Straight-line easy-tear polyethylene composite film, method of making and use

Abstract

The application provides a straight-line easy-to-tear polyethylene composite film, a preparation method and application thereof. The composite film comprises a longitudinal stretch polyethylene film and an easy-to-tear polyethylene film which are arranged in layers, wherein the easy-to-tear polyethylene film is formed by flow casting and co-extrusion to form an outer layer A, a core layer A and an inner layer A in sequence, a cyclic olefin copolymer is added in the core layer A, and the outer layer A is attached to one side of the longitudinal stretch polyethylene film. The stretch ratio of the longitudinal stretch polyethylene film is 3-7 times, and the composite film is torn along the longitudinal direction. Through the interlayer cooperation of MDOPE and special SPE, the tearing performance of the inner and outer layers is highly matched, the tearing path strictly extends along the longitudinal direction, and the straight-line tearing effect is presented, the edge is flat, free of burrs and bifurcation, and meanwhile, the SPE layer has excellent water vapor barrier performance. The application also provides a preparation method of the composite film and application thereof in various packaging bags, and under the premise of maintaining the recyclability of single PE material, the composite film has high barrier property, good mechanical strength and straight-line easy-to-tear property.

Description

Technical Field

[0001] This invention relates to the field of composite film technology, and in particular to a straight-line, easily tearable polyethylene composite film, as well as a method for preparing and applying such a composite film. Background Technology

[0002] With increasingly stringent environmental regulations and growing consumer focus on sustainable packaging, recyclable design of flexible packaging composite films has become an important direction for industry development. Among them, single PE material has gained widespread research and application due to its good recyclability and low environmental impact.

[0003] To meet the requirements of barrier properties and mechanical strength in different packaging scenarios, various improvement solutions have been developed in the existing technology. For example, CN113002100B and CN114228289A respectively coat high-barrier coatings on MDOPE substrates, achieving high barrier performance under a single material system; CN117645061 improves the impact resistance of large-capacity stand-up pouches through structural design, solving the problem of bag breakage due to drops; CN119300982A discloses a laminate composed of a longitudinally oriented film and a sealing layer, pointing out that low tear strength is mainly achieved by longitudinally stretched film (such as MDOPE).

[0004] However, in practical applications, existing single-PE composite films still suffer from insufficient tearability. Although MDOPE has a certain degree of tearability in the longitudinal direction, the inner sealing layer, made of ordinary PE material, does not possess good tear resistance. This results in a relatively high tearing force when the overall composite film is torn, and the tearing path is difficult to control, often leading to slanted, forked, or inability to tear in a straight line. This problem is particularly prominent in cosmetic packaging (such as mask pouches and serum pouches), where the opening experience is crucial. The difficulty in neatly and easily tearing the packaging directly impacts the consumer's experience and the product's added value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and optimize the linear tearability of polyethylene composite films in the prior art.

[0006] To achieve the above objectives, the technical solution provided by the present invention is as follows.

[0007] A linear easy-tear polyethylene composite film includes a longitudinally stretched polyethylene film and an easy-tear polyethylene film stacked together; the easy-tear polyethylene film includes an outer layer A, a core layer A, and an inner layer A stacked together by casting and co-extrusion; by weight percentage, The outer layer A contains 95-99% high-density polyethylene and 1-5% opening agent; Core layer A comprises 69-85% high-density polyethylene, 9%-16% linear low-density polyethylene, and 6%-15% cyclic olefin copolymer; Inner layer A contains 93-97% metallocene linear low-density polyethylene, 2-4% slip agent, and 1-3% opening agent; The outer layer A is bonded to one side of the longitudinally stretched polyethylene film, the stretch ratio of the longitudinally stretched polyethylene film is 3-7 times, and the composite film is torn along the longitudinal direction of the longitudinally stretched polyethylene film.

[0008] Optionally, the longitudinally stretched polyethylene film comprises an outer layer B, a core layer B, and an inner layer B stacked sequentially; by mass percentage, The outer layer B comprises 60-70% high-density polyethylene, 20-30% medium-density polyethylene, 5-10% linear low-density polyethylene, and 2-4% opening agent; Core layer B comprises: 45-55% medium-density polyethylene and 45-55% high-density polyethylene; The inner layer B comprises: 60-70% high-density polyethylene, 20-30% medium-density polyethylene, 3-7% linear low-density polyethylene, 2-4% slip agent, and 1-3% opening agent.

[0009] Optionally, at least one of a biaxially oriented polyethylene film, an aluminized cast polyethylene film, or an aluminized biaxially oriented polyethylene film may be disposed between the longitudinally stretched polyethylene film and the easy-tear polyethylene film.

[0010] Optionally, the biaxially oriented polyethylene film has a transverse stretch ratio of 8-10 times and a longitudinal stretch ratio of 3-5 times. And / or, the biaxially oriented polyethylene film comprises an outer layer C, a core layer C, and an inner layer C stacked sequentially; by mass percentage, The outer layer C comprises 65-75% bimodal high-density polyethylene, 10-20% medium-density polyethylene, 8-15% metallocene linear low-density polyethylene, and 2-4% opening agent; The core layer C comprises 25-35% bimodal linear low-density polyethylene, 45-55% high-density polyethylene, and 15-25% medium-density polyethylene; The inner layer C includes: 65-75% high-density polyethylene, 22-28% linear low-density polyethylene, 1-3% slip agent, and 0.5-1.5% opening agent.

[0011] Optionally, the surface of the longitudinally stretched polyethylene film is coated with a polyvinyl alcohol coating.

[0012] Secondly, the present invention provides a method for preparing the above-mentioned straight-line easy-tear polyethylene composite film, comprising the following steps: S1. The raw material particles of outer layer B, core layer B and inner layer B are heated to a molten state by an extruder, and formed into film bubbles by the die head and air ring. They are then naturally cooled, preheated, stretched to the required thickness by the longitudinal stretching unit with a stretching ratio of 3-7 times, and then cooled, shaped, corona treated, trimmed, and wound up to obtain MDOPE film. S2. The raw material particles of outer layer A, core layer A, and inner layer A are heated to a molten state in an extruder, flow out through the die, are rapidly cooled by cold rollers, corona treated, trimmed, and wound up to obtain an SPE film. S3. Using a dry or solvent-free lamination process, the film is laminated with an SPE membrane. After obtaining the composite membrane semi-finished product, it is cured, slit, and tear-off openings are set.

[0013] Optionally, before S3, an intermediate layer may be prepared, such as a BOPE film, MCPE (metallized cast polyethylene) film, or mBOPE film, as needed. And / or, wherein the method for preparing BOPE film includes heating and melting raw material particles through an extruder, forming them through a die, cooling them with cold water, preheating them, stretching them through a longitudinal stretching unit, shaping them, cooling them, preheating them, stretching them laterally, shaping them, cooling them, corona treatment them, trimming them, and winding them up.

[0014] Optionally, before S3, the MDOPE film is unwound, a PVA coating is applied to the surface, the wet adhesive amount is 8-12g, the adhesive concentration is 8-12%, and then dried, cooled, and rewound in an oven to obtain the MDOPE-PVA film.

[0015] Optionally, the tear includes a straight tear, the length of which is in the same direction as the longitudinal direction of the longitudinally stretched polyethylene film.

[0016] Thirdly, the present invention provides applications of the above-mentioned straight-line easy-tear polyethylene composite film, including at least one of the following: facial mask bag, essence bag, eye mask bag, lotion bag, facial cleanser bag, foundation bag, makeup remover bag; shampoo bag, conditioner bag, shower gel bag; condiment bag, instant noodle sauce packet, frozen food packaging, snack food bag, laundry detergent bag, fabric softener bag, and dishwashing liquid bag.

[0017] The advantages and beneficial effects of this invention are as follows: This invention utilizes the interlayer combination of MDOPE and a specially formulated SPE, taking advantage of the easily tearable characteristics of MDOPE in the longitudinal direction, combined with an easily tearable PE inner layer containing a cyclic olefin copolymer in the core layer, to achieve a high degree of matching in the tear performance of the inner and outer layers. Traditional composite films often exhibit skewed, forked, or even broken tear lines when torn, leading to spillage of the packaging contents or the inability to tear further. The tear path of the composite film of this invention extends strictly along the longitudinal direction of MDOPE, presenting a neat, straight tear effect with smooth, burr-free, and forked tear edges.

[0018] In particular, the SPE layer itself has extremely high water vapor barrier properties. When the thickness is 60-90μm, its water vapor permeability can be as low as <1 g / (㎡·24h), making it suitable for products such as dry foods and instant powders that have strict moisture protection requirements.

[0019] The composite film of this invention maintains the recyclability of single PE material while taking into account high barrier properties, excellent mechanical strength and good straight tearability, making it suitable for high value-added products with comprehensive requirements for packaging functionality, environmental protection and consumer experience. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the composite membrane shown in this invention.

[0021] Figure 2 This is a schematic diagram of the tear structure after the composite film bag is made according to the present invention. Detailed Implementation

[0022] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It is to be understood that the specific embodiments described herein are merely illustrative of this application and not intended to limit it. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0023] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0024] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly or implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0025] This invention provides a linear easy-tear polyethylene composite film, comprising a longitudinally stretched polyethylene film and an easy-tear polyethylene film stacked together; the easy-tear polyethylene film comprises an outer layer A, a core layer A, and an inner layer A stacked sequentially by casting and co-extrusion; by mass percentage, the outer layer A comprises 95-99% high-density polyethylene and 1-5% opening agent; the core layer A comprises 69-85% high-density polyethylene, 9%-16% linear low-density polyethylene, and 6%-15% cyclic olefin copolymer; the inner layer A comprises 93-97% metallocene linear low-density polyethylene, 2-4% slip agent, and 1-3% opening agent; the outer layer A is adhered to one side of the longitudinally stretched polyethylene film, the stretch ratio of the longitudinally stretched polyethylene film is 3-7 times, and the composite film is torn along the longitudinal direction of the longitudinally stretched polyethylene film.

[0026] In practical applications, although MDOPE films inherently possess a certain tendency to tear due to the high orientation of their longitudinal molecular chains, this tearability is relative and unstable. If MDOPE is simply laminated with ordinary PE films, cracks tend to initiate rapidly within the MDOPE layer during tearing. However, once the cracks extend to the inner layer of ordinary PE, the randomly entangled molecular chains of the ordinary PE result in ductile fracture, requiring the absorption of a large amount of energy and leading to an increase in overall tear force. More seriously, the tearing path of the ordinary PE inner layer is highly random, often deviating along weak points or thickness fluctuations in the film, causing the crack to rapidly shift from longitudinal to transverse or oblique propagation, ultimately resulting in branching, tearing, or even inability to tear completely.

[0027] To this end, the present invention introduces a cyclic olefin copolymer into the core layer A of the SPE. The cyclic olefin copolymer, when blended with high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE), forms a rigid dispersed phase within the continuous PE phase. During tearing, the cyclic olefin copolymer dispersed phase acts as a stress concentration point, inducing streaks that propagate directionally along the longitudinal direction of the MDOPE, thereby achieving matching of the tear paths between the inner and outer layers.

[0028] Furthermore, the rigid structure of the cyclic olefin copolymer increases the modulus of core layer A, preventing energy dissipation due to excessive deformation of the inner layer during tearing, and further reducing the overall tear force. The high proportion of HDPE in outer layer A provides good heat resistance and mechanical support, while the opening agent ensures the opening performance during casting.

[0029] The inner layer A is made of metallocene linear low-density polyethylene (mLLDPE), which has a narrow molecular weight distribution and low initial modulus, providing excellent heat-sealing performance and low-temperature toughness. The addition of a slip agent reduces the coefficient of friction, facilitating bag making and filling; the opening agent prevents film rolls from sticking together. The outer layer A of SPE is bonded to one side of MDOPE, allowing the tearing force to be effectively transferred from MDOPE to the stress concentration point of the cyclic olefin copolymer in the SPE core layer A when the composite film is torn longitudinally along the MDOPE. If the stretch ratio is less than 3 times, the MDOPE molecular chains are insufficiently oriented, and the tear path is prone to deviation; if it is greater than 7 times, the film is prone to microcracks during stretching, resulting in decreased mechanical properties.

[0030] The outer layer A uses a high proportion of HDPE, reducing or avoiding interlaminar slippage or energy dissipation between the outer layer A and the core layer A. The inner layer A uses metallocene linear low-density polyethylene, which has good low-temperature toughness and heat-sealing strength, ensuring that the inner layer A will not fracture prematurely or produce random tearing during tearing. As a result, the tearing behavior of SPE is no longer isotropic random ductile fracture, but rather directional brittle propagation along the longitudinal direction of MDOPE.

[0031] In some embodiments, to further improve the interlayer compatibility between MDOPE and SPE and optimize the overall mechanical properties of the composite film, the longitudinally stretched polyethylene film includes an outer layer B, a core layer B, and an inner layer B stacked sequentially; by mass percentage, the outer layer B includes 60-70% high-density polyethylene, 20-30% medium-density polyethylene, 5-10% linear low-density polyethylene, and 2-4% opening agent; the core layer B includes 45-55% medium-density polyethylene and 45-55% high-density polyethylene; the inner layer B includes 60-70% high-density polyethylene, 20-30% medium-density polyethylene, 3-7% linear low-density polyethylene, 2-4% slip agent, and 1-3% opening agent.

[0032] The outer layer B and middle layer B, through the ratio of HDPE to MDPE, ensure effective orientation of molecular chains during longitudinal stretching, while avoiding uneven stretching caused by the poor flowability of pure HDPE. The LLDPE and slip agent added to the inner layer B improve the interfacial bonding between the MDPE and the SPE outer layer A, while also preventing film adhesion and facilitating unwinding.

[0033] Optionally, at least one of the following can be incorporated between the longitudinally stretched polyethylene film and the easy-tear polyethylene film: biaxially stretched polyethylene film, aluminized cast polyethylene film, or aluminized biaxially stretched polyethylene film. The biaxially stretched polyethylene film, through bidirectional stretching in both the longitudinal and transverse directions, orients the molecular chains in a two-dimensional direction, forming a denser crystalline structure and improving its barrier properties against oxygen and water vapor. The aluminized layer further reduces water vapor permeability. When the intermediate layer is BOPE, it, along with MDOPE and SPE, is made of polyethylene, and the overall composite film retains the recyclability of a single PE layer. Simultaneously, the high modulus of BOPE provides additional tensile rigidity to the composite film, preventing bag deformation during high-speed filling or transportation.

[0034] When a BOPE layer is further placed between MDOPE and SPE, it is generally understood in the art that BOPE, after bidirectional stretching in both the longitudinal and transverse directions, exhibits good tearability in both directions. Even if the initial tear direction is oblique, the tear path often automatically veers to the longitudinal or transverse direction, rather than spreading randomly along the oblique direction. This means that the tear direction of BOPE is bidirectionally selective, capable of spreading either longitudinally or transversely. For this reason, those skilled in the art often have the concern that inserting a BOPE layer between MDOPE and SPE might divert tear stress due to the transverse tearability of BOPE when the longitudinal tearing force guided by MDOPE is transferred to the BOPE layer, thereby impairing the overall linear tearability of the composite film.

[0035] Testing and verification have shown that the addition of BOPE enhances the straight-line tear-resistant effect. The BOPE used in this invention has an outer layer C containing 65% to 75% bimodal high-density polyethylene, giving this layer a high elastic modulus and making its mechanical behavior closer to that of MDOPE. The core layer C is a blend of bimodal linear low-density polyethylene and high-density polyethylene, with a moderate modulus and a certain degree of plastic deformation capability, which can gently absorb the impact energy during crack propagation without causing bifurcation. The inner layer C forms good interfacial compatibility with the outer layer A of SPE. In this way, the entire composite film forms a smooth transition path from high modulus to moderate modulus and then back to high modulus in the thickness direction. When a crack originates from MDOPE, it can propagate stably and continuously along this path, neither being blocked by a sudden increase in modulus nor deflected by a sudden decrease in modulus.

[0036] The biaxially oriented polyethylene (BOP) film has a transverse stretch ratio of 8-10 times and a longitudinal stretch ratio of 3-5 times. The BOP film comprises an outer layer C, a core layer C, and an inner layer C stacked sequentially. By mass percentage, the outer layer C comprises 65-75% bimodal high-density polyethylene (HDPE), 10-20% medium-density polyethylene (MDPE), 8-15% metallocene linear low-density polyethylene (LLDPE), and 2-4% opening agent. The core layer C comprises 25-35% bimodal LLDPE, 45-55% HDPE, and 15-25% MLDPE. The inner layer C comprises 65-75% HDPE, 22-28% LLDPE, 1-3% slip agent, and 0.5-1.5% opening agent.

[0037] It should be noted that bimodal polyethylene refers to polyethylene resin with a molecular weight distribution exhibiting two peaks, simultaneously containing both high and low molecular weight fractions. Without using bimodal materials, adding a large proportion of pure HDPE can lead to film breakage or uneven thickness during biaxial stretching due to poor melt flowability. Examples of bimodal HDPEs that can be used in this invention include Dow DGDA-6098NT7 or Borouge FB5600. In the outer layer C, bimodal HDPE is compounded with MDPE and mLLDPE, ensuring both tensile film-forming properties and improved surface scratch resistance.

[0038] In some embodiments, a polyvinyl alcohol (PVA) coating may be applied to the surface of the longitudinally stretched polyethylene film. The PVA coating exhibits excellent oxygen barrier properties, while its water solubility facilitates coating processing. After coating, the PVA layer forms hydrogen bonds with the MDOPE surface, making it less prone to peeling off.

[0039] This invention also provides a method for preparing the above-mentioned straight-line easy-tear polyethylene composite film, comprising the following steps: S1. The raw material particles of outer layer B, core layer B and inner layer B are heated to a molten state by an extruder, and formed into film bubbles by the die head and air ring. They are then naturally cooled, preheated, stretched to the required thickness by the longitudinal stretching unit with a stretching ratio of 3-7 times, and then cooled, shaped, corona treated, trimmed, and wound up to obtain MDOPE film. S2. The raw material particles of outer layer A, core layer A and inner layer A are heated to a molten state by an extruder, flow out through the die head, are rapidly cooled by cold rollers, corona treated, trimmed, and wound up to obtain SPE film; S3. Using a dry or solvent-free lamination process, the film is laminated with an SPE membrane. After obtaining the composite membrane semi-finished product, it is cured, slit, and tear-off openings are set.

[0040] In S1, the membrane bubble is preheated to 90-110℃ after natural cooling, and then stretched by the longitudinal stretching unit to ensure the high longitudinal orientation of the MDOPE molecular chains. If the preheating temperature is too low, crystal points or membrane breakage are likely to occur during stretching; if the temperature is too high, the orientation degree decreases, and the straight tearability weakens. In S2, rapid cooling by the cold roller causes the SPE surface layer to solidify quickly, preventing excessive crystallization and agglomeration of the cyclic olefin copolymer in the core layer, ensuring that it exists as a nanoscale dispersed phase. This is key to achieving uniform stress concentration and straight tearing. If the cooling rate is too slow, the cyclic olefin copolymer will form micron-sized agglomerates, leading to excessive local stress and bifurcation during tearing. Dry lamination uses polyurethane adhesive, with the coating amount controlled at 2.5-3.5 g / ㎡, curing temperature 45-55℃, and time 48-72 hours. Solvent-free lamination does not require drying and is more environmentally friendly, but requires the adhesive to have good wettability to the PE interface.

[0041] After compound curing, tearing slits are set along the longitudinal direction of MDOPE during winding and slitting to obtain the final product.

[0042] In some embodiments, to increase the intermediate barrier layer or adjust the rigidity and stiffness of the composite film, before S3, the preparation of an intermediate layer is further included, preparing a BOPE film, MCPE film, or mBOPE film as needed; and / or, wherein the method for preparing the BOPE film includes heating and melting raw material particles through an extruder, forming them through a die, cooling them with cold water, preheating them, stretching them through a longitudinal stretching unit, shaping them, cooling them, preheating them, stretching them laterally, shaping them, cooling them, corona treatment them, trimming them, and winding them up. It should be noted that in the preparation of BOPE, the longitudinal stretching ratio is usually controlled at 3-5 times, the transverse stretching ratio is controlled at 8-10 times, and the longitudinal stretching is performed first, followed by the transverse stretching.

[0043] After longitudinal stretching, the membrane needs to be fully cooled and then preheated to the transverse stretching temperature (110-130℃) to prevent the molecular chains from relaxing before transverse stretching. Cold water cooling (water temperature 10-20℃) can quickly set the membrane and maintain its longitudinal orientation. If cooling is insufficient, the longitudinal orientation structure will be partially destroyed during subsequent transverse stretching, resulting in increased longitudinal tear strength and decreased straightness. By controlling the ratio of longitudinal to transverse stretching, the mechanical anisotropy of the composite membrane in different directions can be adjusted, further optimizing its straight-line tear performance.

[0044] In some embodiments, to enhance barrier properties by coating with a PVA coating, before step S3, the MDOPE film is unwound, and a PVA coating is applied to its surface. The wet adhesive amount is 8-12 g, and the adhesive concentration is 8-12%. After drying in an oven, cooling, and rewinding, an MDOPE-PVA film is obtained. Too low a wet adhesive amount will result in discontinuous PVA layers and reduced barrier effect; too high an amount (greater than 12 g / m²) will lead to incomplete drying and easy adhesion. An adhesive concentration of 8-12% ensures good leveling properties of the coating liquid, forming a uniform thickness coating without pinholes.

[0045] To ensure the tear direction is strictly guided, the tear includes a straight tear, the length of which is aligned with the longitudinal direction of the longitudinally stretched polyethylene film. The length of the straight tear is preferably 3-5 mm. The tear can be simultaneously die-cut during the bag-making process using laser or mechanical die-cutting.

[0046] This invention also provides applications of the aforementioned straight-line easy-tear polyethylene composite film, including at least one of the following: facial mask bags, essence bags, eye mask bags, lotion bags, facial cleanser bags, foundation bags, makeup remover bags; shampoo bags, conditioner bags, shower gel bags; condiment bags, instant noodle sauce packets, frozen food packaging, snack food bags, laundry detergent bags, fabric softener bags, and dishwashing liquid bags. Taking facial mask bags as an example, consumers need to tear the bag along the side to open it. If ordinary PE composite film is used, the tearing often results in skew or splitting, causing the essence to spill or the bag to not open neatly. However, with the composite film of this invention, the tear path strictly extends along the longitudinal direction of MDOPE, with smooth edges, improving the opening experience. For large-capacity packaging such as laundry detergent, the straight-line easy-tear property also makes it easier for consumers to control the opening size and avoid excessive pouring. At the same time, since the entire composite film is made of a single PE material, it conforms to the recyclable design of flexible packaging.

[0047] Example 1 This embodiment provides a method for preparing a straight-line easy-tear polyethylene composite film, specifically including the following steps: S1. Weigh the following raw materials by weight percentage: outer layer B: HDPE 65%, MDPE 25%, LLDPE 7%, opening agent 3%; core layer B: MDPE 50%, HDPE 50%; inner layer B: HDPE 65%, MDPE 25%, LLDPE 5%, slip agent 3%, opening agent 2%. Add each layer of raw material particles separately to three extruders, heat to a molten state, and form a film bubble through an annular die and air ring. Allow to cool naturally to room temperature. Then preheat the film bubble to 100°C and stretch it through a longitudinal stretching unit at a stretch ratio of 5 times to achieve the required thickness (approximately 25μm). After cooling and setting, corona treatment, edge trimming, and winding, obtain the MDOPE film.

[0048] S2. Weigh the following raw materials by mass percentage: outer layer A: HDPE 97%, opening agent 3%; core layer A: HDPE 77%, LLDPE 12%, cyclic olefin copolymer (COC), using Polyplastics TOPAS 8007F-600 8%; inner layer A: LLDPE 95%, slip agent 3%, opening agent 2%. Add each layer of raw material particles to three extruders, heat to a molten state, set the extruder temperature to 190-230℃, flow out through the casting die, rapidly cool and set under cooling water at 20℃, then corona treatment, edge trimming, and winding to obtain an SPE film with a thickness of approximately 60μm.

[0049] S3. Using a solvent-free lamination process, the printed surface of the MDOPE film obtained in S1 is used as the lamination surface and laminated with the outer layer A side of the SPE film obtained in S2. The lamination speed is 150m / min, and the adhesive application rate is controlled at 1.8-2.2g / ㎡. The semi-finished composite film is cured at 50℃ for 72 hours. After curing, it is cut to the required size, and a straight tear is made along the longitudinal direction of the MDOPE film with a tear length of 5mm and a cut depth of 20% of the total film thickness, thus obtaining a straight-line easy-tear polyethylene composite film.

[0050] Performance of this embodiment: Longitudinal tear force (GB / T 16578) is 10.7N. Tear path straightness deviation (the maximum vertical distance between the actual tear path and the straight trajectory of the two easy-tear openings) is less than 1.5mm / 80mm, and the splitting rate is approximately 2% in 500 tear tests. Water vapor transmission rate is 0.831g / (㎡·24h).

[0051] Example 2 The difference between this embodiment and Embodiment 1 is that the MDOPE membrane adopts a three-layer structure. The outer layer B contains 70% HDPE, 20% MDPE, 6% LLDPE, and 4% opening agent; the core layer B contains 55% MDPE and 45% HDPE; and the inner layer B contains 70% HDPE, 20% MDPE, 5% LLDPE, 3% slip agent, and 2% opening agent. The MDOPE stretch ratio is 4 times. The remaining steps are the same as in Embodiment 1.

[0052] Performance of this embodiment: longitudinal tear strength is 12.2N, straightness deviation is less than 1.8mm / 80mm, and there is no bifurcation. Water vapor transmission rate is 0.792g / (㎡·24h).

[0053] Example 3 The difference between this embodiment and Embodiment 1 is that a BOPE layer is added between MDOPE and SPE before S3 lamination. The preparation method of the BOPE film is as follows: The outer layer C raw materials are weighed according to the following mass percentages: bimodal HDPE Dow DGDA-6098NT7 70%, MDPE 15%, mLLDPE 12%, and opening agent 3%; the core layer C raw materials are: bimodal LLDPE 30%, biaxial HDPE 50%, and MDPE 20%; the inner layer C raw materials are: HDPE 70%, LLDPE 25%, slip agent 3%, and opening agent 2%. The raw materials of each layer are melted in an extruder, formed by a die, cooled with cold water at 15°C, preheated to 95°C, with a longitudinal stretch ratio of 4 times, shaped and cooled, then preheated to 120°C, with a transverse stretch ratio of 8 times, shaped and cooled, corona treated, and the edges are trimmed and wound up to obtain a BOPE film with a thickness of approximately 25μm. Step S3 is adjusted as follows: After printing on the MDOPE film, it is dry-laminated with BOPE film with an adhesive application rate of 3.1 g / m², then laminated with SPE film, cured, and slit into bags. The remaining steps are the same as in Example 1.

[0054] Performance of this embodiment: longitudinal tear strength is 8.7N, straightness deviation is less than 1.2mm / 80mm, no splitting was found in 5000 sample tests, and the yield rate is 99.8%. Water vapor transmission rate is 0.788g / (㎡·24h).

[0055] Example 4 The difference between this embodiment and Embodiment 1 is that the MDOPE membrane surface is coated with a PVA coating. Specifically, before S3 lamination, the MDOPE membrane is unwound, and a polyvinyl alcohol (PVA) aqueous solution is coated on its surface at a wet adhesive amount of 10 g / m², with an adhesive concentration of 10%. After drying in an oven, cooling, and rewinding, an MDOPE-PVA membrane is obtained. Then, the non-lamination side of the MDOPE-PVA membrane, with the PVA side facing outwards, is laminated with the SPE membrane. The remaining steps are the same as in Embodiment 1.

[0056] Performance of this embodiment: longitudinal tear strength is 10.5N, straightness deviation is less than 1.5mm / 80mm, and there is no bifurcation. Oxygen permeability is 2.3cm. 3 / (㎡·24h·0.1MPa), . The water vapor transmission rate is 0.751g / (㎡·24h).

[0057] Example 5 The difference between this embodiment and Embodiment 3 is that the BOPE layer is replaced with an aluminized biaxially oriented polyethylene film (mBOPE), which is prepared using a vacuum evaporation process. Embodiment 3 is adjusted as follows: after printing the mBOPE film, it is laminated with the mBOPE film with the aluminized side facing the mBOPE side, and then laminated with the SPE film. The remaining steps are the same as in Embodiment 3.

[0058] Performance of this embodiment: longitudinal tear strength is 3.6N, straightness deviation is less than 1mm / 80mm, and there is no bifurcation. Water vapor transmission rate is reduced to below 0.2 g / (㎡·24h), and oxygen transmission rate is <0.05cm. 3 / (㎡·24h·0.1MPa).

[0059] Comparative Example 1 The difference between this comparative example and Example 1 is that the SPE film is replaced with a regular cast PE film without the addition of cyclic olefin copolymers, and the formulation is 80% LLDPE, 20% LDPE, and a thickness of 60 μm. The remaining steps are the same as in Example 1.

[0060] The longitudinal tear force of this comparative example was 33.1N, and the tear path was severely skewed. More than 60% of the samples showed bifurcation or could not be torn in a straight line.

[0061] Comparative Example 2 The difference between this comparative example and Example 1 is that the content of the cyclic olefin copolymer in the SPE core layer A is adjusted to 3%, and the HDPE content is increased accordingly to 82%. The remaining steps are the same as in Example 1.

[0062] The longitudinal tear force of this comparative example was 14.4N, the straightness deviation was about 2.5mm / 80mm, and about 25% of the samples showed bifurcation.

[0063] Comparative Example 3 The difference between this comparative example and Example 1 is that, in S2, when preparing the SPE film, the cooling roller water temperature is set to 40°C instead of 20°C, resulting in a reduced cooling rate. The remaining steps are the same as in Example 1.

[0064] The longitudinal tearing force of this comparative example was 8.8 N, the straightness deviation was approximately 1.5 mm / 80 mm, and about 15% of the samples showed bifurcation. SEM observation showed that the cyclic olefin copolymers in the SPE core layer agglomerated into micron-sized particles with a particle size of approximately 2-5 μm, rather than a nano-sized dispersed phase.

[0065] Comparative Example 4 The difference between this comparative example and Example 1 is that the tear is a diamond-shaped tear with a larger radius, rather than a straight tear. The remaining steps are the same as in Example 1.

[0066] The longitudinal tear force of this comparative example is 17.7N, which is a very large initial tear force, making it easy for the composite film to delaminate after tearing.

[0067] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A straight-line easy-tear polyethylene composite film, comprising a longitudinally stretched polyethylene film and an easy-tear polyethylene film stacked together; The easy-tear polyethylene film comprises an outer layer A, a core layer A, and an inner layer A, which are sequentially stacked by casting and co-extrusion; by mass percentage, the outer layer A comprises 95-99% high-density polyethylene and 1-5% opening agent; Core layer A comprises 69-85% high-density polyethylene, 9%-16% linear low-density polyethylene, and 6%-15% cyclic olefin copolymer; Inner layer A contains 93-97% metallocene linear low-density polyethylene, 2-4% slip agent, and 1-3% opening agent; The outer layer A is bonded to one side of the longitudinally stretched polyethylene film, the stretch ratio of the longitudinally stretched polyethylene film is 3-7 times, and the composite film is torn along the longitudinal direction of the longitudinally stretched polyethylene film.

2. The straight-line easy-tear polyethylene composite film according to claim 1, characterized in that, The longitudinally stretched polyethylene film comprises an outer layer B, a core layer B, and an inner layer B stacked sequentially. By weight percentage, the outer layer B comprises 60-70% high-density polyethylene, 20-30% medium-density polyethylene, 5-10% linear low-density polyethylene, and 2-4% opening agent; the core layer B comprises 45-55% medium-density polyethylene and 45-55% high-density polyethylene; and the inner layer B comprises 60-70% high-density polyethylene, 20-30% medium-density polyethylene, 3-7% linear low-density polyethylene, 2-4% slip agent, and 1-3% opening agent.

3. The straight-line easy-tear polyethylene composite film according to claim 1, characterized in that, Between the longitudinally stretched polyethylene film and the easy-tear polyethylene film, at least one of the following is provided: biaxially stretched polyethylene film, aluminized cast polyethylene film, or aluminized biaxially stretched polyethylene film.

4. The straight-line easy-tear polyethylene composite film according to claim 3, characterized in that, The biaxially oriented polyethylene film has a transverse stretch ratio of 8-10 times and a longitudinal stretch ratio of 3-5 times. And / or, the biaxially oriented polyethylene film comprises an outer layer C, a core layer C, and an inner layer C stacked sequentially; by mass percentage, the outer layer C comprises 65-75% bimodal high-density polyethylene, 10-20% medium-density polyethylene, 8-15% metallocene linear low-density polyethylene, and 2-4% opening agent; the core layer C comprises 25-35% linear low-density polyethylene, 45-55% bimodal high-density polyethylene, and 15-25% medium-density polyethylene; the inner layer C comprises 65-75% bimodal high-density polyethylene, 22-28% linear low-density polyethylene, 1-3% slip agent, and 0.5-1.5% opening agent.

5. The straight-line easy-tear polyethylene composite film according to claim 1, characterized in that, The surface of the longitudinally stretched polyethylene film is coated with a polyvinyl alcohol coating.

6. A method for preparing a straight-line easy-tear polyethylene composite film according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The raw material particles of outer layer B, core layer B and inner layer B are heated to a molten state by an extruder, and formed into film bubbles by the die head and air ring. They are then naturally cooled, preheated, stretched to the required thickness by the longitudinal stretching unit with a stretching ratio of 3-7 times, and then cooled, shaped, corona treated, trimmed, and wound up to obtain MDOPE film. S2. The raw material particles of outer layer A, core layer A and inner layer A are heated to a molten state by an extruder, flow out through the die head, are rapidly cooled by cold rollers, corona treated, trimmed, and wound up to obtain SPE film; S3. Using a dry or solvent-free lamination process, the film is laminated with an SPE membrane. After obtaining the composite membrane semi-finished product, it is cured, slit, and tear-off openings are provided.

7. The preparation method according to claim 6, characterized in that, Before S3, the preparation of an intermediate layer is also included, and BOPE membrane, MCPE membrane or mBOPE membrane are prepared as needed; And / or, wherein the method for preparing the BOPE membrane includes, The raw material particles are heated and melted in an extruder, shaped through a die, cooled with cold water, preheated, stretched by a longitudinal stretching unit, shaped, cooled, preheated, stretched laterally, shaped, cooled, corona treated, trimmed, and wound up.

8. The preparation method according to claim 6, characterized in that, Before S3, the MDOPE film is unwound, and a PVA coating is applied to the surface. The wet adhesive amount is 8-12g, and the adhesive concentration is 8-12%. After drying in an oven, cooling, and rewinding, the MDOPE-PVA film is obtained.

9. The preparation method according to claim 6, characterized in that, The tear includes a straight tear, the length of which is in the same direction as the longitudinal direction of the longitudinally stretched polyethylene film.

10. The application of a straight-line easy-tear polyethylene composite film according to any one of claims 1 to 5, characterized in that, This includes at least one of the following: face mask pouches, serum pouches, eye mask pouches, lotion pouches, facial cleanser pouches, foundation pouches, makeup remover pouches; shampoo pouches, conditioner pouches, shower gel pouches; condiment pouches, instant noodle sauce packets, frozen food packaging, snack food pouches, laundry detergent pouches, fabric softener pouches, and dish soap pouches.

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