Low-moisture active isocyanate and preparation method thereof

Abstract

The invention relates to low-moisture active isocyanate and a preparation method thereof, and belongs to the technical field of isocyanate synthesis. The preparation method comprises the following steps: firstly, blocking isocyanate ends of isocyanate propyl triethoxy silane and 3-isocyanate propyl trimethoxy silane by using a pyrazole blocking agent, and then converting the blocked isocyanate ends of the isocyanate propyl triethoxy silane and the 3-isocyanate propyl trimethoxy silane with gamma-methacryloyloxy propyl triisopropoxy silane to form a multi-branched diisocyanate-terminated intermediate; high steric hindrance of the multi-branched chain significantly reduces the water vapor transmittance, the sealing agent can prevent the isocyanate end from reacting with water vapor during storage and processing, and the active isocyanate end released by heating participates in crosslinking during subsequent application; the low-moisture active isocyanate is obtained by blending, compounding and modifying with oleamide and a photoinitiator, and is subjected to UV curing in subsequent application, so that the surface energy is further reduced, and the contact with water is reduced. The isocyanate prepared by the method disclosed by the invention has the effect of low moisture.

Description

Technical Field

[0001] This invention relates to the field of isocyanate synthesis technology, specifically to a low-moisture reactive isocyanate and its preparation method. Background Technology

[0002] Isocyanates, due to their highly reactive isocyanate ends, are widely used in coatings, adhesives, and composite materials, where they can impart excellent mechanical properties and weather resistance through cross-linking reactions. However, existing isocyanates have significant technical drawbacks: Firstly, the highly reactive isocyanate ends readily react with moisture in the environment during storage, transportation, and processing, leading not only to cross-linking failure and performance degradation but also to defects such as bubbles and delamination, severely impacting the quality and lifespan of subsequent products. Secondly, conventional isocyanates have high molecular structure regularity and low steric hindrance, allowing moisture to easily penetrate their molecular layers, resulting in high moisture permeability in the final product, which is insufficient to meet the low moisture sensitivity requirements of electronic packaging and high-weather-resistant coatings.

[0003] While existing technologies employ methods to temporarily seal the isocyanate ends with blocking agents, most of these agents have stringent dissociation conditions and do not incorporate molecular structure design to enhance steric hindrance. Some methods that reduce water vapor transmission rate by adjusting the structure neglect surface energy optimization, failing to minimize contact between moisture and the isocyanate surface. Therefore, there is an urgent need to develop an isocyanate preparation technology that balances storage stability, low water vapor transmission rate, and surface water resistance. Summary of the Invention

[0004] The purpose of this invention is to provide a low-moisture reactive isocyanate and its preparation method, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a low-moisture reactive isocyanate, comprising the following steps: (1) Mix isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane at a mass ratio of 2~4:1~2 and stir at room temperature for 30 min under nitrogen atmosphere to form a droplet; mix pyrazole blocking agent and organic solvent at a mass ratio of 1.5~2.5:10 and stir at room temperature for 15 min to form a mixture. Stir at 70~80℃ and slowly add 0.2~0.4 times the mass of the mixture to the mixture. After the addition is complete, keep stirring and react for 2~4 h to obtain a silane mixture with blocked isocyanate ends; (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.2~0.5 and stirred for 15 min. Then, 0.4~0.6 times the mass of the silane mixture of buffer solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the dropwise addition was completed, the temperature was raised to 60~70℃ and refluxed for 1~2 h. 0.3~0.5 times the mass of the buffer solution of neutralizing agent was added for neutralization. The temperature was lowered and the neutralizing agent was removed by filtration. The filtrate was distilled under reduced pressure for 2 h to obtain the multi-branched diisocyanate-terminated intermediate. (3) Mix the intermediate, surface modifier, photoinitiator and organic solvent in a mass ratio of 1~2:0.1~0.2:0.01:10, heat to 80℃ and stir for 30 min to obtain low moisture activity isocyanate.

[0006] Furthermore, the organic solvent in step (1) is toluene.

[0007] Furthermore, the pyrazole blocking agent in step (1) is 3,5-dimethylpyrazole.

[0008] Furthermore, the acceleration rate of the slow drop is 2 drops / s.

[0009] Furthermore, the buffer solution in step (2) is a 0.1M aqueous solution of boric acid.

[0010] Furthermore, the neutralizing agent in step (2) is sodium bicarbonate solid particles.

[0011] Furthermore, the reaction process of the multi-branched diisocyanate-terminated intermediate in step (2) is as follows: .

[0012] Furthermore, the surface modifier in step (3) is oleic acid amide.

[0013] Furthermore, the photoinitiator in step (3) is Irgacure1173.

[0014] Furthermore, an application of a low-moisture-activity isocyanate is characterized by the following steps: 60-80 parts by weight of a polyol are heated to 100°C and vacuum dehydrated for 1 hour; 80-120 parts by weight of toluene, 50-70 parts by weight of the low-moisture-activity isocyanate, and 0.2 parts by weight of a catalyst are added; the mixture is then heated to 150°C and stirred for 3 hours; the mixture is cooled to 50°C and uniformly coated onto a substrate to a thickness of 50 μm; and then the coating is examined at a wavelength of 365 nm and a power of 100 mW / cm². 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

[0015] Furthermore, the polyol is: polycaprolactone diol with a molecular weight of 1000.

[0016] Furthermore, the catalyst is stannous octoate.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: This invention first blocks the isocyanate ends of isocyanate-based propyltriethoxysilane and 3-isocyanate-based propyltrimethoxysilane with a pyrazole blocking agent, and then forms a multi-branched diisocyanate-terminated intermediate with γ-methacryloyloxypropyltriisopropoxysilane through hydrolysis and condensation. The high steric hindrance formed by the multi-branched chain significantly reduces water vapor permeability. At the same time, the blocking agent blocks the isocyanate ends, preventing them from reacting with water vapor during storage and processing. In subsequent applications, the blocking agent is dissociated by heating or other conditions, releasing the active isocyanate ends to participate in the crosslinking reaction. After further modification by blending with oleamide and a photoinitiator, a low-moisture active isocyanate is obtained. In subsequent applications, UV curing further reduces surface energy and minimizes contact with moisture. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The test methods for various indicators of the low-moisture-activity isocyanate prepared in the following embodiments are as follows: Water vapor transmission rate test: According to GB / T21529-2008, use a Langguang W3 / 300 instrument with gravimetric method, effective test area 50cm². 2 The sample was first conditioned at 23℃ / 50%RH for 40h, then clamped on a permeation cup containing anhydrous calcium chloride. The instrument parameters were set to 38℃ / 90%RH. The instrument automatically weighed the sample and calculated the water vapor transmission rate of the membrane.

[0020] Abrasion resistance test: The polyurethane coatings prepared in Examples 1-5 and Comparative Examples 1-5 were placed under 0000# steel wool with a 500g weight load. The polyurethane coatings were moved back and forth 20 times, and the surface scratches were observed: 0-5 scratches were recorded as excellent; 5-20 scratches were recorded as good; and more than 20 scratches were recorded as poor.

[0021] Storage test: The isocyanates prepared in Examples 1-5 and Comparative Examples 1-5 were placed at 23℃ / 50%RH for 10 days to prepare sample films. The films were then clamped on a permeation cup containing anhydrous calcium chloride. The instrument parameters were set to 38℃ / 90%RH. The instrument automatically weighed the films and calculated the water vapor transmission rate.

[0022] Example 1 (1) Isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane were mixed at a mass ratio of 2:1 and stirred at 300 rpm for 30 min at room temperature under a nitrogen atmosphere to form a droplet; 3,5-dimethylpyrazole and toluene were mixed at a mass ratio of 1.5:10 and stirred at 200 rpm for 15 min at room temperature to form a mixture. The mixture was stirred at 300 rpm at 70 °C, and a droplet of 0.2 times the mass of the mixture was slowly added to the mixture at a dropping rate of 2 drops / s. After the addition was completed, the mixture was stirred for 2 h to obtain a silane mixture with closed isocyanate ends. (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.2 and stirred at 500 rpm for 15 min. Then, 0.4 times the mass of the silane mixture of 0.1 M boric acid aqueous solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the addition was completed, the temperature was raised to 60 °C and refluxed for 1 h. 0.3 times the mass of 0.1 M boric acid aqueous solution of sodium bicarbonate solid particles were added to neutralize. The temperature was lowered and the sodium bicarbonate solid particles were removed by filtration. The filtrate was distilled at 70 °C and vacuum degree of 0.1 kPa for 2 h to remove toluene, alcohols and water generated in the reaction, and to obtain a multi-branched diisocyanate-terminated intermediate. (3) The intermediate, oleamide, Irgacure1173 and toluene were mixed in a mass ratio of 1:0.1:0.01:10 and heated to 80°C and stirred at 300 rpm for 30 min to obtain a low-moisture active isocyanate. (4) Heat 60 parts by weight of polycaprolactone diol with a molecular weight of 1000 to 100°C and dehydrate under vacuum for 1 hour. Add 80 parts by weight of toluene, 50 parts by weight of low-moisture reactive isocyanate and 0.2 parts by weight of stannous octoate. Heat to 150°C and stir at 500 rpm for 3 hours. Cool to 50°C and coat evenly onto the substrate to a thickness of 50 μm. Then, pass the coating through a microscope at a wavelength of 365 nm and a power of 100 mW / cm. 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

[0023] Example 2 (1) Isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane were mixed at a mass ratio of 2.5:1.2 and stirred at 300 rpm for 30 min at room temperature under a nitrogen atmosphere to form a droplet; 3,5-dimethylpyrazole and toluene were mixed at a mass ratio of 1.8:10 and stirred at 200 rpm for 15 min at room temperature to form a mixture. The mixture was stirred at 300 rpm at 72 °C and a droplet of 0.25 times the mass of the mixture was slowly added to the mixture at a dropping rate of 2 drops / s. After the addition was completed, the mixture was stirred for 2.5 h to obtain a silane mixture with closed isocyanate ends. (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.25 and stirred at 500 rpm for 15 min. Then, 0.45 times the mass of the silane mixture of 0.1 M boric acid aqueous solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the addition was completed, the temperature was raised to 62 °C and refluxed for 1.2 h. 0.35 times the mass of 0.1 M boric acid aqueous solution of sodium bicarbonate solid particles were added to neutralize. The temperature was lowered and the sodium bicarbonate solid particles were removed by filtration. The filtrate was distilled at 70 °C and vacuum degree of 0.1 kPa for 2 h to remove toluene, alcohols and water generated in the reaction, and to obtain a multi-branched diisocyanate-terminated intermediate. (3) The intermediate, oleamide, Irgacure1173 and toluene were mixed in a mass ratio of 1.2:0.12:0.01:10 and heated to 80°C and stirred at 300 rpm for 30 min to obtain a low-moisture active isocyanate. (4) Heat 65 parts by weight of polycaprolactone diol with a molecular weight of 1000 to 100°C, dehydrate under vacuum for 1 hour, add 90 parts by weight of toluene, 55 parts by weight of low-moisture reactive isocyanate and 0.2 parts by weight of stannous octoate, heat to 150°C and stir at 500 rpm for 3 hours, cool to 50°C, and evenly coat onto the substrate with a coating thickness of 50 μm. Then, pass the coating through a wavelength of 365 nm and a power of 100 mW / cm. 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

[0024] Example 3 (1) Isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane were mixed at a mass ratio of 3:1.5:10 and stirred at room temperature at 300 rpm for 30 min under a nitrogen atmosphere to form a droplet; 3,5-dimethylpyrazole and toluene were mixed at a mass ratio of 2:10 and stirred at room temperature at 200 rpm for 15 min to form a mixture. The mixture was stirred at 75°C at 300 rpm and a droplet of 0.3 times the mass of the mixture was slowly added to the mixture at a dropping rate of 2 drops / s. After the addition was completed, the mixture was stirred for 3 h to obtain a silane mixture with closed isocyanate ends. (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.35 and stirred at 500 rpm for 15 min. Then, 0.5 times the mass of the silane mixture of 0.1 M boric acid aqueous solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the addition was completed, the temperature was raised to 65 °C and refluxed for 1.5 h. 0.4 times the mass of 0.1 M boric acid aqueous solution of sodium bicarbonate solid particles were added to neutralize. The temperature was lowered and the sodium bicarbonate solid particles were removed by filtration. The filtrate was distilled at 70 °C and vacuum degree of 0.1 kPa for 2 h to remove toluene, alcohols and water generated in the reaction, and to obtain a multi-branched diisocyanate-terminated intermediate. (3) The intermediate, oleamide, Irgacure1173 and toluene were mixed in a mass ratio of 1.5:0.15:0.01:10 and heated to 80°C and stirred at 300 rpm for 30 min to obtain a low-moisture active isocyanate. (4) Heat 70 parts by weight of polycaprolactone diol with a molecular weight of 1000 to 100°C, dehydrate under vacuum for 1 hour, add 100 parts by weight of toluene, 60 parts by weight of low-moisture reactive isocyanate and 0.2 parts by weight of stannous octoate, heat to 150°C and stir at 500 rpm for 3 hours, cool to 50°C, and evenly coat onto the substrate with a coating thickness of 50 μm. Then, pass the coating through a wavelength of 365 nm and a power of 100 mW / cm. 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

[0025] Example 4 (1) Isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane were mixed at a mass ratio of 3.5:1.8 and stirred at 300 rpm for 30 min at room temperature under a nitrogen atmosphere to form a droplet; 3,5-dimethylpyrazole and toluene were mixed at a mass ratio of 2.2:10 and stirred at 200 rpm for 15 min at room temperature to form a mixture. The mixture was stirred at 300 rpm at 78 °C and a droplet of 0.35 times the mass of the mixture was slowly added to the mixture at a dropping rate of 2 drops / s. After the addition was completed, the mixture was stirred for 3.5 h to obtain a silane mixture with blocked isocyanate ends. (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.45 and stirred at 500 rpm for 15 min. Then, 0.55 times the mass of the silane mixture of 0.1 M boric acid aqueous solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the addition was completed, the temperature was raised to 68 °C and refluxed for 1.8 h. 0.45 times the mass of 0.1 M boric acid aqueous solution of sodium bicarbonate solid particles were added to neutralize. The temperature was lowered and the sodium bicarbonate solid particles were removed by filtration. The filtrate was distilled at 70 °C and vacuum degree of 0.1 kPa for 2 h to remove toluene, alcohols and water generated in the reaction, and to obtain a multi-branched diisocyanate-terminated intermediate. (3) The intermediate, oleamide, Irgacure1173 and toluene were mixed in a mass ratio of 1.8:0.18:0.01:10 and heated to 80°C and stirred at 300 rpm for 30 min to obtain a low-moisture active isocyanate. (4) Heat 75 parts by weight of polycaprolactone diol with a molecular weight of 1000 to 100°C, dehydrate under vacuum for 1 hour, add 110 parts by weight of toluene, 65 parts by weight of low-moisture reactive isocyanate and 0.2 parts by weight of stannous octoate, heat to 150°C and stir at 500 rpm for 3 hours, cool to 50°C, and evenly coat onto the substrate with a coating thickness of 50 μm. Then, pass the coating through a wavelength of 365 nm and a power of 100 mW / cm. 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

[0026] Example 5 (1) Isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane were mixed at a mass ratio of 4:2 and stirred at 300 rpm for 30 min at room temperature under a nitrogen atmosphere to form a droplet; 3,5-dimethylpyrazole and toluene were mixed at a mass ratio of 2.5:10 and stirred at 200 rpm for 15 min at room temperature to form a mixture. The mixture was stirred at 300 rpm at 80 °C and a droplet of 0.4 times the mass of the mixture was slowly added to the mixture at a dropping rate of 2 drops / s. After the addition was completed, the mixture was stirred for 4 h to obtain a silane mixture with closed isocyanate ends. (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.5 and stirred at 500 rpm for 15 min. Then, 0.6 times the mass of the silane mixture of 0.1 M boric acid aqueous solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the addition was completed, the temperature was raised to 70 °C and refluxed for 2 h. 0.5 times the mass of 0.1 M boric acid aqueous solution of sodium bicarbonate solid particles were added to neutralize. The temperature was lowered and the sodium bicarbonate solid particles were removed by filtration. The filtrate was distilled at 70 °C and vacuum degree of 0.1 kPa for 2 h to remove toluene, alcohols and water generated in the reaction, and to obtain a multi-branched diisocyanate-terminated intermediate. (3) The intermediate, oleamide, Irgacure1173 and toluene were mixed in a mass ratio of 2:0.2:0.01:10 and heated to 80°C and stirred at 300 rpm for 30 min to obtain a low-moisture active isocyanate. (4) 80 parts by weight of polycaprolactone diol with a molecular weight of 1000 were heated to 100°C and vacuum dehydrated for 1 hour. 120 parts by weight of toluene, 70 parts by weight of low-moisture reactive isocyanate, and 0.2 parts by weight of stannous octoate were added. The mixture was heated to 150°C and stirred at 500 rpm for 3 hours. The mixture was then cooled to 50°C and uniformly coated onto a substrate with a coating thickness of 50 μm. The coating was then examined at a wavelength of 365 nm and a power of 100 mW / cm. 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

[0027] Comparative Example 1 The difference between Comparative Example 1 and Example 3 lies in step (1). Step (1) is changed to: 3,5-dimethylpyrazole and toluene are mixed at a mass ratio of 2:10 and stirred at 200 rpm for 15 min at room temperature to form a mixture. The mixture is stirred at 300 rpm at 75°C. 3-isocyanate-propyltrimethoxysilane, which is 0.3 times the mass of the mixture, is slowly added dropwise to the mixture at a rate of 2 drops / s. After the addition is complete, the mixture is stirred for 3 h to obtain a silane mixture with the isocyanate end blocked. The remaining steps are the same as in Example 3.

[0028] Comparative Example 2 The difference between Comparative Example 2 and Example 3 lies in step (1). Step (1) is changed to: 3,5-dimethylpyrazole and toluene are mixed at a mass ratio of 2:10 and stirred at 200 rpm for 15 min at room temperature to form a mixture. The mixture is stirred at 300 rpm at 75°C, and isocyanate-propyltriethoxysilane is slowly added dropwise to the mixture at a rate of 2 drops / s, with 0.3 times the mass of the mixture. After the addition is complete, the mixture is stirred for 3 h to obtain a silane mixture with the isocyanate end blocked. The remaining steps are the same as in Example 3.

[0029] Comparative Example 3 The difference between Comparative Example 3 and Example 3 lies in step (1). Step (1) is changed to: mixing isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane at a mass ratio of 3:1.5, stirring at 300 rpm for 30 min at room temperature under a nitrogen atmosphere to form a silane mixture, and the remaining steps are the same as in Example 3.

[0030] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that step (2) is omitted, and step (3) is changed to: mixing silane mixture, oleamide, Irgacure1173 and toluene in a mass ratio of 1.5:0.15:0.01:10, heating to 80°C and stirring at 300 rpm for 30 min to obtain low moisture active isocyanate, and the remaining steps are the same as in Example 3.

[0031] Comparative Example 5 The difference between Comparative Example 5 and Example 3 lies in step (3). Step (3) is changed to: mixing the intermediate, Irgacure1173 and toluene in a mass ratio of 1.5:0.01:10, heating to 80°C and stirring at 300 rpm for 30 min to obtain a low-moisture active isocyanate. The remaining steps are the same as in Example 3.

[0032] Example of effect Table 1 below shows the performance analysis results of the low-moisture reactive isocyanates of Examples 1 to 5 and Comparative Examples 1 to 5 of the present invention.

[0033] Table 1

[0034] A comparison of the experimental data on water vapor transmission rate between the examples and the comparative examples reveals that the present invention first blocks the isocyanate ends of isocyanate-based propyltriethoxysilane and 3-isocyanate-based propyltrimethoxysilane with pyrazole blocking agents, and then converts them with γ-methacryloyloxypropyltriisopropoxysilane into a multi-branched diisocyanate-terminated intermediate. The high steric hindrance of the multi-branched structure significantly reduces water vapor transmission rate. After being blended and modified with oleamide and photoinitiator, a low-moisture-activity isocyanate is obtained. In subsequent applications, UV curing further reduces surface energy and minimizes contact with moisture. A comparison of the experimental data on storage performance between the examples and the comparative examples reveals that the present invention uses blocking agents to block the isocyanate ends, preventing them from reacting with water vapor during storage and processing. A comparison of the experimental data on abrasion resistance between the examples and the comparative examples reveals that the present invention endows the coating with excellent abrasion resistance through a three-dimensional cross-linked network formed by the hydrolysis and condensation of three silanes, the cross-linking of isocyanate and polyol, and photocross-linking.

[0035] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A low-moisture reactive isocyanate, characterized in that, Includes the following steps: (1) Mix isocyanate-propyltriethoxysilane and 3-isocyanate-propyltrimethoxysilane at a mass ratio of 2~4:1~2 and stir at room temperature for 30 min under nitrogen atmosphere to form a droplet; mix pyrazole blocking agent and organic solvent at a mass ratio of 1.5~2.5:10 and stir at room temperature for 15 min to form a mixture. Stir at 70~80℃ and slowly add 0.2~0.4 times the mass of the mixture to the mixture. After the addition is complete, keep stirring and react for 2~4 h to obtain a silane mixture with blocked isocyanate ends; (2) Under ice-water bath, the silane mixture and γ-methacryloxypropyltriisopropoxysilane were mixed at a mass ratio of 1:0.2~0.5 and stirred for 15 min. Then, 0.4~0.6 times the mass of the silane mixture of buffer solution was added dropwise while stirring. The dropwise acceleration rate was 2 mL / min. After the dropwise addition was completed, the temperature was raised to 60~70℃ and refluxed for 1~2 h. 0.3~0.5 times the mass of the buffer solution of neutralizing agent was added for neutralization. The temperature was lowered and the neutralizing agent was removed by filtration. The filtrate was distilled under reduced pressure for 2 h to obtain the multi-branched diisocyanate-terminated intermediate. (3) Mix the intermediate, surface modifier, photoinitiator and organic solvent in a mass ratio of 1~2:0.1~0.2:0.01:10, heat to 80℃ and stir for 30 min to obtain low moisture activity isocyanate.

2. The low-moisture reactive isocyanate according to claim 1, characterized in that, The organic solvent mentioned in step (1) is toluene.

3. The low-moisture reactive isocyanate according to claim 1, characterized in that, The pyrazole blocking agent in step (1) is 3,5-dimethylpyrazole.

4. The low-moisture reactive isocyanate according to claim 1, characterized in that, The slow drop acceleration rate in step (1) is 2 drops / s.

5. The low-moisture reactive isocyanate according to claim 1, characterized in that, The buffer solution in step (2) is a 0.1M aqueous solution of boric acid.

6. The low-moisture reactive isocyanate according to claim 1, characterized in that, The neutralizing agent in step (2) is sodium bicarbonate solid particles.

7. The low-moisture reactive isocyanate according to claim 1, characterized in that, The reaction process of the multi-branched diisocyanate-terminated intermediate in step (2) is as follows: .

8. The low-moisture reactive isocyanate according to claim 1, characterized in that, The surface modifier mentioned in step (3) is oleic acid amide.

9. The low-moisture reactive isocyanate according to claim 1, characterized in that, The photoinitiator in step (3) is Irgacure1173.

10. The application of a low-moisture reactive isocyanate, characterized in that, 60-80 parts by weight of polyol were heated to 100°C and vacuum dehydrated for 1 hour. Then, 80-120 parts by weight of toluene, 50-70 parts by weight of low-moisture-activity isocyanate, and 0.2 parts by weight of catalyst were added. The mixture was heated to 150°C and stirred for 3 hours. The mixture was then cooled to 50°C and uniformly coated onto a substrate to a thickness of 50 μm. Finally, the coating was examined at a wavelength of 365 nm and a power of 100 mW / cm². 2 A polyurethane coating was obtained by irradiating the product with ultraviolet light for 2 minutes.

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