Waterborne polyurethane adhesive and preparation method thereof

Abstract

The invention discloses a waterborne polyurethane adhesive and a preparation method thereof, and relates to the technical field of adhesives. The preparation method comprises the following steps: step 1, stirring dihydric alcohol, diisocyanate and water-based organic silicon to react; adding a hydrophilic chain extender and a tackifying chain extender into the mixture, and stirring for reaction; then adjusting the pH value, adding deionized water, emulsifying, and carrying out reduced pressure distillation to obtain a waterborne polyurethane emulsion; 2, the waterborne polyurethane emulsion, the wetting agent, the defoaming agent, the thickening agent and the flatting agent are stirred and mixed to be uniform, and the waterborne polyurethane adhesive is obtained. Wherein the waterborne polyurethane adhesive is prepared from the following raw material components in parts by weight: 60 to 80 parts of waterborne polyurethane emulsion, 0.5 to 2 parts of a wetting agent, 0.3 to 1.5 parts of a de-foaming agent, 0.2 to 1 part of a thickening agent and 0.3 to 1.2 parts of a flatting agent.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a water-based polyurethane adhesive and its preparation method. Background Technology

[0002] Waterborne polyurethane adhesives, due to their advantages such as no VOC emissions, environmental friendliness, high bonding strength, and good film-forming properties, have become an important alternative to traditional solvent-based adhesives, with increasing demand in packaging, textiles, and building materials. However, existing waterborne polyurethane adhesives still have several shortcomings in practical applications: First, conventional waterborne polyurethane adhesives have poor initial tack, making it difficult to meet the needs of rapid bonding; second, the hydrophilic-hydrophobic balance of waterborne polyurethane molecular chains is difficult to control, resulting in poor water resistance and a significant decrease in bonding strength after immersion in water, affecting durability; third, the film-forming and leveling properties of conventional waterborne polyurethane adhesives are easily affected by the raw material ratio, and their storage stability and applicability to construction also need improvement.

[0003] Based on this, the present invention provides a waterborne polyurethane adhesive with excellent comprehensive properties such as bonding performance and washability, which is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a waterborne polyurethane adhesive and its preparation method to solve the problems mentioned in the background art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: A method for preparing a waterborne polyurethane adhesive includes the following steps: Step 1: First, stir the diol, diisocyanate, and water-based organosilicon to react; then add the hydrophilic chain extender and the thickening chain extender and stir to react; then adjust the pH, add deionized water, emulsify, and distill under reduced pressure to obtain the water-based polyurethane emulsion. Step 2: Add the waterborne polyurethane emulsion, wetting agent, defoamer, thickener, and leveling agent to the reaction vessel, stir and mix well to obtain the waterborne polyurethane adhesive.

[0006] Further, the waterborne polyurethane adhesive comprises the following raw material components in parts by weight: 60-80 parts of waterborne polyurethane emulsion, 0.5-2 parts of wetting agent, 0.3-1.5 parts of defoamer, 0.2-1 parts of thickener, and 0.3-1.2 parts of leveling agent.

[0007] Further, the preparation method of the waterborne polyurethane emulsion is as follows: under a nitrogen atmosphere, dehydrated diol, diisocyanate, waterborne organosilicon, dibutyltin dilaurate, and acetone are added to a reaction vessel, stirred and mixed, and reacted at 70~85℃ for 2~4h; then hydrophilic chain extender and thickening chain extender are added, and the reaction is continued to be carried out at a constant temperature and stirred for 1~2h; the temperature is lowered to 30~45℃, triethylamine is added to adjust the pH, then deionized water is added, and high-speed emulsification is carried out for 1~3h; acetone is removed by vacuum distillation to obtain the waterborne polyurethane emulsion.

[0008] Furthermore, the aqueous polyurethane emulsion preparation comprises the following raw material components in parts by weight: 25-35 parts of diol, 18-28 parts of diisocyanate, 4-6 parts of aqueous organosilicon, 0.03-0.08 parts of dibutyltin dilaurate, 15-25 parts of acetone, 4-8 parts of hydrophilic chain extender, 1-3 parts of tackifying chain extender, 70-90 parts of deionized water, and triethylamine to adjust the pH to 7-7.5.

[0009] Furthermore, the diol is a polyether diol, including but not limited to one or more combinations of polytetrahydrofuran ether diol, polyoxypropylene diol, polyether N-210, polyether N-220, and polyether N-240, with an average molecular weight of 1000-2000.

[0010] Furthermore, the diisocyanate is one or a combination of two of isophorone diisocyanate and hexamethylene diisocyanate.

[0011] Further, the preparation method of the aqueous organosilicon is as follows: Under a nitrogen atmosphere, octamethylcyclotetrasiloxane, siloxane-terminated polyethylene glycol, tetramethylammonium hydroxide, and anhydrous ethanol are added to a reaction vessel, stirred and mixed, and reacted at 50-70°C for 2-4 hours; amino-based siloxanes are added dropwise, and the reaction is maintained at this temperature and stirred for 1-3 hours; then esterified carboxyl-based siloxanes are added dropwise, and the reaction is maintained at this temperature and stirred for 1-3 hours; the temperature is lowered to room temperature, and a 10wt% dichloromethane solution of trifluoroacetic acid is added, and the reaction is stirred for 1-2 hours; dichloromethane is removed by vacuum distillation, and the temperature is maintained at 150-160°C for 30-60 minutes; the temperature is lowered to 40-50°C, and triethylamine is added to adjust the pH; the reaction is then carried out by vacuum distillation to obtain the aqueous organosilicon.

[0012] Further, the aqueous organosilicon preparation comprises the following raw material components in parts by weight: 4-5 parts of octamethylcyclotetrasiloxane, 1.5-2.5 parts of siloxane-terminated polyethylene glycol, 0.05-0.1 parts of tetramethylammonium hydroxide, 4-6 parts of anhydrous ethanol, 0.8-1.5 parts of aminosiloxane, 0.6-1.2 parts of esterified carboxylsiloxane, 2.4-3 parts of a dichloromethane solution of trifluoroacetic acid, and triethylamine to adjust the pH to 7-8.

[0013] Furthermore, the average molecular weight of the siloxane-terminated polyethylene glycol is 400-2000.

[0014] Furthermore, the amino-based siloxanes include, but are not limited to, one or more combinations of γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropylmethyldimethoxysilane, and γ-aminopropylmethyldiethoxysilane.

[0015] Furthermore, the esterified carboxyl siloxane is an esterified modified carboxyl siloxane, and its preparation method is as follows: add the carboxyl siloxane to anhydrous ethanol, stir and mix for 30-60 min, then add 98 wt% concentrated sulfuric acid, stir and react at 60-70℃ for 1-3 h, and after it cools naturally to room temperature, distill under reduced pressure to obtain the esterified carboxyl siloxane.

[0016] Furthermore, the preparation of the esterified carboxyl siloxane includes the following raw material components in parts by weight: 1.25-1.5 parts of carboxyl siloxane, 2.5-3 parts of anhydrous ethanol, and 0.05-0.15 parts of concentrated sulfuric acid.

[0017] Furthermore, the carboxylated siloxane is prepared by referring to the preparation method of carboxylated silane coupling agent disclosed in the prior art CN115947750A "Carboxylated silane coupling agent and preparation method thereof".

[0018] Furthermore, the hydrophilic chain extender is 2,2-dihydroxymethylpropionic acid.

[0019] Furthermore, the thickening and chain extender is a polyamide polyamine, which is prepared by referring to the preparation method of polyamide polyamine prepolymer disclosed in the prior art CN115044036A "A method for preparing polyamide polyamine epichlorohydrin resin".

[0020] Furthermore, the wetting agent is a nonionic polyoxyethylene ether wetting agent.

[0021] Furthermore, the defoamer is an organosilicon defoamer.

[0022] Furthermore, the thickener is one or a combination of two of hydroxyethyl cellulose thickeners or polyurethane thickeners.

[0023] Furthermore, the leveling agent is a polyether-modified silicone leveling agent.

[0024] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) In this invention, under the action of tetramethylammonium hydroxide, octamethylcyclotetrasiloxane undergoes ring opening and polymerizes with siloxane-terminated polyethylene glycol to form a copolymer structure that combines hydrophobic segments of polysiloxane and hydrophilic segments of polyethylene glycol. Then, amino and ester groups are further introduced into the structure by stepwise grafting of amino-based siloxanes and esterified carboxyl-based siloxanes. The reason for the esterification modification of carboxyl groups is to utilize the protective effect of ester groups on carboxyl groups, thereby avoiding side reactions between amino and carboxyl groups. After subsequent treatment with trifluoroacetic acid, the ester groups can be further reduced to carboxyl groups. After the introduction of trifluoroacetic acid, the pH of the reaction system becomes acidic. At this time, the amino group will be protonated, which can also avoid the amidation side reaction with carboxyl groups during subsequent purification at 150~160℃. Finally, triethylamine is added to adjust the pH, so that the protonated amino group is reduced to a free amino group, thereby preparing an aqueous organosilicon containing hydrophilic polyethylene glycol segments, hydrophobic polydimethylsiloxane segments, and amino and carboxyl groups. Among them, siloxane-terminated polyethylene glycol, as a hydrophilic segment, endows organosilicon with excellent hydrophilicity and water dispersibility, improving its compatibility with waterborne polyurethane; the polydimethylsiloxane backbone provides water resistance, weather resistance, and low surface energy properties; amino groups can participate in subsequent polyurethane chemical bonding, thereby realizing the modification of polyurethane by waterborne organosilicon; and carboxyl groups are used to improve the adhesive properties of the adhesive.

[0025] (2) In this invention, waterborne organosilicon is the core modifying component of waterborne polyurethane emulsion. By chemically bonding it with the polyurethane molecular chain, the performance of waterborne polyurethane adhesive is improved from multiple dimensions. First, hydrophilic polyethylene glycol segments are introduced into the waterborne polyurethane, which greatly improves the compatibility between the waterborne organosilicon segments and the waterborne polyurethane system, ensuring the stability of the waterborne polyurethane emulsion. Second, hydrophobic siloxane segments are introduced into the waterborne polyurethane, which can improve the water resistance of the adhesive and ensure the long-term stability of the adhesive. At the same time, the siloxane segments can also combine with the polyethylene glycol segments to optimize the rigidity and flexibility of the adhesive film, ensuring film formation and preventing the adhesive film layer from becoming brittle. Subsequently, hydrophilic chain extenders and tackifying chain extenders are added. The hydrophilic chain extender participates in the polyurethane chain extension reaction through hydroxyl groups, increasing the polymer molecular weight and cohesive strength. The carboxyl groups it contains are neutralized to form hydrophilic groups, ensuring the stability of polyurethane water dispersion and enhancing the interfacial adhesion with polar substrates. The tackifier and chain extender contain multiple amino active sites, which can further improve the crosslinking density and intermolecular forces of the system, significantly enhancing the initial tack, peel strength, and cohesive strength of the adhesive, and improving the mechanical properties of the adhesive layer. Ultimately, through the synergistic effect of the waterborne silicone, hydrophilic chain extender, and tackifier / chain extender, the waterborne polyurethane adhesive ensures uniform and stable dispersion in water, while also exhibiting high adhesive strength, good film-forming properties, and excellent water resistance and aging resistance.

[0026] (3) Wetting agents are used to reduce the surface tension between the waterborne polyurethane adhesive and the substrate, thereby improving the wettability and interfacial bonding of the adhesive, and have a significant positive effect on the bonding performance of the waterborne polyurethane adhesive; defoamers and leveling agents are used to improve the film-forming properties and leveling properties of the adhesive, and improve the bonding stability of the waterborne polyurethane adhesive; thickeners can adjust the viscosity of the adhesive and improve the applicability of the waterborne polyurethane adhesive for construction. With the reasonable combination of various additives, the comprehensive performance of the waterborne polyurethane adhesive prepared by this invention is further optimized.

[0027] In summary, this invention has comprehensively prepared a waterborne polyurethane adhesive with excellent overall performance, including bonding and water resistance. It greatly solves the defects of traditional waterborne polyurethane adhesives and demonstrates significant practicality and application value. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] It should be noted that the following quantities are by weight, and there are no special restrictions on the suppliers of all raw materials involved in this invention. Exemplary examples include: In the following examples, siloxane-terminated polyethylene glycol, catalog number R-12081, with an average molecular weight of 1000, was purchased from Xi'an Ruixi Biotechnology Co., Ltd. The carboxylated siloxanes are prepared according to the preparation method of carboxylated silane coupling agents disclosed in the existing technology CN115947750A "Carboxylated Silane Coupling Agents and Their Preparation Methods". The specific preparation method is as follows: under nitrogen protection, piperazine propyltrimethoxysilane and chloroform are added to a reaction vessel, stirred and mixed, then acrylic acid is added, and the reaction is stirred at room temperature for 0.5 h. Chloroform is distilled off under normal pressure, and then distilled under reduced pressure to obtain carboxylated siloxanes (carboxylated triethoxysilanes); wherein the mass ratio of piperazine methyltrimethoxysilane, acrylic acid and chloroform is 1:0.19:2. The polyamide polyamine was prepared by referring to the preparation method of polyamide polyamine prepolymer disclosed in the existing technology CN115044036A "A Preparation Method of Polyamide Polyamine Epichlorohydrin Resin"; the specific preparation method is as follows: adipic acid and diethylenetriamine are added to a reaction vessel, stirred and mixed, then 98wt% concentrated sulfuric acid is added, and the mixture is stirred and reacted at 120℃ for 10h. After it is naturally cooled to room temperature, it is distilled under reduced pressure to obtain polyamide polyamine; wherein, the mass ratio of adipic acid, diethylenetriamine and concentrated sulfuric acid is 1:0.71:0.055. Polytetrahydrofuran ether diol, molecular weight 1500; isophorone diisocyanate; dibutyltin dilaurate; octamethylcyclotetrasiloxane, CAS No. 556-67-2; tetramethylammonium hydroxide; γ-aminopropyltrimethoxysilane; 2,2-dimethylolpropionic acid, CAS No. 4767-03-7; piperazinepropyltrimethoxysilane, CAS No. 40762-28-5; acrylic acid; adipic acid; diethylenetriamine; AEO-9 type fatty alcohol polyoxyethylene ether; SGR1830 type defoamer; PUR-50A type polyurethane thickener; BYK-333 type polyether modified silicone leveling agent; HA-304W type waterborne polyurethane adhesive, solid content 39±1wt%; and other raw materials are all commercially available; each part by weight is 50g. Example 1: A method for preparing a waterborne polyurethane adhesive:

[0030] S1: Preparation of waterborne polyurethane emulsion: S11: Preparation of esterified carboxyl siloxanes: 1.375 parts of carboxylated triethoxysilane were added to 2.75 parts of anhydrous ethanol and stirred for 45 min. Then, 0.1 parts of 98 wt% concentrated sulfuric acid were added and stirred at 65 °C for 2 h. After it cooled naturally to room temperature, it was distilled under reduced pressure to obtain esterified carboxyl siloxanes. S12: Preparation of aqueous organosilicon: Under a nitrogen atmosphere, 4.5 parts of octamethylcyclotetrasiloxane, 2 parts of siloxane-terminated polyethylene glycol, 0.075 parts of tetramethylammonium hydroxide, and 5 parts of anhydrous ethanol were added to a reaction vessel and stirred until homogeneous. The mixture was stirred at 60°C for 3 hours. 1.15 parts of γ-aminopropyltrimethoxysilane were added dropwise and stirred at this temperature for 2 hours. Then, 0.9 parts of esterified carboxyl siloxane were added dropwise and stirred at this temperature for 2 hours. The mixture was cooled to room temperature, and 2.7 parts of a 10wt% trifluoroacetic acid solution in dichloromethane were added and stirred for 1.5 hours. Dichloromethane was removed by vacuum distillation, and the mixture was kept at 155°C for 45 minutes. The mixture was cooled to 45°C, and triethylamine was added to adjust the pH to 7.5. The mixture was then distilled at vacuum to obtain aqueous organosilicon. S13: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 5 parts of waterborne organosilicon, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 6 parts of 2,2-dimethylolpropionic acid and 2 parts of polyamide polyamine were added, and the reaction was continued with stirring for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added, and the mixture was emulsified at high speed for 2 hours. The acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion. S2: Add 70 parts of waterborne polyurethane emulsion, 1.25 parts of AEO-9 type fatty alcohol polyoxyethylene ether, 0.9 parts of SGR1830 type defoamer, 0.6 parts of PUR-50A type polyurethane thickener, and 0.9 parts of BYK-333 type polyether modified silicone leveling agent to a reaction vessel, stir and mix well to obtain waterborne polyurethane adhesive. Example 2: A method for preparing a waterborne polyurethane adhesive: Example 2 is based on Example 1, but with adjustments made to the raw material composition of the waterborne polyurethane adhesive, while keeping other processes unchanged. The details are as follows:

[0031] S2: Add 70 parts of waterborne polyurethane emulsion, 0.5 parts of AEO-9 type fatty alcohol polyoxyethylene ether, 0.3 parts of SGR1830 type defoamer, 0.2 parts of PUR-50A type polyurethane thickener, and 0.3 parts of BYK-333 type polyether modified silicone leveling agent to a reaction vessel, stir and mix well to obtain waterborne polyurethane adhesive. Example 3: A method for preparing a waterborne polyurethane adhesive: Example 3 is based on Example 1, but with adjustments made to the raw material composition of the waterborne polyurethane adhesive, while other processes remain unchanged, as follows:

[0032] S2: Add 70 parts of waterborne polyurethane emulsion, 2 parts of AEO-9 type fatty alcohol polyoxyethylene ether, 1.5 parts of SGR1830 type defoamer, 1 part of PUR-50A type polyurethane thickener, and 1.2 parts of BYK-333 type polyether modified silicone leveling agent to a reaction vessel, stir and mix well to obtain waterborne polyurethane adhesive. Example 4: A method for preparing a waterborne polyurethane adhesive: Example 4 is based on Example 1, but with the following adjustment: the amount of water-based organosilicon added, while other processes remain unchanged, as follows:

[0033] S13: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 4 parts of waterborne organosilicon, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 6 parts of 2,2-dimethylolpropionic acid and 2 parts of polyamide polyamine were added, and the reaction was continued with stirring for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added, and the mixture was emulsified at high speed for 2 hours. The acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion. Example 5: A method for preparing a waterborne polyurethane adhesive: Example 5 is based on Example 1, with the following adjustment: the amount of water-based organosilicon added, while other processes remain unchanged, as follows:

[0034] S13: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 6 parts of waterborne organosilicon, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 6 parts of 2,2-dimethylolpropionic acid and 2 parts of polyamide polyamine were added, and the reaction was continued with stirring for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added, and the mixture was emulsified at high speed for 2 hours. The acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion. The following is a control experiment based on Example 1, with comparative examples 1 to 6, as detailed below:

[0035] Comparative Example 1: A method for preparing a waterborne polyurethane adhesive: Comparative Example 1 is based on Example 1, with the following adjustment: siloxane-terminated polyethylene glycol is not added during the preparation of the aqueous organosilicon, while other processes remain unchanged. Specifically:

[0036] S12: Preparation of aqueous organosilicon: Under a nitrogen atmosphere, 4.5 parts of octamethylcyclotetrasiloxane, 0.075 parts of tetramethylammonium hydroxide, and 5 parts of anhydrous ethanol were added to a reaction vessel and stirred until homogeneous. The mixture was stirred at 60°C for 3 hours. 1.15 parts of γ-aminopropyltrimethoxysilane were added dropwise and stirred at this temperature for 2 hours. Then, 0.9 parts of esterified carboxyl siloxane were added dropwise and stirred at this temperature for 2 hours. The mixture was cooled to room temperature, and 2.7 parts of a 10wt% trifluoroacetic acid solution in dichloromethane were added and stirred for 1.5 hours. Dichloromethane was removed by vacuum distillation, and the mixture was kept at 155°C for 45 minutes. The mixture was cooled to 45°C, and triethylamine was added to adjust the pH to 7.5. The mixture was then distilled at vacuum to obtain aqueous organosilicon.

[0037] Comparative Example 2: A method for preparing a waterborne polyurethane adhesive: Comparative Example 2 is based on Example 1, with the following adjustment: During the preparation of the aqueous organosilicon, the esterification modification of carboxyl siloxanes (carboxylated triethoxysilanes) is not performed, while other processes remain unchanged. Specifically:

[0038] S1: Preparation of waterborne polyurethane emulsion: S11: Preparation of aqueous organosilicon: Under a nitrogen atmosphere, 4.5 parts of octamethylcyclotetrasiloxane, 2 parts of siloxane-terminated polyethylene glycol, 0.075 parts of tetramethylammonium hydroxide, and 5 parts of anhydrous ethanol were added to a reaction vessel and stirred until homogeneous. The mixture was stirred at 60°C for 3 hours. 1.15 parts of γ-aminopropyltrimethoxysilane were added dropwise and stirred at the same temperature for 2 hours. Then, 0.9 parts of carboxyl siloxane (carboxylated triethoxysilane) were added dropwise and stirred at the same temperature for 2 hours. The mixture was cooled to room temperature, and 2.7 parts of a 10wt% trifluoroacetic acid solution in dichloromethane were added and stirred for 1.5 hours. Dichloromethane was removed by vacuum distillation, and the mixture was kept at 155°C for 45 minutes. The mixture was cooled to 45°C, and triethylamine was added to adjust the pH to 7.5. The mixture was then distilled at the same temperature to obtain aqueous organosilicon.

[0039] Comparative Example 3: A method for preparing a waterborne polyurethane adhesive: Comparative Example 3 is based on Example 1, with the following adjustment: waterborne organosilicon is not added in the preparation of the waterborne polyurethane emulsion, while other processes remain unchanged. Specifically:

[0040] S12: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 6 parts of 2,2-dimethylolpropionic acid and 2 parts of polyamide polyamine were added, and the reaction was continued to be carried out at the same temperature and stirred for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added, and the mixture was emulsified at high speed for 2 hours. The acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion.

[0041] Comparative Example 4: A method for preparing a waterborne polyurethane adhesive: Comparative Example 4 is based on Example 1, with the following adjustment: 2,2-dimethylolpropionic acid is not added in the preparation of the waterborne polyurethane emulsion, while other processes remain unchanged. Specifically:

[0042] S13: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 5 parts of waterborne organosilicon, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 2 parts of polyamide polyamine were added, and the reaction was continued with stirring for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added, emulsified at high speed for 2 hours, and acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion.

[0043] Comparative Example 5: A method for preparing a waterborne polyurethane adhesive: Comparative Example 5 is based on Example 1, with the following adjustment: polyamide polyamine is not added during the preparation of the waterborne polyurethane emulsion, while other processes remain unchanged. Specifically:

[0044] S13: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 5 parts of waterborne organosilicon, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 6 parts of 2,2-dimethylolpropionic acid were added, and the reaction was continued with stirring for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added. The mixture was emulsified at high speed for 2 hours, and acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion.

[0045] Comparative Example 6: A method for preparing a waterborne polyurethane adhesive: Comparative Example 6 is based on Example 1, with the following adjustment: waterborne polyurethane emulsion is directly used as the waterborne polyurethane adhesive, while other processes remain unchanged. Specifically:

[0046] S13: Preparation of waterborne polyurethane emulsion: Under a nitrogen atmosphere, 30 parts of dehydrated polytetrahydrofuran ether diol, 23 parts of isophorone diisocyanate, 5 parts of waterborne organosilicon, 0.06 parts of dibutyltin dilaurate, and 20 parts of acetone were added to a reaction vessel, stirred and mixed, and reacted at 78°C for 3 hours; then 6 parts of 2,2-dimethylolpropionic acid and 2 parts of polyamide polyamine were added, and the reaction was continued with stirring for 1.5 hours; the temperature was lowered to 38°C, triethylamine was added to adjust the pH to 7.2, and then 80 parts of deionized water were added, and the mixture was emulsified at high speed for 2 hours. The acetone was removed by vacuum distillation to obtain the waterborne polyurethane emulsion, i.e., the waterborne polyurethane adhesive.

[0047] Comparative Example 7: Commercially available HA-304W waterborne polyurethane adhesive. Performance testing: The waterborne polyurethane adhesives prepared in Examples 1-5 and Comparative Examples 1-7 were uniformly coated onto the surface of a PVC substrate measuring 200 mm (length) × 25 mm (width) × 1.5 mm (thickness) using a coater. The coating amount was 40 ± 2 g / m². 2 A PVC substrate coated with water-based polyurethane adhesive was left to stand at room temperature for 5 minutes, then baked at 70°C for 4 minutes. Next, another PVC substrate was bonded to the adhesive surface and compacted under a pressure of 1 MPa for 15 seconds to obtain a bonded sample. The bonded sample was then subjected to initial tack strength testing, peel strength testing after complete curing, and water resistance testing. The specific testing methods are as follows:

[0048] (1) Initial bond strength test: After the bonded sample has been pressed for 15 minutes, the 180° peel strength test is performed according to the standard of GB / T 2790-1995, with a peel rate of 100 mm / min. (2) Peel strength test: After the adhesive has been bonded and compacted for 24 hours, the adhesive sample is subjected to a 180° peel strength test according to the standard of GB / T 2790-1995, with a peel rate of 100 mm / min. (3) Water resistance test: After the bonding and compaction for 24 hours, the bonded sample is completely immersed in water at 25°C for 24 hours. After taking it out and wiping off the surface moisture, the bonded sample is subjected to a 180° peel strength test according to the standard of GB / T 2790-1995, with a peel rate of 100 mm / min. The peel strength retention rate of the bonded sample is calculated by: peel strength after immersion / peel strength before immersion × 100% = peel strength retention rate (%). The water resistance of the water-based polyurethane adhesive is evaluated based on this.

[0049] The specific test data results are shown in Table 1 below: Table 1 Results Analysis: The data in Table 1 above show that: Comparing Examples 1 and 2-3: In Example 2, the performance of the waterborne polyurethane adhesive was significantly reduced due to the decrease in the amount of additives; in Example 3, the amount of additives was increased, but the performance did not fluctuate significantly and tended to be stable. Comparing Examples 1 and 4-5: In Example 4, due to the reduced amount of waterborne silicone, the degree of modification of waterborne polyurethane decreased, resulting in a significant decrease in the adhesive properties and water resistance of the waterborne polyurethane adhesive; In Example 5, the increased amount of waterborne silicone slightly reduced the compatibility between waterborne polyurethane and silicone, leading to a decrease in the relevant properties of the waterborne polyurethane adhesive, but due to the higher silicone content and more hydrophobic siloxane segments, the water resistance was slightly improved. Comparing Example 1 with Comparative Examples 1-6: Comparative Examples 1-6 lacked the relevant technical features of the present invention, resulting in a significant decrease in initial tack strength, peel strength after curing, and peel strength retention rate, demonstrating the necessity of the design of each component and related technical solution of the present invention.

[0050] In summary, this invention has comprehensively prepared a waterborne polyurethane adhesive with excellent overall performance, including bonding and water resistance. It greatly solves the defects of traditional waterborne polyurethane adhesives and demonstrates significant practicality and application value.

[0051] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a waterborne polyurethane adhesive, characterized in that: Includes the following steps: Step 1: First, stir the diol, diisocyanate, and water-based organosilicon to react; then add the hydrophilic chain extender and thickening chain extender and stir to react; then adjust the pH, add deionized water, emulsify, and distill under reduced pressure to obtain water-based polyurethane emulsion. Step 2: Mix the waterborne polyurethane emulsion, wetting agent, defoamer, thickener, and leveling agent to obtain the waterborne polyurethane adhesive. The waterborne polyurethane adhesive comprises the following raw material components in parts by weight: 60-80 parts waterborne polyurethane emulsion, 0.5-2 parts wetting agent, 0.3-1.5 parts defoamer, 0.2-1 part thickener, and 0.3-1.2 parts leveling agent.

2. The method for preparing a waterborne polyurethane adhesive according to claim 1, characterized in that: The method for preparing the waterborne polyurethane emulsion is as follows: Under a nitrogen atmosphere, diol, diisocyanate, waterborne organosilicon, dibutyltin dilaurate, and acetone are stirred and mixed, and reacted at 70-85°C; then hydrophilic chain extender and thickening chain extender are added, and the reaction is continued with stirring at the same temperature; the temperature is lowered to 30-45°C, then triethylamine is added to adjust the pH, followed by the addition of deionized water, emulsification, and acetone is removed by vacuum distillation to obtain the waterborne polyurethane emulsion; The aqueous polyurethane emulsion is prepared by the following raw material components in parts by weight: 25-35 parts of diol, 18-28 parts of diisocyanate, 4-6 parts of aqueous organosilicon, 0.03-0.08 parts of dibutyltin dilaurate, 15-25 parts of acetone, 4-8 parts of hydrophilic chain extender, 1-3 parts of tackifying chain extender, 70-90 parts of deionized water, and triethylamine is used to adjust the pH to 7-7.

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3. The method for preparing a waterborne polyurethane adhesive according to claim 2, characterized in that: The method for preparing the aqueous organosilicon is as follows: Under a nitrogen atmosphere, octamethylcyclotetrasiloxane, siloxane-terminated polyethylene glycol, tetramethylammonium hydroxide, and anhydrous ethanol are stirred and mixed, and reacted at 50-70°C; amino-based siloxanes are added dropwise, and the mixture is stirred while maintaining the temperature; esterified carboxyl-based siloxanes are added dropwise, and the mixture is stirred while maintaining the temperature; the mixture is cooled to room temperature, and a dichloromethane solution of trifluoroacetic acid is added, and the mixture is stirred while reacting; dichloromethane is removed by vacuum distillation, and the mixture is kept at 150-160°C; the mixture is cooled to 40-50°C, and triethylamine is added to adjust the pH; the mixture is then distilled under vacuum to obtain the aqueous organosilicon. The aqueous organosilicon preparation comprises the following raw material components in parts by weight: 4-5 parts of octamethylcyclotetrasiloxane, 1.5-2.5 parts of siloxane-terminated polyethylene glycol, 0.05-0.1 parts of tetramethylammonium hydroxide, 4-6 parts of anhydrous ethanol, 0.8-1.5 parts of aminosiloxane, 0.6-1.2 parts of esterified carboxylsiloxane, 2.4-3 parts of a dichloromethane solution of trifluoroacetic acid, and triethylamine to adjust the pH to 7-8.

4. The method for preparing a waterborne polyurethane adhesive according to claim 3, characterized in that: The average molecular weight of the siloxane-terminated polyethylene glycol is 400-2000.

5. The method for preparing a waterborne polyurethane adhesive according to claim 3, characterized in that: Esterified carboxyl siloxanes are esterified modified carboxyl siloxanes. The preparation method is as follows: add carboxyl siloxanes to anhydrous ethanol, stir and mix well, then add 98wt% concentrated sulfuric acid, stir and react at 60~70℃, and after it cools naturally to room temperature, distill under reduced pressure to obtain esterified carboxyl siloxanes. The preparation of the esterified carboxyl siloxane includes the following raw material components in parts by weight: 1.25-1.5 parts carboxyl siloxane, 2.5-3 parts anhydrous ethanol, and 0.05-0.15 parts concentrated sulfuric acid.

6. The method for preparing a waterborne polyurethane adhesive according to claim 2, characterized in that: The diol is a polyether diol, including one or more of polytetrahydrofuran ether diol, polypropylene oxide diol, polyether N-210, polyether N-220, and polyether N-240, with an average molecular weight of 1000-2000; the diisocyanate is one or a combination of two of isophorone diisocyanate and hexamethylene diisocyanate.

7. The method for preparing a waterborne polyurethane adhesive according to claim 2, characterized in that: The hydrophilic chain extender is 2,2-dihydroxymethylpropionic acid.

8. The method for preparing a waterborne polyurethane adhesive according to claim 2, characterized in that: The thickening and chain extender is a polyamide polyamine.

9. The method for preparing a waterborne polyurethane adhesive according to claim 1, characterized in that: The wetting agent is a nonionic polyoxyethylene ether wetting agent; the defoamer is an organosilicone defoamer; the thickener is one or a combination of two of hydroxyethyl cellulose thickener or polyurethane thickener; and the leveling agent is a polyether-modified organosilicone leveling agent.

10. The waterborne polyurethane adhesive prepared by the method according to any one of claims 1 to 9.

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