Polyurethane hot melt adhesive for PVC film lamination and preparation method thereof

Abstract

The present invention relates to the technical field of hot melt adhesives, and specifically to a polyurethane hot melt adhesive for PVC film lamination and a preparation method thereof. The polyurethane hot melt adhesive comprises the following weight components: 20-40 parts of polyester polyol, 30-60 parts of polyether polyol, 5-15 parts of modified titanium dioxide, 10-20 parts of tackifying resin, 40-80 parts of diphenylmethane diisocyanate, 0.2-1.0 parts of catalyst, 0.5-1.0 parts of leveling agent, and 0.2-0.5 parts of defoaming agent. The polyurethane hot melt adhesive prepared by the present invention has excellent adhesion, excellent heat resistance and stability, thereby extending the service life of the PVC film.

Description

Technical Field

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

[0002] With the wide application of PVC film in packaging, printing, furniture and other fields, the requirements for the lamination quality and performance of PVC film are getting higher and higher. In order to improve the surface quality and adhesion of PVC film, people began to study and develop polyurethane hot melt adhesive suitable for PVC film lamination. Polyurethane hot melt adhesive has excellent bonding performance and weather resistance, can provide good bonding effect in PVC film lamination, and can adapt to various processing conditions, so it has become an ideal choice for PVC film lamination.

[0003] However, the bonding strength of traditional polyurethane hot melt adhesive is unstable. After the PVC film is bonded, its bonding strength decreases or fluctuates over time, resulting in unstable bonding quality. Some polyurethane hot melt adhesives have poor moisture and heat resistance and are prone to stratification or falling off in humid or high temperature environments, affecting the service life and bonding effect of the PVC film.

[0004] Therefore, we propose a polyurethane hot melt adhesive for PVC film lamination and a preparation method thereof. Summary of the invention

[0005] The object of the present invention is to provide a polyurethane hot melt adhesive for PVC film lamination and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0007] A method for preparing a polyurethane hot melt adhesive for PVC film lamination comprises the following steps:

[0008] The polyester polyol, polyether polyol, modified titanium dioxide and tackifying resin are vacuum dehydrated at 110-130°C for 2-3h, cooled to 60-70°C, and diphenylmethane diisocyanate is added under nitrogen protection, and reacted at 100-130°C for 1-2h; then a catalyst, a leveling agent and a defoaming agent are added, and the reaction is carried out at 100-130°C for 0.5-1.5h, and then vacuum evacuation is carried out until no bubbles appear to obtain a polyurethane hot melt adhesive.

[0009] Furthermore, the polyurethane hot melt adhesive includes the following components by weight: 20-40 parts of polyester polyol, 30-60 parts of polyether polyol, 5-15 parts of modified titanium dioxide, 10-20 parts of tackifying resin, 40-80 parts of diphenylmethane diisocyanate, 0.2-1.0 parts of catalyst, 0.5-1.0 parts of leveling agent, and 0.2-0.5 parts of defoaming agent.

[0010] Furthermore, the preparation method of the modified titanium dioxide is as follows:

[0011] Step S1: Evenly mix nano titanium dioxide, anhydrous ethanol and deionized water, add γ-glycidyloxypropyltrimethoxysilane, react at 30-50° C. for 22-24 hours, and obtain epoxidized titanium dioxide after centrifugation, washing and drying;

[0012] Step S2: Under nitrogen protection, maleic anhydride and N, N'-dimethylformamide are mixed uniformly, the temperature is raised to 60-70°C, a mixed solution of 2-(4-aminophenyl)-5-aminobenzimidazole and N, N'-dimethylformamide is added dropwise for 0.5-1.0h, the mixture is reacted for 2-4h, the mixture is cooled to room temperature, filtered, washed and dried to obtain an intermediate; Under nitrogen protection, the intermediate and xylene are mixed uniformly, p-toluenesulfonic acid and p-hydroxyanisole are added, the mixture is refluxed and dehydrated at 100-110°C, cyclodehydrated for 5-7h, and a maleimide compound is obtained after rotary evaporation, filtration, washing, recrystallization and drying;

[0013] Step S3: uniformly mix the maleimide compound, epoxidized titanium dioxide, toluene and 2-methylimidazole, react at 30-40° C. for 5-7 hours, and obtain modified titanium dioxide by rotary evaporation.

[0014] In the above technical scheme, the surface of nano titanium dioxide is modified by γ-glycidyloxypropyltrimethoxysilane to introduce epoxy groups to obtain epoxidized titanium dioxide; the amidation reaction is carried out between maleic anhydride and the amino group at one end of 2-(4-aminophenyl)-5-aminobenzimidazole to introduce a rigid benzimidazole ring structure; in the reaction, the mass ratio of maleic anhydride and 2-(4-aminophenyl)-5-aminobenzimidazole is precisely controlled to retain the amino group at the other end so as to further react with the epoxidized titanium dioxide, thereby improving the heat resistance of titanium dioxide.

[0015] Furthermore, in step S1, the mass ratio of nano-titanium dioxide to anhydrous ethanol, deionized water, and γ-glycidyloxypropyltrimethoxysilane is 1:(6-8):(2-3):(0.1-0.3).

[0016] Furthermore, in step S2, the mass ratio of maleic anhydride to N,N'-dimethylformamide is 1:(10-12), and the mass ratio of 2-(4-aminophenyl)-5-aminobenzimidazole to N,N'-dimethylformamide is 1:(10-12).

[0017] Furthermore, in step S2, the mass ratio of maleic anhydride to 2-(4-aminophenyl)-5-aminobenzimidazole is 1:(2.1-2.3).

[0018] Furthermore, in step S2, the mass ratio of the intermediate, xylene, p-toluenesulfonic acid and p-hydroxyanisole is 1:(4-6):(0.1-0.3):(0.01-0.02).

[0019] Furthermore, in step S3, the mass ratio of the maleimide compound, epoxidized titanium dioxide, toluene and 2-methylimidazole is 1:(4-6):(15-25):(0.01-0.03).

[0020] Furthermore, the preparation method of the tackifying resin is as follows:

[0021] Step (1): mix hydrogenated rosin resin, epichlorohydrin and 2,3-epoxypropyltrimethylammonium chloride evenly, react at 105-115°C for 3-5h, cool to 70-80°C, add maleic anhydride and p-hydroxyanisole, mix evenly, react for 2-4h, and obtain modified rosin;

[0022] Step (2): Under nitrogen protection, 1,3,5-triglycidyl-S-triazinetrione, 2,4,6-trihydroxybenzoic acid and dimethyl sulfoxide are mixed evenly, tetrabutylammonium bromide is added, and the mixture is reacted at 100-120°C for 3-5 hours, the temperature is lowered to 30-40°C, L-cysteine ​​and acetic acid are added, the mixture is reacted for 2-4 hours, and the mixture is subjected to rotary evaporation to obtain a thiol-containing polyol;

[0023] Step (3): uniformly mix the modified rosin and the mercapto-containing polyol, add a photoinitiator, and irradiate with ultraviolet light to obtain a tackifying resin.

[0024] In the above technical scheme, the carboxyl groups in the hydrogenated rosin resin and epichlorohydrin undergo an epoxy ring-opening reaction to generate hydroxyl groups, and then maleic anhydride and hydroxyl groups react to introduce carbon-carbon double bonds and carboxyl groups to obtain modified rosin; a large number of hydroxyl groups and rigid benzene ring structures are introduced by an epoxy ring-opening reaction between the epoxy groups in 1,3,5-triglycidyl-S-triazinetrione and the carboxyl groups in 2,4,6-trihydroxybenzoic acid, and then the amino groups in L-cysteine ​​react with the remaining epoxy groups to introduce thiol groups to obtain a thiol-containing polyol containing a triazinetrione structure and a rigid benzene ring structure, which has excellent heat resistance; finally, a thiol-ene click reaction is performed between the double bonds in the modified rosin and the thiol-containing polyol to obtain a tackifying resin rich in carboxyl groups and hydroxyl groups, which can participate in the polymerization process of polyurethane molecules, thereby improving the adhesion and heat resistance of the hot melt adhesive.

[0025] Furthermore, in step (1), the modified rosin comprises the following components by weight: 10-20 parts of hydrogenated rosin resin, 4-6 parts of epichlorohydrin, 0.02-0.05 parts of 2,3-epoxypropyltrimethylammonium chloride, 3-6 parts of maleic anhydride, and 0.01-0.03 parts of p-hydroxyanisole.

[0026] Furthermore, in the step (2), the mass ratio of 1,3,5-triglycidyl-S-triazinetrione to 2,4,6-trihydroxybenzoic acid, dimethyl sulfoxide and tetrabutylammonium bromide is 1:(0.8-1.1):(3-5):(0.01-0.03).

[0027] Furthermore, in step (2), the mass of L-cysteine ​​is 0.4-0.6 times the mass of 1,3,5-triglycidyl-S-triazinetrione, and the mass of acetic acid is 0.01-0.03 times the mass of L-cysteine.

[0028] Furthermore, in step (3), the tackifying resin comprises the following components by weight: 10-20 parts of modified rosin, 15-30 parts of mercapto-containing polyol, and 3-5 parts of photoinitiator.

[0029] Furthermore, the photoinitiator is 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0030] Furthermore, the process conditions of the ultraviolet irradiation are: irradiation wavelength 360-400nm, irradiation time 20-40min, irradiation intensity 20-35mW / cm 2 .

[0031] Furthermore, the catalyst is dibutyltin dilaurate.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. A polyurethane hot melt adhesive for PVC film lamination and a preparation method thereof are disclosed, wherein the surface of nano titanium dioxide is modified to introduce epoxy groups to obtain epoxidized titanium dioxide; a rigid benzimidazole ring structure is introduced by amidation reaction between maleic anhydride and the amino group at one end of 2-(4-aminophenyl)-5-aminobenzimidazole to obtain a maleimide compound; finally, the remaining amino group of the maleimide compound is further reacted with the epoxidized titanium dioxide to improve the heat resistance of the titanium dioxide so that it can be stably used in a high temperature environment; at the same time, the titanium dioxide is better combined with the polyurethane hot melt adhesive through the modification treatment, thereby improving the heat resistance and stability of the polyurethane hot melt adhesive.

[0034] 2. A polyurethane hot melt adhesive for PVC film lamination of the present invention and a preparation method thereof, wherein the carboxyl groups in hydrogenated rosin resin and epichlorohydrin undergo an epoxy ring-opening reaction to generate hydroxyl groups, and then maleic anhydride and hydroxyl groups react to introduce carbon-carbon double bonds and carboxyl groups to obtain modified rosin; a large number of hydroxyl groups and rigid benzene ring structures are introduced by an epoxy ring-opening reaction between the epoxy groups in 1,3,5-triglycidyl-S-triazinetrione and the carboxyl groups in 2,4,6-trihydroxybenzoic acid, and then the amino groups in L-cysteine ​​react with the remaining epoxy groups to introduce thiol groups to obtain a thiol-containing polyol, which contains a triazinetrione structure and a rigid benzene ring structure and has excellent heat resistance; finally, a thiol-ene click reaction is performed between the double bonds in the modified rosin and the thiol-containing polyol to obtain a tackifying resin rich in carboxyl groups and hydroxyl groups, which can participate in the polymerization process of polyurethane molecules and improve the adhesion and heat resistance of the hot melt adhesive. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

[0036] In this embodiment, polyester polyol: brand Dynacoll 7360; polyether polyol: brand ED56-200; nano titanium dioxide: rutile type, particle size is 20nm; leveling agent: model KYC-615; defoaming agent: model BYK-028; hydrogenated rosin resin: brand Foralyn 90 of Eastman, USA.

[0037] In the following examples and comparative examples, 1 part is equal to 10 g.

[0038] Embodiment 1: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following process:

[0039] 20 parts of polyester polyol, 30 parts of polyether polyol, 5 parts of modified titanium dioxide and 10 parts of tackifying resin were vacuum dehydrated at 110°C for 2 hours, cooled to 60°C, and 40 parts of diphenylmethane diisocyanate were added under nitrogen protection, and reacted at 100°C for 1 hour; 0.2 parts of catalyst, 0.5 parts of leveling agent and 0.2 parts of defoaming agent were added, and reacted at 100°C for 0.5 hours, and then vacuum evacuated until no bubbles appeared to obtain a polyurethane hot melt adhesive;

[0040] The preparation method of modified titanium dioxide is as follows:

[0041] Step S1: 5 parts of nano titanium dioxide, 30 parts of anhydrous ethanol and 10 parts of deionized water are mixed evenly, 0.5 parts of γ-glycidyloxypropyltrimethoxysilane are added, and the mixture is reacted at 30° C. for 22 hours. After centrifugation, washing and drying, epoxidized titanium dioxide is obtained;

[0042] Step S2: Under nitrogen protection, 1.25 parts of maleic anhydride and 12.5 parts of N, N'-dimethylformamide are mixed uniformly, the temperature is raised to 60 ° C, 2.63 parts of 2-(4-aminophenyl)-5-aminobenzimidazole and 26.3 parts of N, N'-dimethylformamide are added dropwise, the dripping is completed in 0.5 h, the reaction is carried out for 2 h, the reaction is cooled to room temperature, and the intermediate is obtained after filtering, washing and drying; Under nitrogen protection, 1.25 parts of the intermediate and 5 parts of xylene are mixed uniformly, 0.125 parts of p-toluenesulfonic acid and 0.013 parts of p-hydroxyanisole are added, and reflux water separation and cyclodehydration are carried out at 100 ° C for 5 h, and the maleimide compound is obtained after rotary evaporation, filtering, washing, recrystallization and drying;

[0043] Step S3: 1.25 parts of a maleimide compound, 5 parts of epoxidized titanium dioxide, 18.75 parts of toluene and 0.013 parts of 2-methylimidazole were mixed evenly, reacted at 30° C. for 5 h, and subjected to rotary evaporation to obtain modified titanium dioxide;

[0044] The preparation method of the tackifying resin is as follows:

[0045] Step (1): 10 parts of hydrogenated rosin resin, 4 parts of epichlorohydrin and 0.02 parts of 2,3-epoxypropyltrimethylammonium chloride are mixed evenly, reacted at 105°C for 3 hours, cooled to 70°C, 3 parts of maleic anhydride and 0.01 parts of p-hydroxyanisole are added, mixed evenly, and reacted for 2 hours to obtain modified rosin;

[0046] Step (2): Under nitrogen protection, 25 parts of 1,3,5-triglycidyl-S-triazinetrione, 20 parts of 2,4,6-trihydroxybenzoic acid and 75 parts of dimethyl sulfoxide are mixed evenly, 0.25 parts of tetrabutylammonium bromide are added, and the mixture is reacted at 100°C for 3 hours, cooled to 30°C, and 15 parts of L-cysteine ​​and 0.15 parts of acetic acid are added, and the mixture is reacted for 2 hours, and rotary evaporated to obtain a thiol-containing polyol;

[0047] Step (3): 10 parts of modified rosin and 15 parts of mercapto-containing polyol were mixed evenly, 3 parts of photoinitiator were added, and after ultraviolet irradiation (irradiation wavelength 360nm, irradiation time 20min, irradiation intensity 35mW / cm 2 ), to obtain a tackifying resin.

[0048] Embodiment 2: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following process:

[0049] 30 parts of polyester polyol, 50 parts of polyether polyol, 10 parts of modified titanium dioxide and 15 parts of tackifying resin were vacuum dehydrated at 120°C for 2.5 hours, cooled to 65°C, and 60 parts of diphenylmethane diisocyanate were added under nitrogen protection, and reacted at 120°C for 1.5 hours; 0.8 parts of catalyst, 0.8 parts of leveling agent and 0.3 parts of defoaming agent were added, and reacted at 120°C for 1 hour, and then vacuum evacuated until no bubbles appeared to obtain a polyurethane hot melt adhesive;

[0050] The preparation method of modified titanium dioxide is as follows:

[0051] Step S1: 10 parts of nano titanium dioxide, 70 parts of anhydrous ethanol and 25 parts of deionized water are mixed evenly, 3 parts of γ-glycidyloxypropyltrimethoxysilane are added, and the mixture is reacted at 40° C. for 23 hours. After centrifugation, washing and drying, epoxidized titanium dioxide is obtained;

[0052] Step S2: Under nitrogen protection, 2 parts of maleic anhydride and 22 parts of N, N'-dimethylformamide are mixed uniformly, the temperature is raised to 65 ° C, 4.4 parts of 2-(4-aminophenyl)-5-aminobenzimidazole and 48.4 parts of N, N'-dimethylformamide are added dropwise, the dripping is completed in 0.8 h, the reaction is carried out for 3 h, the reaction is cooled to room temperature, and the intermediate is obtained after filtering, washing and drying; Under nitrogen protection, 2 parts of the intermediate and 10 parts of xylene are mixed uniformly, 0.4 parts of p-toluenesulfonic acid and 0.03 parts of p-hydroxyanisole are added, and reflux water separation and cyclodehydration are carried out at 105 ° C for 6 h, and the maleimide compound is obtained after rotary evaporation, filtering, washing, recrystallization and drying;

[0053] Step S3: 2 parts of maleimide compound, 10 parts of epoxidized titanium dioxide, 40 parts of toluene and 2-methylimidazole were mixed evenly, reacted at 35° C. for 6 hours, and subjected to rotary evaporation to obtain modified titanium dioxide;

[0054] The preparation method of the tackifying resin is as follows:

[0055] Step (1): 15 parts of hydrogenated rosin resin, 5 parts of epichlorohydrin and 0.03 parts of 2,3-epoxypropyltrimethylammonium chloride are mixed evenly, reacted at 110°C for 4 hours, cooled to 75°C, 5 parts of maleic anhydride and 0.02 parts of p-hydroxyanisole are added, mixed evenly, and reacted for 3 hours to obtain modified rosin;

[0056] Step (2): Under nitrogen protection, 40 parts of 1,3,5-triglycidyl-S-triazinetrione, 36 parts of 2,4,6-trihydroxybenzoic acid and 160 parts of dimethyl sulfoxide were mixed evenly, 0.8 parts of tetrabutylammonium bromide were added, and the mixture was reacted at 110°C for 4 hours, and then the temperature was lowered to 35°C, and 20 parts of L-cysteine ​​and 0.04 parts of acetic acid were added, and the mixture was reacted for 3 hours, and then rotary evaporated to obtain a thiol-containing polyol;

[0057] Step (3): 15 parts of modified rosin and 20 parts of mercapto-containing polyol were mixed evenly, 4 parts of photoinitiator were added, and after ultraviolet irradiation (irradiation wavelength 380nm, irradiation time 30min, irradiation intensity 25mW / cm 2 ), to obtain a tackifying resin.

[0058] Embodiment 3: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following process:

[0059] 40 parts of polyester polyol, 60 parts of polyether polyol, 15 parts of modified titanium dioxide and 20 parts of tackifying resin were vacuum dehydrated at 130°C for 3 hours, cooled to 70°C, and 80 parts of diphenylmethane diisocyanate were added under nitrogen protection, and reacted at 130°C for 2 hours; 1.0 part of catalyst, 1.0 part of leveling agent and 0.5 part of defoaming agent were added, and reacted at 130°C for 1.5 hours, and then vacuum evacuated until no bubbles appeared to obtain a polyurethane hot melt adhesive;

[0060] The preparation method of modified titanium dioxide is as follows:

[0061] Step S1: 15 parts of nano titanium dioxide, 120 parts of anhydrous ethanol and 45 parts of deionized water are mixed evenly, 4.5 parts of γ-glycidyloxypropyltrimethoxysilane are added, and the mixture is reacted at 50° C. for 24 hours. After centrifugation, washing and drying, epoxidized titanium dioxide is obtained;

[0062] Step S2: Under nitrogen protection, 2.5 parts of maleic anhydride and 30 parts of N, N'-dimethylformamide are mixed uniformly, the temperature is raised to 70°C, 5.75 parts of 2-(4-aminophenyl)-5-aminobenzimidazole and 69 parts of a mixed solution of N, N'-dimethylformamide are added dropwise, the dripping is completed in 1 hour, the reaction is carried out for 4 hours, the mixture is cooled to room temperature, filtered, washed and dried to obtain an intermediate; Under nitrogen protection, 2.5 parts of the intermediate and 15 parts of xylene are mixed uniformly, 0.75 parts of p-toluenesulfonic acid and 0.05 parts of p-hydroxyanisole are added, and the mixture is refluxed and dehydrated at 110°C for 7 hours, and the maleimide compound is obtained after rotary evaporation, filtration, washing, recrystallization and drying;

[0063] Step S3: 2.5 parts of a maleimide compound, 15 parts of epoxidized titanium dioxide, 62.5 parts of toluene and 0.075 parts of 2-methylimidazole were mixed evenly, reacted at 40° C. for 7 hours, and subjected to rotary evaporation to obtain modified titanium dioxide;

[0064] The preparation method of the tackifying resin is as follows:

[0065] Step (1): 20 parts of hydrogenated rosin resin, 6 parts of epichlorohydrin and 0.05 parts of 2,3-epoxypropyltrimethylammonium chloride are mixed evenly, reacted at 115°C for 5 hours, cooled to 80°C, 6 parts of maleic anhydride and 0.03 parts of p-hydroxyanisole are added, mixed evenly, and reacted for 4 hours to obtain modified rosin;

[0066] Step (2): Under nitrogen protection, 75 parts of 1,3,5-triglycidyl-S-triazinetrione, 82.5 parts of 2,4,6-trihydroxybenzoic acid and 375 parts of dimethyl sulfoxide were mixed evenly, 2.25 parts of tetrabutylammonium bromide were added, and the mixture was reacted at 120°C for 5 hours, and the temperature was lowered to 40°C, and 30 parts of L-cysteine ​​and 0.9 parts of acetic acid were added, and the mixture was reacted for 4 hours, and then rotary evaporated to obtain a thiol-containing polyol;

[0067] Step (3): 20 parts of modified rosin and 30 parts of mercapto-containing polyol were mixed evenly, 5 parts of photoinitiator were added, and after ultraviolet irradiation (irradiation wavelength 400nm, irradiation time 40min, irradiation intensity 35mW / cm 2 ), to obtain a tackifying resin.

[0068] Comparative Example 1: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following processes:

[0069] Compared with Example 2, Comparative Example 1 added 5 parts of tackifier, and the other steps were the same as Example 2.

[0070] Comparative Example 2: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following processes:

[0071] Compared with Example 2, the modified titanium dioxide in Comparative Example 2 is replaced by nano titanium dioxide of the same weight, and the other steps are the same as those in Example 2.

[0072] Comparative Example 3: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following processes:

[0073] The preparation method of modified titanium dioxide is as follows:

[0074] Step S1: 10 parts of nano titanium dioxide, 70 parts of anhydrous ethanol and 25 parts of deionized water are mixed evenly, 3 parts of γ-glycidyloxypropyltrimethoxysilane are added, and the mixture is reacted at 40° C. for 23 hours. After centrifugation, washing and drying, epoxidized titanium dioxide is obtained;

[0075] Step S2: Under nitrogen protection, 2 parts of maleic anhydride and 22 parts of N, N'-dimethylformamide are mixed uniformly, the temperature is raised to 65 ° C, 2.2 parts of 2-(4-aminophenyl)-5-aminobenzimidazole and 48.4 parts of N, N'-dimethylformamide are added dropwise, the dripping is completed in 0.8 h, the reaction is carried out for 3 h, the reaction is cooled to room temperature, and the intermediate is obtained after filtering, washing and drying; Under nitrogen protection, 2 parts of the intermediate and 10 parts of xylene are mixed uniformly, 0.4 parts of p-toluenesulfonic acid and 0.03 parts of p-hydroxyanisole are added, and reflux water separation and cyclodehydration are carried out at 105 ° C for 6 h, and the maleimide compound is obtained after rotary evaporation, filtering, washing, recrystallization and drying;

[0076] Step S3: 2 parts of maleimide compound, 10 parts of epoxidized titanium dioxide, 40 parts of toluene and 2-methylimidazole were mixed evenly, reacted at 35° C. for 6 hours, and subjected to rotary evaporation to obtain modified titanium dioxide;

[0077] Compared with Example 2, the mass ratio of maleic anhydride to 2-(4-aminophenyl)-5-aminobenzimidazole in Comparative Example 3 is 1:1.1, and the other steps are the same as those in Example 2.

[0078] Comparative Example 4: A method for preparing a polyurethane hot melt adhesive for PVC film lamination, comprising the following processes:

[0079] Compared with Example 2, in Comparative Example 4, the tackifier is replaced with hydrogenated rosin resin of the same weight, and the other steps are the same as those of Example 2.

[0080] Experiment: The polyurethane hot melt adhesives obtained in Examples 1-3 and Comparative Examples 1-4 were used to prepare samples, and their properties were tested and the test results were recorded:

[0081] The melt viscosity was tested according to HG / T 660-1999 standard: a lamina viscometer was used for testing, the speed was 50 r / min, the temperature was 120°C, the time detection was set to 60 s, the sample was placed on the lamina to be melted, and then tested.

[0082] The final bonding strength was tested according to GB / T 7124-2008 standard: After the two PVC film bonding substrates were dusted and degreased, they were horizontally bonded with molten polyurethane hot melt adhesive. The bonding area was 12.5mm×25mm and the adhesive thickness was 0.2mm. After the bonding was completed, they were cured at 25℃ / 50% RH for 7 days, and the final bonding strength was measured using an electronic universal testing machine.

[0083] According to GB / T 7124-2008 standard, the heat resistance of hot melt adhesive was tested by preparing samples: the samples were cured at 25℃ / 50%RH for 7 days, then placed in a 120℃ oven for 24 hours, and the tensile shear strength was tested using a 120℃ high and low temperature tensile testing machine to evaluate its heat resistance.

[0084] Test Results

[0085]

[0086] According to the data in the above table, we can clearly draw the following conclusions:

[0087] 1. Compared with Examples 1-3, the adhesion and heat resistance of the product obtained in Comparative Example 1 are both reduced, indicating that the performance of the polyurethane hot melt adhesive prepared by the present invention is affected by its component ratio. Reducing the amount of tackifier added will lead to poor adhesion and heat resistance.

[0088] 2. Compared with Examples 1-3, the adhesion and heat resistance of the products obtained in Comparative Examples 2 and 4 are both reduced, which shows that the present invention improves the heat resistance and stability by modifying the nano-titanium dioxide to better combine titanium dioxide with the polyurethane hot melt adhesive; compared with hydrogenated rosin resin, the tackifier prepared by the present invention has better adhesion and heat resistance.

[0089] 3. Compared with Examples 1-3, the heat resistance of the product obtained in Comparative Example 3 decreases. It can be seen that if the amount of 2-(4-aminophenyl)-5-aminobenzimidazole added is reduced, the maleic anhydride will react with the amino group completely and cannot further react with the epoxidized titanium dioxide, thereby causing the heat resistance of the polyurethane to deteriorate.

[0090] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process method article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process method article or device.

[0091] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a polyurethane hot melt adhesive for PVC film lamination, characterized in that: The steps include: Dehydrate polyester polyol, polyether polyol, modified titanium dioxide and tackifying resin under vacuum at 110-130°C for 2-3h, cool to 60-70°C, add diphenylmethane diisocyanate under nitrogen protection, and react at 100-130°C for 1-2h; then add catalyst, leveling agent and defoaming agent, react at 100-130°C for 0.5-1.5h, and then vacuum evacuate until no bubbles appear to obtain polyurethane hot melt adhesive; The preparation method of the modified titanium dioxide is as follows: Step S1: Evenly mix nano titanium dioxide, anhydrous ethanol and deionized water, add γ-glycidyloxypropyltrimethoxysilane, react at 30-50° C. for 22-24 hours, and obtain epoxidized titanium dioxide after centrifugation, washing and drying; Step S2: Under nitrogen protection, maleic anhydride and N, N'-dimethylformamide are mixed uniformly, the temperature is raised to 60-70°C, a mixed solution of 2-(4-aminophenyl)-5-aminobenzimidazole and N, N'-dimethylformamide is added dropwise for 0.5-1.0h, the mixture is reacted for 2-4h, the mixture is cooled to room temperature, filtered, washed and dried to obtain an intermediate; Under nitrogen protection, the intermediate and xylene are mixed uniformly, p-toluenesulfonic acid and p-hydroxyanisole are added, the mixture is refluxed and dehydrated at 100-110°C, cyclodehydrated for 5-7h, and a maleimide compound is obtained after rotary evaporation, filtration, washing, recrystallization and drying; Step S3: uniformly mixing the maleimide compound, epoxidized titanium dioxide, toluene and 2-methylimidazole, reacting at 30-40° C. for 5-7 hours, and performing rotary evaporation to obtain modified titanium dioxide; The polyurethane hot melt adhesive comprises the following components by weight: 20-40 parts of polyester polyol, 30-60 parts of polyether polyol, 5-15 parts of modified titanium dioxide, 10-20 parts of tackifying resin, 40-80 parts of diphenylmethane diisocyanate, 0.2-1.0 parts of catalyst, 0.5-1.0 parts of leveling agent, and 0.2-0.5 parts of defoaming agent; In step S2, the mass ratio of maleic anhydride to 2-(4-aminophenyl)-5-aminobenzimidazole is 1:(2.1-2.3); The preparation method of the tackifying resin is as follows: Step (1): mix hydrogenated rosin resin, epichlorohydrin and 2,3-epoxypropyltrimethylammonium chloride evenly, react at 105-115°C for 3-5h, cool to 70-80°C, add maleic anhydride and p-hydroxyanisole, mix evenly, react for 2-4h, and obtain modified rosin; Step (2): Under nitrogen protection, 1,3,5-triglycidyl-S-triazinetrione, 2,4,6-trihydroxybenzoic acid and dimethyl sulfoxide are mixed evenly, tetrabutylammonium bromide is added, and the mixture is reacted at 100-120°C for 3-5 hours, the temperature is lowered to 30-40°C, L-cysteine ​​and acetic acid are added, the mixture is reacted for 2-4 hours, and the mixture is subjected to rotary evaporation to obtain a thiol-containing polyol; Step (3): uniformly mix the modified rosin and the mercapto-containing polyol, add a photoinitiator, and irradiate with ultraviolet light to obtain a tackifying resin.

2. The method for preparing a polyurethane hot melt adhesive for PVC film lamination according to claim 1, characterized in that: In the step (1), the modified rosin comprises the following components by weight: 10-20 parts of hydrogenated rosin resin, 4-6 parts of epichlorohydrin, 0.02-0.05 parts of 2,3-epoxypropyltrimethylammonium chloride, 3-6 parts of maleic anhydride, and 0.01-0.03 parts of p-hydroxyanisole.

3. The method for preparing a polyurethane hot melt adhesive for PVC film lamination according to claim 1, characterized in that: In the step (2), the mass ratio of 1,3,5-triglycidyl-S-triazinetrione to 2,4,6-trihydroxybenzoic acid, dimethyl sulfoxide and tetrabutylammonium bromide is 1:(0.8-1.1):(3-5):(0.01-0.03).

4. The method for preparing a polyurethane hot melt adhesive for PVC film lamination according to claim 1, characterized in that: In the step (3), the tackifying resin comprises the following components by weight: 10-20 parts of modified rosin, 15-30 parts of mercapto-containing polyol, and 3-5 parts of photoinitiator.

5. The method for preparing a polyurethane hot melt adhesive for PVC film lamination according to claim 1, characterized in that: The process conditions of the ultraviolet irradiation are: irradiation wavelength 360-400nm, irradiation time 20-40min, irradiation intensity 20-35mW / cm 2 .

6. A polyurethane hot melt adhesive for PVC film lamination prepared according to the preparation method according to any one of claims 1 to 5.

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