High-elasticity hand-scraping waterproof polyurethane coating based on modified MDI prepolymer and preparation method of high-elasticity hand-scraping waterproof polyurethane coating

Abstract

The invention belongs to the technical field of coatings, and provides a high-elasticity hand-scraping waterproof polyurethane coating based on a modified MDI prepolymer and a preparation method of the high-elasticity hand-scraping waterproof polyurethane coating. The modified MDI prepolymer is used as a core crosslinking component, and when the modified MDI prepolymer reacts with the modified polyether polyol and the modified polyester polyol, a high-density polyurethane network structure can be uniformly formed. The aromatic ring structure of the MDI prepolymer significantly enhances the chemical stability and weather resistance of the system, the modified polyether polyol and the modified polyester polyol are used as copolymerization components, and the flexibility of the molecular structure is regulated by introducing an acrylic acid group, a silicon-oxygen bond and a flexible ester bond respectively; in addition, through the synergistic effect of the modified polyether polyol and the polyester polyol, a silicon-oxygen bond and an acrylic acid group are respectively introduced, so that the weather resistance of the coating is enhanced. The polyurethane coating prepared by the invention has high elasticity, water resistance and weather resistance, and meets the long-term use requirement in a complex environment.

Description

Technical Field

[0001] The invention belongs to the technical field of coatings and relates to a high-elasticity hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer and a preparation method thereof. Background Art

[0002] Polyurethane coatings are widely used in the fields of construction, automobiles, electronics, etc. due to their excellent physical and chemical properties. Traditional polyurethane coatings are usually prepared by reacting MDI (diphenylmethane diisocyanate) with polyols. With the improvement of coating performance requirements, single MDI coatings can no longer meet the needs of high elasticity and high durability. Therefore, the development of coatings based on modified MDI prepolymers has become an important research direction. Modified MDI prepolymers can effectively improve the elasticity and water resistance of coatings by introducing different modifiers, so that they can still maintain good performance under extreme environments. In addition, hand-scraped coatings are particularly suitable for coating of complex structures and irregular surfaces due to their convenient construction and wide applicability. The Chinese patent application with publication number CN107286309A prepared a low-VOC high-performance two-component hand-scraped polyurea waterproof coating, and its preparation method contains carbon black and fumed silica. These fillers are easy to aggregate during high-speed stirring and are difficult to fully disperse. Although these ingredients can improve the strength and wear resistance of the coating, they may reduce the flexibility of the coating. Therefore, it is necessary to develop a highly elastic hand-scraped waterproof polyurethane coating based on modified MDI prepolymer. Summary of the invention

[0003] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a highly elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer and a preparation method thereof. The aromatic ring structure of the MDI prepolymer significantly enhances the chemical stability and weather resistance of the system. Modified polyether polyols and modified polyester polyols are used as copolymer components, and acrylic groups, silane bonds and flexible ester bonds are introduced respectively to regulate the flexibility of the molecular structure, thereby meeting the needs of actual production.

[0004] To achieve this object, the present invention adopts the following technical solutions:

[0005] In a first aspect, the present invention provides a method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer, the preparation method comprising:

[0006] Step S1, heating diphenylmethane diisocyanate to a first temperature, then adding dicyclohexylmethane diisocyanate, adjusting the temperature to a second temperature for sufficient reaction, then adding m-xylyl diisocyanate to continue the reaction, continuing to add vinyl triethoxysilane, raising the temperature to a third temperature for continued reaction, then adding hydroxyethyl acrylate and a catalyst, maintaining the third temperature for continued reaction, then adding maleic anhydride and an initiator, maintaining the third temperature for continued reaction, then adding glycidyl methacrylate, maintaining the third temperature for continued reaction, adding polycaprolactone diol, continuing the reaction at the third temperature to obtain modified diphenylmethane diisocyanate, mixing the modified diphenylmethane diisocyanate with polytetrahydrofuran, continuing the reaction at the third temperature to obtain a diphenylmethane diisocyanate prepolymer;

[0007] Step S2, heating the polyether polyol to a third temperature, adding an initiator and glycidyl methacrylate, heating to a fourth temperature for sufficient reaction, adding isobornyl acrylate to continue the reaction, adjusting the temperature to the second temperature, adding γ-methacryloxypropyltrimethoxysilane and stannous acetate, heating to a third temperature for sufficient reaction, and obtaining a modified polyether polyol;

[0008] Step S3, heating the polyester polyol to the third temperature, adding dimethyl propanediol and a catalyst, raising the temperature to the fifth temperature under nitrogen protection for full reaction, cooling to 100° C., adding dicyclohexylmethane-4,4′-diisocyanate, raising the temperature to the fifth temperature for further reaction, and then adding caprolactone for full reaction to obtain a modified polyester polyol;

[0009] Step S4, adding diphenylmethane diisocyanate prepolymer, modified polyether polyol, modified polyester polyol, filler, dibutyltin dioctoate, additives, antioxidants and ultraviolet absorbers in sequence, stirring and mixing at a sixth temperature at a first stirring speed, and obtaining a high-elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer after vacuum degassing.

[0010] The aromatic ring structure of MDI (diphenylmethane diisocyanate) is the source of the rigid molecular skeleton. Its symmetry and high reactivity make it easy to react with hydroxyl groups to form polyurethane bonds. The aromatic ring provides strong mechanical strength and chemical corrosion resistance in the molecular structure. Dicyclohexylmethane diisocyanate is an alicyclic isocyanate that provides high flexibility and resistance to ultraviolet aging. The alicyclic structure is not as rigid as the aromatic ring, and can increase the proportion of flexible segments, thereby improving the toughness of the coating. The aromatic ring of m-phenylenediisocyanate contains two isocyanate groups, and the symmetry of the meta-substitution helps to form a uniform cross-linked network, providing a rigid effect. However, due to its meta-position structure, the molecular chain has a certain rotatability, which increases the flexibility of the molecular chain. The triethoxysilane group of vinyltriethoxysilane is gradually hydrolyzed to form silanols in the reaction, and then forms a siloxane bond through a condensation reaction. The siloxane bond is an extremely stable chemical structure that gives the coating weather resistance and chemical corrosion resistance. The introduction of the siloxane bond also forms a dense inorganic barrier that prevents the penetration of external moisture, oxygen and corrosive chemicals. The hydroxyl group on the hydroxyethyl acrylate molecule is a nucleophilic reagent that can undergo a nucleophilic addition reaction with the diphenylmethane diisocyanate group to generate a new polyurethane segment. In the diphenylmethane diisocyanate group, the carbon atom exhibits strong electrophilicity due to being connected to highly electronegative nitrogen and oxygen, which makes it easy to be attacked by nucleophilic reagents (such as the oxygen atom in the hydroxyl group). The oxygen atom in the hydroxyl group carries a lone pair of electrons and attacks the electrophilic carbon atom in the diphenylmethane diisocyanate group to form a negatively charged intermediate, which then undergoes proton transfer to generate the final urethane structure, i.e., the polyurethane segment, providing a dynamically adjustable molecular network and enhancing the flexibility and elasticity of the material.

[0011] The maleic anhydride molecule contains a five-membered anhydride group (anhydrous diacid structure), which is a highly active chemical group that can undergo a ring-opening reaction with the hydroxyl or amine group in the system to form an ester bond or an amide bond, respectively. The anhydride group is a strong electrophilic center, consisting of two carbonyl groups and a carboxyl oxygen atom. The carboxyl oxygen atom easily attracts electrons, making the two carbonyl carbon atoms in the anhydride ring show strong electrophilicity. The hydroxyl group acts as a nucleophilic reagent, and the lone pair of electrons on its oxygen atom attacks the carbonyl carbon atom of the anhydride group, resulting in the opening of the anhydride ring, generating a carboxylic acid and an ester bond. The nitrogen atom in the amine group is a stronger nucleophilic reagent that can attack the carbonyl carbon atom of the anhydride group. After the anhydride ring is opened, a carboxylic acid and an amide bond are formed. The ester bond and the amide bond are two highly stable chemical bonds, which increase the cross-linking of the molecular chain and enhance the chemical strength and durability of the molecular network. At the same time, the maleic anhydride molecule also contains a carbon-carbon double bond, which is an unsaturated conjugated structure and can participate in free radical polymerization. The double bond electron cloud density in the maleic anhydride molecule is high, which is easily attacked by free radicals, and electron transfer is generated while a new free radical is generated in the double bond. The generated new free radical will continue to attack other molecules containing double bonds to generate chain growth reactions. Since the double bonds of maleic anhydride can be cross-linked with other double bond molecules, a highly cross-linked three-dimensional network is finally formed. The free radical polymerization of the double bonds of maleic anhydride provides additional cross-linking points for the system, greatly improving the compactness of the molecular network. Diisopropyl peroxide also promotes the free radical polymerization of double bonds in the system. Under heating conditions, the peroxide bond of diisopropyl peroxide is homolytically cleaved to generate two isopropyl radicals. The generated free radicals have unpaired electrons and show strong reactivity, especially adding to the double bonds in the system (such as the double bonds of the acrylic acid group or the double bonds of maleic anhydride), initiating free radical polymerization, further initiating chain growth and cross-linking reactions. Maleic anhydride reacts with hydroxyl or amine groups to form ester bonds or amide bonds, thereby improving the strength and stability of the chemical network. The carbon-carbon double bonds increase the cross-linking points through free radical polymerization to construct a three-dimensional cross-linked network. Diisopropyl peroxide acts as a free radical initiator to initiate the polymerization of acrylic acid groups and maleic anhydride double bonds in the system, significantly increasing the cross-linking density, thereby giving the coating better weather resistance.

[0012] Polypropylene glycol is a typical polyether polyol with multiple hydroxyl groups in its molecule. When heated, the peroxide bond of diisopropyl peroxide will be homolytically cleaved to generate two isopropyl free radicals, which can be used as an initiator to promote the free radical polymerization reaction of acrylic acid groups. Glycidyl methacrylate contains both active epoxy groups and methacrylic acid double bonds. The epoxy group has a high ring tension and is easily attacked by nucleophilic reagents (such as the hydroxyl group of polypropylene glycol), resulting in nucleophilic ring-opening reaction to generate ether bonds. The acrylate molecule contains a cage-like isoborneol structure and an acrylic acid group. The acrylic acid group participates in polymerization under the initiation of free radicals, further increasing the crosslinking density of the system. The polymerization of double bonds further enhances the mechanical strength and weather resistance of the coating. γ-Methacryloyloxypropyltrimethoxysilane contains three methoxysilanes and one methacryloxy group. The methoxysilane group will hydrolyze to generate silanols, and form silicon-oxygen bonds through condensation reactions. The methacryloxy group and other acrylic acid groups are crosslinked through free radical polymerization, further enhancing the crosslinking density of the molecular network. Dimethylpropanediol is a low molecular weight diol that can introduce flexible chain segments, adjust the molecular structure of polyester and improve flexibility. Dicyclohexylmethane-4,4'-diisocyanate has good flexibility and anti-aging properties. Its isocyanate group reacts with the hydroxyl group in polycarbonate diol to generate polyurethane bonds. At the same time, caprolactone is an open-ring cyclic ester that generates flexible chain segments through esterification reaction with the hydroxyl group in the system, thereby improving the flexibility of the polyester chain.

[0013] As a preferred technical solution of the present invention, in step S1, the mass ratio of diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, meta-xylyl diisocyanate, and vinyl triethoxysilane is (100-120): (2-3.6): (1-2.4): (3-6).

[0014] In some optional instances, the first temperature is 60-70°C, for example, it can be 60.0°C, 61.0°C, 62.0°C, 63.0°C, 64.0°C, 65.0°C, 66.0°C, 67.0°C, 68.0°C, 69.0°C or 70.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0015] In some optional instances, the second temperature is 70-80°C, for example, it can be 70.0°C, 71.0°C, 72.0°C, 73.0°C, 74.0°C, 75.0°C, 76.0°C, 77.0°C, 78.0°C, 79.0°C or 80.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0016] In some optional examples, the reaction time of adding dicyclohexylmethane diisocyanate is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0017] In some optional examples, the reaction time of adding meta-xylylenediisocyanate is 1-2h, for example, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0018] In some optional instances, the third temperature is 80-90°C, for example, it can be 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0019] In some optional examples, the reaction time of adding vinyltriethoxysilane is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] In some optional examples, the catalyst is stannous octoate.

[0021] In some optional examples, the reaction time for adding the catalyst is 1-2h, for example, 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0022] In some optional examples, the initiator is dicumyl peroxide.

[0023] In some optional examples, the reaction time for adding the initiator is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0024] In some optional examples, the reaction time for adding glycidyl methacrylate is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0025] In some optional examples, the reaction time for adding polycaprolactone diol is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0026] In some optional examples, the mass ratio of the polytetrahydrofuran to diphenylmethane diisocyanate is (3-4):1, for example, it can be 3:1, 3.1:1, 3.2:1, 3.3:1, 3.4:1, 3.5:1, 3.6:1, 3.7:1, 3.8:1, 3.9:1 or 4:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0027] In some optional examples, the reaction time of adding polytetrahydrofuran is 3-4h, for example, it can be 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] As a preferred technical solution of the present invention, in step S2, the polyether polyol is polypropylene glycol, and the mass ratio of the polyether polyol, initiator, glycidyl methacrylate, isobornyl acrylate, γ-methacryloxypropyltrimethoxysilane, and stannous acetate is (100-120): (1-2.4): (10-18): (2-3.6): (3-6): (0.1-0.6).

[0029] In some optional examples, the initiator is dicumyl peroxide.

[0030] In some optional instances, the fourth temperature is 90-95°C, for example, it can be 90.0°C, 90.5°C, 91.0°C, 91.5°C, 92.0°C, 92.5°C, 93.0°C, 93.5°C, 94.0°C, 94.5°C or 95.0°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] In some optional examples, the reaction time at the fourth temperature is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0032] In some optional examples, the reaction time for adding isobornyl acrylate is 1-2h, for example, it can be 1.0h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h or 2.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0033] In some optional examples, the reaction time of adding stannous acetate is 3-4h, for example, it can be 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0034] As a preferred technical solution of the present invention, in step S3, the mass ratio of the polyester polyol, dimethyl propylene glycol and the catalyst is (100-120): (5-8.4): (0.1-0.6).

[0035] In some optional examples, the catalyst is tetrabutyl titanate.

[0036] In some optional instances, the fifth temperature is 120-130°C, for example, it can be 120°C, 121°C, 122°C, 123°C, 124°C, 125°C, 126°C, 127°C, 128°C, 129°C or 130°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0037] In some optional examples, the reaction time at the fifth temperature is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0038] In some optional examples, the reaction time of adding dicyclohexylmethane-4,4'-diisocyanate is 3-4h, for example, it can be 3.0h, 3.1h, 3.2h, 3.3h, 3.4h, 3.5h, 3.6h, 3.7h, 3.8h, 3.9h or 4.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0039] In some optional examples, the reaction time for adding caprolactone is 2-3h, for example, it can be 2.0h, 2.1h, 2.2h, 2.3h, 2.4h, 2.5h, 2.6h, 2.7h, 2.8h, 2.9h or 3.0h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] As a preferred technical solution of the present invention, in step S4, the mass ratio of the diphenylmethane diisocyanate prepolymer, modified polyether polyol, modified polyester polyol, filler, and dibutyltin dioctoate is (100-120): (40-50): (30-40): (30-40): (0.5-1).

[0041] In some optional examples, the filler is one or more of talc, titanium dioxide, silicon dioxide, mica powder, and kaolin.

[0042] In some optional examples, the mass ratio of the diphenylmethane diisocyanate prepolymer, the auxiliary agent, the antioxidant, and the ultraviolet absorber is (100-120): (2-3): (0.1-0.5): (1-2).

[0043] In some optional examples, the antioxidant is antioxidant 1010.

[0044] In some optional examples, the ultraviolet absorber is UV-326.

[0045] In some optional instances, the sixth temperature is 50-60°C, for example, it can be 50°C, 51°C, 52°C, 53°C, 54°C, 55°C, 56°C, 57°C, 58°C, 59°C or 60°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0046] In some optional examples, the first stirring speed is 1500-2000rpm, for example, it can be 1500rpm, 1550rpm, 1600rpm, 1650rpm, 1700rpm, 1750rpm, 1800rpm, 1850rpm, 1900rpm, 1950rpm or 2000rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0047] In some optional examples, the stirring time is 20-30 min, for example, it can be 20 min, 21 min, 22 min, 23 min, 24 min, 25 min, 26 min, 27 min, 28 min, 29 min or 30 min, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0048] In a second aspect, the present invention provides a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer obtained by the preparation method described in the first aspect.

[0049] Compared with the prior art, the present invention has the following beneficial effects: (1) the hydroxyl group of hydroxyethyl acrylate provides an active site for reacting with the isocyanate group, so that the system can form a chemically cross-linked polyurethane network. The cross-linked structure can effectively improve the stability of the material, reduce the segment breakage caused by ultraviolet radiation or thermal oxidation degradation, enhance the anti-ultraviolet ability of the coating, improve the light aging resistance, and maintain good appearance and mechanical properties under long-term exposure to outdoor environments; (2) the isoborneol ring structure significantly improves the hardness of the coating by providing a rigid skeleton of the polymer chain, and the acrylic acid group can participate in free radical polymerization, further improve the cross-linking density, and give the coating excellent mechanical properties; (3) the triethoxysilane group of vinyl triethoxysilane is gradually hydrolyzed to form silanol in the reaction, and then forms a silicon-oxygen bond through a condensation reaction. The introduction of the silicon-oxygen bond also forms a dense inorganic barrier, which improves the hydrophobicity of the material and prevents the penetration of external moisture, oxygen and corrosive chemicals. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 A flow chart of a method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer provided in Examples 1-6 of the present invention;

[0051] Figure 2 This is a SEM image of a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer prepared in Example 1 of the present invention;

[0052] Figure 3The contact angle of the highly elastic hand-scrapeable waterproof polyurethane coating based on the modified MDI prepolymer prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0053] The technical solution of the present invention is described in detail below in conjunction with specific embodiments and their accompanying drawings. The embodiments recorded herein are specific embodiments of the present invention, which are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limitations on the embodiments of the present invention and the scope of protection of the present invention. In addition to the embodiments recorded herein, those skilled in the art can also adopt other obvious technical solutions based on the contents disclosed in the claims of this application and its specification, including technical solutions that adopt any obvious replacements and modifications to the embodiments recorded herein.

[0054] The chemical reagents used in the examples and comparative examples of the present invention are all commercially available products.

[0055] Example 1

[0056] This embodiment provides a method for preparing a highly elastic hand-scrape waterproof polyurethane coating based on a modified MDI prepolymer, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0057] Step S1, heat 105g of diphenylmethane diisocyanate (MDI) to 63°C, add 2.4g of dicyclohexylmethane diisocyanate, adjust the temperature to 72°C to fully react for 1.2h, add 1.4g of m-xylyl diisocyanate and continue to react for 1.3h, continue to add 3.6g of vinyl triethoxysilane, raise the temperature to 83°C and continue to react for 2.1h, then add 1.9g of hydroxyethyl acrylate and 0.24g of stannous octoate, keep 83°C and continue The mixture was reacted for 1.3 hours, and then 2.4 g of maleic anhydride and 0.63 g of diisopropylbenzene peroxide were added, and the reaction was continued at 83° C. for 1.4 hours. Then 1.6 g of glycidyl methacrylate was added, and the reaction was continued at 83° C. for 2.2 hours. 2.9 g of polycaprolactone diol was added, and the reaction was continued at 83° C. for 2.1 hours to obtain modified MDI. 40 g of modified MDI was mixed with 156 g of polytetrahydrofuran, and the reaction was continued at 83° C. for 3.3 hours to obtain an MDI prepolymer.

[0058] Step S2, heating 109g of polypropylene glycol to 83°C, adding 1.3g of diisopropylbenzene peroxide and 11g of glycidyl methacrylate, heating to 92°C and fully reacting for 2.5h, then adding 2.6g of isobornyl acrylate and continuing to react for 1.3h, adjusting the temperature to 73°C, adding 3.6g of γ-methacryloxypropyltrimethoxysilane and 0.14g of stannous acetate, heating to 83°C and fully reacting for 3.3h to obtain modified polypropylene glycol;

[0059] Step S3, heating 107g of polycarbonate diol to 84°C, adding 3.9g of dimethyl propylene glycol and 2.9g of tetrabutyl titanate, raising the temperature to 122°C under nitrogen protection for full reaction for 2.2h, cooling to 100°C, adding 4.2g of dicyclohexylmethane-4,4'-diisocyanate, raising the temperature to 122°C for further reaction for 3.3h, and then adding 2.8g of caprolactone for full reaction for 2.1h to obtain modified polycarbonate diol;

[0060] Step S4, 109g of MDI prepolymer, 43g of modified polypropylene glycol, 34g of modified polycarbonate diol, 33g of filler, 0.59g of dibutyltin dioctoate, 2.2g of additive, 0.25g of antioxidant 1010 and 1.3g of UV-326 are added and mixed, and the mixture is stirred at 54°C and 1500rpm for 23min, and a high elastic hand-scrapeable waterproof polyurethane coating based on the modified MDI prepolymer is obtained after vacuum degassing.

[0061] Figure 2 This is a SEM image of the highly elastic hand-scrapeable waterproof polyurethane coating based on the modified MDI prepolymer prepared in this example. It can be seen that the coating surface is smooth, dense and has no obvious irregular shapes; Figure 3 This is the contact angle of the polyurethane coating prepared in this example with water, and the contact angle is 136°, indicating that the coating has a good hydrophobic effect.

[0062] Example 2

[0063] This embodiment provides a method for preparing a highly elastic hand-scrape waterproof polyurethane coating based on a modified MDI prepolymer, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0064] Step S1, heat 112g of diphenylmethane diisocyanate (MDI) to 65°C, add 2.9g of dicyclohexylmethane diisocyanate, adjust the temperature to 73°C to fully react for 1.4h, add 2.3g of m-xylyl diisocyanate and continue to react for 1.5h, continue to add 4.1g of vinyl triethoxysilane, raise the temperature to 85°C and continue to react for 2.4h, then add 1.2g of hydroxyethyl acrylate and 0.33g of stannous octoate, keep 85°C and continue The mixture was reacted for 1.5 hours, and then 2.3 g of maleic anhydride and 0.88 g of diisopropylbenzene peroxide were added, and the reaction was continued at 85° C. for 1.6 hours. Then 1.3 g of glycidyl methacrylate was added, and the reaction was continued at 85° C. for 2.4 hours. 2.1 g of polycaprolactone diol was added, and the reaction was continued at 85° C. for 2.3 hours to obtain modified MDI. 40 g of the modified MDI was mixed with 133 g of polytetrahydrofuran, and the reaction was continued at 85° C. for 3.5 hours to obtain an MDI prepolymer.

[0065] Step S2, heating 103g of polypropylene glycol to 84°C, adding 1.8g of diisopropylbenzene peroxide and 16g of glycidyl methacrylate, heating to 91°C and fully reacting for 2.2h, then adding 2.2g of isobornyl acrylate and continuing to react for 1.5h, adjusting the temperature to 72°C, adding 3.1g of γ-methacryloxypropyltrimethoxysilane and 0.19g of stannous acetate, heating to 84°C and fully reacting for 3.1h to obtain modified polypropylene glycol;

[0066] Step S3, heating 112g of polycarbonate diol to 81°C, adding 3.2g of dimethyl propylene glycol and 2.6g of tetrabutyl titanate, raising the temperature to 124°C under nitrogen protection for full reaction for 2.4h, cooling to 100°C, adding 3.2g of dicyclohexylmethane-4,4'-diisocyanate, raising the temperature to 124°C for further reaction for 3.5h, and then adding 2.4g of caprolactone for full reaction for 2.3h to obtain modified polycarbonate diol;

[0067] Step S4, 105g MDI prepolymer, 41g modified polypropylene glycol, 31g modified polycarbonate diol, 31g filler, 0.66g dibutyltin dioctoate, 2.5g additive, 0.19g antioxidant 1010 and 1.5g UV-326 are added and mixed, and the mixture is stirred at 52°C and 1600rpm for 24min, and a high elastic hand-scrapeable waterproof polyurethane coating based on the modified MDI prepolymer is obtained after vacuum degassing.

[0068] Example 3

[0069] This embodiment provides a method for preparing a highly elastic hand-scrape waterproof polyurethane coating based on a modified MDI prepolymer, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0070] Step S1, heat 110g of diphenylmethane diisocyanate (MDI) to 67°C, add 3.6g of dicyclohexylmethane diisocyanate, adjust the temperature to 75°C to fully react for 1.6h, add 1.5g of m-xylyl diisocyanate and continue to react for 1.1h, continue to add 5.2g of vinyl triethoxysilane, raise the temperature to 87°C and continue to react for 2.1h, then add 1.7g of hydroxyethyl acrylate and 0.57g of stannous octoate, keep 87°C and continue The mixture was reacted for 1.3 hours, and then 3.0 g of maleic anhydride and 0.72 g of diisopropylbenzene peroxide were added, and the reaction was continued at 87° C. for 1.3 hours. Then 2.3 g of glycidyl methacrylate was added, and the reaction was continued at 87° C. for 2.5 hours. 2.6 g of polycaprolactone diol was added, and the reaction was continued at 87° C. for 2.4 hours to obtain modified MDI. 40 g of modified MDI was mixed with 142 g of polytetrahydrofuran, and the reaction was continued at 87° C. for 3.2 hours to obtain an MDI prepolymer.

[0071] Step S2, heating 110g of polypropylene glycol to 81°C, adding 1.5g of diisopropylbenzene peroxide and 13g of glycidyl methacrylate, heating to 90°C and fully reacting for 2.5h, then adding 3.1g of isobornyl acrylate and continuing to react for 1.3h, adjusting the temperature to 75°C, adding 4.9g of γ-methacryloxypropyltrimethoxysilane and 0.42g of stannous acetate, heating to 81°C and fully reacting for 3.1h to obtain modified polypropylene glycol;

[0072] Step S3, heating 115g of polycarbonate diol to 83°C, adding 5.7g of dimethyl propylene glycol and 2.1g of tetrabutyl titanate, raising the temperature to 126°C under nitrogen protection for full reaction for 2.6h, cooling to 100°C, adding 3.7g of dicyclohexylmethane-4,4'-diisocyanate, raising the temperature to 126°C for further reaction for 3.6h, and then adding 2.1g of caprolactone for full reaction for 2.6h to obtain modified polycarbonate diol;

[0073] Step S4, adding and mixing 108g of MDI prepolymer, 44g of modified polypropylene glycol, 38g of modified polycarbonate diol, 31g of filler, 0.72g of dibutyltin dioctoate, 2.2g of additive, 0.24g of antioxidant 1010 and 1.7g of UV-326, stirring and mixing at 55°C and 1700rpm for 26min, and obtaining a high elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer after vacuum degassing.

[0074] Example 4

[0075] This embodiment provides a method for preparing a highly elastic hand-scrape waterproof polyurethane coating based on a modified MDI prepolymer, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0076] Step S1, 104g of diphenylmethane diisocyanate (MDI) was heated to 62°C, 3.1g of dicyclohexylmethane diisocyanate was added, the temperature was adjusted to 77°C for full reaction for 1.3h, 1.9g of m-xylyl diisocyanate was added and the reaction was continued for 1.3h, 5.8g of vinyl triethoxysilane was added, the temperature was raised to 82°C for further reaction for 2.6h, 2.3g of hydroxyethyl acrylate and 0.17g of stannous octoate were added, and the temperature was maintained at 82°C for further reaction. The reaction was continued for 1.7 hours, and then 2.5 g of maleic anhydride and 1.1 g of diisopropylbenzene peroxide were added, and the reaction was continued at 82° C. for 1.4 hours, and then 2.0 g of glycidyl methacrylate was added, and the reaction was continued at 82° C. for 2.1 hours, and 2.4 g of polycaprolactone diol was added, and the reaction was continued at 82° C. for 2.5 hours to obtain modified MDI, and 40 g of modified MDI was mixed with 127 g of polytetrahydrofuran, and the reaction was continued at 82° C. for 3.5 hours to obtain an MDI prepolymer;

[0077] Step S2, heating 114g of polypropylene glycol to 83°C, adding 2.3g of diisopropylbenzene peroxide and 12g of glycidyl methacrylate, heating to 95°C and fully reacting for 2.6h, then adding 3.5g of isobornyl acrylate and continuing to react for 1.5h, adjusting the temperature to 77°C, adding 3.5g of γ-methacryloxypropyltrimethoxysilane and 0.38g of stannous acetate, heating to 85°C and fully reacting for 3.4h to obtain modified polypropylene glycol;

[0078] Step S3, heating 104g of polycarbonate diol to 87°C, adding 5.1g of dimethyl propylene glycol and 3.5g of tetrabutyl titanate, raising the temperature to 127°C under nitrogen protection for full reaction for 2.1h, cooling to 100°C, adding 3.1g of dicyclohexylmethane-4,4'-diisocyanate, raising the temperature to 127°C for further reaction for 3.2h, and then adding 3.1g of caprolactone for full reaction for 2.1h to obtain modified polycarbonate diol;

[0079] Step S4, adding 111g of MDI prepolymer, 42g of modified polypropylene glycol, 33g of modified polycarbonate diol, 35g of filler, 0.79g of dibutyltin dioctoate, 2.3g of additives, 0.36g of antioxidant 1010 and 1.4g of UV-326, stirring and mixing at 58°C and 1800rpm for 24min, and obtaining a high-elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer after vacuum degassing.

[0080] Example 5

[0081] This embodiment provides a method for preparing a highly elastic hand-scrape waterproof polyurethane coating based on a modified MDI prepolymer, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0082] Step S1, 112g of diphenylmethane diisocyanate (MDI) was heated to 66°C, 2.5g of dicyclohexylmethane diisocyanate was added, the temperature was adjusted to 74°C for full reaction for 1.5h, 2.2g of m-xylyl diisocyanate was added and the reaction was continued for 1.4h, 4.5g of vinyl triethoxysilane was added, the temperature was raised to 88°C for further reaction for 2.3h, 2.0g of hydroxyethyl acrylate and 0.39g of stannous octoate were added, and the temperature was maintained at 88°C for further reaction. The reaction was continued for 1.3 hours, and then 3.5 g of maleic anhydride and 1.0 g of diisopropylbenzene peroxide were added, and the reaction was continued at 88° C. for 1.1 hours, and then 1.7 g of glycidyl methacrylate was added, and the reaction was continued at 88° C. for 2.5 hours, and 3.0 g of polycaprolactone diol was added, and the reaction was continued at 88° C. for 2.7 hours to obtain modified MDI, and 40 g of modified MDI was mixed with 136 g of polytetrahydrofuran, and the reaction was continued at 88° C. for 3.3 hours to obtain an MDI prepolymer;

[0083] Step S2, heating 103g of polypropylene glycol to 82°C, adding 2.0g of diisopropylbenzene peroxide and 17g of glycidyl methacrylate, heating to 92°C and fully reacting for 2.4h, then adding 2.5g of isobornyl acrylate and continuing to react for 1.3h, adjusting the temperature to 73°C, adding 5.6g of γ-methacryloxypropyltrimethoxysilane and 0.26g of stannous acetate, heating to 82°C and fully reacting for 3.7h to obtain modified polypropylene glycol;

[0084] Step S3, heating 116g of polycarbonate diol to 89°C, adding 4.2g of dimethyl propylene glycol and 3.2g of tetrabutyl titanate, raising the temperature to 129°C under nitrogen protection for full reaction for 2.3h, cooling to 100°C, adding 5.1g of dicyclohexylmethane-4,4'-diisocyanate, raising the temperature to 125°C for further reaction for 3.6h, and then adding 3.5g of caprolactone for full reaction for 2.5h to obtain modified polycarbonate diol;

[0085] Step S4, adding and mixing 114g of MDI prepolymer, 46g of modified polypropylene glycol, 37g of modified polycarbonate diol, 32g of filler, 0.88g of dibutyltin dioctoate, 2.6g of additive, 0.44g of antioxidant 1010 and 1.9g of UV-326, stirring and mixing at 60°C and 1900rpm for 23min, and obtaining a high elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer after vacuum degassing.

[0086] Example 6

[0087] This embodiment provides a method for preparing a highly elastic hand-scrape waterproof polyurethane coating based on a modified MDI prepolymer, such as Figure 1 As shown, the preparation method specifically comprises the following steps:

[0088] Step S1, 107g of diphenylmethane diisocyanate (MDI) was heated to 62°C, 2.8g of dicyclohexylmethane diisocyanate was added, the temperature was adjusted to 77°C for full reaction for 1.9h, 2.0g of m-xylyl diisocyanate was added and the reaction was continued for 1.6h, 3.1g of vinyl triethoxysilane was added, the temperature was raised to 86°C for further reaction for 2.2h, 2.1g of hydroxyethyl acrylate and 0.44g of stannous octoate were added, and the temperature was maintained at 86°C for further reaction. The reaction was continued for 1.8 hours, and then 2.9 g of maleic anhydride and 0.63 g of diisopropylbenzene peroxide were added, and the reaction was continued at 86° C. for 1.6 hours, and then 1.5 g of glycidyl methacrylate was added, and the reaction was continued at 86° C. for 2.3 hours, and 2.7 g of polycaprolactone diol was added, and the reaction was continued at 86° C. for 2.4 hours to obtain modified MDI, and 40 g of modified MDI was mixed with 147 g of polytetrahydrofuran, and the reaction was continued at 86° C. for 3.3 hours to obtain an MDI prepolymer;

[0089] Step S2, heating 117g of polypropylene glycol to 86°C, adding 1.7g of dicumyl peroxide and 18g of glycidyl methacrylate, heating to 94°C and fully reacting for 2.2h, then adding 2.1g of isobornyl acrylate and continuing to react for 1.4h, adjusting the temperature to 76°C, adding 5.9g of γ-methacryloxypropyltrimethoxysilane and 0.51g of stannous acetate, heating to 85°C and fully reacting for 3.5h to obtain modified polypropylene glycol;

[0090] Step S3, heating 110g of polycarbonate diol to 86°C, adding 4.7g of dimethyl propylene glycol and 2.4g of tetrabutyl titanate, raising the temperature to 126°C under nitrogen protection for full reaction for 2.6h, cooling to 100°C, adding 5.7g of dicyclohexylmethane-4,4'-diisocyanate, raising the temperature to 126°C for further reaction for 3.4h, and then adding 2.5g of caprolactone for full reaction for 2.7h to obtain modified polycarbonate diol;

[0091] Step S4, adding and mixing 119g of MDI prepolymer, 44g of modified polypropylene glycol, 39g of modified polycarbonate diol, 36g of filler, 0.96g of dibutyltin dioctoate, 2.8g of additive, 0.41g of antioxidant 1010 and 2.0g of UV-326, stirring and mixing at 57°C and 2000rpm for 26min, and obtaining a high elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer after vacuum degassing.

[0092] Comparative Example 1

[0093] This comparative example provides a method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer. The difference from Example 1 is that in step S1, the mass of hydroxyethyl acrylate is adjusted to 3.7 g. Compared with Example 1, the mass of hydroxyethyl acrylate is increased by 1.8 g. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer. The difference from Example 1 is that in step S1, the mass of hydroxyethyl acrylate is adjusted to 0.1 g. Compared with Example 1, the mass of hydroxyethyl acrylate is reduced by 1.8 g. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0096] Comparative Example 3

[0097] This comparative example provides a method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer. The difference from Example 1 is that in step S2, the mass of isobornyl acrylate is adjusted to 5.1 g. Compared with Example 1, the mass of isobornyl acrylate is increased by 2.5 g. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0098] Comparative Example 4

[0099] This comparative example provides a method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer. The difference from Example 1 is that in step S2, the mass of isobornyl acrylate is adjusted to 0.1 g. Compared with Example 1, the mass of isobornyl acrylate is reduced by 2.5 g. The other process parameters and operating conditions are exactly the same as those in Example 1.

[0100] The test standard for the weather resistance of the polyurethane coating prepared in the present invention is GB / T 1865-2009; the test standard for the hardness is GB / T 6739-2022; the test standard for the water resistance is GB / T 1733-1993; and the test standard for the tensile strength and elongation at break is JG-T172-2014. The test results are shown in Table 1.

[0101] Table 1 Test results of high elasticity hand-scrape waterproof polyurethane coatings based on modified MDI prepolymers prepared in Examples 1-6 and Comparative Examples 1-4

[0102]

[0103] It can be seen from the data in the table that the weather resistance, hardness, water resistance and tensile strength of Comparative Example 1 are all lower than those of Example 1, and the strain rate at break is higher than that of Example 1; the weather resistance, hardness, water resistance, tensile strength and strain rate at break of Comparative Example 2 are all lower than those of Example 1. This is because in Comparative Example 1, the amount of hydroxyethyl acrylate is excessive, and more acrylic acid groups are introduced, which are prone to photo-oxidative degradation under ultraviolet irradiation, resulting in accelerated aging rate of the coating; excessive acrylic acid segments will form flexible chains or low molecular segments, thereby reducing the overall cross-linking density and hardness; the hydroxyl groups in the hydroxyethyl acrylate molecules are hydrophilic groups, and excessive hydroxyethyl acrylate will introduce more hydroxyl groups into the coating, and these hydrophilic sites will increase the affinity of the material surface to water and reduce water resistance; excessive hydroxyethyl acrylate leads to uneven cross-linking density, and more low molecular segments or flexible segments may be formed in the coating, and the overall strength of the network decreases; the proportion of flexible segments increases, reducing the overall rigidity of the system, and at the same time, the low cross-linking density area of ​​the acrylic acid segments will increase the ductility of the system to a certain extent. In Comparative Example 2, insufficient hydroxyethyl acrylate leads to a decrease in the number of acrylic groups in the system, a decrease in crosslinking density, and a decrease in weather resistance; insufficient hydroxyethyl acrylate leads to a decrease in crosslinking points and a decrease in the hardness of the coating; insufficient hydroxyethyl acrylate reduces the amount of hydroxyl groups introduced, and the hydrophobicity of the material surface may be slightly improved. Due to insufficient crosslinking density, microstructural defects increase, making it easier for moisture to pass through the coating, resulting in reduced water resistance; insufficient hydroxyethyl acrylate leads to a decrease in the number of crosslinking points, an incomplete polyurethane network structure, insufficient physical and chemical bonding between molecular chains, and a decrease in tensile strength; the crosslinking density is reduced, the flexibility and ductility of the material are insufficient, brittle fracture is prone to occur in stress concentration areas, and the tensile strain rate decreases.

[0104] It can be seen from the data in the table that the water resistance and tensile strength of Comparative Example 3 are lower than those of Example 1, the weather resistance remains unchanged, and the hardness and fracture strain rate are higher than those of Example 1; the weather resistance, hardness, water resistance and tensile strength of Comparative Example 4 are lower than those of Example 1, and the fracture strain rate is higher than that of Example 1. This is because in Comparative Example 3, the isoborneol structure in isoborneol acrylate contains an asymmetric saturated cyclic skeleton, has high chemical stability to ultraviolet rays, and the weather resistance of the coating remains unchanged; the isoborneol ring structure is a chemical unit with high rigidity, and excessive use will lead to excessive crosslinking density or rigid segment ratio of the coating, thereby increasing the hardness of the coating; excessive isoborneol acrylate may lead to uneven crosslinking density in the coating, excessive local rigid segment ratio, and may form microcracks or defects, resulting in decreased water resistance; the isoborneol ring structure will make the crosslinking structure of the coating more compact and rigid, increase the tensile stress resistance of the coating, and excessive amount will cause the coating to become too brittle and lose certain ductility and toughness, so the tensile strength increases and the fracture strain rate decreases. In Comparative Example 4, insufficient isobornyl structure leads to decreased UV resistance and aging resistance, and decreased weather resistance of the coating; the proportion of isobornyl acrylate in the coating structure is reduced, and the cross-linking density is reduced, resulting in decreased hardness; low cross-linking density increases the water absorption and moisture permeability of the coating, and decreased water resistance; insufficient isobornyl acrylate leads to insufficient rigid segments, decreased cross-linking density and tensile strength within the molecule, and an excessively high proportion of flexible segments, thereby decreasing tensile strength and increasing fracture strain rate.

[0105] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer, characterized in that: The preparation method is: Step S1, heating diphenylmethane diisocyanate, adding dicyclohexylmethane diisocyanate, heating to react, then adding m-xylyl diisocyanate and vinyl triethoxysilane to react, then adding hydroxyethyl acrylate and a catalyst to continue the reaction, adding maleic anhydride and an initiator to react, then adding glycidyl methacrylate to react, adding polycaprolactone diol to react to obtain modified diphenylmethane diisocyanate, mixing the modified diphenylmethane diisocyanate with polytetrahydrofuran, and reacting to obtain a diphenylmethane diisocyanate prepolymer; Step S2, heating the polyether polyol and adding an initiator and glycidyl methacrylate, heating the reaction and then adding isobornyl acrylate, adjusting the temperature and adding γ-methacryloxypropyltrimethoxysilane and stannous acetate to react to obtain a modified polyether polyol; Step S3, heating the polyester polyol and adding dimethyl propylene glycol and a catalyst, heating the mixture under nitrogen protection for reaction, cooling the mixture to 100° C., adding dicyclohexylmethane-4,4'-diisocyanate for reaction, and then adding caprolactone for reaction to obtain a modified polyester polyol; Step S4, adding diphenylmethane diisocyanate prepolymer, modified polyether polyol, modified polyester polyol, filler, dibutyltin dioctoate, additives, antioxidants and ultraviolet absorbers in sequence and mixing, and obtaining a high-elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer after vacuum degassing.

2. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer according to claim 1, characterized in that: In step S1, The mass ratio of the diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, meta-xylylene diisocyanate and vinyl triethoxysilane is (100-120): (2-3.6): (1-2.4): (3-6).

3. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer according to claim 1, characterized in that: In step S1, The mass ratio of diphenylmethane diisocyanate, hydroxyethyl acrylate, catalyst, maleic anhydride and initiator is (100-120): (1-2.4): (0.1-0.6): (2-3.6): (0.5-1.2); The catalyst is stannous octoate; The initiator is dicumyl peroxide.

4. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer according to claim 1, characterized in that: In step S1, The mass ratio of diphenylmethane diisocyanate, glycidyl methacrylate and polycaprolactone diol is (100-120): (1-2.4): (2-3.6); The mass ratio of the polytetrahydrofuran to diphenylmethane diisocyanate is (3-4):

1.

5. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer according to claim 1, characterized in that: In step S2, The mass ratio of the polyether polyol, initiator, glycidyl methacrylate, isobornyl acrylate, γ-methacryloxypropyltrimethoxysilane and stannous acetate is (100-120): (1-2.4): (10-18): (2-3.6): (3-6): (0.1-0.6); The initiator is dicumyl peroxide.

6. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer according to claim 1, characterized in that: In step S3, The mass ratio of the polyester polyol, dimethyl propylene glycol and the catalyst is (100-120): (5-8.4): (0.1-0.6); The catalyst is tetrabutyl titanate.

7. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer according to claim 1, characterized in that: In step S3, The mass ratio of the polyester polyol, dicyclohexylmethane-4,4'-diisocyanate and caprolactone is (100-120):(3-6):(2-3.6).

8. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer according to claim 1, characterized in that: In step S4, The mass ratio of the diphenylmethane diisocyanate prepolymer, the modified polyether polyol, the modified polyester polyol, the filler and the dibutyltin dioctoate is (100-120): (40-50): (30-40): (30-40): (0.5-1); The filler is one or more of talc, titanium dioxide, silicon dioxide, mica powder and kaolin.

9. The method for preparing a highly elastic hand-scrapeable waterproof polyurethane coating based on modified MDI prepolymer according to claim 1, characterized in that: In step S4, The mass ratio of the diphenylmethane diisocyanate prepolymer, the auxiliary agent, the antioxidant, and the ultraviolet absorber is (100-120): (2-3): (0.1-0.5): (1-2); The auxiliary agent is one or more of hydroxypropyl methylcellulose and polyvinyl alcohol; The antioxidant is antioxidant 1010; The ultraviolet absorber is UV-326.

10. A highly elastic hand-scrapeable waterproof polyurethane coating based on a modified MDI prepolymer obtained according to the preparation method according to any one of claims 1 to 9.

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