preparation method of component A, the first temperature is 100-105°C, the vacuum degree of reduced pressure dehydration is less than 100Pa, the time is 2-2.5h, and the pressure relief method is to introduce nitrogen; the second temperature is 80-90°C, the reaction time is 1.5-2h; the third temperature is 60-65°C, and the vacuum degassing time is 10-15 minutes.

6. The method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil according to claim 5, characterized in that: The preparation method of the B component is: adding a difunctional polyester polyol, a multifunctional polyether polyol and a self-made modified epoxy resin into a reaction kettle, heating to a first temperature, decompressing and dehydrating, cooling to a second temperature, vacuuming and degassing, and obtaining the B component.

7. The method for preparing a two-component solvent-free polyurethane adhesive for composite bonding of PET and aluminum foil according to claim 6, characterized in that: In the preparation method of component B, the first temperature is 100-105°C, the vacuum degree of decompression and dehydration is less than 100Pa, and the time is 2-2.5h; the second temperature is 60-65°C, and the vacuum degassing time is 10-15 minutes.

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