Diethyltoluenediamine / dimethyl thio toluenediamine compound polyurethane curing agent and preparation method thereof

Abstract

The invention discloses a diethyl toluenediamine / dimethyl thio toluenediamine compound polyurethane curing agent and a preparation method thereof, and belongs to the technical field of anticorrosive paints.The preparation method comprises the steps that a self-synthesized weather-resistant modifier is added, the weather-resistant modifier is obtained by grafting isocyanate modified mica and benzotriazole through a reaction, and then the weather-resistant modifier is prepared; the surface of the isocyanate modified mica is rich in isocyanate sites and large in specific surface area, on one hand, benzotriazole is fixed in a chemical bonding mode, on the other hand, the large specific surface area and ion exchange performance between modified mica layers after intercalation are utilized, benzotriazole is adsorbed, and falling and migration are avoided; on the basis of the advantages of diethyl toluenediamine and dimethyl thio toluenediamine, active amino groups contained in molecules and isocyanate groups in a polyurethane prepolymer are subjected to rapid addition reaction to generate urea bonds, the reaction activity is far higher than that of aliphatic amine, rapid curing can be achieved at medium and low temperatures, cured polyurethane forms a compact cross-linked network, and the curing effect is good. High flexibility is shown.

Description

[0001] This invention belongs to the field of anti-corrosion coating technology, specifically a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent and its preparation method. Background Technology

[0002] Anti-corrosion coatings are an important type of coating in the coatings industry, applicable to construction, metal protection, and other fields. They possess excellent adhesion, aging resistance, and corrosion prevention properties. With economic development and the improvement of people's living standards, the anti-corrosion coatings industry is placing greater emphasis on the combination of safety, environmental protection, and performance. Developing anti-corrosion coatings that are resistant to salt spray, acids and alkalis, salt water, and water, while also exhibiting good adhesion, is a key research focus in this field.

[0003] CN107987698A discloses a water-based anti-corrosion coating containing modified graphene oxide. The coating comprises component A and component B in a volume ratio of 10:1. Component A is composed of the following raw materials in the indicated mass percentages: 45-48% polyurethane emulsion, 0.1-1.0% modified graphene oxide, 1.0-1.2% tripropylene glycol monobutyl ether, 0.2-0.3% sodium dehydroacetate, 32% precipitated barium sulfate, 0.1% polydimethylsiloxane, 0.2% thickener, and the balance being deionized water. Component B is composed of the following raw materials in the indicated mass percentages: 50% curing agent and 50% deionized water. This water-based anti-corrosion coating exhibits good water resistance, salt spray resistance, and corrosion resistance, as well as high hardness, strong weather resistance, and good adhesion. However, since this is a water-based coating, how to meet the requirements of salt spray resistance, acid and alkali resistance, salt water resistance, water resistance, and good adhesion for non-water-based coatings remains a key research focus in this field.

[0004] Chinese Patent No. CN109575225B discloses a graphene oxide-modified curing agent, a polyurethane coating, its preparation method, and its application. This invention utilizes graphene oxide-modified diisocyanate and unmodified diisocyanate as curing agents to ensure the presence of active reactive groups and to guarantee good curing performance when used in coatings. During film formation, graphene oxide is attached to the coating resin, enhancing the coating's resistance to salt spray, acids and alkalis, salt water, water, and adhesion. However, the diisocyanate in this solution includes toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, or hexamethylene diisocyanate, all of which are aromatic diisocyanates. The aromatic ring structure of these diisocyanates is prone to photo-oxidation under light, causing the coating to gradually yellow. Summary of the Invention

[0005] The purpose of this invention is to provide a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent and its preparation method. By adding a self-synthesized weather-resistant modifier, which is an isocyanate-modified mica and 2-(2,4-dihydroxyphenyl)-2H-benzotriazole through reaction grafting, the isocyanate-modified mica utilizes its abundant isocyanate sites and large specific surface area to fix benzotriazole through chemical bonding on the one hand, and to adsorb benzotriazole by utilizing the large specific surface area and ion exchange performance between the intercalated modified mica layers, thus preventing detachment and migration.

[0006] The objective of this invention can be achieved through the following technical solutions: A method for preparing a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent includes the following steps: Step 1: Expand mica sheets using the interlayer permeation effect of dimethyl sulfoxide to obtain pretreated mica sheets. Then, use hexadecyltrimethylammonium bromide to intercalate into the mica interlayer through ion exchange. After hydrothermal reaction, modified mica is obtained.

[0007] Step 2: The isocyanate groups of isophorone diisocyanate are added to the hydroxyl groups on the surface of modified mica through an addition reaction, thereby covalently grafting the isocyanate groups onto the mica surface to obtain isocyanate-modified mica.

[0008] Step 3: The phenolic hydroxyl groups of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole react with the isocyanate groups on the surface of mica modified with isocyanate, and then undergo a carbamate reaction under the action of dibutyltin dilaurate to obtain a weather-resistant modifier.

[0009] Step 4: The hydroxyl groups contained in the weather-resistant modifier structure undergo ring-opening with epichlorohydrin under the action of benzyltriethylammonium chloride. After the reaction is completed, the alkaline conditions provided by calcium oxide and sodium hydroxide promote dehydration and ring closure, and a stable epoxy group is formed again to obtain the epoxy weather-resistant modifier.

[0010] Step 5: The epoxy groups in the epoxy weather-resistant modifier are ring-opened using diethyltoluenediamine and dimethylthiotoluenediamine to obtain a diamine-compound polyurethane curing agent.

[0011] Furthermore, the specific preparation steps for pretreated mica sheets are as follows: Mica powder, dimethyl sulfoxide, and deionized water were added to a reaction vessel at a ratio of 20-30g: 150-200mL: 18-20mL. The mixture was stirred at 60-70℃ and 500-600r / min for 24-26h, allowed to cool naturally to room temperature, and centrifuged at 1000-1200r / min for 3-4min. The product was washed 2-4 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70℃ for 1-2h to obtain pretreated mica flakes. Furthermore, the specific preparation steps of modified mica are as follows: Pretreated mica flakes and methanol were added to a polytetrafluoroethylene reactor and hydrothermally reacted for 12-14 h at 100-110 °C and 500-600 r / min. The supernatant was removed, and hexadecyltrimethylammonium bromide was added. The hydrothermal reaction was continued for another 12-14 h. The mixture was centrifuged at 3000-3200 r / min for 2-4 min, filtered, and the product was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The product was then vacuum dried at 60-70 °C for 1 h to obtain modified mica.

[0012] Furthermore, the ratio of pretreated mica sheets, methanol, and cetyltrimethylammonium bromide is 14-20g: 18-20mL: 15-18g.

[0013] Furthermore, the specific preparation steps for isocyanate-modified mica are as follows: Isophorone diisocyanate, butanone, and N-ethylpyrrolidone were added to a reaction vessel and stirred at 80-85℃ and 500-600 r / min for 30-40 min. Then, modified mica was added and kept at this temperature for 40-50 min. The mixture was then heated to 80-90℃ and kept at this temperature for another 40-50 min. After filtration, the precipitate was washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then dried under vacuum at 60-70℃ for 1-2 h to obtain isocyanate-modified mica.

[0014] Furthermore, the ratio of isophorone diisocyanate, butanone, N-ethylpyrrolidone and modified mica is 40-50g: 40-42g: 30-35g: 15-20g.

[0015] Furthermore, the specific preparation steps of the weather-resistant modifier are as follows: Isocyanate-modified mica, 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and butanone were added to a reaction vessel and stirred for 30-40 min at 70-85℃ and 500-600 r / min. Then, dibutyltin dilaurate was added and the mixture was kept at this temperature for 100-120 min. The mixture was filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The precipitate was then vacuum dried at 60-70℃ for 1-2 h to obtain the weather-resistant modifier.

[0016] Furthermore, the ratio of isocyanate-modified mica, 2-(2,4-dihydroxyphenyl)-2H-benzotriazole, butanone and dibutyltin dilaurate is 32-35g:15-20g:120-140mL:1-2g.

[0017] Furthermore, the specific preparation steps of the epoxy weather-resistant modifier are as follows: The weather-resistant modifier and epichlorohydrin were added to a reaction vessel and stirred for 20-25 min at 20-25℃ and 400-500 r / min. Then, benzyltriethylammonium chloride was added as a catalyst, and the mixture was heated to 115-120℃ and reacted for another 2-3 h. After the reaction was completed, the temperature was lowered to 60-70℃, and calcium oxide and sodium hydroxide were added. The reaction was continued for another 3-4 h. The mixture was then filtered and the unreacted epichlorohydrin was removed by rotary evaporation to obtain the epoxy weather-resistant modifier.

[0018] Furthermore, the ratio of weather-resistant modifier, epichlorohydrin, benzyltriethylammonium chloride, calcium oxide, and sodium hydroxide is 20-22g: 500-600mL: 0.5-0.6mL: 5-6g: 4-6g.

[0019] Furthermore, the specific preparation steps for the compounded polyurethane curing agent are as follows: Epoxy-modified weather-resistant modifier and isopropanol were added to a reaction vessel at a ratio of 20-22g:300-400mL. The mixture was stirred at 80-85℃ and 500-600r / min for 30-40min to obtain a mixed solution. Then, diethyltoluenediamine, dimethylthiotoluenediamine and glacial acetic acid were stirred and mixed and added to the mixed solution. The reaction was continued at the temperature for 3-4h. After filtration, the precipitate was washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70℃ for 1-2h to obtain a compound polyurethane curing agent.

[0020] Furthermore, the ratio of diethyltoluenediamine, dimethylthiotoluenediamine, glacial acetic acid, and the mixed solution is 40-50 mL: 50-60 mL: 3-4 g: 300-400 mL.

[0021] The beneficial effects of this invention are: In the compound polyurethane curing agent of this invention, a self-synthesized weather-resistant modifier is added. The weather-resistant modifier is isocyanate-modified mica and 2-(2,4-dihydroxyphenyl)-2H-benzotriazole grafted together. The isocyanate-modified mica utilizes its abundant isocyanate sites and large specific surface area to fix benzotriazole through chemical bonding on the one hand, and to adsorb benzotriazole by utilizing the large specific surface area and ion exchange performance between the intercalated modified mica layers, thus preventing detachment and migration.

[0022] The compound polyurethane curing agent prepared in this invention, based on the advantages of diethyltoluenediamine and dimethylthiotoluenediamine, contains active amino groups in its molecule, which undergo a rapid addition reaction with the isocyanate groups in the polyurethane prepolymer to form urea bonds. The reactivity is much higher than that of aliphatic amines, and rapid curing can be achieved at medium and low temperatures. The rigid structure of the aromatic ring and the strong polarity of the urea bond enable the cured polyurethane to form a dense cross-linked network, exhibiting high flexibility. The conjugated structure of its aromatic ring itself can endow the cured product with excellent thermal stability, and it still has good performance under thermo-oxidative aging conditions, which can extend the service life of polyurethane materials.

[0023] The modified mica of this invention, through hot water exfoliation, increases the interlayer spacing. Utilizing subsequent adsorption and fixation with benzotriazole, its layered inorganic structure acts as a reinforcing phase in the curing agent. Combined with the urea bond network formed by the curing of organic amines, it forms a hybrid structure of rigid inorganic sheets and flexible organic segments through chemical bonds and physical entanglement. This structure effectively disperses stress, enabling the cured polyurethane to maintain high flexibility while also possessing higher hardness, wear resistance, and deformation resistance. The layered structure of mica provides physical protection against ultraviolet radiation, creating a dual protection of chemical absorption and physical barrier with benzotriazole. Attached Figure Description

[0024] Figure 1 This is a scanned electronic image of mica powder.

[0025] Figure 2 Scanning electron image and transmission electron image of weather-resistant modifier.

[0026] Figure 3 This is a particle size distribution diagram of mica nanosheets.

[0027] Figure 4 This is a particle size distribution diagram of the weather-resistant modifier. Detailed implementation method. 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.

[0028] Example 1: A method for preparing a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent, comprising the following steps: S1: Add 20g of mica powder, 150mL of dimethyl sulfoxide and 18mL of deionized water to a reaction vessel, stir for 24h at 60℃ and 500r / min, cool naturally to room temperature, centrifuge at 1000r / min for 3min, wash the product twice with deionized water and anhydrous ethanol respectively, and dry under vacuum at 60℃ for 1h to obtain pretreated mica flakes; Add 14g of pretreated mica flakes and 18mL of methanol to a polytetrafluoroethylene reaction vessel, hydrothermally react for 12h at 100℃ and 500r / min, remove the supernatant, add 15g of hexadecyltrimethylammonium bromide, continue hydrothermal reaction for 12h, centrifuge at 3000r / min for 2min, filter, wash the product twice with deionized water and anhydrous ethanol respectively, and dry under vacuum at 60℃ for 1h to obtain modified mica.

[0029] S2: Add 40g of isophorone diisocyanate, 40g of butanone and 30g of N-ethylpyrrolidone to a reaction vessel, stir for 30min at 80℃ and 500r / min, then add 15g of modified mica, keep warm for 40min, heat to 80℃, keep warm for another 40min, filter, wash the precipitate twice with deionized water and anhydrous ethanol respectively, and dry under vacuum at 60℃ for 1h to obtain isocyanate modified mica.

[0030] S3: Add 32g of isocyanate-modified mica, 15g of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 120mL of butanone to a reaction vessel, stir at 70℃ and 500r / min for 30min, then add 1g of dibutyltin dilaurate, continue to keep warm for 100min, filter, wash the precipitate twice with deionized water and anhydrous ethanol respectively, and dry under vacuum at 60℃ for 1h to obtain the weather-resistant modifier.

[0031] S4: Add 20g of weather-resistant modifier and 500mL of epichlorohydrin to a reactor, stir for 20min at 20℃ and 400r / min, then add 0.5mL of benzyltriethylammonium chloride as a catalyst, heat to 115℃, and continue the reaction for 2h. After the reaction is completed, cool down to 60℃, add 5g of calcium oxide and 4g of sodium hydroxide, and continue the reaction for 3h. Filter, and remove unreacted epichlorohydrin by rotary evaporation to obtain the epoxy weather-resistant modifier.

[0032] S5: Add 20g of epoxy-modified weather-resistant modifier and 300mL of isopropanol to the reaction vessel, stir for 30min at 80℃ and 500r / min to obtain a mixed solution, then add 40mL of diethyltoluenediamine, 50mL of dimethylthiotoluenediamine and 3g of glacial acetic acid to 300mL of the mixed solution, continue to keep warm for 3h, filter, wash the precipitate twice with deionized water and anhydrous ethanol respectively, and vacuum dry at 60℃ for 1h to obtain diamine compound polyurethane curing agent.

[0033] Example 2: A method for preparing a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent, comprising the following steps: S1: Add 25g of mica powder, 175mL of dimethyl sulfoxide and 19mL of deionized water to a reaction vessel, stir for 25h at 65℃ and 550r / min, cool naturally to room temperature, centrifuge at 1100r / min for 3.5min, wash the product three times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 65℃ for 1.5h to obtain pretreated mica flakes; Add 17g of pretreated mica flakes and 19mL of methanol to a polytetrafluoroethylene reaction vessel, hydrothermally react for 13h at 105℃ and 550r / min, remove the supernatant, add 16.5g of hexadecyltrimethylammonium bromide, continue hydrothermal reaction for 13h, centrifuge at 3100r / min for 3min, filter, wash the product three times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 65℃ for 1h to obtain modified mica.

[0034] S2: Add 45g of isophorone diisocyanate, 41g of butanone and 32.5g of N-ethylpyrrolidone to a reaction vessel and stir for 35min at 82.5℃ and 550r / min. Then add 17.5g of modified mica, keep warm for 45min, heat to 85℃, keep warm for another 45min, filter, wash the precipitate 2.5 times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 65℃ for 1.5h to obtain isocyanate modified mica.

[0035] S3: Add 33.5g of isocyanate-modified mica, 17.5g of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 130mL of butanone to a reaction vessel, stir for 35min at 77.5℃ and 550r / min, then add 1.5g of dibutyltin dilaurate, continue to keep warm for 110min, filter, wash the precipitate 2.5 times with deionized water and anhydrous ethanol respectively, and vacuum dry at 65℃ for 1.5h to obtain the weather-resistant modifier.

[0036] S4: Add 21g of weather-resistant modifier and 550mL of epichlorohydrin to a reactor and stir for 22.5min at 22.5℃ and 450r / min. Then add 0.55mL of benzyltriethylammonium chloride as a catalyst, heat to 117.5℃, and continue the reaction for 2.5h. After the reaction is completed, cool down to 65℃, add 5.5g of calcium oxide and 5g of sodium hydroxide, and continue the reaction for 3.5h. Filter and remove unreacted epichlorohydrin by rotary evaporation to obtain the epoxy weather-resistant modifier.

[0037] S5: Add 21g of epoxy-modified weather-resistant modifier and 350mL of isopropanol to the reaction vessel, and stir for 35min at 82.5℃ and 550r / min to obtain a mixed solution. Then, stir and mix 45mL of diethyltoluenediamine, 55mL of dimethylthiotoluenediamine and 3.5g of glacial acetic acid and add them to 350mL of the mixed solution. Continue to keep the reaction at the temperature for 3.5h. Filter, wash the precipitate with deionized water and anhydrous ethanol 2.5 times each, and vacuum dry at 65℃ for 1.5h to obtain the diamine compound polyurethane curing agent.

[0038] Example 3: A method for preparing a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent, comprising the following steps: S1: Add 30g of mica powder, 200mL of dimethyl sulfoxide and 20mL of deionized water to a reaction vessel, stir for 26h at 70℃ and 600r / min, cool naturally to room temperature, centrifuge at 1200r / min for 4min, wash the product with deionized water and anhydrous ethanol 4 times each, and vacuum dry at 70℃ for 2h to obtain pretreated mica sheets; Add 20g of pretreated mica sheets and 20mL of methanol to a polytetrafluoroethylene reaction vessel, hydrothermally react at 110℃ and 600r / min for 14h, remove the supernatant, add 18g of hexadecyltrimethylammonium bromide, continue hydrothermal reaction for 14h, centrifuge at 3200r / min for 4min, filter, wash the product with deionized water and anhydrous ethanol 4 times each, and vacuum dry at 70℃ for 1h to obtain modified mica.

[0039] S2: Add 50g of isophorone diisocyanate, 42g of butanone and 35g of N-ethylpyrrolidone to a reaction vessel, stir for 40min at 85℃ and 600r / min, then add 20g of modified mica, keep warm for 50min, heat to 90℃, keep warm for another 50min, filter, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 70℃ for 2h to obtain isocyanate modified mica.

[0040] S3: Add 35g of isocyanate-modified mica, 20g of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and 140mL of butanone to a reaction vessel, stir at 85℃ and 600r / min for 40min, then add 2g of dibutyltin dilaurate, continue to keep warm for 120min, filter, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and dry under vacuum at 70℃ for 2h to obtain the weather-resistant modifier.

[0041] S4: Add 22g of weather-resistant modifier and 600mL of epichlorohydrin to a reactor, stir for 25min at 25℃ and 500r / min, then add 0.6mL of benzyltriethylammonium chloride as a catalyst, heat to 120℃, and continue the reaction for 3h. After the reaction is completed, cool down to 70℃, add 6g of calcium oxide and 6g of sodium hydroxide, and continue the reaction for 4h. Filter, remove unreacted epichlorohydrin by rotary evaporation, and obtain the epoxy weather-resistant modifier.

[0042] S5: Add 22g of epoxy-modified weather-resistant modifier and 400mL of isopropanol to the reaction vessel, stir for 40min at 85℃ and 600r / min to obtain a mixed solution, then add 50mL of diethyltoluenediamine, 60mL of dimethylthiotoluenediamine and 4g of glacial acetic acid to the 400mL mixed solution, continue to keep warm for 4h, filter, wash the precipitate three times with deionized water and anhydrous ethanol respectively, and vacuum dry at 70℃ for 2h to obtain diamine compound polyurethane curing agent.

[0043] Comparative Example 1: Based on Example 3, the modified mica in step S2 was replaced with the mica in step S1.

[0044] Comparative Example 2: Based on Example 3, the weather-resistant modifier in step S4 was replaced with isocyanate-modified mica prepared in step S2.

[0045] Comparative Example 3: Based on Example 3, the epoxy-modified weather-resistant modifier in step S5 was replaced with the weather-resistant modifier prepared in step S3.

[0046] The polyurethane coatings prepared from the diethyltoluenediamine / dimethylthiotoluenediamine compound curing agents obtained in Examples 1-3 and Comparative Examples 1-3 were subjected to performance testing, and the results are shown in Table 1. Component A is obtained by mixing 15g butyl acetate, 5g xylene, 3g dimethyl ester, 42.2g acrylic polyol, 30g titanium dioxide, 1g polyamide wax, 0.8g bentonite, 0.8g BYK-333, 1.4g BYK-154, and 0.8g BYK-024. Component B is obtained by mixing the compounded polyurethane curing agent with the compounded polyurethane curing agent. Component A and component B are mixed at a mass ratio of 4:1 to obtain a polyurethane coating.

[0047] Table 1 As can be seen from Table 1, when the modified mica in step S2 of Comparative Example 1 was replaced with the mica in step S1, the weather resistance was significantly reduced. Without the chemical UV absorption of benzotriazole and the physical barrier of mica, the UV resistance was unqualified, and the water resistance and damp heat resistance were reduced. Due to the lack of UV protection, the urea bonds were easily photo-oxidized and degraded. Without the mica reinforcing phase, the wear resistance was reduced and the adhesion was decreased. Due to the lack of the hybrid structure of rigid inorganic layers and flexible organic segments, the stress dispersion ability was insufficient. Due to the lack of the mica layered barrier to prevent the penetration of acid and alkali media, the coating was easily corroded.

[0048] In Comparative Example 2, the weather-resistant modifier in step S4 was replaced with isocyanate-modified mica prepared in step S2. 2-(2,4-dihydroxyphenyl)-2H-benzotriazole was not added, resulting in the loss of UV resistance. Furthermore, 2-(2,4-dihydroxyphenyl)-2H-benzotriazole contains terminal hydroxyl groups, which can provide conditions for subsequent epoxy modification. The loss of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole prevented epoxy modification, thus preventing the grafting of diethyltoluenediamine and dimethylthiotoluenediamine, leading to a comprehensive deterioration in performance testing.

[0049] In Comparative Example 3, the epoxy-modified weather-resistant modifier in step S5 was replaced with the weather-resistant modifier prepared in step S3. The unmodified mica exhibited poor compatibility with the organic amine curing agent, resulting in uneven dispersion within the coating, decreased adhesion, and substandard boiling water resistance. Furthermore, the lack of chemical bonding grafting and interlayer adsorption fixation of the mica led to rapid migration of benzotriazole during use, resulting in substandard UV resistance and short water and humid heat resistance times.

[0050] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent, characterized in that, Includes the following steps: Step 1: Expand mica sheets using the interlayer permeation effect of dimethyl sulfoxide to obtain pretreated mica sheets. Then, use hexadecyltrimethylammonium bromide to intercalate into the mica interlayer through ion exchange. After hydrothermal reaction, modified mica is obtained. Step 2: The isocyanate groups of isophorone diisocyanate are added to the hydroxyl groups on the surface of modified mica through an addition reaction, thereby covalently grafting the isocyanate groups onto the mica surface to obtain isocyanate-modified mica. Step 3: The phenolic hydroxyl groups of 2-(2,4-dihydroxyphenyl)-2H-benzotriazole react with the isocyanate groups on the surface of mica modified with isocyanate, and then undergo a carbamate reaction under the action of dibutyltin dilaurate to obtain a weather-resistant modifier. Step 4: The hydroxyl groups contained in the weather-resistant modifier structure react with epichlorohydrin under the action of benzyltriethylammonium chloride to undergo ring-opening. After the reaction is completed, the alkaline conditions provided by calcium oxide and sodium hydroxide promote dehydration and ring closure, and a stable epoxy group is formed again to obtain the epoxy weather-resistant modifier. Step 5: The epoxy groups in the epoxy weather-resistant modifier are ring-opened using diethyltoluenediamine and dimethylthiotoluenediamine to obtain a diamine-compound polyurethane curing agent.

2. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 1, characterized in that, The specific preparation steps for the pretreated mica sheets are as follows: Mica powder, dimethyl sulfoxide, and deionized water were added to a reaction vessel at a ratio of 20-30 g: 150-200 mL: 18-20 mL. The mixture was stirred at 60-70 °C and 500-600 r / min for 24-26 h. After naturally cooling to room temperature, the mixture was centrifuged at 1000-1200 r / min for 3-4 min. The product was washed 2-4 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70 °C for 1-2 h to obtain pretreated mica flakes.

3. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 1, characterized in that, The specific preparation steps of the modified mica are as follows: Pretreated mica flakes and methanol were added to a polytetrafluoroethylene reactor and hydrothermally reacted at 100-110℃ and 500-600 r / min for 12-14 h. The supernatant was removed, and hexadecyltrimethylammonium bromide was added. The hydrothermal reaction was continued for another 12-14 h. The mixture was centrifuged at 3000-3200 r / min for 2-4 min, filtered, and the product was washed 2-4 times with deionized water and anhydrous ethanol, respectively. The product was then vacuum dried at 60-70℃ for 1 h to obtain modified mica. The ratio of the pretreated mica sheets, methanol, and hexadecyltrimethylammonium bromide is 14-20g: 18-20mL: 15-18g.

4. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 1, characterized in that, The specific preparation steps for the isocyanate-modified mica are as follows: Isophorone diisocyanate, butanone, and N-ethylpyrrolidone were added to a reaction vessel and stirred at 80-85℃ and 500-600 r / min for 30-40 min. Then modified mica was added, kept at the temperature for 40-50 min, heated to 80-90℃, and kept at the temperature for another 40-50 min. The mixture was filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The precipitate was then dried under vacuum at 60-70℃ for 1-2 h to obtain isocyanate-modified mica. The ratio of isophorone diisocyanate, butanone, N-ethylpyrrolidone and modified mica is 40-50g:40-42g:30-35g:15-20g.

5. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 1, characterized in that, The specific preparation steps of the weather-resistant modifier are as follows: Isocyanate-modified mica, 2-(2,4-dihydroxyphenyl)-2H-benzotriazole and butanone were added to a reaction vessel and stirred for 30-40 min at 70-85℃ and 500-600 r / min. Then, dibutyltin dilaurate was added and the mixture was kept at this temperature for 100-120 min. The mixture was filtered, and the precipitate was washed 2-3 times with deionized water and anhydrous ethanol, respectively. The precipitate was then vacuum dried at 60-70℃ for 1-2 h to obtain the weather-resistant modifier.

6. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 5, characterized in that, The ratio of isocyanate-modified mica, 2-(2,4-dihydroxyphenyl)-2H-benzotriazole, butanone and dibutyltin dilaurate is 32-35g:15-20g:120-140mL:1-2g.

7. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 1, characterized in that, The specific preparation steps of the epoxy weather-resistant modifier are as follows: The weather-resistant modifier and epichlorohydrin were added to a reaction vessel and stirred for 20-25 min at 20-25℃ and 400-500 r / min. Then, benzyltriethylammonium chloride was added as a catalyst, and the mixture was heated to 115-120℃ and reacted for another 2-3 h. After the reaction was completed, the temperature was lowered to 60-70℃, and calcium oxide and sodium hydroxide were added. The reaction was continued for another 3-4 h. The mixture was then filtered and the unreacted epichlorohydrin was removed by rotary evaporation to obtain the epoxy weather-resistant modifier.

8. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 7, characterized in that, The ratio of the weather-resistant modifier, epichlorohydrin, benzyltriethylammonium chloride, calcium oxide, and sodium hydroxide is 20-22g: 500-600mL: 0.5-0.6mL: 5-6g: 4-6g.

9. The preparation method of the diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent according to claim 1, characterized in that, The specific preparation steps of the compound polyurethane curing agent are as follows: Epoxy-modified weather-resistant modifier and isopropanol were added to a reaction vessel at a ratio of 20-22g:300-400mL. The mixture was stirred at 80-85℃ and 500-600r / min for 30-40min to obtain a mixed solution. Then, diethyltoluenediamine, dimethylthiotoluenediamine and glacial acetic acid were stirred and mixed and added to the mixed solution. The reaction was continued at the temperature for 3-4h. After filtration, the precipitate was washed 2-3 times with deionized water and anhydrous ethanol, respectively, and then vacuum dried at 60-70℃ for 1-2h to obtain a compound polyurethane curing agent. The ratio of diethyltoluenediamine, dimethylthiotoluenediamine, glacial acetic acid, and the mixed solution is 40-50 mL: 50-60 mL: 3-4 g: 300-400 mL.

10. A diethyltoluenediamine / dimethylthiotoluenediamine compound polyurethane curing agent, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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