Preparation process of dendritic waterborne epoxy modified polyurethane resin

Abstract

The invention relates to a preparation process of a dendritic waterborne epoxy-modified polyurethane resin, which is characterized in that: firstly, the synthesized epoxy-modified polymer, pentamethylene diisocyanate and macromolecular diol are added to a reaction container, and the reaction is carried out for 2 to 6 hours to obtain an NCO-terminated prepolymer. The synthesized dendritic resin, dihydroxymethyl propionic acid, small molecular diol and catalyst are added, and the temperature is raised to 65 to 85° C. under N2 protection. When the NCO content is 0, the prepolymer is cooled to 50 to 60° C., an organic amine is added, and the reaction is carried out for 0.5 to 1 hour, and acetone is added to reduce the viscosity; the above product is added to deionized water, and finally, the acetone is removed by rotary evaporation to obtain a dendritic waterborne epoxy-modified polyurethane resin. The dendritic waterborne epoxy-modified polyurethane resin prepared by the invention is not inferior to solvent-based polyurethane in terms of adhesion, solvent resistance, water resistance, mechanical properties, surface gloss, feel, etc., and has low cost and is conducive to market promotion.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer resins, and in particular relates to a preparation process of a dendritic waterborne epoxy-modified polyurethane resin. Background Art

[0002] As an environmentally friendly coating, two-component waterborne polyurethane coating is prepared from waterborne polyurethane resin and waterborne polyisocyanate curing agent. It has the advantages of low VOC, adjustable construction performance, good flexibility, etc. In addition, waterborne polyurethane coating avoids combustion or explosion during preparation, storage, transportation and coating, meeting the urgent requirements of safety and environmental protection. The waterborne polyurethane coating is combined with the substrate mainly by hydrogen bonds and van der Waals forces formed between polyurethane molecules, and the adhesion is generally not ideal; in addition, the linear molecules in the molecular structure of waterborne polyurethane have strong crystallinity and low crosslinking density after film formation. In addition, a small amount of hydrophilic groups are introduced into the waterborne polyurethane during the preparation process, so the water resistance of the coating is generally not high. Therefore, the adhesion, water resistance and solvent resistance of waterborne polyurethane coatings are limited in use in certain fields. Summary of the invention

[0003] The technical problem to be solved by the present invention is: a preparation process of a dendritic waterborne epoxy-modified polyurethane resin, and the prepared polyurethane resin has good adhesion, solvent resistance and water resistance.

[0004] The technical solution adopted by the present invention to solve the technical problem is: a preparation process of a dendritic waterborne epoxy-modified polyurethane resin, comprising the following steps:

[0005] (1) Preparing an epoxy-modified polymer: adding a macromolecular diol and an acid anhydride to a reactor, heating the reactor to 60 to 130° C., adding an epoxy resin and a catalyst, wherein the catalyst is one or more of triphenylphosphine, tetrabutylammonium bromide, tetramethylammonium chloride, and N,N-dimethylbenzylamine, and then heating the reactor to 90 to 140° C. to obtain an epoxy-modified polymer;

[0006] (2) Preparation of dendritic resin: methanol, polyamine and acrylate monomer are added to the reactor, and the temperature is raised to 30-45° C. under the protection of N2, and the reaction is kept at this temperature for 20-35 hours, and distilled under reduced pressure and dried in vacuum to obtain an intermediate product of dendritic resin; then, alcoholamine and methanol are added, and the temperature is raised to 30-45° C. under the protection of N2, and the reaction is kept at this temperature for 30-45 hours, and distilled under reduced pressure, filtered, and dried in vacuum to obtain a dendritic resin;

[0007] (3) Preparation of polyurethane resin: Adding the synthesized epoxy-modified polymer, pentamethylene diisocyanate, and macromolecular diol into a reaction vessel, heating to 65-85° C. under N2 protection, and keeping the temperature for reaction for 2-6 hours to obtain an NCO-terminated prepolymer; adding the synthesized dendritic resin, dihydroxymethylpropionic acid, small molecule diol, and catalyst, wherein the catalyst is one of dibutyltin dilaurate, stannous octoate, and bismuth isooctanoate, heating to 65-85° C. under N2 protection, and keeping the temperature for reaction for 2-8 hours, then cooling the prepolymer to 50-60° C., adding an organic amine, and reacting for 0.5-1 hour, and then adding acetone to reduce the viscosity; adding the above product into deionized water, dispersing at high speed for 0.5-2 hours, and finally, removing the acetone by rotary evaporation at 45-60° C. to obtain a dendritic waterborne epoxy-modified polyurethane resin.

[0008] Furthermore, the molar ratio of the macromolecular diol, acid anhydride and epoxy resin in preparing the epoxy-modified polymer is 1:(1-1.2):(0.3-0.6).

[0009] Furthermore, the molar ratio of the polyamine, the acrylate monomer and the alcohol amine in preparing the dendritic resin is 1:(3-7):(3-9).

[0010] Furthermore, the weight ratio of the epoxy-modified polymer, pentamethylene diisocyanate, macromolecular diol, dendritic resin, dimethylol propionic acid, micromolecular diol, catalyst, organic amine, acetone and deionized water in the preparation of the polyurethane resin is (10-50): (25-65): (20-80): (5-7): (5-7): (9-15): (0.03-0.15): (3.5-5.5): (20-60): (150-250).

[0011] Furthermore, the amount of the catalyst used is 0.1 to 0.8% of the total weight of the macromolecular diol, the acid anhydride and the epoxy resin.

[0012] Furthermore, the polyamine is one of ethylenediamine, diethylenetriamine and triethylenetetramine.

[0013] Furthermore, the acrylate monomer is one of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, and trimethylolpropane triacrylate.

[0014] Furthermore, the alcoholamine is one of ethanolamine and diethanolamine.

[0015] Furthermore, the small molecule diol is one or more of 1,6-hexanediol, 1,4-butanediol, methylpropanediol, and propylene glycol.

[0016] Furthermore, the macromolecular diol is one or more of polyether diol and polyester diol.

[0017] The beneficial effects of the present invention are:

[0018] The dendritic waterborne epoxy-modified polyurethane resin prepared by the present invention is added with epoxy-modified polymer and dendritic resin; wherein the epoxy-modified polymer is synthesized by using epoxy resin as raw material, and the prepared epoxy-modified polymer can improve the crosslinking degree of polyurethane resin after copolymerization with isocyanate, thereby improving the stability of polyurethane emulsion, and can improve the adhesion, solvent resistance and water resistance of polyurethane emulsion to form a coating. In addition, the present invention is added with dendritic resin, which has low melt viscosity, excellent solubility, easy film formation, diversified functions and high adhesion to substrates. Compared with traditional linear macromolecules of the same molecular weight, it is not easy to crystallize. Since the molecular structure contains more hydroxyl groups, it can participate in the crosslinking of the system in multiple dimensions, change the crosslinking structure of the coating, and better optimize the physical and chemical properties of the polyurethane emulsion. The present invention uses pentamethylene diisocyanate derived from biomass resources as a raw material. When pentamethylene diisocyanate is used as a hard segment, it has a lower raw material consumption due to a higher isocyanate ratio in its molecule, and the obtained coating has a fast film-forming speed and a high hardness. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the present invention more clear, the present invention is further described in detail below in conjunction with specific implementation methods. It should be understood that these descriptions are only exemplary and are not intended to limit the scope of the present invention.

[0020] The invention provides a preparation process of a dendritic waterborne epoxy-modified polyurethane resin. The waterborne polyurethane resin synthesized by the invention is used for preparing a two-component waterborne polyurethane coating with a waterborne polyisocyanate curing agent.

[0021] The preparation process of the polyurethane resin in the present invention is as follows:

[0022] In a reaction vessel, epoxy-modified polymer, pentamethylene diisocyanate, and macromolecular diol are added, and the temperature is raised to 65-85°C under N2 protection, and the reaction is kept warm for 2-6 hours to obtain an NCO-terminated prepolymer. After that, dendritic resin, dimethylol propionic acid, small molecule diol, and catalyst are added; the temperature is raised to 65-85°C under N2 protection, and the reaction is kept warm for 2-8 hours. When the NCO content is 0, the prepolymer is cooled to 50-60°C, and an organic amine is added to react for 0.5-1 hour. During the neutralization process, acetone is added to reduce the viscosity. The above product is added to deionized water and dispersed at high speed for 0.5-2 hours. Finally, the acetone is removed by rotary evaporation at 45-60°C to obtain a dendritic waterborne epoxy-modified polyurethane resin. Among them, the weight ratio of epoxy modified polymer, pentamethylene diisocyanate, macromolecular diol, dendritic resin, dihydroxymethylpropionic acid, small molecular diol, catalyst, organic amine, acetone and deionized water is (10-50): (25-65): (20-80): (5-7): (5-7): (9-15): (0.03-0.15): (3.5-5.5): (20-60): (150-250).

[0023] Among them, the molecular weight of the above-mentioned macromolecular diol is in the range of 100-4000. Specifically, the above-mentioned macromolecular diol is at least one of polyether diol and polyester diol; the polyether diol is at least one of PPG-600, N210, N204, and PTMG; the polyester diol is at least one of POL-2112, PCDL, and PCL; the small molecule diol is a combination of one or more of 1,6-hexanediol, 1,4-butanediol, methylpropylene glycol and propylene glycol; the catalyst is one of dibutyltin dilaurate, stannous octoate, and bismuth isooctanoate; the organic amine is one of triethylamine and dimethylethanolamine.

[0024] The preparation process of the epoxy modified polymer is as follows:

[0025] In a reactor, macromolecular diol and acid anhydride are added, the temperature is raised to 60-130° C., and the reaction is carried out until the acid value reaches 40-120 mgKOH / g, and epoxy resin and catalyst are added for modification, the temperature is raised to 90-140° C., and the reaction is carried out until the acid value is less than 5 mgKOH / g to obtain an epoxy-modified polymer; wherein the molar ratio of macromolecular diol, acid anhydride and epoxy resin is 1:(1-1.2):(0.3-0.6).

[0026] The molecular weight of the macromolecular diol is in the range of 100-4000. Specifically, the macromolecular diol is at least one of polyether diol and polyester diol; the polyether diol is at least one of PPG-600, N210, N204 and PTMG; the polyester diol is at least one of POL-2112, PCDL and PCL; the acid anhydride is at least one of maleic anhydride, phthalic anhydride, itaconic anhydride, citric anhydride, glutaric anhydride and propionic anhydride; the epoxy resin is a combination of one or more of epoxy resin E-44 and epoxy resin E-51. The catalyst is at least one of triphenylphosphine, tetrabutylammonium bromide, tetramethylammonium chloride and N,N-dimethylbenzylamine; the catalyst is used in an amount of 0.1-0.8% of the total weight of the macromolecular diol, the acid anhydride and the epoxy resin.

[0027] The preparation process of the dendritic resin is as follows:

[0028] Methanol, polyamine and acrylate monomer are added into a reactor, wherein the amount of methanol is 20-30% of the weight of the acrylate monomer and the polyamine, and the temperature is raised to 30-45° C. under N2 protection, and the reaction is kept warm for 20-35 hours, and reduced pressure distillation and vacuum drying are performed to obtain an intermediate product of a dendritic resin; then, an alcohol amine and methanol are added, wherein the amount of methanol is 80-150% of the weight of the intermediate product of the dendritic resin and the alcohol amine, and the temperature is raised to 30-45° C. under N2 protection, and the reaction is kept warm for 30-45 hours, and reduced pressure distillation, filtration and vacuum drying are performed to obtain a dendritic resin; wherein the molar ratio of the polyamine, the acrylate monomer and the alcohol amine is 1:(3-7):(3-9).

[0029] The polyamine is one of ethylenediamine, diethylenetriamine and triethylenetetramine; the acrylate monomer is one of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate and trimethylolpropane triacrylate; and the alcoholamine is one of ethanolamine and diethanolamine.

[0030] Example 1

[0031] 1. Preparation of epoxy modified polymers

[0032] To a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, add 600 g of polyether diol (PPG-600, relative molecular mass is 600) and 148 g of phthalic anhydride, and react at 100°C for 0.5 h until the acid value is below 75 mgKOH / g. Then, add 200 g of epoxy resin (E-51) and 2 g of tetrabutylammonium bromide, and react at 110°C for 3 h until the acid value is below 5 mgKOH / g to obtain an epoxy-modified polymer.

[0033] 2. Preparation of dendritic resin

[0034] Into a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, 904 g of 1,6-hexanediol diacrylate, 60 g of ethylenediamine, and 250 g of catalyst methanol were added, and the mixture was reacted at 35° C. for 30 h under N2 protection. After reduced pressure distillation and vacuum drying, a dendritic resin intermediate was obtained. Subsequently, 1500 g of catalyst methanol and 420 g of diethanolamine were added, and the mixture was reacted at 35° C. for 36 h under N2 protection. After reduced pressure distillation, filtration, and vacuum drying, a dendritic resin was obtained.

[0035] 3. Preparation of polyurethane resin

[0036] Take 500g of the epoxy-modified polymer synthesized in step 1, 460g of pentamethylene diisocyanate, and 290g of polyester diol (POL-2112, relative molecular mass 1000) and add them to a four-necked flask. In nitrogen, react at 80°C for 2h to obtain an NCO-terminated prepolymer. Then, take 65.8g of the dendritic resin prepared in step 2, 65.8g of dihydroxymethylpropionic acid, 0.8g of dibutyltin dilaurate, and 131.6g of 1,6-hexanediol and add them to the flask. React at 80°C for 2h. When the NCO content is 0, cool the prepolymer to 50°C and add 43.9g of triethylamine to neutralize the carboxylic acid reaction for 0.5h. During the neutralization process, add 300g of acetone to reduce the viscosity. Add the above product to 1950g of deionized water and disperse at high speed for 0.5h. Finally, the acetone was removed by rotary evaporation at 50 °C to obtain the dendritic waterborne epoxy-modified polyurethane resin.

[0037] 4. Prepare two-component water-based polyurethane varnish

[0038] The waterborne epoxy-modified polyurethane resin prepared in Example 1 was compounded with a waterborne polyisocyanate curing agent (Covestro Bayhydur XP 2655) at n(NCO):n(OH)=1.4:1 (i.e., the molar ratio of isocyanate group to hydroxyl group) to prepare a two-component waterborne polyurethane varnish.

[0039] Example 2

[0040] 1. Preparation of epoxy modified polymers

[0041] To a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, add 600 g of polyester diol (XCP-44-600, relative molecular mass is 600) and 98 g of maleic anhydride, and react at 110°C for 0.5 h until the acid value becomes below 80 mgKOH / g. Then, add 250 g of epoxy resin (E-44) and 1 g of tetramethylammonium chloride, and react at 110°C for 3 h until the acid value becomes below 5 mgKOH / g to obtain an epoxy-modified polymer.

[0042] 2. Preparation of dendritic resin

[0043] Into a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, 1200 g of tripropylene glycol diacrylate, 60 g of ethylenediamine, and 300 g of catalyst methanol were added, and the mixture was reacted at 35°C for 30 hours under N2 protection. After reduced pressure distillation and vacuum drying, a dendritic resin intermediate was obtained. Subsequently, 1600 g of catalyst methanol and 244 g of ethanolamine were added, and the mixture was reacted at 45°C for 36 hours under N2 protection. After reduced pressure distillation, filtration, and vacuum drying, a dendritic resin was obtained.

[0044] 3. Preparation of polyurethane resin

[0045] Take 400g of the epoxy-modified polymer synthesized in step 1, 460g of pentamethylene diisocyanate, and 400g of polyether diol (N210, relative molecular mass 1000) and add them to a four-necked flask. In nitrogen, react at 80°C for 3h to obtain an NCO-terminated prepolymer. Then, take 60g of the dendritic resin prepared in step 2, 60g of dihydroxymethylpropionic acid, 1g of stannous octoate, and 125g of 1,4-butanediol and add them to the flask. React at 75°C for 2h. When the NCO content is 0, cool the prepolymer to 50°C and add 40g of triethylamine to neutralize the carboxylic acid reaction for 0.5h. During the neutralization process, add 400g of acetone to reduce the viscosity. Add the above product to 2000g of deionized water and disperse at high speed for 0.5h. Finally, remove the acetone by rotary evaporation at 50°C to obtain a dendritic waterborne epoxy-modified polyurethane resin.

[0046] 4. Prepare two-component water-based polyurethane varnish

[0047] The waterborne epoxy-modified polyurethane resin prepared in Example 2 was compounded with a waterborne polyisocyanate curing agent (Covestro Bayhydur XP 2655) at n(NCO):n(OH)=1.4:1 (i.e., the molar ratio of isocyanate group to hydroxyl group) to prepare a two-component waterborne polyurethane varnish.

[0048] Example 3

[0049] 1. Preparation of epoxy modified polymers

[0050] To a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube and a stirrer, add 400 g of polyether diol (N204, relative molecular mass of 400) and 98 g of maleic anhydride, and react at 120°C for 0.5 h until the acid value becomes below 112 mgKOH / g. Then, add 200 g of epoxy resin (E-51) and 2 g of tetrabutylammonium bromide, and react at 120°C for 3 h until the acid value becomes below 5 mgKOH / g to obtain an epoxy-modified polymer.

[0051] 2. Preparation of dendritic resin

[0052] Into a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, 930 g of 1,6-hexanediol diacrylate, 60 g of ethylenediamine, and 313 g of catalyst methanol were added, and the mixture was reacted at 35°C for 30 hours under N2 protection. After reduced pressure distillation and vacuum drying, a dendritic resin intermediate was obtained. Subsequently, 1500 g of catalyst methanol and 440 g of diethanolamine were added, and the mixture was reacted at 35°C for 36 hours under N2 protection. After reduced pressure distillation, filtration, and vacuum drying, a dendritic resin was obtained.

[0053] 3. Preparation of polyurethane resin

[0054] Take 400g of the epoxy-modified polymer synthesized in step 1, 460g of pentamethylene diisocyanate, and 400g of polyether diol (N210, relative molecular mass 1000) and add them to a four-necked flask. In nitrogen, react at 80°C for 3h to obtain an NCO-terminated prepolymer. Then, take 60g of the dendritic resin prepared in step 2, 60g of dihydroxymethylpropionic acid, 1g of stannous octoate, and 125g of 1,4-butanediol and add them to the flask. React at 75°C for 2h. When the NCO content is 0, cool the prepolymer to 50°C and add 40g of triethylamine to neutralize the carboxylic acid reaction for 0.5h. During the neutralization process, add 400g of acetone to reduce the viscosity. Add the above product to 2000g of deionized water and disperse at high speed for 0.5h. Finally, remove the acetone by rotary evaporation at 50°C to obtain a dendritic waterborne epoxy-modified polyurethane resin.

[0055] 4. Prepare two-component water-based polyurethane varnish

[0056] The waterborne epoxy-modified polyurethane resin prepared in Example 3 and a waterborne polyisocyanate curing agent (Covestro Bayhydur XP 2655) were compounded at n(NCO):n(OH)=1.4:1 (i.e., the molar ratio of isocyanate group to hydroxyl group) to prepare a two-component waterborne polyurethane varnish.

[0057] Example 4

[0058] 1. Preparation of epoxy modified polymers

[0059] To a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, add 1000 g of polytetramethylene glycol (PTMG, relative molecular mass is 1000) and 98 g of maleic anhydride, react at 120° C. for 1 h until the acid value is below 51 mgKOH / g, add 250 g of epoxy resin (E-44) and 8 g of triphenylphosphine, react at 100° C. for 3 h until the acid value is below 5 mgKOH / g, and an epoxy-modified polymer is obtained.

[0060] 2. Preparation of dendritic resin

[0061] Into a four-necked flask equipped with a spherical condenser, a nitrogen inlet tube, and a stirrer, 1184 g of trimethylolpropane triacrylate, 60 g of ethylenediamine, and 300 g of catalyst methanol were added, and the mixture was reacted at 30°C for 24 h under N2 protection. After reduced pressure distillation and vacuum drying, an intermediate product of a dendritic resin was obtained. Subsequently, 2000 g of catalyst methanol and 840 g of diethanolamine were added, and the mixture was reacted at 35°C for 36 h under N2 protection. After reduced pressure distillation, filtration, and vacuum drying, a dendritic resin was obtained.

[0062] 3. Preparation of polyurethane resin

[0063] Take 100g of epoxy-modified polymer synthesized in step 1, 430g of pentamethylene diisocyanate, and 700g of polycaprolactone diol (PCL, relative molecular mass 1000) and add them to a four-necked flask. In nitrogen, react at 75°C for 2h to obtain an NCO-terminated prepolymer. Then, 60g of the dendritic resin prepared in step 2, 65g of dimethylolpropionic acid, 1g of dibutyltin dilaurate, and 100g of propylene glycol are added to the flask. React at 80°C for 3h. When the NCO content is 0, the prepolymer is cooled to 50°C and 49g of dimethylethanolamine is added to neutralize the carboxylic acid for 0.5h. During the neutralization process, 500g of acetone is added to reduce the viscosity. The above product is added to 2100g of deionized water and dispersed at high speed for 1.5h. Finally, the acetone is removed by rotary evaporation at 60°C to obtain a dendritic waterborne epoxy-modified polyurethane resin.

[0064] 4. Prepare two-component water-based polyurethane varnish

[0065] The waterborne epoxy-modified polyurethane resin prepared in Example 4 was compounded with a waterborne polyisocyanate curing agent (Covestro Bayhydur XP 2655) at n(NCO):n(OH)=1.4:1 (i.e., the molar ratio of isocyanate group to hydroxyl group) to prepare a two-component waterborne polyurethane varnish.

[0066] Comparative Example

[0067] 1. Preparation of polyurethane resin

[0068] Take 500g of polycarbonate diol (PCDL, relative molecular mass 1000), 460g of hexamethylene diisocyanate, and 290g of polyester diol (POL-2112, relative molecular mass 1000) and add them to a four-necked flask. In nitrogen, react at 80°C for 2h to obtain an NCO-terminated prepolymer. Then, take 65.8g of trimethylolpropane, 65.8g of dimethylolpropionic acid, 0.8g of dibutyltin dilaurate, and 131.6g of 1,6-hexanediol and add them to the flask. React at 85°C for 3h. When the NCO content is 0, cool the prepolymer to 50°C and add 43.9g of triethylamine to neutralize the carboxylic acid for 0.5h. During the neutralization process, add 300g of acetone to reduce the viscosity. Add the above product to 1950g of deionized water and disperse at high speed for 0.5h. Finally, the acetone was removed by rotary evaporation at 50 °C to obtain the waterborne polyurethane resin.

[0069] 2. Prepare two-component waterborne polyurethane varnish

[0070] The waterborne epoxy-modified polyurethane resin prepared in the comparative example was compounded with a waterborne polyisocyanate curing agent (Covestro Bayhydur XP 2655) at n(NCO):n(OH)=1.4:1 (i.e., the molar ratio of isocyanate group to hydroxyl group) to prepare a two-component waterborne polyurethane varnish.

[0071] Performance Testing

[0072] The two-component waterborne polyurethane varnishes prepared in Examples 1 to 4 and Comparative Example 1 were applied to clean glass plates, and the properties of the coating films formed thereon were tested.

[0073] The test items are as follows:

[0074] The solid content of the waterborne polyurethane resin was determined according to the coating solid content determination method GB1725-1979.

[0075] The tensile strength and elongation at break of each specimen were tested according to GB / T 1040-2006.

[0076] The adhesion of each sample was tested according to GB / T 9286-1998.

[0077] The water resistance of each sample was tested according to GB / T 9274-1988.

[0078] The gloss of each sample was tested according to GB / T 1743-1979.

[0079] The hardness of each sample was tested according to GB / T 6739-2006.

[0080] Alcohol resistance test: According to the actual application requirements, wipe the surface of the coating back and forth with cotton wool dipped in 95% ethanol to observe whether the surface is glossy or exposed.

[0081] Hand feel experiment: According to the actual application requirements, touch the surface of the paint with your hand and divide the softness into 5 levels based on the feeling: Level 5 is the best and Level 1 is the worst.

[0082] The test results are shown in Table 1

[0083] Table 1 Coating performance test results

[0084] Test items Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Appearance Milky white with blue light Milky white with blue light Milky white with blue light Milky white with blue light cream Solid content / wt% 42.5 43 41 41.5 39 Tensile strength / MPa 35 37 43 40 33 Elongation at break / % 250 240 229 235 260 Adhesion / Grade 2 2 1 2 3 Water resistance (72h) No change No change No change No change Slight loss of gloss Gloss (60°) / % 96 95.1 95.2 94 90 Hardness / H HB H HB HB B Alcohol resistance / number of times 120 110 124 100 50 Feel Level 5 Level 5 Level 4 Level 5 Level 3

[0085] As can be seen from the above table, in the alcohol resistance test, the coating surface was wiped back and forth with cotton wool dipped in 95% ethanol. The coating formed by the polyurethane varnish prepared in Examples 1-4 lost gloss or exposed the bottom only after wiping for more than 100 times, while the comparative example lost gloss or exposed the bottom after wiping for 50 times. It can be seen that the polyurethane resin prepared by the present invention has good solvent resistance. In the adhesion test, the adhesion of the polyurethane varnish prepared in Examples 1-4 is level 1 or 2, compared with the level 3 adhesion of the comparative example. , which has obvious advantages; in the water resistance experiment, the coating films formed by the varnishes prepared in Examples 1-4 and the comparative example were placed in water for 72 hours. The coating films of Examples 1-4 had no gloss loss or bottom exposure, and the coating films of the comparative example had slight gloss loss. Compared with the comparative example, the polyurethane resin prepared by the present invention has good water resistance; Examples 1-4 are significantly better than the comparative example in mechanical properties such as tensile strength, elongation at break, and hardness; in addition, the coating films formed by Examples 1-4 are also significantly better than the comparative example in properties such as gloss and feel.

[0086] The dendritic waterborne epoxy-modified polyurethane resin prepared by the present invention adopts epoxy resin as raw material to synthesize epoxy-modified polymer, which is used to modify polyurethane emulsion. Epoxy resin has the characteristics of high modulus, high strength and good thermal stability, and has epoxy group and secondary hydroxyl group. After the epoxy-modified polymer prepared by the present invention is copolymerized with isocyanate, the stability of the emulsion is good, and the mechanical properties, adhesion, solvent resistance and water resistance of the coating are significantly improved. The present invention adopts dendritic resin as a chain extender, and the dendritic resin has low melt viscosity, excellent solubility, easy film formation, diversified functions and high adhesion to the substrate. Compared with the traditional linear macromolecules of the same molecular weight, it is not easy to crystallize. Since the molecular structure contains more hydroxyl groups, it can participate in the cross-linking effect of the system in multiple dimensions, change the cross-linking structure of the coating, and better optimize the physical and chemical properties of the polyurethane emulsion. The present invention uses pentamethylene diisocyanate derived from biomass resources as a raw material. When pentamethylene diisocyanate is used as a hard segment, it has a higher isocyanate ratio in the molecule and thus has lower raw material consumption. At the same time, the prepared coating has a fast film-forming speed and a higher hardness.

[0087] The dendritic waterborne epoxy-modified polyurethane resin prepared by the invention is not inferior to solvent-based polyurethane in adhesion, solvent resistance, water resistance, mechanical properties, surface gloss, hand feel, etc., and is greener and non-toxic than solvent-based polyurethane, has no pollution to the environment, has low cost, and is conducive to market promotion.

[0088] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the scope of the present invention through the above description. The technical scope of this invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A process for preparing a dendritic waterborne epoxy-modified polyurethane resin, characterized in that: The following steps are involved: (1) Preparing an epoxy-modified polymer: adding a macromolecular diol and an acid anhydride to a reactor, heating the reactor to 60 to 130° C., adding an epoxy resin and a catalyst, wherein the catalyst is one or more of triphenylphosphine, tetrabutylammonium bromide, tetramethylammonium chloride, and N,N-dimethylbenzylamine, and then heating the reactor to 90 to 140° C. to obtain an epoxy-modified polymer; (2) Preparation of dendritic resin: methanol, polyamine and acrylate monomer are added to the reactor, and the temperature is raised to 30-45° C. under the protection of N2, and the reaction is kept at this temperature for 20-35 hours, and distilled under reduced pressure and dried in vacuum to obtain an intermediate product of dendritic resin; then, alcoholamine and methanol are added, and the temperature is raised to 30-45° C. under the protection of N2, and the reaction is kept at this temperature for 30-45 hours, and distilled under reduced pressure, filtered, and dried in vacuum to obtain a dendritic resin; (3) Preparation of polyurethane resin: adding the synthesized epoxy modified polymer, pentamethylene diisocyanate, and macromolecular diol to a reaction vessel, heating to 65-85° C. under N2 protection, and keeping the temperature for reaction for 2-6 hours to obtain an NCO-terminated prepolymer; adding the synthesized dendritic resin, dihydroxymethylpropionic acid, small molecule diol, and catalyst, wherein the catalyst is one of dibutyltin dilaurate, stannous octoate, and bismuth isooctanoate, heating to 65-85° C. under N2 protection, and keeping the temperature for reaction for 2-8 hours, then cooling the prepolymer to 50-60° C., adding an organic amine, and reacting for 0.5-1 hour, and then adding acetone to reduce the viscosity; adding the above product to deionized water, and dispersing at high speed for 0.5-2 hours, and finally, removing the acetone by rotary evaporation at 45-60° C. to obtain a dendritic waterborne epoxy modified polyurethane resin, The molar ratio of the macromolecular diol, the acid anhydride and the epoxy resin in the step (1) for preparing the epoxy-modified polymer is 1:(1-1.2):(0.3-0.6); the molar ratio of the polyamine, the acrylate monomer and the alcoholamine in the step (2) for preparing the dendritic resin is 1:(3-7):(3-9), and the alcoholamine is one of ethanolamine and diethanolamine.

2. The process for preparing a dendritic waterborne epoxy-modified polyurethane resin according to claim 1, characterized in that: The weight ratio of the epoxy modified polymer, pentamethylene diisocyanate, macromolecular diol, dendritic resin, dimethylol propionic acid, micromolecular diol, catalyst, organic amine, acetone and deionized water in preparing the polyurethane resin is (10-50): (25-65): (20-80): (5-7): (5-7): (9-15): (0.03-0.15): (3.5-5.5): (20-60): (150-250).

3. The process for preparing a dendritic waterborne epoxy-modified polyurethane resin according to claim 1, characterized in that: In the process of preparing the epoxy modified polymer, the amount of the catalyst used is 0.1-0.8% of the total weight of the macromolecular diol, the acid anhydride and the epoxy resin.

4. The process for preparing a dendritic waterborne epoxy-modified polyurethane resin according to claim 1, characterized in that: The polyamine is one of ethylenediamine, diethylenetriamine and triethylenetetramine.

5. The process for preparing a dendritic waterborne epoxy-modified polyurethane resin according to claim 1, characterized in that: The acrylate monomer is one of 1,6-hexanediol diacrylate, tripropylene glycol diacrylate and trimethylolpropane triacrylate.

6. The process for preparing a dendritic waterborne epoxy-modified polyurethane resin according to claim 1, characterized in that: The small molecule diol is one or more of 1,6-hexanediol, 1,4-butanediol, methyl propanediol and propylene glycol.

7. The process for preparing a dendritic waterborne epoxy-modified polyurethane resin according to claim 1, characterized in that: The macromolecular diol is one or more of polyether diol and polyester diol.