Detachable polyurethane structural adhesive with high initial strength as well as preparation method and application thereof

Abstract

The invention discloses a detachable polyurethane structural adhesive with high initial strength, a preparation method of the detachable polyurethane structural adhesive and application of the detachable polyurethane structural adhesive as a battery unit structural adhesive. The structural adhesive is prepared from a component A and a component B in a volume ratio of 1: 1, the component A comprises the following components in parts by weight: 20 parts of polymer polyol, 10-20 parts of castor oil modified polyol, 0.01-1 part of a coupling agent, 0.1-1 part of water and 20-60 parts of a carbon dioxide absorbent; the component B is prepared from the following components in parts by weight: 1 to 20 parts of isocyanate A and 10 to 40 parts of isocyanate prepolymer; the structural adhesive can reach the initial tensile shear strength of 4 MPa or above after being completely cured, the requirement for resisting vibration damage in the transportation process is met, and the structural strength is reduced to a stable value of 0.2 MPa-0. 5 MPa in a short time in a use environment, so that the strength can meet static bonding of a battery unit and can also meet the requirement for vibration damage of the battery unit. And the strength is low, so that the dismounting difficulty during maintenance is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of polyurethane structural adhesives, and in particular to a detachable polyurethane structural adhesive with high initial strength, a preparation method and application thereof. Background Art

[0002] Polyurethane has great development potential in many fields such as foaming materials, structural adhesives, fibers, and elastomers due to its high wear resistance, low thermal expansion coefficient, and good performance designability. At present, the field of energy storage batteries has put forward new requirements for polyurethane structural adhesives, that is, it not only needs to have high strength after full curing to cope with the problem of structural detachment caused by bumps during transportation of energy storage batteries, but also should have the characteristics of easy disassembly of problematic battery cells during inspection and maintenance. However, the above requirements are difficult to achieve simultaneously in the formulation design of polyurethane structural adhesives.

[0003] Traditional polyurethane detachable thermal conductive structural adhesives sacrifice high-strength performance after full curing in order to achieve a full curing strength of about 1MPa for the polyurethane structural adhesive to ensure the static bonding stability of the battery unit while also enabling detachable functions for future repairs and maintenance. However, the bonding strength of 1MPa is not enough to withstand the impact of bumps and vibrations that energy storage batteries experience during long-distance transportation. At the same time, the force required for disassembly is higher than what can be achieved by manpower or simple equipment. This is also an important reason why traditional detachable structural adhesives are difficult to be widely used.

[0004] Based on this, it is necessary to develop a new idea for preparing polyurethane structural adhesives so as to achieve both the requirement of high bonding strength of the structural adhesive after full curing and the requirement of effectively resisting vibration damage caused by long-distance or ocean transportation of energy storage batteries. Summary of the invention

[0005] The purpose of the present invention is to provide a detachable polyurethane structural adhesive with high initial strength to solve the above technical problems.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned detachable polyurethane structural adhesive with high initial strength.

[0007] Another object of the present invention is to provide a use of the above-mentioned polyurethane structural adhesive with high initial strength and being detachable.

[0008] To this end, the technical solution of the present invention is as follows: A detachable polyurethane structural adhesive with high initial strength is composed of a component A and a component B in a volume ratio of 1:1; wherein the component A comprises, by weight, 20 parts of a polymer polyol, 10 to 20 parts of a castor oil-modified polyol, 0.01 to 0.4 parts of a coupling agent, 0.1 to 0.4 parts of water and 20 to 60 parts of a carbon dioxide absorbent; and the component B comprises, by weight, 1 to 20 parts of an isocyanate A and 10 to 40 parts of a terminal isocyanate prepolymer.

[0009] In component A, the polymer polyol may be polyester polyol alone, or a composite of polyester polyol and polyether polyol A, and the weight ratio of polyester polyol to polyether polyol in the composite is ≥1.

[0010] In component A, polyester polyol, polyether polyol A and castor oil modified polyol all use polyol compounds with hydroxyl values ​​of 20mgKOH / g~400mgKOH / g, functionality of 2~6, and molecular weight of 100~10000, and the three are compounded and provide hydroxyl groups. In practical applications, polyester polyol can be specifically used but not limited to RADIANOL1990 produced by Olian Company, polyether polyol A can be specifically used but not limited to F3135 produced by Yantai Wanhua Polyurethane Co., Ltd., and castor oil modified polyol can be specifically used but not limited to refined castor oil produced by Nanjing Xinxu Industry and Trade Co., Ltd.

[0011] According to the conventional configuration mode of component A of polyurethane structural adhesive, component A also includes emulsifier, plasticizer, catalyst, defoamer and filler. As a formula composition of component A in the polyurethane structural adhesive of the present invention, it is composed of 20 parts of polymer polyol, 10 parts to 20 parts of castor oil modified polyol, 0.01 parts to 0.1 parts of emulsifier, 0.01 parts to 0.4 parts of coupling agent, 1 parts to 10 parts of plasticizer A, 0.01 parts to 0.1 parts of catalyst, 0.1 parts to 0.4 parts of water, 1 parts to 5 parts of defoamer, 20 parts to 60 parts of carbon dioxide absorber and 100 parts to 200 parts of filler A in parts by weight.

[0012] According to the conventional configuration mode of component B of the polyurethane structural adhesive, component B also includes a dispersant, a plasticizer and a filler. As a formula composition of component B in the polyurethane structural adhesive of the present invention: component B is composed of 1 to 20 parts of isocyanate A, 10 to 40 parts of terminal isocyanate prepolymer, 0.1 to 5 parts of dispersant, 5 to 15 parts of plasticizer B and 100 to 200 parts of filler B in parts by weight.

[0013] In component B, the isocyanate-terminated prepolymer is produced by the reaction of isocyanate B and polyether polyol B. Excessive isocyanate B causes all hydroxyl groups in polyether polyol B to react with isocyanate groups.

[0014] Isocyanate A and isocyanate B are respectively selected from at least one of 2,4-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate, 4,4'-diisocyanate dicyclohexylmethane, 3-isocyanate methylene-3,5,5-trimethylcyclohexyl isocyanate, 1,6-hexamethylene diisocyanate, polyphenyl polymethylene isocyanate, polycarbodiimide modified MDI (polycarbodiimide modified diphenylmethane diisocyanate), and the two are the same or different compounds.

[0015] The polyether polyol B uses a compound with a hydroxyl value of 20 mgKOH / g to 400 mgKOH / g, a functionality of 2 to 6, and a molecular weight of 100 to 10000. In practical applications, the polyether polyol B uses DL2000D produced by Shandong Bluestar Dongda Chemical Co., Ltd.

[0016] Preferably, the defoaming agent is a non-silicon defoaming agent, which is used to eliminate mechanical bubbles generated after the mixing of component A and component B, and gas components that cannot be completely absorbed by the carbon dioxide absorbent during the curing process; in practical applications, the defoaming agent can specifically use but is not limited to P-590 produced by UCAR Chemical (Shanghai) Co., Ltd.

[0017] Preferably, the emulsifier is used to improve the compatibility of water in component A with the polymer polyol, and specifically at least one of sodium dodecyl sulfate, disodium octadecyl succinamide sulfonate, and disodium 4-(octadecylamino)-4-oxo-2-sulfonic-butyrate is used, and sodium dodecyl sulfate is more preferred.

[0018] Preferably, the coupling agent is mainly used to improve the adhesion of the polyurethane structural adhesive to the substrate and the aging resistance of the fully cured adhesive layer, and a silane coupling agent is specifically selected, and a silane coupling agent containing an epoxy group is more preferably selected. In practical applications, the coupling agent can be specifically used but is not limited to γ-(2,3-epoxypropoxy)propyltrimethoxysilane produced by Hubei Jianghan New Materials Co., Ltd.

[0019] Preferably, plasticizer A and plasticizer B are used to adjust the viscosity and density of each component, and the two are selected from the same type, specifically at least one of didecyl phthalate, di(2-propylheptyl)phthalate, and bisphenol A-bis(diphenyl phosphate), more preferably didecyl phthalate.

[0020] Preferably, the catalyst is used to adjust the operable time and curing speed of the glue after mixing, and an organic metal catalyst is specifically used. In practical applications, the catalyst can specifically be CUCAT-DG02 produced by Guangzhou Yourun Synthetic Materials Co., Ltd. but is not limited thereto.

[0021] Preferably, the carbon dioxide absorbent is at least one of calcium hydroxide, calcium oxide, and silicate cement, and more preferably calcium hydroxide. The carbon dioxide absorbent is used to absorb carbon dioxide generated by the reaction of water and isocyanate, and react to generate calcium carbonate and water, so as to ensure that after the excess isocyanate groups are completely consumed, there are uniformly distributed water molecules in the cured adhesive layer, which is conducive to providing an internal wet heat aging environment in the external dry heat aging environment.

[0022] Preferably, the dispersant is a phosphate dispersant, which is used to improve the compatibility of the filler in the resin matrix; in practical applications, the dispersant may specifically be, but is not limited to, BYK-W9010 produced by BYK Chemical Co., Ltd.

[0023] Preferably, filler A and filler B are used to adjust the viscosity, density and thermal conductivity of the glue and the solidified product, and the two are selected from the same type; the two fillers specifically use aluminum hydroxide fillers; in practical applications, filler A and filler B can specifically use but are not limited to DCN1200U produced by Dongguan Dongchao New Materials Co., Ltd.

[0024] In the process of designing the specific formula of component A and component B of the polyurethane structural adhesive of the present invention, the technical problems existing in the traditional polyurethane structural adhesive are taken into consideration, namely: after being fully cured and in the aging resistance process, the shear strength is basically maintained at 1MPa~2MPa. Although the requirements of static bonding of energy storage batteries and disassembly under appropriate heating conditions are met, the shear strength is difficult to resist the bumps and damage caused by the adhesive layer during long-distance transportation after the initial assembly of the energy storage battery is completed; therefore, the present invention aims to prepare a structural adhesive with a high initial shear strength after being fully cured, but in the process of aging of the adhesive layer as the battery is used for an increasing period of time, the shear strength gradually decays to a low stable value that meets both the static bonding requirements and the disassembly requirements.

[0025] Considering the characteristics of the polyurethane structural adhesive itself, that is, after the structural adhesive is fully cured, the main chain segments in the molecular structure are urethane bonds, and the polymer polyols in its preparation raw materials mostly have ester bonds and ether bonds. These chemical bonds are not easily broken in a thermal aging environment, but are very easy to break in a wet and hot aging environment; and the breaking of chemical bonds directly leads to the loss of strength of the adhesive layer due to aging; considering the characteristics of the use environment of the polyurethane structural adhesive, the aging environment inside the battery is mainly thermal aging, and wet and hot aging accounts for a very small proportion, which leads to the slow aging rate of the polyurethane structural adhesive inside the battery.

[0026] Based on this, the polyurethane structural adhesive of the present invention uses polyester polyol or a composite of polyester polyol and polyether polyol in the component composition design of component A, so that it reacts with the isocyanate in component B, and achieves the purpose of high initial shear strength of the structural adhesive after complete curing. In some specific embodiments, by limiting the number of polyester polyols in component A, or replacing part of the polyester polyols with polyether polyols according to a specified ratio, it is possible to achieve adaptive adjustment of the initial shear strength of the structural adhesive after complete curing, so that it can meet different initial shear strength requirements.

[0027] A certain amount of deionized water is also added to component A to keep moisture in the fully cured polyurethane adhesive layer. The deionized water exists in the fully cured adhesive layer in the form of water, creating conditions for the cured product to form a humid heat aging environment when heated. The easy hydrolysis of polyester polyols can be used to accelerate the aging speed of the polyurethane structural adhesive inside the battery, and achieve the expectation that the shear strength of the structural adhesive will gradually decay during the aging process. Since water will react with isocyanate groups to generate carbon dioxide, a carbon dioxide absorber is also added to component A to allow the structural adhesive to cure without foaming. In some specific embodiments, a large number of comparative experimental results show that the amount of deionized water added affects the simulation time of the wet and hot aging environment. When the amount of deionized water used is too much, the shear strength of the structural adhesive will decay excessively due to the long simulation time of the wet and hot aging environment, and cannot meet the static bonding requirements; conversely, if the amount of deionized water added is too little, the shear strength of the structural adhesive cannot be decayed to meet the detachable requirements; therefore, the control of the amount of deionized water added in component A is the control of the duration of the wet and hot aging environment of the adhesive layer; when the moisture inside the adhesive layer is completely consumed during the aging process inside the structural adhesive, the wet and hot aging environment of the adhesive layer disappears and turns into a thermal aging environment, and the decline in strength is greatly slowed down. At this time, the shear strength of the structural adhesive decays to a low level value that tends to be stable.

[0028] A coupling agent is also added to component A, which has a hydrolysis competitive reaction with the carbamate structure in the polyurethane main chain, and can snatch water and preferentially undergo hydrolysis reaction, thereby adjusting the starting time of the strength decline of the structural adhesive during wet heat aging, to ensure that the polyurethane structural adhesive does not experience shear strength decay prematurely.

[0029] In the component composition of component B of the polyurethane structural adhesive of the present invention, isocyanate A and terminal isocyanate group prepolymer are matched. Based on the differences in isocyanate group content, viscosity, etc. between the two, by adjusting the ratio of the two, the composite of the two is matched with the polyol with different hydroxyl values ​​in component A, thereby ensuring the relative stability of the R value of the polyurethane structural adhesive. The R value is also called the isocyanate index, which is specifically the ratio of the total amount of isocyanate A and the isocyanate group in the terminal isocyanate group prepolymer in component B to the total amount of hydroxyl groups of all polyol compounds in component A. While modifying the traditional polyurethane structural adhesive, the present invention still maintains an R value similar to that of the conventional polyurethane structural adhesive.

[0030] The preparation method of component A of the detachable polyurethane structural adhesive with high initial strength is as follows: polyester polyol, polyether polyol A, castor oil modified polyol, defoamer, plasticizer, filler A and carbon dioxide absorber are added into a stirring kettle, and stirred and mixed evenly under vacuum (≤-0.09MPa) and 25°C-60°C, and then emulsifier, deionized water and coupling agent are added, and mixed evenly under normal pressure and 25°C-60°C to obtain component A.

[0031] The preparation method of component B of the detachable polyurethane structural adhesive with high initial strength is as follows: adding polyether polyol B into a stirring kettle, stirring and dehydrating the mixture under vacuum (≤-0.09MPa) and high temperature conditions of 60°C to 120°C, then adding an excess of isocyanate into the reaction kettle, heating the mixture to 60°C to 120°C for reaction for 2h to 8h, so that the hydroxyl groups of the polyether polyol B are all reacted to obtain a terminal isocyanate prepolymer; then adding isocyanate, dispersant and filler B into the reaction kettle, stirring the mixture at 25°C to 60°C under vacuum (≤-0.09MPa) conditions until the mixture is evenly mixed again, thereby obtaining component B.

[0032] The invention discloses a use of a detachable polyurethane structural adhesive with high initial strength, specifically as a structural adhesive for battery cells.

[0033] After testing, the polyurethane structural adhesive with high initial strength and detachable is found to have a tensile shear strength of >4MPa after mixing and applying until completely cured in accordance with the requirements of GB / T7124-2008; after the tensile shear specimen is aged for 1000h in a 60°C environment, the tensile shear strength is ≤2MPa, which is reduced to the initial shear strength of traditional polyurethane structural adhesives; after aging for 5000h in a 60°C environment, the tensile shear strength of the structural adhesive is between 0.2MPa and 0.5MPa, reaching a shear strength that meets static bonding requirements and is easy to disassemble.

[0034] Compared with traditional polyurethane structural adhesives, the polyurethane structural adhesive with high initial strength and detachableness of the present invention: 1) overcomes the problem of low initial strength after complete curing, so that the polyurethane structural adhesive can reach a tensile shear strength of more than 4MPa after complete curing, meeting the need to resist vibration damage during transportation; 2) in the continuous work after the energy storage battery is fixed and installed, the heat released by the charge and discharge cycle of the energy storage battery (i.e., the thermal environment temperature ≈60°C) can make the polyurethane structural adhesive under the dual effects of external thermal aging and internal moisture erosion. The structural strength is reduced to another stable value (0.2MPa~0.5MPa) in a relatively short time. The strength at this time can not only meet the static bonding of the battery unit, but also has a lower strength to reduce the difficulty of disassembly during maintenance. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with specific examples, but the following examples are by no means intended to limit the present invention in any way.

[0036] In the following examples and comparative examples, the polyester polyol is RADIANOL1990 produced by Olian Company, the polyether polyol A is F3135 produced by Yantai Wanhua Polyurethane Co., Ltd., the castor oil polyol is refined castor oil produced by Nanjing Xinxu Industry and Trade Co., Ltd., the defoamer is P-590 produced by UCAR Chemical (Shanghai) Co., Ltd., the catalyst is CUCAT-DG02 produced by Guangzhou Yourun Synthetic Materials Co., Ltd., and the coupling agent is γ-(2,3-epoxypropoxy)propane produced by Hubei Jianghan New Materials Co., Ltd. )propyltrimethoxysilane, polyether polyol B adopts DL2000D produced by Shandong Bluestar Dongda Chemical Co., Ltd., isocyanate A adopts polyphenyl polymethylene isocyanate PM200 (functionality is 2.7) produced by Yantai Wanhua Polyurethane Co., Ltd., isocyanate B adopts polycarbodiimide modified MDI produced by Yantai Wanhua Polyurethane Co., Ltd., dispersant adopts BYK-W9010 produced by BYK Chemical Co., Ltd., filler A and filler B both adopt DCN1200U produced by Dongguan Dongchao New Materials Co., Ltd. Example 1

[0037] A detachable polyurethane structural adhesive with high initial strength, consisting of component A and component B, is prepared by the following method: Preparation of component A: 10 kg of polyester polyol, 10 kg of polyether polyol A, 10 kg of castor oil polyol, 3 kg of defoamer, 5 kg of didecyl phthalate, 0.02 kg of catalyst, 40 kg of calcium hydroxide and 120 kg of filler A were added into a reactor, the reactor temperature was controlled to be 25°C to 45°C, and after stirring evenly under vacuum conditions, 0.02 kg of sodium dodecyl sulfate, 0.2 kg of deionized water and 0.1 kg of coupling agent were added, and after stirring evenly under normal pressure, the material was discharged and divided into one side of a double-tube hose with a volume ratio of 1:1; Preparation of component B: Add 13.25 kg of polyether polyol B into the reactor, heat and dehydrate at 105 ° C under vacuum conditions to a water content of ≤ 300 ppm, add 13.25 kg of isocyanate B and heat to 80 ° C to react for 2 hours, add 2.75 kg of isocyanate A, 3 kg of dispersant, 11 kg of plasticizer and 160 kg of filler B into the reactor, control the reactor temperature at 25 ° C ~ 45 ° C, stir evenly under vacuum conditions, discharge the material, and divide it into the other side of the double-tube hose with a volume ratio of 1:1. Example 2

[0038] A detachable polyurethane structural adhesive with high initial strength, consisting of component A and component B, is prepared by the following method: Preparation of component A: 15 kg of polyester polyol A, 5 kg of polyether polyol A, 10 kg of castor oil polyol, 3 kg of defoamer, 5 kg of didecyl phthalate, 0.02 kg of catalyst, 40 kg of calcium hydroxide and 120 kg of filler A were added into a reactor, the reactor temperature was controlled to be 25°C to 45°C, and after stirring evenly under vacuum conditions, 0.02 kg of sodium dodecyl sulfate, 0.2 kg of deionized water and 0.1 kg of coupling agent were added, and after stirring evenly under normal pressure, the material was discharged and divided into one side of a double-tube hose with a volume ratio of 1:1; Preparation of component B: Add 11.5 kg of polyether polyol B into the reactor, heat and dehydrate at 105 ° C under vacuum conditions to a water content of ≤ 300 ppm, add 11.5 kg of isocyanate B and heat to 80 ° C to react for 2 hours, add 6.25 kg of isocyanate A, 3 kg of dispersant, 11 kg of plasticizer and 160 kg of filler B into the reactor, control the reactor temperature at 25 ° C ~ 45 ° C, stir evenly under vacuum conditions, discharge the material, and divide it into the other side of the double-tube hose with a volume ratio of 1:1. Example 3

[0039] A detachable polyurethane structural adhesive with high initial strength, consisting of component A and component B, is prepared by the following method: Preparation of component A: 20 kg of polyester polyol A, 10 kg of castor oil polyol, 3 kg of defoamer, 5 kg of didecyl phthalate, 0.02 kg of catalyst, 40 kg of calcium hydroxide and 120 kg of filler A were added into a reactor, the reactor temperature was controlled to be 25°C to 45°C, and after stirring evenly under vacuum conditions, 0.02 kg of sodium dodecyl sulfate, 0.2 kg of deionized water and 0.1 kg were added, and after stirring evenly under normal pressure, the material was discharged and divided into one side of a double-tube rubber hose with a volume ratio of 1:1; Preparation of component B: Add 10kg of polyether polyol B into the reactor, heat and dehydrate at 105°C under vacuum conditions to a water content of ≤300ppm, add 10kg of isocyanate B and heat to 80°C for reaction for 2h, add 9.25kg of isocyanate A, 3kg of dispersant, 11kg of plasticizer and 160kg of filler B into the reactor, control the reactor temperature at 25°C~45°C, stir evenly under vacuum conditions, discharge the material, and dispense it into the other side of the double-tube hose with a volume ratio of 1:1. Example 4

[0040] A polyurethane structural adhesive, consisting of component A and component B, is prepared by the following method: Preparation of component A: 10 kg of polyester polyol A, 10 kg of polyether polyol A, 10 kg of castor oil polyol, 3 kg of defoamer, 5 kg of didecyl phthalate, 0.02 kg of catalyst, 40 kg of calcium hydroxide and 120 kg of filler A were added into a reactor, the reactor temperature was controlled to be 25°C to 45°C, and after stirring evenly under vacuum conditions, 0.02 kg of sodium dodecyl sulfate, 0.2 kg of deionized water and 0.1 kg of coupling agent were added, and after stirring evenly under normal pressure, the material was discharged and divided into one side of a double-tube hose with a volume ratio of 1:1; Preparation of component B: Add 11.25 kg of polyether polyol B into the reactor, heat and dehydrate at 105 ° C under vacuum conditions to a water content of ≤ 300 ppm, add 11.25 kg of isocyanate B and heat to 80 ° C to react for 2 hours, add 6.75 kg of isocyanate A, 3 kg of dispersant, 11 kg of plasticizer and 160 kg of filler B into the reactor, control the reactor temperature at 25 ° C ~ 45 ° C, stir evenly under vacuum conditions, discharge the material, and divide it into the other side of the double-tube hose with a volume ratio of 1:1. Example 5

[0041] A polyurethane structural adhesive, consisting of component A and component B, is prepared by the following method: Preparation of component A: 10 kg of polyester polyol A, 10 kg of polyether polyol A, 10 kg of castor oil polyol, 3 kg of defoamer, 5 kg of didecyl phthalate, 0.02 kg of catalyst, 40 kg of calcium hydroxide and 100 kg of filler A were added into a reactor, the reactor temperature was controlled to be 25°C to 45°C, and after stirring evenly under vacuum conditions, 0.02 kg of sodium dodecyl sulfate, 0.2 kg of deionized water and 0.1 kg of coupling agent were added, and after stirring evenly under normal pressure, the material was discharged and divided into one side of a double-tube rubber hose with a volume ratio of 1:1; Preparation of component B: Add 10kg of polyether polyol B into the reactor, heat and dehydrate at 105°C under vacuum conditions to a water content of ≤300ppm, add 10kg of isocyanate B and heat to 80°C for reaction for 2h, add 9.25kg of isocyanate A, 3kg of dispersant, 11kg of plasticizer and 160kg of filler B into the reactor, control the reactor temperature at 25°C~45°C, stir evenly under vacuum conditions, discharge the material, and dispense it into the other side of the double-tube hose with a volume ratio of 1:1.

[0042] Comparative Example 1 A polyurethane structural adhesive, which is different from Example 2 only in that the amount of water used is increased to 0.5 parts.

[0043] Comparative Example 2 A polyurethane structural adhesive, which is different from Example 2 only in that the amount of water used is increased to 1 part.

[0044] Comparative Example 3 A polyurethane structural adhesive, which is different from Example 2 in that: the amount of coupling agent is increased to 0.5 parts.

[0045] Comparative Example 4 A polyurethane structural adhesive, which is different from Example 2 in that the amount of coupling agent is increased to 1 part.

[0046] Performance Testing: The thermal conductivity, shear performance and aging performance of the polyurethane structural adhesives of the above-mentioned embodiments and comparative examples were tested.

[0047] The thermal conductivity test is carried out according to the method of ISO22007.2 to test the thermal conductivity coefficient of the polyurethane structural adhesive after it is fully cured.

[0048] Shear performance: Shear specimens were prepared according to the method of GB / T7124. The film thickness of the shear specimens was 0.2 mm. They were cured for 168 h in an environment with an ambient temperature of 23±2°C and a relative humidity of 50%±5%. Then, shear strength tests were carried out in an environment with an ambient temperature of 23±2°C and a relative humidity of 50%±5%.

[0049] Aging properties: The 60 ℃ aging properties were tested according to the method of GB / T7124, specifically, shear specimens were prepared, and the specimens were cured for 168 h in an environment with an ambient temperature of 23±2℃ and a relative humidity of 50%±5%RH, and then placed in an oven at a temperature of 60℃ for 200, 400, 600, 800, 1000, 2000, 3000 and 5000 h, respectively. After being taken out, they were left to stand for 24 h in an environment with a temperature of 25±2℃, and then the shear strength was tested.

[0050] The specific test results are shown in Table 1 below.

[0051] Table 1:

[0052] As can be seen from Table 1, 1) In the thermal conductivity test, the thermal conductivity of the five polyurethane structural adhesives prepared in Examples 1 to 5 after being fully cured is 1.2W / m·K to 1.4W / m·K, which is similar to the thermal conductivity of the polyurethane structural adhesive for conventional batteries, so as to meet the requirement that the polyurethane structural adhesive is used to conduct the heat generated by the battery during the use of the battery to avoid damage to the battery due to overheating; 2) In the shear strength test, the initial shear strengths of the five polyurethane structural adhesives prepared by Examples 1 to 5 after complete curing are all greater than 4MPa, meeting the requirement of resisting vibration damage during transportation; according to the test results of Examples 1, 2 and 3, by changing the ratio of polyester polyol and polyether polyol in component A while keeping the total amount of polymer polyol the same and the R value of the system basically the same, the initial shear strength after complete curing can be adjusted; and it can also be seen from the three examples that, as the proportion of polyester polyol in polymer polyol increases, that is, as the content of polyester groups increases, the initial shear strength of the polyurethane structural adhesive after complete curing also gradually increases; among them, as a modified alternative product of conventional polyurethane structural adhesive for batteries, the R value in each example is set to 1.00-1.40, which is an approximate value of the R value of conventional polyurethane structural adhesive for batteries; According to other experimental test results, when the amount of polyester polyol in Example 2 is adjusted to 5 kg, and the amount of polyether polyol is adjusted to 15 kg, and the amounts of other components remain unchanged, the initial shear strength after complete curing is greatly reduced to 3.6 MPa.

[0053] 3) In the aging performance test, the shear strength of the five polyurethane structural adhesives prepared in Examples 1 to 5 gradually decayed and finally reached a stable value as the battery usage time increased under an aging environment of 60°C. The stable shear strength value ranged from 0.2MPa to 0.45MPa, making it easier to disassemble. According to the test results of Example 1, Example 2 and Example 3, when the proportion of polyester polyol in the polymer polyol gradually increases, or even completely replaces the polyether polyol, the shear strength decay time (i.e., the aging time period during which the shear strength decays significantly) gradually becomes faster. The reason for this is that since the hydrolysis resistance of the polyester structure is lower than that of the polyether structure, the shear strength in an aging environment of 60°C will decrease earlier; specifically, the shear strength decay of the polyurethane structural adhesive of Example 1 occurs between aging 400h and aging 600h, the shear strength decay of the polyurethane structural adhesive of Example 2 occurs between aging 200h and aging 400h, and although the shear strength decay of the polyurethane structural adhesive of Example 3 also occurs between aging 200h and aging 400h as shown in Table 1, it is inferred that it should be closer to a certain moment of aging 200h according to the change in the decay amplitude; According to Example 1, Example 4 and Example 5, while keeping the same polymer polyol ratio and the same total amount of the three polyol substances, by increasing the proportion of isocyanate A in component B and slightly adjusting the R value of the system, the start time of shear strength decay of the structural adhesive is gradually advanced, and the final shear strength value after decay is analyzed as follows: the increase in R value increases the molar amount of isocyanate groups, that is, more excess isocyanate groups will react with water and generate more substituted ureas, and in the process of wet heat aging, the hydrolysis resistance of the urea group is much lower than that of the carbamate in the main chain segment of the structural adhesive, which leads to the early start time of decay; specifically, the shear strength decay of the polyurethane structural adhesive of Example 4 and Example 5 occurs between aging 200h and aging 400h, and according to the decay amplitude, it can be inferred that the start time of decay in Example 5 relative to Example 4 will be closer to aging 200h; In summary, in the formula of the polyurethane structural adhesive, the compounding ratio of the two complexes in the polymer polyol of component A, and the compounding ratio between the polyol substance in component A and the isocyanate and terminal isocyanate prepolymer in combination B, comprehensively affect the initial shear strength of the polyurethane structural adhesive and the changing trend of the shear strength during the aging process.

[0054] Compared with Example 2, Comparative Examples 1 and 2 gradually increase the amount of deionized water added in component A, resulting in the shear strength stability value of the polyurethane structural adhesive prepared by the two being too low after attenuation, <0.1 MPa, and unable to meet the static bonding requirements; however, regardless of the embodiment or the comparative example, the shear strength of the structural adhesive after 2000 hours of aging tends to be stable, which indicates that water is continuously consumed during the aging process of the adhesive layer. After the water is completely consumed, the aging state of the adhesive layer changes from wet heat aging to thermal aging, and the strength no longer decreases; in addition, according to other experimental test results, when the amount of deionized water added in component A is too small, the shear strength of the polyurethane structural adhesive after aging for 5000 hours is still higher than 0.5 MPa, which not only fails to meet the detachable requirements, but also the regularity of the strength decline makes it difficult to judge whether it has reached a stable value.

[0055] Compared with Example 2, Comparative Examples 3 and 4 gradually increase the amount of coupling agent added in component A, resulting in a significant delay in the starting time of strength decay of the polyurethane structural adhesives prepared by the two in the aging test. The reasons are analyzed as follows: the silane coupling agent containing epoxy groups protects the carbamate structure due to its hydrophobic effect, and since small molecules react with water more rapidly than substances with large molecular weight, the coupling agent component is easier to hydrolyze than the carbamate structure under heating conditions; as the degree of hydrolysis reaction of the coupling agent increases, the content of the coupling agent becomes less and less, and the degree to which the remaining water molecules participate in the hydrolysis reaction of the carbamate structure gradually increases, which is macroscopically manifested as a delay in the starting time of shear strength decrease; specifically, the starting time of shear strength decrease in Comparative Example 3 is delayed to between aging 600h and aging 800h, while the starting time of shear strength decrease in Comparative Example 4 is delayed to between aging 1000h and aging 2000h, and the shear strength is still increased when the final aging is 5000h, which makes it difficult to judge whether it has decayed to a stable state, and the disassembly requirements cannot be met.

[0056] In summary, the polyurethane structural adhesive with high initial strength and detachable of the present invention has an initial tensile shear strength of >4MPa after being mixed and applied until completely cured; after the tensile shear specimen is aged in an environment of 60°C for 1000h, the tensile shear strength is ≤2MPa, which is reduced to the initial shear strength of the traditional polyurethane structural adhesive; after aging in an environment of 60°C for 5000h, the tensile shear strength of the structural adhesive is between 0.2MPa and 0.5MPa, reaching a shear strength that meets the static bonding requirements and is easy to disassemble.

Claims

1. A detachable polyurethane structural adhesive having high initial strength, characterized in that: It is composed of component A and component B in a volume ratio of 1:1; wherein, Component A includes 20 parts by weight of polymer polyol, 10 to 20 parts of castor oil modified polyol, 0.01 to 0.4 parts of coupling agent, 0.1 to 0.4 parts of water and 20 to 60 parts of carbon dioxide absorbent; component B includes 1 to 20 parts by weight of isocyanate A and 10 to 40 parts of terminal isocyanate prepolymer; The polymer polyol is a polyester polyol, or a composite of a polyester polyol and a polyether polyol A, and the weight ratio of the polyester polyol to the polyether polyol in the composite is ≥1; The isocyanate-terminated prepolymer is produced by the reaction of isocyanate B and polyether polyol B; The polyester polyol, polyether polyol A, polyether polyol B and castor oil modified polyol are all compounds with hydroxyl values ​​of 20 mgKOH / g to 400 mgKOH / g, functionalities of 2 to 6 and molecular weights of 100 to 10,000.

2. The detachable polyurethane structural adhesive with high initial strength according to claim 1, characterized in that: Isocyanate A and isocyanate B are respectively selected from at least one of 2,4-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,6-toluene diisocyanate, 2,4-toluene diisocyanate, 4,4'-diisocyanate dicyclohexylmethane, 3-isocyanate methylene-3,5,5-trimethylcyclohexyl isocyanate, 1,6-hexamethylene diisocyanate, polyphenyl polymethylene isocyanate, and polycarbodiimide modified MDI.

3. The detachable polyurethane structural adhesive with high initial strength according to claim 1, characterized in that: Component A also includes 0.01 to 0.1 parts of emulsifier, 1 to 10 parts of plasticizer A, 0.01 to 0.1 parts of catalyst, 1 to 5 parts of defoamer and 100 to 200 parts of filler A in parts by weight.

4. The detachable polyurethane structural adhesive with high initial strength according to claim 3, characterized in that: The B component also includes 0.1 to 5 parts of a dispersant, 5 to 15 parts of a plasticizer B, and 100 to 200 parts of a filler B in parts by weight.

5. The detachable polyurethane structural adhesive with high initial strength according to claim 3, characterized in that: The coupling agent is a silane coupling agent; the emulsifier is at least one of sodium dodecyl sulfonate, disodium octadecyl succinamide sulfonate, and disodium 4-(octadecylamino)-4-oxo-2-sulfonic-butyrate; the plasticizer A is at least one of didecyl phthalate, di(2-propylheptyl)phthalate, and bisphenol A-bis(diphenyl phosphate); the catalyst is an organic metal catalyst; the defoamer is a non-silicon defoamer; the carbon dioxide absorber is at least one of calcium hydroxide, calcium oxide, and silicate cement; and the filler A is an aluminum hydroxide filler.

6. The detachable polyurethane structural adhesive with high initial strength according to claim 4, characterized in that: The dispersant is a phosphate dispersant; the plasticizer B is at least one of didecyl phthalate, di(2-propylheptyl)phthalate, and bisphenol A-bis(diphenyl phosphate); and the filler B is an aluminum hydroxide filler.

7. The detachable polyurethane structural adhesive with high initial strength according to claim 1, characterized in that: The preparation method of the terminal isocyanate group prepolymer is as follows: adding the dehydrated polyether polyol B and isocyanate B into a stirring kettle, and reacting them at 60° C. to 120° C. for 2 h to 8 h to obtain the terminal isocyanate group prepolymer.

8. A method for preparing a detachable polyurethane structural adhesive having high initial strength as claimed in any one of claims 1 to 7, characterized in that the steps include: Preparation of component A: Add polyester polyol, polyether polyol, castor oil modified polyol, defoamer, plasticizer, filler A and carbon dioxide absorbent into a stirred tank, and stir until uniformly mixed under vacuum at 25°C-60°C, then add emulsifier, deionized water and coupling agent, and continue stirring at normal pressure at 25°C-60°C until uniformly mixed, and discharge; Preparation of component B: Add the terminal isocyanate prepolymer, isocyanate A, plasticizer B, dispersant and filler B into a stirring kettle, and continue stirring under vacuum conditions at 25°C~60°C until the mixture is uniformly mixed, and then discharge the mixture.

9. A use of a detachable polyurethane structural adhesive having high initial strength as claimed in any one of claims 1 to 7, characterized in that: As structural adhesive for battery cells.

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