Production process of EB cured food packaging composite film and product

Abstract

The invention relates to the technical field of high polymer materials and packaging, in particular to a production process of an EB curing food packaging composite film and a product. Comprising the following steps: S1, providing a food-grade packaging base material, and pretreating the packaging base material; the packaging base material at least comprises a first packaging base material and a second packaging base material; s2, coating the pretreated surface of the first packaging base material with an EB adhesive; s3, laminating the pretreated surfaces of the first packaging base material and the second packaging base material coated with the EB adhesive to obtain a composite packaging film; s4, carrying out electron beam curing treatment on the composite packaging film; and S5, cooling and rolling the composite packaging film subjected to electron beam curing treatment to obtain a composite packaging film finished product. The viscosity of the EB adhesive at the temperature of 100 DEG C ranges from 1000 cps to 10000 cps. The obtained composite film is environment-friendly, high in initial positioning capacity, efficient in production, reliable in performance and capable of meeting the use requirements of food packaging materials.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and packaging technology, and in particular to a production process and product of an EB-cured food packaging composite film. Background Technology

[0002] In current production practices within the food packaging composite film industry, solvent-based polyurethane adhesives are widely used as bonding materials. While these adhesives possess mature performance advantages, they also present challenges in the production of food flexible packaging composite films, including high VOC emissions, environmental pollution, residual solvent migration contaminating food, high production safety hazards (flammability and explosion risks), and high energy consumption (requiring drying tunnels tens of meters long to remove solvents).

[0003] To address the environmental concerns associated with traditional adhesives, existing production technologies have attempted to utilize solvent-free polyurethane adhesives in the lamination process of food packaging composite films. However, these adhesives are typically two-component systems requiring precise metering and mixing. Furthermore, their curing reaction is highly dependent on environmental humidity and temperature, necessitating a long curing period of 24-48 hours to achieve final performance. This severely restricts the production efficiency of food packaging composite films, occupies significant inventory space, and extends delivery cycles, resulting in poor practicality.

[0004] Against this backdrop, electron beam (EB) curing technology has gained attention in recent years and has been applied in the field of food flexible packaging due to its advantages such as zero VOC emissions, instantaneous curing (second-level), low energy consumption, and no photoinitiator residue. However, in the production environment of food packaging composite films, EB curing technology still has many problems to be solved.

[0005] Chinese invention patent CN110387208B discloses an electron beam cured composite adhesive, a flexible packaging composite film, and its preparation method. By using the electron beam cured composite adhesive, the problem of low mixing and curing efficiency of solvent-free two-component adhesives at high temperatures is solved, achieving rapid curing and high adhesion of the adhesive, improving production efficiency and reducing quality accidents. It is applicable to various packaging materials. Chinese invention patent application CN120399631A discloses an electron beam cured solvent-free adhesive for flexible packaging and its preparation method. By introducing a terminal hydroxyl hyperbranched polymer prepared from 3-(methacryloyloxy)propyltrimethoxysilane and a dihydroxy quaternary ammonium salt as a crosslinking component into the electron beam cured solvent-free adhesive for flexible packaging, the high adhesion and moisture and heat resistance of the composite film are improved. While these EB curing technologies have solved the environmental problem, they still have drawbacks, such as low adhesive viscosity, insufficient initial positioning ability, and a tendency to cause interlayer displacement during high-speed traction. Especially in multi-layer composite operations, there may be situations where the first adhesive has not yet undergone EB curing when the second adhesive is applied, which can easily lead to displacement or the formation of a "tunnel" effect, affecting the barrier performance of the packaging film.

[0006] Against this backdrop, the food packaging industry urgently needs a production process for food packaging composite films that is environmentally friendly (no VOCs, no PI), has strong initial positioning capabilities, can be produced quickly (no curing period), and has reliable performance. Summary of the Invention

[0007] To address the technical challenges of existing adhesives in simultaneously achieving both environmental friendliness and production efficiency, this invention provides a production process for EB-cured food packaging composite film and the resulting composite film product. Through a specific production process and the combination of EB adhesive, a food packaging composite film product is obtained that is environmentally friendly (VOC-free, PI-free), has strong initial positioning ability, can be produced quickly (no curing period), and has reliable performance. Furthermore, it is highly operable, capable of mass production, and has broad application prospects.

[0008] The first aspect of this invention provides a manufacturing process for an EB-cured food packaging composite film, comprising the following steps: S1. Provide food-grade packaging substrate and pre-treat the packaging substrate; the packaging substrate includes at least a first packaging substrate and a second packaging substrate; S2. Apply EB adhesive to the pretreated surface of the first packaging substrate; S3. Press the pretreated surfaces of the first packaging substrate coated with EB adhesive and the second packaging substrate together to obtain a composite packaging film; S4. Perform electron beam curing treatment on the composite packaging film; S5. Cool and rewind the composite packaging film after electron beam curing to obtain the finished composite packaging film.

[0009] The production process of EB-cured food packaging composite film provided by this invention can realize the production mode of "curing and cutting at the same time". By instantly curing EB, the curing period of tens of hours in the production process of food packaging composite film is completely eliminated, which greatly improves the production efficiency of composite film.

[0010] Optionally, the packaging substrate may be made of at least two of the following materials: biaxially oriented polypropylene (BOPP), polyethylene terephthalate (PET), polyethylene (PE), cast polypropylene (CPP), nylon (PA), and aluminum (Al).

[0011] Further optionally, the composite packaging film includes at least one of the following: BOPP / PET composite structure, PET / CPP composite structure, BOPP / CPP composite structure, PET / PE composite structure, PET / Al composite structure, Al / PE composite structure, PA / Al composite structure, and BOPP / Al composite structure.

[0012] In some implementations, when the packaging substrate is made of aluminum, an aluminized film or aluminum foil may be selected.

[0013] The metallized film can be exemplified as metallized polyester film (VMPET) or metallized cast polypropylene film (VMCPP). Optionally, the thickness of the packaging substrate is 5-500 μm; more preferably 8-100 μm.

[0014] In some embodiments, the composite packaging film is a BOPP / CPP composite structure, that is, the first packaging substrate is BOPP and the second packaging substrate is CPP.

[0015] In some embodiments, the composite packaging film is a PET / PE composite structure, that is, the first packaging substrate is PET and the second packaging substrate is PE.

[0016] In some embodiments, the composite packaging film is a PET / Al composite structure, that is, the first packaging substrate is PET and the second packaging substrate is Al.

[0017] In some embodiments, the composite packaging film may also include a third or fourth packaging substrate, etc., as needed, with the packaging substrates fixed together by EB adhesive. For example, the composite packaging film may be a PET / AL / PE composite structure, where the first packaging substrate is PET, the second packaging substrate is Al, and the third packaging substrate is PE.

[0018] In some embodiments, the pretreatment includes corona treatment or plasma treatment, which can improve the surface energy and wettability of the packaging substrate, facilitating subsequent processing.

[0019] Optionally, the pretreatment in step S1 is specifically corona treatment, and the dyne value of the packaging substrate after corona treatment is 30 dyne / cm or more; it is further optional to be 38 dyne / cm or more.

[0020] Optionally, the EB adhesive is a high-viscosity EB curing adhesive with a solid content of 100%.

[0021] Optionally, the raw materials for preparing the EB adhesive, by weight percentage, include: Oligomers 60-95%; Tackifying resin: 0-30%; Multifunctional active diluent 1-25%; Additives 0-5%; The EB adhesive does not contain solvents, monofunctional reactive diluents, or photoinitiators (PI), and therefore poses no risk of migration or initiator residue, making it safe and environmentally friendly.

[0022] To improve the adhesion and toughness of the adhesive, the oligomer may optionally include one or more combinations of polyurethane acrylate, polyester acrylate, and epoxy acrylate.

[0023] Optionally, the oligomer includes polyurethane acrylate, which is polyacrylate / acrylic acid modified polyurethane or biomass polyurethane acrylate.

[0024] In some embodiments, the raw materials for preparing the EB adhesive, by weight percentage, include: Oligomers 60-85%; Tackifying resin 0-30% (not 0); Multifunctional active diluent 1-10%; Additives 0.5-5%.

[0025] To improve the initial positioning capability of composite film processing, the tackifying resin may optionally include a thermoplastic resin; the thermoplastic resin may include acrylic resin or EVA (ethylene-vinyl acetate copolymer) resin.

[0026] In some embodiments, the oligomer is a polyacrylate / acrylic acid modified polyurethane, and the raw materials for preparing the EB adhesive, by weight percentage, include: Oligomers 70-95%; Multifunctional active diluent 5-25%; Additives: 0.1-5%.

[0027] In some embodiments, the raw materials for preparing the polyacrylate / acrylic acid modified polyurethane include thermoplastic polyacrylate copolymers, polyester polyols, diisocyanates, polymerization inhibitors, and hydroxy acrylates.

[0028] Existing technologies attempt to use polyurethane acrylate (PUA) with reactive diluents to form an all-solid EB-containing curing system. Although this system has certain adhesive properties, its low viscosity results in low initial adhesion before EB curing, making it difficult to implement. This invention innovatively employs a two-component synergistic system of polyacrylate-acrylic modified polyurethane. By combining the rapid initial tack and high transparency of polyacrylate with the heat-resistant cohesiveness and flexible substrate adaptability of polyurethane, it effectively avoids the limitations of single materials in terms of adhesive strength and weather resistance. The resulting polyacrylate / acrylic modified polyurethane composite hot melt adhesive possesses advantages such as transparency, climate stability, excellent initial tack, and abrasion resistance, making it well-suited for the production of food flexible packaging composite films.

[0029] Further optionally, the raw materials for preparing the polyacrylate / acrylic acid modified polyurethane include: 80-200 parts of thermoplastic polyacrylate copolymer, 10-50 parts of polyester polyol, 5-30 parts of diisocyanate, 0.1-1 parts of polymerization inhibitor and 3-15 parts of hydroxy acrylate.

[0030] Optionally, the glass transition temperature (Tg) of the thermoplastic polyacrylate copolymer is -20 to 45°C.

[0031] Optionally, the raw materials for preparing the thermoplastic polyacrylate copolymer include at least a comonomer and an initiator; the amount of initiator added is 0.5-3% of the mass of the comonomer; more preferably, it is 1%.

[0032] Optionally, the raw materials for preparing the thermoplastic polyacrylate copolymer also include polyols; the mass ratio of the polyol to the comonomer is (20-30):(80-120).

[0033] In some embodiments, the polyol includes at least one of polyether polyol, modified castor oil polyol, or soybean oil modified polyol.

[0034] Optionally, the polyol is polypropylene glycol; further optionally, the molecular weight of the polypropylene glycol is 1000-2000.

[0035] Optionally, the polyol is a modified castor oil polyol; further optionally, the modified castor oil polyol has a functionality of 2 and a molecular weight of 430.

[0036] Optionally, based on the total mass of the comonomers, the comonomers comprise: 80-99% basic monomers, 0-5% structural monomers, and 1-15% functional monomers.

[0037] Optionally, the basic monomer includes alkyl acrylates or derivatives thereof, wherein the alkyl carbon number in the basic monomer is 1-20, and examples include n-butyl acrylate, isooctyl acrylate, n-butyl methacrylate, methyl methacrylate, etc.

[0038] In some embodiments, the thermoplastic polyacrylate copolymer contains primary hydroxyl groups in its structure; these primary hydroxyl groups are provided by the structural monomer.

[0039] The structural monomers include acrylates containing primary hydroxyl structures, such as hydroxyethyl acrylate and hydroxyethyl methacrylate.

[0040] Note: The primary hydroxyl structure is a chemical structure in which a hydroxyl group is attached to a primary carbon atom (a carbon atom that is only attached to one other carbon atom), and its general structural formula is -CH2OH.

[0041] Optionally, the functional monomer includes acrylic acid or acrylamide.

[0042] This invention ingeniously introduces the acrylic resin structure into the polyurethane system, utilizing the electron beam (EB) simultaneous curing characteristics of the terminal double bonds of the polyacrylate copolymer and the acrylic-modified polyurethane prepolymer to form an interpenetrating polymer network (IPN) structure under a radiation field. This can further enhance the bonding strength of the hot melt adhesive and ensure its firm adhesion to the substrate surface. The resulting substrate / adhesive / substrate composite structure is strong, reliable, and highly weather-resistant.

[0043] Optionally, the preparation steps of the thermoplastic polyacrylate copolymer include: First, add the polyol into the reaction apparatus and heat it to above 100°C. Then, add the comonomer and 0.5-3% (or 1%) of the comonomer mass as an initiator. After adding the comonomer, keep the temperature for 20-40 minutes and add the remaining initiator. After the addition is complete, keep the temperature for 1-6 hours and discharge the material to obtain the thermoplastic polyacrylate copolymer.

[0044] Optionally, the weight-average molecular weight of the thermoplastic polyacrylate copolymer is 40,000-100,000; examples include 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, etc.

[0045] This invention employs a polymerization method based on polyols, with comonomers and initiators added dropwise. The polymerized product, after removing trace amounts of unreacted monomers, has a solid content of ≥99%.

[0046] Optionally, the polyacrylate / acrylic acid modified polyurethane contains an unsaturated double bond structure.

[0047] Optionally, the preparation steps of the polyacrylate / acrylic acid modified polyurethane include: The thermoplastic polyacrylate copolymer is mixed with polyester polyol and diisocyanate and reacted at 70-80°C for 2-3 hours. Then, a polymerization inhibitor and hydroxy acrylate are added and reacted for 2-5 hours to obtain an acrylic modified polyurethane prepolymer.

[0048] Optionally, the polyester polyol is polymethyl propylene adipate polyol; further optionally, the molecular weight of the polymethyl propylene adipate polyol is 1000-4000.

[0049] The hydroxy acrylates include ethyl hydroxymethacrylate (also known as hydroxyethyl methacrylate, HEMA, CAS number 868-77-9), hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), hydroxybutyl acrylate (HBA), hydroxybutyl methacrylate (HBMA), etc.; and may further be ethyl hydroxymethacrylate.

[0050] This invention provides a flexible and controllable method for preparing polyacrylate / acrylic acid-modified polyurethane. It can either react long-chain diols with isocyanates, then cap the isocyanates before reacting with hydroxyl acrylic acid to obtain an EB-curable acrylic resin; or introduce long-chain diols into an acrylic copolymer system, followed by isocyanate capping to achieve functional modification of the hydroxyl acrylic acid. The innovative use of a two-component synergistic system of polyacrylate-acrylic acid-modified polyurethane leverages the rapid initial tack and high transparency of polyacrylate, combined with the heat-resistant cohesiveness and flexible substrate adaptability of polyurethane. This effectively avoids the limitations of single materials in terms of adhesive strength and weather resistance. The resulting polyacrylate / acrylic acid-modified polyurethane composite hot melt adhesive possesses advantages such as transparency, climate stability, excellent initial tack, and abrasion resistance, making it well-suited for the production of food flexible packaging composite films. By utilizing the EB curing properties of the terminal double bonds of polyacrylate copolymer and acrylic modified polyurethane prepolymer, an interpenetrating polymer network (IPN) structure is formed under a radiation field, which can further improve the bonding strength of hot melt adhesive and ensure its firm adhesion to the substrate surface; the resulting substrate / adhesive layer / substrate composite structure is strong, reliable and weather resistant.

[0051] In some embodiments, the oligomer is a biomass polyurethane acrylate, and the raw materials for preparing the EB adhesive, by weight percentage, include: Biomass polyurethane acrylate 80-95%; Reactive diluent 1-15%; Additives: 0.1-5%.

[0052] Optionally, the raw materials for preparing the biomass polyurethane acrylate include: biomass polyol, diisocyanate, chain extender, hydroxy acrylate end-capping agent, and polymerization inhibitor.

[0053] Further optionally, the raw materials for preparing the biomass polyurethane acrylate, by weight, include: 100-180 parts of biomass polyol, 50-85 parts of diisocyanate, 1-7 parts of chain extender, 10-40 parts of hydroxy acrylate end-capping agent, and 0.05-0.5 parts of polymerization inhibitor.

[0054] Optionally, the biomass polyol includes at least one of castor oil polyol, modified dimer acid polyol, and epoxidized soybean oil polyol.

[0055] Optionally, the number average molecular weight of the biomass polyol is 300-3000.

[0056] Optionally, the functionality of the biomass polyol is ≤3.

[0057] Optionally, the chain extender is an aliphatic diol; further optionally, the aliphatic diol contains an alkyl side chain; further optionally, the aliphatic diol is at least one selected from 1,2-propanediol, 1,3-butanediol, and neopentyl glycol.

[0058] By introducing aliphatic diols containing alkyl side chains as chain extenders into biomass polyurethane acrylates, the regularity of polymer molecular chains can be disrupted, the tendency to crystallize can be reduced, thereby improving the solubility and storage stability of the resin at high temperatures and improving the flexibility of the cured film.

[0059] In some embodiments, the raw materials for preparing the biomass polyurethane acrylate also include 0.01-0.05 parts of catalyst, which is added together with the chain extender.

[0060] Optionally, the catalyst is an organobismuth catalyst; an example of an organobismuth catalyst is DY-20; DY-20 is an organobismuth catalyst with bismuth neodecanoate and neodecanoic acid as the main components, and the supplier is Shanghai Deyin Chemical Co., Ltd.

[0061] Optionally, the preparation steps of the biomass polyurethane acrylate include: Synthetic prepolymer: Under inert gas protection, biomass polyol and diisocyanate are mixed and reacted at 75-85℃ to obtain NCO-terminated prepolymer; Chain extension reaction: The temperature of the NCO end-group prepolymer is lowered to 60-70℃, and a chain extender is added to react and obtain the chain-extended prepolymer; Preparation of biomass polyurethane acrylate: At 60-70℃, add hydroxy acrylate end-capping agent and polymerization inhibitor to the chain-extended prepolymer and react until the -NCO groups are completely reacted to obtain biomass polyurethane acrylate.

[0062] Optionally, the hydroxyacrylate capping agent includes hydroxyethyl methacrylate (HEMA, CAS No. 868-77-9), hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), hydroxybutyl acrylate (HBA), hydroxybutyl methacrylate (HBMA), pentaerythritol triacrylate (PETA), etc.; further, HEA or HPA can be selected to enhance the reactivity.

[0063] Optionally, in step (1), the reaction continues until the -NCO content reaches the theoretical value, generally for 1-5 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours; further, it can be 2 hours.

[0064] Optionally, in step (2), the reaction continues until the -NCO content reaches the theoretical value, generally for 1-5 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, or 5 hours; further, it can be 2 hours.

[0065] In some embodiments, the reaction in step (3) until the -NCO group is completely reacted is detected by infrared spectroscopy, and when 2270 cm⁻¹ is detected... - When the characteristic absorption peak of -NCO in ¹ completely disappears, it means that the -NCO group has completely reacted.

[0066] The biomass polyurethane acrylate prepared by this invention imparts excellent adhesion and reliable toughness to the adhesive, enabling it to be well-suited for the preparation of food flexible packaging composite films. Through specific polymer molecular design, the obtained biomass polyurethane acrylate, when formulated into an EB curing coating solution, exhibits excellent high-temperature coating adaptability. Under high-temperature coating conditions, the adhesive maintains stable viscosity, good leveling properties, and is free of crystal points, further improving the product quality of the food packaging composite film.

[0067] Optionally, the diisocyanate may include IPDI (isophorone diisocyanate), MDI (diphenylmethane diisocyanate), HMDI (hydrogenated MDI), TDI (toluene diisocyanate), HDI (hexamethylene diisocyanate), XDI (m-phenylene diisocyanate), NDI (naphthalene diisocyanate), CHDI (1,4-cyclohexane diisocyanate), TMXDI (tetramethylphenyl diisocyanate), and PDI (terephthalene diisocyanate), etc.

[0068] In some embodiments, the polymerization inhibitor may include p-methoxyphenol (MEHQ), phenothiazine (PTZ), or 2,6-di-tert-butyl-p-cresol (BHT); further alternatively, it may be p-methoxyphenol (also known as p-hydroxyanisole).

[0069] Optionally, the multifunctional reactive diluent includes an acrylic monomer with a functionality of ≥2.

[0070] Optionally, the acrylic monomer with a functionality ≥2 includes at least one of HDDA (1,6-hexanediol diacrylate), TMPTA (trimethylolpropane triacrylate), TPGDA (tripropylene glycol diacrylate), PETA (pentaerythritol triacrylate), BDMA (1,3-butanediol dimethacrylate), HDMA (1,6-hexanediol dimethacrylate), 3EO-TPGDA (ethoxylated tripropylene glycol diacrylate), and trimethylolpropane trimethacrylate; further, it can be selected as HDDA, TMPTA, TPGDA or 3EO-TPGDA, which can effectively adjust the viscosity and reactivity of the adhesive.

[0071] Optionally, the additives include one or more of leveling agents, adhesion promoters, and silane coupling agents; these can improve coating processing performance and enhance the quality of the composite film.

[0072] In some embodiments, the leveling agent may include EFKA3777 (leveling wetting agent), BYK-310 (organosilicon leveling agent), etc.

[0073] In some embodiments, the adhesion promoter may include acrylate phosphate compounds, such as 2-hydroxyethyl methacrylate phosphate (PM-2).

[0074] Optionally, the silane coupling agent may include KH550, KH560, KH570, KH792, KH602, etc.

[0075] Optionally, the adjuvant may also include an antioxidant.

[0076] Further optionally, the antioxidant includes hindered phenolic antioxidants (such as antioxidant 1010) and phosphate ester antioxidants (such as antioxidant 168).

[0077] The present invention does not impose any particular limitation on the preparation method of EB adhesive; any method commonly used in the art can be used, such as mixing the raw materials to obtain the adhesive.

[0078] The EB adhesive provided by this invention has excellent initial positioning ability, which can ensure that the composite film does not shift before curing, simplifying the process and avoiding product quality problems caused by shifting. Moreover, the adhesive formulation system does not require the addition of photoinitiators and solvents, ensuring environmental protection and safety. At the same time, the absence of monofunctional active small molecules fundamentally eliminates the risk of small molecule migration and ensures food safety.

[0079] Optionally, the viscosity of the EB adhesive at 100°C is 1000-10000 cps; examples include 1000 cps, 2000 cps, 3000 cps, 4000 cps, 5000 cps, 6000 cps, 7000 cps, 8000 cps, 9000 cps, and 10000 cps.

[0080] Optionally, when the oligomer is polyacrylate / acrylic acid modified polyurethane, the preparation steps of the EB adhesive include: mixing the polyacrylate / acrylic acid modified polyurethane, reactive diluent, and additives, and melt-blending to obtain the finished EB adhesive. The viscosity of the obtained EB adhesive at 100°C is 1000-10000 cps; examples include 1000 cps, 2000 cps, 2500 cps, 3000 cps, 3200 cps, 4000 cps, 4200 cps, 5000 cps, 5500 cps, 6000 cps, 7000 cps, 8000 cps, 9000 cps, and 10000 cps.

[0081] Optionally, the melt blending conditions are 100-130℃ melt blending for 5-20 minutes.

[0082] Optionally, when the oligomer is biomass polyurethane acrylate, the preparation steps of the EB adhesive include: mixing biomass polyurethane acrylate, reactive diluent, and additives, heating and mixing evenly to obtain the finished EB adhesive.

[0083] Optionally, the coating method in step S2 is multi-roller gravure coating; the number of rollers in multi-roller gravure coating is 3-5.

[0084] Optionally, the amount of EB adhesive applied in step S2 is 1.5-4.0 g / m² (dry weight); examples include 1.5 g / m², 1.6 g / m², 1.7 g / m², 1.8 g / m², 1.9 g / m², 2.0 g / m², 2.1 g / m², 2.2 g / m², 2.3 g / m², 2.4 g / m², 2.5 g / m², 2.6 g / m², 2.7 g / m², 2.8 g / m², 2.9 g / m², 3.0 g / m², 3.1 g / m², 3.2 g / m², 3.3 g / m², 3.4 g / m², 3.5 g / m², 3.6 g / m², 3.7 g / m², 3.8 g / m², 3.9 g / m², and 4.0 g / m².

[0085] Optionally, the coating temperature in step S2 is 60-120℃; examples include 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 110℃, and 120℃.

[0086] Optionally, the pressing pressure in step S3 is 0.2-0.6 MPa, such as 0.2 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, or 0.6 MPa; and the pressing temperature is 10-60℃, such as 10℃, 20℃, 30℃, 40℃, 50℃, or 60℃.

[0087] Optionally, step S4 specifically includes: transferring the composite packaging film to an electron beam curing device via a production line, and radiating it under an inert gas atmosphere to allow the EB adhesive to crosslink instantly.

[0088] Optionally, the inert gas in step S4 is at least one of nitrogen and argon; nitrogen may be selected as the inert gas.

[0089] Optionally, the ambient oxygen content in step S4 is <500ppm.

[0090] To balance the characteristics of the substrate, the curing effect of the adhesive, and production efficiency, the radiation curing conditions in step S4 can optionally be: accelerating voltage 80-300kV, irradiation dose 20-100kGy, and production line transmission speed 50-300m / min.

[0091] Further optionally, when the composite film is a two-layer composite structure, the radiation curing conditions in step S4 are: accelerating voltage 100-200kV, irradiation dose 30-50kGy, and production line transmission speed 100-200m / min.

[0092] Further optionally, when the composite film is a three-layer or higher composite structure, the radiation curing conditions in step S4 are: accelerating voltage 200-300kV, irradiation dose 30-50kGy, and production line transmission speed 100-200m / min.

[0093] In some embodiments, the conditions for radiation curing in step S4 are: accelerating voltage 150kV, irradiation dose 40kGy, and production line conveying speed 150m / min.

[0094] This invention utilizes specific radiation curing conditions to achieve both effective curing and high production efficiency. During the radiation curing stage, a high-energy electron beam penetrates the upper substrate and acts on the adhesive layer, instantly initiating cross-linking and curing to form a strong adhesive layer. This results in a reliable composite film with extremely high production efficiency. Furthermore, the EB curing method of this invention eliminates the need for curing; the finished product, after cooling and winding, can directly proceed to subsequent processes such as slitting and bag making, offering convenient operation without requiring storage space.

[0095] A second aspect of the present invention provides an EB-cured food packaging composite film, wherein the EB-cured food packaging composite film is prepared by the production process described above.

[0096] Optionally, the structure of the EB-cured food packaging composite film includes at least a first packaging substrate layer, an adhesive layer, and a second packaging substrate layer stacked together; further optionally, the structure of the EB-cured food packaging composite film may also include a third packaging substrate layer, a fourth packaging substrate layer, etc., and each packaging substrate layer is fixed by an adhesive layer.

[0097] Optionally, the adhesive layer is a product formed by cross-linking and curing EB adhesive through electron beam irradiation; the adhesive layer has no solvent or photoinitiator residue.

[0098] Beneficial effects: This invention provides a manufacturing process and product for an EB-cured food packaging composite film, which has the following advantages: (1) High safety: The EB production process of this invention uses 100% solid content EB adhesive, which has no solvent added and does not contain photoinitiators, thus fundamentally eliminating the risk of solvent residue and initiator migration. The prepared composite film has extremely high safety and can meet the usage requirements of food packaging scenarios.

[0099] (2) Green and environmentally friendly: The composite membrane of the present invention has zero VOC emissions during production process and does not require a waste gas treatment system, which is environmentally friendly; and the adhesive formula does not contain monofunctional active diluents, further eliminating the possibility of small molecule monomer residues. (3) High efficiency and energy saving: The curing process of the adhesive of the present invention can be completed in seconds, which can realize the production mode of "curing and cutting immediately" without going through a lengthy curing process; this feature greatly improves production efficiency and significantly reduces energy consumption when preparing composite film products. (4) Reliable performance: By optimizing the adhesive formulation and EB curing process conditions, the quality of the resulting composite film is significantly improved, which is reflected in high initial adhesion, strong positioning ability, high peel strength, good heat sealing performance and excellent barrier properties, which can fully meet the requirements of high-end food packaging; By combining the high temperature and low viscosity coating characteristics (coating at 60-120℃) with the instant EB curing process, the low viscosity fluidity advantage of hot melt adhesive in the molten state is fully utilized to achieve high-speed precision coating and significantly improve production efficiency; (5) Wide range of applications: The EB process of this invention is applicable to the combination of various substrates, such as BOPP / CPP, PET / PE, PET / AL / PE and other composite film structures. The product structure is flexible and diverse, and can be selected according to actual needs, with a wide range of applications.

[0100] (6) High operability: The raw materials of the present invention are readily available, the process conditions are simple, the food packaging composite film is cured in seconds and does not require curing. After discharge, it can be directly put into subsequent processes such as cutting and bag making. The method is easy to implement and can meet the requirements of mass production. Detailed Implementation

[0101] The present invention will be further described in detail below through specific embodiments, but the scope of protection of the present invention is not limited thereto; unless otherwise specified, the raw materials and consumables used in the present invention are all commercially available.

[0102] Example 1 This embodiment provides a production process for EB-cured food packaging composite film, including the following steps: S1. Provide food-grade packaging substrate, the packaging substrate including a first packaging substrate and a second packaging substrate; pre-treat the first packaging substrate and the second packaging substrate respectively (corona treatment to make the surface tension reach 38 dyne / cm or more). S2. Apply EB adhesive to the pretreated surface of the first packaging substrate; S3. Press the pretreated surfaces of the first packaging substrate coated with EB adhesive and the second packaging substrate together to obtain a composite packaging film; S4. The composite packaging film is transferred to the electron beam curing device via the production line and cured by radiation in an inert gas atmosphere, which causes the EB adhesive to cross-link instantly; S5. Cool and rewind the composite packaging film after electron beam curing to obtain the finished composite packaging film.

[0103] The pretreatment in step S1 is corona treatment. After corona treatment, the surface tension of both the first and second packaging substrates reaches 38 dyne / cm or higher.

[0104] The composite packaging film has a BOPP / CPP composite structure, that is, the first packaging substrate is BOPP (20μm) and the second packaging substrate is CPP (40μm).

[0105] The raw materials for preparing the EB adhesive, by weight percentage, consist of 75% oligomer (biomass polyurethane acrylate), 10% tackifying resin (EVA resin, Sirbon EVA UE28150), 10% polyfunctional reactive diluent (tripropylene glycol diacrylate), and 5% additives.

[0106] The raw materials for preparing the biomass polyurethane acrylate, by weight, include: 150 parts of biomass polyol, 70 parts of diisocyanate (MDI), 3 parts of chain extender (1,2-propanediol), 13.3 parts of hydroxy acrylate end-capping agent (hydroxyethyl acrylate), 0.2 parts of polymerization inhibitor (MEHQ), and 0.05 parts of catalyst.

[0107] The preparation steps of the biomass polyurethane acrylate include: under inert gas (nitrogen) protection, mixing 100 parts by weight of castor oil diol (Jingri D201, number average molecular weight of 750, functionality of 2) and 50 parts by weight of modified dimer acid diol (Jingri DA20, number average molecular weight of 1000, functionality of 2) in a reaction flask, heating to 120°C, removing moisture under vacuum for 1 hour, then cooling to 60°C, adding 70 parts by weight of MDI and 0 parts by weight of catalyst. 0.05 parts were added, and the temperature was raised to 82±2.5℃ for 2 hours. The NCO value was tested. When the NCO value reached 3.3%, the temperature was lowered to 67.5±2.5℃, and 3 parts of 1,2-propanediol were added. The reaction temperature was maintained at 67.5±2.5℃ for 2 hours, and the NCO value was tested again. When the NCO value reached 2.0%, 0.2 parts of MEHQ and 13.3 parts of hydroxyethyl acrylate were added. The reaction was continued until the NCO infrared peak disappeared, and biomass polyurethane acrylate was obtained.

[0108] The additives include 1% leveling and wetting agent (EFKA377), 2% adhesion promoter (PM-2, 2-hydroxyethyl methacrylate phosphate) and 2% silane coupling agent (KH570).

[0109] The EB adhesive is prepared by mixing the raw materials.

[0110] The viscosity of the EB adhesive at 100°C is 4500 cps.

[0111] The coating method in step S2 is multi-roller gravure coating (specifically, anilox roller); the number of rollers in multi-roller gravure coating is 5.

[0112] In step S2, the amount of EB adhesive applied is 2.0 ± 0.2 g / m² (dry weight).

[0113] The coating temperature in step S2 is 100℃.

[0114] The pressing pressure in step S3 is 0.4 MPa, and the pressing temperature is 30°C.

[0115] In step S4, the inert gas is nitrogen (ambient oxygen content < 200 ppm); the conditions for radiation curing are: accelerating voltage 150 kV, irradiation dose 40 kGy, and production line transmission speed 150 m / min.

[0116] This embodiment also provides an EB-cured food packaging composite film, which is prepared by the production process described above.

[0117] The structure of the EB-cured food packaging composite film includes a first packaging substrate layer, an adhesive layer, and a second packaging substrate layer stacked together; the materials of the first packaging substrate layer and the second packaging substrate layer are described in the performance test.

[0118] The adhesive layer is a product formed by cross-linking and curing EB adhesive through electron beam irradiation; the adhesive layer has no solvent or photoinitiator residue.

[0119] Example 2 This embodiment provides a production process for EB-cured food packaging composite film, and the specific implementation method is the same as in Embodiment 1; the difference is: The raw materials for preparing the EB adhesive, by weight percentage, consist of 70% oligomer (biomass polyurethane acrylate), 15% tackifying resin (thermoplastic acrylic resin, Bonford New Materials Co., Ltd., TRA-7046), 10% polyfunctional reactive diluent (TMPTA), and 5% additives.

[0120] The viscosity of the EB adhesive at 100°C is 2800 cps.

[0121] The multi-roller micro-grooving coating process uses three rollers.

[0122] Example 3 This embodiment provides a production process for EB-cured food packaging composite film, the preparation steps of which include: S1. Provide food-grade packaging substrate, the packaging substrate including a first packaging substrate, a second packaging substrate and a third packaging substrate; pre-treat the first packaging substrate, the second packaging substrate and the third packaging substrate respectively (corona treatment, so that the surface tension reaches more than 38 dyne / cm). The composite packaging film has a PET / Al / PE composite structure, that is, the first packaging substrate is PET (12μm), the second packaging substrate is Al (9μm, aluminized film), and the third packaging substrate is PE (30μm).

[0123] S2. Apply EB adhesive (formulation same as in Example 2) to the pretreated surface of the first packaging substrate to form a PET / Al substrate; then apply EB adhesive to the Al surface of the PET / Al substrate; that is, two laminations are performed; S3. Press the three-layer film structure coated with EB adhesive together to obtain a composite packaging film; S4. The composite packaging film is transferred to the electron beam curing device via the production line and cured by radiation in an inert gas atmosphere, which causes the EB adhesive to cross-link instantly; S5. Cool and rewind the composite packaging film after electron beam curing to obtain the finished composite packaging film.

[0124] The process conditions for S2 to S4 are the same as in Example 2.

[0125] This embodiment also provides an EB-cured food packaging composite film, which is prepared by the production process described above.

[0126] The structure of the EB-cured food packaging composite film includes a first packaging substrate layer (PET), an adhesive layer, a second packaging substrate layer (A1), an adhesive layer, and a third packaging substrate layer (PE) stacked together.

[0127] The adhesive layer is a product formed by cross-linking and curing EB adhesive through electron beam irradiation; the adhesive layer has no solvent or photoinitiator residue.

[0128] Example 4 The specific implementation method is the same as in Example 3; the difference is that the accelerating voltage in step S4 is 250kV.

[0129] Example 5 This embodiment provides a production process for EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 1; the difference lies in that: the raw materials for preparing EB adhesive, by weight, are: 75 parts of oligomer (polyacrylate / acrylic acid modified polyurethane); 20 parts reactive diluent (15 parts TPGDA, 5 parts EO3-TMPTA); 2.5 parts of additives, specifically 0.5 parts of leveling agent (BYK-310) and 2 parts of adhesion promoter.

[0130] The raw materials for preparing the polyacrylate / acrylic acid modified polyurethane, by weight, include: 150 parts of thermoplastic polyacrylate copolymer, 45 parts of polyester polyol, 15 parts of diisocyanate (IPDI), 0.5 parts of polymerization inhibitor (p-methoxyphenol), and 6.5 parts of hydroxy acrylate (ethyl hydroxymethyl acrylate).

[0131] The polyester polyol is polybutylene adipate polyol with a molecular weight of 2000, sourced from Asahikawa Chemical.

[0132] The thermoplastic polyacrylate copolymer contains primary hydroxyl groups in its structure.

[0133] The raw materials for preparing the thermoplastic polyacrylate copolymer, by weight, include 20 parts of polyol, 0.3 parts of antioxidant 1010, 100.2 parts of comonomer and 1 part of initiator.

[0134] The initiator is tert-butyl peroxide-2-ethylhexyl carbonate.

[0135] The polyol is polypropylene glycol 1000, which comes from Jiangsu Haian Petrochemical Plant.

[0136] The comonomer comprises 95 parts of a basic monomer, 0.2 parts of a structural monomer (ethyl hydroxyacrylate), and 5 parts of a functional monomer (acrylic acid).

[0137] The basic monomers include 70 parts of n-butyl methacrylate, 15 parts of isooctyl acrylate, and 10 parts of methyl methacrylate.

[0138] The preparation steps of the EB adhesive include: (1) Preparation of thermoplastic polyacrylate copolymers: First, polypropylene glycol 1000 was added to the reaction apparatus and heated to 130°C under a nitrogen atmosphere. Comonomer and 0.9 parts of initiator were then added dropwise. The dropwise addition time was controlled at 4 hours, and the reaction temperature was maintained at 130±2°C during the dropwise addition. After the dropwise addition was completed, the temperature was kept at that temperature for 30 minutes, and the remaining 0.1 parts of initiator were added dropwise. After the dropwise addition was completed, the reaction was kept at that temperature for 3 hours, and the product was discharged to obtain a thermoplastic polyacrylate copolymer with polypropylene glycol 1000 as the dispersion medium. The weight-average molecular weight of the prepared thermoplastic polyacrylate copolymer was 55000±5000, and the Tg was 16°C.

[0139] (2) Preparation of polyacrylate / acrylic acid modified polyurethane: The thermoplastic polyacrylate copolymer was mixed with a polyester polyol, vacuum dehydrated, and then reacted with diisocyanate at 75°C for 2 hours. Then, a polymerization inhibitor and hydroxy acrylate were added, and the reaction was carried out for 3 hours to obtain polyacrylate / acrylic acid modified polyurethane.

[0140] (3) At 75°C, the polyacrylate / acrylic acid modified polyurethane, reactive diluent and additives are mixed and melt-blended at 100°C for 10 min to obtain the EB adhesive product.

[0141] The viscosity of the EB adhesive at 100°C is 5500 cps.

[0142] Example 6 This embodiment provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 5; the difference is that the amount of oligomer (polyacrylate / acrylic acid modified polyurethane) added to the EB adhesive is 70 parts by weight.

[0143] The raw materials for preparing the polyacrylate / acrylic acid modified polyurethane, by weight, include: 100 parts of thermoplastic polyacrylate copolymer, 30 parts of polyester polyol, 25 parts of diisocyanate, 0.5 parts of polymerization inhibitor, 7.2 parts of hydroxy acrylate, 0.3 parts of antioxidant 1010, and 1 part of initiator.

[0144] The polyol in the thermoplastic polyacrylate copolymer is a modified castor oil polyol with a functionality of 2 and a molecular weight of 430, derived from Ito Corporation.

[0145] The preparation steps of the EB adhesive include: (1) Preparation of thermoplastic polyacrylate copolymer: Modified castor oil polyol and antioxidant 1010 were first added to the reaction apparatus and heated to 130°C under a nitrogen atmosphere. Comonomer and 0.9 parts of initiator were added dropwise. The dropwise addition time was controlled at 5h, and the reaction temperature was maintained at 130±2°C during the dropwise addition. After the dropwise addition was completed, the temperature was kept for 30min, and the remaining 0.1 parts of initiator were added dropwise. After the dropwise addition was completed, the reaction was kept for 3h, and the material was discharged to obtain thermoplastic polyacrylate copolymer with modified castor oil polyol as the dispersion medium. The weight average molecular weight of the prepared thermoplastic polyacrylate copolymer was 55000±5000, and the Tg was 16°C. (2) and (3) are the same as in Example 5.

[0146] The viscosity of the EB adhesive at 100°C is 4200 cps.

[0147] Example 7 This embodiment provides a production process for EB-cured food packaging composite film, and the specific implementation method is the same as that in Embodiment 5; the difference is: The raw materials for preparing the polyacrylate / acrylic acid modified polyurethane, by weight, include: 80 parts of thermoplastic polyacrylate copolymer, 30 parts of polyester polyol, 20 parts of diisocyanate, 0.5 parts of polymerization inhibitor, 10.2 parts of hydroxy acrylate, 0.3 parts of antioxidant 1010, and 1 part of initiator.

[0148] The basic monomers (maintained at 95 parts) include 45 parts of n-butyl methacrylate, 25 parts of n-butyl acrylate, 15 parts of isooctyl acrylate, and 10 parts of methyl methacrylate.

[0149] The preparation steps of the EB adhesive include: (1) Preparation of thermoplastic polyacrylate copolymer: Modified castor oil polyol and antioxidant 1010 were first added to the reaction apparatus and heated to 130°C under a nitrogen atmosphere. Comonomer and 0.9 parts of initiator were added dropwise. The dropwise addition time was controlled at 6h, and the reaction temperature was maintained at 130±2°C during the dropwise addition. After the dropwise addition was completed, the temperature was kept for 30min, and the remaining 0.1 parts of initiator were added dropwise. After the dropwise addition was completed, the reaction was kept for 3h, and the material was discharged to obtain thermoplastic polyacrylate copolymer with modified castor oil polyol as the dispersion medium. The weight average molecular weight of the prepared thermoplastic polyacrylate copolymer was 55000±5000, and the Tg was -8°C. (2) and (3) are the same as in Example 5.

[0150] The viscosity of the EB adhesive at 100°C is 3200 cps.

[0151] Example 8 This embodiment provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 5; the difference being that the amount of oligomer (polyacrylate / acrylic acid modified polyurethane) added to the EB adhesive is 80 parts.

[0152] The raw materials for preparing the polyacrylate / acrylic acid modified polyurethane, by weight, include: 80 parts of thermoplastic polyacrylate copolymer, 30 parts of polyester polyol, 20 parts of diisocyanate (IPDI), 0.5 parts of polymerization inhibitor (p-methoxyphenol), and 7.5 parts of hydroxy acrylate (hydroxyethyl methacrylate).

[0153] The thermoplastic polyacrylate copolymer contains primary hydroxyl groups in its structure.

[0154] The raw materials for preparing the thermoplastic polyacrylate copolymer, by weight, include 30 parts of polyol, 100 parts of comonomer and 0.8 parts of initiator.

[0155] The initiator is tert-butyl peroxide-2-ethylhexyl carbonate.

[0156] The polyol is a modified castor oil polyol with a functionality of 2 and a molecular weight of 430, derived from Ito Corporation.

[0157] The comonomer comprises 95 parts of a basic monomer and 5 parts of a functional monomer (acrylic acid).

[0158] The basic monomers include 45 parts of n-butyl methacrylate, 25 parts of n-butyl acrylate, 15 parts of isooctyl acrylate, and 10 parts of methyl methacrylate.

[0159] The preparation steps of the EB adhesive include: (1) Preparation of thermoplastic polyacrylate copolymer: Modified castor oil polyol and antioxidant 1010 were first added to the reaction device and heated to 130°C under a nitrogen atmosphere. Comonomer and 0.7 parts of initiator were added dropwise. The dropwise addition time was controlled at 3h, and the reaction temperature was maintained at 130±2°C during the dropwise addition. After the dropwise addition was completed, the temperature was kept for 30min, and the remaining 0.1 parts of initiator were added dropwise. After the dropwise addition was completed, the reaction was kept for 3h, and the material was discharged to obtain thermoplastic polyacrylate copolymer with modified castor oil polyol as the dispersion medium. The weight average molecular weight of the prepared thermoplastic polyacrylate copolymer was 75000±5000, and the Tg was -8°C. (2) and (3) are the same as in Example 5.

[0160] The viscosity of the EB adhesive at 100°C is 2500 cps.

[0161] Example 9 This embodiment provides a production process for EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 1; the difference lies in that: the raw materials for preparing EB adhesive, by weight percentage, are: Oligomer (85% biomass polyurethane acrylate); 12% reactive diluent; Additives 3%.

[0162] The reactive diluent is 3EO-TPGDA; the additives are adhesion promoter PM-2 2% and KH560 1%.

[0163] The raw materials for preparing the biomass polyurethane acrylate, by weight, include 150 parts of biomass polyol, 70 parts of diisocyanate (MDI), 3 parts of chain extender (1,2-propanediol), 25 parts of hydroxy acrylate end-capping agent (hydroxyethyl acrylate), 0.2 parts of polymerization inhibitor (MEHQ), and 0.03 parts of catalyst (DY-20).

[0164] The biomass polyol is 100 parts of castor oil diol (Jingri D201) and 50 parts of modified dimer acid polyol (Jingri DA20).

[0165] The preparation steps of the biomass polyurethane acrylate include: (1) Synthesis of prepolymer: Under the protection of inert gas (nitrogen), biomass polyol is added to the reaction flask, heated to 120°C, vacuumed to remove water for 1 hour, cooled to 60°C, diisocyanate is added, heated to 82.5±2.5°C and reacted for 2 hours. The NCO value is tested to be below 3.7%, and NCO end-group prepolymer is obtained. (2) Chain extension reaction: The temperature of the NCO end-group prepolymer was lowered to 67.5±2.5℃, a chain extender and a catalyst were added, and the reaction was kept at the temperature for 2 hours. The NCO value was tested and found to be below 2.2%, and the chain extension prepolymer was obtained. (3) Preparation of biomass polyurethane acrylate: Hydroxyacrylate end-capping agent and polymerization inhibitor are added to the chain-extending prepolymer at 67.5±2.5℃ and the reaction continues until the -NCO groups are completely reacted (infrared spectroscopy detects 2270 cm⁻¹). - The characteristic absorption peak of -NCO ¹ completely disappeared), yielding biomass polyurethane acrylate.

[0166] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 65°C and mixing them evenly to obtain the finished EB adhesive.

[0167] The viscosity of the obtained EB adhesive at 100°C is 2200 cps.

[0168] Example 10 This embodiment provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 9; the difference lies in that: the raw materials for preparing the EB adhesive, by weight percentage, are: Oligomer (90% biomass polyurethane acrylate); 8% reactive diluent; 2% of additives.

[0169] The active diluent is the same as in Example 9, and the additives are adhesion promoter PM-2 1% and KH560 1%.

[0170] The raw materials for preparing the biomass polyurethane acrylate, by weight, include: 150 parts of biomass polyol, 55 parts of diisocyanate (IPDI), 3 parts of chain extender (1,3-butanediol), 12 parts of hydroxy acrylate end-capping agent (hydroxyethyl acrylate), 0.2 parts of polymerization inhibitor (MEHQ), and 0.03 parts of catalyst (DY-20).

[0171] The biomass polyol is castor oil diol (Jingri A4812-1, number average molecular weight of 1000, functionality of 2.2).

[0172] The preparation steps of the biomass polyurethane acrylate include: (1) Synthesis of prepolymer: Under the protection of inert gas (nitrogen), biomass polyol is added to the reaction flask, heated to 120°C, vacuumed to remove water for 1 hour, cooled to 60°C, diisocyanate is added, heated to 82.5±2.5°C and reacted for 2 hours. The NCO value is tested to be below 3.4%, and NCO end-group prepolymer is obtained. (2) Chain extension reaction: The temperature of the NCO end-group prepolymer was lowered to 67.5±2.5℃, a chain extender and a catalyst were added, and the reaction was kept at the temperature for 2 hours. The NCO value was tested and found to be below 2.0%, and the chain-extended prepolymer was obtained. (3) Preparation of biomass polyurethane acrylate: Hydroxyacrylate end-capping agent and polymerization inhibitor are added to the chain-extending prepolymer at 67.5±2.5℃, and the reaction continues until the -NCO groups are completely reacted (infrared spectroscopy detects 2270 cm⁻¹). - The characteristic absorption peak of -NCO ¹ completely disappeared), yielding biomass polyurethane acrylate.

[0173] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 70°C and mixing them evenly to obtain the finished EB adhesive.

[0174] The viscosity of the obtained EB adhesive at 100°C is 3500 cps.

[0175] Example 11 This embodiment provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 9; the difference lies in that: the raw materials for preparing the EB adhesive, by weight percentage, are: Oligomer (88% biomass polyurethane acrylate); 9% reactive diluent; Additives 3%.

[0176] The active diluent is HDDA; the additives are the same as in Example 9.

[0177] The raw materials for preparing the biomass polyurethane acrylate, by weight, include: 125 parts of biomass polyol, 72 parts of diisocyanate (HMDI), 5 parts of chain extender (1,3-butanediol), 21 parts of hydroxy acrylate end-capping agent (hydroxyethyl acrylate), 0.2 parts of polymerization inhibitor (p-hydroxyanisole (MEHQ)), and 0.03 parts of catalyst (DY-20).

[0178] The biomass polyol consists of 25 parts of epoxidized soybean oil polyol (Haierma T13180, number average molecular weight of 1300, functionality of 3) and 100 parts of modified dimer acid polyol (Jingri DA20).

[0179] The preparation steps of the biomass polyurethane acrylate include: (1) Synthesis of prepolymer: Under the protection of inert gas (nitrogen), biomass polyol is added to the reaction flask, heated to 120°C, vacuumed to remove water for 1 hour, cooled to 60°C, diisocyanate is added, heated to 82.5±2.5°C and reacted for 2 hours. The NCO value is tested to be below 6.2%, and NCO end-group prepolymer is obtained. (2) Chain extension reaction: The temperature of the NCO end-group prepolymer was lowered to 67.5±2.5℃, a chain extender and a catalyst were added, and the reaction was kept at the temperature for 2 hours. The NCO value was tested and found to be below 3.8%, and the chain extension prepolymer was obtained. (3) Preparation of biomass polyurethane acrylate: Add hydroxyl acrylate end-capping agent and polymerization inhibitor to the chain-extended prepolymer, and react until the -NCO groups are completely reacted (infrared spectroscopy detects 2270 cm⁻¹). - The characteristic absorption peak of -NCO ¹ completely disappeared), yielding biomass polyurethane acrylate.

[0180] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 75°C and mixing them evenly to obtain the finished EB adhesive.

[0181] The viscosity of the obtained EB adhesive at 100°C is 5500 cps.

[0182] Example 12 This embodiment provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Embodiment 9; the difference lies in that: the raw materials for preparing the EB adhesive, by weight percentage, are: Biomass polyurethane acrylate 95%; 3% reactive diluent; 2% of additives.

[0183] The biomass polyurethane acrylate and reactive diluent are the same as in Example 9; the additives are adhesion promoters, specifically PM-2 1% and KH560 1%.

[0184] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 70°C and mixing them evenly to obtain the finished EB adhesive.

[0185] The viscosity of the obtained EB adhesive at 100°C is 3800 cps.

[0186] Comparative Example 1 This comparative example provides a method for producing food packaging composite films using a conventional dry lamination process, including the following steps: S1. Provide food-grade packaging substrate and pretreat the packaging substrate; the specific solution is the same as in Example 1; S2. Apply solvent-based polyurethane adhesive to the pretreated surface of the first packaging substrate, then contact it with the pretreated surface of the second packaging substrate, and press it together under 0.4 MPa to obtain a composite packaging film; S3. Transfer the composite packaging film to an 80℃ oven for drying to achieve composite film bonding; then cure it in a 50℃ curing chamber for 48 hours. S4. Cool and rewind the cured composite packaging film to obtain the finished composite packaging film.

[0187] The solvent-based polyurethane adhesive is sourced from Guangdong Xinhui Chemical Co., Ltd., and its model number is XF-66F.

[0188] The coating method in step S2 is conventional coating process (specifically microgravure coating), and the amount of adhesive applied is 2.5 g / m² (dry weight).

[0189] The coating temperature in step S2 is 25±2℃.

[0190] This comparative example also provides a conventional curing food packaging composite film, which is prepared by the production process described above; the composite film structure is the same as in Example 1.

[0191] Comparative Example 2 This comparative example provides a method for producing food packaging composite films using a conventional dry lamination process, including the following steps: S1. Provide food-grade packaging substrate and pretreat the packaging substrate; the specific solution is the same as in Example 3; S2. A solvent-based polyurethane adhesive is applied to the pretreated surface of the first packaging substrate to form a PET / Al substrate; then a solvent-based polyurethane adhesive is applied to the Al surface of the PET / Al substrate; that is, two laminations are performed; the substrate is then pressed under 0.4 MPa to obtain a composite packaging film; S3. Transfer the composite packaging film to an 80℃ oven for drying to achieve composite film bonding; then cure it in a 50℃ curing chamber for 48 hours. S4. Cool and rewind the cured composite packaging film to obtain the finished composite packaging film.

[0192] The solvent-based polyurethane adhesive is sourced from Guangdong Xinhui Chemical Co., Ltd., and its model number is XF-66F. Please specify.

[0193] The coating method in step S2 is conventional coating process (specifically microgravure coating), and the amount of adhesive applied is 2.5 g / m² (dry weight).

[0194] The coating temperature in step S2 is 25±2℃.

[0195] This comparative example also provides a conventional curing food packaging composite film, which is prepared by the production process described above; the composite film structure is the same as in Example 3.

[0196] Comparative Example 3 The specific implementation method is the same as in Example 3; the difference is that the accelerating voltage in step S4 is 150kV.

[0197] Comparative Example 4 This comparative example provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Example 1; the difference being: The raw materials for preparing the EB adhesive, by weight percentage, consist of 79% oligomer (polyurethane acrylate), 20% polyfunctional reactive diluent (TMPTA), and 1% additives.

[0198] The preparation method of the polyurethane acrylate is as follows: 100 parts by weight of castor oil diol (Jingri D201) and 50 parts by weight of modified dimer acid diol (Jingri DA20) are mixed in a reaction flask, heated to 120°C, and vacuumed to remove moisture for 1 hour. Then, the temperature is lowered to 60°C, 70 parts by weight of MDI are added, and the temperature is raised to 82±2.5°C for 2 hours. The NCO value is tested. When the NCO value reaches 3.3%, the temperature is lowered to 67.5±2.5°C, 3 parts by weight of 1,2-propanediol are added, and the reaction temperature is maintained at 67.5±2.5°C for 2 hours. The NCO value is then tested. When the NCO value reaches 2.0%, 0.2 parts by weight of methoxyphenol and 13.3 parts by weight of hydroxy acrylate end-capping agent (hydroxyethyl acrylate) are added, and the reaction is continued until the NCO infrared peak disappears, thus obtaining the polyurethane acrylate.

[0199] The additive is the leveling and wetting agent EFKA377.

[0200] The viscosity of the EB adhesive at 100°C is 800 cps.

[0201] The process conditions for S2 to S4 are the same as in Example 2.

[0202] Comparative Example 5 This comparative example provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Example 1; the difference lies in that the EB adhesive is a polyurethane hot melt adhesive, and its preparation steps include: (1) According to the weight, 20 parts of polypropylene glycol 1000 and 30 parts of polybutylene adipate polyol (molecular weight 2000, from Asahikawa Chemical) were mixed, and after vacuum dehydration, they were reacted with 15 parts of IPDI at 75°C for 2 hours. Then, 0.5 parts of p-methoxyphenol and 7.5 parts of ethyl hydroxymethyl acrylate were added, and the mixture was reacted for 3 hours to end cap. (2) While the mixture is still hot, add 20 parts of reactive diluent (15 parts of TPGDA, 5 parts of EO3-TMPTA), 0.5 parts of leveling agent (BYK-310) and 2 parts of silane coupling agent (KH560) to the reaction apparatus and mix at 100°C for 10 minutes to obtain the hot melt adhesive product.

[0203] The viscosity of the obtained hot melt adhesive at 100℃ is 1300cps.

[0204] Comparative Example 6 This comparative example provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Example 1; the difference lies in that the EB adhesive is a polyurethane hot melt adhesive, and its preparation steps include: (1) According to the weight, 20 parts of modified castor oil polyol (difunctional, molecular weight Mn is 430) and 30 parts of polybutylene adipate polyol (molecular weight 2000, from Asahikawa Chemical) were mixed, and after vacuum dehydration, they were reacted with 20 parts of IPDI at 75°C for 2 hours. Then, 0.5 parts of p-methoxyphenol and 6.6 parts of ethyl hydroxymethyl acrylate were added, and the mixture was reacted for 3 hours to end cap. (2) While the mixture is still hot, add 20 parts of reactive diluent (15 parts of TPGDA, 5 parts of EO3-TMPTA), 0.5 parts of leveling agent (BYK-310) and 2 parts of silane coupling agent (KH570) to the reaction apparatus and mix at 100°C for 10 min to obtain the hot melt adhesive product.

[0205] The viscosity of the obtained hot melt adhesive at 100℃ is 2800cps.

[0206] Comparative Example 7 This comparative example provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Example 1; the difference lies in that the EB adhesive is a polyurethane hot melt adhesive, and its preparation steps include: (1) According to the weight, 100 parts of castor oil diol (Jingri D201) and 50 parts of modified dimer acid diol (Jingri DA20) were mixed and heated to 120°C, vacuum dehydrated for 1 hour, and then cooled to 60°C. 70 parts of MDI were added and the temperature was raised to 82.5±2.5°C and reacted for 2 hours. The NCO value was tested. When the NCO value reached 3.3%, the temperature was lowered to 67.5±2.5°C and 3 parts of 1,2-propanediol were added. The reaction temperature was maintained at 67.5±2.5°C and reacted for 2 hours. The NCO value was then tested. When the NCO value reached 2.0%, 0.2 parts of methoxyphenol and 25 parts of hydroxyethyl acrylate were added. The reaction was continued until the NCO infrared peak disappeared, and bio-based polyurethane acrylate was obtained.

[0207] (2) While the mixture is still hot, add 20 parts of reactive diluent (15 parts of TPGDA, 5 parts of EO3-TMPTA), 0.5 parts of leveling agent (BYK-310) and 2 parts of silane coupling agent (KH570) to the reaction apparatus and mix at 100°C for 10 min to obtain the hot melt adhesive product.

[0208] The viscosity of the resulting hot melt adhesive at 100℃ is 2200 cps.

[0209] Comparative Example 8 This comparative example provides a production process for an EB-cured food packaging composite film, with the specific implementation method being the same as in Example 9; the difference is that, by weight percentage, the raw materials for preparing the EB adhesive are: 63% biomass polyurethane acrylate, 33% reactive diluent, and 4% additives.

[0210] The reactive diluent is EO-TPGDA 8% and IBOA 25%; the additive is an adhesion promoter, specifically PM-2 2% and KH560 2%.

[0211] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 60°C and mixing them evenly to obtain the finished EB adhesive.

[0212] The viscosity of the obtained EB adhesive at 30°C is 1200 cps.

[0213] Comparative Example 9 This comparative example provides a production process for EB-cured food packaging composite film, with the specific implementation method being the same as in Example 10; the difference is that, by weight percentage, the raw materials for preparing EB adhesive are: 72% biomass polyurethane acrylate, 25% reactive diluent, and 3% additives.

[0214] The reactive diluent is HDDA; the additive is an adhesion promoter, specifically PM-2 2% and KH560 1%.

[0215] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 60°C and mixing them evenly to obtain the finished EB adhesive.

[0216] The viscosity of the obtained EB adhesive at 30°C is 3800 cps.

[0217] Comparative Example 10 This comparative example provides a production process for EB-cured food packaging composite film, with the specific implementation method being the same as in Example 11; the difference is that, by weight percentage, the raw materials for preparing EB adhesive are: 72% biomass polyurethane acrylate, 25% reactive diluent, and 3% additives.

[0218] The active diluent is IBOA.

[0219] The preparation steps of the EB adhesive include: heating biomass polyurethane acrylate, reactive diluent, and additives to 60°C and mixing them evenly to obtain the finished EB adhesive.

[0220] The viscosity of the obtained EB adhesive at 30°C is 1800 cps.

[0221] Performance testing 1. Peel strength: The initial peel strength and peel strength after curing of the example and comparative samples were tested according to the method of GB / T 8808-1988. The test results are shown in Tables 1-3.

[0222] In Table 1-3, the unit of peel strength is N / 15mm; in the peel strength test, BOPP / CPP refers to the packaging substrate being BOPP (20μm) and CPP (40μm thick); PET / Al refers to the packaging substrate being PET (12μm thick) and Al (9μm thick); PE / AL refers to the packaging substrate being PE (30μm thick) and Al (9μm thick); PET / PE refers to the packaging substrate being PET (12μm thick) and PE (30μm thick).

[0223] 2. Water boiling resistance Samples from Examples 1-4 and Comparative Examples 1-4 were boiled in water at 120°C for 30 minutes. The results were observed to see if cracks or bubbles appeared in the samples. The test results are shown in Table 1.

[0224] 3. Odor of the coating Record whether there is an odor during the coating stage of Examples 5-12 and Comparative Examples 5-10. The test results are recorded in Table 2.

[0225] Table 1

[0226] Table 2

[0227] Table 3

[0228] As can be seen from the data in Table 1, the food packaging composite films (Examples 1-4) prepared using the EB curing method of the present invention have good peel strength and reliable performance. They do not crack or bubble even when boiled in water at high temperatures, thus meeting the requirements for food packaging. Comparative Examples 1 and 2 used solvent-based polyurethane adhesives to prepare composite films. The resulting products had a slight solvent odor and low initial peel strength. Although their strength after curing was comparable to that of Example 1 of the present invention, the production cycle was long, and there was a risk of solvent residue, failing to meet the requirements for food packaging. Comparative Example 3 used the EB curing method to prepare the composite film, but the accelerating voltage during the radiation curing stage was low, and the peel strength of the final product did not show a significant improvement. The data from Comparative Example 4 showed that when the formulation of the EB adhesive was not adjusted within the preferred range, the product exhibited automatic peeling during the boiling water resistance test, failing to meet the requirements for food packaging composite films.

[0229] As can be seen from the data in Table 2, the food packaging composite films prepared using the EB adhesive of the present invention and the specific preparation method in Examples 5-8 have good peel strength, especially with a significant improvement in initial peel strength; at the same time, the peel strength is basically unaffected by the type of substrate, and can meet the usage requirements of various food packaging materials. In contrast, Comparative Examples 5-7, which did not use the EB adhesive system of the present invention, resulted in products with lower initial peel strength, failing to meet usage requirements.

[0230] As can be seen from the data in Table 3, the food flexible packaging composite films prepared using the biomass polyurethane acrylate adhesive of the present invention in Examples 9-12 have high peel strength, strong initial positioning ability, and no odor during coating, which meets the production requirements; while Comparative Examples 8-10 did not use the biomass polyurethane acrylate adhesive system of the present invention, and the final products had extremely low initial peel strength and low peel strength after curing, and had an odor during coating, which did not meet the production requirements.

Claims

1. A production process for an EB-cured food packaging composite film, characterized in that, Includes the following steps: S1. Provide food-grade packaging substrate and pre-treat the packaging substrate; The packaging substrate includes at least a first packaging substrate and a second packaging substrate; S2. Apply EB adhesive to the pretreated surface of the first packaging substrate; S3. Press the pretreated surfaces of the first packaging substrate coated with EB adhesive and the second packaging substrate together to obtain a composite packaging film; S4. Perform electron beam curing treatment on the composite packaging film; S5. Cool and rewind the composite packaging film after electron beam curing to obtain the finished composite packaging film; The viscosity of the EB adhesive at 100°C is 1000-10000 cps.

2. The production process of the EB-cured food packaging composite film according to claim 1, characterized in that, The S4 step specifically includes: transferring the composite packaging film to the electron beam curing device via the production line, and radiating and curing it in an inert gas atmosphere, so that the EB adhesive crosslinks instantly; The conditions for radiation curing in step S4 are: accelerating voltage 80-300kV, irradiation dose 20-100kGy, and production line transmission speed 50-300m / min.

3. The production process of the EB-cured food packaging composite film according to claim 1, characterized in that, In step S2, the amount of EB adhesive applied is 1.5-4.0 g / m², and the coating temperature is 60-120℃.

4. The production process of the EB-cured food packaging composite film according to claim 1, characterized in that, In step S3, the pressing pressure is 0.2-0.6 MPa and the pressing temperature is 10-60℃.

5. The production process of the EB-cured food packaging composite film according to claim 3, characterized in that, The coating method in step S2 is multi-roller gravure coating; the number of rollers in multi-roller gravure coating is 3-5.

6. The production process of the EB-cured food packaging composite film according to claim 1, characterized in that, The raw materials for preparing the EB adhesive, by weight percentage, include: Oligomers 60-95%; Tackifying resin: 0-30%; Multifunctional active diluent 1-25%; Additives 0-5%; The oligomers include one or more of polyurethane acrylates, polyester acrylates, and epoxy acrylates; the EB adhesive does not contain solvents, monofunctional reactive diluents, or photoinitiators.

7. The production process of the EB-cured food packaging composite film according to claim 6, characterized in that, The oligomers include polyurethane acrylates, which are polyacrylate / acrylic acid modified polyurethanes or biomass polyurethane acrylates.

8. An EB-cured food packaging composite film, characterized in that, The EB-cured food packaging composite film is prepared by the production process described in any one of claims 1 to 7.

9. The EB-cured food packaging composite film according to claim 8, characterized in that, The structure of the EB-cured food packaging composite film includes at least a first packaging substrate layer, an adhesive layer, and a second packaging substrate layer stacked together.

10. The EB-cured food packaging composite film according to claim 9, characterized in that, The adhesive layer is a product formed by cross-linking and curing EB adhesive through electron beam irradiation; the adhesive layer has no solvent or photoinitiator residue.

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