Polyurethane heat-conducting pouring sealant with low water absorption rate and preparation method thereof

Abstract

The invention discloses a polyurethane heat-conducting pouring sealant with low water absorption and a preparation method thereof, and belongs to the field of chemical engineering. Through special component selection, the product disclosed by the invention not only can realize normal heat conduction and fireproof performance and strong adhesion, but also is high in density and low in moisture permeability and water absorption rate, completely meets the waterproof requirement of IP68 level, and is very suitable for a sealing layer material of a shell of a device such as a motor.

Description

Technical Field

[0001] The invention relates to the field of chemical industry, and in particular to a polyurethane heat-conducting potting adhesive with low water absorption and a preparation method thereof. Background Art

[0002] In order to ensure that the motor can still operate stably in harsh environments, the electrode compartment shell as a protective component needs to have comprehensive properties such as dustproof, moisture-proof and corrosion-resistant. Generally speaking, the motor compartment shell will be provided with a protective polyurethane potting glue on the surface as a sealing protective layer. However, existing polyurethane potting glue products are difficult to take into account the comprehensive effects of thermal conductivity, waterproofness and fireproofing, especially waterproof performance. Some polyurethane potting glue products have a high water absorption rate after being used for a period of time, which is not only not conducive to the operation of the motor, but also may cause the product's adhesion to decrease and eventually fall off the shell. Summary of the invention

[0003] Based on the defects of the prior art, the purpose of the present invention is to provide a polyurethane thermal conductive potting glue with low water absorption. Through special component selection, it can not only achieve normal thermal conductivity and fire resistance, strong adhesion, but also high density, low moisture permeability and water absorption, which fully meets the IP68 waterproof requirements and is very suitable for sealing layer materials of the outer casings of devices such as motors.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A polyurethane potting adhesive comprises a component A and a component B;

[0006] The A component comprises the following components in parts by weight:

[0007] 5-15 parts of polyether polyol, 10-30 parts of castor oil polyol, 40-70 parts of modified aluminum hydroxide;

[0008] The B component includes the following components in parts by weight:

[0009] 10-60 parts of polyurethane prepolymer, 0-40 parts of isocyanate;

[0010] The polyurethane prepolymer is obtained by reacting polyether polyol, fluorine-containing polyol, polybutadiene polyol and isocyanate;

[0011] The modified aluminum hydroxide is obtained by modifying aluminum hydroxide with at least one of tridecafluorooctyltriethoxysilane, vinyltriethoxysilane, and vinyltri(2-methoxyethoxy)silane;

[0012] The mass ratio of the A component to the B component is (4-6):1.

[0013] Most of the existing polyurethane potting glues cannot take into account the multiple functions of heat conduction, fire prevention and waterproofing, especially in terms of waterproofing. After long-term use, some products will cause performance degradation or even fall off due to high water penetration, which will also directly affect the protective performance of the product. For this reason, in the technical scheme of the present invention, a polyurethane prepolymer prepared from specific raw materials is used as a component raw material. In the raw materials for preparing the prepolymer, the strong inductive effect and volume exclusion reaction of fluorine atoms in the fluorinated polyol will react with the polybutadiene polyol having a hydrophobic structure similar to natural rubber and enter the polymer main chain structure, reducing the surface free energy of the product, thereby inhibiting the water absorption tendency of the product. At the same time, the introduction of fluorinated groups and polybutadiene structures not only retains the excellent mechanical properties and microphase separation characteristics of the polyurethane structure, but also makes the prepared product have high density and low moisture permeability, and exhibits high adhesion and adhesion durability to non-polar and low-polar objects.

[0014] On the other hand, the aluminum hydroxide modified by a specific silane coupling agent in component A of the product will further enhance the hydrophobicity of the product together with the non-polar fatty acid long chain in castor oil polyol, and the addition of castor oil polyol leads to the formation of a polyurethane cross-linked structure. When the cross-linked polyurethane dispersion is cured, the movement of the molecular chain is hindered, and the hydrophilic micro-regions formed are small and closed by the cross-linked region, further reducing the water absorption rate of the product. In addition, based on the special composition of the product, it can also achieve good thermal conductivity and flame retardant properties, without the introduction of additional functional additives, low production cost, and excellent comprehensive performance.

[0015] It should be noted that the "castor oil polyol" in the technical solution of the present invention refers to castor oil containing hydroxyl polyols, which is well known to those skilled in the art, and is generally obtained by further refining crude castor oil, but is not a product synthesized by modifying castor oil and polyols. The latter is mainly referred to as "castor oil modified polyols" known to those skilled in the art, such as castor oil-based polyether polyols, which are different from the substances described in the present invention.

[0016] Preferably, the molecular weight of the polyether polyol in the A component is 300-1000, and the degree of functionality is 2-3.

[0017] Preferably, the castor oil polyol in the component A has a hydroxyl value of 160-168 mgKOH / g and a functionality of 2.5-3.

[0018] Preferably, the modified aluminum hydroxide is tridecafluorooctyltriethoxysilane modified aluminum hydroxide.

[0019] By using triethoxysilane-modified aluminum hydroxide as the filler in the product of the present invention, not only can the high hydrophobicity and water permeability inhibition of the product be achieved in coordination with the organic components, but it also has good organic compatibility, enabling good dispersion uniformity in the product, and the thermal conductivity, flame retardancy and basic mechanical properties of the product are better.

[0020] More preferably, the modified aluminum hydroxide is prepared by the following preparation method:

[0021] At least one of tridecafluorooctyltriethoxysilane, vinyltriethoxysilane and vinyltri(2-methoxyethoxy)silane is dispersed in a solvent, and then aluminum hydroxide is added to mix and heated to reflux. After the solid is separated, it is dried, crushed, ground and sieved to obtain the modified aluminum hydroxide.

[0022] More preferably, the average particle size of the modified aluminum hydroxide is 5 to 10 μm.

[0023] More preferably, when preparing the modified aluminum hydroxide, the mass ratio of aluminum hydroxide to at least one of tridecafluorooctyltriethoxysilane, vinyltriethoxysilane, and vinyltri(2-methoxyethoxy)silane is (400-500):(20-30).

[0024] More preferably, the temperature during the heating reflux is 60 to 90° C. and the time is 40 to 60 min.

[0025] More preferably, the solvent includes at least one of water and alcohol.

[0026] According to common knowledge, those skilled in the art can modify aluminum hydroxide by the above-mentioned modification method, or can modify aluminum hydroxide by other conventional methods such as solvent thermal method, dry mixing method, etc., as long as similar modification effects can be achieved, there is no limitation.

[0027] Preferably, component A of the polyurethane thermal conductive potting glue further includes at least one of a dewatering agent, a defoaming agent, a coupling agent, and a catalyst.

[0028] More preferably, the component A further comprises 0 to 3 parts of a dewatering agent, 0 to 0.1 parts of a defoaming agent, 0 to 2 parts of a coupling agent and 0 to 0.01 parts of a catalyst.

[0029] Based on the role of the key components described above in the product of the present invention, technicians in this field can further introduce some additional processing or functional additives into the components according to the final application scenario of the product or processing requirements. For example, in order to further improve the waterproof performance of the product when used as a protective material and avoid water hanging on the surface of the product, a certain amount of dewatering agent can be further introduced; in order to achieve better uniformity during product preparation and use and avoid the generation of bubbles, a certain amount of defoaming agent can also be introduced into the product; at the same time, the types of additional additives added to the product are not limited thereto. As long as the technical effects of the product concerned in this solution are achieved as expected, the addition of additive ingredients is not restricted.

[0030] More preferably, the dehydrating agent is molecular sieve activation powder.

[0031] More preferably, the defoaming agent is a polysiloxane defoaming agent.

[0032] More preferably, the coupling agent is a siloxane coupling agent; further, the siloxane coupling agent is at least one of γ-glycidyloxypropyltrimethoxysilane, γ-(2,3-epoxypropyloxy)propyltrimethoxysilane, ureidopropyltriethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane, and γ-ureidopropyltrimethoxysilane.

[0033] More preferably, the catalyst is a metal organic catalyst.

[0034] Preferably, the polyurethane prepolymer is obtained by the following preparation method:

[0035] The polyether polyol, the fluorine-containing polyol and the polybutadiene polyol are mixed, and then vacuum-dehydrated at 110-120° C., cooled, and isocyanate is added and reacted at 60-70° C. for 2-3 hours to obtain the polyurethane prepolymer.

[0036] More preferably, the molecular weight of the polyether polyol is 300-1000 and the degree of functionality is 2-3.

[0037] Preferably, the fluorine-containing polyol is at least one of 2,2-difluoro-1,3-propylene glycol, trifluoromethylphenyl glycol, and perfluoropolyether diol.

[0038] More preferably, the fluorine-containing polyol is a perfluoropolyether diol having a molecular weight of 1000 to 2000 g / mol and a functional group degree of 1.5 to 2.5.

[0039] More preferably, the polybutylene polyol is a hydroxy-terminated polybutylene with a molecular weight of 2500 to 3000 g / mol and a functional group degree of 2.2 to 2.4.

[0040] More preferably, the isocyanate is at least one of diphenylmethane diisocyanate and polyphenyl polymethylene polyisocyanate.

[0041] Preferably, when the polyurethane prepolymer is prepared by using polyether polyol, fluorine-containing polyol and polybutadiene polyol, the mass ratio of polyether polyol, fluorine-containing polyol and polybutadiene polyol is (8-10):(1-5):(1-3).

[0042] Preferably, when the polyurethane prepolymer is prepared by using polyether polyol, fluorine-containing polyol and polybutadiene polyol, the mass ratio of polyether polyol, fluorine-containing polyol and polybutadiene polyol is (8-10): (1-4): (1-2).

[0043] Preferably, when the polyurethane prepolymer is prepared by using polyether polyol, fluorine-containing polyol and polybutadiene polyol, the mass ratio of polyether polyol, fluorine-containing polyol and polybutadiene polyol is 8:(1-2):(1-2).

[0044] When less fluorine-containing polyols and polybutadiene polyols are introduced during the preparation of polyurethane prepolymers, the hydrophobicity and waterproof properties of the product cannot be improved. However, if the amount of fluorine-containing polyols introduced is too high, the mechanical properties of the polyurethane potting glue product will be reduced, and fluorine-containing polyols are usually more expensive, which will increase production costs. If the amount of polybutadiene polyol introduced is too high, it will also lead to a decrease in the mechanical properties of the product, and the viscosity of the polyurethane prepolymer will increase significantly, which is not conducive to potting construction. Therefore, when the ratio of the three is within a moderate range, especially preferably within the above-mentioned ratio range, the comprehensive performance of the product is better.

[0045] More preferably, the NCO content of the polyurethane prepolymer is 20-25%.

[0046] Another object of the present invention is to provide a method for preparing the polyurethane potting adhesive, comprising the following steps:

[0047] Mix polyether polyol, castor oil polyol and modified aluminum hydroxide and heat to 110-130° C., then vacuum dry for 2-4 hours, cool to 40-60° C., then add other components and mix evenly under vacuum to obtain component A;

[0048] The polyurethane prepolymer and isocyanate are mixed uniformly under vacuum to obtain component B.

[0049] The preparation method of the polyurethane potting adhesive of the present invention has simple operation steps, low requirements on production conditions and settings, and can realize industrial production.

[0050] Another object of the present invention is to provide a waterproof sealing layer, comprising the polyurethane potting glue of the present invention.

[0051] The polyurethane thermal conductive potting adhesive with low water absorption described in the present invention not only has excellent basic performance based on the special selection of components, but also can achieve comprehensive performance of fire prevention, heat conduction and waterproofness. It is very suitable for waterproof sealing layers for protective shells with great requirements for environmental isolation.

[0052] The beneficial effect of the present invention is that the present invention provides a polyurethane thermal conductive potting glue with low water absorption rate, which can not only achieve normal thermal conductivity and fireproof performance and strong adhesion through special component selection, but also has high density, low moisture permeability and water absorption rate, and fully meets the IP68 waterproof requirements, and is very suitable for the sealing layer material of the outer shell of devices such as motors. DETAILED DESCRIPTION

[0053] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples, the purpose of which is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention, unless otherwise specified, are all commonly used common reagents and instruments.

[0054] Examples 1 to 9

[0055] An embodiment of the polyurethane thermal conductive potting adhesive with low water absorption rate and a preparation method thereof according to the present invention comprises the following steps:

[0056] The polyether polyol, castor oil polyol and modified aluminum hydroxide were mixed and heated to 120°C, then vacuum dried for 3 hours, cooled to 50°C, and then other components were added and mixed uniformly under vacuum to obtain component A;

[0057] The polyurethane prepolymer and isocyanate were mixed under vacuum for 20 minutes until they were uniform, to obtain component B.

[0058] The composition ratio of the A component and the B component is shown in Table 1, and the mass ratio of the A component to the B component is 5:1.

[0059] The polyether polyol is a polyether triol with a molecular weight of 500 g / mol and a functionality of 3;

[0060] The castor oil polyol is first-grade castor oil produced by Fucheng County Huanyu Oil Co., Ltd., with a hydroxyl value of 163 mgKOH / g and a functionality of 2.7;

[0061] The modified aluminum hydroxide 1 is aluminum hydroxide modified with tridecafluorooctyltriethoxysilane (CAS: 51851-37-7);

[0062] The modified aluminum hydroxide 2 is aluminum hydroxide modified with vinyltriethoxysilane (CAS: 78-08-0);

[0063] The modified aluminum hydroxide 3 is aluminum hydroxide modified with γ-aminopropyltriethoxysilane (CAS: 919-30-2);

[0064] The preparation method of the modified aluminum hydroxide 1 to 3 is as follows: 25 g of the modifier is dispersed in a solvent mixed with 100 g of ethanol and 400 g of water, 450 g of aluminum hydroxide is added, the mixture is heated to 70° C. and refluxed for 50 min, and the solid is separated and then dried, crushed, ground, and sieved to obtain the modified aluminum hydroxide with an average particle size of 8 μm.

[0065] The aluminum hydroxide 4 is unmodified and has an average particle size of 8 μm after crushing, grinding and sieving.

[0066] The dehydrating agent is 3A molecular sieve activation powder, and Jiangxi Xintao Technology Co., Ltd. produces 3A molecular sieve activation powder;

[0067] The defoamer is an organic modified polysiloxane, and Guangzhou Wenbo Chemical Company produces LeAd 220 defoamer;

[0068] The coupling agent is γ-glycidyloxypropyltrimethoxysilane;

[0069] The catalyst is a commercially available organic bismuth-zinc catalyst complex;

[0070] The polyurethane prepolymer 1 is a homemade product, and the preparation method is as follows:

[0071] The polyether polyol, the fluorine-containing polyol and the polybutadiene polyol are mixed in a mass ratio of 8:2:2, and then vacuum-dehydrated at 120° C. for 3 hours, cooled to below 40° C., and an equivalent amount of isocyanate is added and reacted at 65° C. for 3 hours to obtain the polyurethane prepolymer; the NCO content of the polyurethane prepolymer is 23%;

[0072] The fluorinated polyol is a perfluoropolyether diol with a molecular weight of 1000 g / mol and a functionality of 2, the polybutadiene polyol is a hydroxy-terminated polybutadiene with a molecular weight of 2800 g / mol and a functionality of 2.3, and the isocyanate is diphenylmethane diisocyanate;

[0073] The polyurethane prepolymer 2 is a homemade product, and the only difference from the polyurethane prepolymer 1 is that the fluorine-containing polyol is 2,2-difluoro-1,3-propylene glycol;

[0074] The polyurethane prepolymer 3 is a homemade product, and the only difference from the polyurethane prepolymer 1 is that the fluorine-containing polyol is trifluoromethylphenyl diol;

[0075] The polyurethane prepolymer 4 is a homemade product, and the only difference from the polyurethane prepolymer 1 is that the polyether polyol, the fluorine-containing polyol, and the polybutadiene polyol are mixed in a mass ratio of 10:1:1;

[0076] The polyurethane prepolymer 5 is a self-made product, and the only difference from the polyurethane prepolymer 1 is that the polyether polyol, the fluorine-containing polyol, and the polybutadiene polyol are mixed in a mass ratio of 8:5:2;

[0077] The polyurethane prepolymer 6 is a self-made product, and the only difference from the polyurethane prepolymer 1 is that the polyether polyol, the fluorine-containing polyol, and the polybutadiene polyol are mixed in a mass ratio of 8:2:3;

[0078] The polyurethane prepolymer 7 is a homemade product, and the only difference from the polyurethane prepolymer 1 is the preparation method:

[0079] The polyether polyol and the fluorine-containing polyol are mixed in a mass ratio of 8:4, and then vacuum-dehydrated at 120° C. for 3 hours, cooled to below 40° C., and an equivalent amount of isocyanate is added and reacted at 65° C. for 3 hours to obtain the polyurethane prepolymer; the NCO content of the polyurethane prepolymer is 23%;

[0080] The polyurethane prepolymer 8 is a homemade product, and the only difference from the polyurethane prepolymer 1 is the preparation method:

[0081] The polyether polyol and the polybutadiene polyol are mixed in a mass ratio of 8:4, and then vacuum-dehydrated for 3 hours at 120° C., cooled to below 40° C., and an equivalent amount of isocyanate is added and reacted at 65° C. for 3 hours to obtain the polyurethane prepolymer; the NCO content of the polyurethane prepolymer is 23%;

[0082] The polyurethane prepolymer 9 is a homemade product, and the only difference from the polyurethane prepolymer 1 is that the fluorinated polyol is replaced by polyethylene glycol, with a molecular weight of 2000 g / mol and a functionality of 2;

[0083] The polyurethane prepolymer 10 is a homemade product, and the only difference from the polyurethane prepolymer 1 is that the polybutadiene polyol is replaced by polytetramethylene glycol, which has a molecular weight of 2000 g / mol and a functionality of 2.

[0084] Comparative Examples 1 to 9

[0085] A polyurethane thermal conductive potting adhesive and a preparation method thereof, which differs from the embodiment only in the component composition, as shown in Table 2.

[0086] Unless otherwise specified, the components and raw materials used in the embodiments and comparative examples of the present invention are all commercially available raw materials, and the components and raw materials used in each parallel experiment are all of the same kind.

[0087] Table 1

[0088]

[0089]

[0090] Table 2

[0091]

[0092]

[0093] Effect Example 1

[0094] In order to verify the performance of the polyurethane thermal conductive potting adhesive of the present invention, the products of each embodiment and comparative example were subjected to the following tests. The test results are shown in Table 3.

[0095] Table 3

[0096]

[0097]

[0098] It can be seen from the table that the viscosity of the polyurethane thermal conductive potting glue prepared by the present invention can be maintained within the range of 3000cps, and the construction will not be affected by excessively high or low viscosity. At the same time, the hardness is relatively high, and the shear strength on the aluminum substrate can reach 7.0MPa and above, and the mechanical performance is excellent. Most importantly, the product has a flame retardancy of UL94 V0 without the introduction of flame retardants, a thermal conductivity of not less than 0.7W / m·K, and excellent thermal conductivity and flame retardancy. The water absorption rate (23°C / 24h) of the product can be maintained within 0.15%, and can also be maintained within 0.7% within a 30-day test period, with low water absorption, good air tightness, and excellent comprehensive waterproof performance. According to the products of Example 1, Example 6-7 and Comparative Examples 4-5, it can be seen that when preparing polyurethane prepolymers, the strong inductive effect and volume exclusion reaction of fluorine atoms in fluorinated polyols are very critical for the low water absorption performance of the product. If this component is missing, or it is replaced by other types of polyols and compounded with polyether polyols and polybutadiene polyols, the prepared products cannot achieve the ideal efficiency, and even affect the viscosity and mechanical strength properties of the product; and in fluorinated polyols, when perfluoropolyether diols are selected, the water absorption of the product is lower. At the same time, fluorinated polyols need to be used in conjunction with polybutadiene polyols. If this component is missing, or other types of polyols are compounded, as shown in Comparative Examples 3 and Comparative Examples 6, the product still cannot reach the expected standard of water absorption while maintaining the performance. According to Examples 1 and Examples 7-9, it can be seen that when the proportion of fluorinated polyols and polybutadiene polyols in the preparation of polyurethane prepolymers is large, the water absorption of the product will be further reduced within a certain range, but the viscosity of the product is improved, and the construction difficulty increases.

[0099] According to the comparison between Comparative Examples 1 to 2 and Examples 1 and 4, it can be seen that when aluminum hydroxide is not modified, the dispersibility and compatibility of the component in the product are poor, and the hydrophobicity cannot be improved. Not only is the viscosity of the prepared product high, the mechanical properties are poor, and the water absorption is also high. After modification with the specific modifying component of the present invention, the comprehensive performance of the product is improved, but if the modifying component is improperly selected, as described in Comparative Example 2, the product cannot achieve the same improvement effect, the water absorption rate is still high, and the mechanical properties are also poor. In addition, in the A component of the present invention, if the content of modified aluminum hydroxide is insufficient, as shown in Comparative Example 8, not only the basic hardness and shear strength of the product cannot be guaranteed, the thermal conductivity is low, the flame retardant grade does not reach UL94 V0, and the water absorption rate of the product is not up to standard, and the castor oil polyol matched with the modified aluminum hydroxide is also indispensable. If castor oil polyol is not introduced, or the amount introduced is too small, as shown in Comparative Examples 7 and 9, the area of ​​the hydrophilic micro-region in the polymer is large, and the water absorption rate of the product cannot reach the standard.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A polyurethane potting adhesive, characterized in that: It includes component A and component B; The A component comprises the following components in parts by weight: 5-15 parts of polyether polyol, 10-30 parts of castor oil polyol, 40-70 parts of modified aluminum hydroxide; The B component includes the following components in parts by weight: 10-60 parts of polyurethane prepolymer, 0-40 parts of isocyanate; The polyurethane prepolymer is obtained by reacting polyether polyol, fluorine-containing polyol, polybutadiene polyol and isocyanate; The modified aluminum hydroxide is obtained by modifying aluminum hydroxide with at least one of tridecafluorooctyltriethoxysilane, vinyltriethoxysilane, and vinyltri(2-methoxyethoxy)silane; The mass ratio of the A component to the B component is (4-6):

1.

2. The polyurethane potting adhesive according to claim 1, characterized in that: The molecular weight of the polyether polyol in the A component is 300-1000, and the degree of functionality is 2-3.

3. The polyurethane potting adhesive according to claim 1, characterized in that: The castor oil polyol in the A component has a hydroxyl value of 160-168 mgKOH / g and a functionality of 2.5-3.

4. The polyurethane potting adhesive according to claim 1, characterized in that: The modified aluminum hydroxide is at least one of tridecafluorooctyltriethoxysilane, vinyltriethoxysilane and vinyltri(2-methoxyethoxy)silane.

5. The polyurethane potting adhesive according to claim 1, characterized in that: Component A of the polyurethane thermal conductive potting glue also includes at least one of a dewatering agent, a defoaming agent, a coupling agent, and a catalyst.

6. The polyurethane potting adhesive as claimed in claim 5, characterized in that: Including at least one of the following (a) to (e): (a) the component A further comprises 0-3 parts of a dewatering agent, 0-0.1 parts of a defoaming agent, 0-2 parts of a coupling agent and 0-0.01 parts of a catalyst; (b) the dehydrating agent is molecular sieve activation powder; (c) the defoamer is a polysiloxane defoamer; (d) the coupling agent is a siloxane coupling agent; the siloxane coupling agent is at least one of γ-glycidyloxypropyltrimethoxysilane, γ-(2,3-epoxypropyloxy)propyltrimethoxysilane, ureidopropyltriethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltrimethoxysilane and γ-ureidopropyltrimethoxysilane; (e) The catalyst is a metal organic catalyst.

7. The polyurethane potting adhesive according to claim 1, characterized in that: The fluorine-containing polyol is at least one of 2,2-difluoro-1,3-propylene glycol, trifluoromethylphenyl glycol, and perfluoropolyether diol, and / or the polybutylene polyol is terminal hydroxyl polybutylene with a molecular weight of 2500-3000 g / mol and a functional group degree of 2.2-2.

4.

8. The polyurethane potting adhesive as claimed in claim 7, characterized in that: When the polyether polyol, the fluorine-containing polyol and the polybutadiene polyol are used to prepare the polyurethane prepolymer, the mass ratio of the polyether polyol, the fluorine-containing polyol and the polybutadiene polyol is (8-10): (1-5): (1-3).

9. The method for preparing the polyurethane potting adhesive according to any one of claims 1 to 8, characterized in that: The following steps are involved: Mix polyether polyol, castor oil polyol and modified aluminum hydroxide and heat to 110-130° C., then vacuum dry for 2-4 hours, cool to 40-60° C., then add other components and mix evenly under vacuum to obtain component A; The polyurethane prepolymer and isocyanate are mixed uniformly under vacuum to obtain component B.

10. A waterproof sealing layer, characterized in that: It comprises the polyurethane potting adhesive as described in any one of claims 1 to 8.

Images