GRS50 recoverable high-transparency film

Abstract

The invention relates to the technical field of high polymer material processing, and discloses a GRS50 recyclable high-transparency film which comprises the following components in parts by weight: high-purity recycled PE particles; native low density polyethylene; a native metallocene polyethylene; a PPA master batch; smooth anti-adhesion composite master batch; the invention discloses a preparation method of a GRS50 recyclable high-transparency film. The preparation method comprises the following steps: drying and dedusting a screened post-consumption PE (Poly Ethylene) film; extruding and granulating at the temperature of 140-150 DEG C and the speed of 50-60 rpm to obtain high-purity recycled PE particles; mixing the particles with the raw material and the auxiliary agent, and carrying out film blowing molding under the conditions that the temperature of a main machine barrel is 150-160 DEG C and the temperature of a die head is 190-205 DEG C; the high-purity recycled PE particles are prepared by directionally screening the recycled PE films and combining the low-temperature low-speed granulation and multi-stage vacuum devolatilization process, the quality of the raw materials is controlled from the source, and thermal degradation and impurity generation are inhibited to the maximum extent in the processing process.

Description

Technical Field

[0001] This invention relates to the field of polymer material processing technology, specifically to a GRS50 recyclable high-transparency film. Background Technology

[0002] With increasing global emphasis on sustainable development, the consumer goods industry is actively responding to GRS (Global Recycling Standard) certification, striving to increase the proportion of post-consumer recycled (PCR) materials in packaging. Polyethylene (PE) film, as the most widely used flexible packaging material, is crucial for achieving a circular economy through recycling. However, transforming recycled PE (rPE) into a highly transparent film that meets the demands of modern product display, rather than being downgraded, presents significant technical challenges. The purpose of this invention is to provide a technical solution that uses a high proportion of rPE as the main raw material to prepare a GRS50 recyclable high-transparency film with excellent optical properties, meeting the market's dual demands for environmental protection and high-quality packaging.

[0003] Currently, several technologies exist in the industry for preparing films using recycled PE. These technologies typically focus on addressing the mechanical properties of recycled materials. By blending recycled PE granules with a large amount of virgin polyolefins (such as LLDPE) and employing a conventional high-temperature extrusion process, films with sufficient tensile strength and toughness can be produced. This method is simple, easy to implement, and the resulting films can meet the requirements of applications with low optical performance requirements, such as for use as transport packaging, garbage bags, or agricultural films, achieving the functional reuse of recycled materials in these fields.

[0004] However, existing technologies have significant limitations in achieving a combination of high recycled content and high optical performance. Firstly, conventional recycling granulation processes often employ high-temperature, high-speed extrusion to maximize production capacity, inevitably leading to thermal degradation and mechanical shear damage to the PE molecular chains, thus impairing the material's optical potential from the outset. Secondly, in the blown film stage, the method of mixing heat-sensitive additives with the main resin in the extruder to undergo a complete thermal history often results in partial inactivation of the additives before they can function, failing to effectively improve melt flowability and film surface quality. Finally, the molding process relying on traditional single-air-ring cooling lacks sufficient cooling rate and uniformity to suppress rapid crystallization of rPE melts containing numerous complex components, directly contributing to high haze and poor transparency in the final film. Therefore, those skilled in the art propose a GRS50 recyclable high-transparency film to address these issues. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a GRS50 recyclable high-transparency film, which solves the technical problems of high haze and poor transparency in films with high recycled material content caused by the decline in the quality of recycled materials, improper processing technology, and insufficient molding control.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a GRS50 recyclable high transparency film.

[0007] The first aspect of this invention provides a GRS50 recyclable high-transparency film, made from the following components in parts by weight: High-purity recycled PE granules: 50-65 parts; Virgin low-density polyethylene: 15-25 parts; Virgin metallocene polyethylene: 15-25 parts; PPA masterbatch: 0.5-1.5 parts; Smooth and anti-blocking composite masterbatch: 1.0-3.0 parts; The high-purity recycled PE particles are prepared from post-consumer PE films rich in low-density polyethylene and metallocene polyethylene.

[0008] In a preferred embodiment, the PPA masterbatch is composed of vinylidene fluoride-hexafluoropropylene copolymer and a carrier resin; the slip-resistant and anti-blocking composite masterbatch is composed of erucamide, synthetic amorphous silica and a carrier resin.

[0009] High-purity recycled PE particles: As the main component of the composition, it uses post-consumer PE film rich in low-density polyethylene and metallocene polyethylene as raw material. The molecular structure of these raw materials has low crystallinity and high light transmittance, which provides the material basis for the high transparency of the final film.

[0010] Virgin low-density polyethylene (LDPE): Its molecular chains have long branched structures and low crystallinity. Blending it with recycled PE particles can further reduce the crystallinity of the entire system, thereby improving transparency.

[0011] Virgin metallocene polyethylene (mPE): It has a narrow molecular weight distribution and uniform distribution of comonomers, which can improve the mechanical properties and optical uniformity of the film.

[0012] PPA masterbatch: Its active fluoropolymer migrates in the melt to the metal surface of the processing equipment to form a dynamic coating, reducing the friction between the melt and the metal wall, eliminating melt cracking, making the film surface smooth, and reducing light scattering caused by surface defects.

[0013] Slip-resistant and anti-blocking composite masterbatch: Erucamide acts as a slip agent, migrating to the surface after the film cools to form a lubricating layer and reduce the film's coefficient of friction; synthetic amorphous silica acts as an anti-blocking agent, forming microscopic bumps on the film surface to separate the film layers and prevent adhesion. The two are combined to achieve the film's functionality.

[0014] In a preferred embodiment, the virgin low-density polyethylene has a melt index of 1.5-2.5 g / 10 min and a density of 0.918-0.925 g / cm³. 3 The virgin metallocene polyethylene has a melt flow index of 0.8-1.2 g / 10 min and a density of 0.915-0.920 g / cm³. 3 Limiting these parameter ranges ensures that the virgin material and the recycled PE granule melt have matched rheological properties during processing, which helps to form a homogeneous blend system.

[0015] A second aspect of this invention provides a method for preparing a GRS50 recyclable high-transparency film, comprising the following steps: S1. Raw material pretreatment: The screened post-consumer PE film is dried and subjected to electrostatic dust removal. S2. Preparation of high-purity recycled PE granules: The treated post-consumer PE film is extruded and granulated at an extruder temperature of 140-150℃ and a screw speed of 50-60rpm to obtain high-purity recycled PE granules. S3. Blown film forming: The high-purity recycled PE particles, virgin low-density polyethylene, virgin metallocene polyethylene, PPA masterbatch and slip-resistant anti-blocking composite masterbatch are mixed by weight and blown into a film; the barrel temperature of the blown film forming machine is set to 150-160℃ and the die head temperature is set to 190-205℃.

[0016] The technical principle of the method of the present invention is explained as follows: Step S1, Raw Material Pretreatment: Drying aims to remove adsorbed moisture from the raw materials. Moisture can cause PE hydrolysis during subsequent high-temperature melting and processing, leading to molecular chain breakage, material performance degradation, and optical defects. Electrostatic dust removal aims to remove micro-dust particles, which can become stress concentration points or degradation initiation points in the melt.

[0017] Step S2, Preparation of High-Purity Recycled PE Particles: This step employs a combination of low-temperature and low-speed process parameters. An extrusion temperature of 140-150℃ and a screw speed of 50-60 rpm are designed to reduce thermal degradation and mechanical shear damage to the PE molecular chains during processing, maximizing the preservation of the raw material's optical properties.

[0018] Step S3, blown film forming: The main barrel temperature is set to 150-160℃ to reduce thermal degradation of the material during its residence time in the barrel; the die temperature is set to 190-205℃ to ensure that the melt has low viscosity and good fluidity when it exits the die, forming a uniform film bubble. This specific "low-high" temperature gradient setting synergistically ensures the maintenance of material properties and the stability of forming quality.

[0019] In a preferred embodiment, in step S1, the drying process of the raw material pretreatment is as follows: the post-consumer PE film is dried by circulating air at a temperature of 40-60°C. This temperature range can effectively remove moisture without causing heat damage to the PE raw material.

[0020] In a preferred embodiment, step S2, the extrusion granulation process further includes a multi-stage vacuum degassing and devolatilization step: a vacuum of -0.05 to -0.06 MPa is set in the initial melting zone of the material, and a vacuum of -0.08 to -0.095 MPa is set in the homogenization zone. This step, by applying different vacuum levels in stages, can gradually remove residual low-boiling-point solvents, moisture, and volatile substances such as oligomers generated during processing from the raw materials, thereby improving the purity of the resulting recovered granules.

[0021] In a preferred embodiment, in step S3, the mixing process for blown film forming employs a step-by-step feeding method: the high-purity recycled PE granules, virgin low-density polyethylene, and virgin metallocene polyethylene are added through the main feed inlet; the PPA masterbatch and the slip-resistant anti-blocking composite masterbatch are added through a side feed inlet located in the middle and rear section of the extruder. This method shortens the heating time of the heat-sensitive additives (PPA, erucamide) in the extruder, reduces the possibility of their decomposition and failure, and ensures that their functions are fully reflected in the final film.

[0022] In a preferred embodiment, during step S3, the blown film forming process employs an internal and external dual-air ring cooling system, with the cooling air temperature controlled at 5-10°C. This powerful and uniform rapid cooling condition can quickly lower the temperature of the molten film bubble below the glass transition temperature, suppressing the crystallization process of PE molecular chains and retaining more amorphous regions in the system, thereby significantly reducing the haze of the film and improving its transparency.

[0023] In a preferred embodiment, during step S3, the blown film forming process involves controlling the blow ratio at 1.5-2.0 and the draw ratio at 15-20. This range of draw ratios allows the PE molecular chains to achieve appropriate orientation in both the transverse and longitudinal directions, which is beneficial for balancing the mechanical and optical properties of the film.

[0024] In a preferred embodiment, the cooling air temperature and airflow of the inner and outer dual-ring cooling system are controlled by: real-time monitoring of the haze of the finished film, and automatically adjusting the temperature and airflow through a closed-loop feedback control system based on the deviation between the monitored value and the preset target value. This step transforms static process parameter settings into dynamic process control, which can compensate for the impact of minor differences between raw material batches and environmental fluctuations on product quality, ensuring a high degree of consistency in the optical performance of the final product.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. This invention produces high-purity recycled PE granules by directional screening of recycled PE film and combining low-temperature, low-speed granulation with multi-stage vacuum devolatilization. This controls the quality of raw materials from the source and minimizes thermal degradation and impurity generation during processing. Compared with existing technologies that simply wash recycled materials and use conventional high-temperature, high-speed granulation, this invention solves the fundamental technical defects of yellowing and poor transparency of recycled granules caused by raw material mixing and secondary processing damage.

[0026] 2. This invention combines high-purity recycled particles with virgin materials of specific properties and innovatively adopts a step-by-step feeding process, adding heat-sensitive additives in the later stages of the melt. This synergistic design of raw material combination and processing method ensures the maximum performance of each component, overcoming the shortcomings of traditional blending processes where all materials undergo a complete thermal history together, leading to premature decomposition and failure of additives, which in turn affects the final film surface quality and optical performance.

[0027] 3. In the blown film forming stage, this invention applies a special temperature gradient of "low temperature of the main unit and high temperature of the die head", and matches it with forced low temperature rapid cooling and online optical closed-loop feedback control. The integration of this series of precision processes realizes precise control of the melt from plasticization, forming to solidification. Unlike the conventional approach of relying on adjusting the cooling rate or temperature alone, this invention breaks through the bottleneck of difficulty in balancing recycled material content and film transparency under traditional processes through the synergistic effect of multiple physical fields, enabling films with high recycled material content to achieve optical quality comparable to virgin materials. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the specification of the present invention. 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.

[0029] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0030] Experimental materials: Post-consumer PE film: It is a mixture of fragments obtained from the recycling, sorting, cleaning and crushing of commercially available food packaging films of brand A (GTZR model), brand B (LZR model), and brand C (R98-5 model). Its main components are low-density polyethylene and metallocene polyethylene.

[0031] Virgin low-density polyethylene (LDPE): CAS No.: 9002-88-4.

[0032] Virgin metallocene polyethylene (mPE): CAS No.: 25087-34-7 (ethylene-hexene copolymer).

[0033] Linear low-density polyethylene (LLDPE, masterbatch carrier): CAS No.: 9002-88-4.

[0034] Vinylidene fluoride-hexafluoropropylene copolymer (PPA active material): CAS No.: 9011-17-0.

[0035] Erucamide: Purity ≥ 98%; CAS No.: 112-84-5.

[0036] Synthesized amorphous silica: average particle size 4.5 μm; CAS No.: 7631-86-9.

[0037] Preparation Example 1: Preparation of PPA masterbatch (PPA-MB): 20 parts by weight of vinylidene fluoride-hexafluoropropylene copolymer powder and 80 parts by weight of linear low-density polyethylene granules were placed in a high-speed mixer and premixed for 10 minutes at 500 rpm. The uniformly mixed material was fed into a co-rotating twin-screw extruder (L / D=44) through a loss-in-weight feeder for melt blending. The extruder temperatures were set as follows: 165°C from the feed zone to the compression zone (zones 1-4), 185°C from the melt zone to the homogenization zone (zones 5-8), and the die temperature was 185°C. The screw speed was set to 350 rpm. After cooling in a water bath, the extrudate was pelletized into granular PPA masterbatch by a string pelletizer, labeled as PPA-MB.

[0038] Preparation Example 2: Preparation of Slip-resistant and Anti-blocking Composite Masterbatch (SA-MB): 10 parts by weight of erucamide, 15 parts by weight of synthetic amorphous silica, and 75 parts by weight of linear low-density polyethylene granules were placed in a high-speed mixer and premixed for 15 minutes at 400 rpm. The uniformly mixed material was fed into a co-rotating twin-screw extruder (L / D = 44) via a loss-in-weight feeder for melt blending. The extruder temperatures were set as follows: 155°C from the feed zone to the compression zone (zones 1-4), 170°C from the melt zone to the homogenization zone (zones 5-8), and the die temperature was 170°C. The screw speed was set to 300 rpm. After cooling in a water bath, the extrudate was pelletized into granular slip-resistant and anti-blocking composite masterbatch, labeled SA-MB, by a pelletizer.

[0039] Example 1: Step 1: Raw material pretreatment: Post-consumer PE film fragments were placed in a pretreatment device equipped with a circulating air system and an electrostatic generator. First, the circulating air system was activated, introducing hot air at 50°C for continuous drying for 30 minutes. After drying, the ion air generator was activated to perform electrostatic elimination and dust removal treatment on the material for 5 minutes.

[0040] Step 2: Preparation of high-purity recycled PE particles: The PE film fragments processed in step 1 were fed into a twin-screw extruder granulator via a loss-in-weight feeder. The temperature of all heating zones in the extruder was set to 145°C, and the screw speed was set to 55 rpm. Simultaneously, vacuum pumps were activated in sections 5 and 9 of the extruder, maintaining a vacuum of -0.055 MPa in section 5 and -0.09 MPa in section 9. After the melt was extruded through the die, it was granulated by an underwater pelletizing system to obtain high-purity recycled PE granules.

[0041] Step 3: Film blowing and forming: The materials are combined in the following proportions by weight: 60 parts of high-purity recycled PE granules, 20 parts of virgin low-density polyethylene, 18.5 parts of virgin metallocene polyethylene, 0.5 parts of PPA-MB obtained in Preparation Example 1, and 1.0 part of SA-MB obtained in Preparation Example 2.

[0042] A step-by-step feeding method is adopted: high-purity recycled PE granules, virgin low-density polyethylene and virgin metallocene polyethylene are fed into the blown film extruder through the main feed port; PPA-MB and SA-MB are fed through the side feed port set in the middle and rear section of the extruder.

[0043] The main barrel temperature of the blown film extruder is set to 155℃, and the die temperature to 195℃. The internal and external dual-air ring cooling system is activated, and the cooling air temperature is set to 8℃. The blow-up ratio is set to 1.8, and the draw ratio to 18. Simultaneously, the online optical monitoring instrument and PID closed-loop control system are activated, and the target haze value is set to 4.5%. The system automatically adjusts the cooling airflow to maintain stable product haze. The final film product is obtained by winding.

[0044] Example 2: Step 1: Raw material pretreatment: Post-consumer PE film fragments were placed in a pretreatment device equipped with a circulating air system and an electrostatic generator. First, the circulating air system was activated, introducing hot air at 40°C for 45 minutes of continuous drying. After drying, the ion air generator was activated to perform electrostatic elimination and dust removal treatment on the material for 5 minutes.

[0045] Step 2: Preparation of high-purity recycled PE particles: The PE film fragments processed in step 1 are fed into a twin-screw extruder granulator via a loss-in-weight feeder. The temperature of all heating zones in the extruder is set to 140℃, and the screw speed is set to 50 rpm. Simultaneously, vacuum pumps are activated in sections 5 and 9 of the extruder, maintaining a vacuum of -0.05 MPa in section 5 and -0.08 MPa in section 9. After the melt is extruded through the die, it is granulated by an underwater pelletizing system to obtain high-purity recycled PE granules.

[0046] Step 3: Film blowing and forming: The materials are combined in the following proportions by weight: 50 parts of high-purity recycled PE granules, 25 parts of virgin low-density polyethylene, 23.5 parts of virgin metallocene polyethylene, 0.5 parts of PPA-MB obtained in Preparation Example 1, and 1.0 part of SA-MB obtained in Preparation Example 2.

[0047] A step-by-step feeding method is adopted: high-purity recycled PE granules, virgin low-density polyethylene and virgin metallocene polyethylene are fed into the blown film extruder through the main feed port; PPA-MB and SA-MB are fed through the side feed port set in the middle and rear section of the extruder.

[0048] The main barrel temperature of the blown film extruder is set to 150℃, and the die temperature to 190℃. The internal and external dual-air ring cooling system is activated, and the cooling air temperature is set to 5℃. The blow-up ratio is set to 1.5, and the draw ratio to 15. Simultaneously, the online optical monitoring instrument and PID closed-loop control system are activated, and the target haze value is set to 4.0%. The system automatically adjusts the cooling airflow to maintain stable product haze. The final film product is obtained by winding.

[0049] Example 3: Step 1: Raw material pretreatment: Post-consumer PE film fragments were placed in a pretreatment device equipped with a circulating air system and an electrostatic generator. First, the circulating air system was activated, introducing hot air at 60°C for continuous drying for 30 minutes. After drying, the ion air generator was activated to perform electrostatic elimination and dust removal treatment on the material for 5 minutes.

[0050] Step 2: Preparation of high-purity recycled PE particles The PE film fragments processed in step 1 are fed into a twin-screw extruder granulator via a loss-in-weight feeder. The temperature of all heating zones in the extruder is set to 150℃, and the screw speed is set to 60 rpm. Simultaneously, vacuum pumps are activated in sections 5 and 9 of the extruder, maintaining a vacuum of -0.06 MPa in section 5 and -0.095 MPa in section 9. After the melt is extruded through the die, it is granulated by an underwater pelletizing system to obtain high-purity recycled PE granules.

[0051] Step 3: Film blowing and forming: The materials were combined in the following proportions by weight: 65 parts of high-purity recycled PE granules, 15 parts of virgin low-density polyethylene, 17.0 parts of virgin metallocene polyethylene, 1.5 parts of PPA-MB prepared in Preparation Example 1, and 1.5 parts of SA-MB prepared in Preparation Example 2.

[0052] A step-by-step feeding method is adopted: high-purity recycled PE granules, virgin low-density polyethylene and virgin metallocene polyethylene are fed into the blown film extruder through the main feed port; PPA-MB and SA-MB are fed through the side feed port set in the middle and rear section of the extruder.

[0053] The main barrel temperature of the blown film extruder is set to 160℃, and the die temperature to 205℃. The internal and external dual-air ring cooling system is activated, and the cooling air temperature is set to 10℃. The blow-up ratio is set to 2.0, and the draw ratio to 20. Simultaneously, the online optical monitoring instrument and PID closed-loop control system are activated, and the target haze value is set to 5.0%. The system automatically adjusts the cooling airflow to maintain stable product haze. The final film product is obtained by winding.

[0054] Comparative Example 1: Compared with Example 1, the difference is that: unscreened, commercially available ordinary post-consumer PE mixed recycled material is used instead of the high-purity recycled PE particles in Example 1; and in step 3, the main barrel temperature and the die head temperature are both set to 180°C, conventional single-air ring air cooling is used, and the cooling air temperature is not controlled.

[0055] Comparative Example 2: Compared with Example 1, the difference is that in step 2, during the preparation of high-purity recycled PE particles, the temperature of all heating zones of the extruder is set to 200°C, the screw speed is set to 150 rpm, and the vacuum exhaust system is not activated.

[0056] Comparative Example 3: Compared with Example 1, the difference is that in step 3, when blowing film, a conventional mixing and feeding method is used, that is, all components are premixed in a high-speed mixer and then fed into the blown film extruder together from the main feed port.

[0057] Comparative Example 4: Compared with Example 1, the difference is that PPA-MB is not added during the blown film forming process in step 3, and its weight parts are replaced by virgin low-density polyethylene.

[0058] Comparative Example 5: Compared with Example 1, the difference is that in step 3, when blowing film, the internal cooling part of the inner and outer dual air ring cooling system is turned off, and only the outer air ring is used for cooling, and the online optical monitoring instrument and PID closed-loop control system are not activated.

[0059] Test Example 1: Test method: Thin film samples obtained in Examples 1-3 and Comparative Examples 1-5 were conditioned for 24 hours at a temperature of 23±2℃ and a relative humidity of 50±5%. Subsequently, tests were conducted according to the following standards: 1. Haze and Total Transmittance Test: The test was conducted using a BYK Haze-gard plus haze meter according to ASTM D1003-13 standard. Five 100mm × 100mm samples were cut for each sample, and the test results were taken as the arithmetic mean.

[0060] 2. Gloss Test: According to ASTM D2457-13 standard, a BYK micro-TRI-gloss three-angle gloss meter was used to conduct the test at an incident angle of 60°. Five different locations were tested for each sample, and the arithmetic mean of the test results was taken.

[0061] Test results: Table 1: Optical performance test results of the thin films in the examples and comparative examples Results analysis: Table 1 shows that the films prepared in Examples 1-3 all had significantly lower haze values ​​than all comparative examples, while their total transmittance and 60° gloss values ​​were higher than all comparative examples. This indicates that the technical solution provided by this invention can effectively improve the optical properties of recycled PE films. Comparative Example 1, using unscreened ordinary recycled materials and conventional processes, had the highest haze and the worst optical performance. Comparative Example 2, using high-temperature, high-speed granulation, resulted in accelerated thermal degradation of the material. Although it was better than Comparative Example 1, its haze was still much higher than the examples. This confirms the effectiveness of low-temperature, low-speed granulation combined with multi-stage vacuum devolatilization process in protecting the molecular structure of materials and removing volatile impurities.

[0062] Comparative Example 3, using conventional mixed feeding, exhibited inferior optical performance compared to Example 1. This indicates that a step-by-step feeding method reduces the decomposition of heat-sensitive additives, allowing them to function more effectively and thus improving film quality. Comparative Example 4 showed that the lack of PPA masterbatch led to a decrease in film optical performance, confirming the role of PPA masterbatch in eliminating melt fracture and improving surface smoothness. Comparative Example 5 demonstrated that forced, uniform low-temperature quenching is a key process step in achieving low haze and high transparency; conventional cooling methods alone cannot achieve the same technical effects.

[0063] The technical solutions in Examples 1-3, through the synergistic effect of a systematic design of the entire process from raw material screening, low-damage granulation, precision formula design, special blown film technology to closed-loop process control, ultimately achieve the technical effect of preparing films with low haze, high light transmittance and high gloss under high recycled material content.

[0064] Test Example 2: Test method: Thin film samples prepared in Examples 1-3 and Comparative Examples 1-5 were conditioned for 24 hours at a temperature of 23±2℃ and a relative humidity of 50±5%. Subsequently, they were tested according to ASTM D882-12 standard.

[0065] 1. Sample preparation: Cut five strip samples with a width of 25.4 mm and a length of 150 mm along the longitudinal (MD) and transverse (TD) directions of the film, respectively.

[0066] 2. Testing Procedure: Clamp the specimen on the fixture of the universal testing machine, and set the initial mark spacing to 50 mm. Stretch the specimen at a tensile speed of 500 mm / min until it breaks. Record the maximum load and elongation at fracture.

[0067] 3. Result Calculation: Based on the recorded values, the tensile strength and elongation at break of the film in the MD and TD directions were calculated respectively. The final result was the arithmetic mean of the test results of 5 samples.

[0068] Test results: Table 2: Mechanical property test results of the films in the examples and comparative examples Results analysis: The data in Table 2 show that the films prepared in Examples 1-3 exhibit high levels of tensile strength and elongation at break in both the longitudinal and transverse directions, comparable to those in Comparative Examples 3-5. The mechanical properties of Comparative Examples 1 and 2 are significantly lower than those of the other groups, highlighting the necessity of the directional screening of raw materials, low-temperature low-damage granulation, and vacuum devolatilization steps in this invention. These steps reduce the breakage and degradation of polymer molecular chains caused by raw material mixing and thermal and mechanical shearing during secondary processing, thereby maintaining the mechanical fundamentals of the material.

[0069] A comparison of the data from Examples 1-3 and Comparative Examples 3-5 shows that the stepwise feeding, the application of PPA masterbatch, and the change in cooling method have relatively little impact on the macroscopic mechanical properties of the film. This indicates that the core innovation of this invention lies primarily in improving the optical properties of the film while effectively maintaining its essential mechanical properties as a packaging material. The solution of this invention does not sacrifice the physical strength and toughness of the material in exchange for improved optical properties.

[0070] The technical solution of this invention ensures the molecular structural integrity of the blend system with high recycled material content through source control and low-damage processing. Simultaneously, by blending with specific grades of virgin metallocene polyethylene and virgin low-density polyethylene, and setting appropriate blow-up and draw ratios, the molecular chains achieve proper orientation, ultimately yielding a film product with both excellent optical and mechanical properties.

[0071] Test Example 3: Test method: Thin film samples obtained in Examples 1-3 and Comparative Examples 1-5 were conditioned for 24 hours at a temperature of 23±2℃ and a relative humidity of 50±5%. Subsequently, the coefficient of friction between the inner and inner surfaces of the film was tested using a friction coefficient meter according to ASTM D1894-14 standard.

[0072] 1. Sample preparation: Cut a 200mm×100mm sample from each sample as the substrate of the test platform, and cut another 63.5mm×63.5mm sample and wrap it around a slider with a mass of 200g.

[0073] 2. Testing Procedure: Fix the substrate sample on a horizontal test platform and place the wrapped slider on the substrate. Start the instrument, and the slider moves relative to the substrate at a speed of 150 mm / min. The instrument automatically records the maximum static friction force at the moment the slider begins to move, as well as the average dynamic friction force during the slider's movement.

[0074] 3. Result Calculation: The instrument automatically calculates the static friction coefficient and dynamic friction coefficient based on the recorded frictional force and the normal pressure of the slider. Five sets of tests are conducted for each sample, and the arithmetic mean of the test results is taken.

[0075] Test results: Table 3: Surface tribological properties test results of the films in the examples and comparative examples Results analysis: The data in Table 3 show that the films prepared in Examples 1-3 all have relatively low static and dynamic coefficients of friction. Comparative Examples 1 and 2 have the highest coefficients of friction, which is attributed to their poorer surface quality and higher surface defects. The coefficient of friction in Comparative Example 3 is higher than that in Example 1, which verifies the effectiveness of the step-feed process: this process reduces the potential decomposition of the slip agent erucamide due to prolonged heating at the extruder tip, allowing it to migrate more completely to the film surface, thereby reducing the coefficient of friction.

[0076] Comparing the data from Example 1 and Comparative Example 4 reveals that the application of PPA masterbatch also contributes to reducing the coefficient of friction. The mechanism lies in PPA's ability to improve melt flowability, resulting in a smoother film surface. This provides a good foundation for the uniform distribution and effective action of the slip agent. Therefore, a lack of PPA leads to a decrease in film surface quality, thereby affecting its surface friction properties.

[0077] Examples 1-3 demonstrate how incorporating a smooth, anti-blocking composite masterbatch into the formulation and employing a step-by-step feeding process to protect the activity of additives, while simultaneously utilizing PPA masterbatch and a precision blown film process, ensures a smooth film surface. These combined technical features result in a final product with a low coefficient of friction. This property is essential for the smooth operation of the film during subsequent high-speed processing such as winding, slitting, and automated packaging.

Claims

1. A GRS50 recyclable high-transparency film, characterized in that, The components include the following parts by weight: High-purity recycled PE granules: 50-65 parts; Virgin low-density polyethylene: 15-25 parts; Virgin metallocene polyethylene: 15-25 parts; PPA masterbatch: 0.5-1.5 parts; Smooth and anti-blocking composite masterbatch: 1.0-3.0 parts; The high-purity recycled PE particles are prepared from post-consumer PE films rich in low-density polyethylene and metallocene polyethylene.

2. The GRS50 recyclable high-transparency film according to claim 1, characterized in that, The PPA masterbatch is composed of vinylidene fluoride-hexafluoropropylene copolymer and carrier resin; the slip-resistant and anti-blocking composite masterbatch is composed of erucamide, synthetic amorphous silica and carrier resin.

3. The GRS50 recyclable high-transparency film according to claim 1, characterized in that, The virgin low-density polyethylene has a melt flow index of 1.5-2.5 g / 10 min and a density of 0.918-0.925 g / cm³. 3 The virgin metallocene polyethylene has a melt flow index of 0.8-1.2 g / 10 min and a density of 0.915-0.920 g / cm³. 3 .

4. A method for preparing the GRS50 recyclable high-transparency film according to any one of claims 1-3, characterized in that, Includes the following steps: S1. Raw material pretreatment: The screened post-consumer PE film is dried and subjected to electrostatic dust removal. S2. Preparation of high-purity recycled PE granules: The treated post-consumer PE film is extruded and granulated at an extruder temperature of 140-150℃ and a screw speed of 50-60rpm to obtain high-purity recycled PE granules. S3. Blown film forming: The high-purity recycled PE particles, virgin low-density polyethylene, virgin metallocene polyethylene, PPA masterbatch and slip-resistant anti-blocking composite masterbatch are mixed by weight and blown into a film; the barrel temperature of the blown film forming machine is set to 150-160℃ and the die head temperature is set to 190-205℃.

5. The method for preparing a GRS50 recyclable high-transparency film according to claim 4, characterized in that, In step S1, the drying process of the raw material pretreatment is as follows: the post-consumer PE film is dried by circulating air at a temperature of 40-60℃.

6. The method for preparing a GRS50 recyclable high-transparency film according to claim 4, characterized in that, In step S2, the extrusion granulation process also includes a multi-stage vacuum degassing and devolatilization step: a vacuum of -0.05 to -0.06 MPa is set in the initial melting zone of the material, and a vacuum of -0.08 to -0.095 MPa is set in the homogenization zone of the material.

7. The method for preparing a GRS50 recyclable high-transparency film according to claim 4, characterized in that, In step S3, the mixing process for blown film forming adopts a step-by-step feeding method: the high-purity recycled PE particles, virgin low-density polyethylene and virgin metallocene polyethylene are added through the main feed port; the PPA masterbatch and slip-resistant anti-blocking composite masterbatch are added through the side feed port located in the middle and rear section of the extruder.

8. The method for preparing a GRS50 recyclable high-transparency film according to claim 4, characterized in that, In step S3, during the blown film forming process, an inner and outer dual-air ring cooling system is used for cooling, and the cooling air temperature is controlled at 5-10℃.

9. The method for preparing a GRS50 recyclable high-transparency film according to claim 4, characterized in that, In step S3, during the blown film forming process, the blow-up ratio is controlled at 1.5-2.0, and the draw ratio is controlled at 15-20.

10. The method for preparing a GRS50 recyclable high-transparency film according to claim 8, characterized in that, The cooling air temperature and air volume of the inner and outer dual-ring cooling system are controlled by the following method: real-time monitoring of the haze of the finished film, and automatic adjustment of temperature and air volume through a closed-loop feedback control system based on the deviation between the monitored value and the preset target value.

Images