A blocked polyurethane resin composition and a method for curing the same, a blocked polyurethane prepolymer

Abstract

The application provides a blocked polyurethane resin composition, a curing method thereof and a blocked polyurethane prepolymer. The blocked polyurethane resin composition comprises a blocked polyurethane prepolymer and an amine curing agent; the molar ratio of the blocked NCO group in the blocked polyurethane prepolymer to the amino group in the amine curing agent is 0.9:1-1:0.9; the raw materials of the blocked polyurethane prepolymer comprise a polymeric polyol, a diisocyanate, a synergist and a blocking agent; the polymeric polyol comprises an aliphatic polyurethane prepolymer and a polyphenylene ether diol; and the diisocyanate is XDI. The application designs the specific composition of the blocked polyurethane resin composition, and further designs the molecular chain structure of the blocked polyurethane prepolymer, so that the blocked polyurethane resin composition with the properties of yellowing resistance and high gloss is obtained.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane materials technology, specifically relating to a closed polyurethane resin composition and its curing method, and a closed polyurethane prepolymer. Background Technology

[0002] Polyurethane materials used for manufacturing exterior parts typically require high resistance to yellowing. Therefore, a large number of aliphatic monomers, including aliphatic polyether polyols and aliphatic diisocyanates, are often used in the molecular structure design. Commonly used aliphatic polyether polyols in the prior art include PPG (polypropylene glycol), PEG (polyethylene glycol), and PTMEG (polytetramethylene ether glycol); commonly used diisocyanates in the prior art include aliphatic diisocyanates such as HDI (hexamethylene diisocyanate) and IPDI (isophorone diisocyanate). These diisocyanates have high resistance to yellowing and are suitable for manufacturing exterior parts. However, the polyurethane produced in this way usually cannot achieve the desired gloss.

[0003] Toluene diisocyanate (TDI), an aromatic diisocyanate, can improve the surface gloss of polyurethane when used as a raw material in its preparation. However, due to its molecular structure limitations, it leads to poor yellowing resistance in polyurethane. Polyphenylene ether glycol (PPE) can impart better gloss to polyurethane and improve its yellowing resistance, thus addressing the problem of poor yellowing resistance caused by TDI. However, PPE cannot be added arbitrarily in the actual preparation of polyurethane materials: small amounts are insufficient to improve the product's gloss, while excessive amounts will significantly reduce the low-temperature performance of the polyurethane.

[0004] Existing technologies struggle to find a polyurethane structural design that balances yellowing resistance with high gloss and low-temperature flexural strength. Therefore, developing a novel polyurethane resin composition that possesses excellent yellowing resistance, high gloss, and good low-temperature flexural strength has become a pressing technical problem. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a blocked polyurethane resin composition and its curing method, as well as a blocked polyurethane prepolymer. By designing the specific composition of the blocked polyurethane resin composition and further designing the molecular chain structure of the blocked polyurethane prepolymer, the present invention obtains a blocked polyurethane resin composition with excellent resistance to yellowing, high gloss, and good low-temperature flexural strength.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a blocked polyurethane resin composition, the blocked polyurethane resin composition comprising a blocked polyurethane prepolymer and an amine curing agent; the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent is 0.9:1-1:0.9; the raw materials for preparing the blocked polyurethane prepolymer include a polymeric polyol, a diisocyanate, a synergist, and a blocking agent; the polymeric polyol includes an aliphatic polyether polyol and a polyphenylene ether diol, wherein the mass percentage of the aliphatic polyether polyol is ≥75% and the mass percentage of the polyphenylene ether diol is 10-20% based on a 100% mass percentage of the polymeric polyol; the diisocyanate is isophthalic dimethyl diisocyanate (XDI).

[0007] To prepare a polyurethane material that combines yellowing resistance and high gloss, this invention designs the specific composition of the blocked polyurethane resin composition and further designs the raw materials for preparing the blocked polyurethane prepolymer, thereby completing the design of the polyurethane molecular chain structure and obtaining a blocked polyurethane resin composition with excellent yellowing resistance, high gloss, and good low-temperature flexural strength.

[0008] The presence of ether bonds in the polyphenylene ether glycol (PPE) molecule imparts a certain degree of flexibility to polyurethane resins; the presence of benzene rings in the PPE molecule gives polyurethane resins rigid characteristics and improves their weather resistance. While the use of PPE ether glycol can give polyurethane resins both weather resistance and light reflection modification, adding small amounts does not achieve the desired gloss level, and adding large amounts will lead to a decrease in the low-temperature flexural strength of the polyurethane resin.

[0009] XDI has a benzene ring structure, but the conjugation between the benzene ring and NCO in its molecular structure is broken by methylene groups. This characteristic allows it to still maintain high resistance to yellowing. Therefore, simply introducing XDI will not reduce the yellowing resistance of polyurethane resin. XDI is well-known for its ability to improve the light transmittance of polyurethane, but XDI alone cannot directly produce a positive improvement effect on the gloss of polyurethane, precisely because the conjugation between the benzene ring and NCO in its molecular structure is broken by methylene groups. This invention creatively discovers that when a blocked polyurethane resin composition is cured to the ideal degree of curing, and polyphenylene ether glycol and XDI are simultaneously introduced into the polyurethane resin, excellent gloss can be achieved in the polyurethane material. While we are reluctant to be bound by rigid principles, the following explanation can be offered: When polyphenylene ether glycol (PPE) and XDI are simultaneously introduced into polyurethane resin, the PPE structure in the polyurethane resin molecular chain not only contributes to improving the high gloss of the polyurethane resin itself, but also affects the chemical environment of XDI, which is chemically bonded to the PPE structure. This allows the benzene ring structure in XDI to also contribute to improving the high gloss of the polyurethane resin, mitigating the adverse effects of the methylene groups in XDI. In particular, when only XDI is selected as the diisocyanate in the polyurethane resin, ensuring that all diisocyanates bonded to PPE are XDI, the gloss of the polyurethane resin can be significantly improved, further confirming the above findings.

[0010] The polymer polyol uses aliphatic polyether polyol as the main raw material to improve the low-temperature flexural strength of the material. In this invention, there are no special restrictions on the selection of aliphatic polyether polyols; commonly used aliphatic polyether diols in the art are applicable. Exemplary examples include, but are not limited to, any one or at least two combinations of polypropylene glycol (PPG), trifunctional polypropylene glycol initiated with methylpropylene glycol or glycerol, polyethylene glycol (PEG), or polytetramethylene ether glycol (PTMEG). Typical but non-limiting combinations include: a combination of polypropylene glycol and trifunctional polypropylene glycol initiated with methylpropylene glycol or glycerol; a combination of polypropylene glycol, polyethylene glycol, and polytetramethylene ether glycol; a combination of polypropylene glycol, trifunctional polypropylene glycol initiated with methylpropylene glycol or glycerol, polyethylene glycol, and polytetramethylene ether glycol, etc.

[0011] This invention achieves low shrinkage of cured polyurethane even with a small amount of polyphenylene ether glycol (PPE) and XDI through the synergistic effect of PPE and XDI, while simultaneously imparting high reflectivity, resulting in a high gloss level in the polyurethane material. Furthermore, this invention controls the mass percentage of PPE in the polymer polyol to within 10-20%, allowing it to work synergistically with XDI to prepare a blocked polyurethane resin composition with excellent overall performance. Insufficient PPE content leads to poor gloss in the polyurethane resin; excessive PPE content results in poor low-temperature flexural strength of the blocked polyurethane resin composition.

[0012] This invention utilizes the synergistic effect of polyphenylene ether glycol (PPE) and XDI, and further leverages the synergistic effect of the rigid structure (benzene ring) in PPE and XDI, to prepare a closed-cell polyurethane prepolymer with low shrinkage characteristics, requiring only a small amount of PPE. Low shrinkage characteristics and ideal degree of curing are prerequisites for achieving stable performance properties in the closed-cell polyurethane resin composition. Both must be satisfied simultaneously to ensure that the polyurethane material obtained from the closed-cell polyurethane resin composition has a highly smooth surface. If only a closed-cell polyurethane prepolymer with low shrinkage characteristics is used, but the degree of curing of the closed-cell polyurethane resin composition is not ideal, the synergistic effect of the rigid structure in the PPE and XDI in the closed-cell polyurethane prepolymer will fail, resulting in poor performance of the final polyurethane material. This invention adjusts the curing formulation of the blocked polyurethane resin composition and further controls the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent to be 0.9:1-1:0.9, so that the blocked polyurethane prepolymer achieves the ideal degree of curing during the curing process. At the same time, this invention obtains a blocked polyurethane prepolymer with low shrinkage characteristics through the synergistic effect of polyphenylene ether glycol and XDI, ensuring that the surface of the final polyurethane material has high smoothness, so that the polyurethane material has both good resistance to yellowing and gloss.

[0013] In this invention, the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent is 0.9:1 to 1:0.9, for example, it can be 0.9:1, 0.92:1, 0.94:1, 0.96:1, 0.98:1, 1:1, 1:0.98, 1:0.96, 1:0.94, 1:0.92 or 1:0.9, etc.

[0014] Based on the mass percentage content of the polymer polyol being 100%, the mass percentage content of the aliphatic polyether polyol is ≥75% (e.g., it can be 75%, 78%, 80%, 81%, 84%, 86%, 88%, or 90%), and the mass percentage content of the polyphenylene ether diol is 10-20% (e.g., it can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%).

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The purpose and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0016] Preferably, the amine curing agent includes any one or a combination of at least two of 3,3-diethyl-4,4-diaminodiphenylmethane (MOEA), 4,4-diaminodiphenylmethane (MDA), 3,3-dimethyl-4,4-diaminodicyclohexylmethane (DMDC), or adipic acid dihydrazide (ADH).

[0017] Preferably, the polymeric polyol further includes polyhydrogenated butadiene glycol.

[0018] Preferably, the mass percentage of the polyhydrogenated butadiene glycol is 2-5% based on the mass percentage of the polymer polyol being 100%, for example, it can be 2%, 2.2%, 2.5%, 2.7%, 3%, 3.3%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, or 5%, etc.

[0019] In this invention, the use of polyhydrobutadiene glycol introduces a polyhydrobutadiene glycol structure into the polyurethane molecular chain, lowering the glass transition temperature of the polyurethane resin and improving its low-temperature resistance. This allows the polyurethane resin to maintain good flexibility and low-temperature flexural strength in cold environments. However, excessive use of polyhydrobutadiene glycol can degrade the gloss of the paper roll material; therefore, its content should be controlled below 5%. This invention, by controlling the amount of polyhydrobutadiene glycol in the polymer polyol to 2-5%, obtains a polyurethane material that simultaneously possesses good flexibility, good low-temperature flexural strength, and high gloss.

[0020] Preferably, the molar ratio of the NCO group in the diisocyanate to the hydroxyl group in the polymer polyol is (1.5-2.0):1, for example, it can be 1.5:1, 1.55:1, 1.6:1, 1.65:1, 1.7:1, 1.75:1, 1.8:1, 1.85:1, 1.9:1, 1.95:1 or 2.0:1, etc.

[0021] The molar ratio of diisocyanate groups to hydroxyl groups, i.e., the R value, is adjusted to (1.5-2.0):1 in this invention to further ensure the regularity and uniform distribution of the polyurethane resin structure.

[0022] Preferably, the number average molecular weight of the polyphenylene ether diol is 1000-2000, for example, it can be 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000.

[0023] Preferably, the number average molecular weight of the polyhydrogenated butadiene glycol is 1000-4000, for example, it can be 1000, 1200, 1500, 1800, 2000, 2300, 2600, 2800, 3000, 3300, 3600, 3800 or 4000.

[0024] Preferably, the number average molecular weight of the aliphatic polyether polyol is 1000-6000, for example, it can be 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500 or 6000.

[0025] It should be noted that this invention does not impose any special restrictions on the specific selection of synergists and blocking agents; commonly used synergists and blocking agents in the art are applicable. Furthermore, this invention does not impose any special restrictions on the amount of synergists and blocking agents used; the amount can be designed according to actual conditions. In the actual preparation process, the amount of blocking agent used is determined to ensure that the NCO group content in the blocked polyurethane prepolymer is 0%, i.e., until all the NCO groups contained in intermediate 2 are blocked. For example, based on 100 parts by weight of the polymer polyol, the mass fraction of the blocking agent can be 5-12 parts (e.g., 5, 6, 7, 8, 9, 10, 11, or 12 parts, etc.).

[0026] Preferably, the raw materials for preparing the closed-cell polyurethane prepolymer further include stabilizers and activators. It should be noted that the present invention does not impose any special restrictions on the specific selection of stabilizers and activators; commonly used stabilizers and activators in the art are applicable. Similarly, the present invention does not impose any special restrictions on the specific amount of stabilizers and activators used, and can be designed according to actual conditions.

[0027] Preferably, the content of blocked NCO groups in the blocked polyurethane prepolymer is 2.1-2.6 wt%, for example, it can be 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, or 2.6 wt%.

[0028] The NCO content of the blocked polyurethane prepolymer can be obtained by measuring the NCO content of intermediate 2 and calculating the content of the blocking agent added in step (3).

[0029] Preferably, the viscosity of the closed-cell polyurethane prepolymer at 25°C is 4.0 × 10⁻⁶. 4 -1.0×10 5 cps, for example, could be 4×10 4 cps, 4.5×10 4 cps, 5×10 4 cps, 5.5×10 4 cps, 6×10 4 cps, 6.5×10 4 cps, 7×10 4 cps, 7.5×10 4 cps, 8×10 4 cps, 8.5×10 4 cps, 9×10 4 cps, 9.5×10 4 cps or 1.0×10 5 CPS, etc.

[0030] Preferably, the closed-cell polyurethane prepolymer is prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol, synergist and stabilizer, diisocyanate is added to it and reacted to obtain intermediate 1; (2) Add an activator to intermediate 1 obtained in step (1), react, and obtain intermediate 2; (3) Add a blocking agent to the intermediate 2 obtained in step (2) to carry out the end-capping reaction and obtain the blocked polyurethane prepolymer.

[0031] Preferably, the mixing temperature in step (1) is 60-65°C, for example, it can be 60°C, 61°C, 62°C, 63°C, 64°C or 65°C.

[0032] Preferably, the temperature of the reaction in step (1) is 90-95℃ (e.g., 90℃, 91℃, 92℃, 93℃, 94℃ or 95℃, etc.), and the time is 1-3 h (e.g., 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc.).

[0033] Preferably, the reaction in step (1) further includes a post-processing step, wherein the post-processing method includes cooling to below 60°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C.

[0034] Preferably, the reaction temperature in step (2) is 80-85℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃ or 85℃, etc.

[0035] Preferably, the content of NCO groups in the intermediate 2 is 2.2-2.8 wt%, for example, it can be 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, or 2.8 wt%, etc.

[0036] The reaction time in step (2) is adjusted according to the content of NCO groups in the final intermediate 2. The reaction is stopped when the content of NCO groups in intermediate 2 reaches 2.2-2.8 wt%. The reaction time in step (2) can be, for example, 3-5 h, such as 3 h, 3.5 h, 4 h, 4.5 h or 5 h.

[0037] Preferably, step (2) further includes a post-processing step after the reaction, and the post-processing method includes cooling to below 60°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C.

[0038] Preferably, the temperature of the end-capping reaction in step (3) is 60-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, etc.

[0039] Preferably, the NCO group content in the closed polyurethane prepolymer obtained in step (3) is 0 wt%.

[0040] The reaction time of the end-capping reaction in step (3) is adjusted according to the NCO group content in the final closed polyurethane prepolymer. When the NCO content in the closed polyurethane prepolymer is 0 wt%, the reaction is stopped.

[0041] In a second aspect, the present invention provides a method for curing a closed polyurethane resin composition as described in the first aspect, the curing method comprising the following steps: The blocked polyurethane prepolymer and amine curing agent are mixed and cured to complete the curing of the blocked polyurethane resin composition.

[0042] Preferably, the curing temperature is 140-200℃ (e.g., 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, or 200℃, etc.), and the time is ≥4 min (e.g., 4 min, 5 min, 6 min, 7 min, 8 min, 9 min, 10 min, 11 min, 12 min, 13 min, 14 min, or 15 min, etc.).

[0043] Thirdly, the present invention provides a closed polyurethane prepolymer, which is used to prepare a closed polyurethane resin composition as described in the first aspect; The blocked polyurethane prepolymer includes polymer polyol residues, diisocyanate residues, synergist residues, and blocking agent residues; The raw materials for preparing the blocked polyurethane prepolymer include polymeric polyols, diisocyanates, synergists, and blocking agents; the polymeric polyols include aliphatic polyether polyols and polyphenylene ether diols, with the polymeric polyol content being 100% by mass, the aliphatic polyether polyol content being ≥75% (e.g., 75%, 78%, 80%, 81%, 84%, 86%, 88%, or 90%), and the polyphenylene ether diol content being 10-20% (e.g., 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%); the diisocyanate includes isophthalic diisocyanate.

[0044] It should be noted that "residue" refers to the part that enters the polymer chain after the raw material is polymerized. For example, after HO-A-OH and NCO-B-NCO are polymerized, the parts that enter the molecular chain are -A- and -B-, respectively. The part of the polymer diol that enters the polymer chain after polymerization is called the polymer diol residue (i.e., "-A-"). The part of the diisocyanate that enters the polymer chain is called the diisocyanate residue (i.e., "-B-").

[0045] Preferably, the polymeric polyol further includes polyhydrobutadiene glycol.

[0046] Preferably, the mass percentage of the polyhydrogenated butadiene glycol is 2-5% based on the mass percentage of the polymer polyol being 100%, for example, it can be 2%, 2.2%, 2.5%, 2.7%, 3%, 3.3%, 3.6%, 3.8%, 4%, 4.2%, 4.4%, 4.6%, 4.8%, or 5%, etc.

[0047] Preferably, the number average molecular weight of the polyphenylene ether diol is 1000-2000, for example, it can be 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900 or 2000.

[0048] Preferably, the number average molecular weight of the polyhydrogenated butadiene glycol is 1000-4000, for example, it can be 1000, 1200, 1500, 1800, 2000, 2300, 2600, 2800, 3000, 3300, 3600, 3800 or 4000.

[0049] Preferably, the number average molecular weight of the aliphatic polyether polyol is 1000-6000, for example, it can be 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500, 5000, 5500 or 6000.

[0050] Preferably, the raw materials for preparing the closed polyurethane prepolymer also include stabilizers and activators.

[0051] Preferably, the molar ratio of the NCO group in the diisocyanate to the hydroxyl group in the polymer polyol is (1.5-2.0):1, for example, it can be 1.5:1, 1.55:1, 1.6:1, 1.65:1, 1.7:1, 1.75:1, 1.8:1, 1.85:1, 1.9:1, 1.95:1 or 2.0:1, etc.

[0052] Preferably, the content of blocked NCO groups in the blocked polyurethane prepolymer is 2.1-2.6 wt%, for example, it can be 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, or 2.6 wt%.

[0053] Preferably, the viscosity of the closed-cell polyurethane prepolymer at 25°C is 4.0 × 10⁻⁶. 4 -1.0×10 5 cps, for example, could be 4×10 4 cps, 4.5×10 4 cps, 5×10 4 cps, 5.5×10 4 cps, 6×10 4 cps, 6.5×10 4 cps, 7×10 4 cps, 7.5×10 4 cps, 8×10 4 cps, 8.5×10 4 cps, 9×10 4cps, 9.5×10 4 cps or 1.0×10 5 CPS, etc.

[0054] Preferably, the closed-cell polyurethane prepolymer is prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol, synergist and stabilizer, diisocyanate is added to it and reacted to obtain intermediate 1; (2) Add an activator to intermediate 1 obtained in step (1), react, and obtain intermediate 2; (3) Add a blocking agent to the intermediate 2 obtained in step (2) to carry out the end-capping reaction and obtain the blocked polyurethane prepolymer.

[0055] Preferably, the mixing temperature in step (1) is 60-65°C, for example, it can be 60°C, 61°C, 62°C, 63°C, 64°C or 65°C.

[0056] Preferably, the temperature of the reaction in step (1) is 90-95℃ (e.g., 90℃, 91℃, 92℃, 93℃, 94℃ or 95℃, etc.), and the time is 1-3 h (e.g., 1 h, 1.5 h, 2 h, 2.5 h or 3 h, etc.).

[0057] Preferably, the reaction in step (1) further includes a post-processing step, wherein the post-processing method includes cooling to below 60°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C.

[0058] Preferably, the reaction temperature in step (2) is 80-85℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃ or 85℃, etc.

[0059] Preferably, the content of NCO groups in the intermediate 2 is 2.2-2.8 wt%, for example, it can be 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, or 2.8 wt%, etc.

[0060] The reaction time in step (2) is adjusted according to the content of NCO groups in the final intermediate 2. The reaction is stopped when the content of NCO groups in intermediate 2 reaches 2.1-2.9 wt. The reaction time in step (2) can be, for example, 3-5 h, such as 3 h, 3.5 h, 4 h, 4.5 h or 5 h.

[0061] Preferably, step (2) further includes a post-processing step after the reaction, and the post-processing method includes cooling to below 60°C, for example, 40°C, 42°C, 44°C, 46°C, 48°C, 50°C, 52°C, 54°C, 56°C, 58°C or 60°C.

[0062] Preferably, the temperature of the end-capping reaction in step (3) is 60-80℃, for example, it can be 60℃, 62℃, 64℃, 66℃, 68℃, 70℃, 72℃, 74℃, 76℃, 78℃ or 80℃, etc.

[0063] Preferably, the NCO group content in the closed polyurethane prepolymer obtained in step (3) is 0 wt%.

[0064] The reaction time of the end-capping reaction in step (3) is adjusted according to the NCO group content in the final closed polyurethane prepolymer. When the NCO content in the closed polyurethane prepolymer is 0 wt%, the reaction is stopped.

[0065] Compared with the prior art, the present invention has the following beneficial effects: (1) By designing the raw materials for preparing the closed polyurethane prepolymer, and further using specific amounts of polyphenylene ether diol and XDI in synergistic combination, the present invention completes the design of the polyurethane molecular chain structure, and obtains a closed polyurethane resin composition that has both good yellowing resistance and high gloss, as well as good low temperature flexural resistance.

[0066] (2) By controlling the molar ratio of the NCO group blocked in the blocked polyurethane prepolymer and the amino group in the amine curing agent within a specific range in the blocked polyurethane resin composition, and by optimizing the curing process parameters of the blocked polyurethane resin composition, the blocked polyurethane resin composition can achieve an ideal degree of curing during the curing process, thereby obtaining a blocked polyurethane resin composition with excellent comprehensive performance. Detailed Implementation

[0067] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0068] Terms and Definitions In this invention, the term "residue" refers to the portion of the raw material that enters the polymer chain after polymerization. For example, after HO-A-OH and NCO-B-NCO are polymerized, the portions that enter the molecular chain are -A- and -B-, respectively. The portion of the polymer diol that enters the polymer chain after polymerization is called the polymer diol residue (i.e., "-A-"), and the portion of the diisocyanate that enters the polymer chain is called the diisocyanate residue (i.e., "-B-").

[0069] Amine curing agents The role of amine curing agents is to chemically crosslink with the NCO groups of the blocked polyurethane prepolymer, thereby forming a chemical network structure. This invention selects amine curing agents as the curing agents for the blocked polyurethane prepolymer to ensure that the reaction between the two forms a stable chemical network structure, achieving a stable material state and maintaining the smoothness of the surface during leveling, which is crucial for obtaining high reflectivity. The amine curing agents can be selected from 3,3-diethyl-4,4-diaminodiphenylmethane (MOEA), 4,4-diaminodiphenylmethane (MDA), 3,3-dimethyl-4,4-diaminodicyclohexylmethane (DMDC), or adipate dihydrazide (ADH), etc.

[0070] The amine curing agents selected in the following examples are conventional amine curing agents. The selection of the raw materials for the amine curing agents does not constitute a constraint on the technical solution.

[0071] Polyether polyols For example, the polyether polyol includes any one or at least two combinations of polypropylene glycol (PPG), trifunctional polypropylene glycol, polyethylene glycol (PEG), or polytetramethylene ether glycol (PTMEG), wherein typical but non-limiting combinations include: a combination of polypropylene glycol and trifunctional polypropylene glycol, a combination of polypropylene glycol, polyethylene glycol, and polytetramethylene ether glycol, and a combination of polypropylene glycol, trifunctional polypropylene glycol, polyethylene glycol, and polytetramethylene ether glycol.

[0072] The polyol is a combination of polypropylene triol with a number average molecular weight of 3000, polypropylene glycol with a number average molecular weight of 2000, and polypropylene glycol with a number average molecular weight of 4000, in a ratio of 8:5:4; and / or, the polyol is a combination of polypropylene triol with a number average molecular weight of 3000, polytetrahydrofuran ether glycol with a number average molecular weight of 2000, and polypropylene glycol with a number average molecular weight of 4000, in a ratio of 8:5:4; and / or, the polyol is a combination of polypropylene triol with a number average molecular weight of 4800 and polypropylene glycol with a number average molecular weight of 1000, in a ratio of 4:1.

[0073] The polyether polyols and combinations thereof selected in the following examples are conventional polyether polyols. The selection of polyether polyol raw materials does not constitute a constraint on the technical solution.

[0074] sealant Blocking agents are common reaction aids in polyurethane synthesis. Their well-known function is to block NCO groups in the system, making them less likely to react with moisture in the air at room temperature, thus improving storage stability. Blocked polyurethane prepolymers, after being end-capped with blocking agents, have no NCO end groups and can coexist with amine curing agents. During curing, the blocking agent groups reach their deblocking temperature and release NCO. Commonly used blocking agents include acetanilide or pyrazole compounds.

[0075] The blocking agents 3,5-dimethylpyrazole and butanone oxime selected in the following examples are conventional NCO blocking agents. The choice of blocking agent does not constitute a constraint on the technical solution.

[0076] Synergist Synergists are common reaction aids in the synthesis of polyurethane. Their function is well-known: the active hydrogen in the synergist reacts with NCO and attaches to the molecular chain of the polyurethane prepolymer, giving the closed-type polyurethane prepolymer a self-leveling function. Polyether-modified organosilicon synergists, etc., can be selected.

[0077] The synergists selected in the following examples are conventional synergists used in polyurethane polymerization. The selection of synergists does not constitute a constraint on the technical solution.

[0078] For example, with the total mass parts of polymer polyol and diisocyanate being 100 parts, the mass parts of the synergist are 0.5-3 parts (e.g., 0.5 parts, 1 part, 1.5 parts, 2 parts, 2.5 parts, 2.5 parts, or 3 parts, etc.). In the embodiments of the present invention, those skilled in the art can adjust the dosage according to the actual experimental conditions.

[0079] Other additives In the preparation of closed-cell polyurethane prepolymers, some commonly used additives can be added to the system according to actual needs. These additives do not participate in the reaction. Surfactants are common additives in polyurethane synthesis, and their function is to promote the reaction between isocyanate and the hydroxyl groups of polyol. This invention does not impose any special restrictions on the specific selection of the surfactant; commonly used surfactants in the art are applicable. The surfactant can be selected from any one or a combination of at least two of Valikat Zn 1910 produced by Umicore and BICAT 8 / BICAT 8118 produced by Leading Chemical Company. For example, based on a total mass fraction of 100 parts of polymer polyol and diisocyanate, the mass fraction of the surfactant is 0.005-0.02 parts (e.g., 0.005 parts, 0.007 parts, 0.008 parts, 0.01 parts, 0.012 parts, 0.014 parts, 0.016 parts, 0.018 parts, or 0.02 parts, etc.), and those skilled in the art can adjust the amount according to actual experimental conditions.

[0080] Stabilizers are common reaction aids in polyurethane synthesis, serving to prevent vigorous cross-linking reactions and gelation. They are reaction aids with polymerization inhibition functions. This invention does not impose any special restrictions on the specific selection of stabilizers; commonly used stabilizers in the art are applicable. The stabilizer may be triphenylphosphine and / or benzoyl chloride. For example, based on a total mass fraction of 100 parts of polymer polyol and diisocyanate, the mass fraction of stabilizer is 0.005-0.02 parts (e.g., 0.005 parts, 0.007 parts, 0.008 parts, 0.01 parts, 0.012 parts, 0.014 parts, 0.016 parts, 0.018 parts, or 0.02 parts, etc.). Those skilled in the art can adjust the amount according to actual experimental conditions.

[0081] Unless otherwise specified, all numerical values ​​representing components, reaction conditions or defined component parameters in this document shall in all cases be understood as approximate measurements, such as an approximation of 80.1°C as 80°C.

[0082] The reactant component information and component sources in the following examples and comparative examples are shown in Table 1 below: Table 1 The test method for the NCO content in intermediate 2 obtained by step (2) of the closed polyurethane prepolymer provided in the following examples and comparative examples is as follows: Refer to Chapter 13, Section 13.1.4 of "Polyurethane Resins and Their Applications" for the NCO content in prepolymer and trace NCO content in crosslinked elastomer. When conducting the test, take 10g of the sample to be tested. The viscosity test method for closed polyurethane prepolymer is as follows: using an LVT dial viscometer from Brookfield Instruments, USA, rotor size 4 / 64, rotation speed 12 rpm; Judgment of the degree of curing of the closed polyurethane resin composition: Refer to the method described in GB / T 1040.3-2006, use the Shimadzu AGS-X electronic universal testing machine to conduct tensile tests, determine the 100% elastic modulus (E) of the sample, and the tensile rate for determining the 100% elastic modulus is 2 mm / min. Where: F—force in the elongation direction (N); S—cross-sectional area (mm²) 2 L—gauge length (mm); —Elongation (mm), 100% modulus of elasticity refers to ; The method for judging the degree of curing is as follows: Place the test sample at 145℃ for 1 minute, re-measure 100% of the elastic modulus, calculate the deviation value, and if the deviation is less than 5%, it is considered to be fully cured; otherwise, it is judged to be not fully cured.

[0083] Example 1 This embodiment provides a blocked polyurethane resin composition and its curing method. The blocked polyurethane resin composition includes a blocked polyurethane prepolymer (100 parts by weight) and 3,3-diethyl-4,4-diaminodiphenylmethane (8 parts by weight). The molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in 3,3-diethyl-4,4-diaminodiphenylmethane is 1:1. The raw materials for preparing the closed polyurethane prepolymer include polymeric polyol, XD1, synergist 1, blocking agent, activator, and stabilizer; based on the mass percentage of polymeric polyol being 100%, the polymeric polyol includes the following components in mass percentage: 82% polypropylene glycol, 13% polyphenylene ether glycol, 5% polyhydrogenated butadiene glycol 1; and diisocyanate XDI. The above-mentioned closed-cell polyurethane prepolymer was prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol (100 g), synergist 1 (1.2 g), and stabilizer (10 mg) at 60 °C, XDI (16.8 g) was added to it, and after reacting at 92 °C for 2 h, the temperature was lowered to 50 °C to obtain intermediate 1; (2) Add 10 mg of activator to intermediate 1 obtained in step (1), react at 85 °C until the NCO content is 2.8 wt% (measured value, the same below), stop the reaction, cool down to 50 °C, and obtain intermediate 2 with NCO content of 2.8 wt%; (3) Add blocking agent (7.6 g) to intermediate 2 obtained in step (2), and carry out end-capping reaction at 70°C until the NCO content is 0 wt%, and stop the reaction to obtain the blocked polyurethane prepolymer; The content of blocked NCO groups in the blocked polyurethane prepolymer is 2.6 wt% (calculated based on the NCO content of intermediate 1, the same below); the viscosity of the blocked polyurethane prepolymer at 25°C is 7.1 × 10⁻⁶. 4 cps.

[0084] The curing method for the closed-cell polyurethane resin composition provided in this embodiment is as follows: After uniformly mixing the blocked polyurethane prepolymer and 3,3-diethyl-4,4-diaminodiphenylmethane, the mixture was coated onto release paper with a coating thickness of 0.2 mm. The mixture was then cured at 140 °C for 6 min to complete the curing of the blocked polyurethane resin composition, resulting in a fully cured test sample.

[0085] Example 2 This embodiment provides a blocked polyurethane resin composition and its curing method. The blocked polyurethane resin composition comprises (100 parts by weight) and 3,3-diethyl-4,4-diaminodicyclohexylmethane (6.5 parts by weight). The molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent is 0.9:1. The raw materials for preparing the closed polyurethane prepolymer include polymeric polyol, diisocyanate, synergist 1, blocking agent, activator, and stabilizer; based on the polymeric polyol's mass percentage of 100%, the polymeric polyol comprises the following components in mass percentage: 58% polypropylene glycol, 30% polytetrahydrofuran ether glycol, 10% polyphenylene ether glycol, and 2% polyhydrobutadiene glycol 1; the diisocyanate is XDI; The above-mentioned closed-cell polyurethane prepolymer was prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol (100 g), synergist 1 (1.2 g) and stabilizer (10 mg) at 65 °C, XDI (15.1 g) was added to it, and after reacting at 95 °C for 1.5 h, the temperature was lowered to 55 °C to obtain intermediate 1; (2) Add 10 mg of activator to intermediate 1 obtained in step (1), react at 80 °C until the NCO content is 2.2 wt%, stop the reaction, cool down to 55 °C, and obtain intermediate 2 with NCO content of 2.2 wt%; (3) Add a blocking agent (5.8 g) to intermediate 2 obtained in step (2), and carry out the end-capping reaction at 80°C until the NCO content is 0 wt%, and stop the reaction to obtain the blocked polyurethane prepolymer; The content of blocked NCO groups in the blocked polyurethane prepolymer is 2.1 wt%; the viscosity of the blocked polyurethane prepolymer at 25°C is 8.3 × 10⁻⁶. 4 cps.

[0086] The curing method for the closed-cell polyurethane resin composition provided in this embodiment is as follows: After uniformly mixing the blocked polyurethane prepolymer and 3,3-diethyl-4,4-diaminodicyclohexylmethane, the mixture was coated onto release paper with a coating thickness of 0.1 mm. The mixture was then cured at 160 °C for 5 min to complete the curing of the blocked polyurethane resin composition, resulting in a fully cured test sample.

[0087] Example 3 This embodiment provides a blocked polyurethane resin composition and its curing method. The blocked polyurethane resin composition includes a blocked polyurethane prepolymer (100 parts by weight) and 4,4-diaminodiphenylmethane (4.9 parts by weight). The molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent is 1:0.9. The raw materials for preparing the closed polyurethane prepolymer include polymeric polyol, diisocyanate, synergist 2, blocking agent, activator, and stabilizer; based on the polymeric polyol's mass percentage of 100%, the polymeric polyol includes the following components in mass percentage: 77% polytetrahydrofuran ether diol, 20% polyphenylene ether diol, and 3% polyhydrobutadiene diol 2; the diisocyanate is XDI; The above-mentioned closed-cell polyurethane prepolymer was prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol (100 g), synergist 2 (3.5 g) and stabilizer (10 mg) at 62 °C, XDI (15.8 g) was added to it, and the mixture was reacted at 90 °C for 2.5 h. Then the temperature was lowered to 50 °C to obtain intermediate 1. (2) Add 10 mg of activator to intermediate 1 obtained in step (1), react at 85°C until the NCO content is 2.4 wt%, stop the reaction, cool down to 50°C, and obtain intermediate 2 with NCO content of 2.4 wt%; (3) Add a blocking agent (6.6 g) to intermediate 2 obtained in step (2), and carry out the end-capping reaction at 60°C until the NCO content is 0 wt%, and stop the reaction to obtain the blocked polyurethane prepolymer; The content of blocked NCO groups in the blocked polyurethane prepolymer is 2.3 wt%; the viscosity of the blocked polyurethane prepolymer at 25°C is 9.5 × 10⁻⁶. 4 cps.

[0088] The curing method for the closed-cell polyurethane resin composition provided in this embodiment is as follows: After uniformly mixing the blocked polyurethane prepolymer and 4,4-diaminodiphenylmethane, the mixture was coated onto release paper with a coating thickness of 0.3 mm. The mixture was then cured at 180°C for 8 min to complete the curing of the blocked polyurethane resin composition, resulting in a fully cured test sample.

[0089] Example 4 This embodiment provides a blocked polyurethane resin composition and its curing method. The blocked polyurethane resin composition includes a blocked polyurethane prepolymer (100 parts by weight) and 4,4-diaminodiphenylmethane (6.2 parts by weight). The molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent is 1:1. The raw materials for preparing the blocked polyurethane prepolymer include polymeric polyol, diisocyanate, synergist 2, blocking agent, activator, and stabilizer; based on the polymeric polyol's mass percentage of 100%, the polymeric polyol comprises the following components in mass percentage: 81% polypropylene glycol, 15% polyphenylene ether glycol, 1% polyhydrogenated butadiene glycol 1, and 3% polyhydrogenated butadiene glycol 2; the diisocyanate is XDI; The above-mentioned closed-cell polyurethane prepolymer was prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol (100 g), synergist 2 (0.6 g) and stabilizer (10 mg) at 60 °C, XDI (16.6 g) was added to it, and after reacting at 92 °C for 2 h, the temperature was lowered to 50 °C to obtain intermediate 1; (2) Add 10 mg of activator to intermediate 1 obtained in step (1), react at 85 °C until the NCO content is 2.8 wt%, stop the reaction, cool down to 50 °C, and obtain intermediate 2 with NCO content of 2.8 wt%; (3) Add a blocking agent (7.5 g) to intermediate 2 obtained in step (2), and carry out the end-capping reaction at 70°C until the NCO content is 0 wt%, and stop the reaction to obtain the blocked polyurethane prepolymer; The content of blocked NCO groups in the blocked polyurethane prepolymer is 2.6 wt%; the viscosity of the blocked polyurethane prepolymer at 25°C is 8.6 × 10⁻⁶. 4 cps.

[0090] The curing method for the closed-cell polyurethane resin composition provided in this embodiment is as follows: After uniformly mixing the blocked polyurethane prepolymer and 4,4-diaminodiphenylmethane, the mixture was coated onto release paper with a coating thickness of 0.3 mm. The mixture was then cured at 200 °C for 4 min to complete the curing of the blocked polyurethane resin composition and obtain the test sample.

[0091] Example 5 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: Replacing all 5% of the polyhydrogenated butadiene glycol 1 with polypropylene glycol; the resulting closed-cell polyurethane prepolymer had a viscosity of 7.7 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0092] Compared to Example 1, Example 5 did not use polyhydrogenated butadiene glycol in the polymer polyol used to prepare the blocked polyurethane prepolymer, resulting in poorer low-temperature flexural strength of the blocked polyurethane resin composition.

[0093] Example 6 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The polymer polyol comprises the following components in weight percentage: 85% polypropylene glycol, 10% polyphenylene ether glycol, and 5% polyhydrogenated butadiene glycol; the resulting closed-cell polyurethane prepolymer has a viscosity of 6.4 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0094] Example 7 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The polymer polyol comprises the following components in weight percentage: 75% polypropylene glycol, 20% polyphenylene ether glycol, and 5% polyhydrogenated butadiene glycol; the resulting closed-cell polyurethane prepolymer has a viscosity of 7.8 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0095] Example 8 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The blocked polyurethane resin composition comprises a blocked polyurethane prepolymer (100 parts by weight) and 3,3-diethyl-4,4-diaminodiphenylmethane (8.9 parts by weight), such that the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in 3,3-diethyl-4,4-diaminodiphenylmethane is 0.9:1. Other conditions are the same as in Example 1.

[0096] Example 9 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The blocked polyurethane resin composition comprises a blocked polyurethane prepolymer (100 parts by weight) and 3,3-diethyl-4,4-diaminodiphenylmethane (7.2 parts by weight), such that the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in 3,3-diethyl-4,4-diaminodiphenylmethane is 1:0.9. Other conditions are the same as in Example 1.

[0097] Example 10 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The curing method of the closed polyurethane resin composition provided in this embodiment is as follows: curing at 140°C for 4 min to complete the curing of the closed polyurethane resin composition and obtain a fully cured test sample. Other conditions are the same as in Example 1.

[0098] Example 11 This embodiment provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The curing method of the closed polyurethane resin composition provided in this embodiment is as follows: curing at 200°C for 10 min to complete the curing of the closed polyurethane resin composition and obtain a fully cured test sample. Other conditions are the same as in Example 1.

[0099] Comparative Example 1 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: Two percent of polypropylene oxide glycol was replaced with polyhydrogenated butadiene glycol 1, meaning the polymer polyol comprised the following components by mass percentage: 80% polypropylene oxide glycol, 13% polyphenylene ether glycol, and 7% polyhydrogenated butadiene glycol 1; the resulting closed-cell polyurethane prepolymer had a viscosity of 6.2 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0100] Compared with Example 1, Comparative Example 1 used too much polyhydrogenated butadiene glycol in the polymer polyol used to prepare the blocked polyurethane prepolymer. Although this improved the low-temperature flexural strength of the blocked polyurethane resin composition, it also made the gloss of the blocked polyurethane resin composition extremely poor.

[0101] Comparative Example 2 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The 6% polyphenylene ether glycol was replaced with polypropylene oxide glycol, meaning the polymer polyol comprised the following components by mass percentage: 88% polypropylene oxide glycol, 7% polyphenylene ether glycol, and 5% polyhydrogenated butadiene glycol; the resulting closed-cell polyurethane prepolymer had a viscosity of 6.0 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0102] Compared with Example 1, Comparative Example 2 used too little polyphenylene ether diol in the polymer polyol used to prepare the blocked polyurethane prepolymer, resulting in a decrease in the gloss of the blocked polyurethane resin composition.

[0103] Comparative Example 3 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: 12% of polypropylene oxide glycol was replaced with polyphenylene ether glycol, meaning the polymer polyol comprised the following components by mass percentage: 70% polypropylene oxide glycol, 25% polyphenylene ether glycol, and 5% polyhydrogenated butadiene glycol; the resulting closed-cell polyurethane prepolymer had a viscosity of 8.2 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0104] Compared with Example 1, Comparative Example 3 used too much polyphenylene ether diol in the polymer polyol used to prepare the blocked polyurethane prepolymer, which led to the deterioration of the low-temperature flexural strength of the blocked polyurethane resin composition.

[0105] Comparative Example 4 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The polyphenylene ether glycol was completely replaced with polypropylene oxide glycol, meaning the polymer polyol comprised the following components by mass percentage: 95% polypropylene oxide glycol and 5% polyhydrogenated butadiene glycol 1; the resulting closed-cell polyurethane prepolymer had a viscosity of 4.3 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0106] Compared with Example 1, Comparative Example 4 did not use polyphenylene ether glycol in the polymer polyol used to prepare the blocked polyurethane prepolymer, which resulted in a serious deterioration of the gloss of the blocked polyurethane resin composition.

[0107] Comparative Example 5 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The diisocyanate is composed of XDI and HDI (hexamethylene diisocyanate) in a mass ratio of 95:5; the resulting blocked polyurethane prepolymer has a viscosity of 4.7 × 10⁻⁶ at 25°C. 4 cps; Other conditions are the same as in Example 1.

[0108] Compared with Example 1, Comparative Example 5 used a mixture of XDI and HDI to prepare a blocked polyurethane prepolymer. It was found that the introduction of small amounts of other isocyanates would interfere with the polymerization of XDI residues with polyphenylene ether glycol residues, resulting in a decrease in the gloss of the blocked polyurethane resin composition.

[0109] Comparative Example 6 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The diisocyanate is TDI (toluene diisocyanate); the viscosity of the prepared blocked polyurethane prepolymer at 25°C is 3.2 × 10⁻⁶. 4 cps; Other conditions are the same as in Example 1.

[0110] Compared with Example 1, Comparative Example 6 uses a mixture of TDI to prepare a blocked polyurethane prepolymer. Due to the conjugation effect between the benzene ring and NCO in TDI, the blocked polyurethane resin composition has poor resistance to yellowing.

[0111] As can be seen from the comparison of Comparative Examples 5, 6 and Example 1, the present invention, through the synergistic effect of polyphenylene ether glycol and XDI, can prepare a closed polyurethane prepolymer with low shrinkage characteristics with only a small amount of polyphenylene ether glycol. Finally, a closed polyurethane resin composition with excellent yellowing resistance, high gloss and good low-temperature flexural strength was prepared.

[0112] Comparative Example 7 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The blocked polyurethane resin composition comprises a blocked polyurethane prepolymer (100 parts by weight) and 3,3-diethyl-4,4-diaminodiphenylmethane (10 parts by weight), such that the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in 3,3-diethyl-4,4-diaminodiphenylmethane is 0.8:1. Other conditions were the same as in Example 1. After the closed polyurethane resin composition was cured, the test sample was not completely cured.

[0113] Comparative Example 8 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The blocked polyurethane resin composition comprises a blocked polyurethane prepolymer (100 parts by weight) and 3,3-diethyl-4,4-diaminodiphenylmethane (6.4 parts by weight), such that the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in 3,3-diethyl-4,4-diaminodiphenylmethane is 1:0.8. Other conditions were the same as in Example 1. After the closed polyurethane resin composition was cured, the test sample was not completely cured.

[0114] Compared with Comparative Examples 7 and 8, if the molar ratio of the blocked NCO group in the blocked polyurethane prepolymer to the amino group in 3,3-diethyl-4,4-diaminodiphenylmethane is not within the range of 0.9:1-1:0.9, the blocked polyurethane resin composition cannot reach the ideal degree of curing during the subsequent curing process, resulting in poor surface smoothness and poor gloss of the polyurethane material made from the blocked polyurethane resin composition.

[0115] Comparative Example 9 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The curing method for the closed polyurethane resin composition provided in this comparative example is as follows: curing at 110°C for 12 min; Other conditions were the same as in Example 1. After the closed polyurethane resin composition was cured, the test sample was not completely cured.

[0116] Compared with Comparative Example 9 and Example 1, if the temperature of the blocked polyurethane resin composition is too low during the curing process, even if the curing time is extended, the ideal degree of curing cannot be achieved, resulting in poor gloss and poor low-temperature flexural resistance of the blocked polyurethane resin composition.

[0117] Comparative Example 10 This comparative example provides a closed-type polyurethane resin composition and its curing method, which differs from Example 1 in that: The curing method for the closed polyurethane resin composition provided in this comparative example is: curing at 220°C for 6 min; Other conditions were the same as in Example 1. After the closed polyurethane resin composition was cured, the test sample was not completely cured.

[0118] Compared with Comparative Example 10 and Example 1, if the temperature of the blocked polyurethane resin composition is too high during the curing process, the blocked polyurethane resin composition will not be able to reach the ideal degree of curing, resulting in poor gloss, poor yellowing resistance, and poor low-temperature flexural resistance of the blocked polyurethane resin composition.

[0119] The performance of the blocked polyurethane resin compositions or test samples provided in the above embodiments and comparative examples was tested, and the specific test methods are as follows: Gloss: Standard test according to GB / T 8807-1988 "Test Method for Specular Gloss of Plastics", 20° angle, unit GU; Yellowing resistance rating: Tested by irradiation with two 15W UVB ultraviolet lamps for 4 hours, and the rating is determined according to GB / T 250-2008 "Textiles - Tests for Color Fastness - Assessment of Color Change - Gray Scale". Low-temperature flexural resistance: tested using a GOTECH vertical cold resistance testing machine, model GT-7006-V50; The performance test results are shown in Table 2 below: Table 2 As can be seen from the above, this invention, through the design of the raw materials for preparing the closed polyurethane prepolymer, and the combined effect of specific amounts of polyphenylene ether glycol and XDI, completes the design of the polyurethane molecular chain structure, resulting in a closed polyurethane resin composition that has both good resistance to yellowing and high gloss, as well as good low-temperature resistance.

[0120] This invention designs the molecular chain structure of a blocked polyurethane prepolymer by synergistic effects of polyphenylene ether glycol (PPE) and XDI, and by controlling the amount of PPE within a specific range. Simultaneously, this invention controls the molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent within a specific range in the blocked polyurethane resin composition. Furthermore, by optimizing the curing process parameters of the blocked polyurethane resin composition, an ideal degree of curing can be achieved during the curing process, resulting in a blocked polyurethane resin composition with excellent overall performance.

[0121] The applicant declares that the detailed process flow of this invention is illustrated by the above embodiments, but this invention is not limited to the above detailed process flow, that is, it does not mean that this invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of raw materials for the product of this invention, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A blocked polyurethane resin composition, characterized in that, The blocked polyurethane resin composition includes a blocked polyurethane prepolymer and an amine curing agent; The molar ratio of the blocked NCO groups in the blocked polyurethane prepolymer to the amino groups in the amine curing agent is 0.9:1 to 1:0.

9. The raw materials for preparing the closed polyurethane prepolymer include polymeric polyol, diisocyanate, synergist, and blocking agent; The polymer polyol includes aliphatic polyether polyol and polyphenylene ether diol. Based on the polymer polyol's mass percentage content of 100%, the aliphatic polyether polyol's mass percentage content is ≥75%, and the polyphenylene ether diol's mass percentage content is 10-20%. The diisocyanate is m-phenylenedimethyl diisocyanate.

2. The blocked polyurethane resin composition according to claim 1, characterized in that, The amine curing agent includes any one or a combination of at least two of 3,3-diethyl-4,4-diaminodiphenylmethane, 4,4-diaminodiphenylmethane, and 3,3-dimethyl-4,4-diaminodicyclohexylmethane.

3. The blocked polyurethane resin composition according to claim 1 or 2, characterized in that, The polymer polyol also includes hydrogenated butadiene glycol; Preferably, the mass percentage of the polyhydrogenated butadiene glycol is 2-5%, based on a polymer polyol mass percentage of 100%.

4. The blocked polyurethane resin composition according to any one of claims 1-3, characterized in that, The raw materials for preparing the closed-type polyurethane prepolymer also include stabilizers and activators.

5. The blocked polyurethane resin composition according to any one of claims 1-4, characterized in that, The content of blocked NCO groups in the blocked polyurethane prepolymer is 2.1-2.6 wt%; Preferably, the viscosity of the closed-cell polyurethane prepolymer at 25°C is 4.0 × 10⁻⁶. 4 -1.0×10 5 cps.

6. The blocked polyurethane resin composition according to any one of claims 1-5, characterized in that, The closed-cell polyurethane prepolymer is prepared by the following method, which includes the following steps: (1) After mixing the polymer polyol, synergist and stabilizer, diisocyanate is added to it and reacted to obtain intermediate 1; (2) Add an activator to intermediate 1 obtained in step (1), react, and obtain intermediate 2; (3) Add a blocking agent to the intermediate 2 obtained in step (2) to carry out the end-capping reaction and obtain the blocked polyurethane prepolymer.

7. The blocked polyurethane resin composition according to claim 6, characterized in that, The mixing temperature in step (1) is 60-65℃; Preferably, the reaction in step (1) is carried out at a temperature of 90-95°C for 1-3 hours. Preferably, the reaction in step (1) further includes a post-processing step, wherein the post-processing method includes cooling to below 60°C; Preferably, the reaction temperature in step (2) is 80-85℃; Preferably, the content of NCO groups in intermediate 2 is 2.2-2.8 wt%; Preferably, the reaction in step (2) further includes a post-processing step, wherein the post-processing method includes cooling to below 60°C; Preferably, the temperature of the end-capping reaction in step (3) is 60-80℃; Preferably, the NCO group content in the closed polyurethane prepolymer obtained in step (3) is 0 wt%.

8. A method for curing the blocked polyurethane resin composition according to any one of claims 1-7, characterized in that, The curing method includes the following steps: The blocked polyurethane prepolymer and amine curing agent are mixed and cured to complete the curing of the blocked polyurethane resin composition.

9. The curing method according to claim 8, characterized in that, The curing temperature is 140-200℃ and the time is ≥4 min.

10. A closed-cell polyurethane prepolymer, characterized in that, The blocked polyurethane prepolymer is used to prepare the blocked polyurethane resin composition according to any one of claims 1-5; The blocked polyurethane prepolymer includes polymer polyol residues, diisocyanate residues, synergist residues, and blocking agent residues; The raw materials for preparing the blocked polyurethane prepolymer include polymeric polyols, diisocyanates, synergists, and blocking agents; the polymeric polyols include aliphatic polyether polyols and polyphenylene ether glycols, with the mass percentage of the polymeric polyols being 100%, the mass percentage of the aliphatic polyether polyols being ≥75%, and the mass percentage of the polyphenylene ether glycols being 10-20%; the diisocyanate includes isophthalic diisocyanate. Preferably, the polymeric polyol further includes hydrogenated butadiene glycol; Preferably, based on a polymer polyol content of 100%, the mass percentage content of the hydrogenated butadiene glycol is 2-5%. Preferably, the content of blocked NCO groups in the blocked polyurethane prepolymer is 2.1-2.6 wt%; Preferably, the viscosity of the closed-cell polyurethane prepolymer at 25°C is 4.0 × 10⁻⁶. 4 -1.0×10 5 cps.

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