Heat-sealing master batch, biaxially oriented polyethylene heat-sealing film and preparation method of biaxially oriented polyethylene heat-sealing film

Abstract

The invention relates to the field of films, in particular to a heat-sealing master batch, a biaxially oriented polyethylene heat-sealing film and a preparation method of the biaxially oriented polyethylene heat-sealing film, and the heat-sealing master batch comprises copolymerized polyethylene, 6-10 wt% of long branched chain-short branched chain comb-shaped branched polyethylene and 8-12 wt% of itaconic acid monomethyl ester grafted polyethylene; the content of the long branch chain is 0.5-1 mol%, and the content of the short branch chain is 2-5 mol%; the long branch chain is a polyethylene chain segment, the carbon atom number of the polyethylene chain segment is 10-100, and the short branch chain is C3-C9 straight chain saturated normal alkyl; the grafting rate of the monomethyl itaconate in the monomethyl itaconate grafted polyethylene is 1 to 2 percent. Through the synergistic effect of the long branch chain-short branch chain comb-shaped branched polyethylene and the itaconic acid monomethyl ester grafted polyethylene, the heat-sealing initial temperature is reduced, so that the heat-sealing window is widened, the melt strength is improved to resist pressure fracture, the interface defects of a heat-sealing layer and a core layer are reduced, and the problem that the heat-sealing strength of the BOPE heat-sealing film is insufficient is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of thin films, in particular to a heat-sealing master batch, a biaxially oriented polyethylene heat-sealing film and a preparation method thereof. BACKGROUND

[0002] Under the dual driving of the increasingly deepening global environmental protection concept and the upgrading iteration of the packaging industry, the greenization and functionalization of packaging materials have become the core trend of industry development. Biaxially oriented polyethylene (BOPE) film, with its excellent performance after biaxial stretching, such as excellent impact resistance and pinhole resistance at low temperatures, provides reliable protection for the packaging of various products. In addition, as a single recyclable material, BOPE film realizes lightweight production, meets environmental protection requirements, and promotes the green and recyclable development of materials, so it has been widely used in rice packaging, laundry detergent packaging, frozen food packaging and many other industries. Heat-sealing film is an important application of BOPE film. At present, the mainstream BOPE heat-sealing film adopts a three-layer composite structure design, which includes an upper surface layer, a core layer and a heat-sealing layer. The upper surface layer gives the film a specific appearance or function, the core layer ensures the overall mechanical properties of the film, and the heat-sealing layer undertakes the key function of packaging sealing. However, in actual application, the heat-sealing layer of the BOPE heat-sealing film exposes the problem of insufficient heat-sealing strength, which makes the packaging prone to delamination at the heat-sealing part when under pressure, seriously affecting the sealing performance and reliability of the packaging, and posing a potential threat to the packaging quality and transportation and storage safety of the product. SUMMARY

[0003] Therefore, the purpose of the present application is to provide a heat-sealing master batch, a biaxially oriented polyethylene heat-sealing film and a preparation method thereof. The heat-sealing master batch of the present application, by adding long-chain branched-short-chain branched comb-branched polyethylene and itaconic acid monomethyl ester grafted polyethylene, the short-chain branched comb-branched polyethylene and the polar side chain of itaconic acid monomethyl ester grafted polyethylene destroy the crystalline regularity of copolymerized polyethylene, cooperatively reduce the heat-sealing starting temperature and thus broaden the heat-sealing temperature window; the long-chain branched comb-branched polyethylene forms a three-dimensional network through physical entanglement to improve the cohesive strength and the melt strength to resist pressure rupture; the itaconic acid monomethyl ester grafted polyethylene can improve the interface between the heat-sealing layer and the core layer and reduce interface defects; the two form a performance synergy effect, which improves the insufficient heat-sealing strength problem of the existing BOPE heat-sealing film.

[0004] The technical solution of the present application is realized by the following way: A heat sealing master batch, comprising copolymerized polyethylene, 6-10 wt% long-chain branched-short-chain branched comb-shaped branched polyethylene, 8-12 wt% itaconic acid monomethyl ester grafted polyethylene; the content of long-chain branches in the long-chain branched-short-chain branched comb-shaped branched polyethylene is 0.5-1 mol%, and the content of short-chain branches is 2-5 mol%; the long-chain branches are polyethylene segments, and the number of carbon atoms of the polyethylene segments is 10-100; the short-chain branches are C3-C9 straight-chain saturated normal alkyl groups; and the grafting rate of itaconic acid monomethyl ester in the itaconic acid monomethyl ester grafted polyethylene is 1-2%.

[0005] The inventor finds through a large number of practices that the main reasons for the insufficient heat sealing strength of the BOPE heat sealing film are as follows: on the one hand, the existing heat sealing master batch for the heat sealing layer has the problem of high heat sealing temperature, and high temperature can cause the heat sealing layer to excessively melt and even degrade, destroy the molecular chain structure, cause the mechanical properties to suddenly decrease, and finally cause the material to be brittlely broken from the heat sealing root; on the other hand, the melt strength of the heat sealing layer is low, and the heat sealing layer and the interface are prone to be broken in the heat sealing pressure process, causing the heat sealing strength to be insufficient, thereby affecting the heat sealing effect of the package and the packaging quality of the product.

[0006] The heat sealing master batch disclosed in the application, by adding long-chain branched-short-chain branched comb-shaped branched polyethylene and itaconic acid monomethyl ester grafted polyethylene with a suitable content, the short-chain branches of the comb-shaped branched polyethylene and the polar side groups of the itaconic acid monomethyl ester grafted polyethylene destroy the crystallization regularity of the main component copolymerized polyethylene in the heat sealing master batch, cooperatively reduce the heat sealing starting temperature and widen the heat sealing temperature window; the long-chain branches of the comb-shaped branched polyethylene form a three-dimensional network through physical entanglement to improve the cohesive strength and the melt strength to resist pressure rupture; the itaconic acid monomethyl ester grafted polyethylene can improve the interfacial compatibility of the heat sealing layer and the core layer and reduce the interfacial defects; and the two form a performance synergistic effect, thereby improving the insufficient heat sealing strength problem of the prepared BOPE heat sealing film.

[0007] The long-chain branch-short-chain branch comb-branched polyethylene has a linear main chain as a skeleton, long-chain branches and short-chain branches form a "comb-branched" structure, the main chain is like a "comb handle", the long and short-chain branches are like "comb teeth", and are tightly connected through covalent bonds, and the whole presents a regular comb-shaped topological structure. The short-chain branches are C3-C9 straight-chain saturated n-alkyl groups, and dense distribution inhibits crystallization. The long-chain branches are polyethylene segments, and the number of carbon atoms of the polyethylene segments is 10-100, and sparse distribution regulates the melt strength. The synergistic effect of the long-chain branch-short-chain branch comb-branched polyethylene can realize multiple optimization: the short-chain branches can destroy the regularity of the polyethylene main chain itself, so that the crystallinity of the comb-branched polyethylene is reduced, and the crystallization ability of the main component copolymerized polyethylene is also reduced, thereby the starting heat sealing temperature of the heat sealing master batch is reduced, and the prepared heat sealing layer can be melted at a lower temperature to realize "low-temperature heat sealing", and the heat sealing temperature window is widened; the long-chain branches themselves increase the spatial steric hindrance of the molecular chain to slow down the crystallization rate during cooling, and because the length is close to the main chain segment, strong entanglement can occur between the long-chain branches and the main chain or the branches of adjacent molecules during melting, which significantly improves the intermolecular cohesion of the heat sealing layer, and after cooling and solidification, the entanglement structure becomes the main support of the heat sealing strength, which can improve the delamination phenomenon of the heat sealing part caused by external force after heat sealing, at the same time, the long-chain branches form a dynamic three-dimensional network through intermolecular physical entanglement, which is beneficial to resisting melt flow deformation during heat sealing to delay the deformation rate of the high-temperature melt, and to enhancing the melt rupture resistance performance, so as to avoid the phenomenon that the edge of the heat sealing area is excessively compressed, the inner layer film is thinned or even broken (i.e. "root cutting"), and finally the melt strength and heat sealing performance of the prepared heat sealing layer are improved through the molecular chain entanglement and crystallization regulation mechanism.

[0008] On this basis, if the addition amount of the long-chain branch-short-chain branch comb-branched polyethylene is less than 6wt%, on the one hand, it is not conducive to the formation of a stable physical three-dimensional network structure in the heat sealing layer, which leads to insufficient cohesion support and unobvious heat sealing strength improvement, and also cannot effectively enhance the melt pressure rupture resistance performance, on the other hand, it is not conducive to reducing the crystallization ability of the main component copolymerized polyethylene in the heat sealing layer, thereby the heat sealing temperature cannot be effectively reduced; if the addition amount of the long-chain branch-short-chain branch comb-branched polyethylene is greater than 10wt%, it will lead to excessive intermolecular entanglement to form a dense three-dimensional network, which hinders the diffusion and interface fusion of the melt segment, makes it difficult for the molecular chains of the heat sealing interface to fully fuse, is not conducive to ensuring the heat sealing strength, and also cannot effectively reduce the heat sealing starting temperature and widen the heat sealing temperature window together with itaconic acid monomethyl ester grafted polyethylene, which will lead to abnormal increase of the melt system viscosity of the heat sealing master batch, and significantly reduce the processing stability and increase the processing difficulty.

[0009] If the content of long-chain branches in the long-chain branch-short-chain branch comb branched polyethylene is less than 0.5 mol%, the content of short-chain branches is greater than 5 mol%, the proportion of long-chain branches is too low to form enough intermolecular entanglement in the heat sealing layer, the cohesion of the heat sealing layer is weak, the proportion of short-chain branches is too high to excessively destroy the crystallization of the main component copolymerized polyethylene, which leads to a significant decrease in the crystallinity of the heat sealing master batch, further weakening the intermolecular cohesion, and after heat sealing and cooling, the prepared heat sealing layer has poor resistance to external force, the heat sealing strength is significantly reduced, and the heat sealing layer is prone to delamination, in addition, due to the excessively high melt flowability, the prepared heat sealing layer is prone to problems such as uneven thickness and poor processing stability, and the production efficiency is affected; if the content of long-chain branches in the long-chain branch-short-chain branch comb branched polyethylene is greater than 1 mol%, the content of short-chain branches is less than 2 mol%, the proportion of long-chain branches is too high to cause excessive intermolecular entanglement, forming an excessively dense three-dimensional network, hindering the diffusion and interface fusion of the molten chain segments, and the proportion of short-chain branches is low, which still cannot effectively inhibit the crystallization of the main component copolymerized polyethylene in the heat sealing layer, and after cooling, it is still easy to form a rigid crystal structure, further inhibiting the fusion of the interface molecular chain, the heat sealing strength shows a downward trend, and due to the excessively high rigidity, the heat sealing layer is prone to brittle cracking, and the excessive entanglement of long-chain branches significantly increases the melt viscosity, affecting film formation and processing.

[0010] Although the addition of long-chain branch-short-chain branch comb branched polyethylene to a certain extent helps to reduce the crystallization of the heat sealing layer, due to its great compatibility with the main component copolymerized polyethylene, the degree of reduction in the heat sealing temperature is still limited, and therefore, the heat sealing temperature needs to be further reduced to widen the heat sealing temperature window of the BOPE heat sealing film. Therefore, the present application also adds a certain content of itaconic acid monomethyl ester grafted polyethylene to the heat sealing master batch, which is beneficial to destroy the regularity of the molecular structure of the main component copolymerized polyethylene in the heat sealing layer, loosen the stacking of the molecular chains, reduce the intermolecular van der Waals force, make the copolymerized polyethylene chain segments move and entangle with each other at a lower temperature, interfere with the crystallization process of the copolymerized polyethylene, reduce the crystallinity, and make the copolymerized polyethylene more easily diffuse at a lower temperature and heat sealing pressure, further reduce the melting temperature of the heat sealing master batch, widen the melting range, and realize low-temperature heat sealing, thereby widening the heat sealing temperature window of the BOPE heat sealing film.

[0011] In addition, the addition of itaconic acid monomethyl ester grafted polyethylene is also beneficial to synergize with long-chain branch-short-chain branch comb branched polyethylene to further enhance the intermolecular force and thereby improve the heat sealing strength. The polar groups of itaconic acid monomethyl ester grafted polyethylene can form stronger interactions through hydrogen bonds, so that the molecular chains are more easily close to each other and entangle under pressure when the heat sealing master batch is melted, and form a more compact interface after cooling, thereby synergizing with the long-chain branch entanglement in the long-chain branch-short-chain branch comb branched polyethylene to significantly improve the heat sealing strength, and the existence of hydrogen bonds can also enhance the impact resistance and low temperature resistance of the heat sealing layer, and effectively improve the delamination of the heat sealing interface after heat sealing.

[0012] On this basis, if the addition amount of itaconic acid monomethyl ester grafted polyethylene is less than 8wt%, the crystallization damage to the main component of the heat sealing layer, copolymerized polyethylene, is limited, resulting in that the overall crystallinity of the heat sealing master batch does not decrease obviously, the molecular chain still maintains a relatively strong ordered arrangement, the initial heat sealing temperature is still relatively high, and the cohesion of the prepared heat sealing layer is slightly improved, and the heat sealing strength is not significantly improved; if the addition amount of itaconic acid monomethyl ester grafted polyethylene is greater than 12wt%, a large number of polar functional groups strongly destroy the regularity of the molecular chain of the copolymerized polyethylene, significantly reduce the crystallinity and even form a large number of amorphous regions, the ordered arrangement of the molecular chain is severely broken, resulting in that the heat resistance of the heat sealing layer is significantly reduced, which is not conducive to the smoothness of the subsequent film preparation process, and the heat sealing layer is prone to stick to the roller and other phenomena; at the same time, excessive polar groups can cause excessive interaction between molecules, form a local dense polar network, hinder the diffusion and entanglement of the molten molecular chain, inhibit the full contact of the molecular chain at the interface, finally the heat sealing strength is reduced, even the interface layering at the heat sealing place occurs, and it is also not conducive to the uniformity of the dispersion of itaconic acid monomethyl ester grafted polyethylene in the heat sealing layer. In addition, the excessive polar groups can significantly enhance the intermolecular force, sharply increase the melt viscosity, hinder the movement of the chain segment, and greatly reduce the melt flowability, resulting in that the extrusion pressure increases sharply, the material is prone to be retained or the die is prone to be blocked, and the processing difficulty is significantly increased.

[0013] If the grafting rate of itaconic acid monomethyl ester in the itaconic acid monomethyl ester grafted polyethylene is less than 1%, the damage to the regularity of the polyethylene main chain is weak due to the small number of polar groups, the main chain still maintains a relatively high crystalline order, the crystalline structure needs a relatively high temperature to be melted, so the initial heat sealing temperature of the heat sealing master batch is relatively high, and the heat sealing temperature window is narrow; if the grafting rate of itaconic acid monomethyl ester grafted polyethylene is greater than 2% and the melt index is less than 5g / 10min, excessive polar functional groups cause excessive interaction between molecules, form an excessively dense polar network, hinder the diffusion and entanglement of the molten molecular chain, and the increase of the spatial steric hindrance of the grafted chain caused by the high grafting rate inhibits the contact of the interface molecular, although the polar effect is enhanced, but the cohesion is reduced due to the insufficient entanglement, finally the heat sealing strength is reduced, even the interface layering at the heat sealing place occurs; at the same time, the excessive polar groups can significantly enhance the intermolecular force, sharply increase the melt viscosity, hinder the movement of the chain segment, and greatly reduce the melt flowability, resulting in that the extrusion pressure increases sharply, the material is prone to be retained or the die is prone to be blocked, and the processing difficulty is significantly increased.

[0014] Further, the long-chain-short-chain comb-branched polyethylene is prepared by using ethylene as a polymerization monomer under the catalysis of a main catalyst TiCl4 and an auxiliary catalyst Ni(acac)2, forming polyethylene with linear polyethylene as a main chain and polyethylene segments as long chains, on the basis of which, C3-C9 short chains are introduced into the linear polyethylene main chain under the synergistic action of a functional auxiliary triazine compound, and finally the long-chain-short-chain comb-branched polyethylene is prepared.

[0015] Further, the long-chain branched-short-chain branched comb-branched polyethylene has a melt index of 1.0-2.0 g / 10 min measured at 190℃ under a load of 2.16 kg.

[0016] Further, the itaconic acid monomethyl ester grafted polyethylene is obtained by melt grafting reaction of 83-95 wt% of the copolymerized polyethylene, 3-15 wt% of the itaconic acid monomethyl ester, 0.1-1 wt% of the initiator and 0.1-1 wt% of the antioxidant. Specifically, the preparation method of the itaconic acid monomethyl ester grafted polyethylene comprises the following steps: weighing 83-95 wt% of the copolymerized polyethylene, 3-15 wt% of the itaconic acid monomethyl ester, 0.1-1 wt% of the initiator and 0.1-1 wt% of the antioxidant and putting them into a high-speed mixer to mix them evenly, and then putting the mixed materials into a twin-screw extruder to perform melt grafting reaction at 180-190℃, under the action of high temperature and screw shearing, the initiator decomposes to generate free radicals, which initiates grafting of the itaconic acid monomethyl ester to the polyethylene molecular chain to obtain the itaconic acid monomethyl ester grafted polyethylene. Preferably, the copolymerized polyethylene used for preparing the itaconic acid monomethyl ester grafted polyethylene is the same as the copolymerized polyethylene in the heat-sealing masterbatch.

[0017] Further, the itaconic acid monomethyl ester grafted polyethylene has a melt index of 5-10 g / 10 min measured at 190℃ under a load of 2.16 kg.

[0018] The application further provides a biaxially stretched polyethylene heat-sealing film, comprising an upper surface layer, a core layer and a heat-sealing layer arranged in sequence; the core layer comprises copolymerized polyethylene; and the heat-sealing layer comprises the heat-sealing masterbatch according to any one of the application.

[0019] Further, the copolymerized polyethylene in the heat-sealing layer and the core layer has a melt index of 2-5 g / 10 min measured at 190℃ under a load of 2.16 kg, and the copolymerized polyethylene comprises one or more of binary copolymerized polyethylene and ternary copolymerized polyethylene, the binary copolymerized polyethylene is formed by copolymerization of one of propylene, butene, hexene or octene with ethylene, and the ternary copolymerized polyethylene comprises ethylene-propylene-butene ternary copolymer.

[0020] Further, the upper surface layer comprises 50-70 wt% of linear low-density polyethylene and 30-50 wt% of polypropylene.

[0021] Further, the linear low density polyethylene has a melt index of 5-15 g / 10 min measured at 190℃ under a load of 2.16 kg, and the polypropylene has a melt index of 1-4 g / 10 min measured at 230℃ under a load of 2.16 kg, the polypropylene including one or more of homopolymer polypropylene and copolymer polypropylene, the copolymer polypropylene including one or more of ethylene-propylene binary copolymer polypropylene and ethylene-propylene-butylene ternary copolymer polypropylene. By limiting the melt index of the linear low density polyethylene and the melt index of the polypropylene, a certain melt index difference is maintained between the polypropylene and the linear low density polyethylene, so that the overall haze of the upper surface layer is in a more ideal state, which is beneficial to the matt effect of the upper surface layer. If the melt index difference is too large, the polypropylene is difficult to disperse and is prone to crystal points, resulting in poor matt effect. If the melt index difference is too small, the two phases are well compatible, which is not conducive to the matt effect of the upper surface layer and reduces the haze of the film.

[0022] Further, the core layer includes 99.0-99.5 wt% copolymer polyethylene and 0.5-1.0 wt% antistatic agent masterbatch. The effective content of the antistatic agent in the antistatic agent masterbatch is 20-40 wt%, and the carrier is copolymer polyethylene.

[0023] Further, the heat-sealing layer further includes 0.5-1.0 wt% antiblocking agent masterbatch, the effective content of the antiblocking agent in the antiblocking agent masterbatch is 6 wt%, the antiblocking agent is fumed silica, the particle size D50 of the antiblocking agent masterbatch is 5 µm, and the carrier is copolymer polyethylene.

[0024] The application also provides a preparation method of the bidirectional stretched polyethylene heat-sealing film, including the following steps: the raw materials of each layer are weighed and mixed uniformly under dry conditions, and then the obtained resin of each layer is added to each extruder; the resin of each layer is melted and plasticized in each extruder, metered by a metering pump, and converged at a T-shaped die to form a thick sheet through different extruder channels; the thick sheet is cooled by a chilling roller, shaped, and then enters a longitudinal stretching zone for longitudinal stretching, and then enters a transverse stretching zone for transverse stretching, the film is finished after bidirectional stretching, and then edge trimming and cutting are performed, followed by corona treatment and winding to obtain a BOPE matt film.

[0025] In order to better understand and implement, the application is described in detail below. DETAILED DESCRIPTION

[0026] It should be clear that the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0027] The terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the present application. As used in the description of the embodiments of the present application and the appended claims, the singular forms "a," "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It also will be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0028] The implementations described in the following exemplary embodiments are illustrative of the embodiments consistent with the present application and are not meant to limit the scope of the application as encompassed by the claims. Rather, they are exemplary of apparatus and methods consistent with some aspects of the present application as set forth in the appended claims. In the description of the embodiments of the present application, it will be understood that the terms "first", "second", "third", etc. are used merely as labels, and are not intended to impose ordinal, numerical or chronological import unless expressly so indicated. The terms "first", "second", "third", etc. are used to distinguish between similar objects, and are not necessarily used to describe a particular sequential or chronological order, nor are they used to indicate or imply relative importance.

[0029] Further, in the description of the embodiments of the present application, "a plurality" means two or more, unless otherwise indicated. "And / or" describes associated objects in association with the associated relationship, which means that there can be three relationships, for example, A and / or B, which can represent: A exists alone, A and B exist together, and B exists alone. The character " / " generally represents a "or" relationship between the associated objects.

[0030] It should be understood that the embodiments of the present application are not limited to the precise construction that has been described above and that various modifications and changes can be effected therein by those skilled in the art without departing from the scope of the application. The scope of the embodiments of the present application is limited only by the appended claims.

[0031] The embodiment of the present application provides a heat-sealing master batch, which comprises copolymerized polyethylene, 6-10 wt% long-chain branch-short-chain branch comb-branched polyethylene, and 8-12 wt% itaconic acid monomethyl ester grafted polyethylene; the content of long-chain branches in the long-chain branch-short-chain branch comb-branched polyethylene is 0.5-1 mol%, and the content of short-chain branches is 2-5 mol%; the long-chain branches are polyethylene segments, and the number of carbon atoms of the polyethylene segments is 10-100; the short-chain branches are C3-C9 straight-chain saturated normal alkyl groups; and the grafting rate of itaconic acid monomethyl ester in the itaconic acid monomethyl ester grafted polyethylene is 1-2%.

[0032] Further, the long-chain-short-chain comb-branched polyethylene is prepared by forming polyethylene with linear polyethylene as main chain and polyethylene segment as long chain branch under catalysis of main catalyst TiCl4 and auxiliary catalyst Ni(acac)2, and then introducing C3-C9 short chain into the linear polyethylene main chain under synergistic effect of functional auxiliary triazine compound.

[0033] Further, the melt index of the long-chain-short-chain comb-branched polyethylene is 1.0-2.0 g / 10 min under 190℃ and 2.16 kg load.

[0034] Further, the itaconic acid monomethyl ester grafted polyethylene is obtained by melt grafting reaction of 83-95 wt% copolymerized polyethylene, 3-15 wt% itaconic acid monomethyl ester, 0.1-1 wt% initiator and 0.1-1 wt% antioxidant. Specifically, the preparation method of the itaconic acid monomethyl ester grafted polyethylene comprises the following steps: weighing 83-95 wt% copolymerized polyethylene, 3-15 wt% itaconic acid monomethyl ester, 0.1-1 wt% initiator and 0.1-1 wt% antioxidant into a high-speed mixer and mixing them uniformly, and then adding the mixed material into a twin-screw extruder to perform melt grafting reaction at 180-190℃, so that the initiator decomposes to generate free radicals under the action of high temperature and screw shearing, and the itaconic acid monomethyl ester is grafted onto the molecular chain of the copolymerized polyethylene to obtain the itaconic acid monomethyl ester grafted polyethylene.

[0035] Further, the melt index of the itaconic acid monomethyl ester grafted polyethylene is 5-10 g / 10 min under 190℃ and 2.16 kg load.

[0036] The application further provides a biaxially stretched polyethylene heat-seal film, which comprises an upper surface layer, a core layer and a heat-seal layer arranged in sequence; the core layer comprises copolymerized polyethylene; and the heat-seal layer comprises the heat-seal master batch of any one of the above.

[0037] Further, the melt index of the copolymerized polyethylene in the heat-seal layer and the core layer is 2-5 g / 10 min under 190℃ and 2.16 kg load, the copolymerized polyethylene comprises one or more of binary copolymerized polyethylene and ternary copolymerized polyethylene, the binary copolymerized polyethylene is formed by copolymerization of one of propylene, butene, hexene or octene and ethylene, and the ternary copolymerized polyethylene comprises ethylene-propylene-butene ternary copolymer.

[0038] Further, the upper surface layer comprises 50-70 wt% linear low-density polyethylene and 30-50 wt% polypropylene.

[0039] Further, the linear low density polyethylene has a melt index of 5-15 g / 10 min measured at 190℃ under a load of 2.16 kg; the polypropylene has a melt index of 1-4 g / 10 min measured at 230℃ under a load of 2.16 kg, the polypropylene including one or more of homopolymer polypropylene and copolymer polypropylene, the copolymer polypropylene including one or more of ethylene-propylene binary copolymer polypropylene and ethylene-propylene-butylene ternary copolymer polypropylene.

[0040] Further, the core layer includes 99.0-99.5 wt% copolymer polyethylene and 0.5-1.0 wt% antistatic agent masterbatch. The effective content of the antistatic agent in the antistatic agent masterbatch is 20-40 wt%, and the carrier is copolymer polyethylene.

[0041] Further, the heat-sealing layer further includes 0.5-1.0 wt% anti-blocking agent masterbatch, the effective content of the anti-blocking agent in the anti-blocking agent masterbatch is 6 wt%, the anti-blocking agent is fumed silica, the particle size D50 of the anti-blocking agent masterbatch is 5 µm, and the carrier is copolymer polyethylene.

[0042] The application also provides a preparation method of the bidirectional stretched polyethylene heat-sealing film, including the following steps: the raw materials of each layer are weighed and mixed according to the proportion under dry conditions, and then the obtained resin of each layer is added to each extruder; the resin of each layer is melted and plasticized in each extruder, and then is metered by a metering pump, and is converged at a T-shaped die to form a thick sheet through different extruder channels; the thick sheet is cooled by a chilling roller, and after shaping, is first stretched in a longitudinal stretching zone, and then is stretched in a transverse stretching zone, and after the bidirectional stretching of the film is completed, the edges are trimmed, and then the film is subjected to corona treatment and winding to obtain a BOPE matt film.

[0043] The physical property indexes of the embodiments or comparative examples of the application and the test methods thereof are as follows: The initial heat-sealing temperature is determined according to the GB / T21302-2007 standard; The heat-sealing strength is determined according to the GB / T21302-2007 standard; It should be noted that the proportions in the embodiments or comparative examples of the application are all weight percentages (wt%), and the components and contents of each layer in the embodiments and comparative examples of the application are shown in Table 1.

[0044] Table 1

[0045] In the embodiments and comparative examples listed in the present application, the content of linear low density polyethylene in the upper surface layer is 58wt%, and the content of polypropylene is 42wt%; as a feasible other implementation, the content of linear low density polyethylene in the upper surface layer can be selected between 50-70wt%, and the content of polypropylene in the upper surface layer can be selected between 30-50wt%; In the embodiments and comparative examples listed in the present application, the linear low density polyethylene in the upper surface layer is an ethylene-butene binary copolymer, and the melt index is 10g / 10min measured at 190℃ under a load of 2.16kg; as a feasible other implementation, the melt index of linear low density polyethylene can be selected between 5-15g / 10min; In the embodiments and comparative examples listed in the present application, the polypropylene in the upper surface layer is a homopolymer polypropylene, and the melt index of the polypropylene is 1.5g / 10min measured at 230℃ under a load of 2.16kg; as a feasible other implementation, the polypropylene can use one or more of homopolymer polypropylene and copolymer polypropylene, the copolymer polypropylene can be one or more of ethylene-propylene binary copolymer polypropylene and ethylene-propylene-butene ternary copolymer polypropylene, and the melt index of the polypropylene can be selected between 1-4g / 10min; In the embodiments and comparative examples listed in the present application, the copolymer polyethylene in the core layer and the heat-sealing layer is a propylene-ethylene binary copolymer polyethylene, and the melt index of the copolymer polyethylene is 4g / 10min measured at 190℃ under a load of 2.16kg; as a feasible other implementation, the melt index of the copolymer polyethylene can be selected between 2-5g / 10min; In the embodiments and comparative examples listed in the present application, the effective component of the antistatic agent masterbatch in the core layer is glycerol monostearate, and the carrier is propylene-ethylene binary copolymer polyethylene; the anti-blocking agent masterbatch in the heat-sealing layer is fumed silica with a particle size D50 of 5µm, and the carrier is propylene-ethylene binary copolymer polyethylene.

[0046] In the embodiments and comparative examples listed in the present application, the long-chain branches of the long-chain-short-chain comb-branched polyethylene are polyethylene segments, the number of carbon atoms of the polyethylene segments is 20, and the number of carbon atoms of the short-chain branches is 6, i.e. n-hexyl.

[0047] Example 1 The present embodiment provides a biaxially oriented polyethylene heat-sealing film, which comprises an upper surface layer, a core layer and a heat-sealing layer arranged in sequence. The preparation method of the resin of each layer of the biaxially oriented polyethylene heat-sealing film of the present embodiment comprises the following steps: The upper surface layer resin is prepared by mixing 58 wt% linear low density polyethylene and 42 wt% polypropylene in a high-speed mixer, and then extruding the mixture in a twin-screw extruder at an extrusion temperature of 245°C. The extruded strip is cooled, dried, cut, screened, and packaged to obtain the upper surface layer resin.

[0048] The core layer resin is prepared by uniformly mixing 99.2 wt% copolymerized polyethylene and 0.8 wt% antistatic agent masterbatch.

[0049] The heat-sealing layer resin is prepared by uniformly mixing 81.5 wt% copolymerized polyethylene, 6 wt% long-chain-short-chain comb-branched polyethylene (having a melt index of 1.5 g / 10 min at 190°C under a load of 2.16 kg, a long-chain branch content of 0.75 mol%, and a short-chain branch content of 3.5 mol%), 12 wt% itaconic acid monomethyl ester grafted polyethylene (having a melt index of 7.5 g / 10 min at 190°C under a load of 2.16 kg, and a grafting rate of 1.5%), and 0.5 wt% anti-blocking agent masterbatch.

[0050] The preparation method of the bidirectional stretched polyethylene heat-sealing film of the present embodiment includes the following steps: The raw materials of the upper surface layer, the core layer, and the heat-sealing layer are weighed and uniformly mixed under dry conditions to obtain the resin of each layer, which is then added to the corresponding extruder. The temperature of the core layer and the heat-sealing layer extruders is 240°C, and the temperature of the upper surface layer extruder is 245°C. The resin of each layer is melted and plasticized in the corresponding extruder, and then measured by a metering pump. The resins of different layers are combined at the T-shaped die to form a thick sheet. The thick sheet is cooled by a chilling roller and then stretched longitudinally in the longitudinal stretching zone at a stretching ratio of 5 times and a temperature of 110°C. Then, the film is stretched transversely in the transverse stretching zone at a stretching ratio of 8 times and a temperature of 125°C. After the film is stretched bidirectionally, it is trimmed and cut, and then subjected to corona treatment and winding to obtain the BOPE matt film.

[0051] The total thickness of the film is 22 µm, including an upper surface layer thickness of 1.7 µm, a core layer thickness of 19.5 µm, and a heat-sealing layer thickness of 0.8 µm.

[0052] Example 2 The present embodiment provides a bidirectional stretched polyethylene heat-sealing film, which includes an upper surface layer, a core layer, and a heat-sealing layer arranged in sequence. The preparation method of the resin of each layer of the bidirectional stretched polyethylene heat-sealing film of the present embodiment includes the following steps: The upper surface layer resin is prepared by mixing 58 wt% linear low density polyethylene and 42 wt% polypropylene in a high-speed mixer, and then extruding the mixture in a twin-screw extruder at an extrusion temperature of 245°C. The extruded strip is cooled, dried, cut, screened, and packaged to obtain the upper surface layer resin.

[0053] The heat-seal layer resin was prepared by uniformly mixing 81.5 wt% copolymerized polyethylene, 10 wt% long-chain branch-short-chain branch comb-branched polyethylene (melt index of 1.5 g / 10 min measured at 190°C under a load of 2.16 kg; long-chain branch content of 0.75 mol%, short-chain branch content of 3.5 mol%), 8 wt% itaconic acid monomethyl ester grafted polyethylene (melt index of 7.5 g / 10 min measured at 190°C under a load of 2.16 kg; grafting rate of 1.5%), and 0.5 wt% antiblocking agent masterbatch.

[0054] The preparation method of the biaxially oriented polyethylene heat-seal film of this example was the same as that of Example 1, and thus is not described again.

[0055] The total thickness of the film was 22 µm, of which the upper skin layer was 1.7 µm thick, the core layer was 19.5 µm thick, and the heat-seal layer was 0.8 µm thick.

[0056] Example 3 This example provides a biaxially oriented polyethylene heat-seal film, which comprises an upper skin layer, a core layer, and a heat-seal layer arranged in sequence. The preparation method of the resin of each layer of the biaxially oriented polyethylene heat-seal film of this example comprises the following steps: The upper skin layer resin was prepared in the same manner as in Example 1, and thus is not described again. The core layer resin was prepared in the same manner as in Example 1, and thus is not described again.

[0057] The heat-seal layer resin was prepared by uniformly mixing 81.5 wt% copolymerized polyethylene, 8 wt% long-chain branch-short-chain branch comb-branched polyethylene (melt index of 1.5 g / 10 min measured at 190°C under a load of 2.16 kg; long-chain branch content of 0.75 mol%, short-chain branch content of 3.5 mol%), 10 wt% itaconic acid monomethyl ester grafted polyethylene (melt index of 7.5 g / 10 min measured at 190°C under a load of 2.16 kg; grafting rate of 1.5%), and 0.5 wt% antiblocking agent masterbatch.

[0058] The preparation method of the biaxially oriented polyethylene heat-seal film of this example was the same as that of Example 1, and thus is not described again.

[0059] The total thickness of the film was 22 µm, of which the upper skin layer was 1.7 µm thick, the core layer was 19.5 µm thick, and the heat-seal layer was 0.8 µm thick.

[0060] Example 4 This example provides a biaxially oriented polyethylene heat-seal film, which comprises an upper skin layer, a core layer, and a heat-seal layer arranged in sequence. The preparation method of the resin of each layer of the biaxially oriented polyethylene heat-seal film of this example comprises the following steps: The upper surface layer resin was prepared in the same manner as in Example 1. The core layer resin was prepared in the same manner as in Example 1. The heat-sealable layer resin was prepared by uniformly mixing 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branch-short-chain branch comb-branched polyethylene (having a melt index of 2 g / 10 min measured at 190°C under a load of 2.16 kg; a long-chain branch content of 0.5 mol%, and a short-chain branch content of 5.0 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 10 g / 10 min measured at 190°C under a load of 2.16 kg; a grafting ratio of 1.0%), and 0.5 wt% of the antiblocking agent master batch.

[0061] The heat-sealable layer resin was prepared by uniformly mixing 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branch-short-chain branch comb-branched polyethylene (having a melt index of 2 g / 10 min measured at 190°C under a load of 2.16 kg; a long-chain branch content of 0.5 mol%, and a short-chain branch content of 5.0 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 10 g / 10 min measured at 190°C under a load of 2.16 kg; a grafting ratio of 1.0%), and 0.5 wt% of the antiblocking agent master batch.

[0062] The biaxially-stretched polyethylene heat-sealable film of the present example was prepared in the same manner as in Example 1.

[0063] The total thickness of the film was 22 µm, wherein the thickness of the upper surface layer was 1.7 µm, the thickness of the core layer was 19.5 µm, and the thickness of the heat-sealable layer was 0.8 µm.

[0064] Example 5 The biaxially-stretched polyethylene heat-sealable film of the present example was prepared in the same manner as in Example 1. The upper surface layer resin was prepared in the same manner as in Example 1. The core layer resin was prepared in the same manner as in Example 1. The heat-sealable layer resin was prepared by uniformly mixing 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branch-short-chain branch comb-branched polyethylene (having a melt index of 2 g / 10 min measured at 190°C under a load of 2.16 kg; a long-chain branch content of 0.5 mol%, and a short-chain branch content of 5.0 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 10 g / 10 min measured at 190°C under a load of 2.16 kg; a grafting ratio of 1.0%), and 0.5 wt% of the antiblocking agent master batch.

[0065] The heat-sealable layer resin was prepared by uniformly mixing 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branch-short-chain branch comb-branched polyethylene (having a melt index of 2 g / 10 min measured at 190°C under a load of 2.16 kg; a long-chain branch content of 0.5 mol%, and a short-chain branch content of 5.0 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 10 g / 10 min measured at 190°C under a load of 2.16 kg; a grafting ratio of 1.0%), and 0.5 wt% of the antiblocking agent master batch.

[0066] The biaxially-stretched polyethylene heat-sealable film of the present example was prepared in the same manner as in Example 1.

[0067] The total thickness of the film was 22 µm, wherein the thickness of the upper surface layer was 1.7 µm, the thickness of the core layer was 19.5 µm, and the thickness of the heat-sealable layer was 0.8 µm.

[0068] Comparative Example 1 This comparative example provides a biaxially oriented polyethylene heat-sealable film, which comprises an upper surface layer, a core layer and a heat-sealable layer arranged in sequence. The preparation method of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper surface layer resin: same as Example 1, and thus no further description is given.

[0069] Preparation of the core layer resin: same as Example 1. Thus no further description is given.

[0070] Preparation of the heat-sealable layer resin: 99.5 wt% of the copolymerized polyethylene and 0.5 wt% of the antiblocking agent masterbatch were uniformly mixed to obtain the heat-sealable layer resin.

[0071] The preparation method of the biaxially oriented polyethylene heat-sealable film of this comparative example is the same as that of Example 1, and thus no further description is given.

[0072] The total thickness of the film is 22 µm, wherein the thickness of the upper surface layer is 1.7 µm, the thickness of the core layer is 19.5 µm, and the thickness of the heat-sealable layer is 0.8 µm.

[0073] Comparative Example 2 This comparative example provides a biaxially oriented polyethylene heat-sealable film, which comprises an upper surface layer, a core layer and a heat-sealable layer arranged in sequence. The preparation method of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper surface layer resin: same as Example 1, and thus no further description is given.

[0074] Preparation of the core layer resin: same as Example 1. Thus no further description is given.

[0075] Preparation of the heat-sealable layer resin: 91.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branched-short-chain branched comb-branched polyethylene (having a melt index of 1.5 g / 10 min measured at 190 °C under a load of 2.16 kg; a long-chain branch content of 0.75 mol%, and a short-chain branch content of 3.5 mol%), and 0.5 wt% of the antiblocking agent masterbatch were uniformly mixed to obtain the heat-sealable layer resin.

[0076] The preparation method of the biaxially oriented polyethylene heat-sealable film of this comparative example is the same as that of Example 1, and thus no further description is given.

[0077] The total thickness of the film is 22 µm, wherein the thickness of the upper surface layer is 1.7 µm, the thickness of the core layer is 19.5 µm, and the thickness of the heat-sealable layer is 0.8 µm.

[0078] Comparative Example 3 This comparative example provides a biaxially oriented polyethylene heat-sealable film, which comprises an upper surface layer, a core layer and a heat-sealable layer arranged in sequence. The preparation method of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper surface layer resin: same as Example 1, and thus no further description is given.

[0079] Core layer resin preparation: same as example 1. Therefore, no further description is made.

[0080] Heat-seal layer resin preparation: 89.5wt% copolymerized polyethylene, 10wt% itaconic acid monomethyl ester grafted polyethylene (melt index of 7.5g / 10min measured at 190℃ under a load of 2.16kg; grafting rate of 1.5%), 0.5wt% anti-blocking agent masterbatch were uniformly mixed to obtain the heat-seal layer resin.

[0081] The preparation method of the biaxially stretched polyethylene heat-seal film of the present comparative example is same as example 1, therefore, no further description is made.

[0082] The total thickness of the film is 22µm, wherein the thickness of the upper skin layer is 1.7µm, the thickness of the core layer is 19.5µm, and the thickness of the heat-seal layer is 0.8µm.

[0083] Comparative example 4 The present comparative example provides a biaxially stretched polyethylene heat-seal film, which comprises an upper skin layer, a core layer and a heat-seal layer arranged in sequence. The preparation method of the biaxially stretched polyethylene heat-seal film of the present comparative example comprises the following steps: Upper skin layer resin preparation: same as example 1, therefore, no further description is made.

[0084] Core layer resin preparation: same as example 1. Therefore, no further description is made.

[0085] Heat-seal layer resin preparation: 71.5wt% copolymerized polyethylene, 8wt% long-chain branch-short-chain branch comb-branched polyethylene (melt index of 1.5g / 10min measured at 190℃ under a load of 2.16kg; long-chain branch content of 0.75mol%, short-chain branch content of 3.5mol%), 20wt% itaconic acid monomethyl ester grafted polyethylene (melt index of 7.5g / 10min measured at 190℃ under a load of 2.16kg; grafting rate of 1.5%), 0.5wt% anti-blocking agent masterbatch were uniformly mixed to obtain the heat-seal layer resin.

[0086] The preparation method of the biaxially stretched polyethylene heat-seal film of the present comparative example is same as example 1, therefore, no further description is made.

[0087] The total thickness of the film is 22µm, wherein the thickness of the upper skin layer is 1.7µm, the thickness of the core layer is 19.5µm, and the thickness of the heat-seal layer is 0.8µm.

[0088] Comparative example 5 The present comparative example provides a biaxially stretched polyethylene heat-seal film, which comprises an upper skin layer, a core layer and a heat-seal layer arranged in sequence. The preparation method of the biaxially stretched polyethylene heat-seal film of the present comparative example comprises the following steps: Upper skin layer resin preparation: same as example 1, therefore, no further description is made.

[0089] Core layer resin preparation: same as Example 1. Therefore, no further description is made.

[0090] Heat-seal layer resin preparation: 71.5 wt% copolymerized polyethylene, 18 wt% long-chain branch-short-chain branch comb-branched polyethylene (melt index of 1.5 g / 10 min measured at 190 °C under a load of 2.16 kg; long-chain branch content of 0.75 mol%, short-chain branch content of 3.5 mol%), 10 wt% itaconic acid monomethyl ester grafted polyethylene (melt index of 7.5 g / 10 min measured at 190 °C under a load of 2.16 kg; grafting rate of 1.5%), 0.5 wt% antiblocking agent masterbatch were uniformly mixed to obtain the heat-seal layer resin.

[0091] The preparation method of the biaxially stretched polyethylene heat-seal film of the present comparative example is the same as that of Example 1. Therefore, no further description is made.

[0092] The total thickness of the film was 22 µm, wherein the thickness of the upper skin layer was 1.7 µm, the thickness of the core layer was 19.5 µm, and the thickness of the heat-seal layer was 0.8 µm.

[0093] Comparative Example 6 The present comparative example provides a biaxially stretched polyethylene heat-seal film, which comprises an upper skin layer, a core layer and a heat-seal layer arranged in sequence. The preparation method of the resin of each layer of the biaxially stretched polyethylene heat-seal film of the present comparative example comprises the following steps: Preparation of the upper skin layer resin: same as Example 1. Therefore, no further description is made.

[0094] Preparation of the core layer resin: same as Example 1. Therefore, no further description is made.

[0095] Heat-seal layer resin preparation: 81.5 wt% copolymerized polyethylene, 8 wt% long-chain branch-short-chain branch comb-branched polyethylene (melt index of 1.8 g / 10 min measured at 190 °C under a load of 2.16 kg; long-chain branch content of 0.2 mol%, short-chain branch content of 3.5 mol%), 10 wt% itaconic acid monomethyl ester grafted polyethylene (melt index of 7.5 g / 10 min measured at 190 °C under a load of 2.16 kg; grafting rate of 1.5%), 0.5 wt% antiblocking agent masterbatch were uniformly mixed to obtain the heat-seal layer resin.

[0096] The preparation method of the biaxially stretched polyethylene heat-seal film of the present comparative example is the same as that of Example 1. Therefore, no further description is made.

[0097] The total thickness of the film was 22 µm, wherein the thickness of the upper skin layer was 1.7 µm, the thickness of the core layer was 19.5 µm, and the thickness of the heat-seal layer was 0.8 µm.

[0098] Comparative Example 7 This comparative example provides a biaxially oriented polyethylene heat-sealable film comprising an upper skin layer, a core layer and a heat-sealable layer arranged in sequence. The method for preparing the resins of the layers of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper skin layer resin: same as in Example 1, and thus not described again.

[0099] Preparation of the core layer resin: same as in Example 1. Thus not described again.

[0100] Preparation of the heat-sealable layer resin: 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branched-short-chain branched comb-branched polyethylene (having a melt index of 0.8 g / 10 min measured at 190 °C under a load of 2.16 kg; long-chain branch content of 0.75 mol%, short-chain branch content of 1.0 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 7.5 g / 10 min measured at 190 °C under a load of 2.16 kg; grafting rate of 1.5%), and 0.5 wt% of the antiblocking agent masterbatch were uniformly mixed to obtain the heat-sealable layer resin.

[0101] The method for preparing the biaxially oriented polyethylene heat-sealable film of this comparative example is the same as in Example 1, and thus not described again.

[0102] The total thickness of the film was 22 pm, wherein the thickness of the upper skin layer was 1.7 pm, the thickness of the core layer was 19.5 pm, and the thickness of the heat-sealable layer was 0.8 pm.

[0103] Comparative Example 8 This comparative example provides a biaxially oriented polyethylene heat-sealable film comprising an upper skin layer, a core layer and a heat-sealable layer arranged in sequence. The method for preparing the resins of the layers of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper skin layer resin: same as in Example 1, and thus not described again.

[0104] Preparation of the core layer resin: same as in Example 1. Thus not described again.

[0105] Preparation of the heat-sealable layer resin: 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branched-short-chain branched comb-branched polyethylene (having a melt index of 4.0 g / 10 min measured at 190 °C under a load of 2.16 kg; long-chain branch content of 0.75 mol%, short-chain branch content of 7.0 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 7.5 g / 10 min measured at 190 °C under a load of 2.16 kg; grafting rate of 1.5%), and 0.5 wt% of the antiblocking agent masterbatch were uniformly mixed to obtain the heat-sealable layer resin.

[0106] The method for preparing the biaxially oriented polyethylene heat-sealable film of this comparative example is the same as in Example 1, and thus not described again.

[0107] The total thickness of the film was 22 pm, wherein the thickness of the upper skin layer was 1.7 pm, the thickness of the core layer was 19.5 pm, and the thickness of the heat-sealable layer was 0.8 pm.

[0108] Comparative Example 9 This comparative example provides a biaxially oriented polyethylene heat-sealable film comprising an upper skin layer, a core layer, and a heat-sealable layer arranged in sequence. The method for preparing the resins of the layers of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper skin layer resin: same as in Example 1, and thus not described again.

[0109] Preparation of the core layer resin: same as in Example 1. Thus, not described again.

[0110] Preparation of the heat-sealable layer resin: 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branched-short-chain branched comb-branched polyethylene (having a melt index of 0.5 g / 10 min measured at 190 °C under a load of 2.16 kg; a long-chain branch content of 2.0 mol%, and a short-chain branch content of 3.5 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 7.5 g / 10 min measured at 190 °C under a load of 2.16 kg; a grafting rate of 1.5%), and 0.5 wt% of the antiblocking agent masterbatch were mixed uniformly to obtain the heat-sealable layer resin.

[0111] The method for preparing the biaxially oriented polyethylene heat-sealable film of this comparative example was the same as in Example 1, and thus not described again.

[0112] The total thickness of the film was 22 pm, wherein the thickness of the upper skin layer was 1.7 pm, the thickness of the core layer was 19.5 pm, and the thickness of the heat-sealable layer was 0.8 pm.

[0113] Comparative Example 10 This comparative example provides a biaxially oriented polyethylene heat-sealable film comprising an upper skin layer, a core layer, and a heat-sealable layer arranged in sequence. The method for preparing the resins of the layers of the biaxially oriented polyethylene heat-sealable film of this comparative example comprises the following steps: Preparation of the upper skin layer resin: same as in Example 1, and thus not described again.

[0114] Preparation of the core layer resin: same as in Example 1. Thus, not described again.

[0115] The heat-seal layer resin was prepared by uniformly mixing 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branch-short-chain branch comb-branched polyethylene (having a melt index of 1.5 g / 10 min measured at 190°C under a load of 2.16 kg; a long-chain branch content of 0.75 mol%, and a short-chain branch content of 3.5 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 15 g / 10 min measured at 190°C under a load of 2.16 kg; a grafting rate of 0.5%), and 0.5 wt% of the antiblocking agent masterbatch.

[0116] The biaxially stretched polyethylene heat-seal film of the present comparative example was prepared by the same method as that of Example 1, and thus a repeated description will not be given.

[0117] The total thickness of the film was 22 µm, wherein the upper skin layer had a thickness of 1.7 µm, the core layer had a thickness of 19.5 µm, and the heat-seal layer had a thickness of 0.8 µm.

[0118] Comparative Example 11 The present comparative example provides a biaxially stretched polyethylene heat-seal film including an upper skin layer, a core layer, and a heat-seal layer disposed in sequence. The method for preparing the resin of each layer of the biaxially stretched polyethylene heat-seal film of the present comparative example includes the following steps: The upper skin layer resin was prepared by the same method as that of Example 1, and thus a repeated description will not be given.

[0119] The core layer resin was prepared by the same method as that of Example 1, and thus a repeated description will not be given.

[0120] The heat-seal layer resin was prepared by uniformly mixing 81.5 wt% of the copolymerized polyethylene, 8 wt% of the long-chain branch-short-chain branch comb-branched polyethylene (having a melt index of 1.5 g / 10 min measured at 190°C under a load of 2.16 kg; a long-chain branch content of 0.75 mol%, and a short-chain branch content of 3.5 mol%), 10 wt% of the itaconic acid monomethyl ester grafted polyethylene (having a melt index of 15 g / 10 min measured at 190°C under a load of 2.16 kg; a grafting rate of 0.5%), and 0.5 wt% of the antiblocking agent masterbatch.

[0121] The biaxially stretched polyethylene heat-seal film of the present comparative example was prepared by the same method as that of Example 1, and thus a repeated description will not be given.

[0122] The total thickness of the film was 22 µm, wherein the upper skin layer had a thickness of 1.7 µm, the core layer had a thickness of 19.5 µm, and the heat-seal layer had a thickness of 0.8 µm.

[0123] The results of the performance test of the biaxially stretched polyethylene heat-seal films of Examples 1-5 and Comparative Examples 1-11 are shown in Table 2 below.

[0124] Table 2

[0125] From the performance test data, the bidirectional stretched polyethylene heat-seal film of the embodiments 1-5 of the present application solves the problem of insufficient heat-seal strength of the existing BOPE heat-seal film, and has low initial heat-seal temperature and smooth production, under the synergistic effect of the specific long-chain-short-chain comb-branched polyethylene and itaconic acid monomethyl ester grafted polyethylene in the heat-seal layer.

[0126] The bidirectional stretched polyethylene heat-seal film of Comparative Example 1 does not add long-chain-short-chain comb-branched polyethylene and itaconic acid monomethyl ester grafted polyethylene in the heat-seal layer, and the prepared heat-seal film has high initial heat-seal temperature and poor heat-seal strength.

[0127] The bidirectional stretched polyethylene heat-seal film of Comparative Example 2 only adds long-chain-short-chain comb-branched polyethylene in the heat-seal layer, and does not add itaconic acid monomethyl ester grafted polyethylene, so that the molecular chain still maintains a strong ordered arrangement, resulting in that the initial heat-seal temperature is still relatively high, the cohesion of the prepared heat-seal layer is not improved, and the heat-seal strength is relatively low.

[0128] The bidirectional stretched polyethylene heat-seal film of Comparative Example 3 only adds itaconic acid monomethyl ester grafted polyethylene in the heat-seal layer, and does not add long-chain-short-chain comb-branched polyethylene, so that the heat-seal master batch does not have enough cohesion to support, the heat-seal strength is not improved enough, the prepared heat-seal film has a relatively high initial heat-seal temperature and poor heat-seal strength.

[0129] The bidirectional stretched polyethylene heat-seal film of Comparative Example 4 adds too much itaconic acid monomethyl ester grafted polyethylene in the heat-seal layer, the ordered arrangement of the molecular chain is seriously broken, the heat resistance of the heat-seal layer is significantly reduced, the initial heat-seal temperature is significantly reduced, but the heat-seal strength is relatively low due to the excessive polar functional groups, and many films are broken during the production process, which is not easy to form a film.

[0130] The bidirectional stretched polyethylene heat-seal film of Comparative Example 5 adds too much long-chain-short-chain comb-branched polyethylene in the heat-seal layer, the intermolecular entanglement is excessive, the molecular chains of the heat-seal interface are difficult to fully contact, and the main chain regularity is excessively destroyed, so that the prepared heat-seal film has a high initial heat-seal temperature and poor heat-seal strength, and many films are broken during the production process, which is not easy to form a film.

[0131] The bidirectional stretched polyethylene heat-seal film of Comparative Example 6 has too little long-chain content and too high short-chain content in the long-chain-short-chain comb-branched polyethylene in the heat-seal layer, so that the intermolecular entanglement cannot be formed enough, and the main chain regularity is excessively destroyed, so that the prepared heat-seal film has a high initial heat-seal temperature and poor heat-seal strength, and poor stability.

[0132] The content of the short-chain in the long-chain-short-chain comb-branched polyethylene in the heat-seal layer of the biaxially stretched polyethylene heat-seal film of Comparative Example 7 is too low, and the content of the long-chain is too high, which causes excessive entanglement between molecules, and the molecular chains in the heat-seal interface are difficult to fully contact, and the content of the short-chain is low, which causes the crystallinity of the copolyethylene to increase to further inhibit the fusion of the interface molecular chains, and the heat-seal strength shows a downward trend, the prepared heat-seal film has high initial heat-seal temperature and poor heat-seal strength, and many films are broken during production, and it is difficult to form a film.

[0133] The content of the short-chain in the long-chain-short-chain comb-branched polyethylene in the heat-seal layer of the biaxially stretched polyethylene heat-seal film of Comparative Example 8 is too high, the content of the long-chain is too low, and the prepared heat-seal film has high initial heat-seal temperature, poor heat-seal strength, and poor stability.

[0134] The content of the long-chain in the long-chain-short-chain comb-branched polyethylene in the heat-seal layer of the biaxially stretched polyethylene heat-seal film of Comparative Example 9 is too high, the content of the short-chain is low, and the prepared heat-seal film has high initial heat-seal temperature, low heat-seal strength, and many films are broken during production, and it is difficult to form a film.

[0135] The grafting rate of the itaconic acid monomethyl ester in the itaconic acid monomethyl ester grafted polyethylene of the biaxially stretched polyethylene heat-seal film of Comparative Example 10 is too low, the number of polar functional groups such as carboxyl groups (-COOH) and ester groups (-COOCH3) in the molecular chain is small, the main chain still has high crystalline order, the crystalline structure needs high temperature to melt, and the promoting effect on molecular chain entanglement is not obvious, the cohesive force in the heat-seal layer is weakly improved, and the prepared heat-seal film has high initial heat-seal temperature and poor heat-seal strength, and poor stability The grafting rate of the itaconic acid monomethyl ester in the itaconic acid monomethyl ester grafted polyethylene of the biaxially stretched polyethylene heat-seal film of Comparative Example 11 is too high, a large number of polar functional groups strongly destroy the regularity of the main chain, the ordered arrangement of the molecular chain is broken, and only low temperature is needed to melt, the initial heat-seal temperature is significantly reduced, in addition, excessive polar functional groups cause excessive interaction between molecules, hinder the diffusion and entanglement of the molten molecular chains, and the high grafting rate increases the steric hindrance of the grafted chain, which inhibits the contact of the interface molecular chains, the prepared heat-seal film has high initial heat-seal temperature, which leads to poor heat-seal strength and poor stability.

[0136] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and the present application also intends to include these modifications and improvements.

Claims

1. A heat-seal masterbatch, characterized in that, The long-chain-short-chain comb-branched polyethylene is prepared by using ethylene as the polymerization monomer under the catalysis of main catalyst TiCl4 and auxiliary catalyst Ni(acac)2, forming polyethylene with linear polyethylene as the main chain and polyethylene segment as the long-chain branch, and then introducing C3-C9 short-chain on the linear polyethylene main chain under the synergistic effect of functional auxiliary triazine compound.

2. The heat-seal masterbatch according to claim 1, characterized in that, The melt index of the long-chain-short-chain comb-branched polyethylene is 1.0-2.0 g / 10 min under the load of 2.16 kg at 190 ℃.

3. The heat-seal masterbatch of claim 1, wherein, The itaconic acid monomethyl ester grafting polyethylene is obtained by melt grafting reaction of 83-95 wt% copolymerized polyethylene, 3-15 wt% itaconic acid monomethyl ester, 0.1-1 wt% initiator and 0.1-1 wt% antioxidant.

4. The heat-seal masterbatch of claim 1, wherein, The melt index of the itaconic acid monomethyl ester grafting polyethylene is 5-10 g / 10 min under the load of 2.16 kg at 190 ℃.

5. The heat-seal masterbatch of claim 1, wherein, The upper surface layer, the core layer and the heat-sealing layer are sequentially arranged; the core layer comprises copolymerized polyethylene; and the heat-sealing layer comprises the heat-sealing master batch as claimed in any one of claims 1-5.

6. A biaxially oriented polyethylene heat-sealable film, characterized in that, The melt index of the copolymerized polyethylene in the core layer and the heat-sealing layer is 2-5 g / 10 min under the load of 2.16 kg at 190 ℃, and the copolymerized polyethylene comprises one or more of binary copolymerized polyethylene and ternary copolymerized polyethylene, the binary copolymerized polyethylene is formed by copolymerization of one of propylene, butene, hexene or octene and ethylene, and the ternary copolymerized polyethylene comprises ethylene-propylene-butene ternary copolymer.

7. The biaxially oriented polyethylene heat sealable film according to claim 6, characterized in that, The upper surface layer comprises 50-70 wt% linear low-density polyethylene and 30-50 wt% polypropylene.

8. The biaxially-oriented polyethylene heat-sealable film according to claim 6, characterized in that, The melt index of the linear low-density polyethylene is 5-15 g / 10 min under the load of 2.16 kg at 190 ℃; and the melt index of the polypropylene is 1-4 g / 10 min under the load of 2.16 kg at 230 ℃, and the polypropylene comprises one or more of homopolymerized polypropylene and copolymerized polypropylene, and the copolymerized polypropylene comprises one or more of ethylene-propylene binary copolymerized polypropylene and ethylene-propylene-butene ternary copolymerized polypropylene.

9. The biaxially oriented polyethylene heat sealable film according to claim 8, characterized in that, The method comprises the following steps:

10. A process for the production of a biaxially oriented polyethylene heat-seal film according to any one of claims 6 to 9, characterized in that, ​ The raw materials of each layer are weighed and mixed according to the proportion under dry conditions, and then the obtained resin of each layer is added into each extruder; the resin of each layer is melted and plasticized in each extruder, and then is metered by a metering pump, and is converged at a T-shaped die through different extruder channels to form a thick sheet; the thick sheet is cooled by a chilling roller, and after shaping, is first introduced into a longitudinal stretching zone for longitudinal stretching, and then is introduced into a transverse stretching zone for transverse stretching, and after the biaxial stretching of the film is completed, the film is trimmed and cut, and then is subjected to corona treatment and winding to obtain the biaxially stretched polyethylene heat-seal film.

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