Polyurethane hot melt adhesive for bonding and preparation method thereof

Abstract

The invention relates to a polyurethane hot melt adhesive for bonding and a preparation method thereof, belonging to the technical field of polyurethane hot melt adhesives. The polyurethane hot melt adhesive comprises the following raw materials: 40-50 parts of plant-based polyol, 20-25 parts of hydroxyl-terminated fluoropolysiloxane, 10-20 parts of reinforcing modifier, 15-25 parts of isocyanate, 0.05-0.1 parts of catalyst, 1-3 parts of antioxidant, 2-4 parts of adhesion promoter and 5-8 parts of filler. In the technical scheme of the invention, the reinforcing modifier is obtained by combining 2,5-thiophenedicarboxylic acid methyl ester with carboxymethyl chitosan and then with maleopimaric acid; the plant-based polyol is prepared by combining epoxidized vegetable oil with sorbitol through a ring-opening reaction; the plant-based polyol, hydroxyl-terminated fluoropolysiloxane, reinforcing modifier, isocyanate, catalyst, antioxidant, adhesion promoter and filler are mixed to prepare the polyurethane hot melt adhesive; the bonding performance, water resistance, high temperature resistance and mechanical properties of the polyurethane hot melt adhesive are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane hot melt adhesives, and in particular relates to a polyurethane hot melt adhesive for bonding and a preparation method thereof. Background Art

[0002] Polyurethane hot melt adhesive is a type of hot melt adhesive that is made of polyurethane resin or prepolymer as the main material, mixed with catalysts, antioxidants, adhesion promoters, fillers, etc. Polyurethane hot melt adhesive can be divided into thermoplastic polyurethane elastomer hot melt adhesive and reactive polyurethane hot melt adhesive, and reactive polyurethane hot melt adhesive can be divided into moisture-curing type and closed type. Moisture-curing polyurethane hot melt adhesive is a new type of environmentally friendly isocyanate-terminated reactive polyester adhesive. When used, it is first heated and melted to be evenly applied. After the application of the glue, it is first physically cured to produce initial bonding strength, and then chemically cured to form a strong cross-linked network structure to achieve the final bonding strength. Compared with traditional thermoplastic polyurethane hot melt adhesive, reactive polyurethane hot melt adhesive has better bonding strength, chemical resistance, heat resistance, hydrolysis resistance, etc., which makes this type of hot melt adhesive widely used in various aspects such as the automotive industry, shoemaking industry, fabrics, wood industry, and electronics industry.

[0003] In the prior art, polyurethane hot melt adhesives for bonding still have the following defects: 1) Although polyurethane hot melt adhesives have good bonding strength to textile fabrics, wood, polar plastics, etc., their bonding effect to non-polar materials (such as polypropylene plastics) is poor, which limits their scope of application; 2) In polyurethane hot melt adhesives, since the polyurethane main chain contains more polar groups, it is easily hydrolyzed when it comes into contact with water, resulting in a decrease in its bonding performance, and its water resistance needs to be further improved; 3) At higher temperatures, the mechanical properties of polyurethane hot melt adhesives change greatly, and its high temperature resistance needs to be further enhanced. Summary of the invention

[0004] The purpose of the present invention is to provide a polyurethane hot melt adhesive for bonding and a preparation method thereof, wherein 2,5-thiophenedicarboxylic acid methyl ester is combined with carboxymethyl chitosan to obtain a rigid chain extender; 2,5-thiophenedicarboxylic acid methyl ester is combined with chitosan to effectively improve the bonding strength of the polyurethane hot melt adhesive, enhance its adhesion to various substrate surfaces, and enhance the mechanical properties and thermal stability of the polyurethane hot melt adhesive; the rigid chain extender is combined with maleopimaric acid to obtain a reinforcing modifier; the hydrolysis resistance of the polyurethane hot melt adhesive can be further improved, and its mechanical properties and thermal stability can also be enhanced; a plant-based polyol is prepared by a ring-opening reaction of epoxidized vegetable oil and sorbitol, so that the polyurethane hot melt adhesive has good adhesion. The invention discloses a novel polyurethane hot melt adhesive having a hydroxyl-terminated fluoropolysiloxane and a hydroxyl-terminated polydimethylsiloxane. The polyurethane hot melt adhesive has ...

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] A polyurethane hot melt adhesive for bonding, comprising the following raw materials in parts by weight: 40-50 parts of plant-based polyol, 20-25 parts of hydroxyl-terminated fluoropolysiloxane, 10-20 parts of reinforcing modifier, 15-25 parts of isocyanate, 0.05-0.1 parts of catalyst, 1-3 parts of antioxidant, 2-4 parts of adhesion promoter and 5-8 parts of filler;

[0007] The plant-based polyol is prepared by combining epoxidized vegetable oil and sorbitol through a ring-opening reaction;

[0008] The preparation method of the reinforcing modifier comprises the following steps:

[0009] A1: Combine 2,5-thiophenedicarboxylic acid methyl ester with carboxymethyl chitosan to obtain a rigid chain extender;

[0010] A2: Combine the rigid chain extender with maleopimaric acid to obtain a reinforcing modifier.

[0011] Furthermore, the preparation method of the plant-based polyol comprises the following steps:

[0012] Sorbitol is dissolved in deionized water to obtain a sorbitol solution, which is then heated to 60-70° C., epoxidized vegetable oil and fluoroboric acid are added to the sorbitol solution, and stirred in a water bath at 60-70° C. for 4-6 hours, sodium carbonate is added to neutralize the fluoroboric acid, and the plant-based polyol is obtained by vacuum distillation.

[0013] In the above reaction process, sorbitol has a hydroxyl group and the epoxidized vegetable oil has an epoxy group. The epoxy group in the epoxidized vegetable oil can combine with the hydroxyl group in sorbitol through a ring-opening reaction, so that sorbitol is grafted onto the epoxidized vegetable oil to obtain a plant-based polyol.

[0014] Furthermore, the mass ratio of sorbitol to deionized water is 0.5-1.5:15-20.

[0015] Furthermore, the epoxidized vegetable oil is epoxidized castor oil.

[0016] Furthermore, the preparation method of the epoxidized castor oil comprises the following steps:

[0017] Castor oil and formic acid are mixed evenly, then added into a hydrogen peroxide aqueous solution, and reacted at 60° C. for 5 hours. After the reaction is completed, the product is dissolved in dichloromethane, washed with deionized water and a saturated sodium bicarbonate aqueous solution to remove residual hydrogen peroxide and formic acid, then washed with a saturated sodium chloride solution to remove residual moisture, and then dried with anhydrous sodium sulfate, filtered to remove anhydrous sodium sulfate, and vacuum dried at 60° C. to obtain epoxidized castor oil.

[0018] In the above reaction process, hydrogen peroxide reacts with formic acid in situ to generate strong oxidizing formic acid, and the carbon-carbon double bonds on the castor oil monomer are oxidized into new epoxy groups, and finally epoxidized castor oil is obtained.

[0019] Furthermore, step A1 is specifically as follows:

[0020] Dissolve methyl 2,5-thiophenedicarboxylate in methanol at 45-55° C., then add carboxymethyl chitosan, and stir to react at 45-55° C. for 22-24 hours. After the reaction is completed, remove the methanol by rotary evaporation, then wash with acetone and filter to obtain a rigid chain extender.

[0021] In the above reaction process, methyl 2,5-thiophene dicarboxylate has an ester group, and carboxymethyl chitosan has a hydroxyl group and an amino group. The amino group in carboxymethyl chitosan can combine with the ester group in methyl 2,5-thiophene dicarboxylate, and the carboxymethyl chitosan and methyl 2,5-thiophene dicarboxylate are combined together to obtain a rigid chain extender.

[0022] Furthermore, the mass ratio of methyl 2,5-thiophenedicarboxylate to methanol is 7-7.5:80-100.

[0023] Furthermore, step A2 is specifically as follows:

[0024] The maleopimaric acid and the rigid chain extender are uniformly mixed, and then dibutyltin dilaurate is added, and the temperature is raised to 115-125° C. under a nitrogen atmosphere, and the reaction is carried out for 1-3 hours, and the temperature is further raised to 235-245° C. and the reaction is carried out for 5-7 hours to finally obtain a reinforcing modifier.

[0025] In the above reaction process, maleopimaric acid has a carboxyl group and the rigid chain extender has a hydroxyl group. The carboxyl group in maleopimaric acid can be combined with the hydroxyl group in the rigid chain extender through an esterification reaction. The rigid chain extender and maleopimaric acid are combined to obtain a reinforcing modifier.

[0026] Furthermore, the mass ratio of maleopimaric acid to rigid chain extender is 0.5-1.5:1.5-2.5.

[0027] Furthermore, the preparation method of maleopimaric acid comprises the following steps:

[0028] Abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid are uniformly mixed, and then stirred for reaction at 185-195° C. for 1.5-2.5 hours, cooled to room temperature, and recrystallized with acetic acid to finally obtain maleopimaric acid.

[0029] In the above reaction process, the two carbon-carbon double bonds of abietic acid are conjugated to generate levorotatory pimaric acid through an isomerization reaction, levorotatory pimaric acid acts as a conjugated diene, and maleic anhydride acts as a dienophile. Levorotatory pimaric acid and maleic anhydride undergo a Diels-Alder reaction to finally obtain maleopimaric acid.

[0030] Furthermore, the mass ratio of abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid is 19-21:6-7:0.2-0.3:35-45.

[0031] A method for preparing a polyurethane hot melt adhesive for bonding comprises the following steps:

[0032] Weigh the raw materials in parts by mass, put the plant-based polyol, hydroxyl-terminated fluoropolysiloxane and reinforcing modifier into a reaction kettle, heat to 120-140°C, vacuum dehydrate under stirring, then cool to 70-80°C, add isocyanate, react at 70-80°C for 1-2h, add catalyst, antioxidant, adhesion promoter and filler under nitrogen protection, continue to react at 70-80°C for 0.5-1.5h, vacuum degassing until no bubbles appear, discharge the material, seal and package to obtain the polyurethane hot melt adhesive for bonding.

[0033] Furthermore, the hydroxyl-terminated fluoropolysiloxane is obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane in a mass ratio of 1:1.

[0034] Furthermore, the isocyanate is obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate in a mass ratio of 1:1.

[0035] Furthermore, the catalyst is at least one of dibutyltin dilaurate, triethylenediamine, and N-methylimidazole.

[0036] Furthermore, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, 2,6-di-tert-butyl-p-cresol, and antioxidant 2246-S.

[0037] Furthermore, the adhesion promoter is at least one of 3-mercaptopropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane and γ-aminopropyltriethoxysilane.

[0038] Furthermore, the filler is at least one of calcium carbonate, carbon black and nano-silicon dioxide.

[0039] Furthermore, the vacuum dehydration time is 2-4 hours, and the vacuum degree is controlled to be 0.07-0.09 MPa.

[0040] Beneficial effects of the present invention:

[0041] (1) In the technical scheme of the present invention, methyl 2,5-thiophenedicarboxylate is combined with carboxymethyl chitosan to obtain a rigid chain extender; methyl 2,5-thiophenedicarboxylate contains a thiophene ring, and the heteroatoms on the thiophene ring can interact with the carbonyl group of the ester group on the polyurethane chain, so that the groups on the polyurethane chain can form non-covalent bonds with the surfaces of various substrates (such as metals, plastics, etc.), thereby achieving strong adhesion. Carboxymethyl chitosan can be used as a reinforcing filler in the polyurethane prepolymer and as a chain extender to enhance the performance of the polyurethane. Methyl 2,5-thiophenedicarboxylate is combined with chitosan to obtain a rigid chain extender, which is not It can effectively improve the bonding strength of polyurethane hot melt adhesive, enhance its adhesion to various substrate surfaces, and enhance the mechanical properties and thermal stability of polyurethane hot melt adhesive. At the same time, the hydroxyl groups on carboxymethyl chitosan also provide reaction sites for subsequent reactions; the rigid chain extender is combined with maleopimaric acid to obtain a reinforcing modifier; maleopimaric acid is obtained by Diels-Alder reaction of abietic acid and maleic anhydride, and maleopimaric acid is combined with a rigid chain extender. Maleopimaric acid has a hydrophobic skeleton, which can further improve the hydrolysis resistance of polyurethane hot melt adhesive, and also enhance its mechanical properties and thermal stability.

[0042] (2) In the technical scheme of the present invention, the plant-based polyol is prepared by combining epoxidized vegetable oil and sorbitol through a ring-opening reaction. The epoxidized vegetable oil and sorbitol are combined to obtain a plant-based polyol with a high hydroxyl value, which can be further reacted with isocyanate to achieve the purpose of chemical cross-linking, so that the polyurethane hot melt adhesive has better bonding properties and improves its water resistance and thermal stability. At the same time, the plant-based polyol can replace traditional petrochemical products (such as polyester or polyether polyols), which is more green and environmentally friendly; the hydroxyl-terminated fluoropolysiloxane is obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane, which can further improve the high temperature resistance of the polyurethane hot melt adhesive; the isocyanate is obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate, which can further improve the bonding properties and high temperature resistance of the polyurethane hot melt adhesive.

[0043] (3) In the technical scheme of the present invention, methyl 2,5-thiophenedicarboxylate is combined with carboxymethyl chitosan and then with maleopimaric acid to obtain a reinforcing modifier, and a plant-based polyol is obtained by combining epoxidized vegetable oil with sorbitol. The plant-based polyol, hydroxyl-terminated fluoropolysiloxane, reinforcing modifier, isocyanate, catalyst, antioxidant, adhesion promoter and filler are mixed to finally obtain a polyurethane hot melt adhesive for bonding. This can not only improve the bonding performance, mechanical properties and thermal stability of the polyurethane hot melt adhesive, but also enhance the water resistance and high temperature resistance of the polyurethane hot melt adhesive. At the same time, the obtained polyurethane hot melt adhesive for bonding has good environmental protection, expands its application range, and has good comprehensive performance. DETAILED DESCRIPTION

[0044] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0045] The specific parameters of the raw materials used in the present invention are as follows:

[0046] Hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane), CAS: 68607-77-2, was provided by Zhengzhou Alpha Chemical Co., Ltd.; hydroxypropyl-terminated polydimethylsiloxane (HPMS, number average molecular weight of 1500, purchased from Sinopharm Chemical Reagent Co., Ltd.), dried at 110 °C before use; triphenylmethane triisocyanate, CAS: 2422-91-5, was provided by Shanghai Yien Chemical Technology Co., Ltd.; dimethyltriphenylmethane tetraisocyanate, CAS: 28886-07-9, was provided by Qingdao Baiyi Chemical Co., Ltd.; 2,5-thiophenedicarboxylic acid methyl ester, CAS: 4282-34-2, was provided by Shanghai Titan Technology Co., Ltd.; carboxymethyl chitosan, CAS: 83512-85-0, was provided by Shanghai McLean Biochemical Technology Co., Ltd.

[0047] Example 1

[0048] Preparation of plant-based polyols, the specific steps are:

[0049] According to the mass ratio of sorbitol to deionized water being 0.5:15, sorbitol is dissolved in deionized water to obtain a sorbitol solution, which is then heated to 60° C., epoxidized castor oil (the mass of epoxidized castor oil is 20wt% of the mass of sorbitol) and fluoroboric acid (the mass of fluoroboric acid is 1wt% of the mass of sorbitol) are added to the sorbitol solution, and stirred in a water bath at 60° C. for 4 hours, sodium carbonate (the mass of sodium carbonate is equal to the mass of fluoroboric acid) is added to neutralize the fluoroboric acid, and plant-based polyols are obtained by vacuum distillation;

[0050] Wherein, the preparation method of epoxidized castor oil comprises the following steps:

[0051] According to the mass ratio of castor oil to formic acid being 20:7.5, castor oil and formic acid are uniformly mixed, and then added into a 30wt% hydrogen peroxide aqueous solution (the mass of the hydrogen peroxide aqueous solution is 85wt% of the mass of castor oil), and reacted at 60°C for 5h. After the reaction is completed, the product is dissolved in dichloromethane (the mass of dichloromethane is 2 times the mass of castor oil), and washed with deionized water and saturated sodium bicarbonate aqueous solution 3 times (the mass of deionized water and saturated sodium bicarbonate aqueous solution each time is 2 times the mass of castor oil) to remove residual hydrogen peroxide and formic acid, and then washed with saturated sodium chloride solution 3 times (the mass of the saturated sodium chloride solution each time is 2 times the mass of castor oil) to remove residual moisture, and then dried with anhydrous sodium sulfate, filtered to remove anhydrous sodium sulfate, and vacuum dried at 60°C to obtain epoxidized castor oil;

[0052] Preparation of reinforcing modifier, the specific steps are:

[0053] A1: According to the mass ratio of methyl 2,5-thiophenedicarboxylate to methanol being 7:80, methyl 2,5-thiophenedicarboxylate was dissolved in methanol at 45°C, and then carboxymethyl chitosan (the mass of carboxymethyl chitosan was 83wt% of the mass of methyl 2,5-thiophenedicarboxylate) was added, and the mixture was stirred at 45°C for 22h. After the reaction, methanol was removed by rotary evaporation, and then washed with acetone for 3 times (the mass of acetone each time was 40wt% of the mass of deionized water) and filtered to obtain a rigid chain extender;

[0054] A2: Maleopimaric acid and the rigid chain extender were mixed evenly in a mass ratio of 0.5:1.5, and then dibutyltin dilaurate was added (the mass of dibutyltin dilaurate was 1wt% of the mass of maleopimaric acid), and the temperature was raised to 115°C under a nitrogen atmosphere, and the reaction was carried out for 1h, and the temperature was further raised to 235°C and the reaction was carried out for 5h to finally obtain a reinforcing modifier;

[0055] Wherein, the preparation method of maleopimaric acid comprises the following steps:

[0056] According to the mass ratio of abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid being 19:6:0.2:35, abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid are uniformly mixed, and then stirred at 185° C. and 500 rpm for 2.5 hours, cooled to room temperature, and recrystallized with acetic acid at 75° C. for 3 times (the mass of acetic acid each time is equal to the mass of the above acetic acid), and finally maleopimaric acid is obtained;

[0057] A polyurethane hot melt adhesive for bonding, comprising the following raw materials in parts by weight: 40 parts of plant-based polyol, 20 parts of hydroxyl-terminated fluoropolysiloxane, 10 parts of reinforcing modifier, 15 parts of isocyanate, 0.05 parts of dibutyltin dilaurate, 1 part of antioxidant 1076, 2 parts of 3-mercaptopropyltrimethoxysilane and 5 parts of calcium carbonate;

[0058] The preparation method comprises the following steps:

[0059] Weigh the raw materials in parts by mass, put the plant-based polyol, hydroxyl-terminated fluoropolysiloxane and reinforcing modifier into a reaction kettle, heat to 120°C, vacuum dehydrate for 2 hours under stirring, control the vacuum degree to 0.07 MPa, then cool to 70°C, add isocyanate, react at 70°C for 1 hour, add dibutyltin dilaurate, antioxidant 1076, 3-mercaptopropyltrimethoxysilane and calcium carbonate under nitrogen protection, continue to react at 70°C for 0.5 hour, vacuum degassing until no bubbles appear, discharge, seal and package to obtain a polyurethane hot melt adhesive for bonding;

[0060] Among them, the hydroxyl-terminated fluoropolysiloxane is obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane in a mass ratio of 1:1; the isocyanate is obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate in a mass ratio of 1:1.

[0061] Example 2

[0062] Preparation of plant-based polyols, the specific steps are:

[0063] According to the mass ratio of sorbitol to deionized water being 1:18, sorbitol is dissolved in deionized water to obtain a sorbitol solution, which is then heated to 65° C., epoxidized castor oil (the mass of epoxidized castor oil is 20wt% of the mass of sorbitol) and fluoroboric acid (the mass of fluoroboric acid is 1wt% of the mass of sorbitol) are added to the sorbitol solution, and stirred in a water bath at 65° C. for 5 hours, sodium carbonate (the mass of sodium carbonate is equal to the mass of fluoroboric acid) is added to neutralize the fluoroboric acid, and plant-based polyols are obtained by vacuum distillation;

[0064] Wherein, the preparation method of epoxidized castor oil comprises the following steps:

[0065] According to the mass ratio of castor oil to formic acid being 20:7.5, castor oil and formic acid are uniformly mixed, and then added into a 30wt% hydrogen peroxide aqueous solution (the mass of the hydrogen peroxide aqueous solution is 85wt% of the mass of castor oil), and reacted at 60°C for 5h. After the reaction is completed, the product is dissolved in dichloromethane (the mass of dichloromethane is 2 times the mass of castor oil), and washed with deionized water and saturated sodium bicarbonate aqueous solution 3 times (the mass of deionized water and saturated sodium bicarbonate aqueous solution each time is 2 times the mass of castor oil) to remove residual hydrogen peroxide and formic acid, and then washed with saturated sodium chloride solution 3 times (the mass of the saturated sodium chloride solution each time is 2 times the mass of castor oil) to remove residual moisture, and then dried with anhydrous sodium sulfate, filtered to remove anhydrous sodium sulfate, and vacuum dried at 60°C to obtain epoxidized castor oil;

[0066] Preparation of reinforcing modifier, the specific steps are:

[0067] A1: According to the mass ratio of methyl 2,5-thiophenedicarboxylate to methanol being 7.3:90, methyl 2,5-thiophenedicarboxylate was dissolved in methanol at 50°C, and then carboxymethyl chitosan (the mass of carboxymethyl chitosan was 83wt% of the mass of methyl 2,5-thiophenedicarboxylate) was added, and the mixture was stirred at 50°C for 23h. After the reaction, methanol was removed by rotary evaporation, and then washed with acetone for 3 times (the mass of acetone each time was 40wt% of the mass of deionized water) and filtered to obtain a rigid chain extender;

[0068] A2: Maleopimaric acid and the rigid chain extender are mixed evenly in a mass ratio of 1:2, and then dibutyltin dilaurate is added (the mass of dibutyltin dilaurate is 1wt% of the mass of maleopimaric acid), and the temperature is raised to 120°C under a nitrogen atmosphere, and the reaction is carried out for 2h, and the temperature is further raised to 240°C and the reaction is carried out for 6h to finally obtain a reinforcing modifier;

[0069] Wherein, the preparation method of maleopimaric acid comprises the following steps:

[0070] According to the mass ratio of abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid being 20:6.5:0.25:40, abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid are uniformly mixed, and then stirred at 190° C. and 600 rpm for 2 hours, cooled to room temperature, and recrystallized with acetic acid at 80° C. for 3 times (the mass of acetic acid each time is equal to the mass of the above acetic acid), and finally maleopimaric acid is obtained;

[0071] A polyurethane hot melt adhesive for bonding, comprising the following raw materials in parts by weight: 45 parts of plant-based polyol, 23 parts of hydroxyl-terminated fluoropolysiloxane, 15 parts of reinforcing modifier, 20 parts of isocyanate, 0.08 parts of triethylenediamine, 2 parts of 2,6-di-tert-butyl-p-cresol, 3 parts of 3-isocyanatepropyltriethoxysilane and 7 parts of carbon black;

[0072] The preparation method comprises the following steps:

[0073] Weigh the raw materials in parts by mass, put the plant-based polyol, hydroxyl-terminated fluoropolysiloxane and reinforcing modifier into a reaction kettle, heat to 130°C, vacuum dehydrate for 3 hours under stirring, control the vacuum degree to 0.08 MPa, then cool to 75°C, add isocyanate, react at 75°C for 1.5 hours, add triethylenediamine, 2,6-di-tert-butyl-p-cresol, 3-isocyanatepropyltriethoxysilane and carbon black under nitrogen protection, continue to react at 75°C for 1 hour, vacuum degassing until no bubbles appear, discharge, seal and package to obtain a polyurethane hot melt adhesive for bonding;

[0074] Among them, the hydroxyl-terminated fluoropolysiloxane is obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane in a mass ratio of 1:1; the isocyanate is obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate in a mass ratio of 1:1.

[0075] Example 3

[0076] Preparation of plant-based polyols, the specific steps are:

[0077] According to the mass ratio of sorbitol to deionized water being 1.5:20, sorbitol is dissolved in deionized water to obtain a sorbitol solution, which is then heated to 70° C., epoxidized castor oil (the mass of epoxidized castor oil is 20wt% of the mass of sorbitol) and fluoroboric acid (the mass of fluoroboric acid is 1wt% of the mass of sorbitol) are added to the sorbitol solution, and stirred in a water bath at 70° C. for 6 hours, sodium carbonate (the mass of sodium carbonate is equal to the mass of fluoroboric acid) is added to neutralize the fluoroboric acid, and plant-based polyols are obtained by vacuum distillation;

[0078] Wherein, the preparation method of epoxidized castor oil comprises the following steps:

[0079] According to the mass ratio of castor oil to formic acid being 20:7.5, castor oil and formic acid are uniformly mixed, and then added into a 30wt% hydrogen peroxide aqueous solution (the mass of the hydrogen peroxide aqueous solution is 85wt% of the mass of castor oil), and reacted at 60°C for 5h. After the reaction is completed, the product is dissolved in dichloromethane (the mass of dichloromethane is 2 times the mass of castor oil), and washed with deionized water and saturated sodium bicarbonate aqueous solution 3 times (the mass of deionized water and saturated sodium bicarbonate aqueous solution each time is 2 times the mass of castor oil) to remove residual hydrogen peroxide and formic acid, and then washed with saturated sodium chloride solution 3 times (the mass of the saturated sodium chloride solution each time is 2 times the mass of castor oil) to remove residual moisture, and then dried with anhydrous sodium sulfate, filtered to remove anhydrous sodium sulfate, and vacuum dried at 60°C to obtain epoxidized castor oil;

[0080] Preparation of reinforcing modifier, the specific steps are:

[0081] A1: According to the mass ratio of methyl 2,5-thiophenedicarboxylate to methanol being 7.5:100, methyl 2,5-thiophenedicarboxylate was dissolved in methanol at 55°C, and then carboxymethyl chitosan was added (the mass of carboxymethyl chitosan was 83wt% of the mass of methyl 2,5-thiophenedicarboxylate), and the mixture was stirred and reacted at 55°C for 24h. After the reaction, methanol was removed by rotary evaporation, and then washed with acetone for 3 times (the mass of acetone each time was 40wt% of the mass of deionized water) and filtered to obtain a rigid chain extender;

[0082] A2: Maleopimaric acid and the rigid chain extender were mixed evenly in a mass ratio of 1.5:2.5, and then dibutyltin dilaurate was added (the mass of dibutyltin dilaurate was 1wt% of the mass of maleopimaric acid), and the temperature was raised to 125°C under a nitrogen atmosphere, and the reaction was carried out for 3 hours, and the temperature was further raised to 245°C and the reaction was carried out for 7 hours to finally obtain a reinforcing modifier;

[0083] Wherein, the preparation method of maleopimaric acid comprises the following steps:

[0084] According to the mass ratio of abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid being 21:7:0.3:45, abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid are uniformly mixed, and then stirred at 195° C. and 700 rpm for 1.5 hours, cooled to room temperature, and recrystallized with acetic acid at 85° C. for 3 times (the mass of acetic acid each time is equal to the mass of the above acetic acid), and finally maleopimaric acid is obtained;

[0085] A polyurethane hot melt adhesive for bonding, comprising the following raw materials in parts by weight: 50 parts of plant-based polyol, 25 parts of hydroxyl-terminated fluoropolysiloxane, 20 parts of reinforcing modifier, 25 parts of isocyanate, 0.1 parts of N-methylimidazole, 3 parts of antioxidant 2246-S, 4 parts of γ-aminopropyltriethoxysilane and 8 parts of nano silicon dioxide;

[0086] The preparation method comprises the following steps:

[0087] Weigh the raw materials in parts by mass, put the plant-based polyol, hydroxyl-terminated fluoropolysiloxane and reinforcing modifier into a reaction kettle, heat to 140°C, vacuum dehydrate for 4 hours under stirring, control the vacuum degree to 0.09 MPa, then cool to 80°C, add isocyanate, react at 80°C for 2 hours, add N-methylimidazole, antioxidant 2246-S, γ-aminopropyltriethoxysilane and nano-silica under nitrogen protection, continue to react at 80°C for 1.5 hours, vacuum degassing until no bubbles appear, discharge, seal and package to obtain a polyurethane hot melt adhesive for bonding;

[0088] Among them, the hydroxyl-terminated fluoropolysiloxane is obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane in a mass ratio of 1:1; the isocyanate is obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate in a mass ratio of 1:1.

[0089] Comparative Example 1

[0090] The difference between this comparative example and Example 3 is that when preparing plant-based polyols, the epoxidized castor oil is replaced by epoxidized soybean oil, and the remaining steps and raw materials are the same as those of Example 3;

[0091] Preparation of plant-based polyols, the specific steps are:

[0092] According to the mass ratio of sorbitol to deionized water being 1.5:20, sorbitol was dissolved in deionized water to obtain a sorbitol solution, which was then heated to 70°C, epoxidized soybean oil (the mass of epoxidized soybean oil was 20wt% of the mass of sorbitol) and fluoroboric acid (the mass of fluoroboric acid was 1wt% of the mass of sorbitol) were added to the sorbitol solution, and the mixture was stirred in a water bath at 70°C for 6 hours, sodium carbonate (the mass of sodium carbonate was equal to that of fluoroboric acid) was added to neutralize the fluoroboric acid, and plant-based polyols were obtained by vacuum distillation.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 3 is that when preparing the reinforcing modifier, the mass of 2,5-thiophenedicarboxylic acid methyl ester in step A1 is replaced by 2,5-furandicarboxylic acid dimethyl ester, and the remaining steps and raw materials are synchronized with Example 3;

[0095] The specific operations of step A1 are:

[0096] According to the mass ratio of dimethyl 2,5-furandicarboxylate to methanol being 7.5:100, dimethyl 2,5-furandicarboxylate was dissolved in methanol at 55°C, and then carboxymethyl chitosan was added (the mass of carboxymethyl chitosan was 83wt% of the mass of dimethyl 2,5-furandicarboxylate), and the reaction was stirred at 55°C for 24h. After the reaction was completed, methanol was removed by rotary evaporation, and then washed with acetone for 3 times (the mass of acetone each time was 40wt% of the mass of deionized water) and filtered to obtain a rigid chain extender.

[0097] Comparative Example 3

[0098] The difference between this comparative example and Example 3 is that when preparing the reinforcing modifier, the mass of carboxymethyl chitosan in step A1 is replaced by ethanolamine, and the remaining steps and raw materials are the same as those in Example 3;

[0099] The specific operations of step A1 are:

[0100] According to the mass ratio of methyl 2,5-thiophenedicarboxylate to methanol being 7.5:100, methyl 2,5-thiophenedicarboxylate was dissolved in methanol at 55°C, and then ethanolamine was added (the mass of ethanolamine was 83wt% of the mass of methyl 2,5-thiophenedicarboxylate), and the reaction was stirred at 55°C for 24h. After the reaction was completed, methanol was removed by rotary evaporation, and then washed with acetone for 3 times (the mass of acetone each time was 40wt% of the mass of deionized water) and filtered to obtain a rigid chain extender.

[0101] Comparative Example 4

[0102] The difference between this comparative example and Example 3 is that when preparing the reinforcing modifier, the mass of maleopimaric acid in step A2 is replaced by abietic acid, and the remaining steps and raw materials are the same as those in Example 3;

[0103] The specific operations of step A2 are:

[0104] According to the mass ratio of abietic acid to rigid chain extender of 1.5:2.5, abietic acid and rigid chain extender were evenly mixed, and then dibutyltin dilaurate was added (the mass of dibutyltin dilaurate was 1wt% of the mass of abietic acid), and the temperature was raised to 125°C under nitrogen atmosphere and reacted for 3h, and then the temperature was continued to be raised to 245°C and reacted for 7h to finally obtain a reinforcing modifier.

[0105] Comparative Example 5

[0106] The difference between this comparative example and Example 3 is that when preparing the polyurethane hot melt adhesive for bonding, the mass of hydroxyl-terminated fluoropolysiloxane is replaced by hydroxypropyl-terminated polydimethylsiloxane, and the remaining steps and raw materials are the same as those in Example 3.

[0107] Comparative Example 6

[0108] The difference between this comparative example and Example 3 is that when preparing the polyurethane hot melt adhesive for bonding, the mass of isocyanate is replaced by dimethyltriphenylmethane tetraisocyanate, and the remaining steps and raw materials are synchronized with Example 3.

[0109] The adhesive polyurethane hot melt adhesive prepared in Examples 1-3 and Comparative Examples 1-6 was tested for adhesive performance, water resistance and high temperature resistance; the final peel strength test was performed according to GB / T 2791-1995, and the adhesive performance was characterized by the final peel strength; water resistance test: the adhesive polyurethane hot melt adhesive prepared in Examples 1-3 and Comparative Examples 1-6 was applied to the surface of polypropylene plastic, the adhesive layer thickness was 3mm, the temperature was controlled at 25°C, the relative humidity was 50%, and after soaking in deionized water at 70°C for 7 days, the peel strength retention rate was tested; high temperature resistance test: the adhesive polyurethane hot melt adhesive prepared in Examples 1-3 and Comparative Examples 1-6 was applied to the surface of polypropylene plastic, the adhesive layer thickness was 3mm, the temperature was controlled at 25°C, the relative humidity was 50%, and it was placed in a constant temperature box at 70°C for 15 minutes, and the peel strength was tested according to GB / T 2791-1995. The test results are shown in Table 1 below:

[0110] Table 1. Performance parameters of polyurethane hot melt adhesives prepared in Examples 1-3 and Comparative Examples 1-6

[0111]

[0112] It can be seen from the data in Table 1 above that, by comparing Comparative Example 1 with Example 3, the test results of the polyurethane hot melt adhesive for bonding prepared by replacing the epoxidized castor oil with epoxidized soybean oil are worse than those of Example 3, indicating that the epoxidized castor oil is combined with sorbitol to obtain a plant-based polyol, and the plant-based polyol can be well combined with isocyanate, further improving the bonding performance, high temperature resistance and water resistance of the polyurethane hot melt adhesive for bonding;

[0113] From the comparison between Comparative Examples 2-4 and Example 3, it can be seen that the mass of 2,5-thiophenedicarboxylic acid methyl ester in step A1 is replaced by 2,5-furandicarboxylic acid dimethyl ester, or the mass of carboxymethyl chitosan in step A1 is replaced by ethanolamine, or the mass of maleopimaric acid in step A2 is replaced by abietic acid, and finally the polyurethane hot melt adhesive for bonding is prepared. The test results are worse than those of Example 3, indicating that the rigid chain extender obtained by combining 2,5-thiophenedicarboxylic acid methyl ester and carboxymethyl chitosan can improve the bonding performance of the polyurethane hot melt adhesive and provide reaction sites for subsequent reactions. The reinforcing modifier is combined with the rigid chain extender to further improve the bonding performance, water resistance and high temperature resistance of the polyurethane hot melt adhesive, and has good mechanical properties.

[0114] By comparing Comparative Examples 5-6 with Example 3, it can be seen that the test results of the polyurethane hot melt adhesive for bonding prepared by replacing the mass of hydroxyl-terminated fluoropolysiloxane with hydroxypropyl-terminated polydimethylsiloxane or replacing the mass of isocyanate with dimethyltriphenylmethane tetraisocyanate are worse than those of Example 3, indicating that the hydroxyl-terminated fluoropolysiloxane obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane can better improve the water resistance and high temperature resistance of the polyurethane hot melt adhesive, and the isocyanate obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate can better enhance the bonding performance and high temperature resistance of the polyurethane hot melt adhesive.

[0115] As can be seen from Table 1 above, the polyurethane hot melt adhesive prepared in Examples 1-3 is prepared by combining methyl 2,5-thiophenedicarboxylate with carboxymethyl chitosan and then with maleopimaric acid to obtain a reinforcing modifier, and preparing a plant-based polyol by combining epoxidized vegetable oil with sorbitol. The plant-based polyol, hydroxyl-terminated fluoropolysiloxane, reinforcing modifier, isocyanate, catalyst, antioxidant, adhesion promoter and filler are mixed to finally prepare a polyurethane hot melt adhesive, which meets the test performance requirements, while the polyurethane hot melt adhesive prepared in Comparative Examples 1-6 does not meet the performance requirements. This shows that the polyurethane hot melt adhesive prepared by the present invention not only has good bonding performance, water resistance, high temperature resistance and mechanical properties, but also has good environmental protection, which expands its application range.

[0116] In the description of the specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0117] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the invention or exceed the scope defined by the claims, they shall all fall within the protection scope of the present invention.

Claims

1. A polyurethane hot melt adhesive for bonding, characterized in that: The invention comprises the following raw materials in parts by weight: 40-50 parts of plant-based polyol, 20-25 parts of hydroxyl-terminated fluoropolysiloxane, 10-20 parts of reinforcing modifier, 15-25 parts of isocyanate, 0.05-0.1 parts of catalyst, 1-3 parts of antioxidant, 2-4 parts of adhesion promoter and 5-8 parts of filler; The plant-based polyol is prepared by combining epoxidized vegetable oil and sorbitol through a ring-opening reaction; The preparation method of the reinforcing modifier comprises the following steps: A1: Combine 2,5-thiophenedicarboxylic acid methyl ester with carboxymethyl chitosan to obtain a rigid chain extender; A2: Combine the rigid chain extender with maleopimaric acid to obtain a reinforcing modifier; The epoxidized vegetable oil is epoxidized castor oil; The hydroxyl-terminated fluoropolysiloxane is obtained by mixing hydroxyl-terminated methyl-3,3,3-trifluoropropyl (siloxane and polysiloxane) and hydroxypropyl-terminated polydimethylsiloxane in a mass ratio of 1:1; The isocyanate is obtained by mixing triphenylmethane triisocyanate and dimethyltriphenylmethane tetraisocyanate in a mass ratio of 1:

1.

2. The polyurethane hot melt adhesive for bonding according to claim 1, characterized in that: The preparation method of the plant-based polyol comprises the following steps: Sorbitol is dissolved in deionized water to obtain a sorbitol solution, which is then heated to 60-70° C., epoxidized vegetable oil and fluoroboric acid are added to the sorbitol solution, and stirred in a water bath at 60-70° C. for 4-6 hours, sodium carbonate is added to neutralize the fluoroboric acid, and the plant-based polyol is obtained by vacuum distillation.

3. The polyurethane hot melt adhesive for bonding according to claim 1, characterized in that: Step A1 is specifically as follows: Dissolve methyl 2,5-thiophenedicarboxylate in methanol at 45-55° C., then add carboxymethyl chitosan, and stir to react at 45-55° C. for 22-24 hours. After the reaction is completed, remove the methanol by rotary evaporation, then wash with acetone and filter to obtain a rigid chain extender.

4. The polyurethane hot melt adhesive for bonding according to claim 1, characterized in that: Step A2 is specifically as follows: The maleopimaric acid and the rigid chain extender are uniformly mixed, and then dibutyltin dilaurate is added, and the temperature is raised to 115-125° C. under a nitrogen atmosphere, and the reaction is carried out for 1-3 hours, and the temperature is further raised to 235-245° C. and the reaction is carried out for 5-7 hours to finally obtain a reinforcing modifier.

5. The polyurethane hot melt adhesive for bonding according to claim 4, characterized in that: The preparation method of maleopimaric acid comprises the following steps: Abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid are uniformly mixed, and then stirred for reaction at 185-195° C. for 1.5-2.5 hours, cooled to room temperature, and recrystallized with acetic acid to finally obtain maleopimaric acid.

6. The polyurethane hot melt adhesive for bonding according to claim 5, characterized in that: The mass ratio of abietic acid, maleic anhydride, p-toluenesulfonic acid and acetic acid is 19-21:6-7:0.2-0.3:35-45.

7. A method for preparing the polyurethane hot melt adhesive for bonding as claimed in any one of claims 1 to 6, characterized in that: The following steps are involved: Weigh the raw materials in parts by mass, put the plant-based polyol, hydroxyl-terminated fluoropolysiloxane and reinforcing modifier into a reaction kettle, heat to 120-140°C, vacuum dehydrate under stirring, then cool to 70-80°C, add isocyanate, react at 70-80°C for 1-2h, add catalyst, antioxidant, adhesion promoter and filler under nitrogen protection, continue to react at 70-80°C for 0.5-1.5h, vacuum degassing until no bubbles appear, discharge the material, seal and package to obtain the polyurethane hot melt adhesive for bonding.

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