Microbubble-containing polyurethane feed liquid, preparation method of product of microbubble-containing polyurethane feed liquid, and testing method of fluidity of polyurethane feed liquid

Abstract

The invention discloses a polyurethane feed liquid containing microbubbles, a preparation method of a product of the polyurethane feed liquid and a testing method of fluidity of the polyurethane feed liquid, the polyurethane feed liquid containing the microbubbles comprises a component A and a component B. The component A comprises, by mass, 50-90% of polyether polyol; 3-10% of a chain extender; 1-5% of an autocatalytic chain extender; 1-15% of a cross-linking agent; 0.5-8% of a pigment; 1-5% of an anti-aging agent; 0.01-2% of a composite catalyst; the component B is isocyanate modified by carbamate; the component A contains microbubbles, and the volume fraction of the microbubbles is 0.1-5%. The polyurethane feed liquid containing the microbubbles is short in gelation time (8-10 s), short in demolding time (25 s), good in fluidity and good in storage stability, the microbubbles can remarkably improve the fluidity of the feed liquid under the condition of the same reaction rate, the requirement for production of skyscreen glass can be met, and a glass edge-covering product produced by using the polyurethane feed liquid is low in odor, low in VOC, good in appearance and good in performance. The defects of bubbles, material shortage, pits, wrinkles and the like are avoided.

Description

Technical Field

[0001] This invention relates to the field of polyurethane reaction injection molding and automotive sunroof glass production, specifically to a method for preparing a polyurethane liquid containing microbubbles and its products, and a method for testing the flowability of the polyurethane liquid. Background Technology

[0002] As a crucial component of vehicles, the manufacturing process and material selection of automotive sunroofs and sunroofs are of paramount importance. Automotive sunroof glass is typically made of polyurethane (PU) through reaction injection molding, possessing excellent physical and mechanical properties and superior processability. However, with the rise of new energy vehicles, the size of sunroof glass has significantly increased, especially for panoramic sunroofs, which have longer perimeters and narrower mold runners. This structural change leads to a substantial increase in the length of the glass edging. Using existing PU materials to produce sunroof products can easily result in incomplete mold filling or even glass cracking. While slowing down the reaction rate and increasing the curing time might fill the mold, the slower reaction rate significantly prolongs demolding time, severely impacting production efficiency. Furthermore, slowing down the reaction rate indirectly leads to a decline in material performance. Therefore, there is an urgent need to develop a new type of polyurethane material that can meet the mold filling requirements of large-perimeter glass edging products, achieve rapid curing and demolding, and ensure stable material flow during the coating process of glass and accessories, minimizing defects such as bubbles and material shortages. The overall goal is to achieve complete coating and rapid demolding of the sunroof glass and its accessories. This will not only solve the problems in existing technologies, but also enable the efficient and high-quality production of sunroof glass for new energy vehicles, meeting the growing needs of the automotive manufacturing industry.

[0003] Regarding issues such as material moldability, rapid demolding, and flow stability in the production of automotive sunroof glass, some solutions exist, but they are generally insufficient.

[0004] Regarding rapid demolding, CN107189028A discloses an environmentally friendly, high-performance, rapid demolding polyurethane reactive injection molding composition. By using composite catalysts and self-catalytic chain extenders, the reactivity of the system can be effectively improved, the amount of catalyst used can be reduced, and the odor and VOCs can be reduced. However, as users accelerate their production cycle, they often require demolding in 30 seconds or less, and demolding in 40 to 45 seconds can no longer meet their requirements.

[0005] CN118027355A discloses a polyurethane material for automotive glass edging and its preparation method, using diamine-modified diphenylmethane diisocyanate to improve demolding speed, achieving demolding in as little as 25 seconds. However, the use of diamine modification can lead to excessively high reactivity of the material, making it difficult to control and causing the initial gelation time to be too fast, preventing complete filling of the mold. Furthermore, the high reactivity of diamine-modified diphenylmethane diisocyanate necessitates the addition of polymerization inhibitors such as adipic acid chloride and phosphoric acid to prevent agglomeration and curing. These inhibitors can affect the polymerization rate and final product performance during polyurethane polymerization, potentially leading to decreased adhesion and insufficient initial strength.

[0006] In terms of optimizing material flowability, existing technologies generally employ formulation optimization, which extends the induction period of the polyurethane reaction, allowing the liquid to gel for a longer time (or open time, flow time, etc.) within the mold, thereby solving the problem of insufficient mold filling. This method is simple and effective, but it also presents many practical problems.

[0007] CN117700687A discloses a method for using an area greater than 1.5m². 2 The polyurethane material used for the sunroof glass edging extends the flow time by adding polypropylene tetraol with pentaerythritol as an initiator. The catalyst is added and used immediately to avoid deactivation after prolonged storage. The flow time is 8-10 seconds, and the demolding time is 25 seconds. However, the polypropylene tetraol increases the viscosity of the liquid, reducing its fluidity and affecting its ability to fill the mold and coat the glass and accessories, leading to appearance defects such as bubbles and insufficient material. Furthermore, the immediate addition of the catalyst increases the number of process steps at the user's site, raising the risk of process control issues.

[0008] CN119591831A discloses a slow-gel, fast-curing polyurethane material using a composite catalyst of N,N-dimethylcyclohexylamine and dimethyltin glycolate, which can achieve a gel time of 10.5 seconds and a rapid demolding time of 30 seconds. However, N,N-dimethylcyclohexylamine is a hazardous chemical with high toxicity and odor, and it cannot be consumed during polymerization. Its residue in the product will cause the odor and VOC of the sunroof product to deteriorate. The dimethyltin glycolate used in this invention has poor hydrolysis resistance. During industrial storage and transportation, the catalyst will gradually decompose, resulting in insufficient material reactivity.

[0009] In the actual production of sunroof glass edging, it is common for large sunroof products and small sunroof products to be produced on the same production line. In this case, extending the gel time can easily lead to quality defects such as bubbles, material shortages, pits, and wrinkles.

[0010] In addition, microbubbles are often added to polyurethane formulations to address the issues of large, uneven pores and high density in polyurethane foam materials. This achieves a fine, uniform foam distribution and improved performance, as seen in standards CN111875838A, CN1263781C, and CN112920448A. However, the addition of microbubbles typically leads to a significant decrease in the material's density and hardness, therefore it is only used for materials with a density below 1.0 g / cm³. 3 Foamed materials. Summary of the Invention

[0011] To address the aforementioned problems in the existing technology, this invention provides a method for preparing a polyurethane liquid containing microbubbles and its products, as well as a method for testing the flowability of the polyurethane liquid. The polyurethane liquid containing microbubbles has a short gel time (8-10s), a short demolding time (25s), good flowability, and good storage stability. Microbubbles can significantly improve the flowability of the liquid under the same reaction rate, which can meet the requirements of skylight glass production. Glass edging products produced using this polyurethane liquid have low odor, low VOC, good appearance, and are free from defects such as bubbles, material shortages, pits, and wrinkles.

[0012] The first aspect of this invention provides a polyurethane liquid containing microbubbles, comprising component A and component B. Component A, by mass fraction, comprises: Polyether polyols 50-90%; Chain extender 3-10%; 1-5% of autocatalytic chain extenders; Crosslinking agent 1-15%; Pigment 0.5-8%; Anti-aging agent 1-5%; Composite catalyst 0.01–2%; Component B is a carbamate-modified isocyanate; The A component contains microbubbles, and the volume fraction of the microbubbles is 0.1-5%, preferably 0.5-1%.

[0013] Preferably, the method for introducing microbubbles into component A is as follows: after uniformly mixing component A, it is added to a grinding device, and gas is introduced to maintain a slight positive pressure in the grinding device. Preferably, the grinding device pressure is 0.08–0.1 MPa, the grinding speed is 1200–1800 r / min, and the grinding time is 5–60 min. The gas is preferably carbon dioxide or nitrogen.

[0014] Preferably, the polyether polyol is one or more of ethylene oxide-propylene oxide co-ether triols with a primary hydroxyl content ≥70% and a number average molecular weight of 3000-6500.

[0015] Preferably, the chain extender is selected from one or more of ethylene glycol, 1,4-butanediol, 1,3-butanediol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,6-hexanediol, dodecanediol, and diethanolamine.

[0016] Preferably, the structural formula of the autocatalytic chain extender is: ; In the formula, x = 2 to 5, R is CyH2y+1, and y = 0 to 2.

[0017] Preferably, the preparation method of the autocatalytic chain extender includes the following steps: (1) Piperazine reacts with some epoxides to give intermediates; (2) The intermediate reacts with the remaining epoxide to obtain a self-catalytic chain extender.

[0018] The epoxy compound is selected from ethylene oxide, propylene oxide, or butane oxide.

[0019] Preferably, in step (1), the molar ratio of piperazine to epoxy compound is 1:2 to 4; the molar ratio of epoxy compound in step (1) to epoxy compound in step (2) is 2:1 to 1:2, preferably 1:1.

[0020] Preferably, in step (1): piperazine and solvent A are added to the reactor, and nitrogen is introduced to fully replace the air in the system; the temperature is raised to 60-70°C, and an epoxy compound is added dropwise. After the addition is complete, the temperature is raised to 75-80°C, and the reaction is maintained for 3-4 hours. The solvent and water are removed to obtain the intermediate.

[0021] Preferably, in step (2): the intermediate is dissolved in a solvent, nitrogen gas is introduced to fully replace the air in the system, the remaining epoxy compound is added dropwise, and the temperature is controlled at 65-75℃; after the addition is complete, concentrated sulfuric acid is added, the temperature is raised to 100-110℃, and the reaction is maintained for 6-8 hours. After the reaction is completed, impurities are removed to obtain the autocatalytic chain extender. The reaction is monitored by HPLC until the characteristic peak intensity of the hydroxyl group disappears, indicating the end of the reaction.

[0022] Preferably, in step (1), solvent A is anhydrous tetrahydrofuran; in step (2), solvent B is xylene, and the mass fraction of concentrated sulfuric acid is 0.5-1.5%.

[0023] Preferably, the composite catalyst is composed of an organic salt of bismuth and a compound containing a tertiary amine structure, wherein the bismuth content is between 15% and 25%, and the compound containing the tertiary amine structure is preferably one or more of triethylenediamine, dimethylcyclohexylamine, tetramethylethylenediamine, tetramethylpropylenediamine, tetramethylhexanediamine, dimethylethanolamine, trimethylhydroxyethylpropylenediamine, and trimethylhydroxyethylethylenediamine. The amount of the composite catalyst is preferably 0.2% to 2%.

[0024] Preferably, the crosslinking agent is one or more selected from glycerol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, and trihydroxyethyl isocyanurate.

[0025] Preferably, the anti-aging agent is selected from one or more of 2-(2′-hydroxy-3′-dodecyl-5′-methylphenyl)benzotriazole, 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)-5-chlorobenzotriazole, 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, bis(3,5-tert-butyl-4-hydroxyphenyl) sulfide, bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, and 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

[0026] Preferably, by mass fraction, component B comprises 60%–95% 4,4'-dicyclohexylmethane diisocyanate, 5%–40% modifier, and 23%–28% isocyanate (NCO) content. The modifier comprises at least one diol and at least one triol. The diol comprises one or more of polypropylene glycol, polytetrahydrofuran glycol, etc., preferably with a molecular weight of 400–4000 for polypropylene glycol and 650–2000 for polytetrahydrofuran glycol. The triol preferably comprises one or more of trimethylolethane, trimethylolpropane, glycerol, etc.

[0027] Preferably, the preparation method of component B is as follows: 4,4'-dicyclohexylmethane diisocyanate and a modifier are reacted to obtain urethane-modified isocyanate; the reaction temperature is preferably 80-90℃, and the reaction time is preferably 2-3h.

[0028] A second aspect of the present invention provides a method for preparing polyurethane articles from a polyurethane liquid containing microbubbles, comprising the following steps: ① Grinding and feeding: After mixing component A evenly, add it to the grinding device, introduce gas to maintain a slight positive pressure in the grinding device, and after grinding, transfer it to the high-pressure machine A tank; add component B to the B tank; ②Injection: Set the material temperature and injection pressure of component A and component B, inject into the mold, and close the mold; ③ Demolding and post-curing.

[0029] Preferably, the material temperature of component A is 35-45℃, the material temperature of component B is 35-45℃, the injection pressure is 15±3MPa, the mold temperature is 110-120℃, and the mold closing pressure is ≥250kN.

[0030] A third aspect of this invention provides a method for testing the flowability of polyurethane liquid, using a trough mold. The method includes the following steps: the trough mold is inclined at 5–35° to the horizontal; the polyurethane liquid is injected from the higher end of the trough mold; timing begins when the injection machine starts and ends when the liquid stops flowing; the gel time is recorded and the flow length is measured. Preferably, the liquid injection volume is 500–1000 g, the injection machine flow rate is 120–250 g / s, and the trough mold temperature is 80–120°C.

[0031] Compared with the prior art, the present invention has the following beneficial effects: 1. By introducing carbon dioxide or nitrogen into component A of the liquid material to form microbubbles, the viscosity of the liquid material is effectively reduced, its flow stability is improved, and the material can quickly fill the mold, solving the problems of large skylights and canopy glass not being able to fully fill the mold and having many bubble defects. 2. The liquid material of the present invention flows stably during the coating process of glass and accessories, and is not prone to defects such as bubbles and material shortage. It overcomes the problems of bubbles and material shortage in the sealing strip in the prior art, and improves product quality and production efficiency. 3. The liquid material of the present invention has good fluidity and curing properties, which can not only meet the requirements of mold filling, but also cure quickly, so that the product can be demolded quickly within 25 to 30 seconds, realizing the predetermined production cycle and significantly improving production efficiency; 4. Microbubbles do not affect the material properties after molding. The product made from the liquid of this invention can meet the various performance requirements of automotive glass edging materials. 5. The autocatalytic chain extender of the present invention adopts a stepwise synthesis method, which makes the reaction milder, reduces side reactions, increases yield, reduces viscosity, and facilitates the flow of the feed liquid; 6. This invention achieves the goal of maintaining the density and hardness of the molded product while reducing the viscosity and improving the fluidity of the liquid by introducing gas into component A to form microbubbles and synergistically matching the reactivity of the two-component polyurethane liquid. Attached Figure Description

[0032] Figure 1 This invention relates to a mold for testing the flowability of polyurethane liquid. Detailed Implementation

[0033] Example 1: Example Composition Components Main polyether: ethylene oxide-propylene oxide co-ether triol, molecular weight 5000, primary hydroxyl content 82%.

[0034] Autocatalytic chain extender: Step 1: Add 0.1 mol piperazine and 25 ml anhydrous THF to a flask, and purge the system with nitrogen three times to replace the air. Heat the system to 60-70°C using an oil bath. Slowly add 0.2 mol propylene oxide dropwise through a constant-pressure dropping funnel at a rate of 1-2 drops / second, maintaining the temperature at 65-75°C during the addition. After the addition is complete, raise the temperature to 75-80°C and maintain the reaction for 3-4 hours. Cool the reaction system to 50-60°C, then remove the solvent and water by rotary evaporation to obtain the intermediate for the next stage.

[0035] Step 2: Dissolve the intermediate in 100 ml of xylene, purge the system with nitrogen to fully replace the air, and slowly add 0.2 mol of propylene oxide dropwise through a constant-pressure dropping funnel, maintaining the temperature at 65–75 °C. After the addition is complete, add 1% (mass fraction) concentrated sulfuric acid, raise the temperature to 100 °C, and maintain the reaction for 8 hours. Monitor the reaction with HPLC until the characteristic peak intensity of the hydroxyl group disappears. After the reaction is complete, remove impurities by vacuum distillation.

[0036] Component A: Main polyether, 84.4 parts; self-catalytic chain extender, 6 parts; ethylene glycol, 6.4 parts; trimethylolpropane, 1.5 parts; carbon black, 0.5 parts; 2-(2′-hydroxy-3′-dodecyl-5′-methylphenyl)benzotriazole, 0.25 parts; bis(3,5-tributyl-4-hydroxyphenyl) sulfide, 0.25 parts; trimethylhydroxyethylpropanediamine, 0.3 parts; BCAT-E20 (Guangzhou Yourun), 0.4 parts.

[0037] Component B: 82.5 parts of 4,4'-dicyclohexylmethane diisocyanate, 9.5 parts of polytetrahydrofuran glycol (molecular weight 1000), and 8.0 parts of polyethylene glycol (molecular weight 400). The NCO mass fraction is 25.2%.

[0038] Component A: Add all materials to the reactor and stir at 35°C for 2 hours.

[0039] Component B: Isocyanate and modifier are added to the reaction vessel simultaneously, heated to 85°C with stirring, reacted for 3 hours, cooled to room temperature, and discharged.

[0040] The process for preparing PU-RIM products from compositions A and B using a high-pressure injection molding machine is as follows: ① Grinding and feeding: Extract component A from the material tank and add it to the grinding device. Purge with nitrogen and maintain the container pressure at 0.1 MPa. Grind with zirconia beads at 1800 r / min for 10 min. Then immediately add it to the high-pressure machine A tank. Add component B of the composition to the B tank. ②Injection: Set the material temperature to 40℃ for component A and 40℃ for component B, and the injection pressure to 14.5MPa. Inject into a mold that has been heated to 110℃, and the mold closing pressure to 262kN.

[0041] ③ Demolding: Demold after 25 seconds.

[0042] ④ Post-curing: Performance was tested after being placed at room temperature for 48 hours.

[0043] ⑤ Free Bubble Test: Using the same process as the molding process, but instead of injecting the molten material into the mold itself, it is injected into a groove-shaped mold measuring 800mm long, 30mm wide, and 50mm deep. The mold is tilted at a 15° angle, and the molten material is injected from the higher end. The pouring volume is 600g, the pouring speed is 150g / s, and the mold temperature is 110℃. Figure 1 As shown. Timing begins immediately when the injection machine is turned on and ends when the liquid stops flowing. The gel time is recorded and the flow length is measured.

[0044] Example 2

[0045] Example Composition Components Main polyether: ethylene oxide-propylene oxide co-polyether triol, molecular weight 6000, primary hydroxyl content 85.5%.

[0046] Autocatalytic chain extender: Step 1: Add 0.2 mol piperazine and 50 ml anhydrous THF to a flask, and purge the system with nitrogen three times to replace the air. Heat the system to 60-70°C using an oil bath. Slowly add 0.5 mol propylene oxide dropwise through a constant-pressure dropping funnel at a rate of 1-2 drops / second, maintaining the temperature at 65-75°C during the addition. After the addition is complete, raise the temperature to 75-80°C and maintain the reaction for 3-4 hours. Cool the reaction system to 50-60°C, then remove the solvent and water by rotary evaporation to obtain the intermediate for the next stage.

[0047] Step 2: Dissolve the intermediate in 150 ml of xylene, purge the system with nitrogen to fully replace the air, and slowly add 0.5 mol of propylene oxide dropwise through a constant-pressure dropping funnel, maintaining the temperature at 65–75 °C. After the addition is complete, add 1% (mass fraction) concentrated sulfuric acid, raise the temperature to 110 °C, and maintain the reaction for 6 hours. Monitor the reaction with HPLC until the characteristic peak intensity of the hydroxyl group disappears. After the reaction is complete, remove impurities by vacuum distillation.

[0048] Component A: Main polyether, 84.5 parts; self-catalytic chain extender, 6 parts; ethylene glycol, 6.5 parts; trimethylolpropane, 1.5 parts; carbon black, 0.5 parts; 2-(2′-hydroxy-5′-methylphenyl)benzotriazole, 0.2 parts; bis(1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, 0.2 parts; trimethylhydroxyethylpropanediamine, 0.3 parts; BCAT-E20 (Guangzhou Yourun), 0.3 parts.

[0049] Component B: 82.5 parts of 4,4'-dicyclohexylmethane diisocyanate, 9.5 parts of polytetrahydrofuran glycol (molecular weight 1000), and 8.0 parts of polyethylene glycol (molecular weight 400). The NCO mass fraction is 25.2%.

[0050] Component A: Add all materials to the reactor and stir at 35°C for 2 hours.

[0051] Component B: Isocyanate and modifier are added to the reaction vessel simultaneously, heated to 88°C with stirring, reacted for 2.5 hours, cooled to room temperature, and discharged.

[0052] The process for preparing PU-RIM products from compositions A and B using a high-pressure injection molding machine is as follows: ① Grinding and feeding: Extract component A from the material tank and add it to the grinding device. Introduce carbon dioxide and maintain the container pressure at 0.08 MPa. At the same time, use zirconia beads to grind at 1200 r / min for 10 min. Then immediately add it to the high-pressure machine A tank. Add component B of the composition to the B tank. ②Injection: Set the material temperature to 40℃ for component A and 40℃ for component B, and the injection pressure to 14.6MPa. Inject into a mold that has been heated to 110℃, and the mold closing pressure to 265kN.

[0053] ③ Demolding: Demold after 25 seconds.

[0054] ④ Post-curing: Performance was tested after being placed at room temperature for 48 hours.

[0055] ⑤ Free Bubble Test: Using the same process as the molding process, but instead of injecting the molten material into the mold itself, it is injected into a groove-shaped mold measuring 800mm long, 30mm wide, and 50mm deep. The mold is tilted at a 15° angle, and the molten material is injected from the higher end. The pouring volume is 600g, the pouring speed is 150g / s, and the mold temperature is 110℃. Figure 1 As shown. Timing begins immediately when the injection machine is turned on and ends when the liquid stops flowing. The gel time is recorded and the flow length is measured.

[0056] Comparative Example 1: The formulations of components A and B are the same as in Example 1. No gas is introduced into component A, and no grinding is performed during the PU-RIM product manufacturing process. Components A and B are directly added to the material tank. Component A does not contain microbubbles.

[0057] Comparative Example 2: Formula reference: Patent document CN119591831A: Component A: 100 parts polypropylene glycol, 0.12 parts composite catalyst, 0.5 parts 1,4-butanediol, 1 part antioxidant 1010, 0.4 parts tris(2-chloroethyl) phosphate, 1 part light stabilizer, and 0.6 parts carbon black; the composite catalyst is formed by compounding N,N-dimethylcyclohexylamine and dimethyltin glycolate in a mass ratio of 7:5.

[0058] Component B: Carbodiimide-modified MDI: 45 parts.

[0059] The process for preparing PU-RIM products using components A and B via a high-pressure injection molding machine is the same as in Example 1, except that component A is introduced with gas and ground to introduce microbubbles.

[0060] Comparative Example 3 The autocatalytic chain extender was synthesized using the one-step method of Example 1 in CN107189028A, replacing the autocatalytic chain extender in Example 1, with the remaining operations being the same as in Example 1.

[0061] Comparative Example 4 The formulations of components A and B are the same as in Example 1, but the grinding process differs as follows: Grinding and feeding: Extract component A from the material tank and add it to the grinding device. Purge with nitrogen and maintain the container pressure at 0.8 MPa. Grind with zirconia beads at 2000 r / min for 10 min. Then add components A and B to the material tank. The volume fraction of microbubbles in component A is 6%.

[0062] Table 1. Comparison of material properties between the examples and comparative examples

Claims

1. A polyurethane liquid containing microbubbles, comprising component A and component B, Component A, by mass fraction, comprises: Polyether polyols 50-90%; Chain extender 3-10%; 1-5% of autocatalytic chain extenders; Crosslinking agent 1-15%; Pigment 0.5-8%; Anti-aging agent 1-5%; Composite catalyst 0.01–2%; Component B is a carbamate-modified isocyanate; The A component contains microbubbles, and the volume fraction of the microbubbles is 0.1-5%, preferably 0.5-1%.

2. The polyurethane liquid according to claim 1, characterized in that, The method for introducing microbubbles into component A is as follows: after mixing component A evenly, add it to the grinding device and introduce gas to maintain a slight positive pressure in the grinding device.

3. The polyurethane liquid according to claim 1, characterized in that, The polyether polyol is one or more of ethylene oxide-propylene oxide co-ether triols with a primary hydroxyl content ≥70% and a number average molecular weight of 3000-6500.

4. The polyurethane liquid according to claim 1, characterized in that, The chain extender is selected from one or more of ethylene glycol, 1,4-butanediol, 1,3-butanediol, diethylene glycol, 1,2-propanediol, 1,3-propanediol, neopentyl glycol, 1,6-hexanediol, dodecanediol, and diethanolamine.

5. The polyurethane liquid according to claim 1, characterized in that, The structural formula of the self-catalytic chain extender is: ； In the formula, x = 2 to 5, R is CyH2y+1, and y = 0 to 2; Preferably, the preparation method of the autocatalytic chain extender includes the following steps: (1) Piperazine reacts with some epoxides to give intermediates; (2) The intermediate reacts with the remaining epoxide to obtain a self-catalytic chain extender.

6. The polyurethane liquid according to claim 1, characterized in that, The composite catalyst consists of an organic salt of bismuth and a compound containing a tertiary amine structure.

7. The polyurethane liquid according to claim 1, characterized in that, The crosslinking agent is selected from one or more of glycerol, 1,2,6-hexanetriol, trimethylolethane, trimethylolpropane, and trihydroxyethyl isocyanurate.

8. The polyurethane liquid according to claim 1, characterized in that, By mass fraction, component B comprises 60%–95% 4,4'-dicyclohexylmethane diisocyanate, 5%–40% modifier, and 23%–28% isocyanate (NCO) content.

9. A method for preparing a polyurethane article from a polyurethane liquid containing microbubbles as described in any one of claims 1-8, comprising the following steps: ① Grinding and feeding: After mixing component A evenly, add it to the grinding device, introduce gas to maintain a slight positive pressure in the grinding device, and after grinding, transfer it to the high-pressure machine A tank; add component B to the B tank; ②Injection: Set the material temperature and injection pressure of component A and component B, inject into the mold, and close the mold; ③ Demolding and post-curing.

10. A method for testing the flowability of polyurethane liquid, using a trough mold, comprising the following steps: The trough mold is inclined at 5 to 35 degrees to the horizontal line. The polyurethane liquid is injected from the higher end of the trough mold. The timing starts when the injection machine starts and ends when the liquid stops flowing. The gel time is recorded and the flow length is measured.

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