A bio-based waterborne polyurethane-acrylate adhesive as well as a preparation method and application thereof

Abstract

This application discloses a bio-based waterborne polyurethane-acrylate adhesive, its preparation method, and its application, relating to the field of waterborne polyurethane-acrylate adhesive technology. This application provides a method for preparing a bio-based waterborne polyurethane-acrylate adhesive through monomer polymerization followed by high-speed dispersion. The polyurethane and acrylate are compounded to form a bimodal particle size distribution, effectively increasing the solid content while ensuring emulsion stability. The multi-arm star-shaped polyurethane containing double bonds prepared by the specific method of this application synergistically combines with the acrylate monomer, achieving efficient grafting of polyurethane and acrylate at the molecular level, constructing a network structure with high crosslinking density, thereby improving the adhesive performance and laying the foundation for the subsequent formation of a stable bimodal particle size distribution.

Description

Technical Field

[0001] This application relates to the field of waterborne polyurethane-acrylate adhesives, and in particular to a bio-based waterborne polyurethane-acrylate adhesive, its preparation method, and its application. Background Technology

[0002] Waterborne polyurethane-acrylate (WPUA) adhesives combine the excellent flexibility of polyurethane with the good weather resistance of acrylate. Using water as the dispersion medium, they are non-toxic, non-flammable, and environmentally friendly, making them widely used in packaging, woodworking, automotive interiors, footwear, electronic packaging, and many other fields. Against the backdrop of the ongoing global push for "dual-carbon" strategies and increasingly stringent environmental regulations in various countries, abandoning traditional petroleum-based raw materials and developing high-performance WPUA adhesives using renewable bio-based raw materials has become an inevitable trend for technological innovation and industrial development in this field, and a key research focus.

[0003] Current WPUA adhesive technology still suffers from numerous core performance defects, severely hindering its high-end and industrial applications. Firstly, many products face challenges such as high latent heat of vaporization, long drying times, and low efficiency, limiting further market expansion and development. Therefore, reducing water content and developing high-solids-content WPUA is of great significance. Secondly, the mechanical properties of these products are significantly weak, with poor tensile strength and elongation at break, making it difficult to meet the demands of high-strength and high-toughness bonding conditions and failing to fully leverage the performance advantages of both polyurethane and acrylate substrates. Finally, adhesive performance is insufficient, with low 180° peel strength. Due to insufficient chemical bonding between polyurethane and acrylate, the bonding relies solely on molecular entanglement, resulting in uneven grafting point distribution and limited interfacial bonding strength, failing to meet the high-performance bonding requirements of high-end applications. In recent years, researchers have made positive progress in improving the compatibility of PU and PA through core-shell structure design, interpenetrating polymer network construction, and in-situ graft polymerization.

[0004] Currently, the main methods for preparing WPUA emulsions include blending, core-shell emulsion polymerization, emulsion copolymerization, and interpenetrating network emulsion polymerization, which can correspondingly produce WPUA blended emulsions, WPUA core-shell emulsions, WPUA copolymer emulsions, and WPUA interpenetrating network emulsions. Among these, physical blending, while simple, suffers from poor compatibility between polyurethane and polyacrylate, making it difficult to fully utilize the performance advantages of both polymers. Core-shell emulsion polymerization involves swelling acrylate monomers into a pre-prepared PU emulsion containing hydrophilic groups, followed by the addition of an initiator to initiate polymerization, effectively improving the water resistance and abrasion resistance of the adhesive. Emulsion copolymerization improves the compatibility of the two phases through chemical bonding, but still suffers from low solids content and insufficient mechanical properties. Interpenetrating network emulsion polymerization, by constructing interpenetrating and entangled networks of two polymers, can improve the overall performance of the material to a certain extent.

[0005] In terms of molecular structure design, hyperbranched WPUA relies on hyperbranched polyurethane acrylate prepolymers, leveraging numerous active groups on the surface to enhance crosslinking, while utilizing the unique topological structure of hyperbranched polymers to improve the curing and peeling properties of adhesives. Star-shaped WPUA constructs a multi-arm star-shaped molecular framework through methods such as the "arm-first, core-later" method, prepolymer method, or multi-arm hybridization method, which can effectively reduce system viscosity and improve the compatibility of soft and hard segments. Summary of the Invention

[0006] Based on this, the purpose of this application is to overcome the shortcomings of the prior art and provide a bio-based waterborne polyurethane-acrylate adhesive that has high solids content, high stability, high mechanical properties and high adhesive strength.

[0007] To achieve the above objectives, a first aspect of this application provides a method for preparing a bio-based waterborne polyurethane-acrylate adhesive, comprising the following steps: S1. The branched core, bio-based polyol, and hydrophilic chain extender are dehydrated, cooled, and then nitrogen is introduced. Diisocyanate and catalyst are added, and the reaction is kept at the temperature. When the NCO content drops to the theoretical value, double bond monomers are added to carry out the end-capping reaction to obtain a multi-arm star polyurethane containing double bonds. S2. Dissolve the multi-arm star-shaped polyurethane containing double bonds in an organic solvent, add acrylate monomers and initiators, react under a nitrogen atmosphere, cool down and add a neutralizing agent for neutralization reaction, add deionized water to the system under stirring, and obtain the bio-based waterborne polyurethane-acrylate adhesive after vacuum rotary evaporation.

[0008] This application provides a unique process of "monomer polymerization followed by high-speed dispersion," in which polyurethane and acrylate are compounded to form a bimodal particle size distribution, effectively increasing the solid content while ensuring emulsion stability. The multi-armed star-shaped polyurethane containing double bonds prepared by the specific method of this application synergistically combines with acrylate monomers, achieving efficient grafting of polyurethane and acrylate at the molecular level. This constructs a network structure with high crosslinking density, improving adhesive performance and laying the foundation for the subsequent formation of a stable bimodal particle size distribution.

[0009] In some embodiments of this application, the schematic diagram of the multi-arm star-shaped polyurethane structure containing double bonds is shown in formula (I): Formula (I); in, It is one of the hydrocarbon skeletons of trimethylolpropane, pentaerythritol, dipentaerythritol, and glycerol after removing the hydroxyl group, such as the hydrocarbon skeleton of trimethylolpropane after removing the hydroxyl group. glycerol's hydrocarbon skeleton after removing the hydroxyl group, etc. ; It is a carbamate group (-NH-CO-O-) formed by the reaction of isocyanate and hydroxyl groups. R1 is one of the hydrocarbon skeletons of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate after removing the isocyanate group, such as the hydrocarbon skeleton of isophorone diisocyanate after removing the isocyanate group. The hydrocarbon skeleton of hexamethylene diisocyanate after removing the isocyanate group The hydrocarbon skeleton of toluene diisocyanate after removing the isocyanate group, etc. ; R2 is one of the hydrocarbon backbones of bio-based polyether polyols and bio-based polycarbonate polyols after removing the hydroxyl groups, such as the hydrocarbon backbone of polytrimethylene ether glycol after removing the hydroxyl groups. The hydrocarbon skeleton of polytetrahydrofuran ether diol after removing the hydroxyl groups ; R3 is one of the hydrocarbon skeletons of 2,2-dimethylolbutyric acid and 2,2-dimethylolpropionic acid after removing the hydroxyl group, such as the hydrocarbon skeleton of 2,2-dimethylolbutyric acid after removing the hydroxyl group. The hydrocarbon skeleton of 2,2-dimethylolpropionic acid after removing the hydroxyl group. ; In some embodiments of this application, the schematic diagram of the multi-arm star-shaped polyurethane structure containing double bonds is shown in formula (II): Equation (II).

[0010] In some embodiments of this application, at least one of the following (1)-(10) is included: (1) The branched core is selected from at least one of trimethylolpropane (TMP), pentaerythritol, dipentaerythritol, and glycerol; (2) The bio-based polyol is selected from at least one of bio-based polyether polyol and bio-based polycarbonate polyol; (3) The hydrophilic chain extender is selected from at least one of 2,2-dimethylolbutyric acid (DMBA) and 2,2-dimethylolpropionic acid (DMPA); (4) The diisocyanate is selected from at least one of isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), and diphenylmethane diisocyanate (MDI); (5) The catalyst is selected from at least one of dibutyltin dilaurate (DBTDL), organobismuth, bismuth neodecanoate, and zinc neodecanoate; (6) The double bond monomer is selected from at least one of pentaerythritol triacrylate (PETA), trimethylolpropane triacrylate (TMPTA), and hydroxyethyl methacrylate (HEMA); (7) The organic solvent is selected from at least one of acetone and butanone; (8) The acrylate monomers include hard monomers and soft monomers, wherein the hard monomers are selected from at least one of methyl methacrylate (MMA) and isobornyl methacrylate (IBOMA), and the soft monomers are selected from at least one of butyl acrylate (BA) and isooctyl acrylate; (9) The initiator is selected from at least one of azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO); (10) The neutralizing agent is selected from at least one of triethylamine (TEA) and N,N-dimethylethanolamine.

[0011] In some embodiments of this application, the number-average molecular weight of the bio-based polyether polyol is 1800-2200 g / mol; and the number-average molecular weight of the bio-based polycarbonate polyol is 450-2100 g / mol.

[0012] In some embodiments of this application, the bio-based polyether polyol is selected from at least one of polytrimethylene ether diol PO3G and polytetrahydrofuran ether diol PTMEG; and / or, the bio-based polycarbonate polyol is selected from at least one of HBE500, HBE1000, HBE2000, HBC500, HBC1000, HBC2000, HPT500, HPT1000, and HPT2000.

[0013] In some embodiments of this application, the bio-based polyether polyol has a bio-based content of 100%; the bio-based polycarbonate polyol has a bio-based content of 40-50%.

[0014] In some embodiments of this application, the acrylate monomer further includes 0.2-2 parts of a functional monomer; the functional monomer is selected from at least one of acrylic acid (AA) and methacrylic acid (MAA).

[0015] In some embodiments of this application, the acrylate monomer comprises 5-30 parts of hard monomer and 5-30 parts of soft monomer.

[0016] In some embodiments of this application, in step S1, the dehydration temperature is 100-110°C, the vacuum degree is -0.05~-0.1MPa, and the dehydration time is 0.5-1.5h; and / or, the temperature is lowered to 70-80°C for heat preservation reaction, and the reaction time is 2-4h; and / or, the end-capping reaction time is 1-3h.

[0017] In some embodiments of this application, in step S2, the reaction temperature under a nitrogen atmosphere is 65-75°C, and the reaction time is 3-5 hours; and / or, the temperature is lowered to 40±2°C for a neutralization reaction, the neutralization reaction time is 15-20 minutes, and the pH is adjusted to 7-9; and / or, the stirring speed is 2000-4000 rpm.

[0018] When this application describes the reaction of a multi-arm star-shaped polyurethane containing double bonds with acrylate monomers, insufficient reactivity and prolonged reaction time occur at excessively low temperatures. Excessively high temperatures significantly increase the risk of side reactions. High temperatures accelerate the side reaction between trace amounts of moisture and -NCO in the system, generating urea bonds and releasing CO2.

[0019] In some embodiments of this application, the raw materials for preparing the multi-arm star-shaped polyurethane containing double bonds include the following components in parts by weight: 1-2.5 parts of branched core, 55-80 parts of bio-based polyol, 4-6 parts of hydrophilic chain extender, 15-30 parts of diisocyanate, 0.03-0.05 parts of catalyst, and 2-10 parts of double bond monomer. The raw materials for preparing the bio-based waterborne polyurethane-acrylate adhesive include the following components in parts by weight: 50-100 parts of multi-arm star-shaped polyurethane containing double bonds, 30-80 parts of organic solvent, 20-50 parts of acrylate monomer, 0.2-0.8 parts of initiator, 4-7 parts of neutralizer, and 100-150 parts of deionized water.

[0020] During actual experiments, the inventors discovered that the weight of the raw materials has a significant impact on the final preparation of multi-arm star-shaped polyurethane with double bonds and bio-based waterborne polyurethane-acrylate adhesive. Only by selecting the specific weight of the raw materials can multi-arm star-shaped polyurethane with double bonds be prepared, and further, bio-based waterborne polyurethane-acrylate adhesive with high solid content, high stability, high mechanical properties and high adhesive strength can be obtained.

[0021] During actual experiments, the inventors discovered that the branched core constructs a multi-arm star-shaped framework in the prepolymerization stage, while the double-bonded monomer introduces multifunctional double bonds in the end-capping stage. The ratio of these two components determines the degree of branching and the crosslinking density of the system. If the proportion of the branched core is too low, there are insufficient branching points, the molecular chain is mainly linear, the crosslinking density is too low, and the mechanical strength and water resistance are insufficient. If the proportion of the branched core is too high, the branching points are too dense, the crosslinking is too high, the system is prone to gelation, and the flexibility decreases.

[0022] During actual experiments, the inventors discovered that the ratio of polyurethane to acrylate monomers determines the ratio of the PU phase to the PA phase, i.e., the relative content of rigidity and flexibility in the system, which directly affects the balance between cohesive strength and flexibility of the adhesive. If the proportion of acrylate monomers is too low, there are too few PA segments, the crosslinking network is incomplete, and the cohesive strength and adhesive strength are insufficient; if the proportion of acrylate monomers is too high, there are too many PA segments, the rigidity of the system increases, the flexibility and elongation at break decrease, and the tendency of PA to homopolymerize increases, resulting in poor compatibility between the two phases.

[0023] In some embodiments of this application, the weight ratio of the branched core to the double bond monomer is 1:(2-10).

[0024] In some embodiments of this application, the weight ratio of the double-bonded multi-arm star-shaped polyurethane to the acrylate monomer is 1:(0.2-0.5).

[0025] This application controls the weight ratio of branched cores to double bond monomers within the above-mentioned range. The branched cores provide a suitable framework structure, and the double bond monomers provide sufficient grafting sites. The two work together to construct a multi-level branched network with moderate crosslinking density, resulting in better performance.

[0026] This application controls the weight ratio of polyurethane to acrylate monomers within the above-mentioned range. PU provides flexibility, and PA provides cohesive strength. The synergy between the two within the above-mentioned range can better improve the overall performance.

[0027] In a second aspect of this application, this application provides a bio-based waterborne polyurethane-acrylate adhesive prepared using the aforementioned method for preparing bio-based waterborne polyurethane-acrylate adhesive.

[0028] In a third aspect, this application provides the application of the aforementioned bio-based waterborne polyurethane-acrylate adhesive in packaging material bonding, automotive interior bonding, electronic packaging, footwear materials, and fabric printing.

[0029] Compared to existing technologies, the advantages of this application are as follows: This application provides a unique process of "monomer polymerization followed by high-speed dispersion," in which polyurethane and acrylate are compounded to form a bimodal particle size distribution, effectively improving the solid content while ensuring emulsion stability. The multi-arm star-shaped polyurethane containing double bonds prepared by the specific method of this application synergistically with the acrylate monomers, achieving efficient grafting of polyurethane and acrylate at the molecular level, constructing a network structure with high crosslinking density, improving adhesive performance, and laying the foundation for the subsequent formation of a stable bimodal particle size distribution. This application uses bio-based polyols as the main soft segment, reducing dependence on petroleum fossil resources and complying with national dual-carbon strategies and global environmental regulations. Attached Figure Description

[0030] Figure 1 The particle size distribution diagram is shown for the bio-based waterborne polyurethane-acrylate adhesive prepared in Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0032] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0033] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0034] Unless otherwise specified, the experimental reagents and instruments used in the embodiments and comparative examples of this invention are all commonly used reagents and instruments, and are all commercially available. Unless otherwise specified, the experimental methods used in the embodiments and comparative examples are conventional methods; and unless otherwise specified, the raw materials used in parallel experiments are from the same batch.

[0035] Example 1 (1) First step: Synthesis of multi-arm star-shaped polyurethane macromolecules (SPU) containing double bonds; In a 250 mL four-necked flask equipped with an electric stirrer, reflux condenser, thermometer, and nitrogen inlet, 1.34 parts of trimethylolpropane (TMP), 70.0 parts of polytrimethylene ether glycol (PO3G-2000), and 4.8 parts of dimethylolbutyric acid (DMBA) were added. The mixture was dehydrated at 105 °C under a vacuum of -0.08 MPa for 1 h. The temperature was then lowered to 75 °C, and under nitrogen protection, 22.0 parts of isophorone diisocyanate (IPDI) and 0.04 parts of dibutyltin dilaurate (DBTDL) were added. The reaction was maintained at this temperature for 2 h. The NCO content was determined using the di-n-butylamine method. When the NCO content decreased to the theoretical value, 6.0 parts of pentaerythritol triacrylate (PETA) were added, and the reaction was continued for 1.5 h to obtain the SPU.

[0036] (2) Second step: graft polymerization and water-based processing; Dissolve 100 parts of the above SPU in 50.0 parts of acetone, add 15.0 parts of methyl methacrylate (MMA), 18.0 parts of butyl acrylate (BA), 1.7 parts of acrylic acid (AA), and 0.3 parts of azobisisobutyronitrile (AIBN), and purge with nitrogen. Heat to 70℃ and reflux for 3.5 h. Cool to 40℃, add 5.6 parts of triethylamine (TEA) to neutralize for 15 minutes, and adjust the pH to 7-8. Slowly add 150 parts of deionized water dropwise while stirring at 3000 rpm, and continue stirring for 30 min. Remove acetone by rotary evaporation under reduced pressure to obtain a milky white bio-based waterborne polyurethane-acrylate adhesive with a bimodal particle size distribution, denoted as WPUA-1.

[0037] Example 2 The preparation method in this embodiment differs from that in Example 1 only in that the temperature of the first step in Example 1 is adjusted from 75℃ to 70℃, the reaction time is adjusted to 3h, and 1.34 parts of TMP are replaced with 1.02 parts of pentaerythritol, keeping the total molar amount of hydroxyl groups unchanged; the stirring speed in the second step is adjusted from 3000rpm to 4000rpm, and the stirring time is adjusted to 15min. All other raw materials and operations are exactly the same, resulting in a milky white bio-based waterborne polyurethane-acrylate adhesive, denoted as WPUA-2.

[0038] Example 3 The preparation method of this embodiment is the same as that of Example 1, except that the amount of DMBA in Example 1 is adjusted from 4.8 parts to 5.2 parts, the amount of PO3G-2000 is adjusted from 70.0 parts to 75.0 parts, the amount of IPDI is adjusted from 22.0 parts to 23.5 parts, and the amount of DBTDL catalyst is adjusted from 0.04 parts to 0.05 parts. All other raw materials and operations are exactly the same, and a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained, which is denoted as WPUA-3.

[0039] Example 4 The preparation method of this embodiment is the same as that of Example 1, except that 6.0 parts of PETA in Example 1 are replaced with 2.60 parts of hydroxyethyl methacrylate (HEMA) to keep the total molar amount of hydroxyl groups unchanged. All other raw materials and operations are exactly the same, and a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained, which is denoted as WPUA-4.

[0040] Example 5 The preparation method of this embodiment differs from that of Example 1 only in that the amount of TMP in Example 1 is adjusted from 1.34 parts to 1.89 parts, while the other raw materials and operations are exactly the same as in Example 1, resulting in a milky white bio-based waterborne polyurethane-acrylate adhesive, denoted as WPUA-5.

[0041] Example 6 The preparation method of this embodiment is the same as that of Example 1, except that the amount of PETA 6.0 parts in Example 1 is adjusted to PETA 9.8 parts. All other raw materials and operations are exactly the same, and a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained, which is denoted as WPUA-6.

[0042] Example 7 The preparation method of this embodiment is the same as that of Example 1, except that the amount of TMP in Example 1 is adjusted from 1.34 parts to 1.0 parts and the amount of PETA is adjusted from 6.0 parts to 4.5 parts. The other raw materials and operations are exactly the same as those in Example 1, and a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained, which is denoted as WPUA-7.

[0043] Example 8 The preparation method of this embodiment differs from that of Example 1 only in that the acrylate monomers in Example 1 are adjusted to 18.8 parts MMA, 22.5 parts BA, and 2.1 parts AA, and the amount of AIBN is increased from 0.3 parts to 0.38 parts. The other raw materials and operations are exactly the same as in Example 1, and a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained, denoted as WPUA-8.

[0044] Comparative Example 1 The only difference between this comparative preparation method and Example 1 is that TMP is not added in the first step, while the remaining raw materials and operations are basically the same as in Example 1. After the same post-treatment, a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained.

[0045] Comparative Example 2 The only difference between this comparative preparation method and Example 1 is that PETA is not added for end-capping in the first step, while the other raw materials and operations are basically the same as in Example 1. After the same post-treatment, a milky white bio-based waterborne polyurethane-acrylate adhesive is obtained.

[0046] Comparative Example 3 The only difference between this comparative preparation method and Example 1 is that the amount of PETA in the first step of Example 1 is adjusted from 6.0 parts to 14.0 parts. The other raw materials and operations are basically the same as in Example 1. Due to the excessive amount of PETA, the crosslinking density of the system is too high, and a stable bio-based waterborne polyurethane-acrylate adhesive cannot be obtained after the same post-treatment.

[0047] Comparative Example 4 Compared with Example 1, the only difference is that the addition of all acrylate monomers (MMA, BA, AA) and initiator (AIBN) in the second step is cancelled. That is, after the first step is completed, SPU is directly dissolved in acetone, cooled and then TEA is added for neutralization. Deionized water is added dropwise under high-speed stirring for emulsification. Acetone is removed by rotary evaporation under reduced pressure to obtain pure multi-arm star-shaped waterborne polyurethane adhesive. Performance testing Solid content: Determined according to GB / T 1725-2007 "Determination of nonvolatile matter content in paints, varnishes and plastics". Weigh 1-2g of adhesive into an aluminum foil dish, dry in an oven at 105℃ for 2h, and calculate the remaining mass fraction.

[0048] Tensile strength and elongation at break: determined according to GB / T 1040.1—2025 "Determination of tensile properties of plastics - Part 1: General". The adhesive is cast into a film with a thickness of about 0.5-1 mm, cut into dumbbell-shaped specimens, and stretched at a speed of 200 mm / min.

[0049] 180° Peel Strength: The test was conducted according to GB / T 2791-1995: "Test Method for 180° Peel Strength of Adhesives - Flexible Materials to Flexible Materials". The adhesive (samples prepared in the examples and comparative examples) was uniformly applied to a flexible substrate, bonded to another flexible substrate, and cured under specified conditions. The resulting samples were then cut into 25 mm wide specimens. A universal testing machine was used to perform a 180° peel test at a peel speed of 300 mm / min. The average peel force during the peeling process was recorded, and the 180° peel strength (N / 25 mm) was calculated.

[0050] Shelf life: to be determined in GB / T 11175-2021, 6.6.2 and 6.6.3.

[0051] The test results are shown in Table 1.

[0052] Table 1 Performance test results of each comparative example and embodiment The particle size distribution of the bio-based waterborne polyurethane-acrylate adhesive prepared in Example 1 is shown in the figure below. Figure 1 As shown, from Figure 1 As can be seen, the particle size distribution is bimodal. Figure 1 This is a particle size distribution diagram of the bio-based waterborne polyurethane-acrylate adhesive prepared in Example 1 of this application. Figure 1 It can be seen that the emulsion particle size exhibits a bimodal distribution, with the first peak size at approximately 109 nm and the second peak size at approximately 213 nm.

[0053] A comparison of Examples 1 and 2 shows that Example 2, by replacing the trifunctional TMP with a tetrafunctional pentaerythritol of equal molar amounts of hydroxyl groups, resulted in an increase in molecular branching points and a slight increase in crosslinking density, thus leading to a slight increase in tensile strength. However, the increased degree of crosslinking limited the stretching of the molecular chains, resulting in a decrease in elongation at break and 180° peel strength. This indicates that while tetrahydroxy-branched cores enhance crosslinking, excessive crosslinking reduces the flexibility and interfacial adhesion of the film. Slightly reducing the reaction temperature from 75°C to 70°C and appropriately extending the reaction time, as well as fine-tuning the stirring process, are all conventional process optimizations and do not substantially affect the product performance.

[0054] A comparison of Examples 1 and 3 shows that increasing the amount of each component simultaneously slightly reduces tensile strength, elongation at break, and peel strength, but the overall performance remains at a high level. This indicates that the formulation system of the present invention has good process tolerance and can achieve excellent comprehensive performance within a wide range of raw material dosages.

[0055] A comparison of Examples 1 and 4 shows that PETA exhibits superior overall performance when used as the end-capping monomer. HEMA contains only a single polymerizable double bond, resulting in a linear graft structure after grafting, which cannot construct a three-dimensional cross-linked network. In contrast, PETA contains three active acrylic double bonds, forming a high-density cross-linked structure during free radical copolymerization, significantly improving the cohesive force, tensile strength, and peel strength of the adhesive layer.

[0056] A comparison of Examples 1 and 5 shows that increasing the amount of TMP increases the branching point density, crosslinking density, and tensile strength, but decreases the elongation at break and peel strength. This is because excessive TMP leads to overly dense branching points, excessively high crosslinking, restricted molecular chain movement, decreased flexibility, and reduced peel strength.

[0057] A comparison of Examples 1 and 6 shows that increasing the amount of PETA slightly increases the crosslinking density and tensile strength; however, excessive crosslinking restricts the molecular chains, resulting in a slight decrease in elongation at break and peel strength, and the overall performance is slightly worse than that of Example 1.

[0058] A comparison of Examples 1 and 7 shows that when the amounts of TMP and PETA are reduced simultaneously and appropriately, the reduction in branched cores leads to a decrease in the density of branching points, and the reduction in double bond monomers leads to a decrease in the number of graftable double bonds, resulting in a decrease in the density of grafting sites and a reduction in crosslinking density. The synergistic reduction of both results in a decrease in tensile strength, elongation at break, peel strength, and solid content.

[0059] Comparing Examples 1 and 8, it can be seen that increasing the amount of acrylate appropriately increases the proportion of PA segments, further improves the solid content, slightly increases the tensile strength, and decreases the elongation at break and peel strength. This indicates that appropriately increasing the amount of acrylate can improve the solid content and rigidity to a certain extent, but if it exceeds the optimal range, the flexibility and adhesion will gradually be impaired.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A method for preparing a bio-based waterborne polyurethane-acrylate adhesive, characterized in that, Includes the following steps: S1. The branched core, bio-based polyol, and hydrophilic chain extender are dehydrated, cooled, and then nitrogen is introduced. Diisocyanate and catalyst are added, and the reaction is kept at the temperature. When the NCO content drops to the theoretical value, double bond monomers are added to carry out the end-capping reaction to obtain a multi-arm star polyurethane containing double bonds. S2. Dissolve the multi-arm star-shaped polyurethane containing double bonds in an organic solvent, add acrylate monomers and initiators, react under a nitrogen atmosphere, cool down and add a neutralizing agent for neutralization reaction, add deionized water to the system under stirring, and obtain the bio-based waterborne polyurethane-acrylate adhesive after vacuum rotary evaporation.

2. The method for preparing the bio-based waterborne polyurethane-acrylate adhesive as described in claim 1, characterized in that, Includes at least one of the following (1)-(10): (1) The branched core is selected from at least one of trimethylolpropane, pentaerythritol, dipentaerythritol, and glycerol; (2) The bio-based polyol is selected from at least one of bio-based polyether polyol and bio-based polycarbonate polyol; (3) The hydrophilic chain extender is selected from at least one of 2,2-dimethylolbutyric acid and 2,2-dimethylolpropionic acid; (4) The diisocyanate is selected from at least one of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, and diphenylmethane diisocyanate; (5) The catalyst is selected from at least one of dibutyltin dilaurate, organobismuth, bismuth neodecanoate, and zinc neodecanoate; (6) The double bond monomer is selected from at least one of pentaerythritol triacrylate, trimethylolpropane triacrylate, and hydroxyethyl methacrylate; (7) The organic solvent is selected from at least one of acetone and butanone; (8) The acrylate monomers include hard monomers and soft monomers, wherein the hard monomers are selected from at least one of methyl methacrylate and isobornyl methacrylate, and the soft monomers are selected from at least one of butyl acrylate and isooctyl acrylate; (9) The initiator is selected from at least one of azobisisobutyronitrile and benzoyl peroxide; (10) The neutralizing agent is selected from at least one of triethylamine and N,N-dimethylethanolamine.

3. The method for preparing the bio-based waterborne polyurethane-acrylate adhesive as described in claim 1, characterized in that, In step S1, the dehydration temperature is 100-110℃, the vacuum degree is -0.05~-0.1MPa, and the dehydration time is 0.5-1.5h. And / or, the temperature is lowered to 70-80℃ for heat preservation reaction, and the reaction time is 2-4 hours; And / or, the end-capping reaction time is 1-3 hours.

4. The preparation method of the bio-based waterborne polyurethane-acrylate adhesive as described in claim 1, characterized in that, In step S2, the reaction temperature under a nitrogen atmosphere is 65-75°C, and the reaction time is 3-5 hours. And / or, the temperature is lowered to 40±2℃ for neutralization reaction, the neutralization reaction time is 15-20 min, and the pH is adjusted to 7-9; And / or, the stirring speed is 2000-4000 rpm.

5. The method for preparing the bio-based waterborne polyurethane-acrylate adhesive as described in claim 1, characterized in that, The raw materials for preparing the multi-arm star-shaped polyurethane containing double bonds include the following components in parts by weight: 1-2.5 parts of branched core, 55-80 parts of bio-based polyol, 4-6 parts of hydrophilic chain extender, 15-30 parts of diisocyanate, 0.03-0.05 parts of catalyst, and 2-10 parts of double bond monomer. The raw materials for preparing the bio-based waterborne polyurethane-acrylate adhesive include the following components in parts by weight: 50-100 parts of multi-arm star-shaped polyurethane containing double bonds, 30-80 parts of organic solvent, 20-50 parts of acrylate monomer, 0.2-0.8 parts of initiator, 4-7 parts of neutralizer, and 100-150 parts of deionized water.

6. The method for preparing the bio-based waterborne polyurethane-acrylate adhesive as described in claim 5, characterized in that, The weight ratio of the branched core to the double bond monomer is 1:(2-10).

7. The method for preparing the bio-based waterborne polyurethane-acrylate adhesive as described in claim 5, characterized in that, The weight ratio of the double-bonded multi-arm star-shaped polyurethane to the acrylate monomer is 1:(0.2-0.5).

8. A bio-based waterborne polyurethane-acrylate adhesive prepared by a method according to any one of claims 1-7.

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