Solvent-free adhesive and preparation method thereof

Abstract

The invention relates to the field of adhesives, and discloses a solvent-free adhesive and a preparation method thereof.The solvent-free adhesive comprises a component A and a component B. The component A is prepared through a reaction of polypropylene glycol, hyperbranched polyester polyol, phosphorus-containing reactive flame-retardant polyester polyol, diphenylmethane diisocyanate and gamma-isocyanate propyl triethoxy silane, and the component B is prepared through a reaction of polyether glycol, hyperbranched polyester polyol, phosphorus-containing reactive flame-retardant polyester polyol, diphenylmethane diisocyanate and gamma-isocyanate propyl triethoxy silane. The preparation method comprises the following steps: dehydrating a polyol mixture, dropwise adding part of diphenylmethane diisocyanate at a first temperature, heating to a second temperature, carrying out a heat preservation reaction, and carrying out dynamic negative pressure degassing treatment during the reaction. According to the invention, hyperbranched polyester polyol and gamma-isocyanate propyl triethoxy silane are introduced, so that the adhesive has high cohesive strength and adhesive force in a humid and hot environment; phosphorus-containing reactive flame-retardant polyol is adopted to endow the adhesive with stable flame-retardant performance, the reaction process of a high-activity system is effectively controlled through segmented temperature control, dropwise adding and dynamic negative pressure degassing processes, and the preparation stability and the comprehensive performance of a product are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of adhesives, in particular to a solvent-free adhesive and a preparation method thereof. BACKGROUND

[0002] Solvent-free adhesives are widely used in many fields due to their advantages of no organic solvent, good environmental protection and high production efficiency. With the development of technology, the market puts forward higher requirements for the comprehensive performance of adhesives. The existing technology still has deficiencies in many aspects.

[0003] In practical applications, adhesives not only need to have sufficient cohesive strength to resist the destruction of the adhesive layer itself, but also need to form stable and durable interfacial bonding with the surface of the substrate. The existing technology often increases the crosslinking density to enhance the cohesive strength, but this leads to a decrease in the flexibility of the adhesive. At the same time, in order to improve the adhesion to inorganic substrates, especially the adhesion durability in a humid and hot environment, the substrate often needs to be pretreated or additional additives are introduced, but these methods are complex in process or difficult to fundamentally solve the problem of interface failure caused by water molecule erosion. Therefore, it is still a technical difficulty to simultaneously achieve high cohesive strength and high adhesion in a humid and hot environment in a single system.

[0004] In addition, in order to meet the safety requirements of application fields, adhesives need to have flame retardant properties. The commonly used method at present is to add flame retardants such as phosphorus-containing or halogen-containing compounds in the adhesive. However, these added flame retardants are only physically blended with the polyurethane matrix, and during use, they migrate, leading to a decrease in flame retardant effect over time and adversely affecting the mechanical properties of the adhesive, such as reducing its cohesive strength or hardness.

[0005] In terms of preparation process, the introduction of high-functionality or high-activity polyols for obtaining high-performance adhesives makes the preparation process of the prepolymer difficult to control. After mixing various active components in the reaction kettle, the reaction is intense and concentrated exothermic, which easily leads to a sharp increase in the viscosity of the system, local overheating, and even gelation. Not only does it affect the stability of production, but also makes it difficult to ensure the batch consistency and quality of the final product. How to effectively control the reaction process of high-activity systems is a challenge in the preparation of high-performance polyurethane adhesives. SUMMARY

[0006] The purpose of the present application is to provide a solvent-free adhesive and a preparation method thereof, which solves the problem that the existing solvent-free adhesives in the prior art are difficult to balance the comprehensive performance of cohesive strength, flame retardancy and adhesion in a humid and hot environment, and the preparation process of high-activity systems is poor in stability.

[0007] To achieve the above purpose, the present application is implemented by the following technical solutions: The first aspect of the present application provides a solvent-free adhesive, which adopts the following technical scheme: The A component is made of polypropylene glycol, hyperbranched polyester polyol, phosphorus-containing reactive flame-retardant polyester polyol, diphenyl methane diisocyanate and gamma-isocyanate propyl triethoxysilane, wherein the weight parts of each raw material are as follows: polypropylene glycol 300-500 parts; hyperbranched polyester polyol 100-250 parts; phosphorus-containing reactive flame-retardant polyester polyol 100-220 parts; diphenyl methane diisocyanate 308-798 parts; gamma-isocyanate propyl triethoxysilane 5-30 parts; and the B component is a polyol curing agent.

[0008] By adopting the above technical scheme, the solvent-free adhesive has good comprehensive performance through the structural combination of each component, wherein the polypropylene glycol serves as the base polyol to provide the flexibility of the polyurethane skeleton; the hyperbranched polyester polyol can form high-density crosslinking points in the adhesive network after curing due to the large number of active end groups in its structure, thereby improving the cohesive strength of the adhesive and making it have good mechanical properties and improved bonding reliability.

[0009] The phosphorus-containing reactive flame-retardant polyester polyol is introduced into the polyurethane molecular chain, and its phosphorus component can form a stable carbonized layer upon thermal decomposition during the combustion of the adhesive, thereby insulating oxygen and heat and capturing free radicals in the gas phase, so as to improve the flame-retardant properties of the adhesive and make it reach a higher limiting oxygen index and flame-retardant grade.

[0010] The diphenyl methane diisocyanate reacts with the polyol to form a polyurethane backbone structure, and the gamma-isocyanate propyl triethoxysilane serves as a functional additive, the isocyanate groups of which can be chemically bonded to the polyurethane network, while the ethoxyl groups of the silane part can be hydrolyzed to form silanol under humid and hot conditions, and then form stable covalent bonds (Si-O-metal bonds) with inorganic substrates (such as metal oxide surfaces), thereby enhancing the bonding force of the adhesive and the substrate interface and its durability in a humid and hot environment, and inhibiting the decrease in bonding strength caused by interface hydrolysis.

[0011] The above component ratio enables the adhesive to achieve a good balance between cohesive strength, flame retardancy and humid-heat adhesion after curing, thereby realizing the synergy of multiple properties.

[0012] Preferably, the molar ratio of the isocyanate groups in the diphenyl methane diisocyanate to the total hydroxyl groups in the polypropylene glycol, the hyperbranched polyester polyol and the phosphorus-containing reactive flame-retardant polyester polyol is 1.6-2.2.

[0013] By adopting the technical scheme, the molar ratio of isocyanate groups to hydroxyl groups is controlled in the range of 1.6-2.2, which helps to form the A component with moderate chain growth and branching degree in the preparation process of the prepolymer, and helps to form a complete polyurethane network at the final curing, and can avoid excessive crosslinking to affect the workability or material brittleness, thereby improving the overall mechanical properties and flexibility of the adhesive.

[0014] Preferably, the weight ratio of the A component to the B component is 100:(15-25).

[0015] By adopting the technical scheme, the weight ratio of the A component to the polyol curing agent B component is controlled in the range of 100:(15-25), which can adjust the degree of curing reaction, help the active functional groups in the system to fully react, form a dense and uniform curing network, thereby helping to obtain good adhesion strength and durability, and helping to control the pot life and curing efficiency after mixing to adapt to production operation.

[0016] Preferably, the phosphorus element mass fraction of the phosphorus-containing reactive flame-retardant polyester polyol is 2.8-4.5%.

[0017] By adopting the technical scheme, the phosphorus element mass fraction of the phosphorus-containing reactive flame-retardant polyester polyol is controlled in the range of 2.8-4.5%, which can provide effective flame retardancy for the adhesive under the premise of little influence on other properties (such as mechanical properties, viscosity) of the adhesive, and help the adhesive to meet the safety standards of the relevant industry.

[0018] Preferably, the hyperbranched polyester polyol is prepared by esterification polycondensation reaction of trimethylolpropane as a central core and dimethylolpropionic acid as an AB2 type monomer.

[0019] By adopting the technical scheme, the hyperbranched polyester polyol is prepared by esterification polycondensation reaction of the monomers trimethylolpropane and dimethylolpropionic acid, and a structure with high branching and controllable number of active end groups is obtained, which provides a basis for constructing a high-density crosslinking network and realizing high cohesive strength of the adhesive.

[0020] Preferably, the phosphorus-containing reactive flame-retardant polyester polyol is prepared by addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and itaconic acid, and then copolyesterification reaction with adipic acid and 1,4-butanediol.

[0021] By adopting the technical scheme, the phosphorus element is combined into the polyol molecule in the form of stable chemical bond through the addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and itaconic acid, and then copolyesterification reaction with adipic acid and 1,4-butanediol, so that the reaction-type flame retardant can long-term maintain its flame retardant performance, is not easy to migrate, and has less influence on the mechanical performance and durability of the adhesive.

[0022] The second aspect of the application provides a preparation method of a solvent-free adhesive, which adopts the following technical scheme: The preparation method of the solvent-free adhesive comprises the following steps: S1, mixing and dehydrating polypropylene glycol, hyperbranched polyester polyol and phosphorus-containing reaction-type flame-retardant polyester polyol; at a first temperature, adding diphenylmethane diisocyanate dropwise into the dehydrated polyol mixture; heating the material to a second temperature for heat preservation reaction, and performing at least one dynamic negative pressure degassing treatment on the reaction system during the addition of diphenylmethane diisocyanate and the heat preservation reaction, and adding γ-isocyanate propyl triethoxysilane for end-capping reaction after cooling to obtain component A; S2, mixing component A obtained in the step S1 with component B prepared in advance according to the weight ratio to obtain the solvent-free adhesive.

[0023] By adopting the technical scheme, the preparation method improves the situation that the high-activity polyol system is prone to gel or out-of-control during preparation of the prepolymer through synergistic control of the reaction process.

[0024] By adding diphenylmethane diisocyanate dropwise at the first temperature instead of adding all at once, the instantaneous concentration of free isocyanate groups (-NCO) in the system is effectively controlled, and the reaction rate per unit time is stoichiometrically reduced, which helps to avoid the concentration of reaction heat due to the high concentration of reactants.

[0025] Meanwhile, the segmented temperature control program of the first temperature and the second temperature is set to regulate the selectivity of the reactions of different active hydroxyl groups. At the lower first temperature, the -NCO group preferentially reacts with the polypropylene glycol hydroxyl group which has small steric hindrance and high activity to perform chain growth; after being heated to the second temperature, sufficient activation energy is provided for the reaction of the -NCO group with the hydroxyl group of the hyperbranched polyester polyol which has large steric hindrance and low activity, so as to promote the formation of the branched and crosslinked network.

[0026] The control of the reaction sequence avoids excessive crosslinking of the high-functionality hyperbranched polyols at the initial stage of the reaction, thereby preventing the rapid increase in the viscosity of the system and the early gelation, and in addition, the dynamic negative pressure degassing treatment performed during the reaction process helps to timely remove the byproduct carbon dioxide generated by the reaction of trace water with -NCO and the dissolved gas entrained in the raw materials, improves the uniformity of heat and mass transfer of the system, and avoids local overheating.

[0027] Through the above comprehensive control of the stoichiometry, reaction kinetics, and mass and heat transfer processes, stable preparation of the multifunctional and high-activity polyurethane system can be achieved, and the synthesis feasibility and quality stability of the final product are improved.

[0028] Preferably, in the S1 step, the first temperature is 55-65℃, the second temperature is 75-85℃, and the dropwise addition of diphenylmethane diisocyanate accounts for 50-70% of the total amount.

[0029] By using the above technical solution, the first temperature is controlled at 55-65℃, the second temperature is controlled at 75-85℃, and the dropwise addition ratio of MDI is controlled, which further refines the stage-by-stage control of the reaction activity, and the setting of the temperature range and the dropwise addition ratio helps to balance between viscosity control and reaction completeness.

[0030] Preferably, in the S1 step, the dynamic negative pressure degassing treatment includes reducing the pressure in the reaction kettle to -0.05MPa to -0.08MPa, maintaining for 5-10 minutes, and then introducing inert gas to restore to normal pressure.

[0031] By using the above technical solution, the specific negative pressure degassing process parameters are set, which helps to effectively remove trace gases and byproducts in the system without causing excessive volatilization of low molecular weight monomers, improving the uniformity of the reaction environment, and further helping to obtain a prepolymer with more regular molecular structure and fewer internal defects.

[0032] Preferably, in the S1 step, the dehydration step has the process conditions of being performed at 105-115℃ and a vacuum degree of -0.090MPa to -0.098MPa for 2-3 hours.

[0033] By using the above technical solution, strict dehydration treatment is performed before the polyurethane reaction, which can effectively avoid the side reaction of water with isocyanate (such as the generation of urea bond and carbon dioxide), and the set dehydration process conditions can reduce the water content in the polyol mixture to a low level, thereby providing protection for the smooth progress of the main reaction and the stability of the performance of the final polyurethane product.

[0034] In summary, the present application includes at least one of the following beneficial technical effects: 1.The present application improves the cohesive strength of the adhesive by introducing hyperbranched polyester polyol in the A component, forming a high-density crosslinked network after curing, and adding gamma-isocyanate propyl triethoxy silane to form chemical bonding at the substrate interface through the silane group, thereby enhancing the adhesion of the adhesive to inorganic substrates and its moisture resistance and heat resistance, so that the solvent-free adhesive prepared has good cohesive strength and interfacial adhesion, improving the reliability of bonding.

[0035] 2.The present application introduces phosphorus elements into the polyurethane molecular chain in the form of chemical bonds by using phosphorus-containing reactive flame-retardant polyester polyol, avoiding the problems of easy migration and affecting material performance of the added flame retardant, so that the adhesive can form an effective carbon layer during combustion, has good flame-retardant performance, and improves the safety of the material.

[0036] 3.In the preparation method of the present application, the process of combining segmented temperature control, dropwise addition of diphenyl methane diisocyanate, and dynamic negative pressure degassing treatment is used to effectively control the reaction process of the high-activity polyol system. By controlling the instantaneous concentration of the reactants and the reaction temperature, the chain growth and branching reactions are orderly guided, and the byproduct gas is removed in time to inhibit the occurrence of local overheating and gelation, improve the stability and operability of the preparation process, and ensure the uniformity and stability of the performance of the final product. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present application will be described below in conjunction with the preparation examples, embodiments, comparative examples, and test examples of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0038] Preparation Examples 1-4: Preparation Example 1: The present preparation example provides a preparation method of high-functionality hyperbranched polyester polyol, comprising the following steps: A 2000 mL four-necked flask equipped with a mechanical stirrer, a water separator, a thermometer, and a nitrogen protection device was charged with trimethylolpropane 134.2 g (1.0 mole fraction) as a central core, dimethylolpropionic acid 2011.8 g (15.0 mole fraction) as an AB2 type monomer, and p-toluenesulfonic acid 2.2 g (0.1% of the total mass of the charge) as a catalyst.

[0039] Under nitrogen protection and stirring, the temperature was programmed to 160℃ for esterification and polycondensation reaction, and the byproduct water was continuously removed through the water separator.

[0040] When the water output reaches 90% of the theoretical value, a vacuum degree of -0.095 MPa is applied, and the reaction is continued for 3 hours under this condition.

[0041] The product acid value is detected periodically, and when the acid value is lower than 1.0 mgKOH / g, the reaction is stopped, and the product is discharged after cooling to below 120℃ to obtain a transparent viscous liquid HBP-1A. The acid value is detected to be 0.8 mgKOH / g.

[0042] Preparation Example 2: The present preparation example provides a preparation method of a hyperbranched polyester polyol, comprising the following steps: The operation of Preparation Example 1 is repeated, except that the amount of dimethylolpropionic acid is adjusted to 2682.4 g (20.0 mole parts).

[0043] Finally, a transparent viscous liquid HBP-1B is obtained. The acid value is detected to be 0.9 mgKOH / g.

[0044] Preparation Example 3: The present preparation example provides a preparation method of a high-phosphorus-content phosphorus-containing reactive flame-retardant polyester polyol, comprising the following steps: Preparation of phosphorus-containing dibasic acid: In a 1000 mL reaction kettle, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide 216.2 g (1.0 mole parts) and itaconic acid 143.1 g (1.1 mole parts) are added, and the temperature is raised to 140℃ for 5 hours to obtain a phosphorus-containing dibasic acid intermediate (DOPO-IA).

[0045] Copolyesterification: After cooling to 80℃, adipic acid 292.2 g (2.0 mole parts) and 1,4-butanediol 360.5 g (4.0 mole parts) are added to the reaction kettle of the previous step, and tetrabutyl titanate 0.9 g (0.1% of the total mass of the feed) is added as a catalyst.

[0046] Polycondensation reaction: Under nitrogen protection, the temperature is programmed to rise to 210℃ for atmospheric esterification, and when the water output approaches the theoretical value, the vacuum polycondensation stage (-0.095 MPa) is entered, until the target range is reached, and after the reaction is completed, the product is discharged after cooling to obtain a light yellow transparent viscous liquid FRP-1A, and the mass fraction of phosphorus element is detected to be 4.5%.

[0047] Preparation Example 4: The present preparation example provides a preparation method of a low-phosphorus-content phosphorus-containing reactive flame-retardant polyester polyol, comprising the following steps: The operation of Preparation Example 3 was repeated, except that the feeding amount of adipic acid in the copolyesterification stage was adjusted to 584.4 g (4.0 mole parts), and the feeding amount of 1,4-butanediol was adjusted to 540.8 g (6.0 mole parts). Finally, a light yellow transparent viscous liquid FRP-1B was obtained. It was detected that the mass fraction of phosphorus element was 2.8%.

[0048] Examples 1-3: Example 1: The present embodiment provides a solvent-free adhesive and a preparation method thereof, comprising the following steps: Preparation of component A: In a 1000 mL jacketed reaction kettle, polypropylene glycol (400 parts by weight), HBP-1A obtained in Preparation Example 1 (175 parts by weight), and FRP-1A obtained in Preparation Example 3 (175 parts by weight) were added, stirring was started, the temperature was raised to 110°C, and a vacuum degree of -0.095 MPa was applied, and dehydration was performed for 2 hours until the water content was less than 0.05%. The temperature was lowered to 60°C for standby, the reaction kettle was sealed, and the cycle operation of three times of vacuum extraction to -0.05 MPa and filling of high-purity nitrogen was performed to replace the gas in the kettle.

[0049] MDI time sequence dropping: the temperature of the material in the kettle was maintained at 60°C. According to the total hydroxyl molar amount of the polyol in the kettle, the NCO / OH molar ratio was set to 1.8:1, the required diphenylmethane diisocyanate (540 parts by weight) was weighed, and 60% (324 parts by weight) of the total mass of diphenylmethane diisocyanate was uniformly dropped into the reaction kettle within 80 minutes. During the dropping, 3 times of dynamic negative pressure degassing and inert gas pulse covering cycle were simultaneously performed, and the operation of each cycle was as follows: the pressure in the reaction kettle was reduced to -0.07 MPa and maintained for 8 minutes, and then the pressure was quickly restored to normal pressure after the nitrogen was quickly introduced to restore the pressure to slightly positive pressure.

[0050] Temperature rising and holding: after the first stage MDI dropping was completed, the temperature of the material in the kettle was raised to 80°C at a temperature rising rate of 1.5°C / min, and the temperature was held for 80 minutes. During this period, the above-mentioned dynamic negative pressure degassing and inert gas pulse covering cycle was performed again for 2 times.

[0051] Silane capping: after the holding was completed, the -NCO content of the system was detected to reach the theoretical design value, the material was cooled to 60°C, and the formula amount of γ-isocyanate propyl triethoxysilane (15 parts by weight) was dropped. The stirring was continued at this temperature for 30 minutes, and after the reaction was completed, it was cooled to below 50°C, and the material was discharged under the protection of nitrogen, and was sealed and packaged to obtain component A.

[0052] Preparation of component B: the component B curing agent (polyether 330N) was dehydrated at 100°C and a vacuum degree of -0.095 MPa for 2 hours to make the water content less than 0.05%, and was sealed for standby after cooling.

[0053] Adhesive preparation: Mix the A component prepared in the previous step with the prepared B component in a weight ratio of 100:20, and stir using a mechanical stirrer at a medium-low speed for 10 minutes until the mixture is uniform, to obtain a usable solvent-free adhesive product.

[0054] Example 2: The present example provides a solvent-free adhesive and a method for preparing the same, comprising the following steps: A component preparation: In a reaction kettle, add polypropylene glycol (300 parts by weight), HBP-1A obtained in Preparation Example 1 (250 parts by weight), and FRP-1B obtained in Preparation Example 4 (220 parts by weight). Heat to 115°C, apply a vacuum degree of -0.098 MPa, and dehydrate for 2.5 hours until the water content is less than 0.05%, then cool to 65°C and complete the inert gas replacement.

[0055] MDI time sequence addition: Maintain the temperature of the kettle contents at 65°C, set the NCO / OH molar ratio to 2.2:1, weigh the required diphenylmethane diisocyanate (798 parts by weight), and add 50% of the total mass of diphenylmethane diisocyanate (399 parts by weight) at a uniform rate into the reaction kettle within 60 minutes, during which 2 dynamic negative pressure degassing cycles (vacuum to -0.08 MPa for 10 minutes) are performed.

[0056] Temperature rise and holding: After the first stage of MDI addition is complete, raise the temperature of the kettle contents to 85°C at a rate of 2.0°C / min, and hold the temperature at this value for 60 minutes, during which 1 more dynamic negative pressure degassing cycle is performed.

[0057] Silane capping: After the holding period is complete and the -NCO content is qualified, cool the material to 65°C, add γ-isocyanate propyl triethoxysilane (30 parts by weight), and continue stirring at this temperature for 20 minutes. After the reaction is complete, cool and discharge the material to obtain the A component.

[0058] B component preparation: Same as Example 1.

[0059] Adhesive preparation: Mix the A component prepared in the previous step with the prepared B component in a weight ratio of 100:25, and mix uniformly to obtain a solvent-free adhesive product.

[0060] Example 3: The present example provides a solvent-free adhesive and a method for preparing the same, comprising the following steps: Preparation of Component A: Polypropylene glycol (500 parts by weight), HBP-1B obtained in Preparation Example 2 (100 parts by weight), and FRP-1A obtained in Preparation Example 3 (100 parts by weight) were added to a reactor. The mixture was heated to 105°C, and a vacuum of -0.090 MPa was applied for dehydration for 3 hours until the water content was below 0.05%. The mixture was then cooled to 55°C and inert gas purging was completed.

[0061] MDI sequential addition: Maintain the material temperature in the reactor at 55℃, set the NCO / OH molar ratio to 1.6:1, weigh the required diphenylmethane diisocyanate (308 parts by weight), and add 70% (215.6 parts by weight) of the total mass of diphenylmethane diisocyanate into the reactor at a uniform rate over 90 minutes. During this period, perform three dynamic negative pressure degassing cycles (evacuate to -0.05MPa and maintain for 5 minutes).

[0062] Heating and Holding: After the first stage of MDI addition is completed, the temperature of the material in the reactor is raised to 75°C at a heating rate of 1.0°C / min. The reaction is held at this temperature for 90 minutes, during which the above dynamic negative pressure degassing cycle is performed twice more.

[0063] Silane end-capping: After the heat preservation is completed and the -NCO content is found to be qualified, the material is cooled to 55°C, and γ-isocyanate-propyltriethoxysilane (5 parts by weight) is added dropwise. The reaction is continued to be stirred at this temperature for 40 minutes. After the reaction is completed, the material is cooled and discharged to obtain component A.

[0064] Preparation of component B: Same as in Example 1.

[0065] Adhesive preparation: Mix component A prepared in the previous step with the prepared component B at a weight ratio of 100:15 to obtain the solvent-free adhesive product.

[0066] Comparative Examples 1-5: Comparative Example 1: Compared with Example 1, the difference lies in the preparation method of component A: after mixing and dehydrating all polyols, the temperature is lowered to 75°C, and the total amount of diphenylmethane diisocyanate in the formulation is added rapidly in one go, and the reaction is carried out at 75-85°C without sequential drop-down, segmented temperature control and dynamic pressure regulation.

[0067] Comparative Example 2: Compared with Example 1, the difference lies in the raw material formulation of component A: hyperbranched polyester polyol HBP-1A is not used, but its weight part is replaced by polypropylene glycol, and the amount of diphenylmethane diisocyanate is adjusted accordingly to maintain the same NCO / OH molar ratio as in Example 1.

[0068] Comparative Example 3: The difference compared with Example 1 is that the raw material formula of A component: no phosphorus-containing reactive flame-retardant polyester polyol FRP-1A is used, and the weight part is replaced by polypropylene glycol, and the amount of diphenyl methane diisocyanate is adjusted accordingly to keep the same NCO / OH molar ratio as Example 1.

[0069] Comparative Example 4: The difference compared with Example 1 is that the preparation method of A component: after the end of the temperature rising and holding step, no silane capping step is performed, and the material is directly cooled out.

[0070] Comparative Example 5: The difference compared with Example 1 is that the preparation method of A component: in the MDI time sequence dropping and temperature rising and holding stage, no dynamic negative pressure degassing and inert gas pulse covering cycle is performed, and the whole reaction process is carried out in a constant nitrogen atmosphere.

[0071] Test Example 1-2: The purpose of this test example is to evaluate the control effect of the preparation method provided by the application on the reaction process of high viscosity and multi-active functional group composite system. By monitoring the key process parameters online, the differences between Example 1 of the application and the traditional one-step feeding method (Comparative Example 1) in the preparation process of the prepolymer are compared.

[0072] Experimental method: The preparation schemes of A component of Example 1 and Comparative Example 1 are respectively carried out in a 1000 mL reaction kettle of the same specification, which is equipped with mechanical stirring, jacket temperature control, vacuum system and online monitoring probe.

[0073] An online rotary viscometer probe and a high-precision armored thermocouple are installed in the reaction kettle, and the probe is fixed below the middle liquid level of the material. From the beginning of the addition of isocyanate component (recorded as 0 minutes), the real-time temperature and viscosity value of the material in the kettle are recorded every 15 minutes. At the same time, the state change of the system in the reaction process is observed and recorded, especially whether there are gel particles or other abnormal phenomena. After the reaction is completed, the macrostate of the final product is evaluated.

[0074] Experimental results: The key parameter monitoring data in the preparation process are recorded in Table 1.

[0075] Table 1. Key parameter monitoring data of A component preparation process Note: >1000 in the table indicates that the viscosity value has exceeded the upper limit of the online viscometer measurement; - indicates that the material of Comparative Example 1 has undergone irreversible gelation, turning into a non-flowing block solid, resulting in the inability to continue effective temperature or viscosity measurement of the material; no in the remarks column indicates that no special process phenomena or abnormal events were observed at that time point.

[0076] Conclusion: The data in Table 1 clearly shows the huge difference between the two preparation methods. Using the process of Example 1, the system temperature strictly follows the set program, with a fluctuation range of less than 1°C, and the viscosity shows a smooth and predictable growth trend, ultimately obtaining a uniform and gel-free liquid prepolymer. In contrast, using the traditional one-step method of Comparative Example 1, about 60 minutes after the addition of MDI, the system temperature shows a reaction exothermic peak as high as 20°C or more, and the viscosity increases exponentially and quickly reaches the gel point, leading to uncontrolled reaction and failure of preparation.

[0077] The present adhesive system contains a highly functional hyperbranched polyester polyol (HBP-1), which has a large number of hydroxyl groups with very high reactivity with the isocyanate groups of MDI.

[0078] In Comparative Example 1, all MDI is introduced into the high-temperature system at once, causing the instantaneous concentration of isocyanate groups and hydroxyl groups to be high, triggering a violent and uncontrollable polymerization reaction, with a reaction rate far exceeding the heat dissipation rate of the system, resulting in local overheating and temperature runaway. High temperature further accelerates the reaction, forming a vicious cycle, ultimately leading to the system gelling prematurely due to excessive crosslinking density before reaching the desired conversion rate.

[0079] The preparation method proposed in the present invention solves this problem through three synergistic mechanisms: By sequentially adding MDI, the instantaneous concentration of reactants is controlled from the perspective of stoichiometry, and by slowly and uniformly adding, the concentration of free -NCO groups in the system is maintained at a low level, reducing the overall reaction rate from the source and avoiding the explosive accumulation of reaction heat.

[0080] By segmenting the temperature control, selective regulation of different active group reactions is achieved from the perspective of reaction kinetics. The low temperature stage (55-65°C) in the early stage is conducive to the chain growth reaction of -NCO groups with the more active polypropylene glycol hydroxyl groups, forming linear or lightly branched low-viscosity intermediates. The subsequent temperature rising and holding stage (75-85°C) provides sufficient energy to drive -NCO to react with the more sterically hindered and less active hyperbranched polyol hydroxyl groups, thereby constructing the final prepolymer network structure. Through an orderly reaction process, excessive crosslinking of high-functionality monomers in the early stage is avoided.

[0081] By dynamic pressure regulation, the reaction environment is optimized from the perspective of mass and heat transfer. Periodic negative pressure operation helps to timely remove reaction by-products (such as trace water and CO2 generated by the reaction of MDI) and trace gases entrained in the monomer, reducing the negative impact of bubbles on material heat transfer and stirring efficiency.

[0082] In summary, the data of this test example strongly prove that the synergistic preparation method adopted by the present application, i.e. time sequence dropping, segmented temperature control and dynamic pressure regulation, is not a simple process optimization, but a necessary technical solution for the successful preparation of multifunctional and high-activity polyurethane systems, which realizes precise control of the kinetics, thermodynamics and mass transfer process of complex reaction systems, thereby ensuring the synthesis feasibility and quality stability of the final product.

[0083] Test Example 2: The purpose of this test example is to characterize and compare the performance of the final cured products of the solvent-free adhesives prepared in the examples and comparative examples, in order to verify the effects of the present application in realizing high cohesive strength, flame retardancy and substrate adhesion, etc.

[0084] Experimental method: Mix the A component and B component prepared in each example and comparative example according to the predetermined ratio, stir uniformly, and then prepare the adhesive samples to be tested. All samples are cured at 25°C and 55% relative humidity for 7 days before performance testing.

[0085] First, visually inspect the uniformity of the mixed adhesive, and use a rotational viscometer to monitor the change in viscosity at 25°C, record the time for the viscosity to double as the pot life, and test the 180° peel strength according to the GB / T2790-1995 standard. The test substrates are composite samples of corona-treated PET film (12μm) and aluminum foil (30μm).

[0086] Place part of the composite sample in a constant temperature and humidity chamber at 80°C and 90% RH for 72 hours, then take it out and condition it for 4 hours in a standard environment, and then test its 180° peel strength again and calculate the strength retention rate. Then prepare standard samples from the cured adhesives, test the limiting oxygen index (LOI) according to the GB / T2406.2-2009 standard, and perform vertical burning test according to the ANSI / UL94-2013 standard.

[0087] Experimental results: The comprehensive performance test data of each group of samples are summarized in Table 2.

[0088] Table 2. Comprehensive performance test data of adhesive products The product of A component in Table cannot be prepared, indicating that the product of A component cannot be prepared due to gelation in the preparation stage of Comparative Example 1; and the subsequent performance test cannot be carried out due to the product of A component.

[0089] Conclusion: The data of the test examples systematically verify the contribution of each functional component and the preparation process of the present application to the performance of the final product.

[0090] Comparing the data of Comparative Example 1 and Comparative Example 2, the 180° peel strength decreases significantly from 4.8 N / 15 mm to 2.1 N / 15 mm after removing the hyperbranched polyester polyol, which confirms that the hyperbranched polymer forms high-density crosslinking points in the cured network through its high functionality, and is the structural basis for achieving high cohesive strength of the adhesive. Without this component, even if other components and processes are the same, sufficient bonding strength cannot be obtained.

[0091] Comparing Comparative Example 1 and Comparative Example 3, the absence of FRP-1A leads to a decrease in limiting oxygen index from 28.5% to 20.8%, and the vertical burning cannot pass, which clearly shows that the phosphorus-containing polyester polyol is the key to obtaining the flame-retardant performance of the adhesive. The mechanism is that the phosphorus-containing component thermally decomposes during combustion to generate a dense carbon layer such as polyphosphoric acid, which plays a role in insulating oxygen and heat, and can capture free radicals in the gas phase to effectively inhibit the combustion process.

[0092] Comparing Comparative Example 1 and Comparative Example 4, the absence of γ-isocyanate propyl triethoxysilane termination does not significantly decrease the initial peel strength of the sample, but the strength retention rate decreases dramatically from 93.8% to 30.6% after experiencing hygrothermal aging, indicating that the isocyanate group at one end of the silane coupling agent molecule is chemically bonded into the polyurethane network, and the other end of the hydrolyzable ethoxysilane group can form a stable Si-O-metal chemical bond with the inorganic substrate (such as the oxide layer on the surface of the aluminum foil) at the interface, thereby improving the stability of the adhesive and substrate interface in a hygrothermal environment.

[0093] Comparing Comparative Example 1 and Comparative Example 5, using the conventional nitrogen protection process (Comparative Example 5) can prepare the product, but the peel strength and strength retention rate after hygrothermal aging are lower than those of Example 1, indicating that the dynamic pressure regulation step in the present application effectively removes trace amounts of dissolved gas and reaction byproducts (CO2) in the system, improves the regularity of the molecular structure of the prepolymer and reduces micro defects in the cured adhesive layer, thereby positively affecting the ultimate mechanical properties and durability of the adhesive.

[0094] In addition, the data comparison between Examples 1, 2 and 3 demonstrates the formula adjustability of the technical solution of the present application. By adjusting the relative proportions of HBP and FRP, a balanced design can be made between high strength (Example 2) and high flame retardance (Example 3) and other different performance focuses, to meet the needs of different application scenarios.

[0095] In summary, the test results show that the present application integrates the three functional components of hyperbranched polymer, phosphorus-containing polyol and organosilane in structure, and is assisted by a precise preparation process that can achieve successful compounding, finally obtaining a multifunctional solvent-free polyurethane adhesive with high cohesive strength, flame retardance and adhesion in humid heat environment, solving the technical problem that the prior art is difficult to balance multiple properties.

Claims

1. A solvent-free adhesive, characterized in that, It contains component A and component B: Component A is made from raw materials comprising the following parts by weight: 300-500 parts of polypropylene glycol; 100-250 parts of hyperbranched polyester polyol; 100-220 parts of phosphorus-containing reactive flame-retardant polyester polyol; 308-798 parts of diphenylmethane diisocyanate; 5-30 parts of γ-isocyanate-propyltriethoxysilane; Component B is a polyol curing agent.

2. The solvent-free adhesive according to claim 1, characterized in that, The molar ratio of the isocyanate group in the diphenylmethane diisocyanate to the total hydroxyl groups in the polypropylene glycol, the hyperbranched polyester polyol, and the phosphorus-containing reactive flame-retardant polyester polyol is 1.6-2.

2.

3. The solvent-free adhesive according to claim 1, characterized in that, The weight ratio of component A to component B is 100:(15-25).

4. The solvent-free adhesive according to claim 1, characterized in that, The phosphorus content of the phosphorus-containing reactive flame-retardant polyester polyol is 2.8-4.5% by mass.

5. The solvent-free adhesive according to claim 1, characterized in that, The hyperbranched polyester polyol was prepared by esterification polycondensation reaction with trimethylolpropane as the central core and dimethylolpropionic acid as the AB2 type monomer.

6. The solvent-free adhesive according to claim 1, characterized in that, The phosphorus-containing reactive flame-retardant polyester polyol is prepared by adding itaconic acid to 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, followed by copolyesterification with adipic acid and 1,4-butanediol.

7. A method for preparing a solvent-free adhesive, characterized in that, Includes the following steps: S1. Polypropylene glycol, hyperbranched polyester polyol, and phosphorus-containing reactive flame-retardant polyester polyol are mixed and dehydrated; diphenylmethane diisocyanate is added dropwise to the dehydrated polyol mixture at a first temperature; the material is heated to a second temperature for heat preservation reaction, and the reaction system is subjected to dynamic negative pressure degassing treatment at least once during the addition of diphenylmethane diisocyanate and heat preservation reaction. After cooling, γ-isocyanate-propyltriethoxysilane is added for end-capping reaction to obtain component A. S2. Mix component A obtained in step S1 with the pre-prepared component B in a weight ratio to obtain the solvent-free adhesive.

8. The method for preparing a solvent-free adhesive according to claim 7, characterized in that, In step S1, the first temperature is 55-65℃, the second temperature is 75-85℃, and the added diphenylmethane diisocyanate accounts for 50-70% of the total amount.

9. The method for preparing a solvent-free adhesive according to claim 7, characterized in that, In step S1, the dynamic negative pressure degassing treatment includes a cycle of reducing the pressure inside the reactor to -0.05MPa to -0.08MPa, maintaining it for 5-10 minutes, and then introducing inert gas to restore it to atmospheric pressure.

10. The method for preparing a solvent-free adhesive according to claim 7, characterized in that, In step S1, the dehydration process is carried out at 105-115℃ and a vacuum of -0.090MPa to -0.098MPa for 2-3 hours.

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