Quick-drying polyurethane hot melt adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of hot melt adhesive processing, and particularly relates to a quick-drying polyurethane hot melt adhesive and a preparation method thereof. The preparation method comprises the following steps: mixing polyether polyol, isocyanate, a chain extender A, a chain extender B, a crystallization promoting agent, a surface drying promoting agent and an auxiliary agent, and carrying out extrusion granulation, wherein the chain extender A is obtained by carrying out a reaction on acrylamide and diethanol amine and then carrying out siloxane modification on the reaction product by utilizing methacryloyloxymethyltrimethoxysilane; and the chain extender B is obtained by reacting tetrakis hydroxymethyl phosphonium sulfate and barium hydroxide octahydrate and oxidizing by hydrogen peroxide. The prepared hot melt adhesive has better viscosity and also has a certain flame-retardant effect.

Description

Technical Field

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

[0002] Polyurethane adhesives refer to adhesives containing urethane or isocyanate groups in the molecular chain. Due to the presence of polar groups such as isocyanate and ureido groups in polyurethane adhesives, they exhibit high polarity and reactivity, and can form covalent bonds and hydrogen bonds with materials containing active hydrogen. Currently, polyurethane adhesives generally include thermoplastic polyurethane, waterborne polyurethane, and reactive polyurethane. Since solvent-based polyurethane adhesives contain a large amount of organic solvents, a large amount of volatile compounds will be generated during use, seriously affecting people's production and living health, and they are gradually being replaced by solvent-free polyurethane adhesives. Among them, reactive polyurethane hot melt adhesives, as a kind of solvent-free adhesives, are widely used in industrial production. Reactive polyurethane hot melt adhesives are prepared from isocyanate-terminated prepolymers as the base material, adding thermoplastic resins, catalysts, fillers, tackifying resins, antioxidants, etc. Reactive polyurethane hot melt adhesives not only have the fast bonding performance of hot melt adhesives, but also react with moisture on the surface of air or substrates to produce chemical cross-linking and curing, significantly improving the bonding strength and heat resistance.

[0003] Chinese Patent with Publication No. CN115725259B discloses a reactive polyurethane hot melt adhesive and a preparation method thereof, which are prepared from polyether polyol, polyester polyol, tackifying resin, thermoplastic resin, polyisocyanate, adhesion promoter and catalyst. By modifying the polyether polyol with polysiloxane and introducing the polysiloxane molecular chain, the molecular chain mutual slip ability of the polyurethane adhesive is improved. At the same time, the polysiloxane-modified polyether polyol, as a compatibilizer for thermoplastic organosilicon polyurethane elastomer and polyester polyol, enables the two to have good compatibility. The prepared polyurethane hot melt adhesive has the properties of high and low temperature resistance and resistance to humid and hot environments, and can meet the long-term operation of automotive polyurethane adhesives under various different working conditions. Chinese Patent with Publication No. CN116285844B discloses a high-elastic polyurethane hot melt adhesive and a preparation method thereof. First, an organometallic ligand catalyst is synthesized, and then a carbon dioxide-based polycarbonate ether polyol is synthesized under the action of carbon dioxide; after pre-polymerizing the polyol with diisocyanate and an organometallic catalyst, a chain extender is added for blending and extrusion granulation. By using polycyclohexene carbonate as the hard segment and lactone polymer as the soft segment, the rigid structure of polycyclohexene carbonate plus its high glass transition temperature endow the obtained polyurethane with a high tensile modulus. The preparation of carbon dioxide-based polycarbonate ether polyol can make full use of the greenhouse gas CO 2, reduce the use of non-renewable resources, reduce pollution, and reduce energy consumption. However, with the widespread application of hot melt adhesives, some industries have put forward requirements for the flame retardant properties of hot melt adhesives. Therefore, the development of a hot melt adhesive with flame retardant properties has become the focus of attention. Summary of the Invention

[0004] To solve the problems existing in the prior art, the present invention provides a fast-drying polyurethane hot melt adhesive and a preparation method thereof. By mixing polyether polyol, isocyanate, chain extender A, chain extender B, crystallization promoter, surface drying promoter, and additives, and extruding and granulating, the obtained hot melt adhesive has good adhesiveness and certain flame retardant effect.

[0005] To solve the above problems, the technical solution provided by the present invention is as follows: A preparation method of a fast-drying polyurethane hot melt adhesive, comprising the following steps: S1. Add diethanolamine and acrylamide aqueous solution to the reactor, stir at room temperature for 3-8 h, and then remove the solvent by a rotary evaporator to obtain a viscous liquid; the mass ratio of diethanolamine to acrylamide aqueous solution is 1-1.5:1; the concentration of acrylamide aqueous solution is 25%-35%; S2. Under an inert atmosphere, preferably a nitrogen atmosphere, add a methanol solution of methacryloyloxymethyltrimethoxysilane to the reactor, heat to 45-60 °C and react for 20-50 min, then add the viscous liquid prepared in step S1 thereto, continuously stir and react for 96-120 h, remove methanol by vacuum distillation to obtain a crude product, dissolve it in acetone, and then remove acetone by vacuum distillation, and repeat the operation 3-5 times to obtain chain extender A; the preparation method of the methanol solution of methacryloyloxymethyltrimethoxysilane is: add methacryloyloxymethyltrimethoxysilane to the methanol solution and stir until dissolved; the mass ratio of methacryloyloxymethyltrimethoxysilane to methanol is 8-18:100; Polyurethane hot melt adhesive is prepared with polyols and polyisocyanates as the main raw materials, supplemented with various additives to obtain a prepolymer capped with -NCO groups. After complete curing, various chemical bonds including hydrogen bonds and urethane bonds will be formed between the molecules of the polyurethane hot melt adhesive through chemical reactions, and these chemical bonds can effectively improve the bonding strength of the polyurethane hot melt adhesive. In steps S1 and S2, first, a viscous liquid is obtained by reacting acrylamide with diethanolamine, and then it is subjected to siloxane modification using methacryloxymethyltrimethoxysilane to finally obtain chain extender A; the reaction between acrylamide and diethanolamine can provide a large number of hydrogen bonds for the prepared hot melt adhesive, effectively enhancing its bonding performance; further modification with methacryloxymethyltrimethoxysilane introduces a large number of siloxane groups into the polyurethane system, greatly increasing the crosslinking density of the curing reaction. Since the siloxane group can undergo a condensation reaction with compounds containing active hydrogen atoms in the substrate to form chemical bonds and does not escape small molecules during the curing process to cause pores in the adhesive layer, the bonding strength can be further improved; in addition, since the siloxane can undergo a hydrolysis reaction in the presence of water to generate silanol, and it will also condense with each other to form a three-dimensional network structure, the prepared hot melt adhesive has higher cohesive strength and weather resistance.

[0006] S3. Add deionized water and an aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate into a reactor. After mixing evenly, add barium hydroxide octahydrate. After the addition is completed, stir and react for 2 - 6 h, and obtain the supernatant through centrifugal separation. Under ice bath conditions, dropwise add an aqueous hydrogen peroxide solution until the potassium iodide starch reagent changes color, then stir for 2 - 4 h, and remove the solvent to obtain chain extender B; among them, barium hydroxide octahydrate is added in a batchwise manner; the mass ratio of deionized water, the aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate, barium hydroxide octahydrate, and the aqueous hydrogen peroxide solution is 100:32 - 40:18 - 25:8 - 16; the concentration of the aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate is 75%; the concentration of the aqueous hydrogen peroxide solution is 20%; During the combustion process, polyurethane materials will release a large amount of soot, toxic gases such as HCN and CO. Hyperbranched polymers have a highly branched three-dimensional structure and a large number of terminal active functional groups. Therefore, in step S3, phosphorus-containing trihydroxy compounds are obtained by reacting phosphonium tetramethylsulfate with barium hydroxide octahydrate and then oxidizing with hydrogen peroxide, which are used as chain extender B to participate in the subsequent preparation of polyurethane hot melt adhesives. The prepared phosphorus-containing polyurethane hot melt adhesive with a hyperbranched structure has more branches in its molecular chain due to the existence of a special hyperbranched structure, which can provide a higher degree of branching, resulting in a large number of terminal groups in the prepared polyurethane hot melt adhesive, enabling it to participate in more chemical reactions and providing stronger adhesion. At the same time, due to its many branch points, the molecular chain is not easily entangled, so it has good fluidity, enabling it to better fill and wet the surface of the adherend, thereby improving the bonding strength. Phosphorus elements can generate compounds such as phosphoric acid and metaphosphoric acid during the combustion process. These compounds, as dehydrating agents, can promote the carbonization of materials to form a protective layer, isolating oxygen and heat, and playing a flame retardant effect. Therefore, due to the introduction of phosphorus-containing compounds, the prepared polyurethane hot melt adhesive also has a certain flame retardant effect.

[0007] S4. Heat the dried polyether polyol to 60 - 80 °C, then add isocyanate, raise the temperature to 100 - 120 °C and react for 4 - 8 h to obtain a prepolymer. Then add chain extender A and chain extender B to it, react for 40 - 60 min, then add a crystallization promoter, a surface drying promoter and an auxiliary agent, stir and react for 20 - 40 min, and then mix and extrude granulate at a high speed of 6000 - 8000 rpm to obtain a quick-drying type polyurethane hot melt adhesive; the mass ratio of polyether polyol, isocyanate, chain extender A, chain extender B, crystallization promoter, surface drying promoter and auxiliary agent is 20 - 35:4 - 7:0.32 - 0.48:0.38 - 0.52:0.1:0.1 - 0.15:0.2 - 0.28; the auxiliary agent is a mixture of antioxidant, light stabilizer, hydrolysis inhibitor, lubricant and catalyst in a mass ratio of 1:1:1:1:1; the isocyanate is one or a mixture of aliphatic diisocyanates, cycloaliphatic diisocyanates, aromatic diisocyanates; the crystallization promoter is one or a mixture of talc powder, fumed silica, titanium dioxide, calcium carbonate; the surface drying promoter is spherical silica or alumina; the antioxidant is one or a mixture of butyl bis(4-methoxyphenyl)phosphinate, antioxidant 1135, antioxidant 801; the light stabilizer is one or a mixture of light stabilizer 770, light stabilizer BW-10LD, UV-3853; the hydrolysis inhibitor is CUWR-AH01 or UN-025; the lubricant is pentaerythritol stearate; the catalyst is dimorpholinodiethylether or dibutyltin dilaurate.

[0008] The present invention also provides a quick-drying polyurethane hot melt adhesive, which is prepared by the above method.

[0009] The present invention has the following beneficial effects: The polyurethane hot melt adhesive prepared by the present invention is mainly composed of polyether polyol and isocyanate, supplemented with chain extender A, chain extender B, crystallization promoter, surface drying promoter and additives. Chain extender A is obtained by reacting acrylamide with diethanolamine and then modifying it with methylacryloxymethyltrimethoxysilane. The reaction of acrylamide with diethanolamine can provide a large number of hydrogen bonds for the prepared hot melt adhesive, which can effectively enhance its bonding performance. Further modification with methylacryloxymethyltrimethoxysilane introduces a large number of siloxane groups into the polyurethane system, which can greatly increase the crosslinking density of the curing reaction and enhance the cohesive strength and weather resistance of the hot melt adhesive. Chain extender B is obtained by reacting phosphonium tetramethylol sulfate with barium hydroxide octahydrate and then oxidizing it with hydrogen peroxide. Due to the introduction of a special hyperbranched structure, the molecular chain has more branches, which can provide a higher degree of branching. At the same time, the prepared polyurethane hot melt adhesive has a large number of terminal groups, which can participate in more chemical reactions and provide stronger adhesion. The introduction of phosphorus-containing compounds makes the prepared polyurethane hot melt adhesive also have a certain flame retardant effect. Specific embodiments

[0010] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present application.

[0011] Diethanolamine (analytical pure), acrylamide (analytical pure), methylacryloxymethyltrimethoxysilane (>97%), methanol (AR, >99.5%), barium hydroxide octahydrate (AR, ≥98%) used in the present invention were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., and polyether polyol PPG (molecular weight 2000) was purchased from Shanghai Macklin Biochemical Co., Ltd. Acetone (AR, ≥99.5%), phosphonium tetramethylol sulfate (75% aqueous solution), diphenylmethane diisocyanate (Acros-414281000) were purchased from Sinopharm Chemical Reagent Co., Ltd. All reagents are commercially available.

[0012] Example 1 A preparation method of a quick-drying polyurethane hot melt adhesive: S1. Add 1.2 parts by weight of diethanolamine and 1 part by weight of an aqueous acrylamide solution to a reactor. After stirring at room temperature for 6 h, remove the solvent by a rotary evaporator to obtain a viscous liquid; the concentration of the aqueous acrylamide solution is 30%. S2. Under a nitrogen atmosphere, add a methanol solution of 25 parts by weight of methacryloxymethyltrimethoxysilane to the reactor. After heating to 50 °C and reacting for 30 min, add 175 parts by weight of the viscous liquid prepared in step S1 thereto, and continuously stir and react for 84 h. Remove methanol by vacuum distillation to obtain a crude product. Dissolve it in acetone, and then remove acetone by vacuum distillation. Repeat the operation 5 times to obtain chain extender A; the preparation method of the methanol solution of methacryloxymethyltrimethoxysilane is: add methacryloxymethyltrimethoxysilane to the methanol solution and stir until dissolved; the mass ratio of methacryloxymethyltrimethoxysilane to methanol is 12:100. S3. Add 100 parts by weight of deionized water and 38 parts by weight of an aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate to a reactor. After mixing evenly, add 20 parts by weight of barium hydroxide octahydrate. After the addition is completed, stir and react for 4 h. Separate the supernatant by centrifugation. Under ice bath conditions, add 12 parts by weight of an aqueous hydrogen peroxide solution dropwise until the potassium iodide starch reagent changes color. Then stir for 3 h and remove the solvent by vacuum distillation to obtain chain extender B; barium hydroxide octahydrate is added in a batchwise manner. Divide barium hydroxide octahydrate into 5 equal parts, add 1 part each time, and the time interval between each addition is 10 min; the concentration of the aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate is 75%, and the concentration of the aqueous hydrogen peroxide solution is 20%. S4. Heat 25 parts by weight of dried polyether polyol to 70 °C, then add 5 parts by weight of isocyanate, raise the temperature to 110 °C and react for 6 h to obtain a prepolymer. Then add 0.42 parts by weight of chain extender A and 0.40 parts by weight of chain extender B thereto, react for 45 min, then add 0.1 part by weight of a crystallization accelerator, 0.12 part by weight of a surface drying accelerator and 0.24 part by weight of an auxiliary agent, stir and react for 30 min, and then mix at a high speed at a rotation speed of 8000 rpm for 10 min, and extrude and pelletize to obtain a quick-drying type polyurethane hot melt adhesive; the isocyanate is diphenylmethane diisocyanate, the crystallization accelerator is talc powder (mesh number, above 6000 mesh), and the surface drying accelerator is spherical silica (D50 is 5 - 10 μm); the auxiliary agent is a mixture of an antioxidant, a light stabilizer, a hydrolysis inhibitor, a lubricant and a catalyst in a mass ratio of 1:1:1:1:1; the antioxidant is dibutyl butylbenzene sulfonate, the light stabilizer is light stabilizer 770, the hydrolysis inhibitor is CUWR - AH01, the lubricant is pentaerythritol stearate, and the catalyst is dibutyltin dilaurate. The drying conditions of the polyether polyol are: vacuum drying at 120 °C for 2 h.

[0013] Example Two This embodiment is different from Embodiment 1 as follows: Specifically, it is as follows: In step S1, 1 part by weight of diethanolamine and 1 part by weight of an acrylamide aqueous solution are added to the reactor, and stirred at room temperature for 4 h. The concentration of the acrylamide aqueous solution is 25%; In step S2, 20 parts by weight of a methanol solution of methacryloxymethyltrimethoxysilane are added to the reactor. After heating to 45 °C and reacting for 20 min, 150 parts by weight of the viscous liquid prepared in step S1 are added thereto, and the reaction is continuously stirred for 96 h. The mass ratio of methacryloxymethyltrimethoxysilane to methanol is 8:100; In step S3, 100 parts by weight of deionized water and 32 parts by weight of an aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate are added to the reactor. After mixing evenly, 18 parts by weight of barium hydroxide octahydrate are added. After the addition is completed, the reaction is stirred for 2 h. Under ice bath conditions, 8 parts by weight of an aqueous hydrogen peroxide solution are added dropwise thereto until the potassium iodide starch reagent changes color, and then stirred for another 2 h and the solvent is removed. The concentration of the aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate is 75%; the concentration of the aqueous hydrogen peroxide solution is 20%; In step S4, 20 parts by weight of polyether polyol after drying is heated to 60 °C, then 4 parts by weight of isocyanate are added, the temperature is raised to 100 °C and reacted for 4 h to obtain a prepolymer. Then, 0.32 part by weight of chain extender A and 0.38 part by weight of chain extender B are added thereto, and the reaction is carried out for 40 min. Then, 0.1 part by weight of crystal nucleating agent, 0.1 part by weight of surface drying accelerator and 0.2 part by weight of auxiliary agent are added thereto, and the reaction is stirred for 20 min.

[0014] The rest refers to Embodiment 1.

[0015] Embodiment 3 This embodiment is different from Embodiment 1 as follows: Specifically, it is as follows: In step S1, 1.5 parts by weight of diethanolamine and 1 part by weight of an acrylamide aqueous solution are added to the reactor, and stirred at room temperature for 8 h. The concentration of the acrylamide aqueous solution is 35%; In step S2, 30 parts by weight of a methanol solution of methacryloxymethyltrimethoxysilane are added to the reactor. After heating to 60 °C and reacting for 50 min, 200 parts by weight of the viscous liquid prepared in step S1 are added thereto, and the reaction is continuously stirred for 120 h. The mass ratio of methacryloxymethyltrimethoxysilane to methanol is 18:100; In step S3, 100 parts by weight of deionized water and 40 parts by weight of an aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate are added to the reactor. After mixing evenly, 25 parts by weight of barium hydroxide octahydrate are added. After the addition is completed, the mixture is stirred and reacted for 6 h. Under the condition of an ice bath, 16 parts by weight of an aqueous hydrogen peroxide solution are added dropwise thereto until the potassium iodide-starch reagent changes color. After stirring for another 4 h, the solvent is removed. The concentration of the aqueous solution of tetrakis(hydroxymethyl)phosphonium sulfate is 75%; the concentration of the aqueous hydrogen peroxide solution is 20%. In step S4, 35 parts by weight of the dried polyether polyol are heated to 80 °C, and then 7 parts by weight of isocyanate are added. The temperature is raised to 120 °C and the reaction is carried out for 8 h to obtain a prepolymer. Then, 0.48 part by weight of chain extender A and 0.52 part by weight of chain extender B are added thereto, and the reaction is carried out for 60 min. Then, 0.1 part by weight of a crystallization promoter, 0.15 part by weight of a surface drying promoter, and 0.28 part by weight of an auxiliary agent are added thereto, and the mixture is stirred and reacted for 40 min.

[0016] The rest refers to Example 1.

[0017] Comparative Example 1 Compared with Example 1, the preparation method of chain extender A in this comparative example is different, and the rest refers to Example 1. Specifically as follows: Among them, the preparation method of chain extender A is as follows: 1.2 parts by weight of diethanolamine and 1 part by weight of an aqueous acrylamide solution are added to the reactor. After stirring at room temperature for 6 h, the solvent is removed by a rotary evaporator to obtain a viscous liquid, which is chain extender A. The concentration of the aqueous acrylamide solution is 30%.

[0018] The preparation method of the hot melt adhesive refers to step S4 in Example 1, and the preparation of chain extender B refers to the preparation method of chain extender B in step S3 in Example 1.

[0019] Comparative Example 2 Compared with Example 1, diethanolamine is used as chain extender A in this comparative example, and the rest refers to Example 1. Specifically as follows: The preparation method of the hot melt adhesive refers to step S4 in Example 1, and the preparation of chain extender B refers to the preparation method of chain extender B in step S3 in Example 1.

[0020] Comparative Example 3 Compared with Example 1, chain extender B is not added during the preparation of the hot melt adhesive in this comparative example, and the rest refers to Example 1. Specifically as follows: The preparation method of the hot melt adhesive is as follows: Heat 25 parts by weight of polyether polyol after drying to 70 °C, then add 5 parts by weight of isocyanate, raise the temperature to 110 °C and react for 6 h to obtain a prepolymer. Then add 0.8 part by weight of chain extender A thereto and react for 45 min. Then add 0.1 part by weight of crystallization promoter, 0.12 part by weight of surface drying promoter and 0.24 part by weight of auxiliary agent thereto, stir and react for 30 min, then mix at a high speed at a rotation speed of 8000 rpm for 10 min, and extrude and pelletize to obtain a fast-drying type polyurethane hot melt adhesive; wherein the isocyanate is diphenylmethane diisocyanate, the crystallization promoter is talcum powder, and the surface drying promoter is spherical silica; wherein the preparation of chain extender A refers to the preparation method of chain extender A in steps S1 and S2 of Example 1.

[0021] Comparative Example 4 Compared with Example 1, in the preparation process of the hot melt adhesive in this comparative example, ethylene glycol amine is used as the chain extender, and the rest refers to Example 1, specifically as follows: The preparation method of the hot melt adhesive is as follows: Heat 25 parts by weight of polyether polyol after drying to 70 °C, then add 5 parts by weight of isocyanate, raise the temperature to 110 °C and react for 6 h to obtain a prepolymer. Then add 0.78 part by weight of chain extender ethylene glycol amine thereto and react for 45 min. Then add 0.1 part by weight of crystallization promoter, 0.12 part by weight of surface drying promoter and 0.24 part by weight of auxiliary agent thereto, stir and react for 30 min, then mix at a high speed at a rotation speed of 8000 rpm for 10 min, and extrude and pelletize to obtain a fast-drying type polyurethane hot melt adhesive; wherein the isocyanate is diphenylmethane diisocyanate, the crystallization promoter is talcum powder, and the surface drying promoter is spherical silica.

[0022] Related tests: Bond strength test: Test the bond strength of the samples obtained in the examples and comparative examples. The bonding performance of the hot melt adhesive is tested according to GB / T7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)". Lap two polycarbonate substrates with dimensions of 100 mm × 25 mm × 2 mm together, and then bond them with the prepared hot melt adhesive. The bonding area is 12.5 mm × 25 mm × 0.2 mm. The samples are cured at 25 °C and 50% RH for 7 d, and then the tensile shear strength is tested. The tensile speed is 5 mm / min. The test results are shown in Table 1.

[0023] Elongation at break test: Test the elongation at break of the samples obtained in the examples and comparative examples. The test method refers to GB / T1040.3-2006 "Determination of Tensile Properties of Plastics Part 3: Test Conditions for Films and Sheets". Inject the hot melt adhesive into the mold and scrape it flat, and cure it at 25 °C and 50% RH for 7 d; cut the cured hot melt adhesive with a cutter to prepare a specimen, and conduct a tensile property test. The tensile speed is 10 mm / min. The test results are shown in Table 1.

[0024] Aging resistance test: After curing the hot melt adhesives prepared in the examples and comparative examples, specimens with a size of 2 cm × 2 cm × 0.2 cm were prepared and placed in a constant temperature and humidity chamber at 68 ± 2 °C and 75 ± 3% relative humidity for 6 months. After 6 months, record whether there are phenomena such as yellowing, oxidation, cracking, blistering and damage on the specimens. If so, it is recorded as unqualified, otherwise it is qualified. The qualification rate of the specimens was recorded for 50 specimens in each group. The test results are shown in Table 1.

[0025] Corrosion resistance: The specimens with a size of 2 cm × 2 cm × 0.2 cm prepared by curing the hot melt adhesives in the examples and comparative examples were subjected to a salt spray test. The test environment temperature was 35 ± 2 °C, the humidity was 95 ± 2%, the test solution was 5 wt% NaCl solution, the spray angle was 25°, the spray rate was 2 mL / 80 cm² / h, and the test time was 400 h. After the test was completed, observe whether there are phenomena such as corrosion, peeling, cracking and blistering on the cured hot melt adhesive. If so, it is recorded as unqualified, otherwise it is qualified. The qualification rate of the specimens was recorded for 50 specimens in each group. The test results are shown in Table 1.

[0026] Table 1 Performance test results It can be seen from the test data in Table 1 that the test results of Examples 1 to 3 are better than those of Comparative Examples 1 to 4, especially the test effect of Example 1 is the best. By comparing the test data of Example 1 with Comparative Example 1 (without siloxane modification of chain extender A), Comparative Example 2 (replacing chain extender A with diethanolamine) and Comparative Example 3 (without adding chain extender B), it can be known that the hot melt adhesive prepared by using chain extender A modified with methacryloxymethyltrimethoxysilane has better performance. This is because introducing a large number of siloxane groups into the polyurethane system can greatly increase the crosslinking density of the curing reaction. At the same time, the siloxane groups can react with the active hydrogen in the substrate to form chemical bonds, which can effectively improve the bonding strength of the hot melt adhesive; and the presence of the siloxane group structure itself will also condense with each other to form a three-dimensional network structure, making the prepared hot melt adhesive have higher cohesive strength and weather resistance.

[0027] UL-94 Flame Retardancy Test: The samples obtained from the examples and comparative examples were subjected to a flame retardancy test. The test results are shown in Table 2. The UL-94 flame retardancy test was carried out using the UL94 vertical burning test method for flame retardant materials in the United States. The specimen size was 130 mm (length) × 20 mm (width) × 2 mm (thickness), and the thickness of the test piece should not exceed 2 mm. The flame retardancy grades increase gradually from HB, V-2, V-1 to V-0; among them: V-0: After a 10-second combustion test on the sample, the dripping matter cannot ignite cotton, the flame goes out within 30 seconds, and no combustibles fall off; V-1: After a 10-second combustion test on the sample, the dripping matter cannot ignite cotton, the flame goes out within 60 seconds, and no combustibles fall off; V-2: After two 10-second combustion tests on the sample, the flame goes out within 60 seconds, and combustibles fall off.

[0028] Open Time Test: The samples obtained from the examples and comparative examples were subjected to an open time test. The test results are shown in Table 2. Open time: Refer to the standard HG / T 3716-2003. The experimental steps are as follows: 1. Put the prepared sample into an oven and heat it to 120°C to melt, and at the same time heat the film applicator to 120°C; 2. The test was carried out in a normal temperature room without air flow; 3. Quickly scrape a 0.1-mm-thick layer of glue onto a smooth flat plate with a film applicator and start timing; 4. After 5 s of timing, cover the first bonding paper strip on the cooling glue layer, and immediately press the pressing surface of the heavy block onto the first bonding paper strip covering the glue layer to apply pressure. Then sequentially cover other bonding paper strips and apply pressure at intervals of 5 s until the glue layer cures and can no longer bond the paper strips; 5. After the glued layer after pasting cools at room temperature for 20 min - 30 min, manually and uniformly peel the bonding paper strip at 90 degrees, and complete the single-piece peeling in about 2 s. Record the percentage of the fiber peeling area of each bonding paper strip and the covering time of this bonding paper strip, in s; 6. Repeat the test according to the above steps, three times in total. The test results show that: The longest covering time with the fiber peeling area of the bonding paper strip greater than 50% of the bonding surface is the open time of the hot melt adhesive, and the range of the three measured values is not greater than 5 s. The test results are expressed as the same value among the three measured values.

[0029] Table 2 Test Results of Flame Retardancy and Open Time As can be seen from the test data in Table 2, the flame retardancy of Examples 1 to 3 and Comparative Examples 1 to 2 is better than that of Comparative Example 3 (without adding chain extender B) and Comparative Example 4 (using ethylene glycol amine as the chain extender). This is because a phosphorus-containing compound is introduced into chain extender B. Since phosphorus can generate compounds such as phosphoric acid and metaphosphoric acid during combustion, these compounds, as dehydrating agents, can promote the carbonization of the material to form a protective layer, isolating oxygen and heat. Therefore, the introduction of chain extender B endows the prepared polyurethane hot melt adhesive with certain flame retardant properties. It can be seen from the test results that the open time of the hot melt adhesives prepared in Examples 1 to 3 is relatively shorter than that of the hot melt adhesives prepared in Comparative Examples 1 to 4.

[0030] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0031] Although the embodiments of the present application have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present application. The scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a quick-drying polyurethane hot melt adhesive, characterized in that: The steps include: S1. Add diethanolamine and acrylamide aqueous solution into the reactor, stir for 3-8 hours at room temperature, and then remove the solvent to obtain a viscous liquid; S2. Under an inert atmosphere, add a methanol solution of methacryloxymethyltrimethoxysilane to a reactor, heat to 45-60° C. and react for 20-50 min, then add the viscous liquid prepared in step S1, continue stirring and react for 96-120 h to obtain a crude product, dissolve it in acetone, and then remove the acetone by reduced pressure distillation, repeat the operation 3-5 times to obtain a chain extender A; S3, add deionized water and tetrakis(hydroxymethyl)phosphonium sulfate aqueous solution into the reactor, mix well and then add barium hydroxide octahydrate, stir and react for 2-6 hours after the addition is completed, centrifuge to obtain a supernatant, add hydrogen peroxide aqueous solution under ice bath conditions until the potassium iodide starch reagent changes color, stir for 2-4 hours, remove the solvent, and obtain chain extender B; S4. Heat the dried polyether polyol to 60-80°C, add isocyanate, raise the temperature to 100-120°C, react for 4-8h to obtain a prepolymer, add chain extender A and chain extender B, react for 40-60min, add a crystallization promoter, a surface drying promoter and an auxiliary agent, stir and react for 20-40min, mix at high speed, extrude and granulate to obtain a quick-drying polyurethane hot melt adhesive.

2. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S1, the mass ratio of diethanolamine to acrylamide aqueous solution is 1-1.5:

1.

3. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S2, the preparation method of the methanol solution of methacryloxymethyltrimethoxysilane is: adding methacryloxymethyltrimethoxysilane to the methanol solution and stirring until dissolved; the mass ratio of methacryloxymethyltrimethoxysilane to methanol is 8-18:

100.

4. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S3, the mass ratio of deionized water, tetrakis(hydroxymethyl)phosphonium sulfate aqueous solution, barium hydroxide octahydrate and hydrogen peroxide aqueous solution is 100:32-42:18-25:8-16.

5. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S4, the mass ratio of polyether polyol, isocyanate, chain extender A, chain extender B, crystallization promoter, surface drying promoter and auxiliary agent is 20-35:4-7:0.38-0.52:0.32-0.48:0.1:0.1-0.15:0.2-0.

28.

6. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S4, the isocyanate is one or a mixture of aliphatic diisocyanate, alicyclic diisocyanate, and aromatic diisocyanate.

7. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S4, the crystallization promoting agent is one or a mixture of talcum powder, fumed silica, titanium dioxide, and calcium carbonate.

8. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S4, the surface drying agent is spherical silica or alumina.

9. The method for preparing the quick-drying polyurethane hot melt adhesive according to claim 1, characterized in that: In step S4, the auxiliary agent is a mixture of an antioxidant, a light stabilizer, an anti-hydrolysis agent, a lubricant and a catalyst in a mass ratio of 1:1:1:1:

1.

10. A quick-drying polyurethane hot melt adhesive prepared by the method according to any one of claims 1 to 9.

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