Polyolefin heat-sealable film, method of manufacture

Abstract

The present application relates to a kind of polyolefin heat-seal film and its preparation method.The heat-seal film includes sequentially stacked in the direction away from content and the raw material glass transition temperature gradient is not less than 10 ℃ heat-seal film, transition film and connecting film.Heat-seal film is made of the ethylene-based polyolefin elastomer of specific density and melt flow rate and plastic body, preferably adding end silane group end polyethylene.Preparation method uses multiple extruders co-extrusion, reverse film blowing process molding, and the connecting layer is carried out corona treatment and temperature control winding.The structure design cooperates specific raw material and process, realizes the low-temperature heat-seal performance of sealing temperature as low as 70-80 ℃, simultaneously, after 7 days ripening at 50 ℃, the unwinding force ratio is not greater than 1.5, effectively solve the problem of low-temperature heat-seal strength deficiency and film layer adhesion, with good mechanical strength and thermal stability.

Description

Technical Field

[0001] This invention relates to the field of composite film technology, specifically to a polyolefin heat-sealing film and a method for preparing the heat-sealing film. Background Technology

[0002] Heat-sealable film is a functional film that achieves material bonding through heating and pressurization. It typically uses polyolefins as the main substrate and is widely used in flexible packaging in the food, pharmaceutical, and daily chemical industries. Its core function lies in forming a high-strength, high-sealing bond layer through heat-activated properties, directly affecting packaging efficiency, sealing reliability, and the preservation of contents. In the current packaging industry, low-temperature heat-sealing technology (heat-sealing temperature ≤100℃) is gradually becoming the mainstream development direction. This not only reduces energy consumption and improves production efficiency but also better meets the packaging needs of heat-sensitive contents (such as frozen foods and biological agents), while reducing high-temperature damage to the substrate, lowering production costs, and extending equipment lifespan.

[0003] Traditional polyolefin films exhibit poor molecular chain mobility at low temperatures, resulting in insufficient heat-sealing strength and a tendency to break during transportation or storage, such as the cracking of seals in frozen food packaging. Furthermore, while existing modification technologies (such as adding EVA) can improve low-temperature heat-sealing performance, they often result in a narrowing of the heat-sealing window, meaning a reduction in the difference between the initial heat-sealing temperature and the adhesion temperature, which affects the process stability of high-speed packaging machines.

[0004] In view of this, there is an urgent need to improve existing polyolefin heat-sealing films to ensure low-temperature heat-sealing performance while improving mechanical strength and thermal stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art, reduce the heat sealing temperature of the heat-sealing film, and alleviate the adhesion problem.

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

[0007] In a first aspect, the present invention provides a polyolefin heat-sealing film, comprising a heat-sealing film, a transition film, and a connecting film, which are sequentially stacked along the direction away from the contents and whose glass transition temperatures gradually increase, wherein the difference in glass transition temperatures between adjacent film layers is not less than 10°C; the heat-sealing film comprises a vinyl polyolefin elastomer and a vinyl polyolefin plastic body. The vinyl polyolefin elastomer is copolymerized with polyethylene from at least two α-polyolefins with different and independent glass transition temperatures, each ranging from -60°C to -10°C, and the vinyl polyolefin elastomer has a density of 0.855 g / cm³. 3 ~0.920g / cm 3Its melt mass flow rate at 190℃ and 2.16kg load is 0.8g / 10min~8.0g / 10min; The vinyl polyolefin elastomer is copolymerized with polyethylene from at least two α-polyolefins with different and independent glass transition temperatures ranging from -50°C to -20°C, and the density of the vinyl polyolefin elastomer is 0.875 g / cm³. 3 ~0.905g / cm 3 Its melt mass flow rate at 190℃ and 2.16kg load is 0.8g / 10min~12.0g / 10min.

[0008] As a preferred technical solution, the α-polyolefin includes at least one selected from 1-hexene, 1-octene, and 4-methyl-1-pentene; and / or The polyethylene is selected from at least two of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and metallocene polyethylene; and / or The polyethylene accounts for 20% to 60% of the mass percentage of the vinyl polyolefin elastomer; the polyethylene accounts for 30% to 70% of the mass percentage of the vinyl polyolefin plastisol.

[0009] As a preferred technical solution, in the heat-sealing film, The vinyl polyolefin elastomer is copolymerized from polyethylene and α-polyolefin via free radical polymerization, ionic polymerization, or coordination polymerization, and the weight-average molecular weight of the vinyl polyolefin elastomer is from 100,000 g / mol to 180,000 g / mol; and / or The vinyl polyolefin elastomer is copolymerized from polyethylene and α-polyolefin through any one of free radical polymerization, ionic polymerization, or coordination polymerization, and the weight-average molecular weight of the vinyl polyolefin elastomer is from 120,000 g / mol to 220,000 g / mol.

[0010] As a preferred technical solution, the transition membrane comprises at least one of ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, polyolefin elastomer, and polyolefin plasmon; and / or The thickness of the transition film is 1.2-3.0 times the thickness of the heat-sealing layer; and / or The melt mass flow rate of the transition film at 190°C and 2.16 kg load is 2.0-8.0 g / 10 min.

[0011] As a preferred technical solution, the side of the connecting film away from the heat-sealing film is corona treated to achieve a surface tension of 35-45 mN / m; and / or The raw material for the connecting membrane includes at least one of linear low-density polyethylene, low-density polyethylene, and metallocene polyethylene; and / or The melt flow rate of the raw material for the connecting membrane at 190°C and 2.16 kg load is 0.5~3.0 g / 10 min.

[0012] As a preferred technical solution, the heat-sealing film, by weight, comprises... Vinyl polyolefin elastomer, 10-40 parts; Vinyl polyolefin plastide, 50-80 parts; Polyethylene, 8-25 parts; 3-8 parts of silane-terminated polyethylene; Processing aids, 2-5 parts; The silane group content of the silane-terminated polyolefin is 0.5-20 mmol / 100g.

[0013] As a preferred technical solution, the end groups of the silyl-terminated polyethylene include any one of trimethoxysilyl, triethoxysilyl, and methyldimethoxysilyl.

[0014] As a preferred technical solution, the initial sealing temperature of the polyolefin heat-sealing film is 75℃~80℃; and / or After the polyolefin heat-sealing film is cured at 50°C and 0.28 MPa for 7 days, the ratio of the unwinding force to the initial unwinding force is no greater than 1.5.

[0015] A method for preparing a polyolefin heat-sealing film includes the following steps: S01. Raw materials for the heat-sealing layer, transition layer and connecting layer are fed into multiple extruders, melted and plasticized and then conveyed to the co-extrusion die. After the melt is extruded from the die, it is blown into shape using a reverse blown film process so that the heat-sealing layer is located on the outside of the film bubble, forming a cylindrical film bubble. S02. The tubular membrane bubble is cooled and then flattened and pulled by traction rollers to form a sheet-like film. S03. Perform corona treatment on one side of the sheet film where the connecting layer is located; after corona treatment, allow the film to pass through at least two cooling rollers for cooling. S04. In an isolated environment with a temperature of 20℃~25℃, wind up the cooled film. S05. Depending on the film thickness and temperature, the film is rolled up or suspended for packaging.

[0016] As a preferred technical solution In S01, the melting and plasticizing temperature is 150~170℃, and the die head temperature is 160~190℃; and / or In S02, the cooling adopts a dual-air ring and / or membrane bubble internal cooling system, and the temperature of the cooling medium is 20℃~25℃; and / or In S03, when the film reaches the traction position, the temperature of the film is controlled at 50~60℃; and / or In S03, the corona treatment causes the surface tension of the bonding layer to reach 38~42 mN / m; and / or In S03, the surface temperature of the cooling roller is 16~25℃, ensuring that the film temperature after cooling does not exceed 25℃; and / or In S04, the temperature difference between the isolation environment and the surface temperature of the cooling roller is less than 5°C; and / or In S05, when the film temperature is not lower than 30°C, the rule for rewinding is as follows: When the film thickness is ≤50μm, the rewinding should be completed within 24 hours; When the film thickness is >50μm, the rewinding is completed within 48 hours; When the film is placed horizontally, it is wrapped with an aluminum foil structure on the outside and is suspended in the packaging.

[0017] Preferably, the aluminum foil structure includes an aluminum-plated film and pearl cotton used in conjunction with it, or aluminum is directly plated onto the pearl cotton.

[0018] The advantages and beneficial effects of this invention are as follows: The heat-sealing layer adopts a composite system of vinyl polyolefin elastomer and plasmon, utilizing the differences between the two materials in terms of glass transition temperature and crystallization behavior: the elastomer provides segmental mobility and resilience at low temperatures, while the plasmon contributes to the melt adhesion strength during the heat-sealing process. This heat-sealing layer, together with the transition layer and connecting layer designed based on the glass transition temperature gradient, constitutes a film with progressively transitioning cohesive strength and interfacial properties, preferably combined with reverse blown film and built-in corona treatment. This avoids performance degradation of the heat-sealing layer due to secondary heating, allowing the film to quickly cross the viscoelastic transition zone after molding and maintain a low temperature environment, inhibiting secondary entanglement and crystallization of molecular chains, thereby exhibiting good low-temperature heat-sealing properties and anti-blocking properties.

[0019] Furthermore, by introducing silane-terminated polyolefins, the low surface energy end groups of which can be oriented to form a stable isolation structure on the film surface, the present invention reduces the adhesion work on the material surface, thereby reducing the heat sealing initiation temperature without weakening the bulk strength; at the same time, its chemical bonding characteristics avoid the migration and precipitation of traditional slip agents, giving the film durable and stable anti-blocking properties. Detailed Implementation

[0020] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below. 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.

[0021] 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.

[0022] 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.

[0023] This invention provides a polyolefin heat-sealing film, comprising a heat-sealing film, a transition film, and a connecting film stacked sequentially along the direction away from the contents, wherein the difference in glass transition temperature between adjacent film materials is not less than 10°C; the heat-sealing film comprises a vinyl polyolefin elastomer and a vinyl polyolefin plastic.

[0024] Vinyl polyolefin elastomers are copolymerized with polyethylene from at least two α-polyolefins with different and independent glass transition temperatures ranging from -60°C to -10°C, and have a density of 0.855 g / cm³. 3 Up to 0.920 g / cm 3 The melt mass flow rate at 190℃ and 2.16kg load is 0.8g / 10min to 8.0g / 10min; the vinyl polyolefin plastide is copolymerized with polyethylene from at least two α-polyolefins with different and independent glass transition temperatures ranging from -50℃ to -20℃, and has a density of 0.875g / cm³. 3 Up to 0.905 g / cm 3 The melt mass flow rate (MFR) at 190℃ and 2.16kg load ranged from 0.8g / 10min to 12.0g / 10min.

[0025] The aforementioned heat-sealable film exhibits a layered structure that gradually hardens from the heat-sealable layer to the connecting layer. The heat-sealable layer uses vinyl polyolefin elastomer and plasmon as the matrix, both of which possess excellent chain segment mobility at low temperatures, thus reducing the heat-seal initiation temperature. The transition layer and connecting layer sequentially increase the glass transition temperature, forming a transition in cohesive strength and interfacial properties. This disperses stress during the heat-sealable process, preventing interlayer delamination or inadequate heat sealing due to excessive temperature gradients. The rheological matching of each layer during the co-extrusion blown film process is controlled by the density and melt flow rate range of the heat-sealable layer material.

[0026] If the density of the vinyl polyolefin elastomer is too low, the material crystallinity will be too low, resulting in insufficient mechanical strength and easy sealing deformation after heat sealing. If the density is too high, the chain segment mobility will decrease, leading to deterioration of low-temperature heat sealing performance. Its MFR is 0.8-8.0 g / 10min. Too low a density will lead to extrusion difficulties and poor film uniformity, while too high a density will result in insufficient melt strength and poor film bubble stability during blown film production. This elastomer is copolymerized with polyethylene from at least two α-polyolefins with different Tg values. Its multi-component Tg design gives it a wide and gentle glass transition region in the range of -60℃ to -10℃, thus maintaining sufficient chain segment mobility during low-temperature heat sealing and providing good thermal adhesion and resilience.

[0027] The density of the vinyl polyolefin plastomer is slightly higher than that of the elastomer, providing a certain degree of rigidity to the heat-sealing layer and preventing seal collapse due to excessive softening during heat sealing. Its melt flow rate (MFR) is 0.8-12.0 g / 10 min, a wide range allowing for adjustment of its rheological behavior according to the co-extrusion process, resulting in good compatibility with the elastomer. This plastomer also utilizes a multi-α-polyolefin copolymer, providing certain crystallization and melting behavior within the -50°C to -20°C range, forming a soft-hard combination with the elastomer: the elastomer is responsible for low-temperature start-up and deformation recovery, while the plastomer primarily contributes to melt bond strength and dimensional stability after heat sealing.

[0028] In some embodiments, to further regulate the composition and properties of the heat-sealing layer, the α-polyolefin includes at least one of 1-hexene, 1-octene, and 4-methyl-1-pentene; the polyethylene is selected from at least two of low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and metallocene polyethylene (mPE); the polyethylene accounts for 20%-60% of its mass percentage in the vinyl polyolefin elastomer and 30%-70% of its mass percentage in the vinyl polyolefin plastome.

[0029] The type and content of α-polyolefins directly affect the branching degree, crystallization behavior, and Tg distribution of the copolymer. The introduction of α-olefins such as 1-hexene and 1-octene can effectively reduce the regularity of the polyethylene chain, inhibit crystallization, lower Tg, and improve low-temperature toughness. The polyethylene component provides the necessary crystalline framework and melt strength. If the polyethylene content in the elastomer is less than 20%, the copolymer is too "soft" and lacks sufficient strength after heat sealing; if it is higher than 60%, the Tg increases, and the low-temperature heat-sealing performance decreases. In the plasmon, appropriately increasing the polyethylene content can enhance the overall rigidity and heat resistance of the heat-sealing layer while maintaining certain low-temperature performance.

[0030] In some embodiments, the weight-average molecular weight of the vinyl polyolefin elastomer is from 100,000 g / mol to 180,000 g / mol; and the weight-average molecular weight of the vinyl polyolefin plastide is from 120,000 g / mol to 220,000 g / mol.

[0031] Molecular weight directly affects melt viscosity, tensile strength, and heat-sealing performance. When the molecular weight of an elastomer is too low, the melt strength is poor, blown film is prone to bubble breakage, and the cohesion of the heat-sealing layer is insufficient. When the molecular weight is too high, the fluidity is poor, and interlayer interface instability is prone to occur during co-extrusion. The molecular weight of a plasmon is slightly higher than that of an elastomer, which can form a certain degree of cross-linking in the blend system, improving the melt elasticity and thermal stability of the heat-sealing layer.

[0032] In some embodiments, in order to construct an effective stress buffer and performance transition layer, the transition membrane comprises at least one of ethylene-vinyl acetate copolymer (EVA), ethylene-acrylate copolymer, polyolefin elastomer, and polyolefin plasmon; the thickness of the transition membrane is 1.2-3.0 times the thickness of the heat-sealing film; and the melt mass flow rate of the transition membrane at 190°C and 2.16 kg load is 2.0-8.0 g / 10 min.

[0033] The transition layer, acting as a bridge between the heat-sealing layer and the connecting layer, serves to mitigate sudden modulus changes caused by glass transition temperature gradients and prevent interlayer delamination due to stress concentration. Its thickness is 1.2-3.0 times that of the heat-sealing layer; too thin and the buffering effect is limited, too thick and it affects the overall film stiffness and cost. The melt flow rate (MFR) is controlled at 2.0-8.0 g / 10 min to ensure its rheological properties fall between those of the heat-sealing layer and the connecting layer, facilitating interlayer melt fusion and interfacial bonding during co-extrusion. In terms of material selection, polar polymers such as EVA can moderately improve adhesion to the connecting layer, while polyolefin materials ensure good compatibility with the heat-sealing layer.

[0034] In some embodiments, the transition layer may employ a multi-layered gradient structure, such as a blend with gradually decreasing EVA content from the inside out, or co-extruded layer by layer polyolefin elastomers with different MFRs, to achieve a smoother transition of glass transition temperature and modulus, and further optimize impact resistance and heat-sealing reliability.

[0035] In some embodiments, to ensure a firm bond between the film and the external substrate and to control adhesion during the winding process, the side of the connecting film away from the heat-sealing film is corona treated to a surface tension of 35-45 mN / m; the raw material of the connecting film includes at least one of linear low-density polyethylene, low-density polyethylene, and metallocene polyethylene; the melt mass flow rate of the raw material of the connecting film at 190°C and 2.16 kg load is 0.5-0.8 g / 10 min.

[0036] The bonding layer is the interface between the film and the external substrate, requiring good mechanical strength, thermal stability, and modifiability. Using LLDPE, LDPE, or mPE, their high crystallinity and molecular weight distribution provide excellent tensile strength and puncture resistance. A low melt flow rate (MFR) of 0.5-0.8 g / 10 min ensures high melt strength and blown film stability, while low flowability helps maintain surface morphology stability during corona treatment. Corona treatment is a step to increase surface tension; controlling it at 35-45 mN / m improves the printability and lamination strength of the bonding layer. If the surface tension is below 35 mN / m, ink or adhesive adhesion will be insufficient; if it is above 45 mN / m, over-treatment may lead to oxidative degradation of the film surface, producing low-molecular-weight substances, which will exacerbate winding adhesion.

[0037] It should be noted that corona treatment can be performed using an internal membrane bubble corona treatment device. This device places electrodes inside the membrane bubble after blown film formation and before the bubble is flattened, and performs corona treatment on the inner surface of the bonding layer. Compared to traditional external corona treatment, internal treatment avoids secondary heating of the heat-sealing layer and prevents a decrease in low-temperature heat-sealing performance due to high-temperature oxidation or molecular chain reconstruction.

[0038] Specifically, the built-in membrane bubble corona discharge device integrates the corona discharge unit directly inside the membrane bubble, performing online treatment on the inner surface of the bonding layer while the membrane is still in its inflated cylindrical shape. The device typically consists of a high-voltage power supply, a discharge electrode array, an insulating support frame, a gas equalization device, and an online monitoring unit. The electrodes are made of corrosion-resistant, highly conductive alloy materials (such as stainless steel or aluminum-magnesium alloy) in strip or mesh form, arranged along the circumferential direction inside the membrane bubble, and fixed to specific positions in the expansion section by insulating ceramic or polymer supports. The high-voltage power supply provides high-frequency, high-voltage current, creating a strong electric field between the electrodes and the inner surface of the membrane bubble, which serves as the ground electrode. This ionizes the air, generating corona discharge, which then oxidizes, etches, and grafts polar groups onto the bonding layer surface.

[0039] Built-in corona discharge equipment is typically placed in the bubble expansion and stabilization section during the blown film traction process, i.e., the area where the bubble has basically completed its inflation, has a constant diameter, and is in a relatively stable position. This section is located above the cooling air ring and before the traction rollers. The internal temperature of the bubble has dropped from 160-190℃ at the die exit to 50-70℃, and the film surface has been initially cured but still retains moderate thermoplasticity.

[0040] In some embodiments, the heat-sealing film comprises, by weight, 10-40 parts of vinyl polyolefin elastomer; 50-80 parts of vinyl polyolefin plastomer; 8-25 parts of polyethylene; 3-8 parts of silane-terminated polyethylene; and 2-5 parts of processing aids; wherein the silane group content of the silane-terminated polyethylene is 0.5-20 mmol / 100g.

[0041] The heat-sealable film uses a vinyl polyolefin elastomer and plasmon to form the main framework, with polyethylene as a crystallization regulator and compatibilizer. The silane groups at the ends of the polyethylene molecules undergo hydrolysis and condensation during processing and post-curing, forming a micro-crosslinked Si-O-Si network inside and on the surface of the film. Firstly, these act as internal lubrication points, migrating to the interface during heat sealing and reducing surface adhesion work, thus allowing the initial sealing temperature to be as low as 90-110℃. Secondly, its chemical bonding properties prevent the migration and precipitation of traditional slip agents.

[0042] In some conventional implementations, maleic anhydride-grafted polyolefin (MAH-g-PO) is sometimes used as a polar modifier to improve the surface properties of polyolefins. However, although MAH-g-PO can improve adhesion to polar materials, its anhydride groups may further react or hydrolyze during high-temperature processing or storage, producing polar groups such as carboxylic acids. This may increase polar interactions on the film surface, exacerbating adhesion problems between film layers in high-temperature and high-humidity environments, and contributing little to reducing the opening temperature.

[0043] Processing aids may include antioxidants, slip agents, antistatic agents, etc., with the total number controlled at 2-5 parts to avoid interfering with the main properties.

[0044] In some embodiments, in order to define the structural features of silyl-terminated polyethylene, the end groups of silyl-terminated polyethylene include any one of trimethoxysilyl, triethoxysilyl, and methyldimethoxysilyl.

[0045] Silyl groups with different alkoxy structures exhibit varying hydrolytic reactivity and steric hindrance. Trimethoxysilyl groups show the highest reactivity, facilitating rapid formation of a surface isolation layer; methyldimethoxysilyl groups, due to their non-reactive methyl group, allow for adjustment of surface energy, enabling finer control of adhesion. The silyl group content should be 0.5-20 mmol / 100g; too low a content results in insignificant modification effects, while too high a content may lead to excessive cross-linking, affecting the film's flexibility.

[0046] The polyolefin heat-sealing film shown in this invention has an initial sealing temperature of 75℃~80℃; after the polyolefin heat-sealing film is cured at 50℃ and 0.28MPa pressure for 7 days, the ratio of the unwinding force to the initial unwinding force is not greater than 1.5.

[0047] "Sealing temperature" refers to the lowest temperature at which the film interface begins to effectively bond under the action of the heat sealer. This invention successfully reduces the sealing temperature to the 75℃~80℃ range, far lower than conventional LDPE / LLDPE heat-sealing films (typically >120℃), making it particularly suitable for packaging heat-sensitive frozen foods, chocolate, and biological agents. "Unwinding force ratio" is one of the indicators for evaluating anti-blocking properties. A ratio of no more than 1.5 indicates that the film can still easily unwind after high-temperature and pressurized storage, with no risk of adhesion failure, meeting the requirements of high-speed automatic packaging machines for film roll stability.

[0048] This invention also provides a method for preparing a polyolefin heat-sealing film, comprising the following steps: S01. Raw materials for the heat-sealing layer, transition layer and connecting layer are fed into multiple extruders, melted and plasticized and then conveyed to the co-extrusion die. After the melt is extruded from the die, it is blown into shape using a reverse blown film process so that the heat-sealing layer is located on the outside of the bubble, forming a cylindrical bubble. S02. Cool the tubular film bubble, and then flatten and pull it through the traction clamping roller to form a sheet film; S03. Perform corona treatment on one side of the sheet film where the connecting layer is located; after corona treatment, allow the film to pass through at least two cooling rollers for cooling. S04. In an isolated environment with a temperature of 20℃-25℃, wind up the cooled film; S05. Depending on the film thickness and temperature, the film is rolled up or suspended for packaging.

[0049] In step S01, multiple extruders are used for co-extrusion to ensure that each layer of raw material is plasticized independently. The melt plasticizing temperature is controlled at 150-170℃ to ensure that the components are fully melted and mixed, while avoiding excessive thermal degradation of the polyethylene chains. The die temperature is 160-190℃, slightly higher than the plasticizing temperature, to ensure consistent melt flow within the die and clear, smooth interlayer interfaces. In the reverse blown film process (heat-sealing layer facing outwards), the heat-sealing layer first contacts the cooling air ring during the blowing process and is rapidly cooled and shaped. The residence time of its molecular chains at high temperatures is shortened, inhibiting molecular chain reconstruction, increased crystallinity, or additive migration that may occur due to secondary heating, thereby better maintaining its low-temperature heat-sealing activity. At the same time, the connecting layer is located inside the film bubble and is less affected by the cooling air, with a relatively higher temperature, which is beneficial for the surface activation reaction during subsequent corona treatment.

[0050] In some embodiments, a co-extrusion structure with three or more layers can be used, such as a five-layer co-extrusion die, wherein a thin functional layer (such as a thin layer containing a higher proportion of terminal silane components) can be added between the heat-sealing layer and the transition layer to further enhance the anti-blocking properties of the heat-sealing interface.

[0051] In step S02, the cooling system employs a dual-air ring combined with internal membrane bubble cooling (IBC). The dual air rings provide gradient cooling to the outer surface of the membrane bubble (heat-sealing layer). The outer air ring has a higher air velocity, achieving rapid cooling and shaping, and locking the amorphous structure of the heat-sealing layer; the inner air ring has a lower air velocity, achieving slow cooling and reducing internal stress. The IBC system cools the connecting layer from inside the membrane bubble, improving overall cooling efficiency, stabilizing the membrane bubble morphology, and reducing the crystallization rate, which is beneficial for obtaining a more uniform crystal size distribution.

[0052] In step S03, corona treatment is performed after the film is flattened, targeting the outer surface of the bonding layer. The corona power and processing speed must be matched to achieve the optimal surface tension range of 38-42 mN / m. After treatment, the film immediately passes through at least two cooling rollers, with the roller surface temperature controlled at 16-25°C, rapidly reducing the film temperature to below 25°C. This reduces or even eliminates the reactivity of the surface free radicals activated by corona treatment, preventing molecular chain migration and recombination or reaction with impurities in the air at high temperatures. This stabilizes the treatment effect and also helps suppress the initial formation of film adhesion caused by residual heat.

[0053] In step S04, winding is carried out in an isolated environment at 20-25°C, which is usually maintained by an air conditioning system, and the temperature difference between the film and the surface of the cooling roller is less than 5°C. The constant temperature and low humidity isolated environment can prevent the film from loosening or wrinkling due to thermal expansion and contraction caused by ambient temperature fluctuations, and can also avoid moisture adsorption affecting the corona treatment effect.

[0054] When the center temperature of the film roll (film temperature) remains above 30°C after winding, it indicates significant internal heat accumulation, necessitating rewinding to release heat and internal stress. For film thicknesses ≤50μm, heat dissipation is faster, requiring rewinding within 24 hours; for thicknesses >50μm, heat dissipation is slower, requiring rewinding within 48 hours. For film rolls requiring horizontal placement or long-distance transport, suspended packaging is used. This involves wrapping the film roll with aluminum foil composite material and then suspending it inside the packaging box, preventing direct contact with the box bottom. The aluminum foil reflects external radiant heat, and the suspension avoids localized pressure concentration at the bottom due to long-term pressure, preventing the risk of adhesion caused by heat and pressure during storage and transportation.

[0055] "Aluminum foil structure" includes, but is not limited to, packaging made of aluminum foil, aluminized film, etc., which is used to reflect light to avoid improper activation of the heat seal layer caused by ambient light or temperature exposure, and to reduce adhesion problems.

[0056] When the film reaches the main traction position, the temperature varies between 50-60℃ depending on the season. Since the Vicat point of the particles in the raw materials is below 50℃, and the accumulated heat of the main traction steel roller eventually reaches the same temperature as the film, cooling water is used to prevent the film from sticking to the main traction steel roller. If the film is laid horizontally, the bottom of the film will be subjected to both weight pressure and heat during transportation, causing it to continue to stick. Therefore, an aluminized film is wrapped around the surface of the roll to reflect heat, and the suspended packaging prevents localized pressure on the film.

[0057] The present invention will be further explained and illustrated below with reference to specific embodiments.

[0058] Example 1: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw materials are vinyl polyolefin elastomer and vinyl polyolefin plasmon, the transition layer raw material is EVA, and the connecting layer raw material is LLDPE. After melting and plasticizing at 155°C, the materials are conveyed to the co-extrusion die, with the die temperature set at 165°C. After the melt is extruded from the die, it is blown into shape using a reverse blown film process, so that the heat-sealing layer is located on the outside of the bubble, forming a cylindrical bubble.

[0059] S02. The cylindrical film bubble is cooled using a double air ring system at a cooling medium temperature of 22°C. Then, it is flattened and drawn by traction rollers to form a sheet-like film.

[0060] S03. The side containing the bonding layer in the sheet film is subjected to corona treatment to achieve a surface tension of 40 mN / m. After corona treatment, the film is cooled sequentially by two cooling rollers with a roller surface temperature of 20°C, reducing the film temperature to 24°C.

[0061] S04. In an isolated environment at 22°C, wind up the cooled film. S05. The film temperature after winding is measured to be 28°C, and the film thickness is 45μm. According to the rules, rewinding should be completed within 20 hours.

[0062] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 75°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.3.

[0063] Example 2: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw materials are vinyl polyolefin elastomer and vinyl polyolefin plasmon, wherein the elastomer has a density of 0.865 g / cm³. 3 The MFR is 2.0 g / 10 min, and the density of the plastisol is 0.885 g / cm³. 3 The MFR is 5.0 g / 10min. The transition layer material is a polyolefin plasmon, and the connecting layer material is metallocene polyethylene. After being melt-plasticized at 165°C, it is conveyed to a co-extrusion die, with the die temperature set at 185°C. After the melt is extruded from the die, it is blown into shape using a reverse blown film process.

[0064] S02. A dual-air ring and internal cooling system are used to cool the cylindrical membrane bubble, with a cooling medium temperature of 24℃. The bubble is then drawn and flattened to form a sheet-like film, at which point the film temperature is 55℃.

[0065] S03. The side of the sheet film containing the connecting layer is subjected to corona treatment to achieve a surface tension of 39 mN / m. The film is then cooled sequentially by two cooling rollers with a roller surface temperature of 18°C.

[0066] S04. Winding is performed in an isolated environment at 24°C, with a temperature difference of 6°C between the ambient temperature and the cooling roller surface. S05. The film temperature after winding is measured to be 32°C, and the film thickness is 60μm. According to regulations, rewinding is completed within 40 hours, followed by suspension packaging.

[0067] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 75°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.4.

[0068] Example 3: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. In the heat-sealing layer raw material, the density of the vinyl polyolefin elastomer is 0.915 g / cm³. 3 The MFR is 7.5 g / 10min; the density of the vinyl polyolefin plastide is 0.900 g / cm³. 3The MFR is 10.0 g / 10min. The transition layer material is ethylene-acrylate copolymer. The connecting layer material is LDPE. After melt plasticizing at 170℃, it is conveyed to the co-extrusion die, and the die temperature is set to 190℃. Reverse blown film process is used for molding.

[0069] S02. Dual-air ring cooling is used, and the cooling medium temperature is 20℃. The film is drawn and flattened to form a sheet-like film.

[0070] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 42 mN / m. After corona treatment, the film is cooled sequentially by two cooling rollers with a roller surface temperature of 22°C and a film temperature of 23°C after cooling.

[0071] S04. Rewind in an isolated environment at 20°C. S05. The film temperature after rewinding is measured to be 29°C, and the film thickness is 38μm. Rewinding is completed within 18 hours.

[0072] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 100°C. After curing for 7 days at 50°C and 0.28 MPa pressure, the ratio of unwinding force to initial unwinding force is 1.2.

[0073] Example 4: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. In the heat-sealing layer, the vinyl polyolefin elastomer is copolymerized from 1-hexene and 1-octene with PE, with PE accounting for 25% by mass; the vinyl polyolefin plastomer is copolymerized from 1-octene with PE, with PE accounting for 40% by mass. The transition layer is made of EVA, and the connecting layer is a mixture of LLDPE and metallocene polyethylene. The materials are melt-plasticized at 160°C, with a die temperature of 175°C, using a reverse blown film process.

[0074] S02. Dual-air ring cooling is used, and the cooling medium temperature is 23℃. The film is drawn and flattened to form a sheet-like film, at which point the film temperature is 58℃.

[0075] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 38 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 17℃.

[0076] S04. Rewind in an isolated environment at a temperature of 21°C. S05. The film thickness is 55μm, the film temperature after rewinding is 31°C, and rewinding is completed within 44 hours.

[0077] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 80°C. After curing at 50°C and 0.28 MPa pressure for 7 days, the ratio of unwinding force to initial unwinding force is 1.35.

[0078] Example 5: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw material has a vinyl polyolefin elastomer with a weight-average molecular weight of 120,000 g / mol and a plastic elastomer with a weight-average molecular weight of 180,000 g / mol. The transition layer raw material is a polyolefin elastomer with a thickness 2.0 times that of the heat-sealing layer and a molecular weight flow rate (MFR) of 5.0 g / 10 min. The connecting layer raw material is LLDPE with an MFR of 0.6 g / 10 min. Melting and plasticizing are performed at 158°C, with a die temperature of 168°C, using a reverse blown film process.

[0079] S02. Cooling is achieved using a dual-air ring and internal cooling system within the membrane bubble, with a cooling medium temperature of 21℃. The membrane is then drawn and flattened to form a sheet-like film, with a film temperature of 52℃.

[0080] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 41 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 19℃.

[0081] S04. Rewind in an isolated environment at a temperature of 23°C. S05. The film thickness is 48μm, the film temperature after rewinding is 27°C, and rewinding is completed within 22 hours.

[0082] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 80°C. After curing for 7 days at 50°C and 0.28 MPa pressure, the ratio of unwinding force to initial unwinding force is 1.25.

[0083] Example 6: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw material, by weight, includes: 15 parts vinyl polyolefin elastomer; 65 parts vinyl polyolefin plastomer; 15 parts PE; 5 parts silane-terminated polyethylene with a silane group content of 3 mmol / 100g and trimethoxysilane end groups; and 3 parts processing aids (antioxidants 1010 and 168, erucamide). The transition layer raw material is EVA, and the connecting layer raw material is metallocene polyethylene. Melting and plasticizing are performed at 162°C, with a die temperature of 172°C, using a reverse blown film process.

[0084] S02. Dual-air ring cooling is adopted, and the cooling medium temperature is 22℃. The film is drawn and flattened to form a sheet-like film, and the film temperature is 54℃.

[0085] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 40 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 20℃.

[0086] S04. Winding is performed in an isolated environment at a temperature of 22°C. S05. The film thickness is 42μm, the film temperature after winding is 26°C, and rewinding is completed within 20 hours.

[0087] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 78°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.1.

[0088] Example 7: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw material, by weight, includes: 35 parts vinyl polyolefin elastomer; 55 parts vinyl polyolefin plasmon; 20 parts PE; 6 parts silane-terminated polyethylene with a silane group content of 15 mmol / 100g and end groups of triethoxysilane; and 4 parts processing aids. The transition layer raw material is an ethylene-acrylate copolymer, and the connecting layer raw material is LLDPE. Melting and plasticizing are performed at 168°C, with a die temperature of 182°C, using a reverse blown film process.

[0089] S02. Cooling is achieved using a dual-air ring and internal cooling system within the membrane bubble, with a cooling medium temperature of 24℃. The membrane is then drawn and flattened to form a sheet-like film, with a film temperature of 56℃.

[0090] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 39 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 21℃.

[0091] S04. Winding is performed in an isolated environment at a temperature of 24°C. S05. The film thickness is 58μm, the film temperature after winding is 33°C, and rewinding is completed within 46 hours.

[0092] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 78°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.45.

[0093] Example 8: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw material, by weight, includes: 25 parts vinyl polyolefin elastomer; 70 parts vinyl polyolefin plasmon; 10 parts PE; 4 parts silane-terminated polyethylene with a silane group content of 0.8 mmol / 100g and end groups of methyldimethoxysilane; and 2.5 parts processing aids. The transition layer raw material is polyolefin plasmon, and the connecting layer raw material is LDPE. Melting and plasticizing are performed at 155°C, with a die temperature of 165°C, using a reverse blown film process.

[0094] S02. Dual-air ring cooling is adopted, and the cooling medium temperature is 20℃. The film is drawn and flattened to form a sheet-like film, and the film temperature is 50℃.

[0095] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 42 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 16℃.

[0096] S04. Rewind in an isolated environment at a temperature of 20°C. S05. The film thickness is 35μm, the film temperature after rewinding is 25°C, and rewinding is completed within 16 hours.

[0097] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 78°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.15.

[0098] Example 9: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into four extruders (five-layer co-extrusion dies). The heat-sealing layer raw materials, by weight, include: 30 parts vinyl polyolefin elastomer; 60 parts vinyl polyolefin plastomer; 18 parts PE; 7 parts silane-terminated polyethylene with a silane group content of 18 mmol / 100g and trimethoxysilane end groups; and 4.5 parts processing aids. A thin functional layer containing a higher proportion of silane-terminated polyethylene is added between the heat-sealing layer and the transition layer. The transition layer raw material is EVA, and the connecting layer raw material is metallocene polyethylene. Melting and plasticizing are performed at 165°C, with a die temperature of 180°C, using a reverse blown film process.

[0099] S02. Cooling is achieved using a dual-air ring and internal cooling system within the membrane bubble, with a cooling medium temperature of 22℃. The membrane is then drawn and flattened to form a sheet-like film, with a film temperature of 53℃.

[0100] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 38 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 18℃.

[0101] S04. Winding is carried out in an isolated environment at a temperature of 22°C. S05. The film thickness is 50μm, the film temperature after winding is 30°C, and rewinding is completed within 24 hours.

[0102] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 94°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.05.

[0103] Example 10: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw material, by weight, includes: 10 parts vinyl polyolefin elastomer; 80 parts vinyl polyolefin plasmon; 8 parts PE; 3 parts silane-terminated polyethylene with a silane group content of 12 mmol / 100g and end groups of triethoxysilane; and 5 parts processing aids. The transition layer raw material is polyolefin elastomer, and the connecting layer raw material is LLDPE. Melting and plasticizing are performed at 170°C, with a die temperature of 190°C, using a reverse blown film process.

[0104] S02. Dual-air ring cooling is adopted, and the cooling medium temperature is 25℃. The film is drawn and flattened to form a sheet-like film, and the film temperature is 60℃.

[0105] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 35 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 25℃.

[0106] S04. Rewind in an isolated environment at 25°C. S05. The film thickness is 65μm, and the film temperature after rewinding is 35°C. Then perform suspended packaging.

[0107] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 80°C. After curing at 50°C and 0.28 MPa pressure for 7 days, the ratio of unwinding force to initial unwinding force is 1.5.

[0108] Example 11: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw materials, by weight, include: 40 parts vinyl polyolefin elastomer; 50 parts vinyl polyolefin plasmon; 25 parts PE; 8 parts silane-terminated polyethylene with a silane group content of 20 mmol / 100g and methyl dimethoxysilane end groups; and 2 parts processing aids. The transition layer raw material is an ethylene-acrylate copolymer, and the connecting layer raw material is a mixture of LDPE and LLDPE. Melting and plasticizing are performed at 150°C, with a die temperature of 160°C, using a reverse blown film process.

[0109] S02. Cooling is achieved using a dual-air ring and internal cooling system within the membrane bubble, with a cooling medium temperature of 20℃. The membrane is then drawn and flattened to form a sheet-like film, with a film temperature of 50℃.

[0110] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 45 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 16℃.

[0111] S04. Winding is carried out in an isolated environment at a temperature of 20°C. S05. The film thickness is 30μm, the film temperature after winding is 24°C, and rewinding is completed within 18 hours.

[0112] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 80°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.0.

[0113] Example 12: S01. Raw materials for the heat-sealing layer, transition layer, and connecting layer are fed into three extruders. The heat-sealing layer raw material, by weight, includes: 20 parts vinyl polyolefin elastomer; 75 parts vinyl polyolefin plastomer; 12 parts PE; 5.5 parts silane-terminated polyethylene with a silane group content of 0.5 mmol / 100g and a trimethoxysilane end group; and 3.5 parts processing aids. The transition layer raw material is EVA, and the connecting layer raw material is metallocene polyethylene. Melting and plasticizing are performed at 152°C, with a die temperature of 162°C, using a reverse blown film process.

[0114] S02. Dual-air ring cooling is adopted, and the cooling medium temperature is 21℃. The film is drawn and flattened to form a sheet-like film, and the film temperature is 51℃.

[0115] S03. The bonding layer is subjected to corona treatment to achieve a surface tension of 36 mN / m. It is then cooled by two cooling rollers to a roller surface temperature of 17℃.

[0116] S04. Winding is performed in an isolated environment at a temperature of 21°C. S05. The film thickness is 40μm, the film temperature after winding is 26°C, and rewinding is completed within 20 hours.

[0117] The polyolefin heat-sealable film prepared in this embodiment has an initial sealing temperature of 79°C. After curing at 50°C and 0.28 MPa for 7 days, the ratio of unwinding force to initial unwinding force is 1.2.

[0118] Comparative Example 1: This comparative example is basically the same as Example 1, except that the density of the vinyl polyolefin elastomer used in the heat-sealing layer is 0.930 g / cm³. 3 The MFR was 0.5 g / 10min. The film prepared in this comparative example had a sealing temperature of 125℃, an unwinding force ratio of 2.8 after curing, poor low-temperature heat-sealing properties, and severe adhesion.

[0119] Comparative Example 2: This comparative example is basically the same as Example 2, except that the density of the vinyl polyolefin plastic body used in the heat-sealing layer is 0.870 g / cm³. 3 The MFR was 15.0 g / 10min. The film prepared in this comparative example had a sealing temperature of 115℃, an unwinding force ratio of 2.1 after curing, insufficient heat sealing strength, and poor bubble formation stability.

[0120] Comparative Example 3: The raw materials and proportions of this comparative example are exactly the same as those of Example 6, the difference being in the preparation process: a forward blown film process is used (the heat-sealing layer is located inside the film bubble), and after the film is flattened and wound up, the bonding layer undergoes a traditional external corona treatment. The film obtained in this comparative example has a sealing temperature of 105°C and an unwinding force ratio of 1.9 after curing. Because the heat-sealing layer is located inside the film bubble and is less affected by the cooling air, and because the external corona treatment causes secondary heating, its performance is somewhat degraded, and its anti-adhesion properties decrease.

[0121] Comparative Example 4: The raw materials and proportions of this comparative example are exactly the same as those of Example 9, the difference being the preparation process: a forward blown film process is used, and the winding environment temperature is 30°C. The film obtained in this comparative example has a sealing temperature of 108°C and an unwinding force ratio of 2.3 after curing. The high-temperature winding environment exacerbates the heat accumulation inside the film roll, leading to prominent adhesion problems.

[0122] Comparative Example 5: The formulation and process of this comparative example are basically the same as those of Example 7, except that an equal mass of maleic anhydride-grafted polyethylene (MAH-g-PE) is used to completely replace the silane-terminated polyethylene in the heat-sealing layer. The film prepared in this comparative example has a sealing temperature of 112°C and an unwinding force ratio of 2.5 after curing. Polar groups lead to unstable surface properties and increased adhesion in humid and hot environments.

[0123] Comparative Example 6: The formulation and process of this comparative example are basically the same as those of Example 8, except that an equal mass of small siloxane molecules (dimethyl silicone oil) is used in the heat-sealing layer raw material, which is simply blended with polyethylene to replace the silane-terminated polyethylene. The film prepared in this comparative example has an initial sealing temperature of 98°C, but the unwinding force ratio after curing is as high as 3.0. The small siloxane molecules migrate and precipitate severely. The initial anti-adhesion is acceptable, but the durability is poor, and it contaminates the heat-sealing interface.

[0124] As can be seen from the above embodiments and comparative examples, the multilayer structure with specific density, melt flow rate and glass transition temperature gradient shown in this invention, combined with a heat-sealing layer formulation based on vinyl polyolefin elastomer / plastic body and silane-terminated polyethylene as the key modification, and with the preparation process of reverse blown film, built-in corona treatment and fine temperature-controlled winding, successfully improves the low-temperature heat-sealing performance and excellent anti-blocking properties of polyolefin heat-sealing film.

[0125] Comparative Examples 1-2 show that the raw material parameters defined in this invention are of great significance for heat sealing performance and processing stability. Comparative Examples 3-4 show that using forward blown film or improper post-processing will damage the heat-sealing layer structure and aggravate adhesion. Comparative Examples 5-6 show that neither maleic anhydride-grafted polyethylene nor physically blended siloxane small molecules can replace the structure and function of silane-terminated polyethylene, and they still have defects in terms of long-term anti-adhesion and interface stability.

[0126] The above embodiments merely illustrate several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but 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 polyolefin heat-sealing film, characterized in that, The material comprises a heat-sealing film, a transition film, and a connecting film stacked sequentially along the direction away from the contents, wherein the difference in glass transition temperature between adjacent film materials is not less than 10°C; the heat-sealing film comprises a vinyl polyolefin elastomer and a vinyl polyolefin plastic. The vinyl polyolefin elastomer is copolymerized with polyethylene from at least two α-polyolefins with different and independent glass transition temperatures, each ranging from -60°C to -10°C, and the vinyl polyolefin elastomer has a density of 0.855 g / cm³. 3 ~0.920g / cm 3 Its melt mass flow rate at 190℃ and 2.16kg load is 0.8g / 10min~8.0g / 10min; The vinyl polyolefin plastic body is copolymerized with polyethylene from at least two α-polyolefins with different and independent glass transition temperatures ranging from -50°C to -20°C, and the vinyl polyolefin plastic body has a density of 0.875 g / cm³. 3 ~0.905g / cm 3 Its melt mass flow rate at 190℃ and 2.16kg load is 0.8g / 10min~12.0g / 10min.

2. The polyolefin heat-sealing film according to claim 1, characterized in that, The α-polyolefin includes at least one selected from 1-hexene, 1-octene, and 4-methyl-1-pentene; and / or The polyethylene is selected from at least two of low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear low-density polyethylene, and metallocene polyethylene; and / or The polyethylene accounts for 20% to 60% of the mass percentage of the vinyl polyolefin elastomer and 30% to 70% of the mass percentage of the vinyl polyolefin plasmid.

3. The polyolefin heat-sealing film according to claim 2, characterized in that, The vinyl polyolefin elastomer has a weight-average molecular weight of 100,000 g / mol to 180,000 g / mol; and / or The weight-average molecular weight of the vinyl polyolefin plastide is from 120,000 g / mol to 220,000 g / mol.

4. The polyolefin heat-sealing film according to claim 3, characterized in that, The transition membrane comprises at least one of ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer, polyolefin elastomer, and polyolefin plasticizer; and / or The thickness of the transition film is 1.2 to 3.0 times the thickness of the heat-sealing film; and / or The melt mass flow rate of the transition film at 190°C and 2.16 kg load is 2.0~8.0 g / 10 min.

5. The polyolefin heat-sealing film according to claim 2, characterized in that, The side of the connecting film away from the heat-sealing film is corona treated to achieve a surface tension of 35~45 mN / m; and / or The raw material for the connecting membrane includes at least one of linear low-density polyethylene, low-density polyethylene, and metallocene polyethylene; and / or The melt flow rate of the raw material for the connecting membrane at 190°C and 2.16 kg load is 0.5~0.8 g / 10 min.

6. The polyolefin heat-sealing film according to any one of claims 1-5, characterized in that, The heat-sealing film comprises, by weight, the following: 10-40 parts of vinyl polyolefin elastomer; 50-80 parts of vinyl polyolefin plasmid; 8-25 parts of polyethylene; 3-8 parts of silane-terminated polyethylene; Processing aids 2-5 parts; The silane group content of the silane-terminated polyethylene is 0.5~20 mmol / 100g.

7. The polyolefin heat-sealing film according to claim 6, characterized in that, The end groups of the silyl-terminated polyethylene include any one of trimethoxysilyl, triethoxysilyl, and methyldimethoxysilyl.

8. The polyolefin heat-sealing film according to any one of claims 1-5, characterized in that, The initial sealing temperature of the polyolefin heat-sealable film is 75℃~80℃; and / or After the polyolefin heat-sealing film is cured at 50°C and 0.28 MPa for 7 days, the ratio of the unwinding force to the initial unwinding force is no greater than 1.

5.

9. A method for preparing a polyolefin heat-sealing film, characterized in that, Includes the following steps: S01. Raw materials for the heat-sealing layer, transition layer and connecting layer are fed into multiple extruders, melted and plasticized and then conveyed to the co-extrusion die. After the melt is extruded from the die, it is blown into shape using a reverse blown film process, so that the heat-sealing layer is located on the outside of the bubble, forming a cylindrical bubble; S02. The tubular membrane bubble is cooled and then flattened and pulled by traction rollers to form a sheet-like film. S03. Perform corona treatment on one side of the sheet film where the connecting layer is located; after corona treatment, allow the film to pass through at least two cooling rollers for cooling. S04. In an isolated environment with a temperature of 20℃~25℃, wind up the cooled film; S05. Depending on the film thickness and temperature, the film is rolled up or suspended for packaging.

10. The method for preparing the polyolefin heat-sealing film according to claim 9, characterized in that, In S01, the melting and plasticizing temperature is 150~170℃, and the die head temperature is 160~190℃; and / or In S02, the cooling adopts a dual-air ring and / or membrane bubble internal cooling system, and the temperature of the cooling medium is 20℃~25℃; and / or In S03, when the film reaches the traction position, the temperature of the film is controlled at 50~60℃; and / or In S03, the corona treatment causes the surface tension of the bonding layer to reach 38~42 mN / m; and / or In S03, the surface temperature of the cooling roller is 16~25℃, ensuring that the film temperature after cooling does not exceed 25℃; and / or In S04, the temperature difference between the isolation environment and the surface temperature of the cooling roller is less than 5°C; and / or In S05, when the film temperature is not lower than 30°C, the rule for rewinding is as follows: When the film thickness is ≤50μm, the rewinding should be completed within 24 hours; When the film thickness is >50μm, the rewinding should be completed within 48 hours; When the film is placed horizontally, it is wrapped with an aluminum foil structure on the outside and is suspended in the packaging.