Low-temperature-resistant polyurethane coating, coating as well as preparation method and application of low-temperature-resistant polyurethane coating

Abstract

The invention discloses a low-temperature-resistant polyurethane coating, a coating as well as a preparation method and application of the low-temperature-resistant polyurethane coating, and belongs to the field of coatings. The low-temperature-resistant polyurethane coating is prepared from the following components in parts by mass: 40 to 850 parts of mercaptan, 90 to 160 parts of an epoxy compound and 20 to 100 parts of isocyanate or isothiocyanate, the mercaptan is a mixture of branched chain multi-mercapto mercaptan and linear mercaptan in a molar ratio of (3.5-4.5): (5.5-6.5). The branched-chain multi-mercapto mercaptan and the linear mercaptan are compounded, the branched-chain multi-mercapto mercaptan provides a cross-linking point, the linear mercaptan provides a flexible interval, and the branched-chain multi-mercapto mercaptan and the linear mercaptan are matched for use according to a certain proportion, so that the balance of a cross-linked network and chain segment movement is optimized, and the polyurethane coating can still keep the dynamic response capability at low temperature (such as liquid nitrogen). The lapping shear strength of the stainless steel is concentrated at 45-55 MPa, the surface hydrophobic angle is 90-120 degrees, and high and low temperature resistance and solvent resistance are excellent.

Description

Technical Field

[0001] The present invention belongs to the field of coatings, and in particular relates to a low-temperature resistant polyurethane coating, a coating, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Solvent-free polyurethanes play a key role in numerous fields, including construction, textiles, electronics, and aerospace, due to their environmental friendliness, low volatile organic compound (VOC) emissions, and excellent chemical adhesion and film-forming properties. As industrial applications demand increased tolerance for materials in extreme environments, solvent-free polyurethanes must also be further enhanced in their ability to withstand these conditions. For example, they must possess properties such as high strength, high and low temperature resistance, fatigue resistance, aging resistance, chemical corrosion resistance, and electrical insulation with enhanced adhesion strength. These properties must be able to withstand extreme temperatures ranging from -130°C to over 300°C, high humidity, high load mechanical stress, and severe corrosion.

[0004] Conventional polyurethanes, in existing technologies, often experience brittle fracture and shedding under extreme conditions due to hindered molecular chain motion, leading to adhesive failure. Studies have used epoxy resin to modify polyurethane, and while the introduction of a rigid ring structure improves mechanical strength, the elongation at break drops sharply at -60°C, making it unsuitable for low-temperature environments. Plasticization with long-chain alkanes improves the material's flexibility, lowering the glass transition temperature. However, the reduced crosslinking density leads to poor solvent resistance, making it difficult to use in organic solvent environments for extended periods. Summary of the Invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a solvent-free polyurethane coating material and a preparation method thereof. The composite thiol-modified polyurethane coating provided by the present invention has excellent performance, high adhesion strength to the surfaces of various types of substances, no solvent pollution to the environment, and excellent low-temperature resistance and solvent resistance.

[0006] This invention aims to address the problems of existing solvent-free polyurethane coatings in extreme environments, such as adhesive degradation, brittle fracture, and shedding, leading to adhesive failure. Traditional solvent-free polyurethane coatings, which are primarily based on a reaction system consisting of hydroxyl polyols and isocyanates, have a flexible structure but insufficient crosslinking density. They are susceptible to corrosion by moisture and organic solvents, leading to interfacial failure. Furthermore, at low temperatures, molecular chain motion is hindered, leading to brittle failure and failure, making them unsuitable for use in extreme environments.

[0007] To overcome the aforementioned technical problems, the present invention proposes a polyurethane material based on a compounded thiol mixture and a method for strengthening its interface in extreme low-temperature environments (-196°C to -60°C). This material is particularly suitable for special applications such as sealing coatings for cryogenic aerospace propellant tanks and anti-icing coatings for polar equipment. The system comprises a thiol, an epoxy compound, and an isocyanate or isothiocyanate. The thiol is a mixture of branched polythiothiols and linear thiols. Branched polythiothiols contain two or more thiol (-SH) groups and exhibit a dendritic or star-shaped molecular chain structure, providing high crosslink density, abundant functional groups, and steric hindrance. Linear thiols contain two or more thiol groups and have a straight molecular chain, which provides segmental freedom of movement and regular packing, imparting flexibility to the molecular chain. The present invention adopts a mixture of branched polythiothiols and linear thiols. The branched polythiothiols provide crosslinking points and the linear thiols provide flexible intervals. The two are used in a certain proportion to optimize the balance between the crosslinking network and the chain segment movement, so that the polyurethane coating can still maintain dynamic response capabilities at low temperatures (such as -196°C liquid nitrogen).

[0008] In order to achieve the above object, the technical solution of the present invention is: The first aspect of the present invention provides a low-temperature resistant polyurethane coating comprising, by mass, 40-850 parts of a thiol, 90-160 parts of an epoxy compound, and 20-100 parts of an isocyanate or an isothiocyanate; The mercaptan is a mixture of branched polythiothiol and linear mercaptan in a molar ratio of (3.5-4.5): (5.5-6.5).

[0009] In some embodiments of the present invention, the branched polythiol thiol functionality is ≥3, and the linear thiol functionality is >1.

[0010] It is understood that the term functionality refers to the number of functional groups that can participate in a condensation reaction on a monomer molecule. Specifically, in the present invention, functionality refers to the number of thiol groups in a branched polythiol thiol molecule or a linear thiol molecule. For example, a branched polythiol thiol having a functionality of 3 means that the branched polythiol thiol molecule contains three thiol groups.

[0011] Higher functionality in branched polythiothiols provides higher crosslink density and solvent resistance for low-temperature resistant polyurethane coatings. Furthermore, the hydrophobic branches (such as long-chain alkyl groups) in branched polythiothiols, combined with the dynamic network of thioether bonds, inhibit water penetration, while the regular segmental arrangement of linear thiols reduces solvent diffusion pathways. Together, these two properties significantly enhance the coating's hydrophobicity and solvent resistance.

[0012] In some embodiments of the present invention, the branched polythiothiols include, but are not limited to, any one of multifunctional thiols, hyperbranched thiols, heteroatom-containing branched thiols, bio-based branched thiols, and fluorine / silicon-containing branched thiols. The above-mentioned branched polythiothiols are conventional commercial products and can be purchased.

[0013] The multifunctional thiols include, but are not limited to, pentaerythritol tetrakis-3-mercaptopropionate (PETMP) and trimethylolpropane tris-3-mercaptopropionate (TMPTMP). PETMP, with a functionality of 4, provides a high crosslink density, enhancing coating hardness and solvent resistance. TMPTMP, with a functionality of 3 and a moderate degree of branching, balances flexibility and a crosslinked network.

[0014] The hyperbranched thiols include but are not limited to the Boltorn™ series of hyperbranched polyester thiol derivatives, whose intramolecular cavities can inhibit low-temperature crystallization, and whose dynamic thioether bonds can enhance the toughness of the coating.

[0015] Among them, the heteroatom-containing branched thiol includes but is not limited to 2,3-bis(2-mercaptoethylthio)propanethiol (DMPT), which contains multiple thioether bonds (-S-), can enhance the dynamic bond exchange ability of the coating and facilitate low-temperature interface reconstruction.

[0016] The bio-based branched-chain thiol includes but is not limited to cysteine-lysine dendrimer polypeptide derivatives, which are biodegradable and suitable for coating medical cryogenic equipment.

[0017] Wherein, the fluorine-containing / silicon-branched thiol is but not limited to perfluoroalkylethylthiol-acrylate copolymer ((CF3(CF2)5CH2CH2SCH2CH2SH) n ), the fluorine segments contained in it can give the coating excellent hydrophobicity (contact angle>120°), reduce the surface energy and inhibit the adhesion of ice crystals.

[0018] In some embodiments of the present invention, the branched polythiothiol is preferably at least one of 2,3-dithio(2-mercapto)-1-propanethiol, pentaerythritol tetrakis-3-mercaptopropionate, and trimethylolpropane tris-3-mercaptopropionate. These three branched polythiothiols have 3-4 functional groups and long-chain alkyl groups, which can provide higher crosslinking density and steric hindrance, thereby better optimizing the balance between the crosslinking network and segmental motion.

[0019] In some embodiments of the present invention, the linear thiol chain length is ≥6, including but not limited to at least one of 1,6-hexanedithiol, 1,8-octanedithiol, 2,2'-thiodiethylmercaptan, 4,4'-dimercaptodiphenyl sulfide, and 2-ethylhexyl thioglycolate. A linear thiol chain length of ≥6 can avoid low-temperature shrinkage stress concentration caused by short chains (such as EDT).

[0020] In some embodiments of the present invention, the epoxy compound includes at least one of ethylene epoxide, cyclohexane oxide, fatty alcohol epoxide, benzene epoxide, fatty acid epoxide, propylene oxide, and ethylene oxide.

[0021] In some embodiments of the present invention, the isocyanate includes but is not limited to at least one or more of toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), polymethylene polyphenyl polyisocyanate (PAPI), vinyl diisocyanate, tetramethylene 1,4-diisocyanate, dodecyl 1,2-diisocyanate, and 3,3-dichloro-4,4'-biphenyl diisocyanate.

[0022] In some embodiments of the present invention, the isothiocyanate is at least one or more of p-phenylenediisocyanate, 1,2-phenylenediisocyanate, and 1,8-octyldiisocyanate.

[0023] The isocyanates or isothiocyanates used in the present invention are conventional commercial products and can be purchased.

[0024] In some embodiments of the present invention, the thiol is a mixture of branched polythiothiols and linear thiols in a molar ratio of 4:6. When the proportion of branched polythiothiols is too high, the coating's crosslinking density is too high, resulting in decreased low-temperature impact toughness. When the proportion of linear thiols is too high, the coating's crosslinking is insufficient, degrading solvent resistance. At this molar ratio, the low-temperature-resistant polyurethane coating exhibits high crosslinking density, high low-temperature impact toughness, and excellent high- and low-temperature resistance and solvent resistance.

[0025] In some embodiments of the present invention, the low-temperature resistant polyurethane coating further comprises an auxiliary agent, including but not limited to any one or more of a leveling agent, a diluent, a thickener, a toughening agent, a defoaming agent, a matting agent, a light stabilizer, a mildew inhibitor, and an antistatic agent.

[0026] It can be understood that the thiol, epoxy compound and isocyanate or isothiocyanate in the low-temperature resistant polyurethane coating of the present invention are film-forming substances of the coating. When using the low-temperature resistant polyurethane coating, those skilled in the art can choose to add suitable additives according to actual needs to further improve the performance of the low-temperature resistant polyurethane coating.

[0027] The present invention does not impose any restrictions on the amount of various additives added. Those skilled in the art can select commonly used dosages in the field according to actual needs. For example, when the additive is a leveling agent, the amount of the leveling agent added is 1%-5% of the total mass of the low-temperature resistant polyurethane coating.

[0028] A second aspect of the present invention provides a method for preparing the above-mentioned low-temperature resistant polyurethane coating, comprising: Method 1: The thiol is mixed with a catalyst, an epoxy compound is added to react, and then a neutralizing agent is added to terminate the reaction to obtain an intermediate; The intermediate is mixed with isocyanate or isothiocyanate and reacted to obtain a low-temperature resistant polyurethane coating; or, Method 2: Mixing part of the mercaptan with a catalyst, adding an epoxy compound to react, and then adding a neutralizing agent to terminate the reaction to obtain an intermediate; The intermediate is mixed with the remaining mercaptan, and then isocyanate or isothiocyanate is added, mixed and reacted to obtain a low-temperature resistant polyurethane coating.

[0029] The preparation method of the low-temperature resistant polyurethane coating provided by the present invention does not use any solvent and is environmentally friendly and pollution-free.

[0030] In some embodiments of the present invention, in the method for preparing the low-temperature resistant polyurethane coating, isocyanate or isothiocyanate is added and mixed, followed by reaction, and various additives are added after the reaction is completed.

[0031] In some embodiments of the present invention, the catalyst is one of triethylenediamine, triethylamine, NN-dimethylethanolamine, trimethylbenzylamine, NN-dimethylcyclohexylamine, benzyltrimethylammonium hydroxide, and dibutyltin dilaurate.

[0032] In some embodiments of the present invention, the neutralizing agent is one of hydrochloric acid, phosphoric acid, formic acid, acetic acid and aminoacetic acid.

[0033] In some embodiments of the present invention, the added amount of the catalyst is 0.1‰-2‰ of the mass of the epoxy compound.

[0034] In some embodiments of the present invention, the amount of the neutralizer added is 0.1‰-2‰ of the mass of the epoxy compound.

[0035] In some embodiments of the present invention, the method 1 specifically includes: The thiol and the catalyst are mixed and stirred in an ice-water bath, and then the epoxy compound is slowly added in batches. After the addition is completed, the reaction is continued; finally, a neutralizing agent is added to terminate the reaction to obtain an intermediate; The intermediate is mixed with isocyanate, stirred at 20-80° C., ultrasonicated, and mixed to obtain a low-temperature resistant polyurethane coating.

[0036] In some embodiments of the present invention, the second method specifically includes: Mixing part of the mercaptan with the catalyst, stirring in an ice-water bath, then slowly adding the epoxy compound in batches, and continuing the reaction after the addition is complete; finally, adding a neutralizing agent to terminate the reaction to obtain an intermediate; The intermediate is mixed with the remaining mercaptan, and then isocyanate or isothiocyanate is added, stirred at 20-80° C., ultrasonicated, and mixed to obtain a low-temperature resistant polyurethane coating.

[0037] The mass ratio of the intermediate to the remaining thiol is 1-5:10, preferably 2-4:10.

[0038] The third aspect of the present invention provides a low-temperature resistant polyurethane coating, which is obtained by applying the above-mentioned low-temperature resistant polyurethane coating or the low-temperature resistant polyurethane coating prepared by the above-mentioned preparation method to the surface of the adhered material and vacuum drying and curing it.

[0039] The low-temperature-resistant polyurethane coating provided by the present invention has excellent performance, is colorless and transparent, has a transparency of over 95%, is non-elastomeric, has a lap shear strength of 45-55 MPa on stainless steel, and has a surface hydrophobic angle of 90°-120°.

[0040] In some embodiments of the present invention, the vacuum drying and curing temperature is 65-150° C., and the time is 1-3 h.

[0041] The fourth aspect of the present invention provides a low-temperature resistant polyurethane coating or a low-temperature resistant polyurethane coating prepared by the above-mentioned preparation method or a low-temperature resistant polyurethane coating for coating on the surface of a metal and / or non-metallic substrate.

[0042] The polyurethane coating prepared by the present invention has the following beneficial technical effects: The low-temperature-resistant polyurethane coating provided by the present invention combines high adhesion, high and low temperature resistance, and solvent resistance. By selecting a mixture of branched polythiothiols and linear thiols and defining a specific ratio between the two to optimize the balance between the crosslinking network and segmental motion, the polyurethane maintains dynamic responsiveness at low temperatures, exhibits high adhesion, and exhibits excellent solvent resistance. It is suitable for use in extreme environments such as superconducting equipment, liquid hydrogen storage tanks, and polar exploration equipment, and maintains good bonding performance within a temperature range of -196°C to 300°C.

[0043] Furthermore, combined with the data from the examples, it can be seen that the polyurethane coating provided by the present invention can firmly adhere to the surfaces of various substrates, such as metals such as stainless steel, glass, ceramics, polytetrafluoroethylene, wood and other materials. In particular, on stainless steel surfaces that have not been treated in any way, the lap shear strength can reach more than 45 MPa. The polyurethane coating provided by the present invention is bonded to the stainless steel surface, and the coating can be maintained for more than 28 days in a liquid nitrogen environment (-196°C). The lap shear strength remains almost unchanged for the first 14 days, and even becomes stronger after being placed in liquid nitrogen for 21 days, reaching 45.35±2.38 MPa. After being placed in liquid nitrogen for 28 days, it can still maintain 97.4%.

[0044] In summary, the present invention optimizes the balance between the cross-linking network and the segment motion in the low-temperature resistant polyurethane coating by combining branched polythiothiols and linear thiols, thereby expanding the application range of the polyurethane coating and making it suitable for extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0046] Figure 1 This is an infrared spectrum of a low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 of the present invention; Figure 2 This is a thermogravimetric analysis of a low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 of the present invention, wherein (a) is a TG graph and (b) is a DTG graph; Figure 3 The light transmittance of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention; Figure 4 This is the anti-graffiti test of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 of the present invention, wherein A is before the test and B is after the test; Figure 5 This is the anti-graffiti test of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 1 of the present invention, wherein A is before the test and B is after the test; Figure 6 This is the anti-graffiti test of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 2 of the present invention, wherein A is before the test and B is after the test; Figure 7 This is the anti-graffiti test of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 3 of the present invention, wherein A is before the test and B is after the test; Figure 8This is the anti-graffiti test of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 4 of the present invention, wherein A is before the test and B is after the test; Figure 9 The adhesion strength of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention on the surface of the stainless steel substrate; Figure 10 The adhesion strength of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention on the surface of the copper substrate; Figure 11 The adhesion strength of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention on the surface of the aluminum substrate; Figure 12 The adhesion strength of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention on the surface of the polytetrafluoroethylene substrate; Figure 13 The adhesive strength of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention in a liquid nitrogen environment; Figure 14 The adhesive strength of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 of the present invention in an environment of 200-280°C. DETAILED DESCRIPTION

[0047] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0048] Example 1 A low-temperature resistant polyurethane coating comprises, by weight, 50 parts of mercaptan, 100 parts of ethylene oxide, and 50 parts of MDI. The mercaptan is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 4:6.

[0049] The preparation method of the low-temperature resistant polyurethane coating comprises the following steps: 50 parts of thiol and 0.05 parts of triethylamine were weighed and placed in a round-bottom flask. A magnetic stirrer was added and magnetically stirred in an ice-water bath for 10 minutes. Then, 100 parts of ethylene oxide were slowly added dropwise to the round-bottom flask in batches, with additions every 15 minutes. After the addition was complete, the reaction was continued for 5 hours. Finally, 0.10 parts of acetic acid was added and the reaction was continued for 0.5 hours. The resulting product and 50 parts of MDI were placed in a glass bottle and stirred at 65°C for 0.6 hours. Ultrasonication was performed 1-2 times for 5 minutes each. After thorough mixing, a low-temperature-resistant polyurethane coating was obtained.

[0050] Example 2 A low-temperature resistant polyurethane coating is disclosed, which differs from Example 1 in that ethylene oxide is replaced by propylene oxide, and the remaining steps are completely consistent with Example 1.

[0051] Example 3 A low-temperature resistant polyurethane coating, which differs from Example 1 in that the thiol is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 4,4'-dimercaptodiphenyl sulfide in a molar ratio of 4:6. The remaining steps are identical to those of Example 1.

[0052] Example 4 A low-temperature resistant polyurethane coating is different from Example 1 in that the thiol is a mixture of pentaerythritol tetrakis-3-mercaptopropionate and 4,4'-dimercaptodiphenyl sulfide in a molar ratio of 4:6. The remaining steps are completely consistent with Example 1.

[0053] Example 5 A low-temperature resistant polyurethane coating, which differs from Example 1 in that the thiol is a mixture of trimethylolpropane tris-3-mercaptopropionate and 4,4'-dimercaptodiphenyl sulfide in a molar ratio of 4:6. The remaining steps are identical to those of Example 1.

[0054] Example 6 A low-temperature resistant polyurethane coating, which differs from Example 1 in that the thiol is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 3.5:6.5. The remaining steps are identical to those of Example 1.

[0055] Example 7 A low-temperature resistant polyurethane coating, which differs from Example 1 in that the thiol is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol at a molar ratio of 4.5:5. The remaining steps are identical to those of Example 1.

[0056] Example 8 A low-temperature resistant polyurethane coating is different from Example 3 in that ethylene oxide is replaced by propylene oxide, MDI is replaced by IPDI, and the remaining steps are exactly the same as those of Example 3.

[0057] Example 9 A low-temperature resistant polyurethane coating is different from Example 1 in that MDI is replaced with p-phenylenediisocyanate, and the remaining steps are completely consistent with Example 1.

[0058] Example 10 A low-temperature resistant polyurethane coating comprises 800 parts of mercaptan, 100 parts of ethylene oxide, and 50 parts of MDI. The mercaptan is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 4:6.

[0059] The preparation method of the low-temperature resistant polyurethane coating comprises the following steps: Measure 50 parts of thiol and 0.05 parts of triethylamine into a round-bottom flask, add a magnet, and place on a magnetic stirrer. Stir magnetically in an ice-water bath for 10 minutes. Then, slowly add 100 parts of ethylene oxide dropwise to the round-bottom flask in batches, adding once every 15 minutes. After the addition is complete, continue the reaction for 5 hours. Finally, add 0.10 parts of acetic acid and react for 0.5 hours.

[0060] 750 parts of mercaptan and the resulting product were mixed in a 10:2 ratio, then placed in a glass bottle with 50 parts of MDI. The mixture was stirred at 65°C for 0.6 hours and ultrasonicated 1-2 times for 5 minutes each. After thorough mixing, a low-temperature-resistant polyurethane coating was obtained.

[0061] Example 11 A low-temperature resistant polyurethane coating comprises 425 parts of mercaptan, 100 parts of ethylene oxide, and 50 parts of MDI. The mercaptan is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 4:6.

[0062] The preparation method of the low-temperature resistant polyurethane coating comprises the following steps: Measure 50 parts of thiol and 0.05 parts of triethylamine into a round-bottom flask, add a magnet, and place on a magnetic stirrer. Stir magnetically in an ice-water bath for 10 minutes. Then, slowly add 100 parts of ethylene oxide dropwise to the round-bottom flask in batches, adding once every 15 minutes. After the addition is complete, continue the reaction for 5 hours. Finally, add 0.10 parts of acetic acid and react for 0.5 hours.

[0063] 375 parts of mercaptan and the resulting product were mixed in a 10:4 ratio, then placed in a glass bottle with 50 parts of MDI. The mixture was stirred at 65°C for 0.6 hours and ultrasonicated 1-2 times for 5 minutes each. After thorough mixing, a low-temperature-resistant polyurethane coating was obtained.

[0064] Example 12 A low-temperature resistant polyurethane coating comprises 800 parts of mercaptan, 100 parts of ethylene oxide, and 50 parts of 1,8-diisothiocyanate. The mercaptan is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 4:6.

[0065] The preparation method of the low-temperature resistant polyurethane coating comprises the following steps: Measure 50 parts of thiol and 0.05 parts of triethylamine into a round-bottom flask, add a magnet, and place on a magnetic stirrer. Stir magnetically in an ice-water bath for 10 minutes. Then, slowly add 100 parts of ethylene oxide dropwise to the round-bottom flask in batches, adding once every 15 minutes. After the addition is complete, continue the reaction for 5 hours. Finally, add 0.10 parts of acetic acid and react for 0.5 hours.

[0066] 750 parts of mercaptan and the resulting product were mixed in a 10:2 ratio, then added to 50 parts of 1,8-diisothiocyanate in a glass bottle. The mixture was stirred at 65°C for 0.6 hours and ultrasonicated 1-2 times for 5 minutes each. After thorough mixing, a low-temperature-resistant polyurethane coating was obtained.

[0067] Comparative Example 1 A low-temperature resistant polyurethane coating is different from Example 1 in that the thiol is 2,3-dithio(2-mercapto)-1-propanethiol. The remaining steps are the same as those of Example 1.

[0068] Comparative Example 2 A low-temperature resistant polyurethane coating is different from Example 1 in that the thiol is 1,6-hexanedithiol. The remaining steps are the same as those of Example 1.

[0069] Comparative Example 3 A low-temperature resistant polyurethane coating is different from Example 1 in that: the thiol is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 3:7.

[0070] Comparative Example 4 A low-temperature resistant polyurethane coating is different from Example 1 in that: the thiol is a mixture of 2,3-dithio(2-mercapto)-1-propanethiol and 1,6-hexanedithiol in a molar ratio of 5:5.

[0071] Performance Verification The low-temperature resistant polyurethane coatings obtained in Examples 1-12 and Comparative Examples 1-4 were applied to the surface of the adhered material and reacted in a vacuum drying oven at 75° C. using a vacuum drying method. After 2 hours, the reaction was completed to obtain a cured low-temperature resistant polyurethane coating.

[0072] The properties of the obtained low-temperature resistant polyurethane coating were tested, as follows: (1) Structural inspection The low-temperature resistant polyurethane coating obtained in Example 1 was made into a low-temperature resistant polyurethane coating and infrared spectroscopy was performed. Figure 1 As shown, the generated carbamate groups can be observed at 3300-3500 cm -1There is -NH stretching vibration at 1700-1730 cm -1 The stretching vibration of the C=O bond at 1530-1560 cm -1 There is CNH stretching vibration at ~1690 cm -1 (C=O) and ~720 cm -1 (CS) appears at the same time, indicating that a thiocarbamate group has been generated. -1 There is a weak peak at , which may be a disulfide bond.

[0073] Similarly, the low-temperature resistant polyurethane coatings prepared from the low-temperature resistant polyurethane coatings obtained in Examples 2-12 and Comparative Examples 3 and 4 also contain carbamate groups and thiocarbamate groups.

[0074] The low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 1 only contains thiocarbamate groups but no carbamate groups.

[0075] The low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 2 contains only carbamate groups and no thiocarbamate groups.

[0076] (2) Thermogravimetric analysis The low-temperature resistant polyurethane coating obtained in Example 1 was subjected to thermogravimetric analysis. Figure 2 As shown in the TG and DTG diagrams, it can be observed that the sample has good thermal stability and decomposition will not occur until above 300°C.

[0077] Similarly, the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 2-12 has good thermal stability and will not decompose until the temperature is between 250°C and 280°C.

[0078] Compared with the thermal stability of the low-temperature resistant polyurethane coating made from the low-temperature resistant polyurethane coating obtained in Example 1, the thermal stability of the low-temperature resistant polyurethane coating made from the low-temperature resistant polyurethane coatings obtained in Comparative Examples 1-4 is worse.

[0079] (3) Light transmittance test The low-temperature resistant polyurethane coatings obtained in the examples and comparative examples were evenly coated on glass slides, respectively, and heated on a heating table at 120° C. to a solid state to obtain a low-temperature resistant polyurethane coating, and the transmittance thereof was tested using a TGL-18 transmittance meter.

[0080] The light transmittance of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 and Comparative Examples 1-4 is as follows: Figure 3As shown, the light transmittance of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 reaches more than 97%, while the light transmittance of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coatings obtained in Comparative Examples 1-4 is lower than 97%.

[0081] Similarly, the light transmittance of the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 2-12 also reached 97%.

[0082] (4) Anti-graffiti detection The low-temperature-resistant polyurethane coatings obtained in the examples and comparative examples were uniformly applied to PVC surfaces using a blade coating method and vacuum-dried at 65°C for 3-4 hours to obtain low-temperature-resistant polyurethane coatings. Graffiti was then applied to the low-temperature-resistant polyurethane coatings using an oil-based marker and a ballpoint pen. Ketchup and coffee were then applied to the coatings, which were then left to stand overnight at room temperature before being wiped.

[0083] like Figure 4 As shown, it can be observed that the ketchup and coffee stains on the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Example 1 are completely erased, and there are slight residues of marker and ballpoint pen graffiti stains.

[0084] like Figure 5 As shown, the ketchup and coffee stains on the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 1 were completely erased, but the oil-based marker and ballpoint pen could not erase them.

[0085] like Figure 6 As shown, the ketchup and coffee stains on the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 2 can be wiped off, but there are traces of soaking, and there are some residues of oil-based markers and ballpoint pens.

[0086] like Figure 7 As shown, the ketchup on the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Example 3 has slight traces after being erased, the coffee can be completely erased, and the oil-based marker and ballpoint pen cannot be erased.

[0087] like Figure 8 As shown, the ketchup and coffee stains on the low-temperature resistant polyurethane coating prepared by the low-temperature resistant polyurethane coating obtained in Comparative Example 4 can be completely erased without leaving any traces, but the oil-based marker and ballpoint pen can only partially erase them, but cannot completely erase them.

[0088] (5) Adhesive strength The low-temperature resistant polyurethane coatings obtained in the examples and comparative examples were applied to different substrates by hot pressing and overlap sheared. The contact area was 125 cm 2 The hot pressing temperature is 120℃ and the hot pressing time is 4.5 h. When the sample is completely dry, a tensile test can be performed using a tensile testing machine.

[0089] After testing, such as Figure 9 、 10 As shown in Figures 11 and 12, the low-temperature-resistant polyurethane coating prepared using the low-temperature-resistant polyurethane coating obtained in Example 1 exhibited an adhesive strength of approximately 45 MPa on stainless steel, approximately 38 MPa on copper, approximately 25 MPa on aluminum, and approximately 1.2 MPa on polytetrafluoroethylene. The adhesive strengths of the low-temperature-resistant polyurethane coatings prepared using the low-temperature-resistant polyurethane coatings obtained in Comparative Examples 1-4 on stainless steel, copper, aluminum, and polytetrafluoroethylene surfaces were all lower than those of Example 1.

[0090] After testing, the adhesion strength of the low-temperature resistant polyurethane coating obtained in Example 2-12 on the stainless steel surface was 37-41 MPa.

[0091] (6) Low temperature resistance test The low-temperature resistant polyurethane coatings obtained in Example 1 and Comparative Examples 1-4 were applied to the surface of a stainless steel substrate and then hot-pressed and cured to obtain a low-temperature resistant polyurethane coating. The coating was placed in a liquid nitrogen (-196°C) environment, and the adhesion strength of the coating to the stainless steel substrate was tested on the 7th, 14th, 21st, and 28th days.

[0092] like Figure 13 As shown, the low-temperature-resistant polyurethane coating prepared from the low-temperature-resistant polyurethane coating obtained in Example 1 maintained its adhesive strength for over 28 days after bonding to stainless steel. The adhesive strength remained virtually unchanged for the first 14 days and even increased significantly after 21 days in liquid nitrogen, reaching 45.35 ± 2.38 MPa. Even after 28 days in liquid nitrogen, 97.4% of the strength was still maintained.

[0093] After the low-temperature resistant polyurethane coating prepared from the low-temperature resistant polyurethane coating obtained in Comparative Examples 1-4 was bonded to stainless steel and placed in a liquid nitrogen environment for 28 days, the adhesive strength gradually decreased.

[0094] (7) High temperature resistance test The low-temperature resistant polyurethane coatings obtained in Example 1 and Comparative Examples 1-4 were applied to the surface of a stainless steel substrate and overlapped and sheared. The contact area of ​​the stainless steel substrate was 125 cm 2 The hot pressing temperature was 120 °C, the hot pressing time was 4.5 h, and the sample was placed in a muffle furnace until it was completely dry. The temperatures were 200 °C, 225 °C, 250 °C, 265 °C and 280 °C for 30 minutes, and then taken out for tensile testing.

[0095] like Figure 14As shown, the low-temperature-resistant polyurethane coating prepared from the low-temperature-resistant polyurethane coating obtained in Example 1 had adhesive strengths of 45.86±4.65, 43.47±1.70, 30.34±2.66, 39.76±0.67, and 8.91±2.34 MPa, respectively, after heating in a muffle furnace at 200°C, 225°C, 250°C, 265°C, and 280°C for 30 minutes. At different temperatures, the adhesive strength of the low-temperature-resistant polyurethane coating obtained in Example 1 was superior to that of Comparative Examples 1-4.

[0096] (8) Corrosion resistance testing The low-temperature-resistant polyurethane coating obtained in Example 1 was applied to a stainless steel substrate and then hot-pressed and cured to produce a low-temperature-resistant polyurethane coating. The coating's adhesive strength was measured after immersion in a 2% potassium permanganate solution. After 72 hours, it reached a maximum of 75% of its initial strength and maintained approximately 47% after 120 hours.

[0097] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A low-temperature resistant polyurethane coating, characterized in that: Calculated by mass, it comprises: 40-850 parts of mercaptan, 90-160 parts of epoxy compound, and 20-100 parts of isocyanate or isothiocyanate; The mercaptan is a mixture of branched polythiothiol and linear mercaptan in a molar ratio of (3.5-4.5): (5.5-6.5).

2. The low-temperature resistant polyurethane coating according to claim 1, characterized in that: The branched polythiol thiol functionality is ≥3, and the linear thiol functionality is >1.

3. The low-temperature resistant polyurethane coating according to claim 2, characterized in that: The branched polythiol mercaptan includes at least one of 2,3-dithio(2-mercapto)-1-propanethiol, pentaerythritol tetrakis-3-mercaptopropionate and trimethylolpropane tris-3-mercaptopropionate; The linear mercaptan includes at least one of 1,6-hexanedithiol, 1,8-octanedithiol, 2,2′-thiodiethylmercaptan, 4,4′-dimercaptodiphenyl sulfide, and 2-ethylhexyl thioglycolate.

4. The low-temperature resistant polyurethane coating according to claim 1, characterized in that: The epoxy compound includes at least one of ethylene epoxide, cyclohexane oxide, fatty alcohol epoxide, benzene epoxide, fatty acid epoxide, propylene oxide and ethylene oxide; The isocyanate is at least one of toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hexamethylene diisocyanate, polymethylene polyphenyl polyisocyanate, vinyl diisocyanate, tetramethylene 1,4-diisocyanate, dodecyl 1,2-diisocyanate and 3,3-dichloro-4,4'-biphenyl diisocyanate; The isothiocyanate is at least one of p-phenylenediisocyanate, 1,2-phenylenediisocyanate and 1,8-octyldiisocyanate.

5. The low-temperature resistant polyurethane coating according to claim 1, characterized in that: The thiol is a mixture of branched polythiothiol and linear thiol in a molar ratio of 4:

6.

6. A method for preparing the low-temperature resistant polyurethane coating according to any one of claims 1 to 5, characterized in that: include: Method 1: The thiol is mixed with a catalyst, an epoxy compound is added to react, and then a neutralizing agent is added to terminate the reaction to obtain an intermediate; The intermediate is mixed with isocyanate or isothiocyanate and reacted to obtain a low-temperature resistant polyurethane coating; or, Method 2: Mixing part of the mercaptan with a catalyst, adding an epoxy compound to react, and then adding a neutralizing agent to terminate the reaction to obtain an intermediate; The intermediate is mixed with the remaining mercaptan, and then isocyanate or isothiocyanate is added, mixed and reacted to obtain a low-temperature resistant polyurethane coating.

7. The preparation method according to claim 6, wherein The catalyst is one of triethylenediamine, triethylamine, NN-dimethylethanolamine, trimethylbenzylamine, NN-dimethylcyclohexylamine, benzyltrimethylammonium hydroxide, and diethylbutylene dilaurate; The neutralizing agent is one of hydrochloric acid, phosphoric acid, formic acid, acetic acid and aminoacetic acid; The amount of the catalyst added is 0.1‰-2‰ of the mass of the epoxy compound; The amount of the neutralizer added is 0.1‰-2‰ of the mass of the epoxy compound.

8. A low-temperature resistant polyurethane coating, characterized in that: The low-temperature resistant polyurethane coating is obtained by coating the low-temperature resistant polyurethane coating according to any one of claims 1 to 5 or the low-temperature resistant polyurethane coating prepared by the preparation method according to any one of claims 6 to 7 on the surface of the adhered material, and vacuum drying and curing the coating.

9. The low-temperature resistant polyurethane coating according to claim 8, characterized in that: The vacuum drying temperature is 65-150° C. and the time is 1-3 h.

10. Use of the low-temperature resistant polyurethane coating according to any one of claims 1 to 5, or the low-temperature resistant polyurethane coating prepared by the preparation method according to claim 6 or 7, or the low-temperature resistant polyurethane according to claim 8 or 9 on a metal and / or non-metal substrate coating.

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