Low-humidity sensitive reactive foaming polyurethane resin and preparation method thereof

Abstract

The invention relates to the field of polyester, and discloses low-humidity sensitive reactive foaming polyurethane resin and a preparation method thereof. The foaming polyurethane resin comprises the following raw materials, the component A comprises the following components in parts by weight: 40-50 parts of polyether polyol, 2-10 parts of a chain extender, 0.1-1 part of a tin amine compound catalyst and 0.05-1 part of water; the tin amine compound catalyst is prepared from DBTDL and DABCO according to the weight ratio of 1 to (0.8 to 1.2); and the component B comprises the following components in parts by weight: 25-35 parts of isocyanate, 10-20 parts of polyether polyol and 0.5-3 parts of a cross-linking agent. According to the invention, through active intervention of environment humidity and temperature, by utilizing a synergistic effect of compounding of specific types and specific proportions of tin amine catalysts, dynamic balance of a foaming reaction and a gel reaction is directly realized in a surface area, and generation of defects such as surface cell rupture and collapse is inhibited from the source; therefore, the foamed polyurethane which is narrow in cell size distribution and has a natural flat and smooth surface is obtained, and meanwhile, a foundation is provided for processing and production of the foamed polyurethane in a high-humidity environment and maintenance of relatively good comprehensive performance of the foamed polyurethane.

Description

Technical Field

[0001] This invention relates to the field of polyester, and more particularly to a low-humidity-sensitive reactive foamed polyurethane resin and its preparation method. Background Technology

[0002] Driven by the "dual carbon" objective, reactive polyurethane (RPU) provides crucial support for the green transformation of automotive leather through solvent-free film-forming processes and superior material properties. As market demands evolve, consumers are increasingly seeking higher-performance and more diverse solvent-free microfiber leather products. Foaming technology has become a key method for improving the lightweight, breathability, fullness, and feel of microfiber leather.

[0003] The foaming technology of polymer coatings is generally divided into physical foaming and chemical foaming. Physical foaming typically includes supercritical fluid foaming and thermally expanding microsphere foaming; the former requires specialized foaming equipment, while the latter is too expensive to be widely used. Chemical foaming is more promising and has a wider range of applications compared to physical foaming. Water, as a chemical foaming agent, has an ODP value of zero and a global warming potential (GWP) value of 1. Its foaming process is simple, suitable for scale-up production, and existing equipment can meet the processing requirements. It is an environmentally friendly, economical, and practical foaming agent.

[0004] Traditional water-blown polyurethane foam is typically foamed at low temperatures (15℃-30℃) and low humidity. However, when foaming in high temperature or high humidity environments, the surface gel and foaming reaction are easily out of balance. Especially when using amine catalysts alone, defects such as cell merging or even rupture, depressions, high open-cell ratio, roughness, and wide cell size distribution are prone to occur on the surface. Surface improvement usually relies on post-processing such as sanding, coating, film coating, or the use of expensive surfactants or additives, but this will significantly increase costs, processes, and waste. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a low-humidity-sensitive reactive foamed polyurethane resin and its preparation method. By actively intervening in environmental humidity and temperature, this invention utilizes the synergistic effect of a specific type and proportion of tinamine catalyst compounded during the critical early stages of the foaming reaction—the rising and skin formation stages—to directly achieve a dynamic balance between the foaming and gelation reactions in the surface region. This suppresses defects such as surface cell rupture and collapse from the source, resulting in foamed polyurethane with a narrow cell size distribution and a naturally smooth surface. This significantly reduces or even eliminates the need for post-processing and provides a foundation for the processing and production of foamed polyurethane in high-humidity environments while maintaining good overall performance.

[0006] The specific technical solution of this invention is as follows:

[0007] First, this invention provides a low-humidity-sensitive reactive foamed polyurethane resin, which has a smooth and flat surface and a cell size of 50~200μm; its raw materials include component A and component B in a weight ratio of 100:90~97. Wherein, by weight:

[0008] Component A comprises: 40-50 parts of polyether polyol, 2-10 parts of small molecule chain extender, 0.1-1 parts of tinamine compound catalyst, and 0.05-1 parts of water.

[0009] Component B is an isocyanate-terminated prepolymer, comprising: 25-35 parts isocyanate, 10-20 parts polyether polyol, and 0.5-3 parts crosslinking agent.

[0010] As described in the background section, physical foaming technology for polymer coatings often cannot be industrialized due to the need for specialized foaming equipment or its high cost. In chemical foaming technology, traditional water-foamed polyurethane typically foams under low temperature (15℃-30℃) and low humidity conditions. The applicant has found that foaming under high temperature or high humidity conditions can easily lead to an imbalance between surface gel and foaming reaction. In particular, when using amine catalysts alone, defects such as cell merging or even rupture, depressions, high open-cell ratio, roughness, and wide cell size distribution are prone to appear on the surface. Surface improvement usually relies on post-processing such as sanding, coating, film coating, or the use of expensive surfactants or additives, which will significantly increase costs, processes, and waste.

[0011] Therefore, this invention discovers that by selecting specific types of tin-based catalysts and amine-based catalysts and combining them, a dynamic balance between the foaming and gelation reactions can be directly achieved on the surface during the critical early stages of the foaming reaction, namely the rise phase and the skin formation phase. This suppresses defects such as surface cell rupture and collapse from the source, resulting in a foamed polyurethane coating with a naturally smooth surface and a narrow cell size distribution (50~200μm), greatly reducing or even eliminating the need for post-processing. Simultaneously, this provides the possibility for RPU to be processed and produced in high-humidity environments while maintaining good overall performance.

[0012] Preferably, the tinamine composite catalyst is DBTDL (dibutyltin dilaurate) and DABCO (1,4-diazabicyclo[2.2.2]octane) in a weight ratio of 1:(0.8-1.2).

[0013] This invention employs a composite catalyst composed of a tin-based catalyst and an amine-based catalyst. Compared to using a single tin-based catalyst or an amine-based catalyst, the prepared foamed polyurethane resin exhibits lower humidity sensitivity and a more naturally smooth surface. Specifically, by using a composite catalyst of a tin-based catalyst and an amine-based catalyst, some lone pair electrons from the N atoms in DABCO fill the empty orbitals of the Sn atoms in DBTDL, forming an N:→Sn coordinate bond and generating an active complex. This complex can alter the selectivity for water and -OH groups in polyols, making it more tolerant of the presence of water than pure DBTDL. When using only DBTDL catalyst, hydrogen bonds gradually form between water molecules and -OH groups, reducing the number of active -OH groups and further slowing down the polyurethane reaction rate. However, when DBTDL is composited with DABCO, the formation of hydrogen bonds is weakened, thus enhancing the effectiveness of DBTDL and reducing its sensitivity to water in high humidity environments. Some free DABCO molecules also possess strong foaming catalytic capabilities. When the ambient humidity increases slightly and a small amount of additional ambient moisture is introduced, the foaming reaction triggered by them is integrated into the main reaction without causing the reaction to run away from control. Its naturally smooth surface and uniform pores are due to the fact that bubbles can nucleate simultaneously and grow stably at similar speeds, which can greatly reduce or even eliminate the need for post-processing.

[0014] Furthermore, this invention has discovered that not all combinations of tin-based catalysts and amine catalysts, regardless of type or ratio, can achieve the aforementioned technical effects; only DBTDL and DABCO exhibit the ideal combination effect. This is because when DBTDL and DABCO catalysts are combined in the aforementioned ratio, the lone pair electrons on the N atom in DABCO can fill the empty orbitals of the Sn atom in DBTDL, forming an N:→Sn coordinate bond, generating a stable active complex. Moreover, the disruption of the bridging bond between the tin atom and the carboxylate ion during the formation of the coordinate bond exposes the long-chain fatty acid anions, whose long carbon chains provide a hydrophobic microenvironment, further reducing sensitivity to water. For other tin-amine catalyst combinations, such as DBTDA combined with tribenzylamine or N,N-dimethyl-p-toluidine, the acetate ion is more easily hydrolyzed or replaced. Furthermore, the high steric hindrance of tribenzylamine or the monodentate structure of N,N-dimethyl-p-toluidine makes it difficult to form stable tin-amine complexes. Similarly, when stannous octoate is combined with tribenzylamine or N,N-dimethyl-p-toluidine, it is easily oxidized and deactivated by water and oxygen. The high steric hindrance of tribenzylamine or the monodentate structure of N,N-dimethyl-p-toluidine further hinders the formation of stable tin-amine complexes. In fact, these tin-amine catalyst combinations, lacking effective coordination bonds, primarily function as independent catalysts.

[0015] If the proportion of DBTDL is too high, the system will tend to gel, resulting in fewer bubble nuclei, limited growth space, small and dense pores, and a high susceptibility to defects caused by external moisture, leading to poor uniformity. Conversely, if the proportion of DABCO is too high, the foaming will be too vigorous, the bubble nuclei size will be unstable, and they will easily merge into large bubbles, causing the internal pores to collapse.

[0016] Preferably, the polyether polyol has a molecular weight of 600-5000 and is selected from one or more of polytetrahydrofuran diol, polypropylene glycol, and polycarbonate diol.

[0017] Preferably, the small molecule chain extender is selected from one or more of 1,4-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, neopentanediol, diethylene glycol, dipropylene glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethylhydroquinone bis(2-hydroxyethyl) ether.

[0018] Preferably, the NCO content in the isocyanate-terminated prepolymer is 20-30%.

[0019] Preferably, the isocyanate is selected from one or more of aliphatic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, and aromatic diisocyanates.

[0020] Preferably, the crosslinking agent is selected from one or more triols such as trimethylolpropane and glycerol.

[0021] Secondly, this invention provides a method for preparing a low-humidity-sensitive reactive foamed polyurethane resin, which includes the following steps:

[0022] 1) Mix the dehydrated polyether polyol and small molecule chain extender evenly to obtain component A.

[0023] 2) The isocyanate, crosslinking agent and dehydrated polyether polyol are stirred and reacted under an inert atmosphere to obtain component B, which is then cooled to 20-30℃ for later use.

[0024] 3) Mix and stir component B and component A to form a mixed resin.

[0025] 4) Pour the mixed resin onto the substrate surface, cure and foam it under constant temperature and humidity conditions, and after drying and peeling, obtain a reactive polyurethane resin with low humidity sensitivity; the constant temperature and humidity environment is selected from one of the following temperature and humidity combinations: 75-85℃+25-35%, 75-85℃+55-65%, or 20-30℃+55-65%.

[0026] This invention utilizes different humidity conditions and selects the aforementioned temperatures for foaming, primarily relying on a near 1:1 mass ratio of DBTDL to DABCO. In this case, DABCO is in excess, and a portion of the DABCO forms an active complex with DBTDL, altering its selectivity for water and -OH groups in the polyol. This makes it more tolerant of water than pure DBTDL. The remaining free DABCO molecules possess strong foaming catalytic capabilities. When the amount of water used increases or the ambient humidity slightly rises during foaming, introducing a small amount of additional ambient moisture, the resulting foaming reaction is integrated into the main reaction without causing runaway. The naturally smooth surface and uniform cell structure result from the simultaneous nucleation of bubbles and their stable growth at similar rates, significantly reducing or even eliminating the need for post-processing. Preferably, the dehydration treatment involves vacuum dehydrating the polyether polyol at 90-110°C for 10-15 hours, followed by cooling to 20-30°C for later use.

[0027] Preferably, in step 2), the conditions for the stirring reaction are: temperature 70-90℃, stirring speed 100-500rpm, and time 1-3h.

[0028] Preferably, in step 3), the mixing conditions are: temperature 20-30℃, relative humidity 25-35%, stirring speed 500-1500rpm, and time 20-40s.

[0029] Stirring components A and B under low humidity conditions can suppress the side reaction between the isocyanate-based prepolymer of component B and water, ensure the initial viscosity stability of the system, prevent the premature formation of bubble nuclei, and provide a uniform reaction matrix for the subsequent foaming of polyurethane resin.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) By actively intervening in environmental humidity and temperature, the present invention utilizes the synergistic effect of specific types and proportions of tinamine catalysts to achieve a dynamic balance between the foaming reaction and the gelation reaction in the surface area during the critical early stage of the foaming reaction, namely the rising stage and the skin formation stage. This suppresses the generation of defects such as surface cell rupture and collapse from the source, thereby obtaining foamed polyurethane with narrow cell size distribution and a naturally flat and smooth surface. This greatly reduces or even eliminates the need for post-processing, and at the same time provides a foundation for the processing and production of foamed polyurethane in high humidity environments and maintaining good comprehensive performance.

[0032] (2) This invention is a solvent-free system with no VOC emissions. It uses water to replace physical foaming agents such as fluoroalkanes (HFCs) and hydrofluoroolefins (HFOs). The ODP value is zero and the global warming potential (GWP) value is 1. The foaming process is simple and existing equipment can meet the production requirements. It is an environmentally friendly, economical and practical foaming method. Attached Figure Description

[0033] Figure 1 Optical microscope images of the in-situ foaming cross sections of RPU resin in Examples 1(a) and 2(b) and Comparative Examples 1(c), 2(d) and 5(ef) of the present invention under the same surface humidity and temperature, different catalysts and water amounts.

[0034] Figure 2 These are optical microscope images of the in-situ foamed surfaces of RPU resin in Examples 2-4 (ac) and Comparative Examples 2-4 (df) of the present invention under the same water volume, different catalysts, surface humidity and temperature conditions.

[0035] Figure 3 Optical images of the in-situ foamed surfaces of RPU resin in Examples 2-4 (ac) and Comparative Examples 2-4 (df) of the present invention under the same water volume, different catalysts, surface humidity and temperature conditions;

[0036] Figure 4 These are optical microscope images of the in-situ foaming cross sections of RPU resin in Comparative Examples 6(a) and 7(b) of the present invention under the same water volume, temperature and surface humidity, and different proportions of tin amine catalyst.

[0037] Figure 5 These are optical microscope images of the in-situ foaming cross sections of RPU resin in Comparative Examples 8(a), 9(b), 10(c), and 11(d) of the present invention under the same water volume, temperature, and surface humidity, and with different types of tin amine 1:1 catalysts. Detailed Implementation

[0038] The present invention will be further illustrated below through several specific embodiments. However, it should be noted that the specific material ratios, process conditions and results described in the embodiments of the present invention are only for illustrating the present invention and cannot be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0039] Example 1

[0040] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0041] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0042] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0043] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of compound catalyst (DBTDL and DABCO with a mass ratio of 1:1) and 0.05 parts of water. Stir at 1000r / min for 30s to form a mixed resin.

[0044] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0045] Example 2

[0046] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0047] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0048] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0049] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 part of compound catalyst (DBTDL and DABCO at a mass ratio of 1:1) and 0.1 part of water. Stir at 1000r / min for 30s to form a mixed resin.

[0050] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0051] Example 3

[0052] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0053] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0054] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0055] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 part of compound catalyst (DBTDL and DABCO at a mass ratio of 1:1) and 0.1 part of water. Stir at 1000r / min for 30s to form a mixed resin.

[0056] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 60%RH for 30 minutes to cure and foam. Then, take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0057] Example 4

[0058] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0059] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0060] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0061] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 part of compound catalyst (DBTDL and DABCO at a mass ratio of 1:1) and 0.1 part of water. Stir at 1000r / min for 30s to form a mixed resin.

[0062] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 25°C and 60%RH for 2 hours to cure and foam. Then, take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0063] Comparative Example 1 (using a single amine catalyst)

[0064] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0065] (2) Mix 43.84 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0066] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0067] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of a single amine catalyst (DABCO) and 0.05 parts of water, and stir at 1000r / min for 30s to form a mixed resin.

[0068] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0069] Comparative Example 2 (using a single amine catalyst)

[0070] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0071] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0072] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0073] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 part of a single amine catalyst (DABCO) and 0.1 part of water, and stir at 1000 r / min for 30 s to form a mixed resin.

[0074] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then, take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off to obtain a fully water-foamed RPU resin.

[0075] Comparative Example 3 (using a single amine catalyst)

[0076] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0077] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0078] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0079] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 part of a single amine catalyst (DABCO) and 0.1 part of water, and stir at 1000 r / min for 30 s to form a mixed resin.

[0080] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 60%RH for 30 minutes to cure and foam. Then, take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0081] Comparative Example 4 (using a single amine catalyst)

[0082] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0083] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0084] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0085] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 part of a single amine catalyst (DABCO) and 0.1 part of water, and stir at 1000 r / min for 30 s to form a mixed resin.

[0086] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn, and let it level naturally by gravity. Then place it in a constant temperature and humidity chamber with preset parameters of 25°C and 60%RH for 2 hours to cure and foam. After taking it out of the constant temperature and humidity chamber, store it in a desiccator for 12 hours and then peel it off to obtain a fully water-foamed RPU resin.

[0087] Comparative Example 5 (using a single tin-based catalyst)

[0088] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0089] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0090] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0091] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of single tin catalyst (DBTDL) and 0.05 parts of water, and stir at 1000r / min for 30s to form a mixed resin.

[0092] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0093] Comparative Example 6 (Tin-based catalyst ratio is too low)

[0094] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0095] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0096] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0097] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of compound catalyst (DBTDL and DABCO at a mass ratio of 1:3) and 0.05 parts of water. Stir at 1000r / min for 30s to form a mixed resin.

[0098] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0099] Comparative Example 7 (excessive proportion of tin-based catalysts)

[0100] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0101] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0102] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0103] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of compound catalyst (DBTDL and DABCO at a mass ratio of 3:1) and 0.05 parts of water. Stir at 1000r / min for 30s to form a mixed resin.

[0104] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0105] Comparative Example 8 (using different types of tin-amine composite catalysts)

[0106] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0107] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0108] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0109] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of compound catalyst (DBTDA and tribenzylamine at a mass ratio of 1:1) and 0.05 parts of water. Stir at 1000r / min for 30s to form a mixed resin.

[0110] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0111] Comparative Example 9 (using different types of tin-amine composite catalysts)

[0112] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0113] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0114] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0115] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of compound catalyst (DBTDA and N,N-dimethyl-p-toluidine at a mass ratio of 1:1) and 0.05 parts of water. Stir at 1000r / min for 30s to form a mixed resin.

[0116] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0117] Comparative Example 10 (using different types of tin amine composite catalysts)

[0118] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0119] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0120] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0121] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of the compound catalyst (stannous octoate and tribenzylamine at a mass ratio of 1:1) and 0.05 parts of water. Stir at 1000r / min for 30s to form a mixed resin.

[0122] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0123] Comparative Example 11 (using different types of tin-amine composite catalysts)

[0124] (1) Dehydrate polytetrahydrofuran under vacuum at 100°C for 12 hours, and then cool it down to about 25°C for later use.

[0125] (2) Mix 43.8 parts of dehydrated polytetrahydrofuran and 7.1 parts of small molecule chain extender 1,4-butanediol evenly to obtain component A for later use.

[0126] (3) Add 32.0 parts of 4,4-methylenebis(phenyl isocyanate) to a two-necked flask, add 1.0 part of crosslinking agent trimethylolpropane and 16.2 parts of dehydrated polytetrahydrofuran, stir at 300 r / min for 2 h at about 80 °C under N2 atmosphere to obtain component B, and cool down to 25 °C for later use.

[0127] (4) Add component B to component A and mix them at a mass ratio of 96.7:100. Add 0.1 parts of the compound catalyst (stannous octoate and N,N-dimethyl-p-toluidine in a mass ratio of 1:1) and 0.05 parts of water. Stir at 1000 r / min for 30 s to form a mixed resin.

[0128] (5) After quickly pouring the mixed resin into the center of the polytetrafluoroethylene board, tilt the substrate on all four sides in turn. After leveling it naturally by gravity, place it in a constant temperature and humidity chamber with preset parameters of 80℃ and 30%RH for 30 minutes to cure and foam. Then take it out of the constant temperature and humidity chamber and store it in a desiccator for 12 hours before peeling it off.

[0129] Performance testing

[0130] The foamed polyurethanes prepared in each embodiment and comparative example were tested, and the results are shown in the table below. Figure 1-5 As shown:

[0131]

[0132] Optical microscope images of the RPU resin in-situ foamed surfaces of Examples 2-4 and Comparative Examples 2-4 are shown below. Figure 2 As shown, the prepared low-humidity-sensitive RPU resin, through the active intervention of ambient temperature and surface humidity, achieves a dynamic balance between foaming and gelation reactions directly on the surface and internal regions by utilizing the synergistic effect of the tin amine catalyst during the critical early stages of the foaming reaction, namely the rising phase and the skin formation phase. This allows the system to expand rapidly at low viscosity and solidify quickly upon reaching the desired volume. This fundamentally suppresses the defects such as cell merging or even rupture, depressions, high open-pore ratio, roughness, and unevenness on the surface of RPU resin using amine catalysts alone during in-situ foaming, resulting in a naturally smooth and flat surface, greatly reducing or even eliminating the need for post-processing.

[0133] like Figure 3 The optical images shown indicate that the RPU resin surfaces foamed in situ using a compound catalyst under different temperature and humidity conditions in Examples 1-3 (ac) are smoother and more even than the RPU resin surfaces foamed in situ using an amine catalyst under high temperature and low humidity conditions in Comparative Example 2 and low temperature and high humidity conditions in Comparative Example 4. Although the RPU resin surface foamed in situ using an amine catalyst under high temperature and high humidity conditions in Comparative Example 3 is relatively smooth, it has obvious cracks and poor mechanical properties.

[0134] In addition, such as Figure 1As shown, in Examples 1(a) and 2(b) of the present invention, the low-humidity and low-sensitivity RPU resin can utilize the synergistic effect of the tin-amine composite catalyst to balance the internal gelation and foaming reaction as the amount of internal in-situ foaming water increases. Compared with Comparative Examples 1(c) and 2(d) which use amine catalysts alone, this avoids the excessive expansion, merging, or even rupture of cells due to insufficient internal cell wall strength, thus stabilizing and shortening the cell size distribution range. In contrast, Comparative Examples 5(e, f) use tin catalysts alone, which mainly promote gelation, resulting in fewer internal cells and uneven cell size distribution.

[0135] This invention uses a specific 1:1 mass ratio of DBTDL-DABCO catalyst to prepare the catalyst, which is superior to using other ratios of DBTDL-DABCO. Figure 4 ) or other types of tin amine catalysts in a 1:1 mass ratio ( Figure 5 The RPU resin prepared by this method exhibits lower humidity sensitivity, a more naturally smooth surface, and a more uniform cell structure. This makes it possible for RPU resin to be used in high humidity environments while still maintaining good overall performance, which is beneficial to the development of solvent-free polyurethane resins in fields such as automotive leather.

[0136] Unless otherwise specified, the raw materials and equipment used in this invention are all commonly used in the field; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0137] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, alterations, and equivalent transformations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A low-humidity-sensitive reactive foamed polyurethane resin, characterized in that, It has a smooth and flat surface and a pore size of 50~200μm; its raw materials include, by weight: Component A: 40-50 parts of polyether polyol, 2-10 parts of chain extender, 0.1-1 parts of tin amine composite catalyst, and 0.05-1 parts of water; the tin amine composite catalyst is dibutyltin dilaurate and 1,4-diazabicyclo[2.2.2]octane in a weight ratio of 1:(0.8-1.2); Component B: 25-35 parts isocyanate, 10-20 parts polyether polyol, and 0.5-3 parts crosslinking agent.

2. The low humidity-sensitive reactive foamed polyurethane resin as described in claim 1, characterized in that: The weight ratio of component A to component B is 100:90~97.

3. The low humidity-sensitive reactive foamed polyurethane resin as described in claim 1 or 2, characterized in that: The polyether polyol has a molecular weight of 600-5000 and is selected from one or more of polytetrahydrofuran diol, polypropylene glycol and polycarbonate diol. The chain extender is selected from one or more of 1,4-butanediol, ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,5-pentanediol, neopentanediol, diethylene glycol, dipropylene glycol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, and 1,4-cyclohexanedimethylhydroquinone bis(2-hydroxyethyl) ether.

4. The low humidity-sensitive reactive foamed polyurethane resin as described in claim 1, characterized in that: The isocyanate-terminated prepolymer contains 20-30% NCO.

5. The low humidity-sensitive reactive foamed polyurethane resin as described in claim 1 or 4, characterized in that: The isocyanate is selected from one or more of aliphatic diisocyanates such as hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, methylcyclohexane diisocyanate, and aromatic diisocyanates; The crosslinking agent is selected from one or more triols such as trimethylolpropane and glycerol.

6. A method for preparing a low-humidity-sensitive reactive foamed polyurethane resin as described in any one of claims 1-5, characterized in that, Includes the following steps: 1) Mix the dehydrated polyether polyol and chain extender evenly to obtain component A; 2) The isocyanate, crosslinking agent and dehydrated polyether polyol are stirred and reacted under an inert atmosphere to obtain component B, which is then cooled to 20-30℃ for later use. 3) Mix and stir component B and component A to form a mixed resin; 4) Pour the mixed resin onto the substrate surface, cure and foam it under constant temperature and humidity conditions, and after drying and peeling, obtain a reactive polyurethane resin with low humidity sensitivity; the constant temperature and humidity environment is selected from one of the following temperature and humidity combinations: 75-85℃+25-35%, 75-85℃+55-65%, or 20-30℃+55-65%.

7. The preparation method according to claim 6, characterized in that: The dehydration process involves vacuum dehydrating the polyether polyol at 90-110℃ for 10-15 hours, and then cooling it to 20-30℃ for later use.

8. The preparation method according to claim 6, characterized in that: In step 2), the conditions for the stirring reaction are: temperature 70-90℃, stirring speed 100-500rpm; time 1-3h.

9. The preparation method according to claim 6, characterized in that: In step 3), the mixing conditions are: temperature 20-30℃, relative humidity 25-35%, stirring speed 500-1500rpm, and time 20-40s.

10. A method for reducing the humidity sensitivity of reactive foamed polyurethane resin, characterized in that, By weight, the following steps are included: 1) Mix 40-50 parts of dehydrated polyether polyol and 2-10 parts of chain extender evenly to obtain component A; 2) Stir 25-35 parts of isocyanate, 0.5-3 parts of crosslinking agent and 10-20 parts of dehydrated polyether polyol under an inert atmosphere to obtain component B, and cool it to 20-30℃ for later use. 3) Mix and stir component B and component A, add 0.1~1 part of tin amine composite catalyst and 0.05~1 part of water to form a mixed resin; the tin amine composite catalyst is dibutyltin dilaurate and 1,4-diazabicyclo[2.2.2]octane in a weight ratio of 1:(0.8~1.2); 4) Pour the mixed resin onto the substrate surface, cure and foam it under constant temperature and humidity conditions, and after drying and peeling, obtain a reactive polyurethane resin with low humidity sensitivity; the constant temperature and humidity environment is selected from one of the following temperature and humidity combinations: 75-85℃+25-35%, 75-85℃+55-65%, or 20-30℃+55-65%.

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