Aqueous polyurethane adhesive material and process for its preparation

Abstract

The application discloses a kind of water-based polyurethane adhesive materials and preparation method thereof, it is related to adhesive material preparation technical field.The component used in the application takes isocyanate, polycaprolactone dihydric alcohol PCL2000 as main raw material, 2,2-bis (hydroxymethyl) propionic acid and the like as hydrophilic chain extender, 1,4-butanediol as small molecule chain extender, triethylamine is neutralizing agent, and hydrophilic polyurethane prepolymer is synthesized, and low-temperature deionized water is added under high-speed shearing to synthesize water-based polyurethane adhesive.The water-based polyurethane adhesive material prepared in the application has high solid content, low water absorption, excellent tensile strength, bonding performance and anti-sagging property.

Description

Technical Field

[0001] This invention relates to the field of adhesive material preparation technology, and more specifically to an aqueous polyurethane adhesive material and its preparation method. Background Technology

[0002] When polyurethane is used in adhesives, it is generally dispersed in organic solvents or water to prepare dispersions or emulsions, which are then sprayed onto the substrate surface. Polyurethane dispersed in organic solvents is called solvent-based polyurethane, while polyurethane dispersed in water is called waterborne polyurethane. However, solvent-based polyurethane adhesives release large amounts of volatile organic compounds (VOCs) during use, causing serious harm to human health and the environment. With the rapid development of industrial technology and the increasing global awareness of environmental protection, environmental regulations in various countries are becoming increasingly stringent. Against this backdrop, waterborne polyurethane, with its advantages of not containing harmful volatile organic compounds (VOCs) during production and use, low toxicity, energy saving and environmental protection, and being more friendly to ecosystems and human health, is gradually replacing traditional solvent-based polyurethane and becoming an important development direction in the adhesive field. Waterborne polyurethane adhesives can effectively solve the environmental and safety problems of traditional solvent-based adhesives. Compared with solvent-based products, green and environmentally friendly waterborne polyurethane adhesives can reduce VOC emissions by more than 95%. Its core characteristic lies in using water as the main solvent. By introducing hydrophilic chain extenders into the molecular backbone, the hydrophilic groups give the emulsion good stability, excellent low-temperature stability, and strong mechanical properties. These characteristics give it significant advantages in environmental performance and transportation safety, demonstrating broad application prospects.

[0003] Waterborne polyurethane retains the inherent properties of polyurethane, such as wear resistance, corrosion resistance, flexibility, and high elasticity. However, due to its water-based dispersion medium, its solid content is low, leading to slower curing rates at room temperature, increased susceptibility to water absorption and swelling, and decreased adhesive performance. To address these issues, its molecular structure needs to be designed and controlled through synthetic modification. In the preparation of waterborne polyurethane adhesives, the solid content can be increased by adjusting the formulation ratio and process conditions, thereby enhancing its storage stability and mechanical properties.

[0004] However, there is still a lack of waterborne polyurethane adhesive materials on the market that combine high solids content, low water absorption, and excellent mechanical properties.

[0005] In existing technologies for preparing two-component waterborne polyurethane adhesives, it is often necessary to introduce trimethylolpropane (TMP) as an internal crosslinking agent and silicone as an external crosslinking agent, and finally, a closed-type waterborne isocyanate curing agent is required to form a two-component adhesive system. Existing methods rely on crosslinking agents to improve the mechanical properties of the adhesive film, which has significant drawbacks: ① The polyhydroxy structure of TMP significantly increases the crosslinking density of the system, resulting in excessively rigid molecular chains and a significant decrease in the flexibility of the adhesive film, making it prone to warping and peeling failure when bonding to flexible substrates; ② The silicone crosslinking agent has poor compatibility with the polyurethane matrix, easily causing phase separation during storage, and the emulsion is prone to stratification and precipitation upon standing, significantly reducing storage stability; ③ The two-component system requires on-site mixing of the curing agent, making the construction process cumbersome, and the curing agent adds to the raw material cost. Uncured mixed waste cannot be recycled, resulting in insufficient environmental friendliness and ease of use; ④ A large number of crosslinking sites increases the gaps between hydrophilic micro-regions inside the adhesive film, leading to a high water absorption rate and poor water resistance and adhesion.

[0006] Therefore, there is still a lack of waterborne polyurethane adhesive materials that can achieve high solids content, low water absorption, and excellent mechanical and anti-sagging properties without the need for internal or external crosslinking agents and with only one component. Summary of the Invention

[0007] In view of this, the present invention provides an aqueous polyurethane adhesive material and a method for preparing the same.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A water-based polyurethane adhesive material, comprising the following raw materials in parts by weight: Polycaprolactone diol 40.0 parts, isocyanate 25.8-40.1 parts, hydrophilic chain extender 2.0-5.0 parts, N-methylpyrrolidone 4.0-10.0 parts, 1,4-butanediol 3.4-4.6 parts, triethylamine (TEA) 0-3.7 parts, water 89.0-113.5 parts.

[0010] The present invention does not add any trimethylolpropane or other internal crosslinking agents, or organosilicon or other external crosslinking agents, and does not require the addition of isocyanate curing agents. It achieves high performance of single-component finished products by relying on molecular chain structure regulation and rheological modification, thereby avoiding the defects of hard and brittle film caused by crosslinking agents.

[0011] Furthermore, the polycaprolactone diol is polycaprolactone diol PCL2000.

[0012] Furthermore, the isocyanate is any one of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), and toluene diisocyanate (TDI), preferably IPDI.

[0013] The above scheme can increase the degree of reaction between polycaprolactone diol PCL2000 and IPDI, allowing them to react fully.

[0014] Furthermore, the equivalence ratio (isocyanate index, R value) of isocyanate group (-NCO) to hydroxyl group (-OH) is 1.3-1.7:1.

[0015] Preferably, the R value is 1.6, and the above scheme can enable the waterborne polyurethane emulsion to have a high solid content and tensile strength.

[0016] Furthermore, the hydrophilic chain extender is any one of 2,2-bis(hydroxymethyl)propionic acid (DMPA), 2,2-dihydroxymethylbutyric acid (DMBA), and sodium salt of 2-[(2-aminoethyl)amino]ethanesulfonate (AAS), preferably DMBA.

[0017] Furthermore, the amount of hydrophilic chain extender added is 3%-6% (based on the mass fraction of the hydrophilic waterborne polyurethane prepolymer), preferably 5%.

[0018] In the above-described scheme of the present invention, the hydrophilic chain extender is DMPA. When its addition amount is 5%, the solid content, tensile strength and hardness of the waterborne polyurethane adhesive material are all high (when its addition amount is low or high, the tensile strength and hardness decrease significantly), and the waterborne polyurethane emulsion has high storage stability.

[0019] When AAS is selected as the hydrophilic chain extender, the amount of triethylamine added is 0.

[0020] Furthermore, the waterborne polyurethane adhesive material also includes 17.1-20.6 parts of a thickener; the thickener is 612NC thickener.

[0021] The use of the thickener described above in this invention can improve the thixotropic index of the emulsion and enhance its anti-sagging properties.

[0022] The present invention also provides a method for preparing the above-mentioned waterborne polyurethane adhesive material, characterized by comprising the following steps: (1) Dry the polycaprolactone diol and hydrophilic chain extender to remove moisture; (2) Polycaprolactone diol was added to isocyanate and stirred to obtain intermediate product A; (3) Add hydrophilic chain extender and 1,4-butanediol to N-methylpyrrolidone, then add intermediate product A and stir to react, and add acetone to adjust the viscosity to obtain intermediate product B; (4) Intermediate product B is mixed with triethylamine and stirred to obtain a hydrophilic polyurethane prepolymer; (5) Cool the hydrophilic polyurethane prepolymer to room temperature, add water precooled to 10°C and emulsify at high speed to obtain crude waterborne polyurethane emulsion.

[0023] (6) The aqueous polyurethane emulsion was allowed to stand at room temperature to defoam, and then acetone was removed by vacuum rotary evaporation to obtain the aqueous polyurethane emulsion.

[0024] Furthermore, the drying and moisture removal in step (1) involves drying at 100°C and 0.08 MPa for 2 hours.

[0025] Furthermore, the stirring rate in step (2) is 300 r / min, the reaction temperature is 80℃, and the reaction time is 1.5 h.

[0026] Furthermore, the stirring rate in step (3) is 300 r / min, the reaction temperature is 70℃, and the reaction time is 3 h; The viscosity after adding acetone is 2000-3000 mPa. s.; Furthermore, the stirring rate in step (4) is 300 r / min, the reaction temperature is 50 °C, and the reaction time is 1 h.

[0027] Furthermore, the shearing rate of the high-speed shearing in step (5) is 1500 r / min, and the emulsification time is 15 min.

[0028] Furthermore, the settling and defoaming time in step (6) is 12 hours; The vacuum degree of the vacuum rotary evaporation is 0.08-0.09 MPa, the evaporation temperature is 30-40℃, and the evaporation time is 1 hour.

[0029] The preparation method of the waterborne polyurethane adhesive material of the present invention further includes step (7): adjusting the pH of the waterborne polyurethane emulsion to 8-9, adding a thickener to the waterborne polyurethane emulsion, and obtaining the waterborne polyurethane adhesive material.

[0030] The raw material system of this invention does not contain crosslinking agents and does not require the addition of curing agents. It can be used directly as a single-component system. By precisely controlling the R value of isocyanate and the amount of hydrophilic chain extender added, a uniform and dense polyurethane molecular network is constructed under the condition of no crosslinking agent assistance. Combined with low-temperature cold water high-speed emulsification process and rheological thickening modification with thickener, it produces multiple advantages that cannot be expected from existing crosslinked WPU adhesives.

[0031] Existing technologies rely on crosslinking agents to introduce a large number of chemical crosslinking points and on crosslinking bonds to improve the strength of the film. However, the crosslinking points are irregularly and centrally distributed, which disrupts the uniformity of molecular chain segments. In contrast, this invention does not use exogenous crosslinking agents and adopts a linear and moderately branched molecular design approach: PCL2000 flexible long-chain polyol is preferably used to provide film toughness, IPDI cyclic aliphatic isocyanate provides rigidity of hard segments, DMPA is uniformly distributed on the molecular chain to introduce discrete ionic hydrophilic groups, and BDO small molecules are uniformly extended to control the ratio of soft and hard segments. The physical entanglement network formed by hydrogen bonds, ionic bonds, and chain segment entanglement between molecular chains replaces the chemical crosslinking network. The molecular chain segments are uniformly distributed, and the separation of soft and hard segment microphases is controllable, thus avoiding the performance defects caused by crosslinking agents from the root of molecular structure.

[0032] Compared to existing cross-linked WPU adhesives: (1) The adhesive film of the present invention has significantly improved flexibility and is applicable to a wider range of substrates: Existing technologies use crosslinking agents to form high-density chemical crosslinks, which restrict the movement of molecular chains, resulting in a hard and brittle adhesive film that is prone to cracking and peeling when bonded to flexible substrates such as leather, fabrics, and soft plastics. This invention, however, does not involve external crosslinking, allowing the molecular chains to extend freely. The adhesive film combines high strength and high elasticity, with a peel strength of up to 8.5 KN / m, a balance that crosslinked two-component adhesives cannot achieve.

[0033] (2) The emulsion of the present invention has significantly improved storage stability and does not separate or precipitate after long-term storage: This invention has no interference from crosslinking components, and the hydrophilic groups of the prepolymer are uniformly dispersed. Low-temperature and high-speed emulsification in cold water forms an emulsion with uniform particle size. Its stability was measured according to GB / T 6753.3-1986. After standing at room temperature for 6 months, there was no stratification or precipitation. In actual standing at room temperature for 1 year, the emulsion showed no stratification or precipitation. The storage period is far superior to existing crosslinking systems, reducing the risk of spoilage during storage.

[0034] (3) This invention is a single-component construction method, which simplifies the process, reduces raw material and labor costs, and allows waste materials to be recycled: Existing technologies mostly employ two-component systems, requiring precise metering and mixing of the curing agent before use. Mixing errors directly lead to adhesive failure, and the mixed slurry has a limited shelf life; expired waste cannot be recycled. This invention, however, is a single-component finished product that can be directly applied after opening the cap, eliminating the need for on-site mixing. It has no shelf-life limitation, and any remaining emulsion can be sealed and reused long-term. This saves on curing agent procurement costs, improves construction efficiency, and results in lower VOC emissions during production and use, further optimizing environmental friendliness.

[0035] (4) The product of the present invention has a significantly reduced water absorption rate and stronger water-resistant adhesive properties: Because a large number of chemical cross-linking points will form irregular hydrophilic pores inside the adhesive film, water can easily penetrate and swell. However, this invention relies on a uniform ionic hydrogen bond network to densely stack molecular chains, without the hydrophilic micro-region aggregation defects caused by cross-linking agents. The water absorption rate of the adhesive film can be controlled at about 10%, which is much lower than that of cross-linked WPU adhesives of the same strength. The attenuation of bonding strength in humid environments is greatly reduced, and the water resistance is improved unexpectedly.

[0036] (5) Excellent rheological anti-sagging properties, allowing for thick coating application without the need for high crosslinking density: Existing technologies rely on crosslinking to increase emulsion viscosity, which easily leads to problems such as paste clumping and poor coating leveling. In contrast, this invention uses 612NC thickener to achieve thixotropic modification, with a thixotropic index (TI) as high as 8.1. It exhibits high static viscosity and anti-sagging properties, as well as low shear viscosity for easy spraying and rolling. It can achieve thick coating in a single application without sagging. This anti-sagging advantage exceeds the expectations of existing technologies without the need for crosslinking agents.

[0037] The beneficial effects of this invention are as follows: (1) The waterborne polyurethane adhesive material prepared by the present invention has the characteristics of high solid content, low water absorption, high tensile strength and high bonding performance.

[0038] (2) The present invention adjusts the type and content of hydrophilic chain extender to change the molecular structure of polyurethane. The resulting polyurethane prepolymer has the characteristics of high hydrophilicity and does not precipitate or separate after long-term storage after emulsification.

[0039] (3) The present invention provides a preparation process in which hydrophilic chain extender is used to introduce hydrophilic groups, which increases the solid content of the material and enhances the tensile strength and adhesion performance of the material.

[0040] (4) This invention does not add any trimethylolpropane or organosilicon crosslinking agent, does not require a matching curing agent, and can be used directly as a single component. It has excellent flexibility, storage stability, water resistance and anti-sagging thick coating performance, and overcomes the multiple defects of existing crosslinked two-component waterborne polyurethane adhesives, such as high brittleness, easy delamination, complicated construction, high water absorption and serious sagging.

[0041] The solution of this invention helps to expand the application fields of waterborne polyurethane adhesive materials and will also strongly promote the development of waterborne polyurethane adhesive material systems. Attached Figure Description

[0042] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0043] Figure 1 This is a graph showing the change in solid content of waterborne polyurethane adhesive materials with different R values.

[0044] Figure 2 The graph shows the changes in tensile strength and hardness of waterborne polyurethane adhesive materials with different R values.

[0045] Figure 3 This graph shows the changes in tensile strength and hardness of waterborne polyurethane adhesives with different types of hydrophilic chain extenders.

[0046] Figure 4 The graph shows the changes in tensile strength and hardness of waterborne polyurethane adhesives with different amounts of hydrophilic chain extenders.

[0047] Figure 5 This is a graph showing the change in water absorption rate of water-based polyurethane adhesive materials.

[0048] Figure 6 This is a graph showing the variation of the T-peel strength of waterborne polyurethane adhesive materials.

[0049] Figure 7 This is a graph showing the changes in the thixotropic properties of waterborne polyurethane adhesive materials. Detailed Implementation

[0050] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0051] Example 1: A waterborne polyurethane adhesive material (1) Place 40g of polycaprolactone diol PCL2000 in a container and remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa. Dissolve 3.85g of DMPA (5% hydrophilic chain extender) in 7.7g of NMP and then remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa.

[0052] (2) Pour the dehydrated polycaprolactone diol PCL2000 into a four-necked flask, place it in an 80℃ constant temperature water bath, install a stirring device and set the speed to 300 rpm. Then slowly add 26.41 g IPDI (R value 1.3) at a rate of 6 drops / min and react for 1.5 h.

[0053] (3) Add DMPA and 3.85g BDO pre-dissolved in NMP to a four-necked flask, and lower the temperature to 70℃. Continue the reaction for 3 hours. During the reaction, add 20g acetone to adjust the viscosity to 2265mPa. s.

[0054] (4) After the reaction is complete, add 2.90g of TEA to neutralize the carboxylic acid, lower the temperature to 50℃, and continue stirring for 1h.

[0055] (5) Transfer the material to the emulsification tank and add 10°C deionized water for high-speed emulsification for 15 minutes.

[0056] (6) After the obtained product was allowed to stand for 12 hours to defoam, it was evaporated for 1 hour using a rotary evaporator at a vacuum of 0.085 MPa and a temperature of 35°C to remove acetone, thus obtaining an aqueous polyurethane emulsion.

[0057] Example 2: A water-based polyurethane adhesive material (1) Place 40g of polycaprolactone diol PCL2000 in a container and remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa. Dissolve 4.42g of DMPA in 8.84g of NMP (5% hydrophilic chain extender), and then remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa.

[0058] (2) Pour the dehydrated polycaprolactone diol PCL2000 into a four-necked flask and place it in an 80°C constant temperature water bath. Install the stirring device and set the speed to 300 rpm. Then slowly add 36.29 g IPDI (R value 1.6) at a rate of 6 drops / min and react for 1.5 h.

[0059] (3) Add DMPA and 4.42 g BDO pre-dissolved in NMP to a four-necked flask, and lower the temperature to 70 °C. Continue the reaction for 3 h. During the reaction, add 20 g acetone to adjust the viscosity to 2358 mPa. s.

[0060] (4) After the reaction is complete, add 3.33g of TEA to neutralize the carboxylic acid, lower the temperature to 50℃, and continue stirring for 1h.

[0061] (5) Transfer the material to the emulsification tank and add 10°C deionized water for high-speed emulsification for 15 minutes.

[0062] (6) After the obtained product was allowed to stand for 12 hours to defoam, it was evaporated for 1 hour using a rotary evaporator at a vacuum of 0.085 MPa and a temperature of 35°C to remove acetone, thus obtaining an aqueous polyurethane emulsion.

[0063] (7) Adjust the waterborne polyurethane emulsion to 8-9, add 19.6g of 612NC thickener to the waterborne polyurethane emulsion, stir evenly, and let stand for 24h to obtain waterborne polyurethane adhesive material.

[0064] Example 3: A water-based polyurethane adhesive material (1) Place 40g of polycaprolactone diol PCL2000 in a container and remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa. Dissolve 2.03g of DMPA in 4.06g of NMP (the amount of hydrophilic chain extender added is 3%) and then remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa.

[0065] (2) Pour the dehydrated polycaprolactone diol PCL2000 into a four-necked flask and place it in an 80°C constant temperature water bath. Install the stirring device and set the speed to 300 rpm. Then slowly add 25.88 g IPDI (R value 1.6) at a rate of 6 drops / min and react for 1.5 h.

[0066] (3) Add DMPA and 3.39 g BDO pre-dissolved in NMP to a four-necked flask, and lower the temperature to 70 °C. Continue the reaction for 3 h. During the reaction, add 20 g acetone to adjust the viscosity to 2695 mPa. s.

[0067] (4) After the reaction is complete, add 1.53g of TEA to neutralize the carboxylic acid, lower the temperature to 50℃, and continue stirring for 1h.

[0068] (5) Transfer the material to the emulsification tank and add 10°C deionized water for high-speed emulsification for 15 minutes.

[0069] (6) After the obtained product was allowed to stand for 12 hours to defoam, it was evaporated for 1 hour using a rotary evaporator at a vacuum of 0.085 MPa and a temperature of 35°C to remove acetone, thus obtaining an aqueous polyurethane emulsion.

[0070] Example 4: A water-based polyurethane adhesive material (1) Place 40g of polycaprolactone diol PCL2000 in a container and remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa. Dissolve 3.86g of AAS in 7.72g of NMP (5% hydrophilic chain extender) and then remove water for 2h in a vacuum drying oven at 100℃ and 0.08Mpa.

[0071] (2) Pour the dehydrated polycaprolactone diol PCL2000 into a four-necked flask and place it in an 80°C constant temperature water bath. Install the stirring device and set the speed to 300 rpm. Slowly add 29.59 g IPDI at a rate of 6 drops / min (R value 1.6) and react for 1.5 h.

[0072] (3) Add AAS dissolved in NMP and 3.86 g BDO to a four-necked flask, and lower the temperature to 70 °C. Continue the reaction for 3 h. During the reaction, add 20 g acetone to adjust the viscosity to 2215 mPa. s.

[0073] (4) After the reaction is complete, transfer the material to an emulsification tank and add 10°C deionized water for high-speed emulsification for 15 min.

[0074] (5) After the product was allowed to stand for 12 hours to defoam, it was evaporated for 1 hour using a rotary evaporator at a vacuum of 0.085 MPa and a temperature of 35°C to remove acetone, thus obtaining an aqueous polyurethane emulsion.

[0075] Based on the scheme of Example 1, the solid content of waterborne polyurethane adhesive materials with different R values ​​was investigated, such as... Figure 1 As shown, Figure 1 This is a graph showing the solid content of waterborne polyurethane adhesives with different R values. Figure 1 It can be seen that the solid content of all samples is above 40%, and it does not fluctuate significantly with the increase of R value, remaining between 41.1% and 46.8%.

[0076] Based on the scheme of Example 1, the changes in tensile strength and hardness of waterborne polyurethane adhesive materials with different R values ​​were investigated, such as... Figure 2 As shown, Figure 2 This graph shows the changes in tensile strength and hardness of waterborne polyurethane adhesive materials with different R values. Figure 2 It can be seen that within the range of R=1.3-1.6, the tensile strength of the waterborne polyurethane film gradually increases from 0.7 MPa to 3.0 MPa as the R value increases; however, the tensile strength decreases when R=1.7. The hardness shows a continuous upward trend with increasing R value. The increase in R value leads to a higher entanglement density of the polyurethane molecular chains, enhancing the inter-chain interaction forces, thereby promoting the improvement of the film's tensile strength and hardness.

[0077] Based on Examples 1 and 3, the effects of different types of hydrophilic chain extenders on waterborne polyurethane adhesives were investigated. Figure 3 The graph shows the changes in tensile strength and hardness of waterborne polyurethane adhesives with different types of hydrophilic chain extenders. Figure 3It is known that the DMPA-based waterborne polyurethane film has a relatively high tensile strength, approximately 2.95 MPa, while the hardness of waterborne polyurethane films formed by the three hydrophilic groups is not significantly different. This difference is mainly attributed to the influence of the chain extender structure and hydrophilicity: carboxylic acid-type hydrophilic chain extenders (such as DMPA) have shorter molecular chains, resulting in a more uniform distribution when grafted onto the polyurethane molecular chains. This facilitates the formation of a network structure with a higher degree of cross-linking, thereby imparting higher tensile strength to the film. In contrast, sulfonic acid-type hydrophilic chain extenders (such as AAS) are too hydrophilic, easily causing local aggregation of hydrophilic groups in the emulsion, leading to uneven distribution of intermolecular forces within the film, and thus a lower tensile strength of only 1.68 MPa.

[0078] Based on Examples 1 and 3, the tensile strength and hardness of waterborne polyurethane adhesive materials with different DMPA addition amounts were investigated. The results are as follows: Figure 4 As shown, Figure 4 The graph shows the changes in tensile strength and hardness of waterborne polyurethane adhesive materials with different DMPA addition amounts. Figure 4 It can be seen that with the increase of DMPA content, the tensile strength gradually increases from 2.60 MPa to 3.48 MPa; however, when the DMPA content is 6%, the tensile strength decreases to 3.07 MPa. The hardness increases with the increase of DMPA content, gradually increasing from 87.67 ± 3.21 HA to 97.67 ± 1.53 HA. These changes are mainly attributed to the effect of DMPA addition on the polyurethane molecular structure: with the increase of DMPA content, more carboxyl groups participate in the reaction to form carboxylate anions, enhancing the crosslinking between molecular chains through ionic bonding; and more carboxyl groups participate in the chain extension reaction, increasing the branching degree and crosslinking density of the molecular chains, thereby enhancing the rigidity of the film and gradually increasing the tensile strength and hardness. However, when the DMPA content is too high, the system becomes too hydrophilic, and excessive hydrophilic groups aggregate in the film to form hydrophilic microregions, diluting the effective crosslinking point density in the molecular chains, leading to a decrease in tensile strength.

[0079] The water absorption rate of waterborne polyurethane adhesive materials was investigated based on Examples 1 and 3, and the results are as follows: Figure 5 As shown, Figure 5 This is a graph showing the change in water absorption rate of water-based polyurethane adhesive materials. Figure 5 It is known that the content of hydrophilic chain extender has the greatest impact on water absorption rate, followed by the type of isocyanate, R value and the type of hydrophilic chain extender. By adjusting the formula, the water absorption rate can be reduced to about 10%.

[0080] The T-peel strength of waterborne polyurethane adhesive materials was investigated based on Examples 1 and 3, and the results are as follows: Figure 6 As shown, Figure 6 This is a graph showing the variation of the T-peel strength of waterborne polyurethane adhesive materials. Figure 6It can be seen that when IPDI is selected as the isocyanate, the R value is 1.6, DMPA is the hydrophilic chain extender, and the amount of DMPA added is 5%, the T peel strength can be increased to about 8.5 KN / m.

[0081] Based on the technical solution of Example 2, the changes in the thixotropic properties of waterborne polyurethane adhesive materials were investigated, and the results are as follows: Figure 7 As shown in the figure, the viscosity of the aqueous polyurethane emulsions with the three thickeners is all above 1000 mPas. The TI value of the WPU emulsion with thickener R299 is 2.3, the TI value of the WPU emulsion with thickener RM12W is 5.4, and the TI value of the WPU emulsion with thickener 612NC is 8.1. This indicates that the emulsion with thickener 612NC has better anti-sagging properties.

[0082] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A water-based polyurethane adhesive material, characterized in that, Including the following parts by weight of raw materials: Polycaprolactone diol 40.0 parts, isocyanate 25.8-40.1 parts, hydrophilic chain extender 2.0-5.0 parts, N-methylpyrrolidone 4.0-10.0 parts, 1,4-butanediol 3.4-4.6 parts, triethylamine 0-3.7 parts, water 89.0-113.5 parts.

2. The waterborne polyurethane adhesive material according to claim 1, characterized in that, The isocyanate is any one of isophorone diisocyanate, hexamethylene diisocyanate, and toluene diisocyanate.

3. The waterborne polyurethane adhesive material according to claim 1, characterized in that, The hydrophilic chain extender is any one of 2,2-bis(hydroxymethyl)propionic acid, 2,2-dihydroxymethylbutyric acid, and sodium salt of 2-[(2-aminoethyl)amino]ethanesulfonate.

4. The waterborne polyurethane adhesive material according to claim 1, characterized in that, The waterborne polyurethane adhesive material further includes 17.1-20.6 parts of a thickener; the thickener is 612NC thickener.

5. A method for preparing the waterborne polyurethane adhesive material according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Dry the polycaprolactone diol and hydrophilic chain extender to remove moisture; (2) Polycaprolactone diol was added to isocyanate and stirred to obtain intermediate product A; (3) Add hydrophilic chain extender and 1,4-butanediol to N-methylpyrrolidone, then add intermediate product A and stir to react, and add acetone to adjust the viscosity to obtain intermediate product B; (4) Intermediate product B is mixed with triethylamine and stirred to obtain a hydrophilic polyurethane prepolymer; (5) Cool the hydrophilic polyurethane prepolymer to room temperature, add water and emulsify at high speed to obtain a crude waterborne polyurethane emulsion; (6) The aqueous polyurethane emulsion was allowed to stand at room temperature to defoam, and then acetone was removed by vacuum rotary evaporation to obtain the aqueous polyurethane emulsion.

6. The method for preparing a waterborne polyurethane adhesive material according to claim 5, characterized in that, The stirring rate in step (2) is 300 r / min, the reaction temperature is 80℃, and the reaction time is 1.5 h.

7. The method for preparing a waterborne polyurethane adhesive material according to claim 5, characterized in that, The stirring rate in step (3) is 300 r / min, the reaction temperature is 70℃, and the reaction time is 3 h; The viscosity after adding acetone is 2000-3000 mPa. s.

8. The method for preparing a waterborne polyurethane adhesive material according to claim 5, characterized in that, The stirring rate in step (4) is 300 r / min, the reaction temperature is 50℃, and the reaction time is 1 h; The high-speed shearing in step (5) has a shearing rate of 1500 r / min and an emulsification time of 15 min.

9. The method for preparing a waterborne polyurethane adhesive material according to claim 5, characterized in that, The settling and defoaming time mentioned in step (6) is 12 hours; The vacuum degree of the vacuum rotary evaporation is 0.8-0.9 MPa, the evaporation temperature is 30-40℃, and the evaporation time is 1 hour.

10. The method for preparing a waterborne polyurethane adhesive material according to claim 5, characterized in that, It also includes step (7): adjusting the pH of the waterborne polyurethane emulsion to 8-9, adding a thickener to the waterborne polyurethane emulsion, and obtaining the waterborne polyurethane adhesive material.

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