Heat-insulating and high-temperature-resistant rigid polyurethane foam material and low-temperature preparation method thereof

Abstract

The invention discloses a heat-insulating and high-temperature-resistant rigid polyurethane foam material and a low-temperature preparation method thereof, and relates to the field of polyurethane foam materials, bismaleimide powder is liquefied and dispersed in polyol through a DA reaction, the reaction time is shortened through catalysis of Lewis acid, the bismaleimide powder is reused as a foaming catalyst, and excellent high and low temperature performance of the polyol is combined, so that the heat-insulating and high-temperature-resistant rigid polyurethane foam material is obtained. A thermal reversible DA adduct is introduced to realize heat absorption and temperature control in the foaming process and low-temperature reconstruction of a rigid cross-linked structure; a low-boiling-point main foaming agent and methyl formate are compounded to reduce gasification heat and system viscosity, and the A / B material preparation temperature is controlled to be lower than or equal to 15 DEG C to avoid loss of the foaming agent. According to the scheme, the problems of powder dispersion, viscosity regulation and control and foaming stability at low temperature are solved, and the foam is endowed with excellent heat insulation and high temperature resistance.

Description

Technical Field

[0001] The present invention relates to the field of polyurethane foam materials, and particularly to a rigid polyurethane foam material with heat insulation and high temperature resistance and a low temperature preparation method thereof. Background Art

[0002] Due to its excellent heat insulation, light weight and designability, polyurethane foam is widely used in fields such as construction, energy, and transportation. In scenarios such as factories in southern regions like Jiangsu, Zhejiang, and Shanghai without heating facilities in winter, strict requirements are imposed on polyurethane foam: it needs to be constructed in a low-temperature environment, have high temperature resistance, and maintain low thermal conductivity and structural stability. However, currently, the main raw materials of polyurethane foam are composed of a polyol component and an isocyanate component. When the temperature is as low as 10°C, the foaming rate of the two components decreases or even no foaming occurs.

[0003] Most of the currently used blowing agents are HCFC-141B with a boiling point of 32°C. When the ambient temperature and the substrate temperature decrease, more heat needs to be condensed during the foaming process to ensure that the physical blowing agent can be vaporized to form polyurethane foam. For example, at a lower temperature, in order to ensure the progress of the foaming process, it is often necessary to adjust the heat generated during the foaming process to ensure the smooth progress of the foaming process. For example, increasing the amount of the chemical blowing agent water or increasing the amount of the catalyst during the foaming process to rapidly generate a large amount of heat to counteract the decrease in ambient temperature. However, this will cause the internal temperature of the foam to rise rapidly, and if not controlled properly, it will cause spontaneous combustion and harm to the foaming process.

[0004] Some researchers also use a method of mixing a low-temperature blowing agent into component B to solve the problem of high viscosity at low temperature. For example, the Chinese invention patent with the publication number CN111647190B realizes the mixing and foaming of the two components at room temperature by changing the formulations of component A and component B and adding a low-temperature blowing agent, so that component B can be mixed evenly at 0°C and component A can be mixed evenly at 50°C, solving the problem that many environmentally friendly blowing agents with low boiling points are difficult to overflow when the material temperature reaches an ultra-low temperature state when used as a component of component A, and at low temperature, due to the high viscosity of polyether, the viscosity is even higher at low temperature, making production impossible. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a rigid polyurethane foam material with heat insulation and high temperature resistance and a low temperature preparation method thereof.

[0006] The purpose of the present invention is achieved by the following technical solutions: <First Aspect> The present invention provides a low temperature preparation method for a rigid polyurethane foam material, comprising the following steps: S1. At 70 - 80 °C, mix bismaleimide and polyol, add dienophile, and add the first catalyst, then stir and react for 3 - 5 h to obtain a DA adduct; S2. Mix the DA adduct, polyether polyol, polyether, second catalyst, ethylene glycol solution of potassium acetate, compound foaming agent, foam stabilizer, water, and flame retardant by stirring at room temperature to obtain a polyurethane blend; S3. Spray the polyurethane blend and polyisocyanate at an ambient temperature of 5 - 15 °C, control the temperature of the polyurethane blend at 8 - 12 °C, and control the temperature of the polyisocyanate at 10 - 15 °C. After complete curing, obtain the polyurethane rigid foam material.

[0007] As an embodiment, the polyol is selected from castor oil or epoxidized castor oil.

[0008] In some embodiments, the polyol is selected from castor oil.

[0009] As an embodiment, the dienophile is selected from one or more of furfuryl alcohol and furfurylamine.

[0010] In some embodiments, the dienophile is selected from furfuryl alcohol.

[0011] As an embodiment, the first catalyst is stannous chloride or stannous octoate.

[0012] In some embodiments, the first catalyst is stannous chloride.

[0013] As an embodiment, the stirring parameter in step S1 or S2 is 150 - 300 rpm.

[0014] In some embodiments, the stirring parameter is 200 rpm.

[0015] As an embodiment, by mass fraction, the dosages of each substance are as follows: 15 - 25 parts of bismaleimide, 80 - 150 parts of polyol, 5 - 10 parts of dienophile, and 0.05 - 0.2 parts of the first catalyst.

[0016] In some embodiments, by mass fraction, the dosages of each substance are as follows: 15 - 25 parts of bismaleimide, 100 parts of polyol, 7 parts of dienophile, and 0.1 part of the first catalyst.

[0017] As an embodiment, the polyether polyol is one or more of 4110, 6305, and 8238.

[0018] In some embodiments, the polyether polyol is 4110.

[0019] As an embodiment, the polyether is 403.

[0020] As an embodiment, the second catalyst is one or more of triethanolamine, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine (PC-41), tris(dimethylaminopropyl)hexahydrotriazine, pentamethyldiethylenetriamine (PC-5), A-33, PT303, triethylenediamine (TEDA), stannous octoate, dibutyltin dilaurate (T-12), MB20, and butyl titanate.

[0021] In some embodiments, the second catalyst is composed of tris(dimethylaminopropyl)hexahydrotriazine and pentamethyldiethylenetriamine.

[0022] In some embodiments, the mass ratio of tris(dimethylaminopropyl)hexahydrotriazine to pentamethyldiethylenetriamine in the second catalyst is 5:2.

[0023] As an embodiment, the concentration of the potassium acetate solution in diethylene glycol is 30-35 wt.%.

[0024] In some embodiments, the concentration of the potassium acetate solution in diethylene glycol is 33 wt.%.

[0025] As an embodiment, the compound blowing agent is composed of a low-boiling blowing agent and methyl formate, and the low-boiling blowing agent is 1,1,1,3,3-pentafluoropropane or chlorotrifluoroethylene.

[0026] In some embodiments, the compound blowing agent is composed of 1,1,1,3,3-pentafluoropropane and methyl formate.

[0027] In some embodiments, the compound blowing agent is composed of chlorotrifluoroethylene and methyl formate.

[0028] As an embodiment, the mass ratio of the low-boiling blowing agent to methyl formate is (7:9):1.

[0029] In some embodiments, by mass, the low-boiling blowing agent is 11 parts and methyl formate is 1.5 parts.

[0030] As an embodiment, the foam stabilizer is one or more of M-8805, M-8808, M-8809, M-88108, M-88109, M-88716, and M-88719.

[0031] In some embodiments, the foam stabilizer is M-88108.

[0032] As an embodiment, the flame retardant is one or more of TCPP, TCEP, TEP, DEEP, and OP-550.

[0033] In some embodiments, the flame retardant is DEEP.

[0034] As an embodiment, the polyisocyanate is selected from polyphenyl polymethylene polyisocyanate.

[0035] As an embodiment, the polyphenyl polymethylene polyisocyanate is one or more of Wanhua PM200, Covestro 44V20, and Huntsman S5005.

[0036] As an embodiment, by mass parts, the amounts of each substance are as follows: 60 - 100 parts of DA adduct, 15 - 25 parts of polyether polyol, 8 - 12 parts of polyether, 2 - 3 parts of the second catalyst, 1 - 2 parts of the diethylene glycol solution of potassium acetate, 10 - 15 parts of compound blowing agent, 0.5 - 1.5 parts of foam stabilizer, 0.3 - 0.5 parts of water, and 8 - 12 parts of flame retardant.

[0037] In some embodiments, by mass parts, the amounts of each substance are as follows: 80 parts of DA adduct, 20 parts of polyether polyol, 10 parts of polyether, 2.8 parts of the second catalyst, 1.5 parts of the diethylene glycol solution of potassium acetate, 12.5 parts of compound blowing agent, 1 part of foam stabilizer, 0.4 parts of water, and 10 parts of flame retardant.

[0038] As an embodiment, in step S2, the stirring time of the polyurethane blend is 30 - 50 min.

[0039] In some embodiments, in step S2, the stirring time of the polyurethane blend is 40 min.

[0040] As an embodiment, in step S3, the polyurethane blend and the polyisocyanate are spray - applied at a low pressure in a mass ratio of (0.95 - 1.05):1.

[0041] In some embodiments, in step S3, the polyurethane blend and the polyisocyanate are spray - applied at a low pressure in a mass ratio of 1:1.

[0042] <Second aspect> The present invention provides a polyurethane rigid foam material prepared by the above - mentioned method.

[0043] As an embodiment, the density of the rigid foam material is 44 - 45 kg / m 3 , the compressive strength is 0.38 - 0.40 MPa, and the thermal conductivity is 0.022 - 0.023 W / (m·K).

[0044] As an embodiment, the dimensional change rate of the rigid foam material after heat preservation at 250 °C for 5 min is ≤0.42%.

[0045] In some embodiments, the dimensional change rate of the rigid foam material after heat preservation at 250 °C for 5 min is between 0.35% and 0.42%.

[0046] As an embodiment, the mass loss rate of the rigid foam material at 250 °C is ≤6.0%.

[0047] In some embodiments, the mass loss rate of the rigid foam material at 250 °C is between 4.5% and 60.%.

[0048] Compared with the prior art, the present invention has the following beneficial effects: The polyurethane foam provided by the present invention, which is suitable for preparation in a low-temperature environment and has both heat insulation and high-temperature resistance properties, achieves performance breakthroughs through multi-dimensional technological innovations, which are mainly reflected in the following aspects: (1) Optimization of low-temperature dispersion preparation and application of high-temperature resistance performance The high-temperature resistant powder used in the present invention is bismaleimide. In the prior art, it is often introduced into the preparation process of polyurethane foam in the form of solid powder. As the temperature decreases, the viscosity of the medium increases, the particle movement ability and dispersion efficiency decrease, and the surface charge of the particles or the adsorption amount of the dispersant decreases, resulting in poor powder dispersibility and increased agglomeration. In the present invention, by using the DA reaction between bismaleimide and furan ring to gradually liquefy and dissolve in polyol (castor oil or epoxy castor oil), the risk of uneven high-temperature resistance performance caused by uneven dispersion of powder materials during the polyurethane foaming process and the decline of foam performance caused by powder material agglomeration are avoided, laying a foundation for the uniformity of foam performance from the raw material dispersion stage.

[0049] (2) High-efficiency liquefaction reaction process In the present invention, castor oil is used as the reaction medium, and stannous chloride or stannous octoate, etc., is used as a catalyst to accelerate the progress of the DA reaction to achieve the liquefaction of bismaleimide powder. Therefore, it can be achieved without the complete progress of the DA reaction. In the present invention, under the conditions of 70-80 °C, adding 1% of the catalyst can liquefy the bismaleimide powder through the DA reaction with furan ring compounds within 3 hours, and the reaction process reaches about 50% and can be used for the subsequent preparation of polyurethane blend. This process breaks through the limitation that the traditional DA reaction needs to be completely carried out, allowing the subsequent blend preparation in a partial reaction stage (about 50% progress), significantly shortening the preparation cycle and improving the industrial production efficiency.

[0050] (3) Reuse of catalyst function and process simplification The Lewis acids used in the present invention (such as stannous chloride or stannous octoate) have dual catalytic activities. First, in the DA reaction stage, they accelerate the DA reaction of bismaleimide to achieve liquefaction. Second, in the polyurethane foaming stage, they act as post-stage catalysts, reducing the dosage of foaming catalysts such as pentamethyldiethylenetriamine. This "one agent for two uses" design simplifies the formulation system, reduces raw material costs, and avoids the process complexity that may be brought about by the cooperation of multiple catalysts.

[0051] (4)Synergistic design of the properties of polyol base materials In the present invention, castor oil or epoxy castor oil is selected as the DA reaction medium and the main polyol of polyurethane foam. The reasons are as follows: The polyol (castor oil or epoxy castor oil) has excellent high-temperature and low-temperature resistance. Its good high-temperature resistance cooperates with bismaleimide to ultimately achieve the high-temperature resistance of polyurethane foam. And its fluidity and low viscosity under low-temperature conditions ensure the smooth progress of the spraying process of polyurethane foaming and molding, realizing the dual adaptation of material properties and processing technology.

[0052] (5)Intelligent regulation of thermoreversible crosslinked structure The DA reaction of bismaleimide and furan compounds in polyol introduces thermoreversible DA adducts into the polyurethane blend. During the foaming process, due to the thermoreversible characteristics of the DA adducts, the dual excellent effects of "endothermic temperature control - low-temperature reconstruction" are achieved. On the one hand, when the instantaneous high heat released during foaming causes the system temperature to rise sharply, the DA adduct undergoes a reverse reaction to absorb part of the heat, effectively suppressing the temperature peak, avoiding the risk of spontaneous combustion caused by local overheating, and ensuring the safety of the foaming process. On the other hand, after the foam is prepared, as the temperature decreases, the reactants generated by the reverse reaction regenerate DA adducts again through the forward DA reaction, supplementing and forming a rigid crosslinked structure in the polyurethane network. The furan ring and maleimide ring can improve the high-temperature resistance and mechanical stability of the polyurethane foam material, realizing the synergistic optimization of the prevention and control of thermal runaway during the processing process and the maintenance of high performance of the final material.

[0053] (6)Synergistic enhancement of the composite foaming agent system A low-boiling main foaming agent (1,1,1,3,3-pentafluoropropane / chlorotrifluoroethylene) is compounded with methyl formate (the best mass ratio range is 7 - 9:1) to form a unique foaming system: The main foaming agent reduces the total amount of heat required for the gasification of the foaming agent; methyl formate reduces the system viscosity due to its excellent solvent properties, solving the processing fluidity problem caused by low temperature. This compounding ratio precisely controls the foam size stability, avoiding density unevenness and performance attenuation caused by ratio deviation.

[0054] (7)Precision temperature control preparation process window The optimal preparation temperature of the A component (polyurethane blend) and the B component (polyisocyanate) provided by the present invention is not higher than 15°C to prevent serious volatilization of the blowing agent, resulting in loss of the blowing agent before foaming, an increase in foam density, and affecting the mechanical properties and thermal conductivity of the polyurethane foam, etc. Detailed implementation manners

[0055] The present invention will be described in detail below with reference to embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several adjustments and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0056] Embodiment 1 This embodiment provides a low-temperature preparation method for a heat-insulating and high-temperature-resistant rigid polyurethane foam material, and the steps are as follows: S1. Preparation of furan / maleimide DA adduct Mix bismaleimide and castor oil, heat up to 70°C, then dropwise add furfuryl alcohol, continue to add the catalyst stannous chloride, and continue to react for 3 h at a stirring speed of 200 rpm until the reaction system presents a light yellow transparent liquid, and the product is named: furan / maleimide DA adduct.

[0057] After testing with a rotational rheometer, the viscosity of the furan / maleimide DA adduct at 10°C is 2840 mPa·s; Before and after the reaction was determined by 1H NMR, 41% of the maleimide groups in bismaleimide participated in the reaction; The hydroxyl value of the furan / maleimide DA adduct was measured by the acylation titration method to be 135 mgKOH / g.

[0058] By mass fraction, the raw materials involved in step S1 are as follows: Bismaleimide: 25 parts; Castor oil: 100 parts; Furfuryl alcohol: 7 parts; Stannous chloride: 0.1 part; S2. Preparation of polyurethane blend By mass fraction, 80 parts of furan / maleimide DA adduct, 20 parts of 4110 polyether polyol, 10 parts of 403 polyether, 0.8 part of pentamethyldiethylenetriamine, 2.0 parts of tris(dimethylaminopropyl)hexahydrotriazine, 1.5 parts of potassium acetate in diglycol solution (concentration 33 wt.%), 11 parts of 1,1,1,3,3-pentafluoropropane, 1.5 parts of methyl formate, 1 part of foam stabilizer M-88108, 0.4 part of water, and 10 parts of flame retardant DEEP (diethyl ethylphosphonate) are stirred at room temperature for 40 minutes to obtain a polyurethane blend.

[0059] After testing with a rotational rheometer, the viscosity of the polyurethane blend at 10 °C is 1240 mPa·s; The hydroxyl value of the polyurethane blend is measured to be 180 mgKOH / g.

[0060] S3. Preparation of polyurethane foam by spraying At an ambient temperature of 10 °C, the temperature of the polyurethane blend is controlled at 10 °C, and the temperature of the polyisocyanate (PM200 produced by Yantai Wanhua in this example) is controlled at 15 °C. The two are in a mass ratio of 1:1 and are sprayed on the stainless-steel surface using a low-pressure spraying foaming machine. After testing, the cream time of the two raw materials after mixing is 4 s, the string time is 7 s, and the non-stick time is 10 s.

[0061] After spraying, it is left at room temperature for 24 hours for curing.

[0062] After the polyurethane foam is completely cured, the skin formed during spraying is removed using a blade, and the foam is polished with sandpaper to obtain the low-temperature preparation of polyurethane foam.

[0063] Example 2 This example provides a low-temperature preparation method for a heat-insulating and high-temperature-resistant rigid polyurethane foam material, and the steps are as follows: S1. Preparation of furan / maleimide DA adduct Bismaleimide and castor oil are mixed and heated to 70 °C. Then, furfuryl alcohol is added dropwise, and catalyst stannous chloride is further added. The reaction continues for 3 h at a stirring speed of 200 rpm until the reaction system presents a light yellow transparent liquid. The product is named: furan / maleimide DA adduct.

[0064] After testing with a rotational rheometer, the viscosity of the furan / maleimide DA adduct at 10 °C is 2760 mPa·s; Before and after the reaction determined by 1H NMR, 47% of the maleimide groups in bismaleimide participated in the reaction; The hydroxyl value of the furan / maleimide DA adduct is measured to be 143 mgKOH / g by acylation titration method.

[0065] By mass fraction, the raw materials involved in step S1 are as follows: Bismaleimide: 20 parts; Castor oil: 100 parts; Furfuryl alcohol: 7 parts; Stannous chloride: 0.1 part; S2. Preparation of polyurethane blend By mass fraction, 80 parts of furan / maleimide DA adduct, 20 parts of 4110 polyether polyol, 10 parts of 403 polyether, 0.8 part of pentamethyldiethylenetriamine, 1.5 parts of potassium acetate diglycol solution (concentration 33 wt.%), 2.0 parts of tris(dimethylaminopropyl)hexahydrotriazine, 1.5 parts of methyl formate, 1 part of foam stabilizer M-88108, 11 parts of 1,1,1,3,3-pentafluoropropane, 0.4 part of water, and 10 parts of flame retardant DEEP (diethyl ethylphosphonate) are stirred at room temperature for 40 minutes to obtain a polyurethane blend.

[0066] After testing with a rotational rheometer, the viscosity of the polyurethane blend at 10°C is 1180 mPa·s; The hydroxyl value of the polyurethane blend is measured to be 191 mgKOH / g.

[0067] S3. Preparation of polyurethane foam by spraying At an ambient temperature of 10°C, the temperature of the polyurethane blend is controlled at 10°C, and the temperature of the polyisocyanate (PM200 produced by Yantai Wanhua in this example) is controlled at 15°C. The two are in a mass ratio of 1:1 and are sprayed on the stainless steel surface using a low-pressure spraying foaming machine. After testing, the cream time of the two raw materials after mixing is 4 s, the stringing time is 6 s, and the non-sticking time is 9 s.

[0068] After spraying, it is left at room temperature for 24 hours for curing.

[0069] After the polyurethane foam is completely cured, the skin formed during spraying is removed with a blade, and the foam is polished with sandpaper to obtain the low-temperature preparation of polyurethane foam.

[0070] Example 3 This example provides a low-temperature preparation method for a heat-insulating and high-temperature-resistant rigid polyurethane foam material, and the steps are as follows: S1. Preparation of furan / maleimide DA adduct Bismaleimide and castor oil are mixed and heated to 70°C. Then, furfuryl alcohol is added dropwise, and the catalyst stannous chloride is further added. The reaction continues for 3 h at a stirring speed of 200 rpm until the reaction system presents a light yellow transparent liquid. The product is named: furan / maleimide DA adduct.

[0071] After testing with a rotational rheometer, the viscosity of the furan / maleimide DA adduct at 10 °C is 2760 mPa·s; Before and after the reaction determined by 1H NMR, 47% of the maleimide groups in bismaleimide reacted; The hydroxyl value of the furan / maleimide DA adduct measured by the acylation titration method is 143 mgKOH / g.

[0072] By mass fraction, the raw materials involved in step S1 are as follows: Bismaleimide: 20 parts; Castor oil: 100 parts; Furfuryl alcohol: 7 parts; Stannous chloride: 0.1 part; S2. Preparation of polyurethane blend By mass fraction, 80 parts of furan / maleimide DA adduct, 20 parts of 4110 polyether polyol, 10 parts of 403 polyether, 0.8 part of pentamethyldiethylenetriamine, 1.5 parts of a diglycol solution of potassium acetate (concentration 33 wt.%), 2.0 parts of tris(dimethylaminopropyl)hexahydrotriazine, 1.5 parts of methyl formate, 1 part of foam stabilizer M-88108, 11 parts of chlorotrifluoroethylene, 0.4 part of water, and 10 parts of flame retardant DEEP (diethyl ethylphosphonate) are stirred at room temperature for 40 minutes to obtain a polyurethane blend.

[0073] After testing with a rotational rheometer, the viscosity of the polyurethane blend at 10 °C is 1240 mPa·s; The hydroxyl value of the polyurethane blend is measured to be 191 mgKOH / g.

[0074] S3. Preparation of polyurethane foam by spraying At an ambient temperature of 10 °C, the temperature of the polyurethane blend is controlled at 10 °C, and the temperature of the polyisocyanate (PM200 produced by Yantai Wanhua in this example) is controlled at 15 °C. The two are sprayed on the stainless-steel surface using a low-pressure spraying foaming machine in a mass ratio of 1:1. After testing, the cream time of the two raw materials after mixing is 3 s, the string time is 6 s, and the non-sticking time is 8 s.

[0075] After spraying, it is left at room temperature for 24 hours for curing.

[0076] After the polyurethane foam is completely cured, the skin formed during the spraying process is removed with a blade, and the foam is polished with sandpaper to obtain the low-temperature preparation of polyurethane foam.

[0077] Example 4 This example provides a low-temperature preparation method for a heat-insulating and high-temperature-resistant rigid polyurethane foam material, and the steps are as follows: S1. Preparation of Furan / Maleimide DA Adduct Mix bismaleimide and castor oil, heat up to 70 °C, then dropwise add furfuryl alcohol, continue to add stannous chloride as catalyst, and continue to react for 3 h at a stirring speed of 200 rpm until the reaction system presents a light yellow transparent liquid. The product is named: Furan / Maleimide DA Adduct.

[0078] After testing by a rotational rheometer, the viscosity of the furan / maleimide DA adduct at 10 °C is 2560 mPa·s; Before and after the reaction determined by 1H NMR, 50% of the maleimide groups in bismaleimide participated in the reaction; The hydroxyl value of the furan / maleimide DA adduct measured by the acylation titration method is 155 mgKOH / g.

[0079] By mass fraction, the raw materials involved in step S1 are as follows: Bismaleimide: 15 parts; Castor oil: 100 parts; Furfuryl alcohol: 7 parts; Stannous chloride: 0.1 part; S2. Preparation of Polyurethane Blend By mass fraction, mix 80 parts of furan / maleimide DA adduct, 20 parts of 4110 polyether polyol, 10 parts of 403 polyether, 0.8 part of pentamethyldiethylenetriamine, 1.5 parts of a diglycol solution of potassium acetate (concentration 33 wt.%), 2.0 parts of tris(dimethylaminopropyl)hexahydrotriazine, 1.5 parts of methyl formate, 1 part of foam stabilizer M-88108, 11 parts of monochlorotrifluoropropene, 0.4 part of water, and 10 parts of flame retardant DEEP (diethyl ethylphosphonate), and stir at room temperature for 40 minutes to obtain a polyurethane blend.

[0080] After testing by a rotational rheometer, the viscosity of the polyurethane blend at 10 °C is 1160 mPa·s; The hydroxyl value of the polyurethane blend is measured to be 202 mgKOH / g.

[0081] S3. Preparation of Sprayed Polyurethane Foam At an ambient temperature of 10 °C, control the temperature of the polyurethane blend at 10 °C and the temperature of the polyisocyanate (PM200 produced by Yantai Wanhua in this example) at 15 °C. Mix them at a mass ratio of 1:1, and use a low-pressure spraying foaming machine to perform a single-layer spray on the stainless-steel surface. After testing, the cream time of the two raw materials after mixing is 3 s, the string time is 6 s, and the non-sticking time is 9 s.

[0082] After spraying, leave it at room temperature for 24 hours for curing.

[0083] After the polyurethane foam is completely cured, a blade is used to remove the skin formed during the spraying process, and the foam is polished with sandpaper to obtain the low-temperature preparation of the polyurethane foam.

[0084] Comparative Example In this comparative example, the reaction time in the preparation method of the furan / maleimide DA adduct was regulated, and it was found that: The preparation steps are the same as those in step S1 of Example 1, and the difference lies in: the reaction time.

[0085] When the reaction time is 1.5 h, a light yellow transparent liquid will not be obtained, and after the reaction is stopped, powders will continuously precipitate, resulting in stratification.

[0086] A reaction time of 3 hours can avoid the problem of stratification caused by the precipitation of the prepared DA adduct during storage. When the time is further extended, it can also be achieved, but the performance improvement is not significant, and instead, the entire reaction process time and energy consumption are increased.

[0087] Test and analysis: The polyurethane foam prepared in the above examples was tested for performance, including foam density, compressive strength, thermal conductivity, foam size change rate after heat preservation at 250 °C for 5 min, and mass loss rate of the foam at 250 °C by thermogravimetric analysis. The results are shown in Table 1: Table 1

[0088] In summary, in the present invention, the bismaleimide powder is liquefied and dispersed in a polyol (such as castor oil or epoxy castor oil) through a DA reaction, the reaction time is shortened by using a Lewis acid catalyst and reused as a foaming catalyst, combined with the excellent high and low temperature performance of the polyol, and a thermoreversible DA adduct is introduced to achieve endothermic temperature control during the foaming process and low-temperature reconstruction of a rigid crosslinked structure; a low-boiling main blowing agent is compounded with methyl formate to reduce the heat of vaporization and the viscosity of the system, and the preparation temperature of the A / B materials is controlled ≤15 °C to avoid the loss of the blowing agent. This solution solves the problems of powder dispersion, viscosity regulation, and foaming stability at low temperatures, and endows the foam with excellent heat insulation and high-temperature resistance performance.

[0089] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various deformations or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing rigid polyurethane foam at low temperature, characterized in that, It includes the following steps: S1. At 70 - 80 °C, mix bismaleimide and polyol, add dienophile, and add the first catalyst, then stir and react for 3 - 5 h to obtain a DA adduct; S2. Mix the DA adduct, polyether polyol, polyether, the second catalyst, a diglycol solution of potassium acetate, compound blowing agent, foam stabilizer, water, and flame retardant at room temperature to obtain a polyurethane mixture; S3. Spray the polyurethane mixture and polyisocyanate at an ambient temperature of 5 - 15 °C, control the temperature of the polyurethane mixture at 8 - 12 °C, and control the temperature of the polyisocyanate at 10 - 15 °C. After complete curing, obtain the polyurethane rigid foam material.

2. The method according to claim 1, wherein It also includes one or more of the following technical features: A. The polyol is selected from castor oil or epoxidized castor oil; B. The dienophile is selected from furfuryl alcohol and / or furfurylamine; C. The first catalyst is stannous chloride or stannous octoate.

3. The method according to claim 1, wherein By mass, the amounts of each substance are as follows: 15 - 25 parts of bismaleimide, 80 - 150 parts of polyol, 5 - 10 parts of dienophile, 0.05 - 0.2 part of the first catalyst.

4. The method according to claim 1, characterized in that, The stirring parameter in step S1 or S2 is 150 - 300 rpm.

5. The method according to claim 1, characterized in that The compound blowing agent consists of a low-boiling blowing agent and methyl formate, and the low-boiling blowing agent is 1,1,1,3,3 - pentafluoropropane or 1-chloro-1,1,2-trifluoroethylene.

6. The method according to claim 5, wherein The mass ratio of the low-boiling blowing agent to methyl formate is (7:9):

1.

7. The method according to claim 1, wherein It also includes one or more of the following technical features: A. The polyether polyol is one or more of 4110, 6305, 8238; B. The polyether is 403; C. The second catalyst is one or more of triethanolamine, 1,3,5-tris(dimethylaminopropyl)hexahydrotriazine (PC-41), tris(dimethylaminopropyl)hexahydrotriazine, pentamethyldiethylenetriamine (PC-5), A-33, PT303, triethylenediamine (TEDA), stannous octoate, dibutyltin dilaurate (T-12), MB20, tetrabutyl titanate; D. The foam stabilizer is one or more of M-8805, M-8808, M-8809, M-88108, M-88109, M-88716, M-88719; E. The flame retardant is one or more of TCPP, TCEP, TEP, DEEP, OP-550.

8. The method according to claim 1, wherein By mass, the amounts of each substance are as follows: 60 - 100 parts of DA adduct, 15 - 25 parts of polyether polyol, 8 - 12 parts of polyether, 2 - 3 parts of the second catalyst, 1 - 2 parts of the diglycol solution of potassium acetate, 10 - 15 parts of compound blowing agent, 0.5 - 1.5 parts of foam stabilizer, 0.3 - 0.5 part of water, 8 - 12 parts of flame retardant.

9. The method according to claim 1, wherein The polyisocyanate is selected from polyphenyl polymethylene polyisocyanate.

10. A rigid polyurethane foam material, characterized in that, It is prepared by the method according to any one of claims 1 to 9.

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