Pet food package with gas adsorption function and preparation method thereof

Abstract

The invention relates to the technical field of food packages, in particular to a pet food package suitable for cold chain storage at 4-18 DEG C and a preparation method of the pet food package, and the pet food package which is high in antifogging property, high in antibacterial activity and high in gas adsorption capacity and meets the national food safety standard for food contact plastic materials and products (GB4806.7-2023) can be prepared on a large scale. And the cold chain storage and transportation requirements of pet foods such as fresh meat staple food cans (containing raw bone and meat ingredients), low-temperature cooked pet foods (such as chicken breast strips), freeze-dried mixed foods (containing fresh meat freeze-dried particles) and the like are met.

Description

Technical Field

[0001] This invention relates to the field of food packaging technology, specifically to a pet food packaging suitable for cold chain storage at 4℃ to -18℃ and its preparation method. It can be used to mass-produce pet food packaging with high anti-fogging properties, high antibacterial activity, and high gas adsorption capacity, which meets the requirements of the National Food Safety Standard for Plastic Materials and Products for Food Contact (GB4806.7-2023). It is suitable for the cold chain storage and transportation needs of pet foods such as fresh meat staple food cans (containing raw meat and bone ingredients), low-temperature cooked pet food (such as chicken breast strips), and freeze-dried mixed food (containing freeze-dried fresh meat pellets). Background Technology

[0002] Pet food packaging needs to address the core issues of "fogging of the film surface, microbial growth, release of spoilage odors, and easy structural damage" under cold chain conditions, but existing technologies have significant shortcomings: 1. Short anti-fogging time: Relying on a single molecular weight anti-fogging agent, the light transmittance of the film surface is less than 75% after 48 hours, and the wear resistance is poor (friction coefficient 0.45), which cannot cover the 7-15 day shelf life; 2. Insufficient antibacterial safety: Existing antibacterial packaging mostly adopts the method of "directly adding nano silver particles", which lacks targeted release regulation: the concentration of antibacterial agent is too high in the early stage of refrigeration, exceeding the limit of 0.05mg / kg specified in GB4806.7-2023; in the later stage of refrigeration, the concentration of antibacterial agent drops below the antibacterial threshold, and the antibacterial rate against Escherichia coli and Salmonella is <80%, which cannot meet the antibacterial needs throughout the entire cycle; 3. Weak gas adsorption capacity: It only adsorbs ammonia (adsorption amount < 8 mg / g), and cannot treat hydrogen sulfide and acetaldehyde. The desorption rate is > 12% after 24 hours, and the odor rebound is obvious. 4. Poor structural stability: Existing packaging often uses a "single adhesive composite" process. The base layer (pure PET) has an impact strength of only 5kJ / m² at -18℃, making it prone to breakage due to impact during cold chain transportation. The interlayer peel strength is ≤2.5N / 15mm, and after three low-temperature cycles (-18℃→4℃), the delamination rate is >30%, leading to the simultaneous failure of anti-fogging, antibacterial, and adsorption functions. Furthermore, existing packaging lacks a low-temperature setting process, making it prone to wrinkles during storage due to the release of internal stress, further damaging the functional layers of the film. 5. Severe storage degradation: After 24 hours of storage at 4℃, the hydrophilicity of the anti-fog layer of existing packaging bags decreases by 20%-25%, and the activity of antibacterial agents decreases by 15%-20%; after 3 months of freezing at -80℃ (for long-term storage of packaging materials), the cracking rate of the film surface is >10%, which cannot meet the time window requirements for multi-center pet food distribution and long-term storage.

[0003] To address the aforementioned shortcomings, this technical solution resolves the safety, functionality, and stability issues of existing technologies through composite layer formulation optimization and phased molding process design.

[0004] Technical problems to be solved 1. Overcome the defects of "short duration and poor wear resistance" in anti-fog treatment, and achieve anti-fog effect of ≥150h, light transmittance ≥88%, and film surface friction coefficient ≤0.28 at 4℃. 2. Overcomes the defects of "blind release and excessive migration" of antibacterial agents, achieving an antibacterial rate of ≥99.9% throughout the shelf life and a nano-silver migration amount of ≤0.005mg / kg; 3. Overcoming the shortcomings of "narrow adsorption range and high desorption rate", it achieves broad-spectrum adsorption of ammonia (≥18mg / g), hydrogen sulfide (≥13mg / g), and acetaldehyde (≥12mg / g), with a desorption rate of ≤3% in 24 hours; 4. Overcome the structural defects of "easy breakage at low temperatures and easy delamination between layers", and improve the impact strength at -18℃ to ≥8.5kJ / m² and the interlayer peel strength to ≥7.5N / 15mm; 5. Overcome the defect of "rapid functional decay" during storage, achieving a functional decay of ≤8% after 24 hours of storage at 4℃ and a cracking rate of ≤1% after 3 months of freezing at -80℃.

[0005] To address the aforementioned technical problems, this invention provides a pet food refrigerated packaging bag with a three-layer composite structure of "substrate layer - antibacterial layer - anti-fog adsorption layer" and its preparation method. Through a closed-loop process of "composite layer formula design → staged molding → finished product testing," a functionally synergistic, safe, and stable packaging system is constructed, as detailed below: 1. Structure and Formulation The packaging bag comprises, from the outside to the inside, a base material layer, an antibacterial layer, and an anti-fog adsorption layer, with a total thickness of 85-105 μm. The composition of each layer (by weight percentage) is as follows. All raw materials comply with the food contact safety requirements of GB4806.7-2023: (1) Substrate layer (thickness 28-35μm, outer support layer) Polyethylene terephthalate (PET): 88-90%, chips (density 1.38g / cm³, melting point 250-255℃), providing basic mechanical support and high temperature resistance, ensuring puncture resistance during cold chain transportation; Polycaprolactone (PCL): 6-8% (molecular weight 80,000, no brittleness at -18℃), improves the low-temperature toughness of the substrate and reduces the risk of impact cracking; Maleic anhydride-grafted PET: 1-2% (grafting rate 1.2±0.1%), enhances the adhesion strength between the subsequent antibacterial layer and the substrate, and avoids interlayer delamination; Antioxidant (1010): 0.2-0.3% (food grade), prevents PCL from oxidizing and degrading during molding, and extends the service life of packaging bags.

[0006] (2) Antibacterial layer (thickness 25-30μm, middle layer function) The product employs a layered design of "targeted carrier + dual-grafting-rate responsive agent" to ensure precise release of the antibacterial agent. The specific composition is as follows: Outer layer (accounting for 60% of the total mass of the antibacterial layer, rapidly activated): Polypropylene (PP): 85-88%, selected (melt flow rate 3g / 10min, 190℃ / 2.16kg), provides the basic structure of antibacterial layer, resistant to low temperature and easy to process; Targeted modified nano-silver-montmorillonite: 7-9% (silver particle size 5-10nm, silver loading 1.3±0.1wt%), surface grafted with galactose (targeting Escherichia coli / Salmonella) and polylysine (targeting Staphylococcus aureus) to enhance antibacterial targeting; Poly(N-isopropylacrylamide)-chitosan graft (40% grafting rate): 2-3% (molecular weight 100,000 ± 10,000), rapidly releases antibacterial agent at low temperature (0-4℃), initiating initial sterilization; Dicumyl peroxide (DCP): 0.7-0.9%, selected (40% content, PP as carrier), to promote the cross-linking of the antibacterial layer with the substrate layer and the anti-fog adsorption layer.

[0007] Inner layer (accounting for 40% of the total antibacterial layer mass, long-lasting effect): Polypropylene (PP): 87-90%, same as the outer PP specification, to ensure interlayer compatibility; Targeted modified nano-silver-montmorillonite: 5-7%, same as the outer layer antibacterial agent specification, reducing the amount of inner layer antibacterial agent and avoiding the risk of migration caused by direct contact with food; Poly(N-isopropylacrylamide)-chitosan graft (20% grafting rate): 3-4%, same as the outer graft specification, slowly releases antibacterial agent at low temperature, maintaining bactericidal effect in the middle and late stages; Dicumyl peroxide (DCP): 0.7-0.9%, same as the outer layer DCP specification, to ensure uniform interlayer crosslinking.

[0008] (3) Anti-fog adsorption layer (thickness 32-40μm, inner layer in contact with food) It adopts a multi-component synergistic design of "multi-molecular weight anti-fogging + broad-spectrum adsorption + metabolic regulation" to replace the traditional single functional layer. The specific composition is as follows: Linear low-density polyethylene (LLDPE): 85-88%, good compatibility with pet food, no odor release; Multimolecular weight polyethylene glycol-acrylic acid copolymer compound: 4-6%, molecular weight 3000:5000:8000=2:1:1. 3000 molecular weight can quickly cover the film surface (0-48h anti-fogging), 5000 molecular weight can maintain the effect in the medium term (48-72h), and 8000 molecular weight can slowly release the effect (72-150h), thus achieving long-lasting anti-fogging effect. Amino-modified nano silica: 3-5%, particle size 20nm, amino content 2.0mmol / g. On the one hand, it enhances the adsorption of acetaldehyde through the Schiff base reaction between amino and acetaldehyde, and on the other hand, it enhances the hardness of the film surface and reduces the coefficient of friction. Hydroxypropyl β-cyclodextrin: 1-3%, purity ≥98%, its hydrophobic cavity can encapsulate hydrogen sulfide / acetaldehyde molecules, reducing the desorption rate after adsorption to below 3%; Triallyl isocyanurate (TAIC): 0.2-0.4%, synergistically crosslinks with DCP to enhance the binding force between the adsorbent support and LLDPE, preventing support detachment; Zinc stearate: 0.6-0.8%, purity ≥99%, acts as a dispersant to prevent the agglomeration of nano-silica and hydroxypropyl β-cyclodextrin, ensuring uniform function.

[0009] 2. Preparation method The preparation method includes three core stages: composite layer formulation preparation, staged molding, and finished product testing. The specific steps are as follows: Phase 1: Preparation of the composite layer formulation (total time: 30-35 minutes) This stage aims to prepare specific raw material mixtures for each layer, providing a functional basis for subsequent molding. Key operations are as follows: 1. Preparation of Targeted Modified Nano-Silver-Montmorillonite (Core Raw Material for Antibacterial Layer) 22.4 kg of nano-silver-montmorillonite and 5 L of sterile deionized water were poured into an ultrasonic dispersion tank equipped with a stirrer. The stirring speed was set to 500 rpm and the ultrasonic time to 15 minutes, ensuring that the particle size was ≤500 nm (≤1 agglomerate per field of view under a microscope at 100x magnification). The temperature was raised to 80°C, and 0.5 kg of galactose and 0.3 kg of polylysine (Sigma, catalog number P4892) were slowly added. The mixture was stirred at a constant temperature for 2 hours (ensuring a grafting rate ≥85%, and the characteristic peak was detected at 1050 cm⁻¹ using an infrared spectrometer). -1 The mixture was transferred to a vacuum dryer, and the temperature was set to 80℃ and the vacuum degree to -0.09MPa. After drying for 4 hours, the targeted modified antibacterial agent was obtained and sealed for later use (stored at 4℃, shelf life 7 days).

[0010] 2. Preparation of mixtures in each layer (1) Substrate layer mixture: 281.6kg PET chips, 25.6kg PCL granules, 0.96kg antioxidant (1010), and 6.4kg maleic anhydride-grafted PET were added to a 500L high-speed mixer. The speed was set to 1800r / min and the temperature to 90℃. The mixture was mixed for 12 minutes to ensure that the materials were uniform (sampling test: melt flow rate 1.8±0.1g / 10min, 250℃ / 2.16kg). (2) Antibacterial layer mixture: Outer layer: 166.2kg PP granules + 13.44kg targeted modified antibacterial agent + 3.36kg 40% grafted graft + 1.34kg DCP, mixed in a high-speed mixer at 1800r / min and 90℃ for 10 minutes; Inner layer: 110.8kg PP granules + 8.96kg targeted modified antibacterial agent + 3.58kg 20% ​​grafted graft + 0.89kg DCP, mixed with the same parameters; After mixing, the melt flow rate was measured by rheometer to be 2.8 ± 0.2 g / 10 min (190℃ / 2.16 kg), and there was no grainy feel when rubbed by hand. (3) Anti-fog adsorption layer mixture: Premix: 5 kg of multi-molecular weight compound + 0.7 kg of zinc stearate, mix at 1200 r / min for 5 minutes; Main mixture: 174kg LLDPE granules + premix + 4kg amino-modified nano silica, mixed at 1500r / min and 80℃ for 8 minutes; Addition mixing: Add 2 kg hydroxypropyl β-cyclodextrin + 0.3 kg TAIC, mix at 1200 r / min and 70℃ for 6 minutes; Samples were taken after mixing: Microscopic observation showed no agglomeration of nano-silica, and the melt flow rate was 2.1±0.1g / 10min (190℃ / 2.16kg).

[0011] Second stage: Phased molding process (total time 34-38 minutes) This stage employs a phased control approach of "melt co-extrusion → in-situ cross-linking → low-temperature setting" to balance the forming quality and functional stability of the packaging bag. Key operations are as follows: 1. Equipment preheating and parameter setting A three-layer co-extrusion blown film machine is used, with gradient preheating of the screws and dies in each layer: Substrate layer screw: Zone 1 245℃, Zone 2 250℃, Zone 3 255℃ (heating rate 5℃ / min, to avoid PET degradation); Antibacterial layer screw (modified with dual feed inlets and added side feed valve): Zone 1 182℃, Zone 2 187℃, Zone 3 192℃; Anti-fog adsorption layer screw (dual-chamber hopper, separating anti-fog and adsorption components): Zone 1 172℃, Zone 2 177℃, Zone 3 182℃; Mold head: substrate layer area 250℃, antibacterial layer area 190℃, anti-fog adsorption layer area 183℃ (the middle area is 3℃ higher to promote the directional distribution of the adsorption carrier); After preheating for 1 hour, use a temperature gun to check the actual temperature of each section. If the error is ≤ ±2℃, proceed to the next step.

[0012] 2. Gradient feeding and membrane bubble formation Feed control: The antibacterial layer is fed synchronously through dual feed ports (outer layer 60kg / h, corresponding to screw speed 30r / min; inner layer 40kg / h, corresponding to screw speed 20r / min); the anti-fog adsorption layer is fed through a dual-chamber hopper (anti-fog main agent 70kg / h, adsorption aid 10kg / h); the substrate layer is fed at 50kg / h (screw speed 25r / min). Bubble control: Start the air compressor, set the inlet pressure to 0.1MPa, and inflate the air ring of the die head to make the bubble diameter reach 560mm (die head diameter 200mm × inflation ratio 2.8). Use a tape measure to evenly measure 6 points with an error ≤ ±5mm. Start the traction machine and set the speed to 3.2m / min (speed gauge verification: 3.2±0.1m / min) to ensure that the bubble is stable and without shaking.

[0013] 3. In-situ UV crosslinking and low-temperature setting Crosslinking: Immediately after extrusion, the membrane bubble is placed in the UV curing channel at a wavelength of 254nm, a power of 100W, and an irradiation time of 15-18 seconds (5cm distance between the membrane surface and the UV lamp, and UV radiometer detection intensity of 80±5mW / cm²), ensuring an interlayer crosslinking degree of ≥85%; Shaping: After cross-linking, the film bubble is cooled by a 25℃ water-cooled roller (with a constant temperature water tank, Jinghong HH-601), and then bonded to a -5℃ low-temperature shaping roller (with a cooling interlayer, power 1.5kW). Shaping takes 5-6 seconds (temperature sensor detects roller surface temperature -5±1℃), inducing PCL crystallization and improving low-temperature toughness.

[0014] Phase 3: Finished product cutting and quality inspection (total time 11-13 minutes) This stage strictly adheres to clinical-grade standards for harvesting finished products, and quality is verified through multi-dimensional testing. Key operations are as follows: 1. Finished product cutting After the composite film is shaped, it is transferred to an automatic cutting and slitting machine. The cutting width is set according to the packaging specifications (200mm for 200g bags, 300mm for 500g bags). The cutting speed is set to 10m / min and the winding tension is set to 50N (tension meter verification: 50±2N). Every 5 rolls are cut, the width error is measured with a tape measure and is ≤±0.5mm to ensure that there are no rough edges (no rough feel to the touch).

[0015] 2. Quality inspection (3 samples per batch, pass rate ≥ 99%) (1) Functional testing: Anti-fogging performance: After refrigeration at 4℃ for 150 hours, the transmittance measured by a transmittance meter is ≥88%; Antibacterial activity: Tested using the film-applied method (GB / T31402-2015), the inhibition rate against Escherichia coli, Salmonella, and Staphylococcus aureus is ≥99.9%; Adsorption capacity: In the sealed container adsorption method, the desorption rate of ammonia ≥18mg / g, hydrogen sulfide ≥13mg / g, and acetaldehyde ≥12mg / g is ≤3% after 24 hours; (2) Structural inspection: Low-temperature impact: -18℃ drop ball impact test (100g steel ball, 1m height), breakage rate ≤1%; Interlayer peel strength: tested with a tensile testing machine at -18℃, peel strength ≥7.5N / 15mm; (3) Safety inspection: Migration amount: Inductively coupled plasma mass spectrometry, the migration amount of silver nanoparticles was ≤0.005 mg / kg; Endotoxin: <0.5 EU / mL using the Limulus Amebocyte Lysate (LonzaLAL003) method; Microorganisms: Plate count method, total aerobic bacteria <10 CFU / mL, molds and yeasts <1 CFU / mL.

[0016] Beneficial effects Compared with existing pet food refrigerated packaging technologies, the packaging bag and its preparation method with synergistic functions of gas adsorption, antibacterial, and anti-fogging provided by this invention have the following significant advantages: 1. Excellent safety features, meeting stringent standards. 2. No surface coating treatment is required for the molding equipment throughout the process, completely eliminating the risk of pet allergies caused by animal-derived antifogging agents / antibacterial agents. All raw materials have passed GB4806.7-2023 food contact safety certification. At the same time, the coating step is eliminated, the operation time is shortened by 3-4 hours, the labor cost is reduced by about 25%, and the coefficient of variation of functional parameters of different batches of products is <10%, solving the problem of "batch instability" in traditional technology.

[0017] 3. Highly efficient and collaborative functions, covering all lifecycle needs. Anti-fogging: Multi-molecular weight compound anti-fogging agent achieves 150h long-lasting anti-fogging (4℃), and the light transmittance is still ≥88% after 150h. The film surface friction coefficient is reduced to 0.28, and the light transmittance decreases by ≤3% after 500 rubs, which is far superior to the existing technology (48h anti-fogging, friction coefficient 0.45). Antibacterial: Targeted modified antibacterial agent + double grafting rate responsive release, antibacterial rate ≥99.9% throughout the shelf life (7-15 days), nano silver migration ≤0.005mg / kg, avoiding "excessive levels in the early stage and failure in the later stage"; Adsorption: Amino-modified nano-silica and hydroxypropyl β-cyclodextrin work synergistically to achieve broad-spectrum adsorption of ammonia (18.5 mg / g), hydrogen sulfide (13.2 mg / g), and acetaldehyde (12.3 mg / g), with a desorption rate of ≤3% in 24 hours, completely solving the problem of putrid odor.

[0018] 4. Stable and reliable structure, adaptable to cold chain environment The PET-PCL blend substrate increases the impact strength at -18℃ to 8.5kJ / m², with an impact breakage rate of ≤1%. The in-situ UV crosslinking + low-temperature setting process results in an interlayer peel strength of ≥7.5N / 15mm. After 5 cycles of low-temperature cycling (-18℃→4℃), the delamination rate is <5%. After 24 hours of storage at 4℃, the functional degradation is ≤8%, and after 3 months of frozen storage at -80℃, the cracking rate is ≤1%, meeting the needs of multi-center distribution and long-term storage. Detailed Implementation

[0019] To more clearly illustrate the technical solution of this invention, the following describes in detail the pet food refrigerated packaging bag and its preparation method, using three specific embodiments (covering the lower, middle, and upper limits of the claim parameters) and four comparative examples (verifying the necessity of the core innovation). All embodiments are based on the core process of this invention: "composite layer formulation preparation → staged molding → finished product testing," with differences only in parameter values, to verify the stability and repeatability of the technical solution.

[0020] Example 1: Preparation of packaging bags based on the lower limit of the claim parameters 1. Preparation of experimental materials (1) Source of raw materials Food contact grade raw materials conforming to GB4806.7-2023 were selected. The specifications and suppliers of key raw materials are shown in the table below:

[0021] (2) Experimental instruments High-speed mixer (Zhangjiagang Green GHR-500), three-layer co-extrusion blown film machine (Guangdong Jinming JM-GC70), UV curing tunnel (Shenzhen Guangyunda UVC-254-100), low-temperature setting roller (with cooling interlayer, power 1.5kW), transmittance meter (Shenzhen Sanenshi NH310), tensile testing machine (Jinan Meister WDW-5), inductively coupled plasma mass spectrometer (Agilent 7900), biosafety cabinet (ESCOAC2-4S1).

[0022] 2. Experimental Procedure (1) First stage: Preparation of composite layer formulation Targeted modified nano-silver-montmorillonite: prepared according to the above method, with a silver loading of 1.2 wt% and a grafting rate of 85%; Substrate layer mixture: 90% PET, 6% PCL, 2% maleic anhydride-grafted PET, 2% antioxidant (1010), mixed at 1800 r / min and 90℃ for 12 minutes; Antibacterial layer mixture: outer layer (PP 88%, targeted antibacterial agent 7%, 40% grafted material 2%, DCP 0.7%), inner layer (PP 90%, targeted antibacterial agent 5%, 20% grafted material 4%, DCP 0.7%), mixed at 1800 r / min and 90℃ for 10 minutes; Anti-fog adsorption layer mixture: 88% LLDPE, 4% multi-molecular weight compound, 3% amino-modified nano silica, 1% hydroxypropyl β-cyclodextrin, 0.2% TAIC, and 0.6% zinc stearate, mixed in stages.

[0023] (2) Second stage: Phased formation Preheating: Screw of substrate layer 245℃ / 250℃ / 255℃, antibacterial layer 182℃ / 187℃ / 192℃, antifog layer 172℃ / 177℃ / 182℃, die head 250℃ / 190℃ / 183℃; Feeding: Antibacterial layer dual feeding (outer layer 60kg / h, inner layer 40kg / h), anti-fog layer dual-cavity feeding (70kg / h + 10kg / h), substrate layer 50kg / h; Crosslinking and setting: UV irradiation for 15 seconds, low temperature setting at -5℃ for 5 seconds.

[0024] (3) Third stage: Finished product testing Cutting: 200mm width, 10m / min speed; Test results: Total thickness 85μm, anti-fogging time 150h (transmittance 88%), antibacterial rate 99.9% (E. coli), ammonia adsorption 18mg / g, peel strength at -18℃ 7.5N / 15mm, nano silver migration 0.005mg / kg, meeting the standards.

[0025] 3. Conclusion of the Example This embodiment operates according to the lower limit of the parameters claimed, and successfully prepares pet food refrigerated packaging bags that meet clinical-grade standards. All functional parameters meet the standards, proving that the technical solution still has stability at the lower limit of the parameters.

[0026] Example 2: Preparation of packaging bags based on intermediate values ​​of claim parameters 1. Preparation of experimental materials The donor materials and instruments are the same as in Example 1, with only some material proportions adjusted.

[0027] 2. Experimental Procedure (1) Preparation of composite layer formulation Substrate layer: 89% PET, 7% PCL, 1.8% maleic anhydride-grafted PET, 25% antioxidant (1010); Antibacterial layer: outer layer (PP 86.5%, targeted antibacterial agent 8%, 40% grafted material 2.5%, DCP 0.8%), inner layer (PP 88.5%, targeted antibacterial agent 6%, 20% grafted material 4%, DCP 0.8%). Anti-fog adsorption layer: 86.5% LLDPE, 5% multi-molecular weight compound, 4% amino-modified nano silica, 2% hydroxypropyl β-cyclodextrin, 0.3% TAIC, and 0.7% zinc stearate.

[0028] (2) Phased molding Preheating parameters remain unchanged; UV irradiation for 16.5 seconds; low-temperature setting at -4.5℃ for 5.5 seconds. Cutting width 300mm, speed 10m / min.

[0029] (3) Test results Total thickness 95μm, anti-fogging time 155h (light transmittance 89.5%), antibacterial rate 99.93% (Salmonella), ammonia adsorption 18.5mg / g, hydrogen sulfide 13.2mg / g, acetaldehyde 12.3mg / g, peel strength at -18℃ 7.8N / 15mm, nano-silver migration 0.004mg / kg, endotoxin <0.3EU / mL.

[0030] 3. Conclusion of the Example This embodiment operates at the intermediate parameter value, and the functional parameters of the packaging bag are optimal, proving that the intermediate value is the optimal choice that balances performance and cost.

[0031] Example 3: Preparation of packaging bags based on the upper limit of the parameters in the claims 1. Preparation of experimental materials The donor materials and instruments are the same as in Example 1, but the proportion of materials is adjusted according to the upper limit of the claims.

[0032] 2. Experimental Procedure (1) Preparation of composite layer formulation Substrate layer: 88% PET, 8% PCL, 1.7% maleic anhydride-grafted PET, 3% antioxidant (1010); Antibacterial layer: outer layer (PP 85%, targeted antibacterial agent 9%, 40% grafted material 3%, DCP 0.9%), inner layer (PP 87%, targeted antibacterial agent 7%, 20% grafted material 4%, DCP 0.9%). Anti-fog adsorption layer: 85% LLDPE, 6% multi-molecular weight compound, 5% amino-modified nano silica, 2% hydroxypropyl β-cyclodextrin, 0.4% TAIC, and 0.8% zinc stearate.

[0033] (2) Phased molding UV irradiation for 18 seconds, followed by low-temperature shaping at -4℃ for 6 seconds; Cutting width 300mm, speed 10m / min.

[0034] (3) Test results The total thickness is 105μm, the anti-fogging effect is 160h (light transmittance is 90%), the antibacterial rate is 99.95% (Staphylococcus aureus), the ammonia adsorption capacity is 19.2mg / g, the hydrogen sulfide is 14.5mg / g, the acetaldehyde is 13.1mg / g, the peel strength at -18℃ is 8.1N / 15mm, and the nano silver migration is 0.003mg / kg. All parameters are optimal.

[0035] 3. Conclusion of the Example This embodiment operates at the upper limit of parameters, and the functional parameters of the packaging bag reach their peak without any waste of raw materials or overperformance, proving that the technical solution is still reliable even at the upper limit of parameters.

[0036] Comparative Design and Performance Verification To verify the necessity of the key technical features of this invention (staged anti-fogging, targeted antibacterial, amino-modified adsorption, and low-temperature setting), four comparative examples were set up, with the remaining operations the same as in Example 2 (intermediate parameter values). The results are as follows: Comparative Example 1: No staged anti-fogging was used (containing a single molecular weight anti-fogging agent throughout the entire process). Differences: The anti-fog adsorption layer uses only PEG-AA with a molecular weight of 5000, without multi-molecular weight compounding; Results: The anti-fog effect lasted for 48 hours (72% light transmittance), and after 150 hours the light transmittance was less than 60%, which could not meet the full-cycle visibility requirements. Conclusion: Multi-molecular-weight staged anti-fogging is the core to ensure long-term visibility, while the duration of single-molecular-weight anti-fogging agents is only 31% of that in Example 2.

[0037] Comparative Example 2: Antibacterial agent without targeted modification (ordinary nano-silver-montmorillonite) Differences: The antibacterial layer uses ungrafted galactose / polylysine nanosilver-montmorillonite; Results: Poor antibacterial uniformity (local inhibition rate 55%), nano-silver migration amount 0.06 mg / kg (exceeding the standard), and inhibition rate against non-pathogenic bacteria 35%; Conclusion: Targeted modification can improve antimicrobial uniformity and safety, while unmodified antimicrobial agents cannot meet food contact standards.

[0038] Comparative Example 3: Adsorption layer without amino modification (ordinary nano silica) Difference: The adsorption layer uses non-amino-modified nano-silica; Results: Acetaldehyde adsorption capacity was 5.2 mg / g (only 42% of that in Example 2), desorption rate was 18% after 24 hours, and there was a noticeable off-odor in the later stage; Conclusion: Amine modification is key to improving acetaldehyde adsorption and reducing desorption rate; conventional adsorption carriers are insufficient.

[0039] Comparative Example 4: No low-temperature setting process Difference: After molding, only water cooling is used for setting, without low-temperature setting at -5℃; Results: Impact strength at -18℃ was 5.2 kJ / m² (only 59% of that in Example 2), and delamination rate was 35% after 3 cycles at low temperature; Conclusion: Low-temperature setting can significantly improve the toughness and interlayer bonding of the substrate, but the structural stability drops sharply after the absence of these properties.

[0040] Overall Conclusion of Examples Through verification in Examples 1-3, this invention can stably prepare high-performance pet food refrigerated packaging bags within the parameter range defined in the claims (thickness 85-105μm, anti-fogging time ≥150h, antibacterial rate ≥99.9%, adsorption capacity ≥18mg / g). Comparative examples further demonstrate that "multi-molecular weight staged anti-fogging," "targeted antibacterial modification," "amino-modified adsorption," and "low-temperature setting" are the core innovations of this invention. This technical solution requires no coating, is simple to operate, and has high safety, meeting the needs of large-scale production and clinical-grade storage and transportation for pet food companies.

Claims

1. A pet food refrigerated packaging bag with synergistic functions of gas adsorption, antibacterial, and anti-fogging, characterized in that, From the outside to the inside, it includes a substrate layer, an antibacterial layer, and an anti-fog adsorption layer, with a total thickness of 85-105μm; The substrate layer is composed of the following components by weight percentage: polyethylene terephthalate (PET) 88-90%, polycaprolactone (PCL) 6-8%, maleic anhydride-grafted PET 1-2%, and antioxidant (1010): 0.2-0.3%; The antibacterial layer has a layered structure, and by weight percentage: Outer layer (accounting for 60% of the total mass of the antibacterial layer): 85-88% polypropylene (PP), 7-9% targeted modified nano-silver-montmorillonite, 2-3% poly(N-isopropylacrylamide)-chitosan graft with a 40% grafting rate, and 0.7-0.9% dicumyl peroxide (DCP); Inner layer (accounting for 40% of the total mass of the antibacterial layer): 87-90% polypropylene (PP), 5-7% targeted modified nano-silver-montmorillonite, 3-4% poly(N-isopropylacrylamide)-chitosan graft with a 20% grafting rate, and 0.7-0.9% dicumyl peroxide (DCP). The anti-fog adsorption layer is composed of the following components by weight percentage: 85-88% linear low-density polyethylene (LLDPE), 4-6% multimolecular-weight polyethylene glycol-acrylic acid copolymer (PEG-AA) compound, 3-5% amino-modified nano silica, 1-3% hydroxypropyl β-cyclodextrin, 0.2-0.4% triallyl isocyanurate (TAIC), and 0.6-0.8% zinc stearate.

2. The pet food refrigerated packaging bag according to claim 1, characterized in that, The targeted modified silver nanoparticles-montmorillonite have a silver particle size of 5-10 nm and a silver loading of 1.2-1.5 wt%. The surface is grafted with galactose and polylysine, with a grafting rate ≥85%. The pretreatment culture medium is X-VIVO15 medium containing 500-1000 U / mL IL-2 and 50-100 ng / mL IL-15.

3. The pet food refrigerated packaging bag according to claim 1, characterized in that, In the multi-molecular-weight polyethylene glycol-acrylic acid copolymer compound, the mass ratio of polyethylene glycol-acrylic acid copolymers with molecular weights of 3000, 5000, and 8000 is 2:1:

1.

4. The pet food refrigerated packaging bag according to claim 1, characterized in that, The amino-modified nano-silica has a particle size of 20 nm, an amino content of 2.0 mmol / g, and is used after being sterilized by filtration through a 0.22 μm filter membrane.

5. The pet food refrigerated packaging bag according to claim 1, characterized in that, The polycaprolactone has a molecular weight of 80,000 and does not become brittle at -18°C; the polypropylene has a melt flow rate of 3 g / 10 min (test conditions: 190°C / 2.16 kg); the linear low-density polyethylene has a melting point of 120-125°C and a density of 0.918 g / cm³.

6. The pet food refrigerated packaging bag according to claim 1, characterized in that, The targeted modified nano-silver-montmorillonite of the outer and inner layers of the antibacterial layer were prepared by "ultrasonic dispersion + 80℃ stirring grafting", with an ultrasonic power of 300W, a stirring time of 2 hours, and a vacuum drying temperature of 80℃ and a vacuum degree of -0.09MPa. During the culture process, half of the medium should be changed every 3 days, and fresh inducing factor combination should be added to maintain the concentration of inducing factor at 80%-120% of the initial concentration.

7. The pet food refrigerated packaging bag according to claim 1, characterized in that, In the anti-fog adsorption layer, hydroxypropyl β-cyclodextrin is food grade with a purity ≥98%; zinc stearate is food grade with a purity ≥99%, and zinc stearate is premixed with the multi-molecular-weight polyethylene glycol-acrylic acid copolymer compound for 5 minutes before being mixed with other components.

8. A method for preparing a pet food refrigerated packaging bag with synergistic gas adsorption-antibacterial-anti-fogging functions as described in any one of claims 2-7, characterized in that, Includes the following steps: (1) Preparation of composite layer formulation: Targeted modified nano-silver-montmorillonite was prepared, and the raw materials of the substrate layer, the outer antibacterial layer, the inner antibacterial layer and the anti-fog adsorption layer were mixed respectively to obtain the mixture of each layer; (2) Staged molding: The mixture of each layer is fed through a three-layer co-extrusion blown film machine in a gradient manner, and the film bubble is formed by inflating the die head. The film bubble is then cross-linked through the ultraviolet curing channel and shaped by the low temperature setting roller. (3) Finished product cutting and testing: After the composite film is cut and shaped according to specifications, its anti-fogging, antibacterial, adsorption, structural stability and safety are tested. Once qualified, it is a finished product.

9. The preparation method according to claim 8, characterized in that, In step (2), the wavelength of the UV curing channel is 254nm, the power is 100W, the distance between the film surface and the UV lamp is 5cm, and the irradiation time is 15-18 seconds to ensure that the interlayer crosslinking degree is ≥85%; the temperature of the die head of the three-layer co-extrusion blown film machine is controlled in zones: 250℃ for the substrate layer area, 190℃ for the antibacterial layer area, and 183℃ for the anti-fog adsorption layer area, with a temperature error of ≤±2℃ for each zone.

10. The preparation method according to claim 8, characterized in that, In step (2), the temperature of the low-temperature shaping roller is -5℃ to -4℃, and the time for the film to be bonded to the shaping roller is 5-6 seconds; in step (3), the qualified standards for the test are: light transmittance ≥88% after refrigeration at 4℃ for 150h, antibacterial rate against Escherichia coli, Salmonella, and Staphylococcus aureus ≥99.9%, ammonia adsorption ≥18mg / g, hydrogen sulfide adsorption ≥13mg / g, acetaldehyde adsorption ≥12mg / g, interlayer peel strength at -18℃ ≥7.5N / 15mm, and nano-silver migration ≤0.005mg / kg.

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