A PUR adhesive suitable for soft, comfortable materials and its preparation method

Abstract

This application relates to the field of polyurethane adhesives and discloses a PUR adhesive suitable for soft, comfortable materials and its preparation method. The PUR adhesive includes an isocyanate-terminated polyurethane prepolymer and a polymer molecular sieve chemically bonded and embedded in the molecular chain of the prepolymer. The polymer molecular sieve is a 2-ethylhexyl acrylate gelatin composite metal-organic framework material, 2-EHA-Gelatin / MOF, which has a regular cubic lattice porous structure with a pore size of 3.5–5.0 Å. This invention solves the technical bottlenecks of existing soft, elastic PUR adhesives, such as slow curing in the middle and later stages and a sharp drop in adhesion under humid and hot conditions. It utilizes a staged synergistic curing mechanism, achieving rapid surface drying in the early stage using an organic bismuth catalyst, and actively transferring polar molecules through the microporous channels of the molecular sieve to accelerate internal curing in the middle and later stages. Simultaneously, it utilizes the cubic lattice structure of the MOF to induce curing and crystallization.

Description

Technical Field

[0001] This application relates to the technical field of polyurethane adhesives, and more specifically, to a PUR adhesive suitable for soft, comfortable materials and a method for preparing the same. Background Technology

[0002] Soft, comfortable materials (such as polyurethane foam, TPU film, and fabrics) are widely used in consumer goods such as sofas, mattresses, and automotive interior upholstery due to their low modulus and high flexibility. This places high demands on the initial adhesion, flexibility, adhesion retention after humid heat aging, and curing uniformity of adhesives. One-component moisture-curing PUR hot melt adhesives are widely used in this field because they do not require mixing of two components, are easy to apply, and exhibit good elasticity after curing.

[0003] However, existing one-component PUR adhesives suffer from the following three major technical bottlenecks:

[0004] (1) Slow curing in the middle and late stages: After the surface drying of moisture-curing PUR adhesive, the colloidal particles are sealed, making it difficult for external moisture to penetrate into the interior, resulting in slow curing speed in the middle and late stages; the surface drying time of traditional soft adhesive system is 45-60 min, which is significantly slower than that of hard adhesive system (30-45 min), and the overall curing efficiency is low.

[0005] (2) Adhesion strength drops sharply under humid and hot conditions: Due to the low content of crystalline molecules such as benzene rings and branches in the molecular structure of soft elastic PUR materials, the adhesion strength drops significantly under humid and hot conditions. After a humid and hot aging test at 90℃ / 90%RH / 240h, the peel strength of traditional soft rubber PUR dropped sharply from 20 N / 5cm to 3-5 N / 5cm, a decrease of more than 80%, which seriously fails to meet the actual use requirements. Although traditional hard rubber PUR has better resistance to humid and hot aging (peel strength dropped from 40 N / 5cm to 35 N / 5cm, with a retention rate of about 87.5%), its rigidity is not suitable for the flexible bonding requirements of soft and comfortable materials.

[0006] (3) Limitations of traditional catalyst systems: Traditional catalysts can only meet the early curing requirements of the surface and room temperature conditions, and cannot effectively promote the continuous curing reaction inside the closed system, which restricts the overall performance of the adhesive.

[0007] Regarding the field of polyurethane adhesives, several related patents have been published. CN114940885A discloses a thermally conductive two-component polyurethane adhesive, in which 4A molecular sieve (0-2 parts) is added to component A as a dehydrating agent, and component B contains isocyanate-terminated polyurethane prepolymer. The adhesive's resistance to damp heat is improved by aromatic polyether polyols and polyolefin polyols, resulting in a thermal conductivity greater than 2 W / m·K. CN116445121A discloses a two-component polyurethane structural adhesive with high-temperature adhesion greater than cohesive strength. 3A molecular sieve water absorbent (4-14 parts) is added to the polymer component, and high-temperature adhesion is enhanced by a combination of modified castor oil polyol and bisphenol A polyether polyol. CN119081633A discloses a thermally conductive polyurethane structural adhesive, in which molecular sieve (5-8 parts) and organic alkali-coated modified inorganic fillers are added to component A, and organic acid-coated modified inorganic fillers are added to component B. The open time is extended through an acid-base neutralization mechanism.

[0008] The aforementioned existing technologies share the following common drawbacks: First, molecular sieves are simply physically mixed into component A (polyol side) as ordinary inorganic dehydrating agents (3A / 4A aluminosilicate type), completely separated from the prepolymer containing NCO groups, and the active mass transfer potential of the microporous channels of molecular sieves is not fully developed; Second, they all adopt a two-component mixing and curing mechanism, which cannot solve the problem of slow curing in the later stages of single-component systems; Third, they are all designed for rigid substrates (thermally conductive structural adhesives such as aluminum shells for power batteries / PET films), and are not suitable for the flexible bonding requirements of soft and comfortable materials; Fourth, the fundamental reason for the poor resistance of soft and elastic PUR to humid heat aging (insufficient crystalline molecules) has not been effectively solved in the aforementioned existing technologies. Summary of the Invention

[0009] The purpose of this invention is to solve the technical problems of existing soft elastic PUR adhesives, such as slow curing speed in the later stages, sharp drop in adhesion under humid and hot conditions, and insufficient resistance to environmental aging.

[0010] To achieve the above-mentioned objectives, this application provides a PUR adhesive suitable for soft, comfortable materials and its preparation method, employing the following technical solution:

[0011] In a first aspect, this application provides a PUR adhesive suitable for soft, comfortable materials, comprising:

[0012] Isocyanate-terminated polyurethane prepolymers; and

[0013] A polymer molecular sieve chemically bonded and embedded in the prepolymer molecular chain;

[0014] The polymer molecular sieve is 2-EHA-Gelatin / MOF, a metal-organic framework material composed of 2-ethylhexyl acrylate gelatin, which has a regular cubic lattice porous structure with a pore size of 3.5–5.0 Å.

[0015] Further, based on 100 parts by weight of the terminal isocyanate-based polyurethane prepolymer, the amounts of each component are as follows:

[0016] 2-EHA-Gelatin / MOF 2~8 portions;

[0017] 0.02~0.1 parts of organic bismuth catalyst.

[0018] Furthermore, the NCO content of the terminal isocyanate-based polyurethane prepolymer is 3-5 wt%.

[0019] Furthermore, the 2-EHA-Gelatin / MOF is composed of the following three parts:

[0020] A gelatin backbone containing active amino groups (-NH2) and hydroxyl groups (-OH);

[0021] Zr-based MOFs; and

[0022] A 2-ethylhexyl acrylate modified layer is grafted onto the gelatin backbone and / or MOF surface.

[0023] Furthermore, the adhesive employs a staged synergistic curing mechanism, the mechanism including:

[0024] Early solidification stage;

[0025] During the mid-to-late curing stages, the microporous channels of the 2-EHA-Gelatin / MOF actively capture and transport external H2O and CO2 molecules; and

[0026] During the crystallization and solidification stage, the MOF induces and accelerates the crystallization of soft segment polyurethane.

[0027] The surface drying time for the initial curing stage is 30-45 minutes;

[0028] The degree of curing of the adhesive at 23℃ / 50% RH for 24 hours is not less than 90%;

[0029] After 240 hours of damp heat aging at 90℃ / 90% RH, the peel strength retention rate is not less than 80%.

[0030] Furthermore, the soft, comfortable material includes polyurethane foam, TPU film, fabric, and leather.

[0031] Secondly, this application provides a method for preparing the PUR adhesive, comprising the following steps:

[0032] S1, Preparation of 2-EHA-Gelatin / MOF: Gelatin solution is prepared by dissolving gelatin in deionized water, Zr-based MOF precursor is added for hydrothermal reaction, MOF crystals are grown in situ on the gelatin framework to obtain Gelatin / MOF composite material, 2-ethylhexyl acrylate and initiator are added for graft modification, and the 2-EHA-Gelatin / MOF is obtained after drying.

[0033] S2, Preparation of prepolymer: Under inert gas protection, polyester polyol is reacted with diisocyanate to prepare isocyanate-terminated polyurethane prepolymer;

[0034] S3, Preparation of adhesive: The prepolymer prepared in step S2 is heated to 80~100℃, and 2-EHA-Gelatin / MOF prepared in step S1 is added. The mixture is stirred to allow the active amino / hydroxyl groups on the molecular sieve to undergo a chemical bonding reaction with the NCO groups of the prepolymer. After cooling, an organic bismuth catalyst is added, stirred evenly, cooled and sealed to obtain the PUR adhesive.

[0035] Furthermore, in step S1, the mass fraction of the gelatin solution is 10~15wt%, and the preparation temperature is 50~60℃;

[0036] In the Zr-based MOF precursor, the molar ratio of zirconium chloride to terephthalic acid is 1:1, the hydrothermal reaction temperature is 110~130℃, and the reaction time is 20~28h.

[0037] The initiator is ammonium persulfate, and the amount used is 0.5~2.0 wt% of the mass of 2-ethylhexyl acrylate. The grafting modification temperature is 65~80℃, and the reaction time is 3~5h.

[0038] Further, in step S2, the polyester polyol has a molecular weight of 1000~4000 and a functionality of 2~3;

[0039] The diisocyanate is 4,4'-diphenylmethane diisocyanate;

[0040] The reaction temperature is 75~85℃, and the reaction time is 2~4 hours.

[0041] Further, in step S3, the amount of 2-EHA-Gelatin / MOF is 2 to 8 wt% of the prepolymer mass; the amount of the organic bismuth catalyst is 0.02 to 0.1 wt% of the prepolymer mass.

[0042] In summary, this application has the following beneficial effects:

[0043] (1) Improved curing efficiency throughout the process: The surface drying time is shortened from 45~60 min for traditional soft glue to 30~45 min, reaching the level of traditional hard glue; the curing degree in 24 hours is not less than 90%, and the curing rate in the middle and late stages is significantly improved compared with the blank control group without the addition of polymer molecular sieves, effectively breaking through the bottleneck of moisture penetration after surface drying and sealing.

[0044] (2) Enhanced adhesion stability: The initial peel strength reaches 35 N / 5cm, which is better than traditional soft rubber (20 N / 5cm); after 90℃ / 90%RH / 240h damp heat aging, the peel strength drops from 35 N / 5cm to 25 N / 5cm, with a strength retention rate of about 71.4% and fluctuations within 10%, which is significantly better than traditional soft rubber (reduction ≥80%), and close to the damp heat aging resistance level of traditional hard rubber (retention rate of about 87.5%), while maintaining the applicability of soft materials.

[0045] (3) Improved resistance to environmental aging: The cubic lattice structure of 2-EHA-Gelatin / MOF promotes curing and crystallization, compensates for the structural defects of insufficient crystalline molecules of soft elastic PUR, improves the service life of adhesives under complex environmental conditions, and broadens its application range in soft and comfortable materials such as sofas, mattresses, and automotive interior soft packs.

[0046] (4) Excellent application adaptability: The adhesive maintains good elasticity after curing and is suitable for flexible bonding of soft porous substrates such as polyurethane foam and TPU film. The bonding force remains stable under compression / tension cycle conditions. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of the 2-EHA-Gelatin / MOF polymer molecular sieve of the present invention, showing the composite composition of gelatin framework, MOF porous structure and 2-EHA modified layer; Detailed Implementation

[0048] The technical solutions and effects of this application will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the invention, not the entire structure.

[0049] Example 1

[0050] This embodiment discloses a PUR adhesive suitable for soft, comfortable materials, the preparation method of which includes:

[0051] S1: Preparation of 2-EHA-Gelatin / MOF polymer sieves

[0052] 10 g of gelatin (food grade, molecular weight approximately 80,000 g / mol) was weighed and added to 90 g of deionized water. The solution was stirred at 300 rpm in a 55°C water bath until completely dissolved, yielding a 10 wt% gelatin solution. 2.33 g of zirconium chloride (ZrCl4, 10 mmol) and 1.66 g of terephthalic acid (BDC, 10 mmol) were added to the gelatin solution, and stirring was continued for 30 min to ensure uniform dispersion of the precursor. The mixture was transferred to a 200 mL PTFE-lined stainless steel autoclave, sealed, and placed in an oven for hydrothermal reaction at 120°C for 24 hours. After the reaction, the mixture was allowed to cool naturally to room temperature. The resulting product was centrifuged at 8000 rpm for 15 min, and the supernatant was discarded. The precipitate was washed three times with 100 mL of deionized water each time. The washed product was then vacuum-dried at 40°C for 24 hours to obtain the gelatin / MOF composite material.

[0053] 5 g of the above gelatin / MOF composite material was dispersed in 50 mL of anhydrous toluene, and 5 g of 2-ethylhexyl acrylate (2-EHA) and 0.05 g of ammonium persulfate (initiator, 1 wt% of 2-EHA) were added. Under nitrogen protection, the mixture was heated to 70 °C and stirred at 200 rpm for 4 hours. After the reaction, the solid product was collected by filtration and washed twice with 30 mL of anhydrous ethanol each time to remove unreacted monomers. Finally, the product was vacuum dried at 40 °C for 12 hours to obtain a 2-EHA-Gelatin / MOF polymer molecular sieve, which was a white to pale yellow powder. Characterization by nitrogen adsorption-desorption testing showed that the BET specific surface area of ​​this molecular sieve was 852 m². 2 / g, with pore sizes mainly distributed between 3.8 and 4.5 Å, exhibiting a regular cubic lattice porous structure.

[0054] S2: Preparation of isocyanate-terminated polyurethane prepolymers

[0055] In a 2L reactor equipped with a nitrogen protection device, mechanical stirrer, and heating mantle, 1000g of polyester polyol (molecular weight 2000, functionality 2, hydroxyl value 56 mg KOH / g) was added. The mixture was heated to 120℃ and dehydrated under a vacuum of -0.095MPa for 2 hours. After dehydration, the temperature was lowered to 80℃, and 450g of 4,4'-diphenylmethane diisocyanate (MDI) was added. The mixture was stirred at 150 rpm under nitrogen protection and reacted at 80℃ for 3 hours. Samples were taken every 30 minutes during the reaction, and the NCO content was determined by di-n-butylamine titration. Heating was stopped when the NCO content stabilized at 3.8~4.2wt%, yielding an isocyanate-terminated polyurethane prepolymer.

[0056] S3: Preparation of PUR adhesive

[0057] The prepolymer prepared in step S2 was heated to 90°C, and 50g (5wt% of the prepolymer mass) of the 2-EHA-Gelatin / MOF polymer molecular sieve prepared in step S1 was added. The mixture was stirred at 300 rpm for 30 minutes to allow the active amino and hydroxyl groups on the molecular sieve to fully react with the NCO groups on the prepolymer molecular chain, achieving chemical bonding and embedding of the molecular sieve into the prepolymer molecular chain. The temperature was then lowered to 80°C, and 0.5g of an organobismuth catalyst (16wt% bismuth content, 0.05wt% of the prepolymer mass) was added. The mixture was stirred for another 10 minutes to ensure uniform dispersion of the catalyst. Finally, the mixture was discharged under nitrogen protection and sealed in aluminum foil tubes to obtain the PUR adhesive.

[0058] Example 2

[0059] This embodiment discloses a PUR adhesive suitable for soft, comfortable materials. The difference from Embodiment 1 lies in the concentration of the gelatin solution in step S1 and the amount of 2-EHA-Gelatin / MOF used in step S3, as detailed below:

[0060] In step S1, the gelatin solution is prepared by weighing 15g of gelatin and adding it to 85g of deionized water to obtain a gelatin solution with a mass fraction of 15wt%. The remaining operations are the same as in Example 1 to obtain 2-EHA-Gelatin / MOF polymer molecular sieve.

[0061] In step S3, the amount of 2-EHA-Gelatin / MOF used was 20 g (i.e., 2 wt% of the prepolymer mass), and the amount of organic bismuth catalyst used was the same as in Example 1. The remaining operations were the same as in Example 1, resulting in the PUR adhesive.

[0062] Example 3

[0063] This embodiment discloses a PUR adhesive suitable for soft, comfortable materials. The difference from Embodiment 1 lies in the amount of 2-EHA-Gelatin / MOF used in step S3, as detailed below:

[0064] In step S3, the amount of 2-EHA-Gelatin / MOF used was 80 g (i.e., 8 wt% of the prepolymer mass), and the amount of organic bismuth catalyst used was the same as in Example 1. The remaining operations were the same as in Example 1, resulting in the PUR adhesive.

[0065] Example 4

[0066] This embodiment discloses a PUR adhesive suitable for soft, comfortable materials. The difference from Embodiment 1 lies in the different hydrothermal reaction conditions of the MOF in step S1, as detailed below:

[0067] In step S1, the hydrothermal reaction temperature is 110°C, and the reaction time is 28 hours. The remaining operations are the same as in Example 1, resulting in PUR adhesive.

[0068] Example 5

[0069] This embodiment discloses a PUR adhesive suitable for soft, comfortable materials. The difference from Embodiment 1 lies in the grafting modification conditions in step S1, as detailed below:

[0070] In step S1, the grafting modification temperature was 80°C, the reaction time was 3 hours, and the amount of ammonium persulfate was 0.025 g (0.5 wt% of the mass of 2-EHA). The remaining operations were the same as in Example 1, and PUR adhesive was obtained.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that 2-EHA-Gelatin / MOF polymer molecular sieve is not added in step S3, as detailed below:

[0073] In step S3, the prepolymer prepared in S2 is heated to 90°C, stirred for 30 minutes, then cooled to 80°C, and 0.5 g of organic bismuth catalyst is added. Stirring continues for 10 minutes. No molecular sieve material is added. The remaining operations are the same as in Example 1, yielding the adhesive.

[0074] Comparative Example 2

[0075] The difference between this comparative example and Example 1 is that commercially available 4A molecular sieve is used instead of 2-EHA-Gelatin / MOF, and a physical mixing method is used instead of chemical bonding and embedding, as detailed below:

[0076] In step S3, 5g of commercially available 4A molecular sieve (aluminosilicate type, pore size approximately 4Å) was taken and activated at 200°C for 4 hours to remove adsorbed water. The prepolymer prepared in S2 was heated to 90°C, stirred for 30 minutes, and then cooled to 80°C. The activated 4A molecular sieve was added, and the mixture was physically stirred at 300 rpm for 10 minutes (at this point, the molecular sieve cannot chemically react with the NCO groups). Then, 0.5g of organic bismuth catalyst was added, and stirring was continued for another 10 minutes. The remaining operations were the same as in Example 1 to obtain the adhesive.

[0077] Comparative Example 3

[0078] The difference between this comparative example and Example 1 is that a Gelatin / MOF composite material without 2-EHA modification is used instead of 2-EHA-Gelatin / MOF, as detailed below:

[0079] In step S1, only the Gelatin / MOF composite material is prepared without the subsequent 2-EHA grafting modification step. That is, the Gelatin / MOF composite material is directly obtained after hydrothermal reaction, washing, and drying and used as an intermediate.

[0080] In step S3, the Gelatin / MOF composite material is added to the prepolymer at a dosage of 5 wt%, and the remaining operations are the same as in Example 1 to obtain the PUR adhesive.

[0081] Comparative Example 4

[0082] The difference between this comparative example and Example 1 is that a commercially available conventional soft rubber type PUR is used as a control, without any modification treatment.

[0083] Comparative Example 5

[0084] The difference between this comparative example and Example 1 is that a commercially available conventional hard plastic PUR is used as a control, without any modification treatment.

[0085] Performance testing

[0086] 1. Preparation of experimental samples

[0087] The PUR adhesives prepared in Examples 1-5 and Comparative Examples 1-3, as well as the commercially available products in Comparative Examples 4-5, were used to prepare test samples according to the following method: The adhesives were heated to 120°C to melt and uniformly coated onto a standard polyurethane foam substrate (density 30 kg / m³). 3 On the surfaces to be bonded, a standard TPU film (100mm×25mm×10mm thick, 0.5mm thick, 100mm×25mm thick) is coated with 150g / m². 2 Immediately bond the polyurethane foam substrate to the TPU film, apply a pressure of 0.2 MPa and hold for 30 seconds, then cure for 72 hours under standard environmental conditions (23°C / 50%RH) to obtain peel strength test specimens. Prepare 5 parallel specimens for each example or comparative example, and take the average value of the test results.

[0088] 2. Testing Methods

[0089] (1) Surface drying time test: After heating the adhesive to 120℃, it is evenly coated on a clean glass plate with a thickness of 0.5mm and immediately placed under standard environmental conditions (23℃ / 50%RH). The surface drying time is measured by the finger touch method. The surface of the adhesive film is not sticky and there is no stringing when the finger is lifted. Each sample is tested 3 times and the average value is taken.

[0090] (2) 24-hour curing degree test: Fourier transform infrared spectroscopy (FTIR) was used for determination. Samples were taken after the adhesive was prepared (initial state) and after curing for 24 hours under standard environmental conditions. Test samples were prepared using the potassium bromide pellet method. In the infrared spectrum, at 2270 cm⁻¹... -1 The characteristic absorption peak of the isocyanate group (-NCO) at 1720 cm⁻¹ -1 The peak area ratio of the reference absorption peak at the carbonyl group (C=O) is used as the basis for quantification. The degree of curing is calculated according to the following formula: Degree of curing (%) = [1 - (the peak area ratio of -NCO in the sample after curing for 24 hours / the peak area ratio of -NCO in the initial sample)] × 100%.

[0091] (3) Initial peel strength test: The prepared test strips were subjected to a 90° peel strength test using a universal testing machine under standard environmental conditions. The test parameters were set as follows: peel speed 100 mm / min, initial clamp distance 50 mm. The maximum peel force during the peeling process was recorded (unit: N / 5 cm). Five parallel strips were tested for each sample, and the average value was taken and the standard deviation was calculated.

[0092] (4) Peel strength test after damp heat aging: The prepared test strips were placed in a constant temperature and humidity test chamber, with the temperature set at 90℃ and the relative humidity at 90%, and continuously aged for 240 hours. After aging, the strips were taken out and placed under standard environmental conditions for 24 hours for conditioning. Then, the 90° peel strength test was performed using the same method as the initial peel strength test. The strength retention rate was calculated using the following formula: Retention rate (%) = (Peel strength after damp heat aging / Initial peel strength) × 100%.

[0093] (5) Adhesion retention rate test after compression / tension cycling: The bonded polyurethane foam / TPU soft film composite samples were subjected to compression / tension cycling tests. The test parameters were set as follows: compressive strain of 30%, cycling frequency of 1Hz, and number of cycles of 1000. After the cycle, the samples were placed under standard environmental conditions for 24 hours, and then the remaining peel strength was tested and compared with the initial peel strength to calculate the retention rate.

[0094] 3. Test Results

[0095] Surface drying time (min) 24h curing degree (%) Initial peel strength (N / 5cm) Peel strength after damp heat aging (N / 5cm) Strength retention rate after aging (%) Strength retention rate after compression cycles (%) Example 1 35 93 35.2 25.1 71.3 92 Example 2 41 85 30.5 16.8 55.1 88 Example 3 32 86 34.8 24.5 70.4 93 Example 4 38 90 33.9 22.7 67.0 90 Example 5 36 91 34.5 23.8 69.0 91 Comparative Example 1 55 68 20.5 3.2 15.6 71 Comparative Example 2 48 72 19.8 4.5 22.7 73 Comparative Example 3 39 87 25.3 12.7 50.2 76 Comparative Example 4 52 75 21.5 3.9 18.1 74 Comparative Example 5 38 92 42.0 36.8 87.6 52

[0096] As shown in the table above, by comparing Example 1 and Comparative Example 5, the PUR adhesive of Example 1 exhibits excellent comprehensive performance in terms of surface drying time (35 minutes), 24-hour curing degree (93%), initial peel strength (35.2 N / 5 cm), and strength retention rate after damp heat aging (71.3%). Its surface drying time is comparable to that of traditional hard adhesive (Comparative Example 5, 38 minutes), which is far superior to that of traditional soft adhesive (Comparative Example 4, 52 minutes). Although its strength retention rate after damp heat aging (71.3%) is slightly lower than that of traditional hard adhesive (87.6%), it is much higher than that of traditional soft adhesive (18.1%) and the blank control group without molecular sieve (Comparative Example 1, 15.6%). At the same time, its strength retention rate after compression cycles is as high as 92%, which is far superior to that of traditional hard adhesive (52%), indicating that it has excellent flexibility and dynamic load durability.

[0097] By comparing Example 1 and Comparative Example 2, it was found that Comparative Example 2, which used ordinary 4A molecular sieves for simple physical mixing, exhibited significantly inferior performance compared to Example 1. The 24-hour curing degree of Comparative Example 2 was only 72%, and the strength retention rate after hygrothermal aging was only 22.7%. This indicates that ordinary inorganic molecular sieves can only play a limited role as passive dehydrating agents and cannot achieve the staged synergistic curing effect brought about by active mass transfer and chemical bonding.

[0098] By comparing Example 1 and Comparative Example 3, Comparative Example 3, using a Gelatin / MOF composite material without 2-EHA modification, showed better performance than Comparative Examples 1 and 2, but still lagged significantly behind Example 1. This indicates that the 2-EHA modification layer is crucial for improving the compatibility between the molecular sieve and the polyurethane matrix, promoting uniform dispersion, and enhancing interfacial adhesion strength.

[0099] By comparing Examples 1 and Examples 2-3, in Example 2, when the dosage of 2-EHA-Gelatin / MOF was 2wt%, all properties were improved, but not significantly, especially the strength retention rate after damp heat aging was only 55.1%. In Example 3, when the dosage was 8wt%, the performance was basically the same as that of Example 1, but the excessive amount of molecular sieve may lead to an increase in the viscosity of the system, affecting the sizing operability.

[0100] By comparing Examples 1 and 4-5, it was found that Examples 4 and 5 had some adjustments in the preparation process parameters. The performance of the products obtained fluctuated slightly compared with Example 1, but remained good overall, indicating that the preparation method of the present invention has a wide range of process adaptability and good repeatability.

[0101] In summary, the technical solution provided in this application creatively designs and synthesizes 2-EHA-Gelatin / MOF polymer molecular sieves and chemically bonds them into the molecular chain of polyurethane prepolymer, successfully constructing a staged synergistic curing mechanism. At the same time, it solves the technical problems of slow curing speed, sharp drop in adhesion under humid and hot conditions, and poor compatibility with soft substrates in existing soft elastic PUR adhesives, and has significant progress and outstanding substantive features.

[0102] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A PUR adhesive suitable for soft, comfortable materials, characterized in that, include: Isocyanate-terminated polyurethane prepolymer; as well as A polymer molecular sieve chemically bonded and embedded in the prepolymer molecular chain; The polymer molecular sieve is 2-EHA-Gelatin / MOF, a metal-organic framework material composed of 2-ethylhexyl acrylate gelatin, which has a regular cubic lattice porous structure with a pore size of 3.5–5.0 Å.

2. The PUR adhesive for soft, comfortable materials according to claim 1, characterized in that, Based on a mass of 100 parts of the terminal isocyanate-based polyurethane prepolymer, the amounts of each component are as follows: 2-EHA-Gelatin / MOF 2~8 portions; 0.02~0.1 parts of organic bismuth catalyst.

3. The PUR adhesive for soft, comfortable materials according to claim 1, characterized in that, The NCO content of the terminal isocyanate-based polyurethane prepolymer is 3-5 wt%.

4. The PUR adhesive for soft, comfortable materials according to claim 1, characterized in that, The 2-EHA-Gelatin / MOF is composed of the following three parts: A gelatin backbone containing active amino groups (-NH2) and hydroxyl groups (-OH); Zr-based MOFs; and A 2-ethylhexyl acrylate modified layer is grafted onto the gelatin backbone and / or MOF surface.

5. The PUR adhesive for soft, comfortable materials according to claim 1, characterized in that, The adhesive employs a staged synergistic curing mechanism, which includes: Early solidification stage; During the mid-to-late curing stages, the microporous channels of the 2-EHA-Gelatin / MOF actively capture and transport external H2O and CO2 molecules; and During the crystallization and solidification stage, the MOF induces and accelerates the crystallization of soft segment polyurethane. The surface drying time for the initial curing stage is 30-45 minutes; The degree of curing of the adhesive at 23℃ / 50% RH for 24 hours is not less than 90%; After 240 hours of damp heat aging at 90℃ / 90% RH, the peel strength retention rate is not less than 80%.

6. The PUR adhesive for soft, comfortable materials according to claim 5, characterized in that, The soft, comfortable materials include polyurethane foam, TPU film, fabric, and leather.

7. A method for preparing the PUR adhesive according to any one of claims 1-6, characterized in that, Includes the following steps: S1, Preparation of 2-EHA-Gelatin / MOF: Gelatin solution is prepared by dissolving gelatin in deionized water, Zr-based MOF precursor is added for hydrothermal reaction, MOF crystals are grown in situ on the gelatin framework to obtain Gelatin / MOF composite material, 2-ethylhexyl acrylate and initiator are added for graft modification, and the 2-EHA-Gelatin / MOF is obtained after drying. S2, Preparation of prepolymer: Under inert gas protection, polyester polyol is reacted with diisocyanate to prepare isocyanate-terminated polyurethane prepolymer; S3, Preparation of adhesive: The prepolymer prepared in step S2 is heated to 80~100℃, and 2-EHA-Gelatin / MOF prepared in step S1 is added. The mixture is stirred to allow the active amino / hydroxyl groups on the molecular sieve to undergo a chemical bonding reaction with the NCO groups of the prepolymer. After cooling, an organic bismuth catalyst is added, stirred evenly, cooled and sealed to obtain the PUR adhesive.

8. The preparation method according to claim 7, characterized in that, In step S1, the mass fraction of the gelatin solution is 10~15wt%, and the preparation temperature is 50~60℃; In the Zr-based MOF precursor, the molar ratio of zirconium chloride to terephthalic acid is 1:1, the hydrothermal reaction temperature is 110~130℃, and the reaction time is 20~28h. The initiator is ammonium persulfate, and the amount used is 0.5~2.0 wt% of the mass of 2-ethylhexyl acrylate. The grafting modification temperature is 65~80℃, and the reaction time is 3~5h.

9. The preparation method according to claim 7, characterized in that, In step S2, the polyester polyol has a molecular weight of 1000~4000 and a functionality of 2~3. The diisocyanate is 4,4'-diphenylmethane diisocyanate; The reaction temperature is 75~85℃, and the reaction time is 2~4 hours.

10. The preparation method according to claim 7, characterized in that, In step S3, the amount of 2-EHA-Gelatin / MOF is 2-8 wt% of the prepolymer mass; the amount of the organic bismuth catalyst is 0.02-0.1 wt% of the prepolymer mass.

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