A kind of blocked curing agent for low-temperature thermal curing and a one-component low-temperature thermal curing polyurethane structural adhesive using the same

Abstract

The present invention provides a low-temperature cured enclosed curing agent, which is prepared as follows: calculated by mass fraction, 100 parts of polyether polyols and 77 to 123 parts of the first isocyanate monomers are mixed to form a first reaction solution, the polyether polyol is selected from at least one of polyoxypropylene diol and polytetramethylene ether diol, and the first isocyanate monomer is selected from liquefied 4,4-diphenylmethane diisocyanate, polyphenyl polymethylene polyisocyanate, HDI trimer, HDI biuret One or more; The first reaction solution is reacted under 60 to 80 ° C conditions, and the free isocyanate group content in the first reaction solution reaches 8 to 12%; Under 40 to 50 ° C conditions, a catalyst and a sealing agent are sequentially added to the first reaction solution, and the isocyanate group content in the first reaction solution is reacted to <0.05%, and a enclosed curing agent is obtained. The enclosed curing agent for low-temperature curing provided by the present invention can be unsealed at a relatively low temperature, greatly reducing the conditions of use and widening the scope of use of the product.

Description

Technical Field

[0001] The present invention relates to the technical field of curing agents, and in particular to a low-temperature heat-curing closed curing agent and a single-component low-temperature heat-curing polyurethane structural adhesive using the same. Background Art

[0002] Polyurethane adhesives are adhesives containing carbamate groups (-NHCOO-) and / or isocyanate groups (-NCO) in the matrix. Polyurethane adhesives contain polar groups such as carbamate groups, isocyanate groups, and urea groups, which can form covalent bonds and hydrogen bonds with materials containing active hydrogen. In addition, by adjusting the formula of polyurethane adhesives, it can also meet the bonding of different materials such as metals, rubber, plastics, wood, leather, fabrics, paper, and ceramics. Polyurethane adhesives can be cured by heating or at room temperature. The bonding process is simple, the operating performance is excellent, and it is not easy to cause defects in the bonding layer.

[0003] There are many design ideas for the currently used heat-curing one-component polyurethane adhesives or coatings, but they all require isocyanate to be blocked to ensure activity. However, the deblocking temperature of the current blocked isocyanate curing agent is generally 160°C. The deblocking temperature is high, the energy consumption is large, and the use conditions are also harsh.

[0004] Therefore, it is necessary to seek an adhesive product that can be unsealed and cured at a lower temperature to meet consumer demand. Summary of the invention

[0005] The purpose of the present invention is to seek a low-temperature heat-curing closed curing agent and a single-component low-temperature heat-curing polyurethane structural adhesive using the same, so as to obtain a polyurethane structural adhesive that can be cured at low temperatures and reduce energy consumption.

[0006] According to one aspect of the present invention, a low-temperature curing blocked curing agent is provided, which is prepared as follows: S1, 100 parts of a polyether polyol and 77 to 123 parts of a first isocyanate monomer are mixed to form a first reaction liquid, wherein the polyether polyol is selected from at least one of polyoxypropylene diol and polytetramethylene ether diol, and the first isocyanate monomer is selected from one or more of liquefied 4,4-diphenylmethane diisocyanate, polyphenyl polymethylene polyisocyanate, HDI trimer, and HDI biuret; S2, the first reaction liquid is reacted at 60 to 80° C. until the isocyanate group content in the first reaction liquid reaches 8 to 12%; S3, at 40 to 50° C., a catalyst and a blocking agent are sequentially added to the first reaction liquid to react until the isocyanate group content in the first reaction liquid is less than 0.05%, thereby obtaining a blocked curing agent.

[0007] The low-temperature curable blocked curing agent prepared by the above method can be cured within the temperature range of 90 to 100 °C. When applied to rubber compound products, it can enable the rubber compound products to be cured and formed at a lower temperature. On the other hand, the above blocked curing agent does not contain highly toxic materials, and its VOCs content is low. It can maintain a low volatility rate and high stability during curing and storage, thus having good safety. Among them, the blocked curing agent provided by the present invention is a special blocked curing agent prepared by a specific method. By monitoring the content of isocyanate groups (NCO content) in the reaction system during the preparation of the blocked curing agent, the viscosity of the blocked curing agent can be controlled within a certain range. After adding the blocked curing agent to other rubber compound products, the viscosity of the formed mixed rubber compound can also be maintained within a suitable range.

[0008] Preferably, the first isocyanate monomer includes liquefied 4,4-diphenylmethane diisocyanate (liquefied MDI).

[0009] The polyurethane structural adhesive prepared using liquefied MDI as the first isocyanate monomer has high bonding strength, good water resistance, and low VOC emission.

[0010] Preferably, the polyether polyol includes polypropylene glycol.

[0011] Preferably, the molecular weight of the polyether polyol is 1000 to 2000.

[0012] Preferably, the water content of the polyether polyol is less than 500 ppm.

[0013] Preferably, the blocking agent is selected from cashew nut oil or modified cashew nut oil.

[0014] On the other hand, the present invention relates to a one-component low-temperature thermosetting polyurethane structural adhesive, which includes the above blocked curing agent; calculated by mass parts, the polyurethane structural adhesive includes 50 to 62 parts of the blocked curing agent, 33 to 48 parts of a modified castor oil polymer, and 3 to 10 parts of an additive, and the additive includes a catalyst.

[0015] The one-component low-temperature thermosetting polyurethane structural adhesive prepared by the above method can be completely cured at a temperature of 90 to 100 °C, reducing energy consumption and increasing safety during use. At the same time, the above polyurethane structural adhesive uses safe and environmentally friendly raw materials, and no highly toxic substances are detected during use and storage. The above polyurethane does not slowly undergo a deblocking reaction at room temperature, thereby increasing its storage stability and greatly expanding the use range of the above polyurethane structural adhesive.

[0016] Preferably, the modified castor oil polymer is prepared as follows: S1. At 40-50 °C, castor oil and a second isocyanate monomer are mixed to form a second reaction solution, and the feeding amounts of castor oil and the second isocyanate monomer are such that R in the second reaction solution is 0.1-0.3; S2. The second reaction solution is reacted at 50-80 °C for 2-3 hours to obtain the modified castor oil polymer; wherein, taking the content of isocyanate groups in the second isocyanate monomer as A1 and the content of hydroxyl groups in the modified castor oil as A2, let R = A1 / A2.

[0017] If the value of R is too small, in order to ensure the smooth progress of the preparation reaction of the polyurethane structural adhesive, it is necessary to increase the input amount of the blocked curing agent, which will lead to an increase in the residual amount of the blocked curing agent in the prepared polyurethane structural adhesive. If the value of R is too large, the prepared polyurethane structural adhesive will have too high a viscosity and is prone to gelation risk. In order to make the modified castor oil polymer have good use effects in the subsequent preparation of polyurethane structural adhesives, it is necessary to control R in the second reaction solution within a certain range.

[0018] Preferably, the second isocyanate monomer is selected from at least one of liquefied 4,4-diphenylmethane diisocyanate (liquefied MDI), 1,6-hexamethylene diisocyanate (HDI), toluene diisocyanate, and 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (IPDI).

[0019] Preferably, the second isocyanate monomer includes liquefied 4,4-diphenylmethane diisocyanate (liquefied MDI).

[0020] Preferably, the modified castor oil is selected from at least one of Basf Sovermol series 805, 750, 819, AC006 and AC009 of Ito Seiyu, and AP11, AP19 and AP21 of Shanghai Jingri.

[0021] Preferably, the water content of castor oil is less than 500 ppm.

[0022] Preferably, the catalyst is selected from at least one of organic bismuth, organic tin and organic zinc catalysts.

[0023] Preferably, the catalyst is selected from at least one of organic bismuth catalysts.

[0024] Preferably, the catalyst is selected from at least one of bismuth isooctanoate and bismuth neodecanoate.

[0025] Preferably, during the preparation of the polyurethane structural adhesive, an auxiliary agent is also required, and the auxiliary agent is selected from at least one of molecular sieve activated powder, pigment and fumed silica.

[0026] In summary, compared with the prior art, the solution provided by the present invention has the following beneficial effects:

[0027] (1) The low-temperature curing blocked curing agent of the present invention can be unblocked at a relatively low temperature, thereby reducing the curing temperature of the polyurethane product and the energy consumption required for curing, thereby greatly broadening its application range.

[0028] (2) The one-component low-temperature heat-curing polyurethane structural adhesive of the present invention avoids the generation of harmful substances during the curing process. The modified castor oil polymer of the present invention has strong nucleophilicity and contains a large amount of active hydrogen, which can quickly react with the free NCO group after decomposition, and no isocyanate is released during the curing process.

[0029] (3) The one-component low-temperature heat-curing polyurethane structural adhesive of the present invention has good storage stability at room temperature. The present invention uses a blocked curing agent and a polyol to prepare the polyurethane structural adhesive, so that the polyurethane structural adhesive will not undergo a deblocking reaction at room temperature, further increasing the room temperature stability of the product and greatly broadening the scope of use of the product. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only embodiments of a part of the present invention, rather than all embodiments.

[0031] Example 1

[0032] This embodiment provides a one-component low-temperature heat-curing polyurethane structural adhesive. In this embodiment, the polyether polyol involved is PPG1000, the first isocyanate monomer is liquefied MDI (brand name: Wanhua MDI-100L), the modified castor oil brand is basf Sovermol805, and the second isocyanate monomer is liquefied MDI (brand name: Wanhua MDI-100L). The preparation method is as follows:

[0033] 1. The sealed curing agent is prepared by the following process:

[0034] S1. Dehydrate the polyether polyol in vacuo at 105-120° C. until the water content is less than 500 ppm. Mix 100 parts of the polyether polyol and 100 parts of the first isocyanate monomer by weight to form a first reaction solution.

[0035] S2. reacting the first reaction liquid at 70° C. until the content of free isocyanate groups in the first reaction liquid reaches 10%.

[0036] S3, cooling the first reaction liquid to 45°C, adding 0.5 parts of catalyst bismuth isooctanoate thereto, stirring evenly, and then dripping 145 parts of blocking agent NX-2026 until the NCO content is less than 0.05%, thereby obtaining a blocked curing agent.

[0037] 2. The modified castor oil polymer is prepared by the following process:

[0038] S1. Vacuum dehydrate 100 parts of modified castor oil at 105 - 120 °C until the water content < 500 ppm. At 45 °C, mix the castor oil and the second isocyanate monomer to form a second reaction solution, and the feeding amounts of the castor oil and the second isocyanate monomer are such that R = 0.3 in the second reaction solution; wherein, taking the isocyanate group content in the second isocyanate monomer as A1 and the hydroxyl group content in the modified castor oil as A2, R = A1 / A2.

[0039] S2. React the second reaction solution at 70 °C for 2.5 hours to obtain the modified castor oil polymer.

[0040] 3. The polyurethane structural adhesive is prepared by the following process:

[0041] In a reaction kettle, add 40 parts of the modified castor oil polymer, 55 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder, stir under vacuum for 1.5 h, control the temperature at 30 ± 1 °C, stir evenly, then add 1 part of the catalyst, and mix thoroughly to obtain the polyurethane structural adhesive.

[0042] Example 2

[0043] This example refers to the method for preparing a one - component low - temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one - component low - temperature thermosetting polyurethane structural adhesive. The types of raw materials used in this example are the same as those used in Example 1 for preparing the one - component low - temperature thermosetting polyurethane structural adhesive.

[0044] This example prepares the polyurethane structural adhesive according to the following method:

[0045] 1. The blocked curing agent is prepared by the following process:

[0046] S1. Vacuum dehydrate 100 parts of polyether polyol at 105 - 120 °C until the water content < 500 ppm; mix 100 parts of the dehydrated polyether polyol and 77 parts of the first isocyanate monomer evenly to form a first reaction solution.

[0047] S2. React the first reaction solution at 70 °C for about 2 hours until the free NCO content in the first reaction solution reaches 8%;

[0048] S3. Cool the first reaction solution to 45 °C, add 0.5 part of the catalyst bismuth isooctanoate to it, stir evenly, and then dropwise add 100 parts of the blocking agent NX - 2026 until the NCO content < 0.05% to obtain the blocked curing agent.

[0049] 2. The modified castor oil polymer is prepared by the following process:

[0050] This step is the same as that in Example 1.

[0051] 3. The polyurethane structural adhesive is prepared by the following process:

[0052] In a reaction kettle, add 37 parts of the modified castor oil polymer, 58 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder, stir under vacuum for 1.5 h, control the temperature at 30 ± 1 °C, stir evenly, then add 1 part of the catalyst, and mix thoroughly to obtain the polyurethane structural adhesive.

[0053] Example 3

[0054] This example refers to the method for preparing a one-component low-temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one-component low-temperature thermosetting polyurethane structural adhesive. The types of raw materials used in this example are the same as those used in Example 1 for preparing the one-component low-temperature thermosetting polyurethane structural adhesive.

[0055] The polyurethane structural adhesive is prepared by the following method in this example:

[0056] 1. The blocked curing agent is prepared by the following process:

[0057] S1. Under the condition of 105 - 120 °C, vacuum dehydrate 100 parts of polyether polyol until the water content < 500 ppm; mix 100 parts of the dehydrated polyether polyol and 123 parts of the first isocyanate monomer evenly to form the first reaction solution.

[0058] S2. React the first reaction solution at 70 °C for about 2 hours until the free NCO content in the first reaction solution reaches 12%;

[0059] S3. Cool the first reaction solution to 45 °C, add 0.5 part of the catalyst bismuth isooctanoate to it, stir evenly, and then dropwise add 185 parts of the blocking agent NX-2026 until the NCO content < 0.05% to obtain the blocked curing agent.

[0060] 2. The modified castor oil polymer is prepared by the following process:

[0061] This step is the same as that in Example 1.

[0062] 3. The polyurethane structural adhesive is prepared by the following process:

[0063] In a reaction kettle, add 42 parts of the modified castor oil polymer, 53 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder, stir under vacuum for 1.5 h, control the temperature at 30 ± 1 °C, stir evenly, then add 1 part of the catalyst, and mix thoroughly to obtain the polyurethane structural adhesive.

[0064] Comparative Example 1

[0065] In this example, a one-component low-temperature thermosetting polyurethane structural adhesive was prepared by referring to the method for preparing a one-component low-temperature thermosetting polyurethane structural adhesive provided in Example 1. The types of raw materials used in this example are the same as those used in Example 1 for preparing the one-component low-temperature thermosetting polyurethane structural adhesive.

[0066] The polyurethane structural adhesive was prepared by the following method in this example:

[0067] 1. The blocked curing agent was prepared by the following process:

[0068] S1. Under the condition of 105 - 120 °C, 100 parts of polyether polyol were dehydrated under vacuum until the water content < 500 ppm; 100 parts of the dehydrated polyether polyol and 61.5 parts of the first isocyanate monomer were mixed evenly to form the first reaction solution.

[0069] S2. The first reaction solution was reacted at 70 °C for about 2 hours until the free NCO content in the first reaction solution reached 6%;

[0070] S3. The first reaction solution was cooled to 45 °C, 0.5 part of the catalyst bismuth isooctanoate was added thereto, and after stirring evenly, 73 parts of the blocking agent NX-2026 were added dropwise until the NCO content < 0.05%, and thus the blocked curing agent was obtained.

[0071] 2. The modified castor oil polymer was prepared by the following process:

[0072] This step was the same as that in Example 1.

[0073] 3. The polyurethane structural adhesive was prepared by the following process:

[0074] In the reaction kettle, 33 parts of the modified castor oil polymer, 62 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder were added, and vacuum stirring was carried out for 1.5 h, the temperature was controlled at 30 ± 1 °C, and after stirring evenly, 1 part of the catalyst was added and mixed evenly, and thus the polyurethane structural adhesive was prepared.

[0075] Comparative Example 2

[0076] In this example, a one-component low-temperature thermosetting polyurethane structural adhesive was prepared by referring to the method for preparing a one-component low-temperature thermosetting polyurethane structural adhesive provided in Example 1. The types of raw materials used in this example are the same as those used in Example 1 for preparing the one-component low-temperature thermosetting polyurethane structural adhesive.

[0077] The polyurethane structural adhesive was prepared by the following method in this example:

[0078] 1. The blocked curing agent is prepared by the following process:

[0079] S1. At 105 - 120 °C, 100 parts of polyether polyol are dehydrated under vacuum until the water content < 500 ppm; 100 parts of the dehydrated polyether polyol and 160 parts of the first isocyanate monomer are mixed evenly to form a first reaction liquid.

[0080] S2. The first reaction liquid reacts at 70 °C for about 2 hours until the free NCO content in the first reaction liquid reaches 14%.

[0081] S3. The first reaction liquid is cooled to 45 °C, 0.5 part of the catalyst bismuth isooctanoate is added thereto, and after stirring evenly, 250 parts of the blocking agent NX - 2026 are added dropwise until the NCO content < 0.05%, thus obtaining the blocked curing agent.

[0082] 2. The modified castor oil polymer is prepared by the following process:

[0083] This step is the same as that in Example 1.

[0084] 3. The polyurethane structural adhesive is prepared by the following process:

[0085] In a reaction kettle, 44 parts of the modified castor oil polymer, 51 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder are added, and vacuum stirring is carried out for 1.5 h while controlling the temperature at 30 ± 1 °C. After stirring evenly, 1 part of the catalyst is added and mixed thoroughly, thus obtaining the polyurethane structural adhesive.

[0086] Example 4

[0087] This example refers to the method for preparing a one - component low - temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one - component low - temperature thermosetting polyurethane structural adhesive. The difference between this example and Example 1 lies in that the polyether polyol raw material selected for the blocked curing agent in the raw material types for preparing the one - component low - temperature thermosetting polyurethane structural adhesive is different. Specifically, this example selects polytetrahydrofuran ether diol as the polyether polyol, and the remaining raw materials and preparation methods are strictly the same as those in Example 1.

[0088] Comparative Example 3

[0089] This example refers to the method for preparing a one - component low - temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one - component low - temperature thermosetting polyurethane structural adhesive. The difference between this comparative example and Example 1 lies in that the polyether polyol raw material selected for the blocked curing agent in the raw material types for preparing the one - component low - temperature thermosetting polyurethane structural adhesive is different. Specifically, this example selects MN1000 as the polyether polyol, and the rest is strictly the same as that in Example 1.

[0090] Example 5

[0091] This example refers to the method for preparing a one - component low - temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one - component low - temperature thermosetting polyurethane structural adhesive. The difference between this example and Example 1 lies in the different second isocyanate monomer raw materials among the raw material types for preparing the one - component low - temperature thermosetting polyurethane structural adhesive. Specifically, this example selects HDI as the second isocyanate monomer. HDI refers to 1,6 - hexamethylene diisocyanate, and the rest of the raw materials are strictly the same as those in Example 1.

[0092] This example prepares the polyurethane structural adhesive according to the following method:

[0093] 1. The blocked curing agent is prepared by the following process:

[0094] This step is the same as that in Example 1.

[0095] 2. The modified castor oil polymer is prepared by the following process:

[0096] This step is the same as that in Example 1.

[0097] 3. The polyurethane structural adhesive is prepared by the following process:

[0098] In a reaction kettle, add 40 parts of the modified castor oil polymer, 55 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder, stir under vacuum for 1.5 h, control the temperature at 30 ± 1 °C, stir evenly, then add 1 part of the catalyst, and mix thoroughly to obtain the polyurethane structural adhesive.

[0099] Example 6

[0100] This example refers to the method for preparing a one - component low - temperature thermosetting polyurethane structural adhesive provided in Example 5 to prepare a one - component low - temperature thermosetting polyurethane structural adhesive. The difference between this example and Example 5 lies in the different second isocyanate monomer raw materials among the raw material types for preparing the one - component low - temperature thermosetting polyurethane structural adhesive. Specifically, this example selects IPDI as the second isocyanate monomer. IPDI refers to 3 - isocyanatomethyl - 3,5,5 - trimethylcyclohexyl isocyanate, and the rest of the raw materials and the preparation method are strictly the same as those in Example 5.

[0101] Comparative Example 4

[0102] This example refers to the method for preparing a one-component low-temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one-component low-temperature thermosetting polyurethane structural adhesive. The difference between this example and Example 1 is that the modified castor oil polymer is not prepared, and commercially available modified castor oil is directly used as the raw material for the polyurethane structural adhesive. Specifically, the modified castor oil produced by BASF with the brand name basf Sovermol805 is selected in this example, and the remaining raw materials are strictly the same as those in Example 1.

[0103] This example prepares the polyurethane structural adhesive according to the following method:

[0104] 1. The blocked curing agent is prepared by the following process:

[0105] This step is the same as that in Example 1.

[0106] 2. The modified castor oil polymer is not prepared in this example.

[0107] 3. The polyurethane structural adhesive is prepared by the following process:

[0108] In the reaction kettle, add 29 parts of modified castor oil, 66 parts of blocked curing agent, and 4 parts of molecular sieve activation powder, stir under vacuum for 1.5 h, control the temperature at 30 ± 1 °C, stir evenly, then add 1 part of catalyst, and mix thoroughly to obtain the polyurethane structural adhesive.

[0109] Example 7

[0110] This example refers to the method for preparing a one-component low-temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one-component low-temperature thermosetting polyurethane structural adhesive. The types of raw materials used in this example are the same as those used in Example 1 for preparing the one-component low-temperature thermosetting polyurethane structural adhesive.

[0111] This example prepares the polyurethane structural adhesive according to the following method:

[0112] 1. The blocked curing agent is prepared by the following process:

[0113] This step is the same as that in Example 1.

[0114] 2. The modified castor oil polymer is prepared by the following process:

[0115] S1. Dehydrate 100 parts of modified castor oil under vacuum at 105 - 120 °C until the water content < 500 ppm. At 45 °C, mix castor oil and the second isocyanate monomer to form a second reaction solution. The feeding amounts of castor oil and the second isocyanate monomer are such that R = 0.1 in the second reaction solution. Wherein, taking the isocyanate group content in the second isocyanate monomer as A1 and the hydroxyl group content in the modified castor oil as A2, R = A1 / A2.

[0116] S2. React the second reaction solution at 70 °C for 2.5 hours to obtain the modified castor oil polymer.

[0117] 3. The polyurethane structural adhesive is prepared by the following process:

[0118] In a reaction kettle, add 33 parts of the modified castor oil polymer, 62 parts of the blocked curing agent, and 4 parts of molecular sieve activated powder. Stir under vacuum for 1.5 h, control the temperature at 30 ± 1 °C, stir evenly, then add 1 part of the catalyst, and mix thoroughly to obtain the polyurethane structural adhesive.

[0119] Comparative Example 5

[0120] This comparative example refers to the method for preparing a one - component low - temperature thermosetting polyurethane structural adhesive provided in Example 1 to prepare a one - component low - temperature thermosetting polyurethane structural adhesive. The difference between this comparative example and Example 1 is that the blocked curing agent is not prepared, and a commercially available 100% solid - content blocked curing agent is directly used as the raw material of the polyurethane structural adhesive. Specifically, the blocked curing agent selected in this example is the blocked curing agent produced by Evonik Industries AG, with the product number B 1358 / 100. The other raw materials and preparation methods are strictly the same as those in Example 1.

[0121] Test Example 1

[0122] Test subjects:

[0123] The test subjects in this test example are the polyurethane structural adhesives prepared in Examples 1 - 3 and Comparative Examples 1 - 2.

[0124] Test method:

[0125] According to "GB / T7124 - 2008", use the test subjects to prepare shear strength test specimens (the bonding surface length is 12.5 mm ± 0.25 mm, and the adhesive layer thickness is 0.2 mm), cure the test subjects under different temperature conditions, and evaluate the shear strength of the test specimens after the test subjects are cured.

[0126] Test results:

[0127] The test results are shown in Table 1. As the curing temperature rises, the shear strength of the cured polyurethane structural adhesive increases, indicating that the higher the temperature, the easier it is to cure completely. The polyurethane structural adhesives prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were cured at 100 °C for 30 minutes. The shear strength of the cured adhesives in Examples 1 to 3 was higher than that in Comparative Examples 1 to 2, that is, the curing temperature required for the polyurethane structural adhesives prepared in Examples 1 to 3 was lower than that in Comparative Examples 1 to 2. This shows that when the content of free isocyanate groups in the first reaction solution reaches 8-12% after the S2 reaction, the prepared polyurethane structural adhesive can be cured and formed at a lower temperature. Among them, when the initial content of free isocyanate groups in the first reaction solution is 10%, the prepared blocked curing agent has the lowest curing temperature, and the shear strength of the polyurethane structural adhesive cured at 100 °C for 30 minutes reaches 5 MPa.

[0128] Table 1. Statistical results of the curing conditions of the test objects in Test Example 1

[0129]

[0130] Test Example 2

[0131] Test objects:

[0132] The test objects in this test example were the polyurethane structural adhesives prepared in Example 1, Example 4 and Comparative Example 3.

[0133] Test method:

[0134] According to "GB / T7124-2008", shear strength test specimens were prepared using the test objects (the length of the bonding surface was 12.5 mm ± 0.25 mm, and the thickness of the adhesive layer was 0.2 mm), and the test objects were cured under different temperature conditions. After the test objects were cured, the shear strength of the test specimens was evaluated.

[0135] Test results:

[0136] Comparing the test results of Example 1, Example 4 and Comparative Example 3 in Table 2, it can be seen that the polyurethane structural adhesives prepared in Example 1 and Example 2 can be completely cured when cured at 100 °C for 30 minutes. However, the polyurethane structural adhesive prepared in Comparative Example 3 could not be cured when cured at 100 °C for 30 minutes. This shows that when at least one of polypropylene glycol and polytetrahydrofuran glycol is selected as the raw material polyether polyol for preparing the blocked curing agent, the prepared polyurethane structural adhesive has a lower curing temperature. Among them, when polypropylene glycol is selected as the raw material polyether polyol of the blocked curing agent, the prepared blocked curing agent has the lowest curing temperature.

[0137] Table 2. Statistical results of the curing conditions of the test objects in Test Example 2

[0138]

[0139] Test Example 3

[0140] Test subjects:

[0141] The test subjects of this test example are the polyurethane structural adhesives prepared in Examples 1, 5, 6 and Comparative Example 4.

[0142] Test method:

[0143] According to "GB / T7124-2008", use the test subjects to prepare shear strength test specimens (the length of the bonding surface is 12.5 mm ± 0.25 mm, and the thickness of the adhesive layer is 0.2 mm), cure the test subjects under different temperature conditions, and evaluate the shear strength of the test specimens after the test subjects are cured.

[0144] Test results:

[0145] Comparing the test results of Example 1, Example 4 and Comparative Example 3 in Table 2, it can be seen that compared with Comparative Example 4, the shear strength of the polyurethane structural adhesives obtained by curing Example 1, Example 5 and Example 6 at 100 °C for 30 minutes is larger, indicating that the curing temperature of Example 1, Example 5 and Example 6 is lower than that of Comparative Example 4. This shows that when the second isocyanate monomer in the raw materials for preparing the modified castor oil polymer is selected from at least one of liquefied MDI, HDI, TDI-80, and IPDI, the prepared polyurethane structural adhesive has a lower curing temperature. Among them, in Example 1, the second isocyanate monomer in the raw materials for preparing the modified castor oil polymer includes liquefied MDI, and the prepared polyurethane structural adhesive has the best curing temperature, high bonding strength, good water resistance, and low VOC emission.

[0146] Table 3. Statistical results of the curing conditions of the test subjects in Test Example 3

[0147]

[0148] Test Example 4

[0149] Test subjects:

[0150] The test subjects of this test example are the polyurethane structural adhesives prepared in Examples 1 and 7.

[0151] Test method:

[0152] According to "GB / T7124-2008", use the test subjects to prepare shear strength test specimens (the length of the bonding surface is 12.5 mm ± 0.25 mm, and the thickness of the adhesive layer is 0.2 mm), cure the test subjects under different temperature conditions, and evaluate the shear strength of the test specimens after the test subjects are cured.

[0153] Test results:

[0154] Comparing the test results of Example 1, Example 4 and Comparative Example 3 in Table 2, it can be seen that the shear strengths of the polyurethane structural adhesives obtained by curing Example 1 and Example 7 at 100 °C for 30 minutes are both relatively large, indicating that the polyurethane structural adhesives prepared in Example 1 and Example 7 have relatively low curing temperatures. This shows that in the preparation of the modified castor oil polymer, when the feeding amounts of castor oil and the second isocyanate monomer satisfy that R in the second reaction solution is 0.1 to 0.3, the prepared polyurethane structural adhesive has a relatively low curing temperature. Among them, in Example 1, R in the second reaction solution is 0.3, and the prepared polyurethane structural adhesive can be cured and formed at a relatively low temperature.

[0155] Table 4. Statistical results of the curing conditions of the test objects in Test Example 4

[0156]

[0157] Test Example 5

[0158] Test objects:

[0159] The test objects of this test example are the polyurethane structural adhesives prepared in Example 1 and Comparative Example 5.

[0160] Test method:

[0161] The polyurethane structural adhesives were prepared respectively according to the contents recorded in Example 1 and Comparative Example 5, and then the prepared polyurethane structural adhesives were placed at room temperature. Samples were taken at different placement times for viscosity growth rate and shear strength tests.

[0162] According to "GB / T 2794-2013", the viscosity growth rate of the polyurethane structure prepared by sampling the test objects at different room temperature placement times was tested.

[0163] According to "GB / T 7124-2008", shear strength test specimens (bonding surface length 12.5 mm ± 0.25 mm, adhesive layer thickness 0.2 mm) were prepared from the polyurethane structural adhesives obtained by sampling the test objects at different room temperature placement times, and the test objects were cured under different temperature conditions. After the test objects were cured, the shear strength of the test specimens was evaluated.

[0164] Test results:

[0165] Comparing the test results shown in Table 5 and Table 6, it can be seen that as the normal temperature storage time increases, the shear strength of the polyurethane structural adhesives prepared in Example 1 and Comparative Example 5 gradually decreases after curing, and the viscosity growth rate increases. Example 1 using the self-made blocked curing agent as a raw material for preparation cured at 100 °C for 30 minutes after storing for one day, and the shear strength of the obtained colloid was 5 MPa, indicating that curing at 100 °C can already be completely cured. While Comparative Example 5 using a commercially available blocked curing agent as a raw material for preparation could not be cured at 100 °C and 120 °C and remained in a liquid state, and could only start to cure at 150 °C. Moreover, for Comparative Example 5 that was cured after storing for one day, the shear strength of the colloid cured at 150 °C for 30 minutes was small, that is, the required curing temperature was high. The shear strength of the polyurethane structural adhesive cured at 150 °C for 30 minutes was only 3.5, which could not fully meet the requirements of daily use. After the polyurethane structural adhesive prepared in Example 1 was stored at normal temperature for 12 months, the shear strength of the polyurethane structural adhesive cured at 100 °C for 30 minutes was still 4.5 MPa, which was only 0.5 MPa lower than the shear strength of the polyurethane structural adhesive cured at 100 °C after storing for one day in Example 1. As the storage time extended, the shear strength of Comparative Example 5 decreased significantly, and the viscosity growth rate increased significantly. After the polyurethane structural adhesive prepared in Comparative Example 5 was stored at normal temperature for 12 months, the shear strength of the polyurethane structural adhesive cured at 150 °C for 30 minutes was only 1.2 MPa.

[0166] This shows that the polyurethane structural adhesive prepared by the present invention has high storage stability at normal temperature. The polyurethane structural adhesive prepared using the blocked curing agent provided by this solution has a low curing temperature and high storage stability at normal temperature, and can maintain a low volatility rate and high stability during the curing and storage processes, thus having good safety.

[0167] Table 5. Evaluation indexes of storage stability of the blocked curing agent in Example 1

[0168]

[0169]

[0170] Table 6. Evaluation indexes of storage stability of the blocked curing agent in Comparative Example 5

[0171]

[0172] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A one-component low-temperature thermosetting polyurethane structural adhesive, characterized in that: Calculated by mass parts, the polyurethane structural adhesive comprises 50 - 62 parts of blocked curing agent, 33 - 48 parts of modified castor oil polymer, and 3 - 10 parts of additives, and the additives include catalysts; The blocked curing agent is prepared in the following manner: S1. Calculated by mass parts, 100 parts of polyether polyol and 77 - 123 parts of first isocyanate monomer are mixed to form a first reaction solution. The polyether polyol is selected from at least one of polyoxypropylene diol and polytetrahydrofuran ether diol, and the molecular weight of the polyether polyol is 1000 - 2000; the first isocyanate monomer is selected from one or more of liquefied 4,4-diphenylmethane diisocyanate, polyphenyl polymethylene polyisocyanate, HDI trimer, and HDI biuret; S2. The first reaction solution is reacted at 60 - 80 °C until the content of free isocyanate groups in the first reaction solution reaches 8 - 12%; S3. At 40 - 50 °C, a catalyst and a blocking agent are sequentially added to the first reaction solution. The blocking agent is blocking agent NX-2026, and the reaction is carried out until the content of isocyanate groups in the first reaction solution < 0.05%, thus obtaining the blocked curing agent; The modified castor oil polymer is prepared in the following manner: S1. At 40 - 50 °C, modified castor oil and a second isocyanate monomer are mixed to form a second reaction solution. The feeding amounts of the modified castor oil and the second isocyanate monomer are such that R in the second reaction solution is 0.1 - 0.3; the modified castor oil is selected from at least one of Basf Sovermol series 805, 750, 819, AC006 and AC009 of Ito Seiyu, and AP11, AP19, and AP21 of Shanghai Jingri; S2. The second reaction solution is reacted at 50 - 80 °C for 2 - 3 hours to obtain the modified castor oil polymer; Wherein, taking the content of isocyanate groups in the second isocyanate monomer as A1 and the content of hydroxyl groups in the modified castor oil as A2, R = A1 / A2.

2. The one-component low-temperature thermosetting polyurethane structural adhesive according to claim 1, characterized in that, the first isocyanate monomer includes liquefied 4,4-diphenylmethane diisocyanate.

3. The one-component low-temperature thermosetting polyurethane structural adhesive according to claim 1, characterized in that, the polyether polyol includes polyoxypropylene diol.

4. The one-component low-temperature thermosetting polyurethane structural adhesive according to claim 1, characterized in that: the water content of the polyether polyol is less than 500 ppm.

5. The one-component low-temperature thermosetting polyurethane structural adhesive according to claim 1, characterized in that, the second isocyanate monomer is selected from at least one of liquefied 4,4-diphenylmethane diisocyanate, 1,6-hexamethylene diisocyanate, toluene diisocyanate, and 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate.

6. The one-component low-temperature thermosetting polyurethane structural adhesive according to claim 1, characterized in that, The second isocyanate monomer includes liquefied 4,4-diphenylmethane diisocyanate.

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