Polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of polymer adhesives, and particularly relates to a polyurethane hot melt adhesive and a preparation method thereof. Modified isocyanate in the polyurethane hot melt adhesive contains a very active functional group NCO, can be combined with carboxyl in modified polypropylene glycol to form an amido bond, can also react with amino in POSS doped polyester resin to form a urea structure, and can also be subjected to an addition reaction with sulfhydrylated silicon dioxide to generate thiocarbamate; on the basis of modified isocyanate, a dense cross-linked network is constructed, and plastic deformation caused by repeated friction is reduced, so that the dry grinding fastness and the wet grinding fastness are improved; meanwhile, an amino group of the modified isocyanate can be combined with a carboxyl group of the modified polypropylene glycol, a sulfonic group of the POSS doped polyester resin and a sulfydryl group of the modified silicon dioxide to form an interpenetrating network structure, so that the folding resistance and the washing fastness of the hot melt adhesive are effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer adhesives, and particularly relates to a polyurethane hot melt adhesive and a preparation method thereof. Background Art

[0002] Polyurethane hot melt adhesives are made by polymerizing polyols and isocyanates. They are a type of green and environmentally friendly adhesive. When heated to a certain temperature, they can be melted into a viscous liquid. After wetting the adherend, they can bond the adherend when cooled to room temperature. Because they do not contain solvents and are environmentally friendly, and at the same time have the advantages of rapid positioning, no solvents, high bonding strength, and a wide bonding range, their current application fields include medical, biological, textile, automotive, household appliances, packaging and other fields.

[0003] Chinese Patent (Publication No. CN115651597B) discloses a high-temperature resistant polyurethane hot melt adhesive and a preparation method thereof. By adding a self-made polyester polyol containing adamantane and biphenyl structures, the high-temperature resistance of the final polyurethane hot melt adhesive is improved. Because the adamantane and biphenyl structures themselves are relatively rigid, the polyester polyol containing adamantane and biphenyl structures is designed into a linear structure to make it have a certain flexibility, so that the cured adhesive layer will not be too hard and brittle to affect its curing strength; the polyol segments in the self-made polyester polyol containing adamantane and biphenyl structures are relatively regular and symmetrical, and are in a solid state at room temperature, which has the effect of shortening the open time. However, this patent does not solve the problems of insufficient dry rubbing fastness and wet rubbing fastness, poor folding resistance, and poor washing fastness existing in polyurethane hot melt adhesives in the prior art, which seriously affect their application scope.

[0004] Therefore, how to modify the composition of polyurethane hot melt adhesives, introduce reinforcing fillers at the same time, and improve the dry rubbing fastness and wet rubbing fastness of hot melt adhesives through the synergistic effect of multiple components, ensure good folding resistance, and improve the washing fastness at the same time has become the key direction to be overcome. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a polyurethane hot melt adhesive and a preparation method thereof, aiming to solve the problems of insufficient dry rubbing fastness and wet rubbing fastness, poor folding resistance, and poor washing fastness existing in polyurethane hot melt adhesives in the prior art.

[0006] The modified isocyanate in the polyurethane hot melt adhesive of the present invention contains a very active functional group NCO, which can not only combine with the carboxyl group in the modified polypropylene glycol to form an amide bond, but also react with the amino group in the POSS-doped polyester resin to form a urea structure, and can also undergo an addition reaction with mercapto-functionalized silica to generate a thiocarbamate. Based on the modified isocyanate, a dense cross-linked network is constructed to reduce plastic deformation caused by repeated friction, thereby improving dry rubbing fastness and wet rubbing fastness; at the same time, the amino group of the modified isocyanate can combine with the carboxyl group of the modified polypropylene glycol, the sulfonic acid group of the POSS-doped polyester resin, and the mercapto group of the modified silica to form an interpenetrating network structure, effectively improving the folding resistance and washing fastness of the hot melt adhesive; therefore, the present invention not only improves the dry rubbing fastness and wet rubbing fastness of the hot melt adhesive, but also ensures good folding resistance and washing fastness, ensuring the long-term reliability of the material.

[0007] The technical solutions adopted by the present invention to solve the above technical problems are as follows: In the first aspect of the present invention, a method for preparing a polyurethane hot melt adhesive is provided, comprising the following steps: Step S1: By weight, 90-100 parts of polypropylene glycol are stirred at 100-105 °C for 20-30 min, then 10-20 parts of phthalic anhydride are added, and the reaction is carried out at 150-160 °C for 4-6 h. After the reaction is completed, distillation is carried out to obtain modified polypropylene glycol; Step S2: By weight, 80-100 parts of sodium lignosulfonate are added to 400-500 parts of deionized water and stirred evenly. The pH is adjusted to 9.2-9.4 with a sodium hydroxide solution, then 50-60 parts of phenol, 40-50 parts of amine-phenyl POSS, and 80-100 parts of formaldehyde are added, and the reaction is carried out at 90-100 °C for 3-5 h. After cooling to room temperature, it is dried to obtain sulfonated amino POSS; 20-30 parts of polyester resin, 6-8 parts of the sulfonated amino POSS, 0.2-0.4 parts of sodium hexametaphosphate, 0.2-0.4 parts of dimethyl silicone oil, 0.4-0.6 parts of benzoyl peroxide, and 0.2-0.4 parts of hydroquinone are added to a high-speed disperser and mixed and stirred for 1-2 h to obtain POSS-doped polyester resin; Step S3: By weight, 8-10 parts of 3-aminopropyltriethoxysilane are added to 80-100 parts of deionized water and stirred evenly, then 50-60 parts of talc are added and stirred for 40-60 min, and then dried to obtain modified talc; 90-100 parts of diphenylmethane diisocyanate, 10-15 parts of the modified talc, and 4-6 parts of ethyl acetate are mixed, first stirred and dispersed for 20-30 min, and then ultrasonically dispersed for 40-60 min to obtain modified isocyanate; Step S4: Add 30 - 45 parts by weight of the modified polypropylene glycol, 20 - 35 parts of liquid polyester polyol, 5 - 15 parts of crystalline polyester polyol, 3 - 8 parts of the POSS - doped polyester resin, 0.5 - 2.0 parts of reinforcing filler, 0.4 - 0.6 parts of antioxidant, and 0.05 - 0.07 parts of inhibitor to a double - planetary stirring kettle. Stir at 120 - 130 °C for 1 - 2 h, evacuate to a vacuum degree of - 0.095 - - 0.097 MPa, cool down to 60 - 70 °C, add 20 - 30 parts of the modified isocyanate and stir for 10 - 20 min, heat up to 110 - 115 °C and react for 50 - 60 min, then add 0.5 - 1.0 parts of chain extender and continue to react for 30 - 40 min. Finally, add 0.05 - 0.07 parts of catalyst and 0.01 - 0.03 parts of leveling agent, stir for 10 - 15 min and then discharge to obtain the polyurethane hot - melt adhesive.

[0008] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the purpose and beneficial effects of the present invention can be better achieved.

[0009] As a preferred technical solution of the present invention, the reinforcing filler is mercapto - functionalized silica; the preparation method of the mercapto - functionalized silica includes: Mix 80 - 90 parts by weight of absolute ethanol, 10 - 20 parts of deionized water, and 4 - 6 parts of ammonia water, stir at 30 - 40 °C for 10 - 20 min, then add 4 - 6 parts of silica and 0.2 - 0.4 parts of (3 - mercaptopropyl)triethoxysilane and stir - react for 20 - 24 h. After the reaction is completed, centrifuge to obtain a solid, wash the solid with absolute ethanol, and dry to obtain the mercapto - functionalized silica.

[0010] As a preferred technical solution of the present invention, the particle size of the silica is 200 - 400 nm.

[0011] The introduction of mercapto - functionalized silica can achieve close contact between silica particles and polyurethane segments, form a relatively dense structure, form a barrier in the hot - melt adhesive matrix, effectively block the penetration of water molecules, reduce the channels for water molecules to enter the material interior, thereby improving the water - fastness.

[0012] As a preferred technical solution of the present invention, the molecular weight of the liquid polyester polyol is 2000 - 5000.

[0013] As a preferred technical solution of the present invention, the melting point of the crystalline polyester polyol is 40 - 60 °C.

[0014] As a preferred technical solution of the present invention, the glass transition temperature of the polyester resin is 0 - 15 °C, and the molecular weight is 30000 - 50000.

[0015] As a preferred technical solution of the present invention, the chain extender is selected from any one or a combination of at least two of ethylene glycol, propylene glycol, and diethylene glycol.

[0016] As a preferred technical solution of the present invention, the antioxidant is antioxidant 1010 or antioxidant 245.

[0017] As a preferred technical solution of the present invention, the inhibitor is benzoyl chloride or phosphoric acid.

[0018] In the second aspect of the present invention, there is provided a polyurethane hot melt adhesive prepared by the method as described in the first aspect.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) The modified isocyanate in the polyurethane hot melt adhesive of the present invention contains a very active functional group NCO, which can not only combine with the carboxyl group in the modified polypropylene glycol to form an amide bond, but also react with the amino group in the POSS-doped polyester resin to form a urea structure, and can also undergo an addition reaction with mercapto-functionalized silica to generate thiocarbamate. Based on the modified isocyanate, a dense crosslinked network is constructed, reducing plastic deformation caused by repeated friction, thereby improving dry rubbing fastness and wet rubbing fastness.

[0020] (2) The modified isocyanate of the present invention introduces talcum powder containing amino groups through blending modification. The talcum powder is uniformly dispersed in the matrix and provides reactive sites through the amino groups. By means of the nucleophilic addition of the amino group to the carboxyl group of the modified polypropylene glycol to form an amide bond, attacking the sulfur atom in the sulfonic acid group by the amino group to generate sulfonamide, and forming a thioamine structure by the reaction of the amino group with the mercapto group, an interpenetrating network structure is obtained, effectively improving the folding resistance of the hot melt adhesive. At the same time, the interpenetrating network structure can form a barrier to prevent moisture from penetrating into the polymer matrix, thereby increasing the washing fastness.

[0021] (3) The polyurethane hot melt adhesive of the present invention synthesizes a polyurethane resin from a polyol and an isocyanate, and improves the initial adhesion by adding a polyester resin with a low softening point and a high molecular weight; the added modified silica, on the one hand, acts as a nucleating agent to form a micro-foamed structure, making the hand feel softer and more elastic, and on the other hand, improves the wear resistance after flocking; the hot melt adhesive of the present invention has excellent water washing resistance and folding resistance, good wear resistance, and does not delaminate after more than 10,000 times, and the surface fluff is intact.

[0022] (4) Carboxyl groups are introduced into the modified polypropylene glycol of the present invention through phthalic anhydride. The terminal carboxyl groups can act as compatibilizers to improve the interfacial compatibility between different components and reduce stress concentration points, so that the material is not prone to cracks or fractures during repeated folding, thereby improving the folding resistance of the polyurethane hot melt adhesive.

[0023] (5) The present invention obtains POSS-doped polyester resin through physical blending modification. The nano-size of POSS enables it to be uniformly dispersed in the polyurethane matrix, reducing stress concentration points. At the same time, its rigid siloxane core can form physical support points inside the material, effectively improving the dry abrasion fastness and wet abrasion fastness of the hot melt adhesive.

[0024] (6) The talcum powder contained in the modified isocyanate of the present invention has a relatively high aspect ratio and plays a "bridge" role in the matrix, which can effectively improve wear resistance. At the same time, the talcum powder treated with 3-aminopropyltriethoxysilane can be uniformly dispersed, providing better lubrication effect and physical barrier effect, ensuring good dry abrasion fastness and wet abrasion fastness. Detailed implementation manners

[0025] To facilitate the understanding of the present invention, the following examples are listed. Those skilled in the art should understand that the examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0026] The sources of some components in the examples and comparative examples are as follows: Polypropylene glycol, product number P103210, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Liquid polyester polyol I, grade XCP-2000IPS, molecular weight 2000, purchased from Asahi Kasei Chemicals (Suzhou) Co., Ltd.; Liquid polyester polyol II, grade FLP-PA1000N, molecular weight 1000, purchased from Asahi Kasei Chemicals (Suzhou) Co., Ltd.; Liquid polyester polyol III, grade XCP-R8500HA, molecular weight 8500, purchased from Asahi Kasei Chemicals (Suzhou) Co., Ltd.; Crystalline polyester polyol, grade dynacoll-7360, melting point 50 °C, purchased from Evonik Specialty Chemicals (Shanghai) Co., Ltd.; Polyester resin, grade Vylon670, glass transition temperature 7 °C, molecular weight 30000, purchased from Toyobo Co., Ltd., Japan; Diphenylmethane diisocyanate, product number MDI-50, purchased from Wanhua Chemical Co., Ltd.; Silica I, product number zkky7767653-0135, particle size 300 nm, purchased from Beijing Zhongke Keyou Technology Co., Ltd.; Silica II, product number S104597, particle size 15 nm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Silica III, product number S118568, particle size 1 mm, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Ethylene glycol, CAS No. 107-21-1, purchased from Shanghai Macklin Biochemical Co., Ltd.; Propylene glycol, CAS No. 57-55-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; Diethylene glycol, CAS No. 111-46-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; Antioxidant 1010, CAS No. 6683-19-8, purchased from Sinopharm Chemical Reagent Co., Ltd.; Antioxidant 245, CAS No. 36443-68-2, purchased from Sinopharm Chemical Reagent Co., Ltd.; Benzoyl chloride, CAS No. 98-88-4, purchased from Shanghai Macklin Biochemical Co., Ltd.; Phosphoric acid, CAS No. 7664-38-2, purchased from Sinopharm Chemical Reagent Co., Ltd.; Catalyst, DMDEE catalyst, CAS No. 6425-39-4, purchased from Hubei Coward Chemical Co., Ltd.; Leveling agent, model BYK-361N, purchased from BYK Chemie GmbH; Phthalic anhydride, CAS No. 85-44-9, purchased from Shanghai Macklin Biochemical Co., Ltd.; Sodium lignosulfonate, CAS No. 8061-51-6, purchased from Shanghai Macklin Biochemical Co., Ltd.; Phenol, CAS No. 108-95-2, purchased from Sinopharm Chemical Reagent Co., Ltd.; Aminophenyl POSS, product number PA74497, purchased from Shanghai Chuangsai Technology Co., Ltd.; Formaldehyde, CAS No. 50-00-0, purchased from Sinopharm Chemical Reagent Co., Ltd.; Sodium hexametaphosphate, CAS No. 10124-56-8, purchased from Shanghai Macklin Biochemical Co., Ltd.; Dimethyl silicone oil, CAS No. 9016-00-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; Benzoyl peroxide, CAS No. 94-36-0, purchased from Shanghai Macklin Biochemical Co., Ltd.; Hydroquinone, CAS No. 123-31-9, purchased from Sinopharm Chemical Reagent Co., Ltd.; 3-Aminopropyltriethoxysilane, CAS No. 919-30-2, purchased from Shanghai Macklin Biochemical Co., Ltd.; Talc powder, product number T109494, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.; Ethyl acetate, CAS No. 141-78-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; Absolute ethanol, CAS No. 64-17-5, purchased from Sinopharm Chemical Reagent Co., Ltd.; Ammonia water, CAS No. 1336-21-6, purchased from Sinopharm Chemical Reagent Co., Ltd.; (3-Mercaptopropyl)triethoxysilane, CAS No. 14814-09-6, purchased from Shanghai Macklin Biochemical Co., Ltd. Example 1

[0027] This example provides a preparation method of a polyurethane hot melt adhesive, which includes the following steps: Preparation of mercapto-functionalized silica: By weight, 90 parts of absolute ethanol, 20 parts of deionized water and 6 parts of ammonia water are mixed, stirred at 40 °C for 10 min, then 6 parts of silica Ⅰ (product number zkky7767653-0135, particle size 300 nm) and 0.4 part of (3-mercaptopropyl)triethoxysilane are added and stirred for reaction for 24 h. After the reaction is completed, the solid is obtained by centrifugation, and the solid is washed with absolute ethanol and dried to obtain the mercapto-functionalized silica.

[0028] Step S1: By weight, 100 parts of polypropylene glycol are stirred at 105 °C for 20 min, then 20 parts of phthalic anhydride are added, and the reaction is carried out at 160 °C for 4 h. After the reaction is completed, distillation is carried out to obtain modified polypropylene glycol; Step S2: By weight, 100 parts of sodium lignosulfonate are added to 500 parts of deionized water and stirred evenly. The pH is adjusted to 9.4 with sodium hydroxide solution, then 60 parts of phenol, 50 parts of amine phenyl POSS and 100 parts of formaldehyde are added, and the reaction is carried out at 100 °C for 3 h. After cooling to room temperature, drying is carried out to obtain sulfonated amino POSS; 30 parts of polyester resin (grade Vylon670, glass transition temperature 7 °C, molecular weight 30000), 8 parts of the sulfonated amino POSS, 0.4 part of sodium hexametaphosphate, 0.4 part of dimethyl silicone oil, 0.6 part of benzoyl peroxide and 0.4 part of hydroquinone are added to a high-speed disperser and mixed and stirred for 2 h to obtain POSS-doped polyester resin; Step S3: By weight, 10 parts of 3-aminopropyltriethoxysilane are added to 100 parts of deionized water and stirred evenly, then 60 parts of talc powder are added and stirred for 60 min, and then dried to obtain modified talc powder; 100 parts of diphenylmethane diisocyanate, 15 parts of the modified talc powder and 6 parts of ethyl acetate are mixed, first stirred and dispersed for 30 min, and then ultrasonically dispersed for 60 min to obtain modified isocyanate; Step S4: Add 45 parts of the modified polypropylene glycol, 35 parts of liquid polyester polyol I (grade XCP-2000IPS, molecular weight of 2000), 15 parts of crystalline polyester polyol (grade dynacoll-7360, melting point of 50 °C), 8 parts of the POSS-doped polyester resin, 2.0 parts of the mercapto-functionalized silica, 0.6 part of antioxidant 1010, and 0.05 - 0.07 part of benzoyl chloride into a double planetary stirring kettle. Stir at 130 °C for 1 h, evacuate to a vacuum degree of -0.097 MPa, cool down to 70 °C, add 30 parts of the modified isocyanate and stir for 20 min, heat up to 115 °C and react for 50 min, then add 1.0 part of ethylene glycol and continue to react for 40 min. Finally, add 0.07 part of catalyst and 0.03 part of leveling agent, stir for 15 min and then discharge to obtain the polyurethane hot melt adhesive. Example 2

[0029] This example provides a preparation method of a polyurethane hot melt adhesive, including the following steps: Preparation of mercapto-functionalized silica: Mix 80 parts of anhydrous ethanol, 10 parts of deionized water, and 4 parts of ammonia water, stir at 30 °C for 10 min, then add 4 parts of silica I (product number zkky7767653-0135, particle size of 300 nm) and 0.2 part of (3-mercaptopropyl)triethoxysilane, stir and react for 20 h. After the reaction is completed, centrifuge to obtain the solid, wash the solid with anhydrous ethanol, and dry to obtain the mercapto-functionalized silica.

[0030] Step S1: Take 90 parts of polypropylene glycol and stir at 100 °C for 20 min, then add 10 parts of phthalic anhydride, react at 150 °C for 6 h. After the reaction is completed, perform distillation to obtain the modified polypropylene glycol; Step S2: Add 80 parts of sodium lignosulfonate into 400 parts of deionized water and stir evenly, adjust the pH to 9.2 with sodium hydroxide solution, then add 50 parts of phenol, 40 parts of amine phenyl POSS, and 80 parts of formaldehyde, react at 90 °C for 5 h, cool to room temperature, and dry to obtain sulfonated amino POSS; Add 20 parts of polyester resin (grade Vylon670, glass transition temperature of 7 °C, molecular weight of 30000), 6 parts of the sulfonated amino POSS, 0.2 part of sodium hexametaphosphate, 0.2 part of dimethyl silicone oil, 0.4 part of benzoyl peroxide, and 0.2 part of hydroquinone into a high-speed disperser, mix and stir for 1 h to obtain the POSS-doped polyester resin; Step S3: Add 8 parts of 3-aminopropyltriethoxysilane to 80 parts of deionized water by weight, stir evenly, then add 50 parts of talcum powder and stir for 40 min, and dry to obtain modified talcum powder; mix 90 parts of diphenylmethane diisocyanate, 10 parts of the modified talcum powder and 4 parts of ethyl acetate, first stir and disperse for 20 min, and then ultrasonically disperse for 40 min to obtain modified isocyanate; Step S4: Add 30 parts of the modified polypropylene glycol, 20 parts of liquid polyester polyol I (grade XCP-2000IPS, molecular weight 2000), 5 parts of crystalline polyester polyol (grade dynacoll-7360, melting point 50 °C), 3 parts of the POSS-doped polyester resin, 0.5 part of the mercapto-functionalized silica, 0.4 part of antioxidant 245 and 0.05 - 0.07 part of phosphoric acid to a double planetary stirring kettle, stir at 120 °C for 2 h, evacuate to a vacuum degree of -0.095 MPa, cool down to 60 °C, add 20 parts of the modified isocyanate and stir for 20 min, heat up to 110 °C and react for 60 min, then add 0.5 part of propylene glycol and continue to react for 30 min, and finally add 0.05 part of catalyst and 0.01 part of leveling agent, stir for 10 min and then discharge to obtain the polyurethane hot melt adhesive. Example 3

[0031] This example provides a method for preparing a polyurethane hot melt adhesive, which includes the following steps: Preparation of mercapto-functionalized silica: Mix 85 parts of absolute ethanol, 15 parts of deionized water and 5 parts of ammonia water by weight, stir at 35 °C for 15 min, then add 5 parts of silica I (product number zkky7767653-0135, particle size 300 nm) and 0.3 part of (3-mercaptopropyl)triethoxysilane and stir to react for 22 h. After the reaction is completed, centrifuge to obtain a solid, wash the solid with absolute ethanol, and dry to obtain the mercapto-functionalized silica.

[0032] Step S1: Add 95 parts of polypropylene glycol by weight, stir at 102 °C for 25 min, then add 15 parts of phthalic anhydride, react at 155 °C for 5 h, and perform distillation after the reaction is completed to obtain modified polypropylene glycol; Step S2: Add 90 parts of sodium lignosulfonate to 450 parts of deionized water by weight, stir evenly, adjust the pH to 9.3 with sodium hydroxide solution, then add 55 parts of phenol, 45 parts of aminophenyl POSS, and 90 parts of formaldehyde, react at 95 °C for 4 h, cool to room temperature, and dry to obtain sulfonated amino POSS; Add 25 parts of polyester resin (grade Vylon670, glass transition temperature 7 °C, molecular weight 30000), 7 parts of the sulfonated amino POSS, 0.3 parts of sodium hexametaphosphate, 0.3 parts of dimethyl silicone oil, 0.5 parts of benzoyl peroxide, and 0.3 parts of hydroquinone to a high-speed disperser, mix and stir for 2 h to obtain POSS-doped polyester resin; Step S3: Add 9 parts of 3-aminopropyltriethoxysilane to 90 parts of deionized water by weight, stir evenly, then add 55 parts of talcum powder and stir for 50 min, dry to obtain modified talcum powder; Mix 95 parts of diphenylmethane diisocyanate, 12 parts of the modified talcum powder, and 5 parts of ethyl acetate, first stir and disperse for 25 min, then ultrasonically disperse for 50 min to obtain modified isocyanate; Step S4: Add 40 parts of the modified polypropylene glycol, 30 parts of liquid polyester polyol I (grade XCP-2000IPS, molecular weight 2000), 10 parts of crystalline polyester polyol (grade dynacoll-7360, melting point 50 °C), 5 parts of the POSS-doped polyester resin, 1.5 parts of the mercapto-functionalized silica, 0.5 parts of antioxidant 1010, and 0.06 parts of benzoyl chloride to a twin-planet stirring kettle, stir at 125 °C for 2 h, evacuate to a vacuum degree of -0.096 MPa, cool to 65 °C, add 25 parts of the modified isocyanate and stir for 15 min, heat up to 112 °C and react for 55 min, then add 0.8 parts of diethylene glycol and continue to react for 35 min, finally add 0.06 parts of catalyst and 0.02 parts of leveling agent, stir for 12 min and then discharge to obtain the polyurethane hot melt adhesive.

[0033] Comparative Example 1 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that commercially available polypropylene glycol is used to replace the modified polypropylene glycol, commercially available polyester resin is used to replace the POSS-doped polyester resin, commercially available diphenylmethane diisocyanate is used to replace the modified isocyanate, and silica I is used to replace the mercapto-functionalized silica.

[0034] Comparative Example 2 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Comparative Example 1 in that the modified polypropylene glycol is used to replace the commercially available polypropylene glycol.

[0035] Comparative Example 3 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Comparative Example 1 in that POSS-doped polyester resin is used to replace commercially available polyester resin.

[0036] Comparative Example 4 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Comparative Example 1 in that modified isocyanate is used to replace commercially available diphenylmethane diisocyanate.

[0037] Comparative Example 5 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Comparative Example 1 in that mercapto-functionalized silica is used to replace silica I.

[0038] Comparative Example 6 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that commercially available polypropylene glycol is used to replace modified polypropylene glycol.

[0039] Comparative Example 7 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that liquid polyester polyol II is used to replace liquid polyester polyol I.

[0040] Comparative Example 8 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that liquid polyester polyol III is used to replace liquid polyester polyol I.

[0041] Comparative Example 9 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that commercially available polyester resin is used to replace POSS-doped polyester resin.

[0042] Comparative Example 10 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that commercially available diphenylmethane diisocyanate is used to replace modified isocyanate.

[0043] Comparative Example 11 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that silica I is used to replace mercapto-functionalized silica.

[0044] Comparative Example 12 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that silica II is used to replace silica I for preparing mercapto-functionalized silica.

[0045] Comparative Example 13 This comparative example provides a method for preparing a polyurethane hot melt adhesive, which is different from Example 1 in that silica Ⅲ is used to replace silica Ⅰ to prepare thiolated silica.

[0046] The properties of the polyurethane hot melt adhesives provided in the above examples and comparative examples were tested. The specific test methods are as follows: (1)Dry and wet rubbing fastness test The dry rubbing fastness and wet rubbing fastness were tested according to the requirements of "GB / T 21196.2-2007 Textiles - Determination of fabric abrasion resistance using the Martindale method - Part 2: Determination of specimen damage".

[0047] (2)Flex resistance test The flex resistance was tested according to the requirements of "QB / T 2714-2018 Leather - Physical and mechanical tests - Determination of flex resistance".

[0048] (3)Water fastness test The water fastness was tested according to the requirements of "GB / T 5713-2013 Textiles - Tests for colour fastness - Colour fastness to water".

[0049] The above performance test data are shown in Table 1.

[0050] Table 1 Performance test results

[0051] As can be seen from the above content, in the present invention, the components of the polyurethane hot melt adhesive, namely polypropylene glycol, polyester resin and isocyanate, are respectively modified, and at the same time, the reinforcing filler thiolated silica is introduced to prepare the polyurethane hot melt adhesive (Examples 1 to 3). Its dry rubbing fastness ≥ 10,000 times, wet rubbing fastness ≥ 10,000 times, the test result of flex resistance is that the fluff is intact, no glue leakage, and the washing fastness is grade 5.

[0052] Compared with Example 1, when using commercially available polypropylene glycol to replace the modified polypropylene glycol, commercially available polyester resin to replace the POSS-doped polyester resin, commercially available diphenylmethane diisocyanate to replace the modified isocyanate, and silica I to replace the mercapto-functionalized silica, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 1); compared with Comparative Example 1, when using the modified polypropylene glycol to replace the commercially available polypropylene glycol, the folding endurance performance improves (Comparative Example 2); compared with Comparative Example 1, when using the POSS-doped polyester resin to replace the commercially available polyester resin, the dry rubbing fastness and wet rubbing fastness become better (Comparative Example 3); compared with Comparative Example 1, when using the modified isocyanate to replace the commercially available diphenylmethane diisocyanate, the dry rubbing fastness and wet rubbing fastness become better (Comparative Example 4); compared with Comparative Example 1, when using the mercapto-functionalized silica to replace silica I, the washing fastness increases (Comparative Example 5); compared with Example 1, when using commercially available polypropylene glycol to replace the modified polypropylene glycol, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 6); compared with Example 1, when using liquid polyester polyol II to replace liquid polyester polyol I, since the molecular weight of liquid polyester polyol II is too small, the hot melt adhesive performance is poor, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 7); compared with Example 1, when using liquid polyester polyol III to replace liquid polyester polyol I, since the molecular weight of liquid polyester polyol III is too large, the hot melt adhesive performance is poor, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 8); compared with Example 1, when using commercially available polyester resin to replace the POSS-doped polyester resin, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 9); compared with Example 1, when using commercially available diphenylmethane diisocyanate to replace the modified isocyanate, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 10); compared with Example 1, when using silica I to replace the mercapto-functionalized silica, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 11); compared with Example 1, when using silica II to replace silica I to prepare the mercapto-functionalized silica, since the particle size of silica II is too small and the modification effect is poor, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 12); compared with Example 1, when using silica III to replace silica I to prepare the mercapto-functionalized silica, since the particle size of silica III is too large and the modification effect is poor, the dry rubbing fastness and wet rubbing fastness become worse, the folding endurance performance decreases, and the washing fastness drops (Comparative Example 13).

[0053] In summary, the modified isocyanate in the polyurethane hot melt adhesive of the present invention contains a very active functional group NCO, which can not only combine with the carboxyl group in the modified polypropylene glycol to form an amide bond, but also react with the amino group in the POSS-doped polyester resin to form a urea structure, and can also undergo an addition reaction with mercapto-functionalized silica to generate thiocarbamate. Based on the modified isocyanate, a dense cross-linked network is constructed to reduce the plastic deformation caused by repeated friction, thereby improving the dry rubbing fastness and wet rubbing fastness. At the same time, the amino group of the modified isocyanate can combine with the carboxyl group of the modified polypropylene glycol, the sulfonic acid group of the POSS-doped polyester resin, and the mercapto group of the modified silica to form an interpenetrating network structure, effectively improving the folding resistance and washing fastness of the hot melt adhesive.

[0054] The applicant declares that the detailed process flow of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of each raw material of the product of the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a polyurethane hot melt adhesive, characterized in that: The following steps are involved: Step S1: mixing 90-100 parts of polypropylene glycol and 10-20 parts of phthalic anhydride by weight and heating them to obtain modified polypropylene glycol; Step S2: adding 80-100 parts of sodium lignin sulfonate to 400-500 parts of deionized water and stirring evenly, adjusting the pH to 9.2-9.4, and then adding 50-60 parts of phenol, 40-50 parts of aminophenyl POSS and 80-100 parts of formaldehyde for sulfonation reaction to obtain sulfonated amino POSS; 20-30 parts of polyester resin, 6-8 parts of the sulfonated amino POSS, 0.2-0.4 parts of sodium hexametaphosphate, 0.2-0.4 parts of dimethyl silicone oil, 0.4-0.6 parts of benzoyl peroxide and 0.2-0.4 parts of hydroquinone are added into a high-speed disperser and mixed and stirred to obtain POSS-doped polyester resin; Step S3: adding 8 to 10 parts of 3-aminopropyltriethoxysilane to 80 to 100 parts of deionized water and mixing them evenly, then adding 50 to 60 parts of talc and stirring them evenly, and drying them to obtain modified talc; mixing 90 to 100 parts of diphenylmethane diisocyanate, 10 to 15 parts of the modified talc and 4 to 6 parts of ethyl acetate, and stirring and dispersing them in turn, and ultrasonically dispersing them to obtain modified isocyanate; Step S4: adding 30 to 45 parts of the modified polypropylene glycol, 20 to 35 parts of liquid polyester polyol, 5 to 15 parts of crystalline polyester polyol, 3 to 8 parts of the POSS-doped polyester resin, 0.5 to 2.0 parts of reinforcing filler, 0.4 to 0.6 parts of antioxidant and 0.05 to 0.07 parts of polymerization inhibitor to a double planetary stirring tank for stirring reaction, and then adding 20 to 30 parts of the modified isocyanate, 0.5 to 1.0 parts of chain extender, 0.05 to 0.07 parts of catalyst and 0.01 to 0.03 parts of leveling agent for catalytic reaction to obtain a polyurethane hot melt adhesive.

2. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The reinforcing filler is mercapto silicon dioxide; The preparation method of the mercaptosilicic acid silica comprises: mixing 80-90 parts of anhydrous ethanol, 10-20 parts of deionized water and 4-6 parts of ammonia water by weight, stirring for 10-20 minutes at 30-40° C., then adding 4-6 parts of silicon dioxide and 0.2-0.4 parts of (3-mercaptopropyl)triethoxysilane and stirring for 20-24 hours, centrifuging to obtain a solid after the reaction is completed, washing the solid with anhydrous ethanol, and drying to obtain the mercaptosilicic acid silica.

3. The method for preparing a polyurethane hot melt adhesive according to claim 2, characterized in that: The particle size of the silicon dioxide is 200-400 nm.

4. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The molecular weight of the liquid polyester polyol is 2000-5000.

5. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The melting point of the crystalline polyester polyol is 40-60°C.

6. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The polyester resin has a glass transition temperature of 0-15° C. and a molecular weight of 30,000-50,000.

7. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The chain extender is selected from any one of ethylene glycol, propylene glycol, and diethylene glycol, or a combination of at least two of them.

8. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The antioxidant is antioxidant 1010 or antioxidant 245; the inhibitor is benzoyl chloride or phosphoric acid.

9. The method for preparing a polyurethane hot melt adhesive according to claim 1, characterized in that: The conditions for the heating reaction in step S1 include: stirring 90-100 parts of polypropylene glycol at 100-105° C. for 20-30 minutes, then adding 10-20 parts of phthalic anhydride, reacting at 150-160° C. for 4-6 hours, and distilling after the reaction is completed; The conditions of the sulfonation reaction in step S2 include: reacting at 90-100° C. for 3-5 hours, cooling to room temperature, and drying; The stirring reaction conditions in step S4 include: stirring at 120-130° C. for 1-2 h, evacuating to a vacuum degree of -0.095-0.097 MPa, and cooling to 60-70° C.; The conditions of the catalytic reaction in step S4 include: first adding 20 to 30 parts of the modified isocyanate and stirring for 10 to 20 minutes, heating to 110 to 115° C. and reacting for 50 to 60 minutes, then adding 0.5 to 1.0 parts of a chain extender and continuing the reaction for 30 to 40 minutes, and finally adding 0.05 to 0.07 parts of a catalyst and 0.01 to 0.03 parts of a leveling agent, stirring for 10 to 15 minutes and then discharging.

10. A polyurethane hot melt adhesive, characterized in that: Prepared according to the method according to any one of claims 1 to 9.

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