Functional polyurethane coating material resistant to high and low temperature impact and preparation process thereof

Abstract

The present application relates to the technical field of high polymer composite material, and discloses a functional polyurethane coating material resistant to high and low temperature impact and a preparation process thereof, which is made of raw materials including polyol component, polyisocyanate, chain extender, inorganic network precursor, silane coupling agent, low temperature urethane reaction catalyst and high temperature latent catalyst.The preparation process realizes time sequence curing through two-stage temperature control: firstly, polyurethane network is preferentially formed by using low temperature catalyst at low temperature; then, by using latent catalyst activation, silica network is generated in situ in the formed polyurethane network by temperature rising.The silane coupling agent constructs chemical bond connection at the interface of organic-inorganic two phases.Through time sequence construction of network structure and interface control, the present application solves the contradiction between low temperature flexibility and high temperature rigidity of the material, so that the coating material has both two kinds of performances and excellent high and low temperature cycle impact resistance.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, and in particular to a functional polyurethane coating material resistant to high and low temperature impacts and its preparation process. Background Technology

[0002] Polyurethane coatings are widely used due to their adjustable mechanical properties, good abrasion resistance, and chemical resistance. However, as a typical polymer, conventional polyurethane materials exhibit a strong temperature dependence in their mechanical properties. As temperature increases, the storage modulus of the material decreases, leading to a decline in its rigidity, dimensional stability, and load-bearing capacity. This limits its application in environments requiring wide temperature ranges, particularly high and low temperature shock environments.

[0003] To improve the heat resistance of polyurethane materials, a common technical approach is to employ an organic-inorganic hybrid method, using a sol-gel process to generate inorganic networks such as silica in situ within the polyurethane matrix. However, in existing technologies, the polyurethane formation reaction and the hydrolysis-condensation reaction of the inorganic precursors typically occur concurrently within the same system. Due to the differences in the mechanisms and kinetics between the urethane esterification reaction and the hydrolysis-condensation reaction, the competition between the two reactions during the process leads to an incomplete network structure and easily triggers macroscopic phase separation, forming heterogeneous inorganic domains.

[0004] Furthermore, if there is a lack of effective chemical bonding between the organic and inorganic phases, the resulting interfacial bonding force will be weak. This suboptimal microstructure not only fails to effectively leverage the reinforcing effect of the inorganic phase but may even impair the overall toughness of the material by introducing interfacial defects. Therefore, hybrid materials prepared through conventional blending or simultaneous reaction processes typically struggle to achieve a true synergistic effect of both low-temperature flexibility and high-temperature rigidity, failing to meet the stringent high- and low-temperature cycling requirements of applications. Summary of the Invention

[0005] The purpose of this invention is to provide a functional polyurethane coating material resistant to high and low temperature impacts and its preparation process. This material needs to be able to withstand high and low temperature cyclic impacts, while solving the technical problem of balancing low-temperature flexibility and high-temperature rigidity.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] In a first aspect, the present invention provides a functional polyurethane coating material resistant to high and low temperature impacts, which is made from raw materials comprising the following parts by weight: 70-90 parts of polyol component; 20-32 parts of polyisocyanate; 2.9-5.0 parts of chain extender; 8.0-15.0 parts of inorganic network precursor; 1.5-2.5 parts of silane coupling agent; 0.05-0.15 parts of catalyst I; and 0.10-0.20 parts of latent catalyst II.

[0008] By employing the above technical solution, during the curing process of the coating material, the internal organic polyurethane network and inorganic silica network are formed stepwise according to a preset temperature program. Its mechanism of action is as follows:

[0009] 1. Low temperature stage: Formation of polyurethane network.

[0010] In the low-temperature range of 35–50°C, catalyst I catalyzes the urethane reaction between the polyol component, polyisocyanate, and chain extender to form a polyurethane network. Under these temperature conditions, the latent catalyst II does not exhibit catalytic activity, and the hydrolysis-condensation reaction of the inorganic network precursor is inhibited.

[0011] 2. High-temperature stage: Formation of the silica network.

[0012] When the temperature rises to 100–120°C, the latent catalyst II decomposes upon heating, releasing an active catalytic substance. This substance catalyzes the in-situ hydrolysis and condensation of the inorganic network precursor within the formed polyurethane network, generating a silica network.

[0013] 3. Construction of organic-inorganic interface chemical bonds.

[0014] One functional group of the silane coupling agent reacts with the polyisocyanate to integrate into the polyurethane network; the alkoxysilane structure at the other end co-condenses with the inorganic network precursor to become part of the silica network. Through the bridging effect of the silane coupling agent, chemical bonds are formed between the organic and inorganic phases, constructing a stable two-phase interface.

[0015] The temporal separation of this network formation process avoids competition between the two network formation reactions, promoting the formation of a uniform interpenetrating structure between the organic and inorganic networks. Stable interfacial bonding enables effective stress transfer between the two phases. Therefore, the resulting material combines the low-temperature flexibility of the polyurethane network with the high-temperature rigidity of the silica network, giving it resistance to high and low temperature impacts.

[0016] Preferably, the latent catalyst II is an amine salt prepared by reacting p-toluenesulfonic acid with a volatile amine. More preferably, the volatile amine has a boiling point of 50–120°C and may be triethylamine or N,N-diisopropylamine.

[0017] Using this technical solution, volatile amines dissociate and volatilize from the amine salt at high temperatures, thereby releasing catalytically active p-toluenesulfonic acid in situ. This temperature-controlled release mechanism is the basis for achieving catalyst II's latency in the low-temperature region and activation in the high-temperature region, and is also a condition for realizing the sequential construction of the network.

[0018] Preferably, the polyol component is composed of polytetrahydrofuran ether diol and polypropylene glycol, wherein the weight ratio of polytetrahydrofuran ether diol to polypropylene glycol is (65-75):(5-15).

[0019] Using this technical solution, the molecular chain structure of polytetrahydrofuran ether diol provides low-temperature flexibility to the coating. The addition of polypropylene glycol can be used to adjust the polarity and regularity of the polyurethane soft segments to improve the mechanical properties of the material.

[0020] Preferably, the polyisocyanate is polymethylene polyphenyl polyisocyanate; the inorganic network precursor is tetraethyl orthosilicate; and the silane coupling agent is 3-aminopropyltriethoxysilane.

[0021] Using this technical solution, polymethylene polyphenyl polyisocyanate exhibits high reactivity. The amino group of 3-aminopropyltriethoxysilane can react with the isocyanate group, and its triethoxysilane end has a reactivity that matches that of tetraethyl orthosilicate, which helps to form a stable organic-inorganic interface.

[0022] Secondly, the present invention provides a preparation process for a functional polyurethane coating material resistant to high and low temperature impacts, comprising the following steps:

[0023] (a) The polyol component is reacted with the polyisocyanate to obtain a polyurethane prepolymer; then the inorganic network precursor and the silane coupling agent are added to the prepolymer and mixed evenly to obtain component A.

[0024] (b) Dissolve the chain extender, catalyst I, and latent catalyst II in an organic solvent to obtain component B;

[0025] (c) Mix component A and component B, perform a first stage of low-temperature curing, and then perform a second stage of high-temperature curing to obtain the functional polyurethane coating material.

[0026] By employing the above technical solution, this process places the reactants and catalysts with different activation conditions into two components, A and B, respectively, and combines them with a two-stage temperature-controlled curing procedure. This method allows the polyurethane network formation reaction and the silica network formation reaction to occur sequentially within different temperature ranges, avoiding kinetic competition and potential structural defects caused by the simultaneous occurrence of the two reactions, and facilitating the formation of a uniform interpenetrating network structure.

[0027] Preferably, in step (c), the temperature for the first stage of low-temperature curing is 35-50°C; and the temperature for the second stage of high-temperature curing is 100-120°C.

[0028] By adopting the above technical solution, the first-stage curing temperature is set at 35–50°C. This temperature range meets the activity requirements of catalyst I, promoting the esterification reaction, while the latent catalyst II remains inactive at this temperature. Setting the second-stage curing temperature at 100–120°C allows the latent catalyst II to decompose and release active substances, thereby catalyzing the formation of the inorganic network.

[0029] Preferably, in step (a), the molar ratio of the -NCO group in the polyisocyanate to the -OH group in the polyol component is 1.8 to 2.2:1.

[0030] By employing the above technical solution, this molar ratio is controlled to prepare a polyurethane prepolymer with -NCO end groups. The -NCO groups reserved on the prepolymer are used to react with the functional groups of the chain extender and silane coupling agent in subsequent steps to ultimately form a cross-linked network. This molar ratio is one of the parameters controlling the molecular weight of the prepolymer and the final network structure.

[0031] Preferably, before reacting the polyol component with the polyisocyanate in step (a), the method further includes a step of dehydrating the polyol component at 110°C and under vacuum conditions.

[0032] The purpose of pre-treating polyol raw materials by dehydration using the above technical solution is to remove trace amounts of moisture. Moisture can react with -NCO groups, affecting the accuracy of stoichiometry and potentially introducing defects such as bubbles into the coating.

[0033] In summary, the present invention has at least one of the following beneficial technical effects:

[0034] 1. The coating material of this invention possesses both low-temperature flexibility and high-temperature dimensional stability. Through a time-curing process, a flexible polyurethane network is preferentially formed at low temperatures, imparting low-temperature toughness to the material; subsequently, a rigid silica network is formed throughout at high temperatures, providing the material with high-temperature modulus and dimensional stability. The synergistic effect of these two network structures enables the material to meet mechanical performance requirements across a wide temperature range.

[0035] 2. The coating material of this invention exhibits excellent resistance to high and low temperature cycling shock. A silane coupling agent is used to establish chemical bonds between the organic polyurethane network and the inorganic silica network. This interfacial bonding allows the two networks to work synergistically under thermal expansion and contraction stresses, effectively transferring and dispersing stress, suppressing stress concentration and microcrack formation caused by interfacial incompatibility, thereby improving the structural integrity of the material under long-term high and low temperature alternating environments.

[0036] 3. The preparation process of this invention is controllable, which is beneficial to ensuring the stability of product performance. By employing a low-temperature active catalyst I and a high-temperature latent catalyst II, and matching a two-stage temperature-controlled curing program, this invention achieves temporal separation between the polyurethane formation reaction and the inorganic hydrolysis-condensation reaction. This process design avoids competition between the two reactions due to their kinetic differences, reduces the formation of network structure defects, and ensures the effective construction of the target interpenetrating network structure. Attached Figure Description

[0037] Figure 1 The Fourier transform infrared spectra of the coating in Example 1 at different curing stages are shown below; (a) is the spectrum at t=0 (initial state, 25℃); (b) is the spectrum at t=3 minutes (after low-temperature curing at 40℃); and (c) is the spectrum at t=6 minutes (after high-temperature curing at 110℃).

[0038] Figure 2 The curves showing the change in dynamic rheological modulus during the curing process of the coating in Example 1 are shown. Among them, (a) is the curve showing the change in storage modulus (G') with time and temperature; and (b) is the curve showing the change in loss modulus (G'') with time and temperature. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the scope of protection of the invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0040] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0041] Polytetrahydrofuran ether diol (PTMG), CAS No.: 25190-06-1, the grade used in this embodiment of the invention is PTMG-2000, its number average molecular weight (Mn) ranges from 1900 to 2100 g / mol, its molecular weight distribution index (PDI) is 1.5 to 1.9, it is a white waxy solid at room temperature, and its glass transition temperature (Tg) is about -85℃.

[0042] Polypropylene glycol (PPG), CAS No.: 25322-69-4, the grade used in this embodiment of the invention is PPG-600, its number average molecular weight (Mn) ranges from 550 to 650 g / mol, its molecular weight distribution index (PDI) is 1.1 to 1.3, and it is a colorless to pale yellow viscous liquid at room temperature.

[0043] Polymethylene polyphenyl polyisocyanate, CAS No.: 9016-87-9. The one used in the embodiments of the present invention is a mixture of the difunctional isomer of diphenylmethane diisocyanate and its polyfunctional homologue, which is a brown transparent liquid with a mass fraction of -NCO group of 33.0-34.0%.

[0044] Preparation Example 1:

[0045] This preparation example provides a method for synthesizing triethylamine p-toluenesulfonate using a latent catalyst, comprising the following steps:

[0046] (1) In a 500mL three-necked flask equipped with a mechanical stirrer, thermometer and constant pressure dropping funnel, add 200mL of anhydrous ethyl acetate, turn on the stirrer and cool it to 0-5℃ in an ice water bath; add 38.1g (0.2mol) of p-toluenesulfonic acid monohydrate in batches to the flask and stir until it is completely dissolved.

[0047] (2) 20.2 g (0.2 mol) of triethylamine was slowly added to the solution in step (1) over 30 minutes using a constant pressure dropping funnel. During the addition process, the temperature of the reaction system was maintained at no more than 10°C by controlling the dropping rate and using an ice-water bath.

[0048] (3) After the addition is complete, remove the ice water bath and continue stirring the reaction for 1 hour at room temperature (20-25℃).

[0049] (4) The reaction mixture was transferred to a rotary evaporator and the solvent was removed by rotary evaporation under vacuum at a water bath temperature of 40°C to obtain a white solid product. The solid product was placed in a vacuum drying oven at 40°C and dried for 5 hours to obtain the final product, triethylamine p-toluenesulfonic acid salt, which was designated as catalyst IIa and sealed for later use.

[0050] Preparation Example 2:

[0051] This preparation example provides a method for synthesizing p-toluenesulfonic acid diisopropylamine salt using a latent catalyst, comprising the following steps:

[0052] (1) In a 500mL three-necked flask equipped with a mechanical stirrer, thermometer and constant pressure dropping funnel, add 200mL of anhydrous ethyl acetate, turn on the stirrer and cool it to 0-5℃ in an ice water bath; add 38.1g (0.2mol) of p-toluenesulfonic acid monohydrate in batches to the flask and stir until it is completely dissolved.

[0053] (2) 20.3 g (0.2 mol) of N,N-diisopropylamine was slowly added dropwise to the solution in step (1) over 30 minutes using a constant pressure dropping funnel. During the dropwise addition, the temperature of the reaction system was maintained at no more than 10°C by controlling the dropwise addition rate and using an ice-water bath.

[0054] (3) After the addition is complete, remove the ice water bath and continue stirring the reaction for 1 hour at room temperature (20-25℃).

[0055] (4) The reaction mixture was transferred to a rotary evaporator and the solvent was removed by rotary evaporation under vacuum at a water bath temperature of 40°C to obtain a white solid product. The solid product was placed in a vacuum drying oven at 40°C and dried for 5 hours to obtain the final product p-toluenesulfonic acid diisopropylamine salt, which was designated as catalyst IIb and sealed for later use. Example 1:

[0056] This embodiment provides a preparation process for a functional polyurethane coating material resistant to high and low temperature impacts, including the following steps:

[0057] (1) Preparation of component A: 68.0 parts by weight of polytetrahydrofuran ether diol (PTMG-2000) and 12.0 parts by weight of polypropylene glycol (PPG-600) were added to a reactor and stirred and dehydrated at 110°C and under vacuum for 2 hours; the temperature was lowered to 60°C and 27.1 parts by weight of polymethylene polyphenyl polyisocyanate (polymerized MDI, with an NCO / OH molar ratio of 2.0:1) were added, the temperature was raised to 78-82°C and the reaction was maintained for 2.5 hours to obtain polyurethane prepolymer; the system was cooled to 55°C and 10.0 parts by weight of tetraethyl orthosilicate (TEOS) and 2.0 parts by weight of 3-aminopropyltriethoxysilane (APTES) were added sequentially and stirred for 30 minutes to obtain component A.

[0058] (2) Preparation of component B: 4.0 parts by weight of 1,4-butanediol (BDO), 0.10 parts by weight of bismuth neodecanoate (catalyst I) and 0.15 parts by weight of catalyst IIa (product of preparation example 1) were dissolved in 50.0 parts by weight of a mixed solvent of ethyl acetate and butanone of equal mass and stirred until clear and transparent to obtain component B.

[0059] (3) Preparation and curing of coating: 119.1 parts by weight of component A obtained in step (1) and 54.25 parts by weight of component B obtained in step (2) are quickly mixed evenly and coated on the surface of the substrate; the coated substrate is first placed in a 40°C oven for 2.0 minutes, and then immediately placed in a 110°C oven for 2.0 minutes for curing; the cured sample is aged at room temperature for 7 days for later use. Example 2:

[0060] This embodiment provides a preparation process for a functional polyurethane coating material resistant to high and low temperature impacts, including the following steps:

[0061] (1) Preparation of component A: 75.0 parts by weight of polytetrahydrofuran ether diol (PTMG-2000) and 5.0 parts by weight of polypropylene glycol (PPG-600) were added to the reactor and stirred and dehydrated at 110°C and vacuum for 2 hours; the temperature was lowered to 60°C and 20.7 parts by weight of polymeric MDI (to make the NCO / OH molar ratio 1.8:1) were added, the temperature was raised to 78-82°C and the reaction was kept at this temperature for 3.0 hours; the system was cooled to 50°C and 8.0 parts by weight of tetraethyl orthosilicate (TEOS) and 1.5 parts by weight of 3-aminopropyltriethoxysilane (APTES) were added in sequence and stirred at this temperature for 30 minutes to obtain component A.

[0062] (2) Preparation of component B: 2.9 parts by weight of 1,4-butanediol (BDO), 0.05 parts by weight of bismuth neodecanoate (catalyst I) and 0.10 parts by weight of catalyst IIa (product of preparation example 1) were dissolved in 40.0 parts by weight of a mixed solvent of ethyl acetate and butanone of equal mass and stirred until clear and transparent to obtain component B.

[0063] (3) Preparation and curing of coating: 110.2 parts by weight of component A obtained in step (1) and 43.05 parts by weight of component B obtained in step (2) are quickly mixed evenly and coated on the surface of the substrate; the coated substrate is first placed in a 35°C oven for 3.0 minutes, and then immediately placed in a 100°C oven for 2.5 minutes for curing; the cured sample is aged at room temperature for 7 days for later use. Example 3:

[0064] This embodiment provides a preparation process for a functional polyurethane coating material resistant to high and low temperature impacts, including the following steps:

[0065] (1) Preparation of component A: 65.0 parts by weight of polytetrahydrofuran ether diol (PTMG-2000) and 15.0 parts by weight of polypropylene glycol (PPG-600) were added to the reactor and stirred and dehydrated at 110°C and vacuum for 2 hours; the temperature was lowered to 60°C and 31.7 parts by weight of polymeric MDI (to make the NCO / OH molar ratio 2.2:1) were added, the temperature was raised to 78-82°C and the reaction was kept at this temperature for 2.5 hours; the system was cooled to 55°C and 15.0 parts by weight of tetraethyl orthosilicate (TEOS) and 2.5 parts by weight of 3-aminopropyltriethoxysilane (APTES) were added in sequence and stirred at this temperature for 40 minutes to obtain component A.

[0066] (2) Preparation of component B: 5.0 parts by weight of 1,4-butanediol (BDO), 0.15 parts by weight of bismuth neodecanoate (catalyst I) and 0.20 parts by weight of catalyst IIb (product of preparation example 2) were dissolved in 60.0 parts by weight of a mixed solvent of ethyl acetate and butanone, and stirred until clear and transparent to obtain component B.

[0067] (3) Preparation and curing of coating: 129.2 parts by weight of component A obtained in step (1) and 65.35 parts by weight of component B obtained in step (2) are quickly mixed evenly and coated on the surface of the substrate; the coated substrate is first placed in a 50°C oven for 1.5 minutes, and then immediately placed in a 120°C oven for 1.5 minutes for curing; the cured sample is aged at room temperature for 7 days for later use.

[0068] Comparative Example 1:

[0069] Compared to Example 1, the differences are as follows: Tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxysilane (APTES) were not added during the preparation of component A; catalyst IIa (the product of Preparation Example 1) was not added to component B; and the amount of 1,4-butanediol (BDO) in component B was adjusted accordingly to make the isocyanate index of the final system similar to that of Example 1. All other aspects remained the same.

[0070] Comparative Example 2:

[0071] The difference from Example 1 is that 3-aminopropyltriethoxysilane (APTES) is not added during the preparation of component A, but tetraethyl orthosilicate (TEOS) is retained. All other aspects are the same.

[0072] Comparative Example 3:

[0073] Compared to Example 1, the difference lies in that: in the preparation of component B, bismuth neodecanoate and catalyst IIa are not used; instead, 0.12 parts by weight of dibutyltin dilaurate (DBTDL) is used as a single catalyst; the coating curing process is carried out in one step at 110°C for 4.0 minutes. All other aspects are the same.

[0074] Comparative Example 4:

[0075] The difference from Example 1 is that catalyst IIa (the product of Example 1) was not added during the preparation of component B. Everything else is the same.

[0076] Test Example 1:

[0077] The experimental steps are as follows:

[0078] (1) Take a sample of the newly prepared mixture of components A and B in Example 1, press it between two KBr salt plates to form a uniform liquid film, place it in the sample cell of a Fourier transform infrared spectrometer with temperature control accessories, and collect the initial spectrum (t=0).

[0079] (2) Heat the sample cell to 40°C and keep it constant. At this temperature, collect infrared spectra every minute for a total of 3 times.

[0080] (3) After completing the spectral acquisition in the 3rd minute, raise the temperature of the sample cell to 110℃.

[0081] (4) Under constant temperature of 110℃, infrared spectra were collected every minute for a total of 3 times.

[0082] (5) Baseline correction was performed on the collected spectral data, and the characteristic absorption peak of the -NCO group (2270 cm⁻¹) was calculated. -1 Characteristic absorption peak of Si-O-Et group (960 cm⁻¹) -1 ) and the characteristic absorption peak of the Si-O-Si network structure (1080 cm⁻¹) -1 The relative intensity of ).

[0083] The experimental results are shown in Table 1 and Figure 1 As shown.

[0084] Table 1. FTIR characteristic peak intensity variation data during the coating curing process in Example 1:

[0085]

[0086] Figure 1 The image shows the superimposed infrared spectra of the coating in Example 1 at three key time points (t=0min, t=3min, t=6min).

[0087] (a) The spectrum at t=0min (initial state, 25℃) shows that at 2270cm -1 There is a sharp and strong characteristic absorption peak of the -NCO group at 1730 cm⁻¹; -1 There was no obvious absorption peak for the C=O group in the vicinity of the urethane ester; at 960 cm⁻¹ -1 Characteristic absorption peaks belonging to Si-O-Et groups can be observed at 1000–1100 cm⁻¹. -1 There are no obvious Si-O-Si network characteristic absorption peaks in the range.

[0088] (b) Spectral data at t=3min (end of low-temperature pre-curing, 40℃): Compared with the initial spectrum, 2270 cm⁻¹ -1 The intensity of the -NCO peak at 1730 cm⁻¹ decreased significantly; meanwhile, the intensity of the -NCO peak at 1730 cm⁻¹ decreased significantly. -1 A new C=O absorption peak was generated at 960 cm⁻¹, indicating that a large number of carbamate structures had been formed; while at 960 cm⁻¹... -1 The intensity of the Si-O-Et peak at the point is basically the same as that in the initial state, with no significant change.

[0089] (c) The spectrum at t=6min (final curing at 110℃) shows: 2270cm -1 The -NCO peak at 960 cm⁻¹ almost completely disappeared;-1 The Si-O-Et peak at 1080 cm⁻¹ has also largely disappeared; the most significant change is at 1080 cm⁻¹. -1 A broad and strong absorption peak appeared nearby, which is attributed to the asymmetric stretching vibration of the Si-O-Si bond and is direct evidence of the formation of the silicon dioxide network.

[0090] Combining the quantitative data in Table 1 and Figure 1 The changes in the spectrum can be observed to reveal the evolution of the chemical structure of the coating in Example 1 during the segmented curing process, thereby analyzing the temporal relationship of different chemical reactions within the system.

[0091] During the low-temperature pre-curing stage at 40℃ (0-3 minutes), such as Figure 1 (b) is shown in comparison with (a), located at 2270cm. -1 The intensity of the characteristic absorption peak of the -NCO group at 1730 cm⁻¹ decreased significantly, with its relative intensity dropping from an initial 0.85 to 0.39. Meanwhile, at 1730 cm⁻¹... -1 The appearance of the C=O peak of the carbamate directly proves that the amino esterification reaction between the isocyanate group and the hydroxyl group is effectively initiated and proceeds rapidly at this stage. Simultaneously, a peak at 960 cm⁻¹... -1 The characteristic absorption peak intensity of the Si-O-Et groups at the site remained at the initial level of around 0.60, without significant attenuation, indicating that the hydrolysis-condensation reaction of TEOS did not occur or its reaction rate was extremely low. The chemical process at this stage mainly involves the chain extension and preliminary cross-linking of the polyurethane prepolymer chains, forming a polyurethane network backbone.

[0092] When the system temperature rises to 110℃ (within 3–6 minutes), the chemical reaction process changes significantly. From Figure 1 (c) It can be seen that the consumption of the -NCO group continues, and its characteristic peak eventually disappears almost completely, indicating that the esterification reaction is approaching completion. The key change is that the characteristic peak of the Si-O-Et group shows a sharp decline, and at the same time, the peak at 1080 cm⁻¹... -1 A broad and strong absorption peak of the Si-O-Si network structure was generated nearby. The data in Table 1 also confirms this; the relative intensity of the Si-O-Et peak rapidly decreased from 0.58 to 0.03, while the relative intensity of the Si-O-Si peak rapidly increased from 0.04 to 0.78. This series of changes demonstrates that the latent catalyst IIa was activated at high temperature, and the released acidic substances efficiently catalyzed the hydrolysis and condensation of TEOS, thereby forming a silica inorganic network.

[0093] In summary, the FTIR in-situ tracking analysis clearly reveals the time-sequential curing mechanism designed in this invention. The system preferentially completes the initial construction of the polyurethane network at low temperatures, while triggering the rapid in-situ formation of the inorganic silica network at high temperatures. This dual network formation process, occurring in a predetermined order, effectively avoids the kinetic interference and competition between the two chemical reactions, and is the foundation for achieving uniformity in the organic-inorganic interpenetrating network structure.

[0094] Test Example 2:

[0095] The experiment used a dynamic rotational rheometer equipped with a parallel plate clamp (25 mm in diameter, 1.0 mm gap) and a Peltier temperature control system. The freshly prepared mixture of components A and B from Example 1 was immediately placed in the center of the lower plate of the rheometer. The upper plate was lowered to the set gap, and any sample overflowing from the edges was scraped off. The test was conducted in the linear viscoelastic region (strain set to 0.5%), with an oscillation frequency of 1 Hz. The temperature program and data acquisition settings are as follows:

[0096] (1) Quickly equilibrate the sample temperature to 40°C and monitor it at this temperature for 10 minutes, recording the changes in storage modulus (G') and loss modulus (G'') over time.

[0097] (2) After 10 minutes, the sample was heated from 40°C to 120°C at a rate of 10°C / min, and the changes of G' and G'' with temperature were recorded.

[0098] The experimental results are shown in Table 2 and Figure 2 As shown.

[0099] Table 2. Rheological modulus change data of the coating in Example 1 during the time-curing process:

[0100]

[0101] Figure 2 This is a double logarithmic coordinate graph showing the changes in storage modulus (G', represented by solid line) and loss modulus (G'', represented by dashed line) of the coating in Example 1 with time and temperature during the time-varying temperature curing process.

[0102] (a) During the isothermal phase at 40°C (0–10 minutes), the system initially exhibited fluid characteristics with G'' > G'. As time progressed, the growth rate of G' was significantly higher than that of G'', and a crossover point (gel point) between G' and G'' appeared at approximately 4 minutes. Subsequently, G' continued to grow and far exceeded G'', indicating that the system had transformed into a gel network structure dominated by elasticity.

[0103] (b) During the heating phase (10–18 minutes), as the temperature rises from 40°C to approximately 70°C, G' shows a slight decrease. Once the temperature exceeds 80°C, G' begins to exhibit a second, much steeper increase than in the first phase, with its value rapidly increasing by more than two orders of magnitude within a short period, from several hundred Pascals to 10 Pascals. 5 The value reaches the Pa level. Finally, at 120°C, G' reaches a high plateau, which is much larger than G'', indicating that a high-modulus solid-state network structure has been formed.

[0104] Table 2 Rheological data and Figure 2 The modulus evolution curve shown reveals the structuring process of the system under a specific temperature program from a macroscopic mechanical perspective.

[0105] During the isothermal range of 40℃ (0–10 minutes), the storage modulus (G') increased from the initial 8 Pa to 750 Pa. During this period, the intersection of G' and loss modulus (G'') was observed at approximately 4 minutes, which is the gel point of the system. The increase in G' and the appearance of the gel point are macroscopic mechanical manifestations of the polyurethane prepolymer undergoing chain extension and cross-linking under the action of catalyst I, forming a polyurethane network. At this point, the system has transformed from its initial liquid state into a gel structure with a certain degree of elasticity.

[0106] During the subsequent heating process, the G' value decreased slightly in the range of 40°C to 70°C, reflecting the softening of the formed polymer network upon heating. When the temperature exceeded 80°C, the G' growth curve showed a distinct second inflection point, with the growth rate accelerating significantly. The modulus value increased from 4.1 × 10⁻⁶ in a short period of 15 minutes (90°C) to 17 minutes (110°C). 3 Pa increased to 8.5 × 10 4 The increase in modulus (Pa) exceeds one order of magnitude. This magnitude of modulus increase cannot be simply attributed to the completion of the remaining polyurethane reaction; it indicates the formation of new high-modulus network structures within the system.

[0107] The time and temperature range in which this modulus jump occurred are consistent with the time and temperature range in which the latent catalyst IIa activated and catalyzed the hydrolysis and condensation of TEOS to form a Si-O-Si network, as shown by the FTIR spectrum in Test Example 1.

[0108] Therefore, the results of dynamic rheological analysis confirmed the curing behavior of the system. In the low-temperature stage, a flexible polyurethane network first forms, providing the basic structure for the system; in the high-temperature stage, a rigid silica network is then generated, significantly increasing the final modulus of the system. The stepwise formation of the two networks in different temperature ranges verifies the feasibility of the time-sequential curing mechanism designed in this technical solution.

[0109] Test Example 3:

[0110] All coating samples from Examples 1-3 and Comparative Examples 1-4 were cured under standard conditions for 7 days before testing, with the dry film thickness controlled at 15±2 μm. The test methods for each performance are as follows:

[0111] Dynamic thermomechanical analysis (DMA): Coated film samples were cut and scanned from -80℃ to 150℃ using a DMA instrument in stretch mode at a heating rate of 3℃ / min. The storage modulus (E') and loss factor (tanδ) were recorded as a function of temperature. The temperature corresponding to the peak value of tanδ was taken as the glass transition temperature (Tg), and the storage modulus value (E') at 100℃ was read. 100 ).

[0112] Hardness and flexibility: Hardness testing was conducted according to GB / T 6739-2006 standard using the pencil hardness method. Flexibility testing was conducted according to GB / T 1731-1993 standard using the T-bend test method, and the minimum T-bend value at which the coating did not crack was recorded.

[0113] Adhesion: According to ASTM D3359 standard (cross-cut test), use a cross-cut knife to cut a grid on the coating surface, apply special tape and quickly peel it off, and evaluate the coating peeling on a scale of 0 to 5.

[0114] High and low temperature cycling test: Place the coated sample in a high and low temperature alternating damp heat test chamber and cycle 50 times. The single cycle program is as follows: maintain at -30℃ for 1 hour; raise the temperature to +80℃ within 30 minutes; maintain at +80℃ for 1 hour; cool down to -30℃ within 30 minutes. After the cycle is completed, visually inspect the surface condition of the coating and retest the adhesion.

[0115] The experimental results are shown in Table 3.

[0116] Table 3. Coating performance test data for the examples and comparative examples:

[0117]

[0118] Table 3 shows the test data reflecting the differences in macroscopic performance of coatings with different formulations. The coatings prepared in Examples 1, 2, and 3 exhibit superior overall performance compared to all comparative examples.

[0119] The coatings in the examples all exhibit low glass transition temperatures (Tg below -43°C), indicating that the materials retain the characteristics of the flexible segments of polytetrahydrofuran ether diol and possess good low-temperature toughness. Simultaneously, they maintain a high storage modulus (E') at 100°C. 100 (All values ​​are greater than 20 MPa), indicating that the material possesses reliable high-temperature dimensional stability. Low Tg and high E' 100 This coexistence reflects the material's wide temperature range adaptability. The coating in the example also performs well in conventional indicators such as hardness, flexibility, and adhesion.

[0120] The formulation of Comparative Example 1 did not contain an inorganic network precursor, and its high-temperature storage modulus was only 5.2 MPa. After undergoing high and low temperature cycling, the coating cracked and the adhesion decreased. This indicates that a simple polyurethane network cannot withstand the internal stress generated by alternating high and low temperatures.

[0121] Comparative Example 2 formulation did not contain the silane coupling agent APTES. Although its high-temperature modulus was improved due to the presence of TEOS, its flexibility and initial adhesion both decreased. The coating failed severely after high and low temperature cycling. This indicates that APTES plays a crucial role in constructing the organic-inorganic two-phase interface layer and improving the compatibility and bonding between the two phases. Without effective interfacial bonding, the inorganic phase cannot effectively disperse stress and may even become a stress concentration point.

[0122] Comparative Example 3 used conventional dibutyltin dilaurate as a catalyst, resulting in an increased Tg, decreased flexibility (T-bend), and a significantly lower high-temperature modulus than the examples. This is attributed to the catalyst's inability to achieve temporal selectivity in the reaction; the polyurethane formation and TEOS hydrolysis-condensation reactions occurred simultaneously and competed with each other, leading to increased network structure defects, severe phase separation, and the inability to form a regular interpenetrating network, thus deteriorating macroscopic properties.

[0123] The formulation of Comparative Example 4 lacks the latent catalyst IIa. Its performance data is similar to that of Comparative Example 1, with an extremely low high-temperature modulus, and it fails the high and low temperature cycling test. This proves that even if the formulation contains TEOS, the hydrolysis and condensation reaction of TEOS cannot proceed effectively without an effective catalyst at high temperatures, the inorganic network cannot be formed, and the material properties cannot be improved.

[0124] In summary, the composite catalytic system and interfacial coupling technology used in the examples enabled the preferential formation of the polyurethane network at low temperatures and the subsequent formation of the silica network at high temperatures. This sequentially constructed interpenetrating network structure is the structural basis for the coating material to simultaneously possess both low-temperature flexibility and high-temperature rigidity, ultimately passing rigorous high and low temperature cycling impact tests.

[0125] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A functional polyurethane coating material resistant to high and low temperature impacts, characterized in that, The material is made from raw materials comprising the following parts by weight: 70-90 parts of polyol component; 20-32 parts of polyisocyanate; wherein the polyisocyanate is a polymethylene polyphenyl polyisocyanate; Chain extender 2.9–5.0 parts; 8.0–15.0 parts of an inorganic network precursor; the inorganic network precursor is tetraethyl orthosilicate; 1.5 to 2.5 parts of silane coupling agent; wherein the silane coupling agent is 3-aminopropyltriethoxysilane; Catalyst I: 0.05–0.15 parts; Catalyst I is bismuth neodecanoate; Latent catalyst II: 0.10–0.20 parts; wherein the latent catalyst II is an amine salt prepared by reacting p-toluenesulfonic acid with a volatile amine, wherein the volatile amine is triethylamine or N,N-diisopropylamine; The coating material is prepared by a process including the following steps: (a) The polyol component is reacted with the polyisocyanate to obtain a polyurethane prepolymer; then the inorganic network precursor and the silane coupling agent are added to the prepolymer and mixed evenly to obtain component A. (b) Dissolve the chain extender, catalyst I, and latent catalyst II in an organic solvent to obtain component B; (c) Mix component A and component B, perform a first stage of low-temperature curing, and then perform a second stage of high-temperature curing to obtain the functional polyurethane coating material; wherein the temperature of the first stage of low-temperature curing is 35-50°C; and the temperature of the second stage of high-temperature curing is 100-120°C.

2. The functional polyurethane coating material resistant to high and low temperature impact according to claim 1, characterized in that, The polyol component is composed of polytetrahydrofuran ether diol and polypropylene glycol, wherein the weight ratio of polytetrahydrofuran ether diol to polypropylene glycol is (65-75):(5-15).

3. A preparation process for a functional polyurethane coating material resistant to high and low temperature impact as described in claim 1 or 2, characterized in that, Includes the following steps: (a) The polyol component is reacted with the polyisocyanate to obtain a polyurethane prepolymer; then the inorganic network precursor and the silane coupling agent are added to the prepolymer and mixed evenly to obtain component A. (b) Dissolve the chain extender, catalyst I, and latent catalyst II in an organic solvent to obtain component B; (c) Mix component A and component B, perform a first stage of low-temperature curing, and then perform a second stage of high-temperature curing to obtain the functional polyurethane coating material; wherein the temperature of the first stage of low-temperature curing is 35-50°C; and the temperature of the second stage of high-temperature curing is 100-120°C.

4. The preparation process according to claim 3, characterized in that, In step (a), the reaction temperature of the polyol component with the polyisocyanate is 78–82 °C, and the reaction time is 2.5–3.0 hours.

5. The preparation process according to claim 3, characterized in that, In step (a), the molar ratio of the -NCO group in the polyisocyanate to the -OH group in the polyol component is 1.8 to 2.2:

1.

6. The preparation process according to claim 3, characterized in that, Before reacting the polyol component with the polyisocyanate in step (a), the method further includes a step of dehydrating the polyol component at 110°C and under vacuum.

Images