Low adsorption low density polyethylene film, its preparation method and application

Abstract

The application discloses a kind of low adsorption low density polyethylene film and preparation method and application thereof, it is related to polymer material technical field;The preparation steps of the film are as follows: low density LDPE resin, two-dimensional nanosheet layer filler is mixed with maleic anhydride grafted polyethylene extrusion, to obtain functional masterbatch A;Low density LDPE resin, the silica microspheres treated with vinyl trimethoxysilane surface and polyolefin elastomer graft dimethylsiloxane or fluorine-containing acrylate copolymer are mixed extrusion, to obtain functional masterbatch B;Low density LDPE resin, functional masterbatch A and functional masterbatch B are mixed extrusion and blow molding, control blow ratio is 3.5-4.0, traction ratio is 8-10;The application is molded by the increase of functional masterbatch B, modularization adding mode, high blow ratio and traction ratio, three synergistically improve performance, finally realize excellent high barrier property and low adsorption in single-layer LDPE film simultaneously.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a low-adsorption, low-density polyethylene film, its preparation method, and its application. Background Technology

[0002] Low-density polyethylene (LDPE), as an important thermoplastic resin, has occupied a pivotal position in the packaging field since its introduction due to its excellent flexibility, good heat-sealing performance, chemical corrosion resistance, high transparency, and relatively low cost. LDPE film is widely used in food packaging, pharmaceutical packaging, heavy-duty bags, shrink film, and many other applications. Traditional LDPE film is usually produced using blow molding or casting processes, which are relatively mature. However, with the upgrading of consumption, the market's performance requirements for packaging materials are becoming increasingly stringent, especially for packaging contents sensitive to oxygen, moisture, odor, and chemical components (such as high-fat foods, precision electronic components, active pharmaceutical preparations, and fragrances). The inherent defects of traditional LDPE film are gradually becoming apparent, mainly in the following two aspects:

[0003] 1. Insufficient gas barrier performance

[0004] LDPE is a non-polar polymer that combines crystalline and amorphous structures. Its molecular chains are relatively loosely arranged and the intermolecular forces are weak, resulting in poor barrier properties against non-polar small molecule gases such as oxygen and carbon dioxide. Its high oxygen permeability will accelerate the oxidation and deterioration of food and the degradation and inactivation of pharmaceuticals inside the packaging, thereby greatly shortening the shelf life of the products. To improve the barrier properties of LDPE, existing technologies mainly employ the following approaches: (1) Multilayer co-extrusion composite: LDPE is co-extruded with high-barrier materials such as ethylene-vinyl alcohol copolymer (EVOH) and polyamide (PA) to form a five- or seven-layer structure such as PE / bonding resin / EVOH / bonding resin / PE; (2) Surface composite high-barrier materials: Barrier coatings such as polyvinylidene chloride (PVDC) and acrylate are applied to the surface of the LDPE film, or vacuum metallization (VMPET) or silicon oxide (SiOx) is applied; (3) Nanofiller modification: Sheet-like inorganic nanofillers (such as montmorillonite, graphene, kaolin, etc.) are added to the LDPE matrix. Theoretically, nanosheets with high aspect ratios can form a "maze effect" in the matrix, effectively extending the permeation path of gas molecules, thereby improving the barrier properties of the material.

[0005] 2. Surface Adsorption and Adhesion

[0006] The flexibility of LDPE molecular chains and its low surface crystallinity result in a certain degree of stickiness on the film surface, especially when the film is freshly produced, at high temperatures, or under stacking pressure. This can easily lead to adhesion between film layers, affecting subsequent automated packaging, printing, and use. Furthermore, as a non-polar material, LDPE has a low surface energy (approximately 31-35 mJ / m²). 2 However, its surface is not completely inert. During production and storage, the film surface easily attracts dust and particles from the air due to electrostatic adsorption, causing product contamination. More importantly, when packaging specific contents, the inner surface of the film may adsorb flavor substances, active ingredients, or oils from the contents, leading to loss of product flavor, reduced efficacy, or unclear packaging. To solve the problems of surface adsorption and adhesion, traditional methods include adding anti-blocking agents, usually micron-sized inorganic particles (such as silica, talc, and calcium carbonate) or organic waxes, and adding slip agents, usually low molecular weight organic compounds such as erucamide and oleamide.

[0007] However, in practical applications, it has been found that there are contradictions in trying to solve the problems of "insufficient barrier properties" and "surface adsorption" of LDPE films. The main contradiction is that when polar nanofillers or surface composite polar high barrier materials are introduced to improve barrier properties, the surface energy of the entire system is increased, thereby aggravating the adsorption of polar contents molecules and leading to enhanced adsorption of LDPE film. On the other hand, when low molecular weight slip agents or anti-blocking agents are introduced to achieve low adsorption, microscopic defects are formed inside the material or adverse interactions occur with the barrier fillers, which in turn destroys the integrity of the barrier performance. Summary of the Invention

[0008] This invention aims to address the technical problem that existing LDPE films cannot synergistically achieve high gas barrier properties and low surface adsorption. The objective is to provide a low-adsorption, low-density polyethylene film, its preparation method, and its applications. By using a functional masterbatch B with a "low-energy microstructure" to reduce the increase in surface energy of the system caused by the high-barrier functional masterbatch A, a modular addition method of the functional masterbatch, and high blow molding with high blow ratio and traction ratio, the performance is synergistically improved. Ultimately, excellent high barrier properties and low adsorption are simultaneously achieved in a single-layer LDPE film.

[0009] This invention is achieved through the following technical solution:

[0010] The first objective of this invention is to provide a method for preparing a low-adsorption, low-density polyethylene film, comprising the following steps:

[0011] Preparation of functional masterbatch A: Low-density LDPE resin, two-dimensional nanosheet filler and maleic anhydride grafted polyethylene are mixed, extruded using a twin-screw extruder, water-cooled into strands, and pelletized to obtain functional masterbatch A;

[0012] Preparation of functional masterbatch B: Low-density LDPE resin, silica microspheres treated with vinyltrimethoxysilane, and polyolefin elastomer grafted with polydimethylsiloxane or fluorinated acrylate copolymer are mixed, and extruded using a twin-screw extruder, water-cooled into strands, and pelletized to obtain functional masterbatch B.

[0013] Low-density LDPE resin, functional masterbatch A and functional masterbatch B are mixed and blown into a single-screw blown film machine. The blow-up ratio is controlled at 3.5-4.0 and the traction ratio is controlled at 8-10 to obtain a low-adsorption low-density polyethylene film.

[0014] This invention first uses low-density LDPE resin as a carrier, and adds two-dimensional nanosheet filler and maleic anhydride-grafted polyethylene. The two-dimensional nanosheet filler has an extremely high aspect ratio and inherent barrier properties. At the same time, the introduction of maleic anhydride-grafted polyethylene greatly improves the interfacial compatibility between the polar two-dimensional nanofiller and the non-polar LDPE matrix, promotes the high-shear melt intercalation and exfoliation of the filler nanosheets in a twin-screw extruder, and makes them stably and uniformly dispersed in the LDPE carrier resin. The functional masterbatch A finally prepared has high barrier function.

[0015] Secondly, this invention uses low-density LDPE resin, vinyltrimethoxysilane-treated silica microspheres, and polyolefin elastomers grafted with polydimethylsiloxane or fluorinated acrylate copolymers. The polyolefin elastomers grafted with polydimethylsiloxane and fluorinated acrylate copolymers can selectively migrate to the film surface or form enriched layers (silicon-rich layers, fluorine-rich layers) in the blend system, thereby significantly reducing the surface free energy of the film. The addition of vinyltrimethoxysilane-treated silica microspheres forms uniformly distributed micron-sized protrusions on the film surface, effectively reducing the macroscopic contact area and achieving physical anti-adhesion. This achieves a synergistic effect of microstructure and low surface energy, constructing a stable "low-energy-microstructure" interface on the film surface, thus achieving low adsorption functionality. Furthermore, compared to conventional nano-silica particles, vinyltrimethoxysilane-treated silica microspheres effectively reduce microscopic defects within the material, avoiding the adverse effects of conventional nano-silica particle addition on barrier properties.

[0016] Finally, the low-density LDPE resin, functional masterbatch A and functional masterbatch B are mixed and melt-extruded, and blow-molded with a high blow-up ratio and traction ratio. Under the stress field of biaxial stretching, the uniformly dispersed two-dimensional nanosheet filler can be induced to align highly along the plane of the film, forming a highly efficient "maze barrier effect" and further improving the barrier performance.

[0017] In summary, the functional masterbatch A used in this invention has high barrier properties, while the functional masterbatch B provides a "low-energy-microstructure" interface, avoiding the increase in surface energy of the system by the high-barrier functional masterbatch A. Furthermore, the modular addition of the high-barrier functional masterbatch A and the low-adsorption functional masterbatch B further reduces adverse interactions between raw materials compared to conventional methods of mixing and melting all raw materials before extrusion. Combined with high blow-up ratio and traction ratio blow molding, the barrier properties are further enhanced. In other words, this invention reduces the increase in surface energy of the system by the high-barrier functional masterbatch A through the "low-energy-microstructure" functional masterbatch B, the modular addition of functional masterbatches, and the high blow-up ratio and traction ratio blow molding; these three factors synergistically improve performance, ultimately achieving excellent high barrier properties and low adsorption properties simultaneously in a single-layer LDPE film.

[0018] Furthermore, the formulation of the functional masterbatch A, by weight, includes: 75-80 parts of LDPE resin, 5-10 parts of two-dimensional nanosheet filler, and 15-20 parts of maleic anhydride-grafted polyethylene.

[0019] Furthermore, the two-dimensional nanosheet filler is organically modified montmorillonite or graphene oxide.

[0020] Furthermore, the maleic anhydride grafting rate of the maleic anhydride-grafted polyethylene is 1-2%.

[0021] Furthermore, the formulation of the functional masterbatch B, by weight, includes: 70-80 parts of LDPE resin, 10-15 parts of silica microspheres surface-treated with vinyltrimethoxysilane, and 10-20 parts of polyolefin elastomer grafted with polydimethylsiloxane or fluorinated acrylate copolymer.

[0022] Furthermore, the PDMS content in the polyolefin elastomer grafted with polydimethylsiloxane is 15-25 wt%, the effective content of the fluorinated acrylate copolymer is not less than 50%, and the carrier is LLDPE.

[0023] Furthermore, the weight ratio of the low-density LDPE resin, functional masterbatch A, and functional masterbatch B is 100:(15-25):(2-5).

[0024] Furthermore, the blow molding temperature is gradually increased from 160°C in the feeding section to 190-210°C in the die head.

[0025] The second objective of this invention is to provide a method for preparing a low-adsorption, low-density polyethylene film, which is prepared by the aforementioned method.

[0026] A third objective of this invention is to provide the application of the low-adsorption, low-density polyethylene film prepared by the aforementioned method in packaging materials.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] 1. The functional masterbatch A used in this invention has high barrier properties, while the functional masterbatch B provides a "low-energy-microstructure" interface, avoiding the increase in surface energy of the system by the high-barrier functional masterbatch A. At the same time, the high-barrier functional masterbatch A and the low-adsorption functional masterbatch B are added in a modular manner, which further reduces the adverse interactions between raw materials compared to conventional raw material mixing and melt extrusion. Combined with high blow-up ratio and traction ratio blow molding, the barrier properties are further improved. In other words, this invention reduces the increase in surface energy of the system by the high-barrier functional masterbatch A through the "low-energy-microstructure" functional masterbatch B, the modular addition of functional masterbatch, and the high blow-up ratio and traction ratio blow molding. The three factors work synergistically to improve the performance, and finally achieve excellent high barrier properties and low adsorption properties in a single-layer LDPE film.

[0029] 2. Compared to complex and expensive multi-layer co-extrusion and vacuum coating technologies, this invention adopts a traditional single-layer blow molding process. It only requires the introduction of specific functional masterbatch into the formula, combined with blow molding parameters with high blow ratio and traction ratio. No major equipment modifications are required, which has extremely high cost-effectiveness and industrial feasibility. Moreover, the film of this invention is a single-material system. Compared with multi-material composite films, its recycling and reuse process is simpler, which is in line with the green and environmentally friendly development direction of the global packaging industry. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0031] The embodiments of the present invention will be described in detail below, but unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0032] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0034] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0035] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other substances not listed may also be included, or that only the listed substances may be included.

[0036] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] The technical solution of the present invention will be further described in detail below with reference to the embodiments.

[0038] It should be noted that the raw materials involved in the embodiments are sourced from:

[0039] Low-density LDPE resin: LDPE 2426H, melt flow rate (MFR, 190℃ / 2.16kg) is 0.75 g / 10min, density is 0.924 g / cm³. 3 Purchased from SABIC.

[0040] Two-dimensional nanosheet fillers: Organically modified montmorillonite (OMMT), model DK2, modified by intercalation of octadecyltrimethylammonium chloride, with a sheet spacing of 3.5 nm, purchased from Zhejiang Fenghong New Material Co., Ltd.; Graphene oxide (GO), with a monolayer ratio of >99% and an average sheet diameter of ~5 μm, was prepared in-house.

[0041] Maleic anhydride-grafted polyethylene (PE-g-MA), MFR 1.5 g / 10min, maleic anhydride grafting rate 1.2%, model CMG9801, purchased from Suzhou Haopu Plastics Technology Co., Ltd.

[0042] Polyolefin elastomer grafted with polydimethylsiloxane (POE-g-PDMS), PDMS content 20 wt%, purchased from Dow Corning.

[0043] Fluorinated acrylate copolymer masterbatch, effective content 50%, carrier is LLDPE, model Unidyne TG-5821, purchased from Daikin Industries, Ltd.

[0044] Spherical silica microspheres, surface-treated with vinyltrimethoxysilane (A-171), with an average particle size of 1.5 μm, model SS-15EX, were purchased from Nippon Shokubai Co., Ltd.

[0045] Furthermore, unless otherwise specified, the experimental methods used in the embodiments are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0046] Example 1

[0047] A method for preparing a low-adsorption, low-density polyethylene film includes the following steps:

[0048] (1) Preparation of functional masterbatch A

[0049] Low-density LDPE resin, organically modified montmorillonite, and maleic anhydride-grafted polyethylene were dried in a vacuum oven at 110°C for 6 hours at a mass ratio of 75:10:15. The dried material was then pre-mixed for 5 minutes at 1000 rpm in a high-speed mixer. The mixture was fed into a co-rotating twin-screw extruder with a diameter of 35 mm and an aspect ratio of 48:1 via a loss-in-weight feeder. The extruder zone temperatures were set as follows: 160°C / 175°C / 190°C / 200°C / 210°C / 215°C / 210°C / 205°C. The screw speed was set to 350 rpm. The melt was extruded, water-cooled, and pelletized to obtain high-barrier functional masterbatch A1.

[0050] (2) Preparation of functional masterbatch B

[0051] Low-density LDPE resin, silica microspheres treated with vinyltrimethoxysilane, and polydimethylsiloxane grafted onto polyolefin elastomer were dried in a vacuum oven at 110°C for 6 hours at a mass ratio of 70:10:20. The dried material was then premixed in a high-speed mixer at 1000 rpm for 5 minutes. The mixture was fed into a co-rotating twin-screw extruder with a diameter of 35 mm and an aspect ratio of 48:1 via a loss-in-weight feeder. The extruder zone temperatures were set to 150°C / 165°C / 180°C / 185°C / 180°C / 175°C. The screw speed was set to 150 rpm (using low shear). The melt was extruded, water-cooled, and pelletized to obtain low-adsorption functional masterbatch B1.

[0052] (3) Film blow molding

[0053] Low-density LDPE resin, functional masterbatch A1, and functional masterbatch B1 were dried in a vacuum oven at 110℃ for 4 hours at a mass ratio of 100:15:3. The uniformly mixed granules were then added to the hopper of a single-screw blow molding machine. The blow molding machine had a screw diameter of 65 mm, a length-to-diameter ratio of 30:1, a die diameter of 120 mm, and a die gap of 1.5 mm. The extruder temperatures were set to 160℃ / 175℃ / 185℃ / 190℃ / 195℃ / 200℃. The blow molding process parameters were set to a blow ratio of 3.5 and a draw ratio of 8, resulting in a low-absorption, low-density polyethylene film with a thickness of 50±5 μm.

[0054] Example 2

[0055] The difference between this embodiment and Embodiment 1 is that:

[0056] In step (3), the mass ratio of low-density LDPE resin, functional masterbatch A1 and functional masterbatch B1 is 100:25:5, and the blow molding process parameters are set as follows: blow ratio 4.0 and traction ratio 8.

[0057] Example 3

[0058] The difference between this embodiment and Embodiment 1 is that:

[0059] In step (1), the mass ratio of low-density LDPE resin, graphene oxide and maleic anhydride grafted polyethylene is 80:5:15, and functional masterbatch A2 is prepared.

[0060] In step (3), the mass ratio of low-density LDPE resin, functional masterbatch A2 and functional masterbatch B1 is 100:10:5, and the blow molding process parameters are set as follows: blow ratio 4.0 and traction ratio 10.

[0061] Example 4

[0062] The difference between this embodiment and Embodiment 1 is that:

[0063] In step (2), the mass ratio of low-density LDPE resin, silica microspheres treated with vinyltrimethoxysilane and fluorinated acrylate copolymer is 80:10:10 to prepare functional masterbatch B2.

[0064] In step (3), the mass ratio of low-density LDPE resin, functional masterbatch A1 and functional masterbatch B2 is 100:15:2, and the blow molding process parameters are set as follows: blow ratio 3.5 and traction ratio 8.

[0065] Comparative Example 1

[0066] The difference between this comparative example and Example 1 is that no functional masterbatch B1 is added.

[0067] Comparative Example 2

[0068] The difference between this comparative example and Example 1 is that no polyolefin elastomer-grafted polydimethylsiloxane is added to the functional masterbatch B1.

[0069] Comparative Example 3

[0070] The difference between this comparative example and Example 1 is that no silica microspheres treated with vinyltrimethoxysilane are added to the functional masterbatch B1.

[0071] Comparative Example 4

[0072] The difference between this comparative example and Example 1 is that in the functional masterbatch B1, ordinary silica microspheres (average particle size 2 μm) are used instead of silica microspheres that have been surface-treated with vinyltrimethoxysilane.

[0073] Comparative Example 5

[0074] The difference between this comparative example and Example 1 is that the modular addition method is not used, that is, all raw materials are dried and then directly proceeded to step (3).

[0075] Comparative Example 6

[0076] The difference between this comparative example and Example 1 is that the blow molding process parameters are set with a blow ratio of 3 and a traction ratio of 6.

[0077] The differences in formulation and process parameters between the above embodiments and comparative examples are shown in Table 1.

[0078] Table 1. Differences in formulation and process parameters between the examples and comparative examples.

[0079]

[0080] The thin film samples prepared in the above embodiments and comparative examples were subjected to performance tests, and the test methods are as follows:

[0081] 1. Oxygen Transmission Rate (OTR): Tested according to ASTM D3985 standard using a MOCON OX-TRAN 2 / 21 gas permeation apparatus. Test conditions: 23℃, 0% RH.

[0082] 2. Water vapor transmission rate (WVTR): Tested according to ASTM F1249 standard using a MOCON PERMATRAN-W 3 / 33 water vapor permeation apparatus. Test conditions: 38℃, 90% RH.

[0083] 3. Haze and gloss: Tested according to ASTM D1003 standard using a haze meter and a gloss meter (60° angle).

[0084] 4. Tensile properties: The longitudinal (MD) and transverse (TD) tensile strength and elongation at break of the film were tested on a universal testing machine in accordance with ASTM D882 standard.

[0085] 5. Dust adsorption test (simulation): After generating static electricity by friction in an environment with a relative humidity of 50%, a 5cm × 5cm film sample is placed in a sealed box filled with talc dust for 10 minutes. After taking it out, the surface is gently blown with compressed air, and then the weight gain is measured. The amount of dust adsorbed per unit area is calculated.

[0086] Table 2. Performance Test Data

[0087]

[0088] As can be seen from the data in Table 2:

[0089] The oxygen and water vapor permeability of the thin film samples in the embodiments of the present invention are very low, which proves that the product of the present invention has excellent high barrier properties. At the same time, the dust adsorption is low, which proves that the surface adsorption of the product of the present invention is effectively improved. It can be seen that the product of the present invention achieves high barrier properties and low adsorption while also having good mechanical properties (tensile strength) and optical properties (haze, gloss), and has excellent comprehensive performance.

[0090] In Comparative Example 1, without the addition of functional masterbatch B, the surface energy increased due to the addition of functional masterbatch A. Although the oxygen permeability and water vapor permeability remained at a low level, the surface adsorption was significantly enhanced, demonstrating that functional masterbatch B plays an important role in reducing surface adsorption.

[0091] Comparative Example 2's functional masterbatch B, lacking polyolefin elastomer-grafted polydimethylsiloxane, could not form an enrichment layer to reduce the film's surface free energy. Relying solely on the physical anti-adhesion effect of the vinyltrimethoxysilane-treated silica microspheres, its adsorption capacity improved compared to the untreated masterbatch B, but still failed to achieve low surface adsorption. Comparative Example 3's functional masterbatch B1, also lacking vinyltrimethoxysilane-treated silica microspheres, could form an enrichment layer on the film surface, but lacked the physical anti-adhesion effect of the vinyltrimethoxysilane-treated silica microspheres. While its adsorption capacity improved compared to the untreated masterbatch B, it still failed to achieve low surface adsorption. Therefore, the data from Examples 1, 2, and 3 show that the polyolefin elastomer-grafted polydimethylsiloxane and the vinyltrimethoxysilane-treated silica microspheres in functional masterbatch B have a synergistic effect. Only by simultaneously adding both raw materials can the surface energy be effectively reduced, achieving low film adsorption.

[0092] In Comparative Example 4, functional masterbatch B uses ordinary silica microspheres instead of silica microspheres treated with vinyltrimethoxysilane. Although the adsorption capacity increases to some extent, it remains at a low level. However, its oxygen permeability and water vapor permeability increase significantly. This is because the addition of ordinary silica microspheres introduces microscopic defects into the material, which has an adverse effect on the barrier properties. It can be seen that the use of silica microspheres treated with vinyltrimethoxysilane in this invention avoids this contradiction and is more conducive to improving both high barrier properties and low adsorption capacity.

[0093] Comparative Example 5 did not use modular addition, but instead used all the materials mixed before extrusion blow molding. Both the barrier properties and low adsorption properties were significantly worse, proving that the modular addition of the present invention is more conducive to improving both high barrier properties and low adsorption properties at the same time.

[0094] Although the formulation of Comparative Example 6 was exactly the same as that of Example 1, the blow molding process parameters used a lower blow-up ratio and draw ratio. The barrier properties (OTR and WVTR) of the film decreased significantly, and the mechanical properties (tensile strength) also decreased to a certain extent. This proves that the synergistic control of high BUR and high TUR used in this invention plays a decisive role in inducing the orientation of nanosheets and achieving high barrier properties. It also proves that only with the synergy of the formulation and high blow-up ratio and draw ratio parameters can this invention achieve the technical effects of high barrier properties and low adsorption at the same time.

[0095] In summary, this invention achieves excellent high barrier properties and low adsorption properties in a single-layer LDPE film by using a functional masterbatch B with "low energy and microstructure" to reduce the increase in surface energy of the system by the high barrier functional masterbatch A, a modular functional masterbatch addition method, and high blow-up ratio and traction ratio blow molding.

[0096] Finally, it should be noted that the above specific embodiments are only used to describe the purpose, technical solution, and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation of the present invention and is not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the foregoing specific embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions or improvements can be made to some or all of the technical features. These modifications, equivalent substitutions, and improvements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A method for preparing a low-adsorption, low-density polyethylene film, characterized in that, Includes the following steps: Preparation of functional masterbatch A: Low-density LDPE resin, two-dimensional nanosheet filler and maleic anhydride grafted polyethylene are mixed, extruded using a twin-screw extruder, water-cooled into strands, and pelletized to obtain functional masterbatch A; Preparation of functional masterbatch B: Low-density LDPE resin, silica microspheres treated with vinyltrimethoxysilane, and polyolefin elastomer grafted with polydimethylsiloxane or fluorinated acrylate copolymer are mixed, and extruded using a twin-screw extruder, water-cooled into strands, and pelletized to obtain functional masterbatch B. Low-density LDPE resin, functional masterbatch A and functional masterbatch B are mixed and blown into a single-screw blown film machine. The blow-up ratio is controlled at 3.5-4.0 and the traction ratio is controlled at 8-10 to obtain a low-adsorption low-density polyethylene film.

2. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The formulation of the functional masterbatch A, by weight, includes: 75-80 parts of LDPE resin, 5-10 parts of two-dimensional nanosheet filler, and 15-20 parts of maleic anhydride-grafted polyethylene.

3. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The two-dimensional nanosheet filler is made of organically modified montmorillonite or graphene oxide.

4. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The maleic anhydride grafting rate of the maleic anhydride-grafted polyethylene is 1-2%.

5. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The formulation of the functional masterbatch B, by weight, includes: 70-80 parts of LDPE resin, 10-15 parts of silica microspheres surface-treated with vinyltrimethoxysilane, and 10-20 parts of polyolefin elastomer grafted with polydimethylsiloxane or fluorinated acrylate copolymer.

6. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The PDMS content in the polyolefin elastomer grafted with polydimethylsiloxane is 15-25 wt%, the effective content of the fluorinated acrylate copolymer is not less than 50%, and the carrier is LLDPE.

7. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The weight ratio of the low-density LDPE resin, functional masterbatch A and functional masterbatch B is 100:(15-25):(2-5).

8. The method for preparing a low-adsorption, low-density polyethylene film according to claim 1, characterized in that, The temperature for blow molding is gradually increased from 160°C in the feeding section to 190-210°C in the die head.

9. A low-adsorption, low-density polyethylene film, characterized in that, It is prepared by the method described in any one of claims 1-8.

10. The application of a low-adsorption, low-density polyethylene film as described in claim 9 in packaging materials.

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