Multilayer composite barrier film and production process thereof

Abstract

The invention discloses a multi-layer composite barrier film and a production process thereof, and belongs to the field of polymer composite materials. Aiming at the problems of obvious performance attenuation, poor interlayer binding force and low step-by-step compounding process efficiency of a barrier film in a humid and hot environment in the prior art, the invention provides a five-layer asymmetric structure design: an outer layer, a bonding layer, a barrier layer, a bonding layer and an inner layer. Wherein the barrier layer is formed by blending EVOH and MAH-PA6 and cooperating with nano montmorillonite to form a multi-barrier network, so that the oxygen permeability is smaller than or equal to 0.3 cm / (m.24h. 0.1 MPa), and the water vapor permeability is smaller than or equal to 1.5 g / (m.24h). The production process innovation comprises five-layer co-extrusion melt flow rate ratio control, three-roller gradient cooling and a bidirectional plasma processing technology, the continuous production speed is larger than or equal to 120 m / min, and the interlayer peeling strength is larger than or equal to 8 N / 15 mm. The barrier property stability is remarkably improved.

Description

Technical Field

[0001] The present invention relates to the field of composite barrier films, and specifically to a multi-layer composite barrier film and its production process. Background Art

[0002] A multi-layer composite barrier film is a high-performance packaging material prepared by a multi-layer material composite technology, aiming to achieve efficient barrier against external factors such as oxygen, water vapor, and light through the synergistic effect of different functional layers, while taking into account mechanical strength, heat sealability, and processing adaptability.

[0003] Existing composite barrier films mostly adopt a single barrier layer (such as EVOH or aluminum foil) design, and there are the following problems: Insufficient barrier performance: It is difficult for a single material to balance the barrier requirements for oxygen and water vapor, and the performance drops significantly especially in high-temperature and high-humidity environments; Poor interfacial bonding strength: The traditional adhesive layer and the barrier layer have poor compatibility and are prone to delamination, affecting long-term stability; Complex production process: Mostly adopt a step-by-step composite process, with high energy consumption and low efficiency, and it is difficult to achieve continuous production.

[0004] Therefore, a multi-layer composite barrier film and its production process are proposed to solve the above problems. Summary of the Invention

[0005] In order to make up for the deficiencies of the prior art, namely the problems of insufficient barrier performance, poor interfacial bonding strength, and complex production process, the present invention proposes a multi-layer composite barrier film and its production process.

[0006] The technical solution adopted by the present invention to solve its technical problems is: A multi-layer composite barrier film, which sequentially includes from outside to inside: an outer layer, a first adhesive layer, a barrier layer, a second adhesive layer, and an inner layer, with a total thickness of 80 - 250 μm, wherein the barrier layer contains a blend of ethylene-vinyl alcohol copolymer (EVOH) and maleic anhydride grafted PA6.

[0007] Preferably, the outer layer is composed of linear low-density polyethylene (LLDPE), polypropylene (PP), and an anti-blocking agent in a mass ratio of 65 - 85:10 - 25:0.5 - 3, and the isotacticity of PP ≥ 95%.

[0008] Preferably, the barrier layer is composed of ethylene-vinyl alcohol copolymer (EVOH), modified polyamide (PA6), and nano-montmorillonite in a mass ratio of 45 - 70:25 - 40:3 - 8, the aspect ratio of montmorillonite > 800, and the ethylene content of EVOH in the barrier layer is 32 - 38 mol%.

[0009] Preferably, the modified polyamide is maleic anhydride grafted polyamide with a grafting rate of 0.8% - 1.5% and a melt index of 12 g / 10 min (230 °C / 2.16 kg).

[0010] Preferably, the first adhesive layer and the second adhesive layer are blends of ethylene - vinyl acetate copolymer (EVA) and polyolefin elastomer (POE) with a mass ratio of EVA:POE = 6:4, where the VA content of EVA is 25 - 33%.

[0011] Preferably, the inner layer is composed of metallocene polyethylene (mPE), antistatic agent, and slip agent in a mass ratio of 85 - 95:2 - 5:0.5 - 1.5.

[0012] The production process of the composite barrier film includes the following steps: Raw material pretreatment: Each layer of raw materials is dried at 80 - 120 °C until the water content < 200 ppm.

[0013] Five - layer co - extrusion molding: Five single - screw extruders are used for synchronous extrusion. The barrel temperature is set as follows: the outer layer is 180 - 200 °C, the adhesive layer is 170 - 185 °C, the barrier layer is 210 - 230 °C, and the inner layer is 175 - 190 °C.

[0014] Die - head compounding: A spiral distributor die - head is used with a die - lip gap of 0.8 - 1.2 mm and a compounding pressure of 8 - 12 MPa.

[0015] Cooling and shaping: Rapid cooling is carried out through double - sided water - cooled rollers. The water temperature is controlled at 15 - 25 °C, and the cooling rate ≥ 30 °C / s.

[0016] Corona treatment: The inner and outer surfaces are subjected to corona treatment with a dyn value of 48 - 52 dyn / cm.

[0017] Rewinding and slitting: The tension is controlled at 15 - 25 N, and the slitting accuracy is ±0.1 mm.

[0018] Preferably, in the five - layer co - extrusion molding, the barrier - layer extruder uses a barrier screw with a length - to - diameter ratio L / D = 32:1 and a compression ratio of 3.0:1. The melt flow rate ratio of the barrier layer to the other layers in the five - layer co - extrusion molding is controlled at 1:0.8 - 1.2, and an infrared temperature - measuring device is set at the die - head outlet to continuously adjust the temperature difference within ±3 °C.

[0019] Preferably, in the cooling and shaping process, a three - roll shaping device is used. The temperature gradient of the roll surface is as follows: the first roll is 50 - 60 °C, the second roll is 35 - 45 °C, and the third roll is 20 - 30 °C. The linear speed difference of the three rolls is set as the first roll: the second roll: the third roll = 1:1.05:1.12, and an ultrasonic atomization device is configured to make the water content on the film surface ≤ 0.1%.

[0020] Preferably, the corona treatment adopts bidirectional plasma treatment, and the surface tension reaches 50-52 dyn / cm.

[0021] The beneficial effects of the present invention are as follows: 1. Through the five-layer asymmetric structure design, the present invention realizes the dual barrier functions of oxygen and water vapor, solves the problem that the performance of traditional single-layer barrier films decays by more than 50% in humid and hot environments, and improves the stability of packaging materials under the conditions of 38°C / 90%RH. 2. Through the design of the EVA / POE dynamic vulcanization adhesive layer (VA content 25-33%, vulcanization degree > 85%), the present invention realizes a lasting bond with an interlayer peel strength > 8 N / 15 mm, solves the defect that the peel strength of traditional adhesive layers decays by more than 60% after aging at 85°C, and improves the structural integrity retention rate of composite films after steam sterilization.

[0022] 3. Through the ternary system of EVOH / MAH-PA6 / nano-montmorillonite (aspect ratio > 800, intercalation rate > 90%), the present invention realizes an ultra-high barrier performance with an oxygen transmission rate reduced to 0.3 cm³ / m²·24 h, solves the technical bottleneck that the oxygen barrier performance of traditional EVOH films drops sharply under high humidity, and improves the performance retention rate of materials in extreme environments.

[0023] 4. Through the control of the melt flow rate ratio (1:0.8-1.2) of five-layer coextrusion and the infrared temperature control system (±3°C), the present invention realizes the online precision forming of 80-250 μm thick films (thickness deviation < ±1.5%), solves the defect of low efficiency of traditional step-by-step composite processes, and improves the continuous production speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a schematic structural diagram of the multi-layer composite barrier film of the present invention; Figure 2 It is a schematic structural diagram of the production process flow chart of the present invention; Figure 3 It is a parameter diagram of five single-screw extruders of the present invention; Figure 4 It is a comparison diagram of the oxygen transmission rate and water vapor transmission rate of the barrier film (with nano-montmorillonite) of the present invention and the traditional EVOH-based barrier film (without nano-montmorillonite).

[0026] In the figure: 1. Outer layer; 2. First adhesive layer; 3. Barrier layer; 4. Second adhesive layer; 5. Inner layer. Specific embodiments

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0028] The following is a further detailed description of the present application in conjunction with the attached Figures 1-4 This application will be further described in detail. Embodiment 1: The embodiment of the present application discloses a multi-layer composite barrier film and its production process, which is applied to the packaging film of medical dialysis instruments.

[0029] Referring to Figures 1 to 3 , a multi-layer composite barrier film, which sequentially includes from outside to inside: an outer layer, a first adhesive layer, a barrier layer, a second adhesive layer and an inner layer, with a total thickness of 80-250 μm, wherein the barrier layer contains a blend of EVOH and maleic anhydride grafted PA6.

[0030] The outer layer is composed of linear low-density polyethylene (LLDPE), polypropylene (PP) and an anti-blocking agent in a mass ratio of 65-85:10-25:0.5-3, and is formed by three-layer co-blending and granulation, wherein the isotacticity of PP ≥ 95%.

[0031] The first adhesive layer and the second adhesive layer are blends of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE), with a mass ratio of EVA:POE = 6:4, and are prepared by dynamic vulcanization with a VA content of 25-33% in EVA.

[0032] The barrier layer is composed of ethylene-vinyl alcohol copolymer (EVOH), modified polyamide (PA6) and nano-montmorillonite in a mass ratio of 45-70:25-40:3-8. The aspect ratio of montmorillonite > 800. The modified polyamide is maleic anhydride grafted polyamide, with a grafting rate of 0.8%-1.5% and a melt index of 12 g / 10 min (230 °C / 2.16 kg). The grafting rate is measured by infrared spectroscopy.

[0033] The preparation of maleic anhydride grafted PA6 includes: After drying PA6 particles in vacuum at 80 °C for 4 hours, mixing them with 1.2 wt% of diisopropylbenzene peroxide initiator and 3 wt% of maleic anhydride monomer, and performing reactive extrusion in a twin-screw extruder. The temperature of the reaction zone is controlled at 235-245 °C, and the residence time is 90 seconds to obtain a modified material with a grafting rate of 1.2% ± 0.15%.

[0034] The aspect ratio of the nano-montmorillonite is measured by a JEOL JEM-2100F field emission transmission electron microscope, and the arithmetic mean of 100 particle measurement values is taken; the oxygen transmission rate is tested according to the standard of GB / T 19789-2005, and the water vapor transmission rate is tested according to GB / T 21529-2008, and the test conditions are 38 °C and 90% RH.

[0035] The first adhesive layer and the second adhesive layer are blends of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE), and the mass ratio of EVA:POE = 6:4, where the VA content of EVA is 25-33%.

[0036] The inner layer consists of metallocene polyethylene (mPE), antistatic agent and slip agent in a mass ratio of 85-95:2-5:0.5-1.5.

[0037] The production process of the composite barrier film includes the following steps: Raw material pretreatment: Each layer of raw materials is dried to a water content of <200 ppm at 80-120 °C. The raw materials of the outer layer (LLDPE / PP / antiblocking agent), the barrier layer (EVOH / modified PA6 / nano-montmorillonite), and the inner layer (mPE / antistatic agent / slip agent) enter a vacuum dryer respectively. The drying temperature: the outer layer is 80-100 °C, the barrier layer is 105-120 °C, and the inner layer is 90-110 °C. Control the water content <200 ppm, and use ultrasonic vibration screening (frequency 40 kHz) to remove agglomerated particles with a particle size >50 μm.

[0038] The nano-montmorillonite in the barrier layer is melt intercalated by a twin-screw extruder (L / D = 52:1), the premixing temperature is 230 °C ± 5 °C, and the residence time is 120-150 seconds. The adhesive layer EVA / POE (6:4) is dynamically vulcanized in a mixer, the vulcanization temperature is 170-180 °C, and the torque control range is 120-150 N·m.

[0039] Five-layer co-extrusion molding: Five single-screw extruders are used for synchronous extrusion. According to the correlation between the thermal decomposition temperature of EVOH and the processing temperature, the temperature gradient is set. The barrel temperature is set as follows: the outer layer is 180-200 °C, the adhesive layer is 170-185 °C, the barrier layer is 210-230 °C, and the inner layer is 175-190 °C. In the five-layer co-extrusion molding, the barrier layer extruder uses a barrier screw, the length-diameter ratio L / D = 32:1, and the compression ratio is 3.0:1. Five single-screw extruders are configured (parameters see Figure 3 )), and the barrier layer extruder uses a barrier screw (compression ratio 3.2:1).

[0040] Die head lamination: A spiral distributor die head is used, the die lip gap is 0.8-1.2 mm, and the lamination pressure is 8-12 MPa.

[0041] Use a spiral distribution die (die lip gap: 1.0 mm ± 0.1 mm), and the runner is designed as follows: Outer layer runner: conical tapering structure (contraction angle: 15°).

[0042] Barrier layer runner: double - helix mixing structure (pitch ratio: 1:1.5).

[0043] Compound pressure: 10 MPa ± 2 MPa, and the melt flow rate difference is controlled within ±5%.

[0044] Cooling and shaping: Rapid cooling is achieved through double - sided water - cooled rollers. The water temperature is controlled at 15 - 25°C, the cooling rate is ≥30°C / s. A three - roller shaping device is used during cooling and shaping. The temperature gradient of the roller surface is: the first roller is 50 - 60°C, the second roller is 35 - 45°C, and the third roller is 20 - 30°C.

[0045] Gradient cooling: The first cooling roller (chrome - plated mirror roller): temperature 55°C ± 2°C, linear speed 25 m / min.

[0046] The second cooling roller (silicone embossing roller): temperature 40°C ± 2°C, pressure 0.15 MPa.

[0047] The third cooling roller (steel smooth roller): temperature 25°C ± 1°C, cooling rate ≥35°C / s.

[0048] The temperature difference on the film surface is controlled within ±1.5°C to prevent uneven crystallinity distribution.

[0049] Use a β - ray thickness gauge (accuracy ±0.1 μm), and collect data every 10 cm.

[0050] The thickness feedback adjustment system automatically adjusts the die lip thermal expansion bolts (adjustment response time < 0.5 s).

[0051] Corona treatment: Perform corona treatment on the inner and outer surfaces with a dyn value of 48 - 52 dyn / cm. The corona treatment uses bidirectional plasma treatment, and the surface tension reaches 50 - 52 dyn / cm.

[0052] Plasma treatment: Double - sided corona treatment: Electrode power 8 kW, treatment speed 30 m / min.

[0053] Surface tension control: The outer layer is 52 dyn / cm ± 1 dyn / cm, and the inner layer is 48 dyn / cm ± 1 dyn / cm.

[0054] Ozone concentration monitoring: < 0.1 ppm (equipped with a UV photolysis purification device).

[0055] Rewinding and slitting: Tension is controlled at 15 - 25 N, and the slitting accuracy is ±0.1 mm.

[0056] Contact type coiler: Initial tension is 18 N, and taper decreasing coefficient is 0.85.

[0057] Rectification accuracy: ±0.2 mm (using CCD vision detection).

[0058] Aging treatment: Keep at a constant temperature of 40 °C in storage for 24 hours to release internal stress.

[0059] As Figure 4 shown, by introducing a synergistic system of maleic anhydride grafted PA6 and nano-montmorillonite, the water vapor transmission rate is reduced to 1.2 - 1.8 g / (m²·24h), and the peel strength is increased to 8 - 12 N / 15 mm.

[0060] Barrier mechanism: EVOH provides molecular-level barrier, nano-montmorillonite lamellae extend the gas permeation path, and modified PA6 enhances interfacial dispersibility.

[0061] Adhesion mechanism: Polar vinyl acetate groups in EVA form hydrogen bonds with the barrier layer, and the POE elastomer relieves thermal stress to avoid cracking.

[0062] Example 2: This application example discloses a multi-layer composite barrier film and its production process, which is applied to the packaging film for medical dialysis instruments.

[0063] Refer to Figures 1 to 3 , a multi-layer composite barrier film, structure: LLDPE(25μm) / EVA-POE(10μm) / EVOH-PA6-MMT(15μm) / EVA-POE(10μm) / mPE(30μm) Production process: Extrusion temperature of the barrier layer is 225 °C, die head pressure is 10 MPa, cooling water temperature is 20 °C, and coiling tension is 20 N Performance indicators: Oxygen transmission rate is 0.3 cm³ / (m²·24h·0.1 MPa), water vapor transmission rate is 1.2 g / (m²·24h), and heat seal strength > 35 N / 15 mm.

[0064] Through the high-rigidity composition of outer layer LLDPE / PP (flexural modulus > 850 MPa) and the flexible design of inner layer mPE (elongation at break > 450%), the material is simultaneously applicable to: rigid medical device tray packaging (remaining unchanged under a static pressure of 50 kg) and vacuum packaging of hose-like devices (not cracking with a bending radius < 3 mm).

[0065] Adopt the two-way plasma treatment technology (Dyne value 50 - 52 dyn / cm) to keep the material stable in the following environments: ethylene oxide sterilization environment (55 °C / RH > 70% for 8 h continuously) and low-temperature storage conditions (peel strength attenuation < 5% after freezing at -40 °C for 6 months).

[0066] Through the barrier screw design (L / D = 32:1, compression ratio 3.0:1) and the closed-loop control of the melt pressure, the stable processing of the following raw materials is ensured: high-viscosity barrier layer materials (melt index 12 g / 10 min), low-density adhesive layer materials (melt index 35 g / 10 min), and complex systems containing nano-fillers (solid content > 8%).

[0067] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A multi-layer composite barrier film, characterized in that, It includes, from outside to inside in sequence: an outer layer (1), a first adhesive layer (2), a barrier layer (3), a second adhesive layer (4) and an inner layer (5), with a total thickness of 80 - 250 μm. The barrier layer contains a blend of EVOH and maleic anhydride grafted PA6.

2. The multi-layer composite barrier film according to claim 1, characterized in that: The outer layer (1) is composed of linear low density polyethylene (LLDPE), polypropylene (PP) and an anti-blocking agent in a mass ratio of 65 - 85:10 - 25:0.5 - 3, where the isotacticity of PP is ≥95%.

3. The multi-layer composite barrier film according to claim 2, wherein: The barrier layer (3) is prepared by melt intercalation of ethylene-vinyl alcohol copolymer (EVOH), maleic anhydride grafted polyamide and organic modified nano-montmorillonite. The ethylene content of EVOH is 32 - 38 mol%, and it satisfies: (EVOH melt index) / (PA6 melt index)=0.8 - 1.

2. The organic modified montmorillonite is modified with cetyltrimethylammonium bromide, and the layer spacing is ≥3.5 nm.

4. The multi-layer composite barrier film according to claim 3, characterized in that: The modified polyamide is maleic anhydride grafted polyamide, with a grafting rate of 0.8% - 1.5% and a melt index of 12 g / 10 min (230 °C / 2.16 kg).

5. A multi-layer composite barrier film according to claim 1, characterized in that: The first adhesive layer (2) and the second adhesive layer (4) are blends of ethylene-vinyl acetate copolymer (EVA) and polyolefin elastomer (POE), with a mass ratio of EVA:POE = 6:4, where the VA content of EVA is 25 - 33%.

6. The multi-layer composite barrier film according to claim 1, wherein: The inner layer (5) is composed of metallocene polyethylene (mPE), an antistatic agent and a slip agent in a mass ratio of 85 - 95:2 - 5:0.5 - 1.

5.

7. A production process applicable to the composite barrier film according to any one of claims 1-6, characterized in that It includes the following steps: Raw material pretreatment: Each layer of raw materials is dried at 80 - 120 °C until the water content is <200 ppm. Five-layer co-extrusion molding: Five single-screw extruders are used for synchronous extrusion. The barrel temperature is set as 180 - 200 °C for the outer layer, 170 - 185 °C for the adhesive layer, 210 - 230 °C for the barrier layer, and 175 - 190 °C for the inner layer. Die head compounding: A spiral distributor die head is used, with a die lip gap of 0.8 - 1.2 mm and a compounding pressure of 8 - 12 MPa. Cooling and shaping: It is rapidly cooled by a double-sided water-cooled roller, with the water temperature controlled at 15 - 25 °C and a cooling rate of ≥30 °C / s. Corona treatment: The inner and outer surfaces are subjected to corona treatment with a dyn / cm value of 48 - 52 dyn / cm. Rewinding and slitting: The tension is controlled at 15 - 25 N, and the slitting accuracy is ±0.1 mm.

8. The production process of the composite barrier film according to claim 7, characterized in that: During the five-layer co-extrusion molding process, the melt pressure of the barrier layer is controlled at 12 - 15 MPa, and the melt pressure of the adhesive layer is 8 - 10 MPa, and it satisfies: barrier layer pressure / adhesive layer pressure = 1.2 - 1.

5. In the five-layer co-extrusion molding, a barrier screw is used for the barrier layer extruder, with a length-diameter ratio L / D = 32:1 and a compression ratio of 3.0:

1. The melt flow rate ratio of the barrier layer to the other layers during the five-layer co-extrusion molding is controlled at 1:0.8 - 1.2, and an infrared temperature measuring device is set at the die head outlet to adjust the temperature difference in real time within ±3 °C.

9. The production process of the composite barrier film according to claim 7, characterized in that: In the cooling and shaping process, a three-roll shaping device is adopted. The temperature gradient of the roll surface is 50 - 60 °C for the first roll, 35 - 45 °C for the second roll, and 20 - 30 °C for the third roll. The linear speed difference of the three rolls is set as the first roll : the second roll : the third roll = 1 : 1.05 : 1.12, and an ultrasonic atomization device is configured to make the water content on the film surface ≤ 0.1%.

10. The production process of the composite barrier film according to claim 7, characterized in that: The corona treatment adopts bidirectional plasma treatment, and the surface tension reaches 50 - 52 dyn / cm.

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