A thinned and lightened PET packaging material and a method for manufacturing the same

Abstract

The application discloses a kind of thinning light weight PET packaging materials and preparation method thereof, it is related to packaging material technical field, the processing method of this application by component composite formula and three-stage gradient stretching, segmented tension heat setting, atmospheric pressure plasma surface treatment, to surface grafting PET's nano SiO2, hydroxylated cellulose nanocrystals and composite modified talc powder are used as synergistic reinforcing system, introduce excellent compatibility PTT resin to solve the problem of nano filler agglomeration;Combined with gradient stretching, form uniform molecular orientation structure, sectional heat setting releases internal stress and improves dimensional stability, plasma microetching improves surface performance.Break through the problem of traditional PET material thinning, performance decreases, realize the overall balance of light weight, mechanical property, optical property and processing performance, can be widely used in high-end beverage, food and other packaging fields.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, specifically to a thinner and lighter PET packaging material and its preparation method. Background Technology

[0002] PET packaging material is a type of polymer packaging material with polyethylene terephthalate (PET) as the main component. It belongs to the most important type of thermoplastic polyester and is commonly known as polyester resin. PET packaging material has the characteristics of being lightweight, highly transparent, strong, and airtight. It is the most important type of thermoplastic polyester and is widely used in beverage bottles, food packaging and other fields. Polyethylene terephthalate is a milky white or light yellow, highly crystalline polymer with a smooth and glossy surface. Its physical form is usually solid, including granules, flakes or films.

[0003] In existing technologies, lightweighting of PET packaging materials is achieved by optimizing the stretching process. However, this process can easily reduce the material's impact strength and drop resistance, making it prone to breakage. To address this, existing technologies add traditional reinforcing agents such as glass fiber, which can significantly improve the material's strength but affect its transparency. Adding traditional nanofillers such as nano-calcium carbonate and nano-montmorillonite can easily cause agglomeration in the PET matrix, resulting in limited reinforcement and decreased toughness. Therefore, these technologies often only improve a single property of the material and cannot simultaneously achieve lightweighting, strength, toughness, and transparency. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a thinner and lighter PET packaging material and its preparation method, thus solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a thinner and lighter PET packaging material, the method comprising the following steps: S1. Dry PET resin and PTT resin at 120~130℃ for 6~8 hours until the moisture content is less than 50ppm. Then, mix the dried PET resin and PTT resin with nano SiO2-g-PET, cellulose nanocrystals, modified talc, antioxidant and lubricant evenly, add them to a twin-screw extruder for melt blending, and extrude and granulate to obtain masterbatch. S2. The masterbatch is dried at 120-130℃ for 4-6 hours, added to a single screw extruder for melt extrusion, and cooled and cast into a sheet by casting rollers to obtain a sheet with a thickness of 0.8-1.2mm. S3. Heat the cast sheet to 70~80℃ and pre-stretch it on a longitudinal stretching machine with a stretching ratio of 1.2~1.5 times to obtain a stretched film; S4. Heat the pre-stretched film to 90-105℃, first perform a second longitudinal stretching on a longitudinal stretching machine with a stretching ratio of 2.5-3.0 times, then put it into a transverse stretching machine and perform transverse stretching at 100-110℃ with a stretching ratio of 3.0-3.5 times to obtain a biaxially stretched film. S5. The biaxially stretched film is subjected to the first stage of heat setting at 180-200℃ for 5-10 seconds. After the first stage of heat setting, the film is subjected to the second stage of heat setting at 150-170℃ for 10-15 seconds to obtain the heat-set film. S6. The heat-set film is sent into an atmospheric pressure plasma treatment device. Argon and oxygen mixed gas is used as the working gas to perform surface micro-etching on both sides of the heat-set film. After treatment, it is cooled to room temperature to obtain a packaging material sheet with a thickness of 10-23μm. The packaging material sheet is then trimmed and rolled up to obtain the finished product of thinned and lightweight PET packaging material.

[0006] Preferably, in step S1, the temperature of the twin-screw extruder is set as follows: Zone 1 240~250℃, Zone 2 250~260℃, Zone 3 260~270℃, Zone 4 260~270℃, Zone 5 255~265℃, Die head 250~260℃, and screw speed 200~300rpm.

[0007] Preferably, in step S2, the temperature of the single-screw extruder is set as follows: Zone 1 245~255℃, Zone 2 255~265℃, Zone 3 260~270℃, Zone 4 260~270℃, Die head 255~265℃, and screw speed is 80~120rpm.

[0008] Preferably, in step S3, the stretching rate of the pre-stretch is 50~100mm / s; in step S4, the stretching rate of the second longitudinal stretch is 150~200mm / s, and the stretching rate of the transverse stretch is 200~250mm / s.

[0009] Preferably, in step S5, the tension of the first heat setting stage is 10~15 N / m, and the tension of the second heat setting stage is 5~8 N / m.

[0010] Preferably, in step S6, the plasma treatment power is 200~400W, the treatment speed is 5~15m / min, the argon flow rate is 10~20L / min, the oxygen flow rate is 1~3L / min, and the distance between the electrode and the heat-setting film is 2~5mm.

[0011] Preferably, the PET packaging material comprises the following raw materials by weight: 88-94 parts PET resin, 2-5 parts PTT resin, 1.2-3.5 parts nano SiO2-g-PET, 0.3-1.5 parts cellulose nanocrystals, 0.4-1.8 parts modified talc, 0.1-0.3 parts antioxidant, and 0.1-0.2 parts lubricant; The grafting rate of the nano-SiO2-g-PET is 15%~25%, and the average particle size of the nano-SiO2 is 15~30nm. The cellulose nanocrystals are subjected to hydroxylation treatment. The diameter of the cellulose nanocrystals is 5~20nm, the length is 100~500nm, and the surface hydroxyl content is 3~5mmol / g. The modified talc powder is prepared by surface treatment with a composite of silane coupling agent KH550 and stearic acid, and the average particle size of the modified talc powder is 1~3μm.

[0012] The PET resin has a viscosity of 0.75~0.85 dL / g and a melting point of 250~260℃; The PTT resin has a viscosity of 0.9-1.1 dL / g and a melting point of 225-235℃.

[0013] The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is calcium stearate or zinc stearate.

[0014] Beneficial effects Compared to existing technologies, this invention provides a method for preparing thinner and lighter PET packaging materials. Relying on a specific composite formulation, gradient stretching, segmented heat setting process, and plasma surface treatment integrated technology, each step achieves a synergistic effect, effectively solving the pain points of traditional PET material thinning processes, such as declining mechanical properties, deteriorating optical properties, and insufficient processing stability. The overall performance is comprehensively improved, demonstrating significant technical advantages. Specific effects are as follows: (1) Synergistic improvement of mechanical properties and lightweighting and thinning This invention employs surface-grafted SiO2-g-PET (grafting rate 15%~25%, average particle size 15~30nm), hydroxylated cellulose nanocrystals (surface hydroxyl content 3~5mmol / g, diameter 5~20nm, length 100~500nm), and KH550 / stearic acid composite modified talc (average particle size 1~3μm) as composite reinforcing components, and introduces PTT resin (2~5 parts) with good compatibility with PET. Through the synergistic effect of multiple scales and components, each reinforcing component is uniformly dispersed in the PET matrix, effectively avoiding the problem of easy agglomeration of traditional nanofillers. At the same time, combined with a specific three-stage gradient stretching process and segmented heat setting, the final PET packaging material can be as thin as 10~23μm. Under the premise of achieving significant thinning and lightweighting, the tensile strength, impact strength, and drop resistance of the material are significantly improved, breaking through the technical bottleneck of the sharp decline in mechanical properties of traditional PET materials during the thinning process.

[0015] (2) Retain excellent optical performance and adapt to the visual requirements of high-end packaging. This invention significantly improves the interfacial compatibility between the reinforcing components and the PET matrix through targeted surface modification of nano-SiO2, cellulose nanocrystals, and talc, effectively reducing light scattering at the interface. Simultaneously, the introduced PTT resin has a similar chemical structure and refractive index to PET, and their blending does not produce significant phase separation. Therefore, while reinforcing and toughening the PET material, it can maintain the material's original high transparency and low haze to the greatest extent, avoiding the problem of decreased transparency caused by traditional reinforcing agents such as glass fiber. Combined with biaxial stretching and plasma micro-etching, surface defects are further eliminated, allowing the material to maintain excellent optical properties even in a thinned state, fully meeting the visual effects and display performance requirements of high-end packaging.

[0016] (3) Comprehensive optimization of gradient orientation structure and processing performance This invention employs a three-stage gradient stretching process: low-temperature pre-stretching (70-80℃, 1.2-1.5 times the original strength), high-temperature second longitudinal stretching (90-105℃, 2.5-3.0 times the original strength), and transverse stretching (100-110℃, 3.0-3.5 times the original strength). It also utilizes segmented tension heat setting: a first stage of high-temperature heat setting (180-200℃, 5-10s, tension 10-15 N / m) followed by a second stage of low-temperature heat setting (150-170℃, 10-15s, tension 5-8 N / m). This specific combination of process parameters enables the PET molecular chains to form a uniform gradient orientation and crystalline structure, avoiding problems such as uneven thickness and wrinkling that are common in traditional stretching processes, significantly improving the film's flatness and dimensional stability. Furthermore, the use of atmospheric pressure plasma for micro-etching on both sides of the film further improves the material's printing adhesion and heat-sealing performance. Ultimately, this achieved a comprehensive improvement in the material's lightweight, mechanical, optical, and processing properties, meeting the stringent requirements of the high-end packaging market for the material's overall performance.

[0017] (4) The overall technical system achieved unexpected synergistic effects. This invention integrates a seven-component composite system with a specific three-stage stretching, segmented heat setting, and plasma treatment process into a unified technical solution, producing effects far exceeding those of single components or simple superposition of conventional processes. In particular, it maintains or even improves mechanical and optical properties while reducing the thickness of PET packaging materials to 10-23 μm, something unpredictable by those skilled in the art based on existing technology. Comparative experimental data shows that using the technical solution of this invention, the material's strength is increased by more than 37.5%, transparency decreases only slightly by 3.4%, and haze increases by only 0.9%, while conventional formulations or processes cannot achieve these indicators at the same thickness. Attached Figure Description

[0018] Figure 1 This is a flowchart illustrating the steps of the PET packaging material preparation method of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Please see Figure 1This invention provides a thinner and lighter PET packaging material and its preparation method. To achieve the above objectives, this invention is implemented through the following technical solution: the raw materials include the following by weight: 94 parts PET resin, 5 parts PTT resin, 3.5 parts SiO2-g-PET (nano SiO2 grafted PET oligomer), 1.5 parts cellulose nanocrystals, 1.8 parts modified talc, 0.3 parts antioxidant, and 0.2 parts lubricant.

[0021] The grafting rate of SiO2-g-PET is 25%, and the average particle size of nano-SiO2 is 30nm; Cellulose nanocrystals were hydroxylated, with a diameter of 20 nm, a length of 500 nm, and a surface hydroxyl content of 5 mmol / g. Modified talc powder was prepared by surface treatment with silane coupling agent KH550 and stearic acid, with an average particle size of 3μm. The viscosity of PET resin is 0.85 dL / g, and its melting point is 260℃. The viscosity of PTT resin is 1.1 dL / g, and the melting point is 235℃. The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is calcium stearate.

[0022] The preparation method includes the following steps: PET resin and PTT resin were dried at 125℃ for 7 hours until the moisture content was less than 50ppm. The dried PET resin and PTT resin were then mixed evenly with SiO2-g-PET, cellulose nanocrystals, modified talc, antioxidant and lubricant. The mixture was then added to a twin-screw extruder for melt blending and extrusion granulation to obtain masterbatch. The temperature settings of the twin-screw extruder were: Zone 1 250℃, Zone 2 260℃, Zone 3 270℃, Zone 4 270℃, Zone 5 265℃, Die head 260℃, and screw speed 300rpm. The masterbatch was dried at 125℃ for 5 hours. After drying, it was added to a single-screw extruder for melt extrusion. The temperature settings of the single-screw extruder were: Zone 1 255℃, Zone 2 265℃, Zone 3 270℃, Zone 4 270℃, Die head 265℃, and screw speed 120 rpm. The casting was cooled and cast by casting rollers to obtain a casting sheet with a thickness of 1.2 mm. The casting sheet was then heated to 80℃ and pre-stretched on a longitudinal stretching machine with a stretching ratio of 1.5 times and a stretching rate of 100 mm / s to obtain a stretched film. The pre-stretched film is heated to 105°C and first subjected to a second longitudinal stretching on a longitudinal stretching machine with a stretching ratio of 3.0 times and a stretching rate of 200 mm / s. Then it is fed into a transverse stretching machine and subjected to transverse stretching at 110°C with a stretching ratio of 3.5 times and a stretching rate of 250 mm / s to obtain a biaxially stretched film. The biaxially stretched biaxial film was subjected to the first stage of heat setting at 200℃ for 10 seconds with a tension of 15 N / m. After the first stage of heat setting, the film was subjected to the second stage of heat setting at 170℃ for 15 seconds with a tension of 8 N / m to obtain the heat-set film. The heat-set film is fed into an atmospheric pressure plasma treatment device. An argon and oxygen mixture is used as the working gas to perform surface micro-etching on both sides of the heat-set film. The plasma treatment power is 400W, the treatment speed is 15m / min, the argon flow rate is 20L / min, the oxygen flow rate is 3L / min, and the distance between the electrode and the heat-set film is 5mm. After treatment, the film is cooled to room temperature to obtain a packaging material sheet. The packaging material sheet is then trimmed and wound to obtain the finished thinned and lightweight PET packaging material.

[0023] Example 2 The raw materials include the following by weight: 91 parts PET resin, 3.5 parts PTT resin, 2.35 parts nano SiO2-g-PET, 0.9 parts cellulose nanocrystals, 1.1 parts modified talc, 0.2 parts antioxidant, and 0.15 parts lubricant. The grafting rate of nano-SiO2-g-PET is 20%, and the average particle size of nano-SiO2 is 22.5 nm; Cellulose nanocrystals were hydroxylated, with a diameter of 12.5 nm, a length of 300 nm, and a surface hydroxyl content of 4 mmol / g. Modified talc powder was prepared by surface treatment with silane coupling agent KH550 and stearic acid. The average particle size of the modified talc powder was 2μm. The viscosity of PET resin is 0.80 dL / g, and its melting point is 255℃. The viscosity of PTT resin is 1.0 dL / g, and the melting point is 230℃. The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is calcium stearate.

[0024] The preparation method includes the following steps: PET resin and PTT resin were dried at 125℃ for 7 hours until the moisture content was less than 50ppm. The dried PET resin and PTT resin were then mixed evenly with SiO2-g-PET, cellulose nanocrystals, modified talc, antioxidant and lubricant. The mixture was then added to a twin-screw extruder for melt blending and extrusion granulation to obtain masterbatch. The temperature settings of the twin-screw extruder were: Zone 1 245℃, Zone 2 255℃, Zone 3 265℃, Zone 4 265℃, Zone 5 260℃, Die head 255℃, and screw speed 250rpm. The masterbatch was dried at 125℃ for 5 hours. After drying, it was added to a single-screw extruder for melt extrusion. The temperature of the single-screw extruder was set as follows: Zone 1 250℃, Zone 2 260℃, Zone 3 265℃, Zone 4 265℃, Die head 260℃, and screw speed 100 rpm. The casting was cooled and cast by casting rollers to obtain a casting sheet with a thickness of 1.0 mm. The casting sheet was then heated to 75℃ and pre-stretched on a longitudinal stretching machine with a stretching ratio of 1.35 times and a stretching rate of 75 mm / s to obtain a stretched film. The pre-stretched film is heated to 97.5℃ and then subjected to a second longitudinal stretching on a longitudinal stretching machine with a stretching ratio of 2.75 times and a stretching rate of 175 mm / s. It is then fed into a transverse stretching machine and subjected to transverse stretching at 105℃ with a stretching ratio of 3.25 times and a stretching rate of 225 mm / s to obtain a biaxially stretched film. The biaxially stretched biaxial film was subjected to the first stage of heat setting at 190°C for 7.5 seconds with a tension of 12.5 N / m. After the first stage of heat setting, the film was subjected to the second stage of heat setting at 160°C for 12.5 seconds with a tension of 6.5 N / m to obtain the heat-set film. The heat-set film is sent to an atmospheric pressure plasma treatment device. A mixture of argon and oxygen is used as the working gas to perform surface micro-etching on both sides of the heat-set film. The plasma treatment power is 300W, the treatment speed is 10m / min, the argon flow rate is 15L / min, the oxygen flow rate is 2L / min, and the distance between the electrode and the heat-set film is 3.5mm. After treatment, the film is cooled to room temperature to obtain a packaging material sheet. The packaging material sheet is then trimmed and wound to obtain the finished thinned and lightweight PET packaging material.

[0025] Example 3 A thinner and lighter PET packaging material comprises the following raw materials by weight: 88 parts PET resin, 2 parts PTT resin, 1.2 parts SiO2-g-PET, 0.3 parts cellulose nanocrystals, 0.4 parts modified talc, 0.1 parts antioxidant, and 0.1 parts lubricant.

[0026] The grafting rate of SiO2-g-PET is 15%, and the average particle size of nano-SiO2 is 15nm. Cellulose nanocrystals, after hydroxylation treatment, have a diameter of 5 nm, a length of 100 nm, and a surface hydroxyl content of 3 mmol / g; Modified talc powder was prepared by surface treatment with silane coupling agent KH550 and stearic acid. The average particle size of the modified talc powder was 1 μm. The viscosity of PET resin is 0.75 dL / g, and its melting point is 250℃. The viscosity of PTT resin is 0.9 dL / g, and the melting point is 225℃. The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is calcium stearate.

[0027] The preparation method includes the following steps: PET resin and PTT resin were dried at 125℃ for 7 hours until the moisture content was less than 50ppm. The dried PET resin and PTT resin were then mixed evenly with nano-SiO2-g-PET, cellulose nanocrystals, modified talc, antioxidants and lubricants. The mixture was then added to a twin-screw extruder for melt blending and extrusion granulation to obtain masterbatch. The temperature settings of the twin-screw extruder were: Zone 1 240℃, Zone 2 250℃, Zone 3 260℃, Zone 4 260℃, Zone 5 255℃, Die head 250℃, and screw speed 200rpm. The masterbatch was dried at 125℃ for 5 hours. After drying, it was added to a single-screw extruder for melt extrusion. The temperature settings of the single-screw extruder were: Zone 1 245℃, Zone 2 255℃, Zone 3 260℃, Zone 4 260℃, Die head 255℃, and screw speed 80 rpm. The casting was cooled by casting rollers to obtain a casting sheet with a thickness of 0.8 mm. The casting sheet was then heated to 70℃ and pre-stretched on a longitudinal stretching machine with a stretching ratio of 1.2 times and a stretching rate of 50 mm / s to obtain a stretched film. The pre-stretched film is heated to 90°C and first subjected to a second longitudinal stretching on a longitudinal stretching machine with a stretching ratio of 2.5 times and a stretching rate of 150 mm / s. Then it is fed into a transverse stretching machine and subjected to transverse stretching at 100°C with a stretching ratio of 3.0 times and a stretching rate of 200 mm / s to obtain a biaxially stretched film. The biaxially stretched biaxial film was subjected to the first stage of heat setting at 180°C for 5 seconds with a tension of 10 N / m. After the first stage of heat setting, the film was subjected to the second stage of heat setting at 150°C for 10 seconds with a tension of 5 N / m to obtain the heat-set film. The heat-set film is fed into an atmospheric pressure plasma treatment device. An argon and oxygen mixture is used as the working gas to perform surface micro-etching on both sides of the heat-set film. The plasma treatment power is 200W, the treatment speed is 5m / min, the argon flow rate is 10L / min, the oxygen flow rate is 1L / min, and the distance between the electrode and the heat-set film is 2.5mm. After treatment, the film is cooled to room temperature to obtain a packaging material sheet. The packaging material sheet is then trimmed and wound to obtain the finished thinned and lightweight PET packaging material.

[0028] Comparative Example 1 Ordinary PET packaging material, 25μm thick, is prepared using the traditional biaxial stretching process, and the raw material is pure PET resin (viscosity 0.80dL / g, melting point 255℃).

[0029] Comparative Example 2 PET packaging material, 25μm thick, made of 97 parts PET resin, 3 parts conventional nano SiO2, 0.2 parts antioxidant, and 0.3 parts lubricant; The same preparation process as in Example 1 was used, but without the addition of PTT resin, cellulose nanocrystals and modified talc, and without plasma treatment.

[0030] Comparative Example 3 PET packaging material, 25μm thick, made of 97 parts PET resin, 3 parts glass fiber, 0.2 parts antioxidant, and 0.3 parts lubricant; The same preparation process as in Example 1 was used, but PTT resin, nano-SiO2-g-PET, cellulose nanocrystals and modified talc were not added, and plasma treatment was not performed.

[0031] Comparative Example 4 PET packaging material, 16μm thick, made of 95 parts PET resin, 2.8 parts SiO2-g-PET, 1.7 parts modified talc, 0.2 parts antioxidant, and 0.3 parts lubricant; The same preparation process as in Example 1 was used, but without the addition of PTT resin and cellulose nanocrystals, and without plasma treatment.

[0032] Comparative Example 5 The PET packaging material is 16μm thick and uses the same raw materials as in Example 1. The same preparation process as in Example 1 was used, but the plasma treatment in step S5 was not performed.

[0033] Comparative Example 6 The difference from Example 1 is that nano-SiO2-g-PET is replaced with ungrafted nano-SiO2 (average particle size 20nm), while the other raw materials and process parameters remain unchanged.

[0034] Comparative Example 7 The difference from Example 1 is that a conventional biaxial stretching process is used: the cast sheet is directly heated to 98°C, stretched longitudinally to 3.64 times (1.3×2.8) at a stretching rate of 180 mm / s, and then stretched transversely to 3.2 times at 105°C at a stretching rate of 220 mm / s, while the other raw materials and parameters remain unchanged.

[0035] Comparative Example 8 The difference from Example 1 is that a single-stage heat setting is used: heat setting is only carried out at 190°C for 20 seconds with a tension of 12 N / m, without a second stage of low-temperature heat setting, while the other raw materials and parameters remain unchanged.

[0036] Comparative Example 9 The difference from Example 1 is that it adopts a traditional preparation process: no pre-stretching, one-time longitudinal stretching, single-stage heat setting, and no plasma treatment; Specific process: The cast sheet is heated to 98℃, stretched longitudinally by 3.64 times and transversely by 3.2 times; it is then heat-set at 190℃ for 20 seconds in a single stage; no plasma treatment is performed to obtain a finished product with a thickness of 16μm, while the other raw materials remain unchanged.

[0037] Test case Test content Thickness: Tested using a thin film thickness gauge according to GB / T6672-2001 standard; Weight: Tested using an electronic balance according to GB / T451.2-2002 standard; Visible light transmittance and haze: tested using a haze meter according to GB / T2410-2008 standard; Table 1 Test data of PET packaging material thickness, basis weight and optical properties ; Tensile strength: The tensile strength was tested using a universal testing machine according to the standard GB / T1040.3-2006, and the longitudinal and transverse tensile strengths were tested separately. Impact resistance: Tested using a pendulum impact testing machine according to GB / T8809-2015 standard; Table 2 Test data of tensile and impact strength properties of PET packaging materials ; Heat seal strength: Tested according to QB / T2358-1998 standard using a heat sealer and universal testing machine. The heat seal temperature is 150℃, the heat seal pressure is 0.2MPa, and the heat seal time is 1s. Print adhesion: Tested using the cross-cut test according to GB / T9286-1998 standard, with grade 0 being the best and grade 5 being the worst; Drop resistance: 500ml of water was placed in a bag made of this material and dropped freely from a height of 1.5m onto a cement ground. The number of drops before the bag broke was recorded. Folding endurance: Fold the film 180°, then unfold it, repeat this process, and record the number of folds before the film breaks; Wrinkle resistance: After folding the film in half, press it with a 1kg weight for 1 hour, and then observe the wrinkles after unfolding. It is divided into 1-5 levels, with level 5 being no obvious wrinkles.

[0038] Table 3 Test data for other properties of PET packaging materials ; As can be seen from the test data in Tables 1-3, the thinned and lightweight PET packaging materials prepared in Examples 1-3 of this invention have better overall performance than all comparative examples, provided that the thickness is reduced by 9.0% to 60.2% and the basis weight is reduced by 8.9% to 59.9% compared with traditional products. This invention is not a simple optimization of a single component or a single process, but rather an integrated technical solution that achieves deep synergistic effects across all stages through component composite formulation, three-stage gradient stretching, segmented tension heat setting, and atmospheric pressure plasma surface treatment. A detailed analysis follows: Comparative Example 9 used the exact same optimized formula as Example 1, but removed all innovative processes (no pre-stretching, single longitudinal stretching, single-stage heat setting, and no plasma treatment). Its longitudinal tensile strength was only 119.6 MPa, a decrease of 13.5% compared to Example 1; its transverse tensile strength was 112.1 MPa, a decrease of 19.8%; and its impact strength was 5.4 kJ / m. 2 The drop resistance decreased by 37.9%, the drop resistance was only 90 times, a decrease of 51.4%, and the wrinkle resistance dropped to level 3; This indicates that even with the performance formulation of this invention, without a matching molding and processing technology, it is impossible to achieve the improvement in mechanical and processing properties after thinning.

[0039] Comparative Example 2 uses the complete process of the present invention, but uses a conventional formula (only adding ungrafted nano-SiO2). Its longitudinal tensile strength is only 116.3 MPa, which is 15.8% lower than that of Example 1. The haze is as high as 4.3%, which is 1.5 times that of Example 1. Moreover, it cannot achieve stable thinning. When thinning to the same thickness, it is easy to break the film. This proves that the composite formula of the present invention is the basis for achieving high-ratio stretching and thinning. Conventional formulas cannot withstand the high-strength stretching process of the present invention. Through single-variable control experiments, the irreplaceability of each technical feature of this invention was verified one by one: Compared with Comparative Example 1 and Comparative Example 6 (using ungrafted nano-SiO2 instead of SiO2-g-PET), Comparative Example 6 showed a 6.1% decrease in longitudinal tensile strength, a 13.7% decrease in transverse tensile strength, a 46.4% increase in haze, and a 2.1% decrease in visible light transmittance. This demonstrates that grafting modification effectively solves the agglomeration problem of nanofillers, significantly improves the interfacial bonding force between the filler and the PET matrix, and avoids the degradation of optical properties caused by light scattering.

[0040] Compared with Comparative Example 1 and Comparative Example 7 (using a conventional one-stretch process), the impact strength of Comparative Example 7 decreased by 23.0%, the flexural endurance decreased by 25.8%, and the wrinkle resistance decreased to level 3. This demonstrates that the gradient process of low-temperature pre-stretching, high-temperature secondary longitudinal stretching, and transverse stretching enables the PET molecular chains to form a uniform gradient orientation structure, avoiding local stress concentration and significantly improving the toughness and processing smoothness of the material. Compared with Comparative Example 1, Comparative Example 8 (which uses single-stage heat setting) showed a 21.2% decrease in folding endurance and a wrinkle resistance of only level 2, making it prone to shrinkage and deformation after long-term use. This demonstrates that the segmented heat setting process, which combines high-temperature shaping to fix orientation and low-temperature relaxation to release internal stress, effectively balances the crystallinity and internal stress of the material, significantly improving dimensional stability and fatigue resistance. Compared with Example 1, Comparative Example 5 (without plasma treatment), the heat seal strength of Comparative Example 5 decreased by 39.2%, and the printing adhesion dropped from level 0 to level 3, which could not meet the printing and heat sealing requirements of high-end packaging. This demonstrates that plasma micro-etching introduces a large number of active functional groups onto the thin film surface, significantly improving the surface energy and interfacial bonding properties of the material.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A method for preparing a thinner and lighter PET packaging material, characterized in that, Includes the following steps: S1. Dry PET resin and PTT resin at 120~130℃ for 6~8 hours until the moisture content is less than 50ppm. Then, mix the dried PET resin and PTT resin with nano SiO2-g-PET, cellulose nanocrystals, modified talc, antioxidant and lubricant evenly, add them to a twin-screw extruder for melt blending, and extrude and granulate to obtain masterbatch. S2. The masterbatch is dried at 120-130℃ for 4-6 hours, added to a single screw extruder for melt extrusion, and cooled and cast into a sheet by casting rollers to obtain a sheet with a thickness of 0.8-1.2mm. S3. Heat the cast sheet to 70~80℃ and pre-stretch it on a longitudinal stretching machine with a stretching ratio of 1.2~1.5 times to obtain a stretched film; S4. Heat the pre-stretched film to 90-105℃, first perform a second longitudinal stretching on a longitudinal stretching machine with a stretching ratio of 2.5-3.0 times, then put it into a transverse stretching machine and perform transverse stretching at 100-110℃ with a stretching ratio of 3.0-3.5 times to obtain a biaxially stretched film. S5. The biaxially stretched film is subjected to the first stage of heat setting at 180-200℃ for 5-10 seconds. After the first stage of heat setting, the film is subjected to the second stage of heat setting at 150-170℃ for 10-15 seconds to obtain the heat-set film. S6. The heat-set film is sent into an atmospheric pressure plasma treatment device. Argon and oxygen mixed gas is used as the working gas to perform surface micro-etching on both sides of the heat-set film. After treatment, it is cooled to room temperature to obtain a packaging material sheet with a thickness of 10-23μm. The packaging material sheet is then trimmed and rolled up to obtain the finished product of thinned and lightweight PET packaging material.

2. The method for preparing a thinner and lighter PET packaging material according to claim 1, characterized in that: In step S1, the temperature of the twin-screw extruder is set as follows: Zone 1 240~250℃, Zone 2 250~260℃, Zone 3 260~270℃, Zone 4 260~270℃, Zone 5 255~265℃, Die head 250~260℃, and screw speed 200~300rpm.

3. The method for preparing a thinner and lighter PET packaging material according to claim 1, characterized in that: In step S2, the temperature of the single-screw extruder is set as follows: Zone 1 245~255℃, Zone 2 255~265℃, Zone 3 260~270℃, Zone 4 260~270℃, Die head 255~265℃, and screw speed 80~120rpm.

4. The method for preparing a thinner and lighter PET packaging material according to claim 1, characterized in that: In step S3, the stretching rate of the pre-stretch is 50~100mm / s; In step S4, the stretching rate of the second longitudinal stretching is 150~200mm / s, and the stretching rate of the transverse stretching is 200~250mm / s.

5. The method for preparing a thinner and lighter PET packaging material according to claim 1, characterized in that: In step S5, the tension of the first heat setting stage is 10~15 N / m, and the tension of the second heat setting stage is 5~8 N / m.

6. The method for preparing a thinner and lighter PET packaging material according to claim 1, characterized in that: In step S6, the power of the plasma treatment is 200~400W, the treatment speed is 5~15m / min, the argon flow rate is 10~20L / min, the oxygen flow rate is 1~3L / min, and the distance between the electrode and the heat-setting film is 2~5mm.

7. The method for preparing a thinner and lighter PET packaging material according to claim 1, characterized in that: The PET packaging material comprises the following raw materials by weight: 88-94 parts PET resin, 2-5 parts PTT resin, 1.2-3.5 parts nano SiO2-g-PET, 0.3-1.5 parts cellulose nanocrystals, 0.4-1.8 parts modified talc, 0.1-0.3 parts antioxidant, and 0.1-0.2 parts lubricant. The grafting rate of the nano-SiO2-g-PET is 15%~25%, and the average particle size of the nano-SiO2 is 15~30nm. The cellulose nanocrystals are subjected to hydroxylation treatment. The diameter of the cellulose nanocrystals is 5~20nm, the length is 100~500nm, and the surface hydroxyl content is 3~5mmol / g. The modified talc powder is prepared by surface treatment with a composite of silane coupling agent KH550 and stearic acid, and the average particle size of the modified talc powder is 1~3μm.

8. The viscosity of the PET resin is 0.75~0.85 dL / g, and the melting point is 250~260℃; The PTT resin has a viscosity of 0.9-1.1 dL / g and a melting point of 225-235℃.

9. The antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1; The lubricant is calcium stearate or zinc stearate.

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