Single-sided online coated bopp ultra-low temperature heat-seal type cigarette film, preparation method and application thereof

Abstract

The application provides a single-sided online coated BOPP ultra-low-temperature heat-seal type cigarette film and a preparation method and application thereof. The BOPP ultra-low-temperature heat-seal type cigarette film is provided with a multi-layer co-extrusion integrated structure of a core layer and upper and lower ultra-low-temperature heat-seal layers, and an online water-based antistatic and smooth coating layer is coated on the surface of the second ultra-low-temperature heat-seal layer on one side, so that the heat-seal starting temperature of the upper and lower surfaces is controlled below 90 DEG C, and the coated surface is provided with good antistatic property and smoothness. Compared with the existing medium and high-temperature heat-seal cigarette film, the BOPP ultra-low-temperature heat-seal type cigarette film can reduce the heat-seal temperature by more than 20 DEG C, reduce the deformation of the cigarette box and the like, the water-based antistatic and smooth coating layer can also improve the film adhesion and improve the high-speed film stability, and the two are synergistic to make the BOPP ultra-low-temperature heat-seal type cigarette film adapt to higher-speed automatic packaging equipment, reduce downtime and improve efficiency. The BOPP ultra-low-temperature heat-seal type cigarette film simultaneously has the support and protection function of the paper box and the heat-seal packaging function of the transparent film, and can be directly used for paperless cigarette packaging.

Description

Technical Field

[0001] This invention belongs to the technical field of functional ILC-BOPP (Inline Coated Biaxially Oriented Polypropylene) film for cigarette packaging. Specifically, it relates to a BOPP ultra-low temperature heat-sealing cigarette film with single-sided online coating, ultra-low temperature heat sealing, high smoothness, high shrinkage, and high flatness, as well as its preparation method and application. It is especially suitable for double-sided heat sealing and anti-counterfeiting packaging in high-speed cigarette packaging machines. Background Technology

[0002] Existing BOPP cigarette films are mostly designed for medium-to-high temperature heat sealing, using co-extrusion or offline coating processes. These designs suffer from the following technical drawbacks: the heat-sealing temperature is too high (≥110℃), limiting heat sealing to high temperatures, making them prone to sticking to packaging and failing to meet the demands of high-speed automated packaging. Furthermore, high-speed packaging can easily lead to cigarette box deformation, film wrinkling, heat-sealing knife sticking, and appearance defects. Offline coating requires secondary rewinding, resulting in numerous processes, high energy consumption, low efficiency, and easy scratching of the film surface, as well as poor coating uniformity. The film's double-sided slip and anti-sticking properties are inconsistent, leading to poor stability during high-speed operation and making it unsuitable for high-end, high-speed cigarette packaging equipment. To address these shortcomings, this invention provides a BOPP cigarette film with single-sided online coating, double-sided ultra-low temperature heat sealing, and integrated continuous production, along with its preparation method.

[0003] Therefore, there is an urgent need to provide a BOPP ultra-low temperature heat-sealing cigarette film with single-sided online coating, double-sided ultra-low temperature heat sealing, and integrated continuous production, as well as its preparation method and application, to solve the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a single-sided online coated BOPP ultra-low temperature heat-sealing cigarette film, its preparation method, and its application, so as to solve the technical problems of existing cigarette films such as high heat-sealing temperature, low offline coating efficiency, and poor stability in high-speed packaging. The BOPP ultra-low temperature heat-sealing cigarette film of this invention has the characteristics of single-sided online coating, double-sided ultra-low temperature heat sealing, online integrated coating, high shrinkage, high smoothness, high transparency, and good antistatic properties.

[0005] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows: In a first aspect, the present invention provides a single-sided online coated BOPP ultra-low temperature heat-sealing cigarette film, comprising a core layer, a first ultra-low temperature heat-sealing layer located on the upper surface of the core layer and a second ultra-low temperature heat-sealing layer located on the lower surface of the core layer, wherein the lower surface of the second ultra-low temperature heat-sealing layer is further coated with a water-based antistatic slip coating; the heat-sealing initiation temperature of both the upper and lower surfaces of the BOPP ultra-low temperature heat-sealing cigarette film is ≤90℃.

[0006] Specifically, this invention prepares BOPP ultra-low temperature heat-sealing cigarette film through a multi-layer co-extrusion integrated structure of the core layer and the upper and lower ultra-low temperature heat-sealing layers. This allows the two heat-sealing layers and the core layer to achieve molecular-level bonding during the extrusion molding process, resulting in better interlayer bonding and structural stability compared to subsequent composite processes, effectively avoiding the risk of interlayer delamination. Based on this structure, the heat-sealing initiation temperature of both the upper and lower surfaces of the BOPP ultra-low temperature heat-sealing cigarette film can be controlled below 90°C, which can reduce the heat-sealing temperature by more than 20°C compared to existing medium-high temperature heat-sealing cigarette films (usually ≥110°C). This helps to reduce problems such as cigarette box deformation caused by high temperature during high-speed packaging, while also reducing the energy consumption of packaging equipment and adapting to higher packaging line speeds.

[0007] Specifically, the lower surface layer employs a layered design of a second ultra-low temperature heat-sealing layer and an antistatic slip coating, functionally separating the heat-sealing and antistatic / slip functions on the same side surface. The second ultra-low temperature heat-sealing layer provides stable and reliable ultra-low temperature heat-sealing performance, while the water-based antistatic slip coating imparts a low coefficient of friction, good antistatic properties, and printability. The two layers function independently without interference, preventing the coating layer from affecting the heat-sealing performance and ensuring that the surface simultaneously possesses stable slip properties and ultra-low temperature heat-sealing characteristics.

[0008] Preferably, the total thickness of the BOPP ultra-low temperature heat-sealing cigarette film is 16–33 μm, the heat-sealing strength of both its upper and lower surfaces is ≥2.5 N / 15 mm, the coefficient of friction is 0.10–0.25, the heat shrinkage rate at 120°C for 5 min is 6.5%–10.5%, and the surface resistivity is less than 10 Ω·cm. 8 Ω.

[0009] Specifically, a moderate thickness range can cover the needs of cigarette packaging from thin to regular sizes; high double-sided heat-sealing strength helps ensure the bonding strength of the heat-sealed parts, reducing the risk of heat-sealing cracks during transportation and storage; a low coefficient of friction facilitates smooth film feeding during high-speed packaging, reducing film adhesion and equipment drag resistance; an appropriate heat shrinkage rate allows the cigarette transparent paper packaging to form a tight and flat appearance after heat sealing, with sufficient tightening effect without causing deformation of the cigarette box or wrinkling of the film due to excessive shrinkage; low surface resistance gives the film good antistatic properties, helping to reduce problems such as electrostatic adsorption of dust, electrostatic discharge, and electrostatic adhesion between films during packaging.

[0010] Preferably, the heat-sealing initiation temperature of the first ultra-low temperature heat-sealing layer is 83-85°C, and its raw materials, by weight, include: 100 parts of ternary copolymer, 10-15 parts of metallocene ultra-low melting point copolymer, 5-10 parts of thermoplastic elastomer, and 3-5 parts of anti-sticking masterbatch; and / or, The core layer raw materials, by weight, include: 100 parts polypropylene main material, 10-15 parts hydrogenated petroleum resin, 0-5 parts antioxidant, and 1-2 parts nucleating agent; and / or, The heat-sealing initiation temperature of the second ultra-low temperature heat-sealing layer is 75-80℃, and its raw materials, by mass parts, include: 100 parts of metallocene ultra-low melting point copolymer, 5-10 parts of thermoplastic elastomer, and 20-30 parts of viscous masterbatch.

[0011] Specifically, the first ultra-low temperature heat-sealing layer uses ternary copolymer as the matrix to construct the basic heat-sealing framework. By introducing metallocene ultra-low melting point copolymer, the melting temperature of the system is further reduced. The thermoplastic elastomer is used to improve the flexibility and heat-sealing strength of the layer. In addition, an anti-stick masterbatch is used to improve the surface anti-sticking performance, which helps to achieve stable and reliable heat sealing at a moderate heat-sealing initiation temperature.

[0012] Specifically, the core layer is made of homopolymer polypropylene to provide the rigidity and stiffness required for the film. The addition of hydrogenated petroleum resin can improve the interlayer compatibility between the core layer and the heat-sealing layers on both sides and adjust the film transparency. Nucleating agents help to refine spherulites and improve crystallization uniformity, while antioxidants can enhance the thermal stability of the film during high-temperature extrusion and biaxial stretching. Specifically, the second ultra-low temperature heat-sealing layer is mainly composed of metallocene ultra-low melting point copolymers, combined with thermoplastic elastomers and viscous masterbatches, which can achieve a lower heat-sealing initiation temperature and better initial tack performance, making it suitable for packaging scenarios that are more sensitive to heat-sealing temperature.

[0013] Preferably, the dyn value of the water-based antistatic slip coating surface is 54–58 dyn / cm, suitable for UV flexographic, gravure, and letterpress printing processes; the raw materials of the water-based antistatic slip coating, by weight, include: 100 parts antistatic coating liquid, 0.3–1.0 parts nano anti-stick slip agent, 0.5–1.0 parts wetting agent, and 5–10 parts deionized water; and / or, The raw materials of the antistatic coating liquid, by mass percentage, include: 20-25% waterborne polyurethane, 8-15% conductive organic matter, 0.8-1.2% waterborne carbodiimide crosslinking agent, 0.1-0.5% nonionic low-foaming wetting agent, and 55-65% deionized water.

[0014] Specifically, the dyne value of the coating surface is controlled within a moderate range, which can provide good ink adhesion for various printing processes such as UV (Ultraviolet) flexographic, gravure, and letterpress printing, thus expanding the printing application range of the cigarette film.

[0015] Specifically, the working fluid of the water-based antistatic slip coating uses a pre-mixed antistatic coating liquid as the base, combined with a nano anti-sticking slip agent to reduce the coefficient of friction of the film and improve its anti-blocking performance. The wetting agent can improve the uniformity of the coating liquid on the film surface, and deionized water is used to adjust the solid content and viscosity of the coating liquid, which is beneficial to the stable operation of the online coating process.

[0016] Specifically, the antistatic coating liquid uses water-based polyurethane as the film-forming matrix, which can provide good coating adhesion and flexibility. Conductive organic matter gives the coating long-lasting antistatic properties, carbodiimide crosslinking agent helps to improve the coating's water resistance and mechanical strength, and non-ionic low-foaming wetting agent can reduce bubbles and pinhole defects during the coating process. The two-stage formulation system allows for flexible control of coating performance, and the water-based system also helps to reduce volatile organic compound emissions. Overall, the smoke film maintains ultra-low temperature heat sealing performance while also having good antistatic smoothness and adaptability to multiple printing processes.

[0017] Secondly, the present invention also provides a method for preparing a BOPP ultra-low temperature heat-sealing cigarette film as described in any of the above claims, comprising the following steps: S10, the first heat-sealing layer material, the core layer material and the second heat-sealing material are added to their respective extruders, melted and plasticized at 210-280°C, and then co-extruded through a multi-layer co-extrusion die and cooled to form a thick sheet; S20, after preheating the thick sheet, it is stretched longitudinally to obtain a longitudinally stretched thick sheet; S30, perform online corona treatment on any surface of the longitudinally stretched thick sheet, and then apply an online water-based antistatic slip coating to the corona-treated surface to obtain a coated sheet; S40 involves simultaneously stretching the coated sheet laterally and then performing online segmented drying and curing, so that the coating curing and lateral stretching are completed at the same time to obtain a BOPP base film. S50 involves sequentially cooling and shaping the BOPP base film, measuring its thickness, trimming its edges, corona treatment, winding, slitting, and packaging it to produce a single-sided online coated BOPP ultra-low temperature heat-sealing cigarette film.

[0018] Specifically, in step S10, the three layers of raw materials are melted separately and then co-extruded in one step through a multi-layer co-extrusion die, enabling the heat-sealing layer and the core layer to achieve molecular-level bonding during extrusion, thus avoiding the risk of interlayer delamination in subsequent composite processes. In step S20, longitudinal stretching ensures that the polypropylene molecular chains are fully oriented longitudinally, providing the film with the required longitudinal strength and stiffness. In step S30, any surface is first subjected to online corona treatment to increase surface energy, followed by online coating of a water-based antistatic slip coating. This integrates the coating process into the biaxial stretching production line, eliminating the need for a secondary rewinding step compared to offline coating. This helps to shorten the production process, reduce energy consumption, minimize film surface scratches, and improve coating efficiency. Layer uniformity; In step S40, transverse stretching and online segmented drying and curing are carried out simultaneously, allowing the water-based coating to gradually dry and cure during transverse stretching. This helps to balance coating performance and production efficiency, and avoids defects such as cracks and pinholes caused by rapid drying or asynchronous stretching. In step S50, a complete set of post-processing steps, including cooling and shaping, thickness measurement, edge trimming, corona treatment, winding, slitting, and packaging, ensures the dimensional stability, thickness uniformity, and final product quality of the film. Overall, this preparation method realizes integrated continuous production from raw material extrusion to finished product slitting and packaging. The process is simplified, the production efficiency is high, the energy consumption is low, and the product performance is stable and controllable.

[0019] Preferably, in step S10, the thick sheet includes a core layer, a first ultra-low temperature heat-sealing layer located on the upper surface of the core layer, and a second ultra-low temperature heat-sealing layer located on the lower surface of the core layer.

[0020] Specifically, the sandwich-type back sheet enables the two heat-sealing layers to form a molecular-level bond with the core layer, avoiding interlayer separation or uneven thickness during subsequent biaxial stretching, and providing a reliable structural basis for the double-sided ultra-low temperature heat-sealing performance of the final BOPP ultra-low temperature heat-sealing cigarette film.

[0021] Preferably, in step S20, the thick sheet is preheated by a preheating roller and then stretched longitudinally by 3.5 to 6.0 times at 90–120°C; and / or, in step S30, online coating is performed using a micro-gravure reverse coating method, with a dry coating weight of 0.1–0.3 g / m². 2 .

[0022] Specifically, in step S20, longitudinal stretching facilitates the full orientation of polypropylene molecular chains in the longitudinal direction, ensuring the longitudinal strength and stiffness of the film while providing a suitable thickness for subsequent transverse stretching. In step S30, online coating is performed using a micro-gravure reverse kissing coating method, and an appropriate amount of dry coating is controlled to achieve uniform thin-layer coating. This ensures the antistatic and slip-resistant effects of the coating without affecting the heat-sealing performance of the heat-sealing layer due to excessive coating thickness or causing problems such as coating cracking and peeling during subsequent transverse stretching.

[0023] Preferably, in step S40, the coated sheet is fed into a tenter frame and stretched 8 to 10 times laterally at 160 to 185°C; the online segmented drying and curing process is divided into three segments, with segmented drying temperatures of 140 to 180°C, 150 to 165°C, and 155 to 175°C respectively.

[0024] Specifically, transverse stretching facilitates the full orientation of polypropylene molecular chains in the transverse direction, enabling the film to achieve balanced mechanical properties and appropriate thermal shrinkage, meeting the requirements of cigarette transparent paper packaging for tightness and dimensional stability. Online segmented drying and curing adopts a three-stage gradient heating method, allowing the water-based coating to gradually dry and cure during transverse stretching, avoiding defects such as cracks and pinholes caused by sudden temperature rises or rapid drying. This promotes the synergistic stability of coating performance and the transverse stretching process, ensuring the adhesion and antistatic slip properties of the final coating.

[0025] Preferably, in step S50, the edge material and waste film generated from the edge trimming, winding, and slitting processes are returned as recycled material to step S10 for the preparation of thick sheets.

[0026] Specifically, the above-mentioned recycling operations can effectively improve the utilization rate of raw materials, reduce raw material consumption and production costs, and reduce waste emissions during the production process, which is conducive to cleaner production. The combined use of recycled materials and virgin materials can further reduce production costs and enhance the market competitiveness of products while ensuring the stability of film performance.

[0027] Thirdly, the present invention also provides a BOPP ultra-low temperature heat-sealing cigarette film as described in any of the above claims, or a BOPP ultra-low temperature heat-sealing cigarette film prepared by any of the above preparation methods, for use in paperless cigarette packaging. The BOPP ultra-low temperature heat-sealing cigarette film simultaneously possesses the supporting and protective function of a paper box and the heat-sealing packaging function of a transparent film.

[0028] Specifically, BOPP ultra-low temperature heat-sealing cigarette film, with its core layer providing rigidity and stiffness, combines the support and protection of a cardboard box with the heat-sealing function of a transparent film. It can replace the two-layer structure of a cardboard box plus an outer transparent film in traditional cigarette packaging, directly achieving boxless, bare packaging of cigarettes. Compared to traditional packaging methods, it eliminates the material cost and packaging process of the outer cardboard box, reducing the overall packaging cost. At the same time, the ultra-low temperature heat-sealing characteristic reduces the impact of high temperatures on the cigarettes, and the anti-static and smooth properties facilitate smooth film feeding during high-speed packaging. The appropriate heat shrinkage rate ensures a tight, flat, and aesthetically pleasing package, thus improving the economy and packaging quality of boxless cigarette packaging.

[0029] The beneficial effects of this invention are as follows: Unlike existing technologies, this invention provides a BOPP ultra-low temperature heat-sealing cigarette film, its preparation method, and its application. The aforementioned BOPP ultra-low temperature heat-sealing cigarette film employs a multi-layer co-extrusion integrated structure with a core layer and upper and lower ultra-low temperature heat-sealing layers. An online water-based antistatic and slip-resistant coating is applied to the surface of the second ultra-low temperature heat-sealing layer on one side, ensuring that the heat-sealing initiation temperature of both the upper and lower surfaces of the cigarette film is controlled below 90°C, while simultaneously providing the coated surface with good antistatic and slip-resistant properties. Based on this structural design, on the one hand, compared to existing medium- and high-temperature heat-sealing cigarette films, the heat-sealing temperature can be reduced by more than 20°C. This effectively reduces problems such as cigarette box deformation during high-speed packaging. On the other hand, its excellent antistatic and slippery properties can improve film adhesion and enhance high-speed film stability. The synergistic effect of these two aspects enables this BOPP ultra-low temperature heat-sealing cigarette film to be adapted to higher-speed automated packaging equipment, reducing downtime and improving packaging production efficiency. Because the core layer provides sufficient rigidity and stiffness, this BOPP ultra-low temperature heat-sealing cigarette film simultaneously possesses the support and protection function of a cardboard box and the heat-sealing packaging function of a transparent film. It can be directly used for cardboard-free cigarette packaging, eliminating the need for traditional outer cardboard boxes and improving the overall quality and production efficiency of cigarette packaging. Attached Figure Description

[0030] Figure 1 A schematic diagram of the layered structure of the single-sided online coated BOPP ultra-low temperature heat-sealing smoke film provided in Example 1; Figure 2 A schematic diagram of the online integrated preparation process of the single-sided online coated BOPP ultra-low temperature heat-sealing cigarette film provided in Example 1; In the attached diagram: 11—core layer; 12—first ultra-low temperature heat-sealing layer; 13—second ultra-low temperature heat-sealing layer; 14—water-based antistatic slip coating. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and are not intended to limit the scope of protection of the present invention to the parameter ranges of the following embodiments. Unless otherwise specified, the reagents or instruments used in the present invention are all conventional products that can be purchased through commercial channels.

[0033] Example 1: Figure 1This is a schematic diagram of the layered structure of the single-sided online coated BOPP ultra-low temperature heat-sealing smoke film provided in Embodiment 1. Figure 1 As shown, the BOPP ultra-low temperature heat-sealing cigarette film has a four-layer structure, which includes, from top to bottom, a first ultra-low temperature heat-sealing layer 12 (upper surface layer), a core layer 11 (middle layer), a second ultra-low temperature heat-sealing layer 13, and a water-based antistatic slip coating 14 (lower surface layer).

[0034] In this embodiment 1, the upper surface is a non-slip surface (the contact surface of the cigarette pack), and the lower surface adopts a composite structure of a second ultra-low temperature heat-sealing layer 13 and a water-based antistatic slip coating 14. The second ultra-low temperature heat-sealing layer 13 is located on the inner side and adjacent to the core layer 11, while the water-based antistatic slip coating 14 is located on the outer side and forms the bottommost surface (slip surface / metal contact surface) of the BOPP ultra-low temperature heat-sealing cigarette film. This composite structure divides the heat-sealing function and the slip and antistatic function into functional zones on the lower surface. The second ultra-low temperature heat-sealing layer 13 is responsible for providing ultra-low temperature heat-sealing performance, while the water-based antistatic slip coating 14 is responsible for giving the surface a low coefficient of friction, good antistatic properties, and printability. The two layers are stacked and composite, each performing its own function, which can avoid the interference of the coating layer on the heat-sealing performance.

[0035] Specifically, in this embodiment 1, the heat-sealing initiation temperature of the first ultra-low temperature heat-sealing layer 12 is 83-85°C, and its raw materials, by mass fraction, include: 100 parts of propylene-ethylene-butene terpolymer random copolymer (brand name KS359), 10 parts of metallocene ultra-low melting point copolymer polypropylene, and 5 parts of SEBS with styrene content greater than 25%. (Styrene-Ethylene-Butylene-Styrene block copolymer) and 5 parts of anti-sticking masterbatch (brand name ABVT22SC).

[0036] Specifically, in this embodiment 1, the raw materials of the core layer 11 (intermediate layer) include, by mass parts: 100 parts homopolymer polypropylene (isotacticity of 97.8% to 98.5%), 10 parts hydrogenated petroleum resin, 1 part antioxidant (antioxidant 1010 + antioxidant 168 composite system, with a mass ratio of 1:1), and 1 part nucleating aid, wherein the nucleating aid is 1,3:2,4-di(3,4-dimethylbenzylmethylene)sorbitol.

[0037] Specifically, in this embodiment 1, the heat-sealing initiation temperature of the second ultra-low temperature heat-sealing layer 13 is 75-80°C, and its raw materials include, by mass parts: 100 parts of metallocene propylene-α-olefin ultra-low melting point copolymer polypropylene (melting point Tm is 80-84°C), 5 parts of SIS (Styrene-Isoprene-Styrene block copolymer, i.e., styrene-isoprene-styrene block copolymer) with a styrene content greater than 25%, and 20 parts of maleic anhydride grafted modified polypropylene viscous masterbatch (maleic anhydride grafting rate greater than 1.5%).

[0038] Specifically, in this embodiment 1, the dyn value of the surface of the water-based antistatic slip coating 14 is 54-58 dyn / cm, making it suitable for UV flexographic, gravure, and letterpress printing processes. The raw materials of the water-based antistatic slip coating 14, by weight, include: 100 parts antistatic coating liquid, 1.0 part nano-silica aqueous dispersion (50% solid content, average particle size 10-20 nm), 1.0 part polyether-modified silicone wetting agent, and 10 parts deionized water.

[0039] Furthermore, the total solids content of the antistatic coating liquid in Example 1 is approximately 15%, and its raw materials, by mass percentage, include: 25% waterborne polyurethane (solids content of 40%), 10% modified poly(3,4-ethylenedioxythiophene) (PEDOT, solids content of 1.5%), 1.0% waterborne carbodiimide crosslinking agent (brands selected from CX-300 and V-02), 0.5% nonionic low-foaming wetting agent, and 60% deionized water; wherein, the nonionic low-foaming wetting agent is ethoxylated acetylenic diol (2,4,7,9-tetramethyl-5-decyn-4,7-diol ethoxylate).

[0040] Please see Figure 2 , Figure 2 This is a schematic diagram of the online integrated preparation process of the single-sided online coated BOPP ultra-low temperature heat-sealing cigarette film provided in Example 1. Figure 2 As shown, the preparation method is carried out according to the following steps: Step (1), Raw material preparation and feeding: Prepare the raw materials for the first ultra-low temperature heat-sealing layer 12, the core layer 11, and the second ultra-low temperature heat-sealing layer 13 according to the formula; wherein, the raw material for the first ultra-low temperature heat-sealing layer 12 is mainly composed of ternary copolymer with added functional additives, the raw material for the core layer 11 is mainly composed of polypropylene with added functional additives, and the raw material for the second ultra-low temperature heat-sealing layer 13 is mainly composed of metallocene ultra-low melting point copolymer polypropylene with added functional additives; the three layers of raw materials are accurately metered by a metering device and then fed into their respective extruders in parallel by a conveying system; Step (2), multi-layer co-extrusion: After the three layers of raw materials are melted and plasticized in their respective extruders, they are co-extruded through a multi-layer co-extrusion die to form a three-layer composite melt (thick sheet) with a core layer 11 and an ultra-low temperature heat-sealing layer located on the upper and lower surfaces of the core layer 11. Step (3), casting: the three-layer composite melt is rapidly cooled and formed by cold rollers to obtain sandwich-shaped thick sheets; Step (4), first thickness measurement (thickness gauge 1): After the casting is completed and before entering the longitudinal drawing process, the thickness gauge 1 performs online thickness measurement on the thick sheet. The measurement data is fed back to the extrusion process in step (2) through the dotted line to form a closed-loop control of the extrusion thickness and adjust the extrusion process parameters in time to ensure uniform thickness of the thick sheet. Step (5), longitudinal stretching: After the thick sheet is preheated by the preheating roller, it enters the longitudinal stretching process and is stretched 5.5 times at 90°C to make the polypropylene molecular chains oriented in the longitudinal direction, giving the film good longitudinal strength and stiffness. Step (6), Online Corona Treatment / Coating (Core Process): After longitudinal stretching, the film is first subjected to online corona treatment to improve surface energy. Then, a water-based antistatic and slip coating 14 is applied online to the corona-treated surface using a micro-gravure coating method. The dry coating amount is 0.15 g / m². 2 This process integrates corona treatment and coating onto the production line between longitudinal and transverse stretching, which is the ILC online coating integrated process, eliminating the need for offline secondary rewinding; Step (7), transverse stretching: The coated film enters the tenter frame and is stretched 8.5 times at 160°C to make the molecular chains oriented in the transverse direction. At the same time, the water-based coating is gradually cured by segmented drying during the transverse stretching process, so as to achieve the simultaneous completion of coating curing and transverse stretching. Step (8), cooling and shaping: After the transverse stretching is completed, the film enters the cooling and shaping section for rapid cooling to eliminate the internal stress generated during the stretching process and stabilize the size and performance of the film; Step (9), second thickness measurement (thickness gauge 2): After cooling and shaping, the thickness gauge 2 performs a second online thickness test on the finished film to monitor the thickness uniformity of the final film, which serves as an important basis for product quality judgment. Step (10), edge trimming: The parts of the film with uneven thickness or irregular edges are trimmed to make the film width meet the product specifications. The trimmed edge material enters the recycling system. Step (11), Corona treatment: After the edge is cut, the film is subjected to surface corona treatment again to further improve the surface energy and dyne value, and improve the ink adhesion in the subsequent printing process; Step (12), winding: After the corona treatment is completed, the film is wound into a large roll by a winding machine, which facilitates the transfer of subsequent aging treatment and slitting processes; Step (13), aging treatment: The large roll of film after winding enters the aging treatment stage, and is left to mature at a certain temperature and time to fully release the internal stress of the film and stabilize its performance; Step (14), Slitting: After the aging process is completed, the large roll of film is slitting into small rolls that meet the customer's specifications by a slitting machine. The defective products generated during the slitting process are returned to the aging process in step (13) for reprocessing. Step (15), Packaging: The qualified small rolls of film are packaged for outer protection to prevent contamination or damage during transportation and storage; Step (16), Finished product: The packaged film is the final product, namely, the single-sided online coated BOPP ultra-low temperature heat-sealed cigarette film, which can be delivered for use; Step (17), edge material / waste piece recycling: The edge material and waste pieces generated in the edge cutting process of step (10) are collected and recycled through the right edge material and waste piece recycling channel and returned to the extrusion process of step (2) as recycled material to be re-feeded. After being mixed with the three layers of new material, they enter the extruder to form a closed loop of raw material recycling and reduce raw material consumption. Step (18), Waste film treatment: The unqualified waste film generated in the time-effect treatment step (13) and the slitting step (14) is collected into the waste film treatment line for centralized collection and disposal, so as to keep the production site clean and achieve standardized management of waste.

[0041] The performance parameters of the BOPP ultra-low temperature heat-sealing cigarette film prepared in Example 1 were tested and found to be as follows: the total thickness of the BOPP ultra-low temperature heat-sealing cigarette film prepared in Example 1 is 28 μm, the initial heat-sealing temperature of the upper and lower surfaces is 80℃ / 83℃, the heat-sealing strength of the upper and lower surfaces is 3.4 / 3.2 N / 15mm, the dynamic friction coefficient between the upper and lower film surfaces and the metal is 0.15 / 0.22, the M (longitudinal) / T (transverse) heat shrinkage rate under the condition of 120℃ for 5 min is 8.5% / 9.0%, and the surface resistivity is less than 10 Ω·cm. 8 Ω.

[0042] The BOPP ultra-low temperature heat-sealing cigarette film prepared in Example 1 can be applied to cigarette transparent paper packaging, high-speed automated packaging, and anti-counterfeiting packaging. In cigarette transparent paper packaging, the lower heat-sealing temperature can reduce the impact of high temperature on cigarette boxes and cigarettes, and the appropriate heat shrinkage rate makes the packaging tight, flat, and aesthetically pleasing. In high-speed automated packaging, the lower coefficient of friction and good antistatic properties facilitate smooth film feeding and reduce downtime, and the ultra-low temperature heat sealing can also adapt to higher linear speeds. In anti-counterfeiting packaging, the double-sided heat-sealing structure and functionalized coating surface can provide more space for anti-counterfeiting design.

[0043] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: (1) The present invention adopts an online integrated production process. Longitudinal stretching, single-sided corona treatment, single-sided coating, transverse stretching and coating curing are completed continuously on the same production line. Compared with offline coating, the secondary rewinding step can be eliminated, which helps to improve production efficiency, reduce energy consumption and reduce film surface scratches. (2) Both sides of the present invention can achieve ultra-low temperature heat sealing (heat sealing start temperature ≤90℃), which can reduce the heat sealing temperature by more than 20℃ compared with the existing medium and high temperature heat sealing cigarette film. This helps to reduce problems such as cigarette box deformation, film wrinkling, and heat sealing sticking during high-speed packaging. The heat sealing positioning is more accurate and the sealing appearance is better. The heat sealing strength of both sides is more uniform and can be adapted to double-sided heat sealing packaging, anti-counterfeiting packaging and high-speed automated cigarette packaging equipment. (3) The double-sided smoothness and anti-adhesion of the BOPP ultra-low temperature heat-sealing cigarette film of the present invention are relatively consistent, which helps to improve the stability of film running during high-speed operation and reduce jamming, deviation and sticking phenomena; the film has a high shrinkage rate, transparency and gloss, which helps to improve the flatness of the cigarette pack appearance. (4) The BOPP ultra-low temperature heat-sealing cigarette film of the present invention adopts a water-based coating system, which does not contain organic solvents, is more environmentally friendly, and meets the relevant food contact safety standards; (5) The BOPP ultra-low temperature heat-sealing cigarette film of the present invention has the rigidity and stiffness provided by the core layer, and at the same time has the supporting and protective function of the paper box and the heat-sealing packaging function of the transparent film. It can replace the two-layer structure of paper box plus outer transparent film in traditional cigarette packaging, and directly realize the paper box-free naked packaging of cigarettes. Compared with the traditional packaging method, it can save the material cost of outer packaging paper box and packaging process, and reduce the overall packaging cost.

[0044] It should be noted that all the above embodiments belong to the same inventive concept, and the descriptions of each embodiment have different focuses. Where the description in a particular embodiment is not detailed, please refer to the description in other embodiments.

[0045] The above embodiments merely illustrate implementation methods 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 single-sided online coated BOPP ultra-low temperature heat-sealing cigarette film, characterized in that, The BOPP ultra-low temperature heat-sealing film includes a core layer, a first ultra-low temperature heat-sealing layer on the upper surface of the core layer, and a second ultra-low temperature heat-sealing layer on the lower surface of the core layer. The lower surface of the second ultra-low temperature heat-sealing layer is also coated with a water-based antistatic slip coating. The heat-sealing initiation temperature of both the upper and lower surfaces of the BOPP ultra-low temperature heat-sealing film is ≤90℃.

2. The BOPP ultra-low temperature heat-sealing cigarette film according to claim 1, characterized in that, The total thickness of the BOPP ultra-low temperature heat-sealing cigarette film is 16–33 μm, the heat-sealing strength of both its upper and lower surfaces is ≥2.5 N / 15 mm, the coefficient of friction is 0.10–0.25, the heat shrinkage rate at 120℃ for 5 min is 6.5%–10.5%, and the surface resistivity is less than 10 Ω·cm. 8 Ω.

3. The BOPP ultra-low temperature heat-sealing cigarette film according to claim 1, characterized in that, The first ultra-low temperature heat-sealing layer has a heat-sealing initiation temperature of 83–85°C, and its raw materials, by mass parts, include: 100 parts ternary copolymer, 10–15 parts metallocene ultra-low melting point copolymer, 5–10 parts thermoplastic elastomer, and 3–5 parts anti-stick masterbatch; and / or, The raw materials for the core layer, by weight, include: 100 parts polypropylene main material, 10-15 parts hydrogenated petroleum resin, 0-5 parts antioxidant, and 1-2 parts nucleating agent; and / or, The heat-sealing initiation temperature of the second ultra-low temperature heat-sealing layer is 75-80°C, and its raw materials include, by mass parts: 100 parts of metallocene ultra-low melting point copolymer, 5-10 parts of thermoplastic elastomer and 20-30 parts of viscous masterbatch.

4. The BOPP ultra-low temperature heat-sealing cigarette film according to claim 1, characterized in that, The surface of the water-based antistatic slip coating has a dyn value of 54–58 dyn / cm. The raw materials of the water-based antistatic slip coating, by weight, include: 100 parts antistatic coating liquid, 0.3–1.0 parts nano-anti-stick slip agent, 0.5–1.0 parts wetting agent, and 5–10 parts deionized water; and / or, The raw materials of the antistatic coating liquid, by mass percentage, include: 20-25% waterborne polyurethane, 8-15% conductive organic matter, 0.8-1.2% waterborne carbodiimide crosslinking agent, 0.1-0.5% nonionic low-foaming wetting agent, and 55-65% deionized water.

5. A method for preparing a BOPP ultra-low temperature heat-sealing cigarette film as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S10, the first heat-sealing layer material, the core layer material and the second heat-sealing material are added to their respective extruders, melted and plasticized at 210-280°C, and then co-extruded through a multi-layer co-extrusion die and cooled to form a thick sheet; S20, the thick sheet is preheated and then longitudinally stretched to obtain a longitudinally stretched thick sheet; S30, perform online corona treatment on any surface of the longitudinally stretched thick sheet, and then apply an online water-based antistatic slip coating to the corona-treated surface to obtain a coated sheet; S40, the coated sheet is subjected to online segmented drying and curing treatment while being stretched laterally, so that the coating curing and lateral stretching are completed simultaneously to obtain a BOPP base film. S50, the BOPP base film is sequentially subjected to cooling and shaping, thickness measurement, edge trimming, corona treatment, winding, slitting and packaging to obtain the BOPP ultra-low temperature heat-sealing cigarette film with single-sided online coating.

6. The preparation method according to claim 5, characterized in that, In step S10, the thick sheet includes the core layer, the first ultra-low temperature heat-sealing layer located on the upper surface of the core layer, and the second ultra-low temperature heat-sealing layer located on the lower surface of the core layer.

7. The preparation method according to claim 5, characterized in that, In step S20, the thick sheet is preheated by a preheating roller and then stretched longitudinally by 3.5 to 6.0 times at 90–120°C; and / or, in step S30, the online coating is performed using a micro-gravure reverse coating method, with a dry coating weight of 0.1–0.3 g / m². 2 .

8. The preparation method according to claim 5, characterized in that, In step S40, the coated sheet is fed into a tenter frame and stretched 8 to 10 times laterally at 160 to 185°C; the online segmented drying and curing process is divided into three segments, with segmented drying temperatures of 140 to 180°C, 150 to 165°C, and 155 to 175°C respectively.

9. The preparation method according to claim 5, characterized in that, In step S50, the edge material and waste film generated from the edge trimming, winding, and slitting processes are all recycled and returned to step S10 for the preparation of the thick sheet.

10. The application of a BOPP ultra-low temperature heat-sealing cigarette film as described in any one of claims 1 to 4, or a BOPP ultra-low temperature heat-sealing cigarette film prepared by the preparation method described in any one of claims 5 to 9, in paperless cigarette packaging, wherein the BOPP ultra-low temperature heat-sealing cigarette film simultaneously possesses the supporting and protective function of a paper box and the heat-sealing packaging function of a transparent film.

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