Two-component polyurethane laminating adhesive and preparation method thereof

Abstract

The invention relates to a two-component polyurethane laminating adhesive and a preparation method thereof, the two-component polyurethane laminating adhesive comprises a component A and a component B, and the weight ratio of the component A to the component B is 100: (15-25); the component A comprises at least one hydroxyl-terminated polyurethane prepolymer and at least one polyester polyol; the number-average molecular weight Mn of the hydroxyl-terminated polyurethane prepolymer is not less than 25000g / mol, and the main chain of the hydroxyl-terminated polyurethane prepolymer comprises a structural unit formed by polyol into which a hydrophobic side chain is introduced; the glass transition temperature Tg of the polyester polyol is not lower than 45 DEG C; the component B comprises at least one isocyanate curing agent, at least one epoxy resin cross-linking agent and at least one medium-resistant auxiliary agent. According to the present invention, the high initial adhesion can be formed within the extremely short time, the excellent peeling strength can be maintained after the long-term contact with the high-polarity solvent, the unification of the high chemical corrosion resistance and the rapid curing performance is achieved, and the flexible package composition is suitable for the high-speed production line and the harsh chemical environment.

Description

Technical Field

[0001] This application relates to the field of adhesive technology, and in particular to a two-component polyurethane laminate adhesive and its preparation method. Background Technology

[0002] Traditional flexible composite packaging has been widely used in the food and daily chemical industries, and its adhesives typically meet basic requirements for peel strength and hydrolysis resistance. However, when the application shifts to highly corrosive media, especially emulsifiable concentrates in pesticide formulations, the performance assurance of conventional polyurethane adhesives faces severe challenges. Pesticide emulsifiable concentrates often contain polar small-molecule organic solvents (such as methanol, xylene, and N-methylpyrrolidone) and strong emulsifiers. These low-molecular-weight media have extremely strong penetrating power, capable of penetrating the surface of the composite film and entering the soft segment structure inside the polyurethane film.

[0003] The fundamental mechanism by which conventional polyurethane adhesives fail when exposed to pesticide solvents is plasticization. Small-molecule solvents penetrate the adhesive layer and occupy the free volume between polymer segments. This leads to a significant decrease in the glass transition temperature (Tg) of the soft segments of the polyurethane. When the Tg of the adhesive film drops below the actual operating temperature (e.g., storage temperature 40°C), the polymer's activity increases dramatically, macroscopically manifested as softening of the adhesive layer and a sharp decrease in cohesion. This phenomenon, known as plasticizing swelling, ultimately causes a rapid decline in the peel strength of the composite film, triggering interlayer delamination and resulting in packaging leakage.

[0004] To enhance chemical resistance, existing technologies typically attempt to increase crosslinking density or introduce rigid structures. However, these methods generally have technical limitations: simply increasing crosslinking density, while forming a more stable network structure, leads to an exponential increase in system viscosity, severely reducing the adhesive's coating performance and pot life, sacrificing production efficiency. Polyurethane hot melt adhesives utilize high-Tg resins to achieve rapid physical positioning, but their final crosslinked network density and durability are insufficient. Their long-term resistance to media is generally inferior to high-performance two-component liquid laminate adhesives, and it is difficult to meet the high positioning strength requirements of high-speed production lines for rapid winding without sacrificing other properties. Summary of the Invention

[0005] This application provides a two-component polyurethane laminate adhesive and its preparation method to solve the problem of poor chemical corrosion resistance of conventional adhesives in related technologies.

[0006] In a first aspect, embodiments of this application provide a two-component polyurethane laminate adhesive, which includes component A and component B, wherein the weight ratio of component A to component B is 100:(15-25). Component A comprises at least one hydroxyl-terminated polyurethane prepolymer and at least one polyester polyol; the number average molecular weight Mn of the hydroxyl-terminated polyurethane prepolymer is not less than 25000 g / mol, and its main chain contains structural units formed by polyols with introduced hydrophobic side chains; the glass transition temperature Tg of the polyester polyol is not less than 45°C. Component B comprises at least one isocyanate curing agent, at least one epoxy resin crosslinking agent, and at least one media-resistant additive.

[0007] In conjunction with the first aspect, in one embodiment, the number-average molecular weight Mn of the hydroxyl-terminated polyurethane prepolymer is 30,000 g / mol to 45,000 g / mol; And / or, the hydrophobic side chain is an ethyl or an alkyl side chain longer than an ethyl; And / or, the polyols with hydrophobic side chains include at least one of 2-ethyl-1,3-hexanediol and 2-butyl-2-ethyl-1,3-propanediol; And / or, the glass transition temperature Tg of the polyester polyol is not lower than 50°C, and its number-average molecular weight Mn is 5000 g / mol to 15000 g / mol; And / or, the weight ratio of the hydroxyl-terminated polyurethane prepolymer to the polyester polyol is 2:1 to 4:1; And / or, the hydroxyl-terminated polyurethane prepolymer is a hydroxyl-terminated prepolymer obtained by polymerizing isocyanate NCO to hydroxyl OH with a molar ratio R of 0.95 to 0.98; And / or, the amount of the epoxy resin crosslinking agent added accounts for 1.5wt% to 6.0wt% of the total mass of component B; And / or, the amount of the media-resistant additive is 0.2wt% to 3.0wt% of the total mass of component B.

[0008] In conjunction with the first aspect, in one embodiment, the media-resistant additive comprises one or more of a high-rigidity copolymer containing anhydride groups and a multifunctional (meth)acrylate crosslinking agent.

[0009] In conjunction with the first aspect, in one embodiment, the highly rigid copolymer containing anhydride groups includes at least one of styrene-maleic anhydride copolymer SMA and isobutylene-maleic anhydride copolymer ISOBAM. And / or, the multifunctional (meth)acrylate crosslinking agent includes at least one of diethylene glycol (4-tricarboxylic anhydride) TMEG and trimethylolpropane trimethacrylate TMPTMA.

[0010] In conjunction with the first aspect, in one embodiment, component B further comprises a silane coupling agent, wherein the amount of the silane coupling agent added is 0.1 wt% to 2.0 wt% of the total mass of component B.

[0011] In conjunction with the first aspect, in one embodiment, the silane coupling agent is selected from aminosilanes or epoxysilanes.

[0012] Secondly, embodiments of this application provide a method for preparing a two-component polyurethane laminated adhesive as described above, comprising: The raw materials of component A are mixed to obtain component A; The raw materials of component B are mixed to obtain component B; Component A and component B are mixed to obtain a two-component polyurethane laminate adhesive.

[0013] Thirdly, embodiments of this application provide an application of the two-component polyurethane laminating adhesive as described above in the lamination of chemically resistant flexible packaging composite films.

[0014] In conjunction with the third aspect, in one embodiment, the chemically resistant flexible packaging composite film is a pesticide flexible packaging composite film, and the two-component polyurethane laminate adhesive achieves a pull-out strength of at least 0.30 MPa within 60 seconds after lamination and cooling.

[0015] Fourthly, embodiments of this application provide a composite flexible packaging material, which is composed of at least two substrate layers bonded together by any of the two-component polyurethane lamination adhesives described above.

[0016] The beneficial effects of the technical solution provided in this application include: This application provides a two-component polyurethane laminate adhesive and its preparation method. By employing a high-molecular-weight hydroxyl-terminated polyurethane prepolymer with hydrophobic side chains, a high-Tg polyester polyol, an epoxy resin crosslinking agent, and a media-resistant additive, a multi-layered synergistic defense system is constructed. This system features a high-molecular-weight polyurethane backbone, hydrophobic side chain spatial barrier, rapid physical positioning of the high-Tg polyester polyol, a polyurethane-epoxy hybrid network, and media-resistant additives filling the free volume. Therefore, it can form high initial tack in a very short time and maintain excellent peel strength even after prolonged contact with highly polar solvents. This achieves a balance between high chemical corrosion resistance and rapid curing performance, making it suitable for flexible packaging lamination in high-speed production lines and harsh chemical environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 A flowchart illustrating the preparation method of the two-component polyurethane laminated adhesive provided in this application embodiment. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. 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.

[0020] This application provides a two-component polyurethane laminate adhesive, which includes component A and component B, wherein the weight ratio of component A to component B is 100:(15-25). Component A comprises at least one hydroxyl-terminated polyurethane prepolymer and at least one polyester polyol; the number-average molecular weight (Mn) of the hydroxyl-terminated polyurethane prepolymer is not less than 25,000 g / mol, and its main chain contains structural units formed by polyols with introduced hydrophobic side chains; the hydroxyl-terminated polyurethane prepolymer has a high number-average molecular weight to ensure that the film has sufficient cohesive strength and solvent swelling resistance after curing. The main chain of the hydroxyl-terminated polyurethane prepolymer contains structural units formed by polyols with introduced hydrophobic side chains. This side chain structure achieves dual regulation through steric hindrance: on the one hand, it interferes with the close packing and hydrogen bonding of the polymer chains of the hydroxyl-terminated polyurethane prepolymer, significantly reducing the viscosity of the prepolymer resin or its solution, thereby meeting the operability requirements of high-speed coating while maintaining a high number-average molecular weight (Mn); on the other hand, it increases the tortuosity of the solvent penetration path at the microscopic level, forcing small molecule solvents to bypass it, thus enhancing the physical barrier properties against solvents.

[0021] The glass transition temperature (Tg) of the polyester polyol is not lower than 45°C. After high-speed lamination, this high-Tg polyester polyol can rapidly transform from a molten state to a high-hardness glassy state or undergo rapid physical crystallization as the composite film cools, forming numerous microcrystalline regions within the film that act as temporary physical crosslinking points. This rapid physical curing characteristic allows the two-component liquid lamination adhesive to achieve extremely high initial tack before chemical crosslinking has fully developed, significantly shortening the positioning time and ensuring smooth winding of the composite film on high-speed production lines.

[0022] As an example, polyester polyols that meet the requirements of high Tg and specific molecular weight can be prepared in-house using the method described in Example 2 of this application. If the polyester polyol is to be purchased directly, it can be, for example, a high Tg polyester resin from Toyobo's Vylon series (such as Vylon 200, Tg≈67℃) or a high crystallinity / high Tg polyester from Evonik's Dynacoll 7000 series (such as Dynacoll 7150).

[0023] Component B comprises at least one isocyanate curing agent, at least one epoxy resin crosslinking agent, and at least one media-resistant additive.

[0024] The isocyanate curing agent may be an aliphatic isocyanate trimer, such as Covestro's Desmodur N3300, Wanhua Chemical's Wanamate HT-100, or Asahi Kasei's DurnateTPA-100, or other commercially available polyisocyanate curing agents with similar functionality.

[0025] During the curing process, the epoxy groups of the epoxy resin crosslinking agent can undergo ring-opening polymerization with the hydroxyl groups in component A to form a chemically bonded polyurethane-epoxy hybrid network. This integrated network significantly improves the bulk modulus and volume stability of the film, prevents localized structural failures caused by solvent penetration, and significantly enhances the film's resistance to solvent swelling and structural stability.

[0026] The epoxy resin crosslinking agent can be a bisphenol A type epoxy resin, such as Sinopec / Bluestar's E-44 or E-51, or Dow Chemical's DER 331, or Hexion's EPON 828, or other equivalent commercially available bisphenol A type epoxy resins.

[0027] The role of media-resistant additives is to improve the ability of polyurethane networks to resist the plasticizing effect of highly polar small molecule solvents through physical or chemical means, and to fill the free volume between polymer chain segments.

[0028] This application solves the contradictions of traditional adhesives in the face of highly polar solvents such as pesticide emulsions, such as easy plasticization and swelling, low peel strength retention, and slow initial curing, by constructing a multi-level synergistic defense mechanism of high molecular weight polyurethane (PU) skeleton, hydrophobic side chain spatial barrier, rapid physical positioning of high Tg polyester polyol, polyurethane-epoxy hybrid network, and directional filling of free volume by microscopic media-resistant additives. It achieves ultra-high chemical corrosion resistance and excellent rapid curing performance.

[0029] The adhesive of this application exhibits excellent performance under extreme chemical corrosion environments. The pull-out strength reaches ≥0.30MPa within 60 seconds after lamination, and the peel strength retention rate can reach over 91% after immersion in a methanol / pesticide activator solution at 40℃ for 20 days. This ensures the structural integrity and safety of composite packaging for pesticides or hazardous chemicals during long-term storage and transportation. It is suitable for composite flexible packaging in high-speed production lines and extreme chemical corrosion environments, and is applicable to various composite structures, especially multi-layer composite structures containing barrier layers, with a wide range of applications.

[0030] In a preferred embodiment, the number-average molecular weight (Mn) of the hydroxyl-terminated polyurethane prepolymer is 30,000 g / mol to 45,000 g / mol; the hydroxyl-terminated polyurethane prepolymer is typically polymerized in a controlled ratio in a reactor with isocyanate and polyol (as described in Example 1 of this application). A molecular weight below 30,000 g / mol of the hydroxyl-terminated polyurethane prepolymer significantly reduces the cohesive energy of the cured network, making it easily plasticized by pesticide solvents and rapidly degraded; while a molecular weight above 45,000 g / mol results in excessively high resin solution viscosity, severely affecting industrial coating operability and making it unsuitable for high-speed recycling printing presses. To achieve this high molecular weight, preferably, the hydroxyl-terminated polyurethane prepolymer is obtained by polymerizing isocyanate NCO to hydroxyl OH with a molar ratio R of 0.95 to 0.98. During synthesis, the molar ratio R of isocyanate NCO to hydroxyl OH is precisely controlled between 0.95 and 0.98. This substoichiometric ratio ensures that the polymer chain can grow sufficiently through stepwise polymerization and ensures that the final polymer chain ends with hydroxyl groups, making it suitable as the main reactant of component A.

[0031] In a preferred embodiment, the hydrophobic side chain is an ethyl or a longer alkyl side chain than an ethyl. For example, the longer alkyl side chain is selected from propyl, butyl, isobutyl, pentyl, hexyl, or 2-ethylhexyl.

[0032] In a preferred embodiment, the polyol with the introduced hydrophobic side chain comprises at least one of 2-ethyl-1,3-hexanediol and 2-butyl-2-ethyl-1,3-propanediol.

[0033] In a preferred embodiment, the glass transition temperature (Tg) of the polyester polyol is not lower than 50°C, and its number-average molecular weight (Mn) is 5000 g / mol to 15000 g / mol.

[0034] In a preferred embodiment, the weight ratio of the hydroxyl-terminated polyurethane prepolymer to the polyester polyol is 2:1 to 4:1.

[0035] In a preferred embodiment, the amount of epoxy resin crosslinking agent added is 1.5wt% to 6.0wt% of the total mass of component B.

[0036] In a preferred embodiment, the amount of the media-resistant additive is 0.2wt% to 3.0wt% of the total mass of component B.

[0037] In a preferred embodiment, the media-resistant additive comprises one or more of a high-rigidity copolymer containing anhydride groups and a multifunctional (meth)acrylate crosslinking agent.

[0038] For example, the high-rigidity copolymer containing anhydride groups includes at least one of styrene-maleic anhydride copolymer (SMA) and isobutylene-maleic anhydride copolymer (ISOBAM). SMA possesses high polarity and high rigidity, and its anhydride groups can react with the hydroxyl groups in the PU system, anchoring SMA molecules within the PU network. This introduces highly rigid nanoscale micro-regions into the polyurethane soft segments, effectively suppressing the plasticizing effect of highly polar small-molecule solvents on the surrounding PU segments through steric hindrance.

[0039] For example, the multifunctional (meth)acrylate crosslinking agent includes at least one of diethylene glycol (4-tricarboxylic anhydride) TMEG and trimethylolpropane trimethacrylate TMPTMA. As a multifunctional active small molecule, TMEG rapidly participates in the reaction during the curing process in regions of the PU network structure that were originally micropores or free volume (FFV) to form local crosslinking points or be physically anchored, effectively "blocking" the penetration pathways of small molecule solvents at the molecular scale.

[0040] Preferably, the combined use of SMA and TMEG achieves synergistic defense against swelling media.

[0041] In a preferred embodiment, component B further comprises a silane coupling agent, wherein the amount of the silane coupling agent added is 0.1 wt% to 2.0 wt% of the total mass of component B. The silane coupling agent is selected from aminosilanes or epoxysilanes to enhance the interfacial adhesion strength between the adhesive and the inorganic substrate (such as aluminum foil).

[0042] See Figure 1As shown in the embodiments of this application, a method for preparing a two-component polyurethane laminated adhesive is also provided, comprising: 101: Mix the raw materials of component A to obtain component A.

[0043] 102: Mix the raw materials of component B to obtain component B.

[0044] 103: Mix component A and component B to obtain a two-component polyurethane laminate adhesive.

[0045] This application also provides an application of a two-component polyurethane laminating adhesive in the lamination of chemically resistant flexible packaging composite films. The chemically resistant flexible packaging composite film is a pesticide flexible packaging composite film. Within 60 seconds of lamination and cooling, the resulting adhesive layer of the two-component polyurethane laminating adhesive reaches a pull-out strength of at least 0.30 MPa.

[0046] This application also provides a composite flexible packaging material, which is composed of at least two substrate layers bonded together by a two-component polyurethane lamination adhesive.

[0047] The technical solution of this application will be clearly and completely described below with reference to the embodiments.

[0048] Unless otherwise specified in the examples, the procedures should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0049] Information on the raw materials used in the embodiments and comparative examples of this application is shown in Table 1.

[0050] Table 1 Experimental Materials

[0051] Example 1 (F1): (1) Preparation of hydroxyl-terminated polyurethane prepolymer (PU-35k) Raw material input and dehydration: PBA-2000, EHD and BDO are added to the reactor and dehydrated at 110℃ under vacuum to ensure that the water content of the system is less than 0.05wt%.

[0052] Polymerization reaction control: Cool to 60℃. Add precisely measured MDI, controlling the NCO / OH molar ratio R to be 0.97. Add DBTL catalyst and heat to 80-85℃ for reaction.

[0053] Molecular weight monitoring and quenching: The number-average molecular weight (Mn) increase was monitored by GPC during the reaction. When Mn reached the target window of 35000 g / mol, EA was immediately added for dilution and the reaction was rapidly quenched by cooling to obtain the intermediate PU-35k solution.

[0054] (2) Preparation of high Tg polyester polyol (PES-10k) Esterification and Polycondensation: IPA and CHDM were added to a reactor and esterification was carried out at 220°C. After esterification, TBT catalyst was added, the temperature was raised to 240°C and vacuum was applied to carry out polycondensation until GPC analysis showed that Mn reached approximately 10500 g / mol and Tg was approximately 55°C.

[0055] (3) Preparation of component A (main agent A-F1) The prepared PU-35k solution and PES-10k solution were added to a mixing vessel at a weight ratio of 100:33.3 (approximately 3:1) and stirred for 30 minutes to obtain the main agent A-F1.

[0056] (4) Preparation of component B (curing agent B-F1) Add 750g of ethyl acetate (EA) to a dry mixing vessel, start stirring, and then slowly add 700g of N-3300, 35g of epoxy resin (E-20), 10.5g of silane coupling agent (KH-560), 7g of SMA-1000, and 3.5g of TMEG-200 in sequence. Stir at room temperature for 1 hour until all components are completely dissolved to obtain curing agent B-F1.

[0057] (5) Preparation of final adhesive (F1) Mix the main agent A-F1 and the curing agent B-F1 at a weight ratio of 100:18, dilute with ethyl acetate to the concentration required for coating, and stir evenly to obtain the adhesive F1 of the present application.

[0058] Example 2 (F2): (1) Preparation of hydroxyl-terminated polyurethane prepolymer (PU-30k): The synthesis method is the same as in Example 1, but the feed ratio is adjusted so that the number average molecular weight Mn is 30000 g / mol.

[0059] (2) Preparation of component A: PU-30k solution and 60% solution of commercially available high Tg polyester polyol Vylon 200 (Toyobo, Tg≈67℃) were mixed at a weight ratio of 4:1 (based on solid content) to obtain main agent A-F2.

[0060] (3) Final adhesive preparation: Mix the main agent A-F2 and the curing agent B-F1 (same as in Example 1) at a weight ratio of 100:15 to obtain adhesive F2.

[0061] Example 3 (F3): (1) Preparation of hydroxyl-terminated polyurethane prepolymer (PU-42k): The synthesis method is the same as in Example 1, but the NCO / OH molar ratio R is controlled to be 0.98, and the number average molecular weight Mn is increased to 42000 g / mol.

[0062] (2) Preparation of component A: PU-42k solution and PES-10k solution (same as in Example 1) were mixed at a weight ratio of 100:33.3 (about 3:1) to obtain the main agent A-F3.

[0063] (3) Preparation of component B (curing agent B-F3): Based on the B-F1 formulation in Example 1, the amount of additives was adjusted as follows: 700g N-3300, 45g epoxy resin E-20, 10.5g KH-560, 14.0g SMA-1000 and 7.0g TMEG-200, diluted with EA to a solid content of 50%.

[0064] (4) Final adhesive preparation: Mix the main agent A-F3 and the curing agent B-F3 in a weight ratio of 100:25 to obtain adhesive F3.

[0065] Comparative Example 1 (CPA) Component A uses a 60% solution of conventional polyester polyol XCP-2000 (Asahikawa Chemical, non-high molecular weight, no special side chain structure, non-high Tg, Tg approximately 35℃), and Component B uses MDI oligomer as curing agent PM-200 (Wanhua Chemical). Specific proportions are shown in Tables 2 and 3.

[0066] Comparative Example 2 (CPC) Component A is the same as component A in Example 1. Component B contains epoxy resin but does not contain SMA and TMEG micro-additives. Specific proportions are shown in Tables 2 and 3.

[0067] Comparative Example 3 (CP-3) The only difference from Example 1 is that conventional PBA-2000 (without EHD side chains) and MDI were used, and the NCO / OH molar ratio R was controlled to be 1.05 to synthesize a linear hydroxyl-terminated polyurethane prepolymer (PU-15k) with a number-average molecular weight Mn≈15000 g / mol, replacing PU-35k in Example 1. The remaining raw materials and proportions of components A and B are exactly the same as in Example 1.

[0068] Comparative Example 4 (CP-4) The only difference from Example 1 is that the conventional polyester polyol XCP-2000 solution (60%) from Comparative Example 1 is used instead of the high Tg polyester polyol (PES-10k) solution from Example 1. The remaining raw materials and proportions of components A and B are exactly the same as in Example 1.

[0069] Comparative Example 5 (CP-5) The only difference from Example 1 is that epoxy resin E-20 is not added in the preparation of component B, while the types and proportions of the other components are exactly the same as in Example 1 B-F1.

[0070] The detailed formulations of the examples and comparative examples are shown in Tables 2 and 3.

[0071] Table 2. Raw material ratio of main agent A (mass, g)

[0072] Table 3 Raw material ratio of curing agent B (mass, g)

[0073] Performance Tests and Results The adhesives obtained in Examples 1-3 and Comparative Examples 1-5 were used for lamination, and their performance was tested after curing (50°C, 7 days).

[0074] The testing methods should refer to the following standards: Pull-out strength (rapid curing performance): Tested at specified time points in accordance with GB / T 2790-1995 "Test method for 180° peel strength of adhesives, flexible materials versus rigid materials".

[0075] Peel strength (after aging): Refer to GB / T 2791-1995 "Test method for peel strength of adhesives, flexible materials to flexible materials".

[0076] Bag immersion test: Refer to GB / T 17409-1998 "Determination of resistance to liquid chemicals for plastic films and sheets" and internal accelerated test method.

[0077] Retort resistance: Refer to the test method for retort resistance in GB / T 10004-2008 "Dry lamination and extrusion lamination of plastic composite films and bags for packaging".

[0078] The results are shown in Tables 4 to 7.

[0079] Table 4 Rapid Curing Performance (Tension Strength, MPa)

[0080] Table 5 Extreme resistance to media aging (peel strength retention rate)

[0081] Test conditions: The PET / PE composite film was immersed in a 30% methanol / 70% pesticide activator solution at 40℃ for 20 days.

[0082] Table 6 Bag Immersion Test (Time to Defect Occurrence, in Hours)

[0083] The composite film with a PET / AI / PE structure was tested and accelerated aging was performed at 60℃.

[0084] Table 7. Resistance to boiling (121℃, 30 minutes)

[0085] in conclusion: Examples 1-3 (F1-F3) all exhibited excellent rapid curing (pull-out strength ≥0.28 MPa within 40 seconds) and high chemical corrosion resistance (strength retention rate 86%-94%), verifying the effectiveness of the technical solution of this application within the parameter range described in the claims.

[0086] Combining Example 1 and Comparative Example 2, since Comparative Example 2 did not add SMA and TMEG, the strength retention rate decreased from 91% in Example 1 to 75%, confirming the key role of media resistance additives in improving long-term solvent resistance performance.

[0087] Combining Example 1 and Comparative Example 3, Comparative Example 3 uses the conventional low molecular weight prepolymer PBA-2000, which has no special side chains. As can be seen from the data in the table, the polyurethane prepolymer without high molecular weight and hydrophobic side chain structure has a significantly reduced cohesive strength and solvent resistance plasticizing ability, resulting in a sharp deterioration of various properties.

[0088] Based on the data in the table, and in conjunction with Example 1 and Comparative Example 4, it can be seen that the lack of rapid physical crosslinking points provided by high Tg polyester not only results in a slightly slower initial positioning speed but also a significant decrease in long-term resistance to media.

[0089] Based on the data in the table, and in conjunction with Example 1 and Comparative Example 5, it can be seen that the absence of the polyurethane-epoxy hybrid network will impair the structural stability of the adhesive layer under high temperature and high humidity conditions (interlayer peeling after cooking) and its long-term chemical resistance.

[0090] The test results above show that the two-component polyurethane laminate adhesive provided in this application successfully achieves a balance between rapid curing and high chemical corrosion resistance through the synergistic effect between the components. Its performance is significantly better than that of the traditional comparative example, and it fully meets the application requirements of flexible packaging in high-speed production lines and harsh chemical environments.

[0091] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A two-component polyurethane laminated adhesive, characterized in that, It includes component A and component B, with a weight ratio of component A to component B of 100:(15-25); Component A comprises at least one hydroxyl-terminated polyurethane prepolymer and at least one polyester polyol; the number average molecular weight Mn of the hydroxyl-terminated polyurethane prepolymer is not less than 25000 g / mol, and its main chain contains structural units formed by polyols with introduced hydrophobic side chains; the glass transition temperature Tg of the polyester polyol is not less than 45°C. Component B comprises at least one isocyanate curing agent, at least one epoxy resin crosslinking agent, and at least one media-resistant additive.

2. The two-component polyurethane laminated adhesive as described in claim 1, characterized in that: The number-average molecular weight Mn of the hydroxyl-terminated polyurethane prepolymer is 30,000 g / mol to 45,000 g / mol; And / or, the hydrophobic side chain is an ethyl or an alkyl side chain longer than an ethyl; And / or, the polyols with hydrophobic side chains include at least one of 2-ethyl-1,3-hexanediol and 2-butyl-2-ethyl-1,3-propanediol; And / or, the glass transition temperature Tg of the polyester polyol is not lower than 50°C, and its number-average molecular weight Mn is 5000 g / mol to 15000 g / mol; And / or, the weight ratio of the hydroxyl-terminated polyurethane prepolymer to the polyester polyol is 2:1 to 4:1; And / or, the hydroxyl-terminated polyurethane prepolymer is a hydroxyl-terminated prepolymer obtained by polymerizing isocyanate NCO to hydroxyl OH with a molar ratio R of 0.95 to 0.98; And / or, the amount of the epoxy resin crosslinking agent added accounts for 1.5wt% to 6.0wt% of the total mass of component B; And / or, the amount of the media-resistant additive is 0.2wt% to 3.0wt% of the total mass of component B.

3. The two-component polyurethane laminate adhesive as described in claim 1, characterized in that: The media-resistant additives include one or more of high-rigidity copolymers containing anhydride groups and multifunctional (meth)acrylate crosslinking agents.

4. The two-component polyurethane laminate adhesive as described in claim 3, characterized in that: The high-rigidity copolymer containing anhydride groups includes at least one of styrene-maleic anhydride copolymer SMA and isobutylene-maleic anhydride copolymer ISOBAM. And / or, the multifunctional (meth)acrylate crosslinking agent includes at least one of diethylene glycol (4-tricarboxylic anhydride) TMEG and trimethylolpropane trimethacrylate TMPTMA.

5. The two-component polyurethane laminate adhesive as described in claim 1, characterized in that: Component B further comprises a silane coupling agent, wherein the amount of the silane coupling agent added is 0.1 wt% to 2.0 wt% of the total mass of component B.

6. The two-component polyurethane laminate adhesive as described in claim 5, characterized in that: The silane coupling agent is selected from aminosilane or epoxysilane.

7. A method for preparing a two-component polyurethane laminated adhesive as described in any one of claims 1 to 6, characterized in that, It includes: The raw materials of component A are mixed to obtain component A; The raw materials of component B are mixed to obtain component B; Component A and component B are mixed to obtain a two-component polyurethane laminate adhesive.

8. The application of a two-component polyurethane laminating adhesive as described in any one of claims 1 to 6 in the lamination of chemically resistant flexible packaging composite films.

9. The application as described in claim 8, characterized in that: The chemical corrosion resistant flexible packaging composite film is a pesticide flexible packaging composite film. The two-component polyurethane laminate adhesive achieves a pull-out strength of at least 0.30 MPa within 60 seconds after lamination and cooling.

10. A composite flexible packaging material, characterized in that: It is composed of at least two substrates bonded together by a two-component polyurethane laminate adhesive as described in any one of claims 1 to 6.

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