A quick-drying polyurethane hot melt adhesive and a preparation method thereof

Abstract

The application 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 polyurethane hot melt adhesive is prepared by mixing polyether polyol, isocyanate, chain extender A, chain extender B, crystallization promoter, surface drying promoter and additives, and then extruding and granulating, wherein the chain extender A is obtained by reacting acrylamide with diethanolamine, and then modifying the reaction product with methacryloyloxy methyl trimethoxysilane to obtain a siloxane; the chain extender B is obtained by reacting tetramethylammonium sulfate and barium hydroxide octahydrate, and then obtaining through hydrogen peroxide oxidation. The prepared hot melt adhesive has good adhesion and certain flame retardation effect.

Description

Technical Field

[0001] This invention belongs to the field of hot melt adhesive processing technology, specifically relating to a fast-drying polyurethane hot melt adhesive and its preparation method. Background Technology

[0002] Polyurethane adhesives are adhesives whose molecular chains contain urethane or isocyanate groups. Due to the presence of polar groups such as isocyanates and urea groups, polyurethane adhesives exhibit high polarity and reactivity, and can form covalent and hydrogen bonds with materials containing active hydrogen. Currently, polyurethane adhesives broadly include thermoplastic polyurethane, waterborne polyurethane, and reactive polyurethane. Solvent-based polyurethane adhesives contain large amounts of organic solvents, generating significant amounts of volatile compounds during use, seriously impacting people's health and daily lives, and are gradually being replaced by solvent-free polyurethane adhesives. Among these, reactive polyurethane hot melt adhesives, as a solvent-free adhesive, are widely used in industrial production. Reactive polyurethane hot melt adhesives are prepared by using isocyanate-terminated prepolymers as a base material, with the addition of thermoplastic resins, catalysts, fillers, tackifying resins, antioxidants, etc. While retaining the rapid bonding performance of hot melt adhesives, reactive polyurethane hot melt adhesives react with moisture from the air or substrate surface to undergo chemical cross-linking and curing, significantly improving bond strength and heat resistance.

[0003] Chinese Patent CN115725259B discloses a reactive polyurethane hot melt adhesive and its preparation method. The adhesive is prepared from polyether polyol, polyester polyol, tackifying resin, thermoplastic resin, polyisocyanate, tackifier, and catalyst. By modifying the polyether polyol with polysiloxane, polysiloxane molecular chains are introduced, enhancing the mutual slippage ability of the polyurethane adhesive's molecular chains. Simultaneously, the polysiloxane-modified polyether polyol acts as a compatibilizer between the thermoplastic silicone polyurethane elastomer and the polyester polyol, ensuring good compatibility between the two. The resulting polyurethane hot melt adhesive exhibits resistance to high and low temperatures and humid heat environments, meeting the long-term operation requirements of automotive polyurethane adhesives under various working conditions. Chinese patent CN116285844B discloses a high-elasticity polyurethane hot melt adhesive and its preparation method. The method involves first synthesizing an organometallic ligand catalyst, then synthesizing a carbon dioxide-based polycarbonate ether polyol under the action of carbon dioxide. This polyol is prepolymerized with diisocyanate and the organometallic catalyst, then blended with a chain extender and extruded to obtain the final product. By using polycyclohexene carbonate as the hard segment and a lactone polymer as the soft segment, the rigid structure of polycyclohexene carbonate, combined with its high glass transition temperature, gives the resulting polyurethane a high tensile modulus. The preparation of the carbon dioxide-based polycarbonate ether polyol can fully utilize the greenhouse gas CO2, 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 raised requirements for the flame-retardant properties of hot melt adhesives. Therefore, developing a hot melt adhesive with flame-retardant properties has become a key focus. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention provides a fast-drying polyurethane hot melt adhesive and its preparation method. The hot melt adhesive is obtained by mixing polyether polyol, isocyanate, chain extender A, chain extender B, crystallizer, surface drying agent and additives, and then extruding and granulating the mixture. The obtained hot melt adhesive has good adhesion and a certain flame retardant effect.

[0005] To solve the above problems, the technical solution provided by the present invention is as follows:

[0006] A method for preparing a fast-drying polyurethane hot melt adhesive includes the following steps:

[0007] S1. Add diethanolamine and acrylamide aqueous solution to the reactor, stir at room temperature for 3-8 hours, and then remove the solvent by rotary evaporator to obtain a viscous liquid; wherein the mass ratio of diethanolamine to acrylamide aqueous solution is 1-1.5:1; and the concentration of acrylamide aqueous solution is 25%-35%;

[0008] S2. Under an inert atmosphere, preferably a nitrogen atmosphere, a methanol solution of methacryloyloxymethyltrimethoxysilane is added to the reactor. The mixture is heated to 45-60℃ and reacted for 20-50 minutes. Then, the viscous liquid prepared in step S1 is added, and the mixture is stirred continuously for 96-120 hours. Methanol is removed by vacuum distillation to obtain a crude product, which is then dissolved in acetone. The acetone is removed by vacuum distillation. This process is repeated 3-5 times to obtain chain extender A. The methanol solution of methacryloyloxymethyltrimethoxysilane is prepared by adding methacryloyloxymethyltrimethoxysilane to a methanol solution and stirring until dissolved. The mass ratio of methacryloyloxymethyltrimethoxysilane to methanol is 8-18:100.

[0009] Polyurethane hot melt adhesives are prepared using polyols and polyisocyanates as main raw materials, supplemented with various additives to obtain prepolymers with -NCO group end caps. After complete curing, the polyurethane hot melt adhesive forms various chemical bonds, including hydrogen bonds and urethane bonds, through chemical reactions between its molecules. These chemical bonds effectively improve the adhesive strength of the polyurethane hot melt adhesive. In steps S1 and S2, a viscous liquid is first obtained by reacting acrylamide with diethanolamine, and then modified with methacryloyloxymethyltrimethoxysilane to obtain chain extender A. The reaction of acrylamide with diethanolamine provides a large number of hydrogen bonds to the prepared hot melt adhesive, effectively enhancing its adhesive properties. Further modification with methacryloyloxymethyltrimethoxysilane introduces a large number of siloxane groups into the polyurethane system, which greatly increases the crosslinking density of the curing reaction. Since siloxanes can undergo condensation reactions with compounds containing active hydrogen atoms in the substrate to form chemical bonds, and small molecules will not escape during the curing process, thus preventing the formation of bubbles in the adhesive layer, the bonding strength can be further improved. In addition, since siloxanes can undergo hydrolysis reactions in the presence of water to generate silanols, they will also condense with each other to form a three-dimensional network structure, resulting in hot melt adhesives with higher cohesive strength and weather resistance.

[0010] S3. Add deionized water and tetramethylolphosphine sulfate aqueous solution to the reactor, mix well, then add barium hydroxide octahydrate. After the addition is complete, stir the reaction for 2-6 hours. Centrifuge to obtain the supernatant. Under ice bath conditions, add hydrogen peroxide aqueous solution dropwise until the potassium iodide starch reagent changes color. Stir for another 2-4 hours, then remove the solvent to obtain chain extender B. The barium hydroxide octahydrate is added in batches. The mass ratio of deionized water, tetramethylolphosphine sulfate aqueous solution, barium hydroxide octahydrate, and hydrogen peroxide aqueous solution is 100:32-40:18-25:8-16; the concentration of tetramethylolphosphine sulfate aqueous solution is 75%; and the concentration of hydrogen peroxide aqueous solution is 20%.

[0011] Polyurethane materials release a large amount of smoke, dust, and toxic gases such as HCN and CO during combustion. Hyperbranched polymers possess highly branched three-dimensional structures and numerous end-group active functional groups. Therefore, in step S3, a phosphorus-containing trihydroxy compound is obtained by reacting tetramethylolphosphine sulfate and barium hydroxide octahydrate followed by oxidative oxidation and hydroxylation. This compound serves as chain extender B, participating in the subsequent preparation of the polyurethane hot melt adhesive. The resulting phosphorus-containing polyurethane hot melt adhesive with a hyperbranched structure exhibits higher branching due to its unique hyperbranched structure, resulting in a large number of end groups that can participate in more chemical reactions and provide stronger adhesion. Simultaneously, due to its numerous branching points, the molecular chains are less prone to entanglement, thus exhibiting good flowability. This allows for better filling and wetting of the adhered surfaces, thereby improving bond strength. During combustion, phosphorus can generate compounds such as phosphoric acid and metaphosphoric acid. These compounds act as dehydrating agents, promoting the carbonization of materials to form a protective layer that isolates oxygen and heat, thus achieving 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.

[0012] S4. After heating the dried polyether polyol to 60-80℃, add isocyanate and raise the temperature to 100-120℃ to react for 4-8 hours to obtain a prepolymer. Then add chain extender A and chain extender B and react for 40-60 minutes. Next, add crystallizer, surface drying agent and additives, stir and react for 20-40 minutes, then mix at high speed at 6000-8000 rpm, extrude and granulate to obtain a fast-drying polyurethane hot melt adhesive. The mass ratio of polyether polyol, isocyanate, chain extender A, chain extender B, crystallizer, surface drying agent and additives is 20-35:4-7:0.32-0.48:0.38-0.52:0.1:0.1-0.15:0.2-0.28. The additives are antioxidants, light stabilizers, anti-hydrolysis agents, and lubricants. The lubricant and catalyst are mixed in a mass ratio of 1:1:1:1:1; the isocyanate is one or a mixture of several aliphatic diisocyanates, alicyclic diisocyanates, and aromatic diisocyanates; the crystallizing agent is one or a mixture of several talc, fumed silica, titanium dioxide, and calcium carbonate; the surface drying agent is spherical silica or alumina; the antioxidant is one or a mixture of several butyl bis(p-oxybenzoate), antioxidant 1135, and antioxidant 801; the light stabilizer is one or a mixture of several light stabilizer 770, light stabilizer BW-10LD, and UV-3853; the anti-hydrolysis agent is CUWR-AH01 or UN-025; the lubricant is pentaerythritol stearate; and the catalyst is dimorpholine diethyl ether or dibutyltin dilaurate.

[0013] The present invention also provides a fast-drying polyurethane hot melt adhesive, which is prepared by the above method.

[0014] The present invention has the following beneficial effects:

[0015] The polyurethane hot melt adhesive prepared in this invention uses polyether polyol and isocyanate as the main raw materials, supplemented by chain extender A, chain extender B, crystallizer, surface drying agent and additives. Chain extender A is obtained by reacting acrylamide with diethanolamine and then modifying it with methacryloyloxymethyltrimethoxysilane. The reaction of acrylamide with diethanolamine can provide a large number of hydrogen bonds to the prepared hot melt adhesive, which can effectively enhance its adhesive properties. Further modification with methacryloyloxymethyltrimethoxysilane 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 tetramethylolphosphine sulfate and barium hydroxide octahydrate and then oxidizing and oxidizing. 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 also gives the prepared polyurethane hot melt adhesive a certain flame retardant effect. Detailed Implementation

[0016] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0017] The diethanolamine (analytical grade), acrylamide (analytical grade), methacryloyloxymethyltrimethoxysilane (>97%), methanol (AR, >99.5%), and barium hydroxide octahydrate (AR, ≥98%) used in this invention were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., the polyether polyol PPG (molecular weight 2000) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., and the acetone (AR, ≥99.5%), tetramethylolphosphine sulfate (75% aqueous solution), and diphenylmethane diisocyanate (Acros-414281000) were purchased from Sinopharm Chemical Reagent Co., Ltd. All reagents were commercially available.

[0018] Example 1

[0019] A method for preparing a fast-drying polyurethane hot melt adhesive:

[0020] S1. Add 1.2 parts by weight of diethanolamine and 1 part by weight of acrylamide aqueous solution to the reactor, stir at room temperature for 6 hours, and then remove the solvent by rotary evaporator to obtain a viscous liquid; wherein the concentration of acrylamide aqueous solution is 30%;

[0021] S2. Under a nitrogen atmosphere, 25 parts by weight of a methanol solution of methacryloyloxymethyltrimethoxysilane were added to the reactor. The mixture was heated to 50°C and reacted for 30 minutes. Then, 175 parts by weight of the viscous liquid prepared in step S1 were added, and the mixture was stirred continuously for 84 hours. The methanol was removed by vacuum distillation to obtain a crude product, which was then dissolved in acetone. The acetone was then removed by vacuum distillation. This process was repeated 5 times to obtain chain extender A. The methanol solution of methacryloyloxymethyltrimethoxysilane was prepared by adding methacryloyloxymethyltrimethoxysilane to a methanol solution and stirring until dissolved. The mass ratio of methacryloyloxymethyltrimethoxysilane to methanol was 12:100.

[0022] S3. Add 100 parts by weight of deionized water and 38 parts by weight of tetramethylolphosphine sulfate aqueous solution to the reactor, mix well, and then add 20 parts by weight of barium hydroxide octahydrate. After the addition is complete, stir the reaction for 4 hours. After centrifugation, obtain the supernatant. Under ice bath conditions, add 12 parts by weight of hydrogen peroxide aqueous solution dropwise until the potassium iodide starch reagent changes color. Stir for another 3 hours, and then remove the solvent by vacuum distillation to obtain chain extender B. The barium hydroxide octahydrate is added in batches, with the barium hydroxide octahydrate divided into 5 equal parts, and 1 part is added at a time interval of 10 minutes. The concentration of tetramethylolphosphine sulfate aqueous solution is 75%, and the concentration of hydrogen peroxide aqueous solution is 20%.

[0023] S4. After heating 25 parts by weight of dried polyether polyol to 70°C, add 5 parts by weight of isocyanate, raise the temperature to 110°C and react for 6 hours 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, react for 45 minutes, then add 0.1 parts by weight of crystallizer, 0.12 parts by weight of surface drying agent and 0.24 parts by weight of additives, stir and react for 30 minutes, then mix at high speed of 8000 rpm for 10 minutes, and extrude and granulate to obtain fast-drying polyurethane thermopolymer. The molten adhesive consists of diphenylmethane diisocyanate as the isocyanate, talc powder (mesh size ≥ 6000 mesh) as the crystallizing agent, and spherical silica (D50 5-10 μm) as the surface drying agent. The additives are an antioxidant, light stabilizer, anti-hydrolysis agent, lubricant, and catalyst mixed in a mass ratio of 1:1:1:1:1. The antioxidant is butyl di-para-oxybenzoate, the light stabilizer is light stabilizer 770, the anti-hydrolysis agent is CUWR-AH01, the lubricant is pentaerythritol stearate, and the catalyst is dibutyltin dilaurate. The polyether polyol is dried under vacuum at 120℃ for 2 hours.

[0024] Example 2

[0025] This embodiment differs from Embodiment 1 in the following ways, as detailed below:

[0026] In step S1, 1 part by weight of diethanolamine and 1 part by weight of acrylamide aqueous solution are added to the reactor and stirred at room temperature for 4 hours. The concentration of the acrylamide aqueous solution is 25%.

[0027] In step S2, 20 parts by weight of a methanol solution of methacryloyloxymethyltrimethoxysilane were added to the reactor, heated to 45°C and reacted for 20 min. Then, 150 parts by weight of the viscous liquid prepared in step S1 were added and the reaction was stirred continuously for 96 h. The mass ratio of methacryloyloxymethyltrimethoxysilane to methanol was 8:100.

[0028] In step S3, 100 parts by weight of deionized water and 32 parts by weight of tetramethylolphosphine sulfate aqueous solution are added to the reactor and mixed thoroughly. Then, 18 parts by weight of barium hydroxide octahydrate are added. After the addition is complete, the mixture is stirred for 2 hours. Under ice bath conditions, 8 parts by weight of hydrogen peroxide aqueous solution are added dropwise until the potassium iodide starch reagent changes color. After stirring for another 2 hours, the solvent is removed. The concentration of the tetramethylolphosphine sulfate aqueous solution is 75%, and the concentration of the hydrogen peroxide aqueous solution is 20%.

[0029] In step S4, 20 parts by weight of dried polyether polyol are heated to 60°C and 4 parts by weight of isocyanate are added. The temperature is raised to 100°C and reacted for 4 hours to obtain a prepolymer. Then, 0.32 parts by weight of chain extender A and 0.38 parts by weight of chain extender B are added and reacted for 40 minutes. Then, 0.1 parts by weight of crystallizer, 0.1 parts by weight of surface drying agent and 0.2 parts by weight of auxiliary agent are added and stirred for 20 minutes.

[0030] The rest are as described in Example 1.

[0031] Example 3

[0032] This embodiment differs from Embodiment 1 in the following ways, as detailed below:

[0033] In step S1, 1.5 parts by weight of diethanolamine and 1 part by weight of acrylamide aqueous solution are added to the reactor and stirred at room temperature for 8 hours. The concentration of the acrylamide aqueous solution is 35%.

[0034] In step S2, 30 parts by weight of a methanol solution of methacryloyloxymethyltrimethoxysilane are added to the reactor, heated to 60°C and reacted for 50 min. Then, 200 parts by weight of the viscous liquid prepared in step S1 are added and the reaction is stirred continuously for 120 h. The mass ratio of methacryloyloxymethyltrimethoxysilane to methanol is 18:100.

[0035] In step S3, 100 parts by weight of deionized water and 40 parts by weight of tetramethylolphosphine sulfate aqueous solution were added to the reactor and mixed thoroughly. Then, 25 parts by weight of barium hydroxide octahydrate were added. After the addition was complete, the mixture was stirred for 6 hours. Under ice bath conditions, 16 parts by weight of hydrogen peroxide aqueous solution was added dropwise until the potassium iodide starch reagent changed color. After stirring for another 4 hours, the solvent was removed. The concentration of the tetramethylolphosphine sulfate aqueous solution was 75%, and the concentration of the hydrogen peroxide aqueous solution was 20%.

[0036] In step S4, 35 parts by weight of dried polyether polyol are heated to 80°C and 7 parts by weight of isocyanate are added. The temperature is raised to 120°C and reacted for 8 hours to obtain a prepolymer. Then, 0.48 parts by weight of chain extender A and 0.52 parts by weight of chain extender B are added and reacted for 60 minutes. Then, 0.1 parts by weight of crystallizer, 0.15 parts by weight of surface drying agent and 0.28 parts by weight of auxiliary agent are added and stirred for 40 minutes.

[0037] The rest are as described in Example 1.

[0038] Comparative Example 1

[0039] Compared with Example 1, the preparation method of chain extender A in this comparative example is different; otherwise, it is the same as in Example 1, as detailed below:

[0040] The preparation method of chain extender A is as follows: 1.2 parts by weight of diethanolamine and 1 part by weight of acrylamide aqueous solution are added to the reactor, stirred at room temperature for 6 hours, and the solvent is removed by rotary evaporator to obtain a viscous liquid, which is chain extender A, wherein the concentration of acrylamide aqueous solution is 30%.

[0041] The preparation method of the hot melt adhesive is the same as step S4 in Example 1, wherein the preparation of chain extender B is the same as step S3 in Example 1.

[0042] Comparative Example 2

[0043] Compared with Example 1, the chain extender A in this comparative example is diethanolamine, and the rest is the same as in Example 1, as follows:

[0044] The preparation method of the hot melt adhesive is the same as step S4 in Example 1, wherein the preparation of chain extender B is the same as step S3 in Example 1.

[0045] Comparative Example 3

[0046] Compared with Example 1, this comparative example does not add chain extender B during the preparation of the hot melt adhesive; the rest is the same as in Example 1, as follows:

[0047] The preparation method of the hot melt adhesive is as follows: 25 parts by weight of dried polyether polyol is heated to 70°C, and 5 parts by weight of isocyanate is added. The temperature is raised to 110°C and reacted for 6 hours to obtain a prepolymer. Then, 0.8 parts by weight of chain extender A is added and reacted for 45 minutes. Then, 0.1 parts by weight of crystallizer, 0.12 parts by weight of surface drying agent and 0.24 parts by weight of additive are added and stirred for 30 minutes. After stirring, the mixture is mixed at a high speed of 8000 rpm for 10 minutes and then extruded and granulated to obtain a fast-drying polyurethane hot melt adhesive. The isocyanate is diphenylmethane diisocyanate, the crystallizer is talc, and the surface drying agent is spherical silica. The preparation of chain extender A is as described in steps S1 and S2 of Example 1.

[0048] Comparative Example 4

[0049] Compared with Example 1, in the preparation process of the hot melt adhesive, ethylene glycolamine was used as a chain extender, and the rest was the same as in Example 1, as follows:

[0050] The preparation method of the hot melt adhesive is as follows: 25 parts by weight of dried polyether polyol are heated to 70°C, and 5 parts by weight of isocyanate are added. The temperature is raised to 110°C and reacted for 6 hours to obtain a prepolymer. Then, 0.78 parts by weight of chain extender ethylene glycolamine are added and reacted for 45 minutes. Then, 0.1 parts by weight of crystallizer, 0.12 parts by weight of surface drying agent and 0.24 parts by weight of additive are added and stirred for 30 minutes. After stirring, the mixture is mixed at a high speed of 8000 rpm for 10 minutes and then extruded and granulated to obtain a fast-drying polyurethane hot melt adhesive. The isocyanate is diphenylmethane diisocyanate, the crystallizer is talc, and the surface drying agent is spherical silica.

[0051] Related tests:

[0052] Bond strength test: The bond strength of the samples obtained in the examples and comparative examples was tested. The bonding performance of the hot melt adhesive was tested according to GB / T7124-2008 "Determination of tensile shear strength of adhesives (rigid material to rigid material)". Two polycarbonate substrates with dimensions of 100mm×25mm×2mm were overlapped together and then bonded with the prepared hot melt adhesive. The bonding area was 12.5mm×25mm×0.2mm. The samples were cured at 25℃ and 50%RH for 7 days, and then the tensile shear strength was tested at a tensile speed of 5mm / min. The test results are shown in Table 1.

[0053] Elongation at break test: The elongation at break of the samples obtained in the examples and comparative examples was tested. The test method was in accordance with GB / T1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". Hot melt adhesive was injected into the mold and smoothed, and cured at 25°C and 50%RH for 7 days. The cured hot melt adhesive was cut into strips with a cutter, and tensile properties were tested at a tensile speed of 10 mm / min. The test results are shown in Table 1.

[0054] Aging resistance test: After curing the hot melt adhesive prepared in the examples and comparative examples, samples of 2cm×2cm×0.2cm were prepared and placed in a constant temperature and humidity chamber at 68±2℃ and 75±3% relative humidity for 6 months. After 6 months, the presence of yellowing, oxidation, cracking, blistering and damage was recorded. If any of these occurred, the sample was considered unqualified, otherwise it was considered qualified. 50 samples were tested in each group and the pass rate of the samples was recorded. The test results are shown in Table 1.

[0055] Corrosion resistance: The hot melt adhesives prepared in the examples and comparative examples were cured to obtain 2cm×2cm×0.2cm samples for salt spray resistance testing. The test environment temperature was 35±2℃, the humidity was 95±2%, the test solution was 5wt% NaCl solution, the spray angle was 25°, the spray rate was 2mL / 80cm² / h, and the test time was 400h. After the test, the cured hot melt adhesive was observed for corrosion, peeling, cracking, and blistering. If any of these occurred, it was considered unqualified; otherwise, it was considered qualified. 50 samples were tested in each group, and the pass rate of the samples was recorded. The test results are shown in Table 1.

[0056] Table 1 Performance Test Results

[0057]

[0058] As can be seen from the test data in Table 1, the test results of Examples 1 to 3 are better than those of Comparative Examples 1 to 4, with Example 1 showing the best performance. A comparison of the test data of Example 1 and 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) shows that the hot melt adhesive prepared using chain extender A modified with methacryloyloxymethyltrimethoxysilane 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. Simultaneously, the siloxane groups can react with the active hydrogen in the substrate to form chemical bonds, effectively improving the bonding strength of the hot melt adhesive. Furthermore, the presence of the siloxane structure itself can condense to form a three-dimensional network structure, resulting in higher cohesive strength and weather resistance in the prepared hot melt adhesive.

[0059] UL-94 Flame Retardant Performance Test: The samples obtained from the examples and comparative examples were subjected to flame retardant performance tests. The test results are shown in Table 2. The UL-94 flame retardant performance test adopted the UL94 vertical burning test method of the American flame retardant material standard. The sample size was 130mm (length) × 20mm (width) × 2mm (thickness), and the thickness of the sample should not exceed 2mm. The flame retardant rating increases progressively from HB, V-2, V-1 to V-0; where: V-0: After a 10-second burning test, the dripping material should not ignite cotton, the flame should extinguish within 30 seconds, and no burning material should fall; V-1: After a 10-second burning test, the dripping material should not ignite cotton, the flame should extinguish within 60 seconds, and no burning material should fall; V-2: After two 10-second burning tests, the flame should extinguish within 60 seconds, and burning material should fall.

[0060] Open Time Test: The open time of the samples obtained from the examples and comparative examples was tested, and the test results are shown in Table 2. Open Time: Refer to standard HG / T 3716-2003. The experimental steps are as follows: 1. Place the prepared sample in an oven and heat it to 120℃ to melt, while simultaneously heating the film scraper to 120℃; 2. The test was conducted in a room temperature without airflow; 3. Quickly scrape a 0.1mm thick layer of adhesive onto a smooth plate using an adhesive film applicator and start timing; 4. After 5 seconds, cover the first adhesive strip onto the cooling adhesive layer, and then press the pressure surface of the weight onto the first adhesive strip covered with the adhesive layer. Then, sequentially cover other adhesive strips and apply pressure at 5-second intervals until the adhesive layer is cured and can no longer be bonded; 5. After the adhesive layer has cooled at room temperature for 20-30 minutes, manually peel the adhesive strip at a 90-degree angle at a uniform speed, completing the peeling of a single piece in about 2 seconds. Record the percentage of fiber peeling area for each adhesive strip and the covering time of that adhesive strip, in seconds; 6. Repeat the above steps three times. The test results are expressed as follows: the longest covering time for the adhesive surface with a fiber peeling area greater than 50% is considered the open time of the hot melt adhesive, and the range of the three measurements should not exceed 5 seconds. The test results are expressed as the same value among the three measurements.

[0061] Table 2. Flame retardancy and open time test results

[0062]

[0063] As can be seen from the test data in Table 2, the flame retardancy of Examples 1-3 and Comparative Examples 1-2 is better than that of Comparative Example 3 (without chain extender B) and Comparative Example 4 (using ethylene glycolamine as a chain extender). This is because chain extender B introduces phosphorus-containing compounds. Since phosphorus can generate compounds such as phosphoric acid and metaphosphoric acid during combustion, these compounds act as dehydrating agents, promoting the carbonization of the material to form a protective layer that isolates oxygen and heat. Therefore, the introduction of chain extender B gives the prepared polyurethane hot melt adhesive a certain degree of flame retardancy. The test results also show that the open time of the hot melt adhesives prepared in Examples 1-3 is relatively shorter than that of the hot melt adhesives prepared in Comparative Examples 1-4.

[0064] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0065] Although embodiments of this application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A process for the preparation of a quick-drying polyurethane hot melt adhesive, characterized in that, The method comprises the following steps: S1, adding diethanolamine and acrylamide aqueous solution into a reactor, stirring at room temperature for 3-8 hours, removing the solvent to obtain a viscous liquid; S2, under inert atmosphere, adding methacryloyloxymethyltrimethoxysilane methanol solution into the reactor, heating to 45-60℃ for 20-50 minutes, then adding the viscous liquid prepared in step S1, continuously stirring for 96-120 hours to obtain a crude product, dissolving the crude product in acetone, then removing the acetone by distillation under reduced pressure, repeating the operation for 3-5 times to obtain the chain extender A; S3, adding deionized water and tetramethylammonium phosphate aqueous solution into a reactor, mixing uniformly, then adding barium hydroxide octahydrate, stirring for 2-6 hours after the addition is completed, centrifuging to obtain supernatant, adding hydrogen peroxide aqueous solution under ice bath condition until the potassium iodide starch reagent changes color, stirring for 2-4 hours, then removing the solvent to obtain the chain extender B; S4, heating the dried polyether polyol to 60-80℃, then adding isocyanate, increasing the temperature to 100-120℃ for 4-8 hours to obtain a prepolymer, then adding the chain extender A and the chain extender B, reacting for 40-60 minutes, then adding a crystallization promoter, a surface drying promoter and an auxiliary agent, stirring for 20-40 minutes, then high-speed mixing, extruding and granulating to obtain the quick-drying polyurethane hot melt adhesive; In step S1, the mass ratio of diethanolamine and acrylamide aqueous solution is 1-1.5:1; In step S2, the preparation method of the methacryloyloxymethyltrimethoxysilane methanol solution is as follows: adding methacryloyloxymethyltrimethoxysilane into methanol solution and stirring until dissolved to obtain the methacryloyloxymethyltrimethoxysilane methanol solution; the mass ratio of methacryloyloxymethyltrimethoxysilane and methanol is 8-18:100; In step S3, the mass ratio of deionized water, tetramethylammonium phosphate aqueous solution, barium hydroxide octahydrate and hydrogen peroxide aqueous solution is 100:32-42:18-25:8-16; 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.

2. The method of claim 1, wherein the quick-drying polyurethane hot melt adhesive is prepared by mixing the polyol, the polyisocyanate, the chain extender, and the curing agent. In step S4, the isocyanate is one or a mixture of several of aliphatic diisocyanate, alicyclic diisocyanate and aromatic diisocyanate.

3. The method of claim 1, wherein the quick-drying polyurethane hot melt adhesive is prepared by mixing the polyol, the polyisocyanate, the chain extender, and the curing agent. In step S4, the crystallization promoter is one or a mixture of several of talc, fumed silica, titanium dioxide and calcium carbonate.

4. The method of claim 1, wherein the quick-drying polyurethane hot melt adhesive is prepared by mixing the polyol, the polyisocyanate, the chain extender, and the curing agent. In step S4, the surface drying promoter is spherical silica or alumina.

5. The method of claim 1, wherein the quick-drying polyurethane hot melt adhesive is prepared by mixing the polyol, the polyisocyanate, the chain extender, and the curing agent. In step S4, the auxiliary agent is a mixture of antioxidant, light stabilizer, anti-hydrolysis agent, lubricant and catalyst according to the mass ratio of 1:1:1:1:

1.

6. A quick-drying polyurethane hot melt adhesive prepared by the method of any one of claims 1-5.

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