A kind of BOPE matte film and preparation method thereof

Abstract

The present invention belongs to the field of thin films, and relates to a BOPE matte film and a preparation method thereof, wherein the BOPE matte film comprises a matte layer, a core layer and a lower surface layer which are arranged in sequence; the matte layer comprises 22-47.5wt% of a first metallocene linear low-density polyethylene, 38-48wt% of polypropylene and 10-30wt% of a propylene-based copolymer, wherein the melting point of the propylene-based copolymer is 140-160°C and the crystallinity is 5-10%; the core layer and the lower surface layer both comprise a second metallocene linear low-density polyethylene. The BOPE matte film of the present invention, by adding a certain proportion of a high-melting-point, highly transparent, low-crystalline propylene-based copolymer into the matte layer, not only improves the temperature resistance of the matte layer, but also improves the matte effect of the matte film, and improves the production efficiency and use efficiency of the matte film.

Description

Technical Field

[0001] The invention relates to the field of films, in particular to a BOPE matte film and a preparation method thereof. Background Art

[0002] With the continuous promotion of single material recyclability, biaxially oriented BOPE film has gradually become a popular packaging material. Among them, BOPE matte film has also attracted the attention of the packaging industry because of its softer texture. The matte principle of BOPE matte film is that during the gradual and rapid stretching of the matte film thick sheet, the incompatible polyolefin phase of its matte layer responds differently to the stretching force due to the difference in viscosity and crystallization rate. The dispersed phase bulges out under stretching to form a rough surface. The matte surface scatters light to different degrees, thereby adjusting the gloss and providing soft gloss and high-end packaging texture.

[0003] In the production of BOPE matte film, the polypropylene phase that crystallizes first in the matte layer is the dispersed phase, commonly known as the island phase of the sea-island structure, and the continuous phase that crystallizes later and has low crystallinity is the sea phase of the sea-island structure. Because the two phases have poor thermodynamic compatibility and a large viscosity difference, the island phase that crystallizes first is more likely to protrude during stretching. However, in BOPE matte film, polyethylene is used as the continuous phase. Although its crystallization temperature is lower than that of the dispersed phase, its crystallization rate is relatively faster and its crystallinity is relatively higher. The excessively fast crystallization rate leads to poor roller adhesion of thick sheets, a narrow stretching window, and difficulty in adjusting the thickness, and at the same time, it is impossible to obtain a good matte effect. In addition, because the matte layer of BOPE matte film uses metallocene linear low-density polyethylene as the continuous phase, its melting point is low. When producing BOPE matte film, its temperature resistance is poor, and the film surface is easily burned by the high-temperature roller to form film surface defects. Therefore, the process personnel produce by cooling, but the production of thick sheet roller adhesion increases the difficulty of production by cooling, and the low production efficiency is also one of the reasons that restrict the expansion of BOPE matte film. Summary of the invention

[0004] Based on this, the purpose of the present invention is to provide a BOPE matte film, which not only improves the temperature resistance of the matte layer, but also improves the matte effect of the matte film, improves the production efficiency and use efficiency of the matte film, and has the advantages of a wide production temperature range and high production efficiency.

[0005] The technical solution of the present invention is achieved by the following methods:

[0006] A BOPE matte film comprises a matte layer, a core layer and a lower surface layer which are arranged in sequence; the matte layer comprises 22-47.5wt% of a first metallocene linear low-density polyethylene, 38-48wt% of polypropylene and 10-30wt% of a propylene-based copolymer, wherein the melting point of the propylene-based copolymer is 140-160°C and the crystallinity is 5-10%; the core layer and the lower surface layer both comprise a second metallocene linear low-density polyethylene.

[0007] The matte effect of BOPE matte film is mainly caused by the surface morphology of the matte layer of the matte film having a certain degree of roughness. When light is irradiated to the film surface, light scattering occurs to varying degrees, resulting in a matte effect. In order to form a sufficient degree of roughness in the matte layer of the matte film, part of the polyolefin phase needs to be convex. In the biaxially stretched matte film, this convexity is formed when two or more incompatible systems have different tensile force responses under a certain viscosity difference and different polyolefins have different relative tensile force responses.

[0008] The inventors found that by properly utilizing the crystallization temperature difference between the two phases in the matte layer, the polypropylene dispersed phase can be more easily hardened and protruded during stretching. The larger the size of the protruding polypropylene dispersed phase, the greater the roughness. At the same time, in order to obtain better roughness, the crystallization temperature or degree of crystallization of the continuous phase should be lower than that of the dispersed phase, because during stretching, the polyethylene phase with a low crystallization temperature or low crystallinity is more likely to extend along the stretching direction, and the dispersed phase with a high crystallization temperature or high crystallinity is more likely to protrude due to its high hardness after crystallization. The polyethylene raw materials used in the existing BOPE matte film generally have a high degree of crystallinity and a low melt index, which leads to high pressure during extrusion. After the polyethylene crystallizes, the thick sheet has a poor roller sticking effect. During high-speed production, the thick sheet swings greatly, affecting the thickness. In this regard, many process personnel will choose to increase the temperature of the extruder of the matte layer of the BOPE matte film to reduce the extrusion pressure. The temperature of the metallocene linear low-density polyethylene melt on the high-speed stretching roller can even reach 135°C. However, the metallocene linear low-density polyethylene melt in the matte layer of the BOPE matte film has low viscosity and low melting point, and is easily coated on the polypropylene phase. In addition, the speed of the longitudinal stretching production stage is slow. After the extrusion temperature is increased, the low melting point of the first metallocene linear low-density polyethylene makes the matte layer easy to stick to the roller and burn. Even if the extrusion temperature is not increased, the matte surface is prone to high-temperature burns when the downstream BOPE matte film is coated. Therefore, the inventors added 10-30wt% of a propylene-based copolymer with better temperature resistance and lower crystallinity to the matte layer of the present invention to replace part of the first metallocene linear low-density polyethylene as the continuous phase, while improving the defects of the existing BOPE matte film, such as poor matte effect and low temperature resistance. On the one hand, the temperature of the longitudinal stretching zone is currently set at 125-135°C during the production of BOPE matte film. The inventors intuitively improved the temperature resistance of the matte layer by adding a propylene-based copolymer with a higher melting point to the matte layer. On this basis, the inventors further found that the change in the melting point of the propylene-based copolymer not only affects the temperature resistance of the matte layer, but also affects the matte effect of the matte layer. Specifically, the inventors found through a large number of practices that the melting point of the propylene-based copolymer added to the matte layer should be controlled at 140-160°C. If the melting point of the propylene-based copolymer is less than 140°C, the matte layer cannot be effectively protected from heat. If the melting point of the propylene-based copolymer is greater than 160°C, the melting point difference is too large, which is likely to cause poor stretching of the matte surface. Preferably, the propylene-based copolymer of the present invention has a melting point of 140°C. The propylene-based copolymer at this melting point has good compatibility with the other materials of the matte layer, can be well dispersed in the polyethylene phase and the polypropylene phase, and can effectively improve the temperature resistance of the matte layer.On the other hand, since lowering the crystallization temperature or crystallinity of the continuous phase in the matt layer is beneficial to achieving coarsening of the film surface during stretching, the degree of light scattering can be increased by increasing the roughness of the film surface. The inventors adopted a propylene-based copolymer with lower crystallinity, and on this basis ensured the smooth production of the matt film. Specifically, the inventors controlled the crystallinity of the propylene-based copolymer at a relatively low level of 5 to 10%. If the crystallinity of the propylene-based copolymer is less than 5%, the melt viscosity is very low, which has certain difficulties in production, processing and feeding. If the crystallinity of the propylene-based copolymer is greater than 10%, a larger amount needs to be added to significantly reduce the total crystallization enthalpy of the continuous phase. Furthermore, the inventors also found that the amount of propylene-based copolymer added should be controlled at 10-30wt%. If the amount of propylene-based copolymer added is less than 10wt%, although the total crystallization enthalpy of the continuous phase decreases and the haze of the matte film is improved to a certain extent, the amount of propylene-based copolymer added is low, and it is not enough to form a continuous amorphous continuous phase after shear dispersion, and the effect of improving the temperature resistance of the matte layer is not obvious; if the amount of propylene-based copolymer added is higher than 30wt%, the tensile strength of the BOPE matte film will be significantly reduced, and the thermal shrinkage ratio of the matte film will be increased. The present invention adds a propylene-based copolymer with a higher melting point and a lower crystallinity in the matt layer and controls the addition amount of the propylene-based copolymer to be 10-30wt%. Based on the characteristics that the propylene-based copolymer has a higher melting point and a lower tensile strength than the first metallocene linear low-density polyethylene, on the one hand, the crystallinity of the continuous phase in the matt layer system is reduced, and the polypropylene phase is more easily protruded during stretching, thereby increasing the roughness of the matt layer. On the other hand, the melting point of the continuous phase is increased, which not only improves the matt effect of the matt film, but also improves the temperature resistance of the matt layer of the BOPE matt film. On the other hand, the matt film can be smoothly produced, thereby improving the production efficiency of the BOPE matt film of the present invention, and can be applied to a wider range of packaging purposes and application scenarios.

[0009] Further, the melt index of the first metallocene linear low-density polyethylene was measured to be 5~15g / 10min at 190°C and 2.16kg, and the melt index of the polypropylene was measured to be 0.1~5g / 10min at 230°C and 2.16kg. The inventors have found through a lot of practice that in the BOPE matte layer composed of the first metallocene linear low-density polyethylene and polypropylene, the low melt index polypropylene has a higher melt viscosity, and the first metallocene linear low-density polyethylene with a relatively high melt index has a low viscosity. During the shear plasticization process, the low-viscosity polyethylene phase is easy to cover the high-viscosity polypropylene phase. The greater the difference in viscosity between the two phases, the greater the roughness of the matte layer during stretching. However, the difference in melt index between metallocene linear low-density polyethylene and polypropylene is too large, and the melt viscosity difference is too large, resulting in the high-viscosity polypropylene being unable to be evenly dispersed in the low-viscosity polyethylene phase. When producing BOPE matte film, there is obvious uneven matte on the film surface, and even causes film breakage. The difference in melt viscosity between the two phases is controlled. The melt viscosity of the continuous phase first metallocene linear low-density polyethylene is lower than the melt viscosity of the dispersed phase polypropylene. The melt index of the first metallocene linear low-density polyethylene is limited to 5~15g / 10min (190℃, 2.16kg), and the melt index of polypropylene is limited to 0.1~5g / 10min (230℃, 2.16kg). If the melt viscosity of the continuous phase first metallocene linear low-density polyethylene is too small, the dispersion uniformity will deteriorate. If the melt viscosity of the continuous phase first metallocene linear low-density polyethylene is too large, the two phases will have a smaller dispersed phase size due to the close viscosity, which is also not conducive to improving the roughness. Therefore, the melt index of the first metallocene linear low-density polyethylene is controlled at 5~15g / 10min, and the melt index of polypropylene is controlled at 0.1~5g / 10min.

[0010] Furthermore, the melt index of the propylene-based copolymer is controlled to be 5-10 g / 10 min under the conditions of 230° C. and 2.16 kg. If the melt index of the propylene-based copolymer is less than 5 g / 10 min, it is not conducive to the fluidity of the matte layer and the improvement of the matte uniformity of the edge of the matte film. If the melt index of the propylene-based copolymer is greater than 10 g / 10 min, the melt viscosity and the dispersed phase are greatly different, which is not conducive to shear dispersion and is not conducive to better maintaining the mechanical strength of the matte layer system.

[0011] Further, the propylene-based copolymer is a propylene-1-butene copolymer, in which the isotacticity of the propylene sequence is 90-93%, and the isotacticity of the 1-butene sequence is 87-90%. It is well known to those skilled in the art that, generally for propylene-1-butene copolymers, the introduction of 1-butene units destroys the sequence structure of the polypropylene chain molecular chain, causing the crystallinity of the polymer to decrease, and the melting temperature decreases significantly with the increase of 1-butene. However, the propylene-1-butene copolymer selected by the present invention is synthesized by an optimized catalytic system using stereo-controlled polymerization, specifically, using alkyl aluminum or alkyl aluminum hydrogenation, external electron donor, supported titanium catalyst and hydrogen as the catalyst system for isotactic polymerization, bulk copolymerization is performed to obtain the propylene-1-butene copolymer, the isotacticity of the 1-butene sequence and the propylene sequence in the obtained propylene-1-butene copolymer is greater than 85%, and with the increase of 1-butene content, the melting temperature of the copolymer rises significantly, so that the propylene-1-butene copolymer has a relatively high melting point, while maintaining a relatively low crystallinity. A propylene-1-butene copolymer consisting of a propylene sequence having an isotacticity of 90-93% and a 1-butene sequence having an isotacticity of 87-90% is selected. If the isotacticity of the propylene sequence is too low, the melting point of the propylene-1-butene copolymer is too low. When added to the matt layer, the matt layer cannot be effectively protected against heat. If the isotacticity of the propylene sequence is too high, the crystallinity of the propylene-1-butene copolymer will increase, which is not conducive to improving the haze of the matt film. If the isotacticity of the 1-butene sequence is too low, the melting point of the 1-butene sequence in the propylene-1-butene copolymer will be too low, which is not conducive to obtaining a propylene-1-butene copolymer with a relatively high melting point. When added to the matt layer, the matt layer cannot be effectively protected against heat. If the isotacticity of the 1-butene sequence is too high, the propylene-1-butene copolymer may be too rigid and not conducive to biaxial stretching.

[0012] Preferably, the 1-butene monomer content in the propylene-1-butene copolymer of the present invention is selected to be 15-35wt%. If the 1-butene content is lower than 15wt%, the isotacticity of the propylene sequence in the propylene-1-butene copolymer increases, and the crystallization enthalpy of the propylene-1-butene copolymer increases, which is not conducive to improving the haze of the matte film. If the 1-butene content is higher than 35wt%, the copolymer may have more side chains, which increases the number of chain segment entanglements, makes chain disentanglement and slippage difficult, and increases the extrusion processing pressure of the polymer.

[0013] Furthermore, the matt layer further comprises 0.3-0.5wt% antioxidant, the antioxidant comprises antioxidant 1010 and antioxidant 168, and the ratio of antioxidant 1010 to antioxidant 168 is 1:3. The antioxidant is added mainly to reduce the cross-linking of the first metallocene linear low-density polyethylene during the high temperature and high pressure extrusion process, thereby causing crystal point defects on the film surface.

[0014] Furthermore, the melt index of the second metallocene linear low-density polyethylene measured at 190° C. and 2.16 kg is 3-10 g / 10 min.

[0015] Furthermore, the core layer comprises 99-99.5wt% of the second metallocene linear low-density polyethylene and 0.5-1wt% of the antistatic agent masterbatch, the base resin of the antistatic agent masterbatch is the second metallocene-catalyzed linear low-density polyethylene, and the effective content of the antistatic agent in the antistatic agent masterbatch is 40wt%.

[0016] Furthermore, the lower surface layer comprises 99-99.5 wt % of a second metallocene linear low-density polyethylene and 0.5-1 wt % of a silica anti-blocking agent masterbatch.

[0017] The present invention also provides a method for preparing any of the above-mentioned BOPE matte films, comprising the following steps: weighing and mixing the resin raw materials of each layer and then melt-extruding them separately, wherein the matte layer extruder is a co-rotating twin-screw extruder, and the core layer and the lower surface smooth layer are extruded by a single screw extruder, and the melts of each layer are merged into a thick sheet after extrusion, and the thick sheet is cooled by a chilling roller and a chilling tank, and the thick sheet is first preheated by longitudinal stretching at a preheating temperature of 125°C, and then longitudinally stretched at a longitudinal stretching multiple of 5 times and a longitudinal stretching temperature of 128°C, followed by longitudinal stretching and shaping, and then transverse stretching and preheating after longitudinal stretching and shaping, and then transverse stretching, at a transverse stretching multiple of 8 times and a transverse stretching temperature of 128°C, and then transverse stretching and shaping, and finally corona treatment, winding and slitting into finished film products.

[0018] In order to better understand and implement the present invention, the present invention is described in detail below. DETAILED DESCRIPTION

[0019] It should be clear that the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the embodiments of the present application.

[0020] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. The singular forms of "a", "said" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms, unless the context clearly indicates other meanings. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more associated listed items.

[0021] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the attached claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects, and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to the specific circumstances.

[0022] In addition, in the description of this application, unless otherwise specified, "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0023] It should be understood that the embodiments of the present application are not limited to the precise structure described above, and various modifications and changes can be made without departing from the scope thereof. The scope of the embodiments of the present application is limited only by the appended claims.

[0024] In the determined matt layer formula, the matt effect is most significantly affected by the addition ratio of the dispersed phase of the matt layer. In order to more conveniently illustrate the effect of the present invention, the weight percentage of the dispersed phase in all the following embodiments is the same, that is, the content of polypropylene in the matt layer is kept unchanged.

[0025] The BOPE matte film of the present invention not only improves the temperature resistance of the matte layer, but also improves the matte effect of the matte film, improves the production efficiency and use efficiency of the matte film, and has the advantages of a wide production temperature range and high production efficiency.

[0026] Further, the melt index of the first metallocene linear low-density polyethylene was measured to be 5~15g / 10min at 190°C and 2.16kg, and the melt index of the polypropylene was measured to be 0.1~5g / 10min at 230°C and 2.16kg. The inventors have found through a lot of practice that in the BOPE matte layer composed of the first metallocene linear low-density polyethylene and polypropylene, the melt viscosity of the polypropylene with a low melt index is greater, and the first metallocene linear low-density polyethylene with a relatively high melt index has a low viscosity. During the shear plasticization process, the low-viscosity polyethylene phase is easy to cover the high-viscosity polypropylene phase. The greater the difference in viscosity between the two phases, the greater the roughness of the matte layer during stretching. However, the difference in melt index between metallocene linear low-density polyethylene and polypropylene is too large, and the melt viscosity difference is too large, resulting in the high-viscosity polypropylene being unable to be evenly dispersed in the low-viscosity polyethylene phase. When producing BOPE matte film, there is obvious uneven matte on the film surface, and even causes film breakage. The difference in melt viscosity between the two phases is controlled. The melt viscosity of the continuous phase first metallocene linear low-density polyethylene is lower than the melt viscosity of the dispersed phase polypropylene. The melt index of the first metallocene linear low-density polyethylene is limited to 5~15g / 10min (190℃, 2.16kg), and the melt index of polypropylene is limited to 0.1~5g / 10min (230℃, 2.16kg). If the melt viscosity of the continuous phase first metallocene linear low-density polyethylene is too small, the dispersion uniformity will deteriorate. If the melt viscosity of the continuous phase first metallocene linear low-density polyethylene is too large, the two phases will have a smaller dispersed phase size due to the close viscosity, which is also not conducive to improving the roughness. Therefore, the melt index of the first metallocene linear low-density polyethylene is controlled at 5~15g / 10min, and the melt index of polypropylene is controlled at 0.1~5g / 10min.

[0027] Furthermore, the melt index of the propylene-based copolymer is measured at 230°C and 2.16kg, and is 5-10g / 10min. If the melt index of the propylene-based copolymer is less than 5g / 10min, it is not conducive to the fluidity of the matte layer and the improvement of the matte uniformity of the edge of the matte film. If the melt index of the propylene-based copolymer is greater than 10g / 10min, the melt viscosity and the dispersed phase are greatly different, which is not conducive to shear dispersion and is not conducive to better maintaining the mechanical strength of the matte layer system.

[0028] Furthermore, the propylene-based copolymer is a propylene-1-butene copolymer, in which the isotacticity of the propylene sequence is 90-93%, and the isotacticity of the 1-butene sequence is 87-90%.

[0029] Further, the propylene-1-butene copolymer, wherein the content of 1-butene is 15-35wt%. The propylene-1-butene copolymer of the present invention is synthesized by using an optimized catalytic system of stereo-controlled polymerization, specifically, using alkyl aluminum or alkyl aluminum hydride, an external electron donor, a supported titanium catalyst and hydrogen as a catalyst system for isotactic polymerization, and performing bulk copolymerization to obtain the propylene-1-butene copolymer. The isotacticity of the 1-butene sequence and the propylene sequence in the obtained propylene-based copolymer is greater than 85%, and with the increase of the 1-butene content, the melting temperature of the copolymer does not decrease but increases significantly. Preferably, the 1-butene monomer content in the propylene-1-butene copolymer of the present invention is selected to be 15-35wt%. If the 1-butene content is lower than 15wt%, the isotacticity of the propylene sequence in the propylene-1-butene copolymer increases, and the crystallization enthalpy of the copolymer increases, which is not conducive to improving the haze of the matte film. If the 1-butene content is higher than 35wt%, the copolymer may have more side chains, which increases the number of chain segment entanglements, makes chain disentanglement and slippage difficult, and increases the extrusion processing pressure of the polymer.

[0030] Furthermore, the matte layer has a thickness of 2-3 μm. The BOPE matte film of the present invention has a thickness of 15-40 μm, and the lower surface glossy layer has a thickness of 1-1.5 μm.

[0031] Furthermore, the matt layer further comprises 0.3-0.5wt% antioxidant, the antioxidant comprises antioxidant 1010 and antioxidant 168, and the ratio of antioxidant 1010 to antioxidant 168 is 1:3. The antioxidant is added mainly to reduce the cross-linking of the first metallocene linear low-density polyethylene during the high temperature and high pressure extrusion process, thereby causing crystal point defects on the film surface.

[0032] Furthermore, the melt index of the second metallocene linear low-density polyethylene measured at 190° C. and 2.16 kg is 3-10 g / 10 min.

[0033] Furthermore, the core layer comprises 99-99.5wt% of the second metallocene linear low-density polyethylene and 0.5-1wt% of the antistatic agent masterbatch, the base resin of the antistatic agent masterbatch is the second metallocene-catalyzed linear low-density polyethylene, and the effective content of the antistatic agent in the antistatic agent masterbatch is 40wt%.

[0034] Furthermore, the lower surface layer comprises 99-99.5 wt % of a second metallocene linear low-density polyethylene and 0.5-1 wt % of a silica anti-blocking agent masterbatch.

[0035] The present invention also provides a method for preparing any of the above-mentioned BOPE matte films, comprising the following steps: weighing and mixing the resin raw materials of each layer and then melt-extruding them separately, wherein the matte layer extruder is a co-rotating twin-screw extruder, and the core layer and the lower surface smooth layer are extruded by a single screw extruder, and the melts of each layer are merged into a thick sheet after extrusion, and the thick sheet is cooled by a chilling roller and a chilling tank, and the thick sheet is first preheated by longitudinal stretching at a preheating temperature of 125°C, and then longitudinally stretched at a longitudinal stretching multiple of 5 times and a longitudinal stretching temperature of 128°C, followed by longitudinal stretching and shaping, and then transverse stretching and preheating after longitudinal stretching and shaping, and then transverse stretching, at a transverse stretching multiple of 8 times and a transverse stretching temperature of 128°C, and then transverse stretching and shaping, and finally corona treatment, winding and slitting into finished film products.

[0036] The physical properties and test methods of the embodiments or comparative examples of the present invention are as follows:

[0037] Melting point and crystallinity were measured by DSC;

[0038] The gloss test is carried out according to GB / T8807-1988 standard, the haze test is carried out according to GB / T2410-2008 standard, and the mechanical property test is carried out according to GB / T1040.3-2006 standard.

[0039] In the heat shrinkage test, the film sample size is 10*10 cm. After being placed in an oven at 110°C for 120 seconds, the longitudinal and transverse shrinkage of the film is tested at room temperature.

[0040] For defect point detection, the statistical cycle is 10,000 meters of online detector winding, and the particle size of the defect points counted is 1mm² and above.

[0041] It should be noted that the proportions described in the embodiments or comparative examples of the present invention are all weight percentages.

[0042] Example 1

[0043] The present embodiment provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The method for preparing each layer of resin of the BOPE matte film of the present embodiment comprises the following steps:

[0044] Preparation of matte layer resin: 42.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 10wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 23.5wt%; the melt index measured at 230°C and 2.16kg is 8.3g / 10min; the crystallinity is 6.1%; the melting point is 140°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 90%, and the isotacticity of the 1-butene sequence is 87%) are uniformly mixed to obtain a matte layer resin.

[0045] Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0046] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the fumed silica masterbatch of the second metallocene linear low density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0047] The preparation method of the BOPE matte film of this embodiment comprises the following steps:

[0048] It is produced on a Bruckner production line with a width of 4.2m. The resin raw materials of each layer are weighed and mixed and then melt-extruded separately. The matt layer extruder is a co-rotating twin-screw extruder with a temperature of 240°C. The core layer and the lower surface smooth layer are extruders with a temperature of 250°C. After the melts of each layer are extruded, they merge into a thick sheet at the T-die head. The thick sheet is cooled by a chilling roller and a chilling tank. The thick sheet is first preheated by longitudinal stretching at a preheating temperature of 125°C, and then longitudinally stretched at a longitudinal stretching multiple of 5 times and a longitudinal stretching temperature of 128°C. Then, it is stretched longitudinally for shaping. After longitudinal stretching and shaping, it is preheated by transverse stretching, and then transversely stretched at a transverse stretching multiple of 8 times and a transverse stretching temperature of 128°C. Then, it is stretched transversely for shaping, and finally corona treatment is performed, and it is rolled and slit into finished film products.

[0049] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0050] Example 2

[0051] The present embodiment provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The method for preparing each layer of resin of the BOPE matte film of the present embodiment comprises the following steps:

[0052] Preparation of matte layer resin: 32.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 20wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 23.5wt%; the melt index measured at 230°C and 2.16kg is 8.3g / 10min; the crystallinity is 6.1%; the melting point is 140°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 90%, and the isotacticity of the 1-butene sequence is 90%) are uniformly mixed to obtain a matte layer resin. Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0053] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the anti-blocking agent masterbatch is the fumed silica masterbatch of the second metallocene linear low density polyethylene, with a melt index of 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0054] The preparation method of the BOPE matte film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0055] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0056] Example 3

[0057] The present embodiment provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The method for preparing each layer of resin of the BOPE matte film of the present embodiment comprises the following steps:

[0058] Preparation of matte layer resin: 32.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 20wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 31.3wt%; the melt index measured at 230°C and 2.16kg is 7.1g / 10min; the crystallinity is 7.46wt%; the melting point is 160°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 93%, and the isotacticity of the 1-butene sequence is 90%) are uniformly mixed to obtain a matte layer resin. Preparation of core layer resin: 99.5 wt % of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt % of the antistatic agent are uniformly mixed to obtain a core layer resin.

[0059] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low-density polyethylene (the melt index measured at 190°C and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent (the fumed silica masterbatch of the second metallocene linear low-density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0060] The preparation method of the BOPE matte film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0061] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0062] Example 4

[0063] The present embodiment provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The method for preparing each layer of resin of the BOPE matte film of the present embodiment comprises the following steps:

[0064] Preparation of matte layer resin: 27.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 25wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 15wt%; the melt index measured at 230°C and 2.16kg is 7.5g / 10min; crystallinity is 6.7%; melting point is 148°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 91%, and the isotacticity of the 1-butene sequence is 88%) are uniformly mixed to obtain a matte layer resin. Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0065] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the anti-blocking agent masterbatch is the fumed silica masterbatch of the second metallocene linear low density polyethylene, with a melt index of 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0066] The preparation method of the BOPE matte film of this embodiment is the same as that of Embodiment 1, so it is not described in detail.

[0067] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0068] Comparative Example 1

[0069] This comparative example provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The preparation method of each layer of resin of the BOPE matte film of this comparative example comprises the following steps:

[0070] Preparation of matt layer resin: 52.5 wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16 kg is 12 g / 10 min), 47 wt% of homopolypropylene (melt index measured at 230°C and 2.16 kg is 0.3 g / 10 min) and 0.5 wt% of antioxidant (antioxidant 1010: antioxidant 168 = 1:3) are uniformly mixed to obtain a matt layer resin.

[0071] Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0072] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the fumed silica masterbatch of the second metallocene linear low density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0073] The preparation method of the BOPE matte film in this comparative example is the same as that in Example 1, so it is not described in detail.

[0074] The total thickness of the matt film is 40 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0075] Comparative Example 2

[0076] This comparative example provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The preparation method of each layer of resin of the BOPE matte film of this comparative example comprises the following steps:

[0077] Preparation of matte layer resin: 47.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 5wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 23.5wt%; the melt index measured at 230°C and 2.16kg is 8.3g / 10min; crystallinity is 6.1%; melting point is 140°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 90%, and the isotacticity of the 1-butene sequence is 90%) are uniformly mixed to obtain a matte layer resin.

[0078] Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0079] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the fumed silica masterbatch of the second metallocene linear low density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0080] The preparation method of the BOPE matte film in this comparative example is the same as that in Example 1, so it is not described in detail.

[0081] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0082] Comparative Example 3

[0083] This comparative example provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The preparation method of each layer of resin of the BOPE matte film of this comparative example comprises the following steps:

[0084] Preparation of matte layer resin: 17.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 35wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 23.5wt%; the melt index measured at 230°C and 2.16kg is 8.3g / 10min; the crystallinity is 6.1%; the melting point is 140°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 90%, and the isotacticity of the 1-butene sequence is 90%) are uniformly mixed to obtain a matte layer resin.

[0085] Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0086] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the fumed silica masterbatch of the second metallocene linear low density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0087] The preparation method of the BOPE matte film in this comparative example is the same as that in Example 1, so it is not described in detail.

[0088] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0089] Comparative Example 4

[0090] This comparative example provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The preparation method of each layer of resin of the BOPE matte film of this comparative example comprises the following steps:

[0091] Preparation of matte layer resin: 42.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 10wt% of propylene-based copolymer (propylene-1-butene copolymer, the comonomer ratio of 1-butene is 23.5wt%; the melt index measured at 230°C and 2.16kg is 8.3g / 10min; the crystallinity is 4.1%; the melting point is 120°C; in the propylene-1-butene copolymer, the isotacticity of the propylene sequence is 70%, and the isotacticity of the 1-butene sequence is 80%) are uniformly mixed to obtain a matte layer resin.

[0092] Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0093] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the fumed silica masterbatch of the second metallocene linear low density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0094] The preparation method of the BOPE matte film in this comparative example is the same as that in Example 1, so it is not described in detail.

[0095] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0096] Comparative Example 5

[0097] This comparative example provides a BOPE matte film, comprising a matte layer, a core layer and a lower surface layer arranged in sequence. The preparation method of each layer of resin of the BOPE matte film of this comparative example comprises the following steps:

[0098] Preparation of matt layer resin: 42.5wt% of the first metallocene linear low-density polyethylene (melt index measured at 190°C and 2.16kg is 12g / 10min), 47wt% of homopolypropylene (melt index measured at 230°C and 2.16kg is 0.3g / 10min), 0.5wt% of antioxidant (antioxidant 1010: antioxidant 168=1:3) and 10wt% of propylene-based copolymer (propylene-1-butene copolymer, comonomer ratio of 1-butene is 23.5wt%; melt index measured at 230°C and 2.16kg is 8.3g / 10min; crystallinity is 40%; melting point is 165°C; propylene sequence isotacticity is 97%, 1-butene sequence isotacticity is 93%) are uniformly mixed to obtain a matt layer resin.

[0099] Preparation of core layer resin: 99.5 wt% of the second metallocene linear low-density polyethylene (melt index measured at 190° C. and 2.16 kg is 2.1 g / 10 min) and 0.5 wt% of antistatic agent masterbatch are uniformly mixed to obtain core layer resin.

[0100] Preparation of lower surface layer resin: Take 99wt% of the second metallocene linear low density polyethylene (the melt index measured at 190℃ and 2.16kg is 2.1g / 10min) and 1wt% of the anti-blocking agent masterbatch (the fumed silica masterbatch of the second metallocene linear low density polyethylene, the melt index is 4g / 10min, and the effective concentration of the fumed silica is 6wt%) and mix them evenly to obtain the lower surface layer resin.

[0101] The preparation method of the BOPE matte film in this comparative example is the same as that in Example 1, so it is not described in detail.

[0102] The total thickness of the matt film is 30 μm, of which the matt layer thickness is 2.8 μm and the lower surface layer thickness is 1.3 μm.

[0103] The performance test results of the BOPE matte films of Examples 1 to 4 and Comparative Examples 1 to 5 are shown in Table 1 below.

[0104] Table 1

[0105]

[0106] In the present invention, the BOPE matte films produced in all embodiments show good matte effect, and as the proportion of the propylene-based copolymer increases, the haze data of the BOPE matte film increases to a certain extent, while the glossiness decreases in inverse proportion.

[0107] From Comparative Examples 1 and 2, it was found that when the low crystallinity propylene copolymer was added to the system, the matte effect of the film surface of Comparative Example 2 began to improve to a certain extent, and the glossiness decreased. In Comparative Example 3, when the propylene copolymer was added to 35wt%, the haze increased significantly.

[0108] In Comparative Example 4, the isotacticity of the propylene sequence and the 1-butene sequence in the propylene-based copolymer is too low, resulting in lower melting point and crystallinity of the propylene-based copolymer. The melt viscosity is very low during the production process, which poses certain difficulties for production processing and feeding, affecting the smoothness of production and production efficiency. Moreover, it can be seen from the data that the number of defects on the matte surface of the prepared matte film is significantly increased, that is, the matte layer cannot be effectively protected against heat, and the heat shrinkage rate is increased. The coating of downstream manufacturers will result in film curling, large overprint positioning deviation and other serious quality problems. However, due to the further reduction in the crystallinity of the propylene-based copolymer, the decrease in the total crystallization enthalpy of the continuous phase will be more obvious, so the matte effect of Comparative Example 4 is improved to a certain extent.

[0109] In Comparative Example 5, the isotacticity of the propylene sequence and the 1-butene sequence in the propylene-based copolymer are too high, resulting in an increase in the melting point and crystallinity of the propylene-based copolymer, which is not conducive to the compatibility of the propylene-based copolymer with other materials of the matte layer, resulting in a thick sheet that is incompatible, causing poor stretching of the matte surface, poor matte uniformity, and affecting the appearance of the matte film.

[0110] From the comparison between Example 2 and Example 3, it can be seen that when the crystallinity of the propylene-based copolymer increases, the glossiness of the matte layer also increases, indicating that the crystallization performance of the continuous phase affects the stretching coarsening of the high-viscosity dispersed phase. In the present invention, the first linear low-density polyethylene as the continuous phase of the matte layer has good structural regularity, and its crystallization enthalpy value is relatively high. The matte effect of the matte layer is poor, but the polypropylene crystallization temperature of the dispersed phase is higher, and the melt viscosity of the dispersed phase is higher than that of the continuous phase. Therefore, the dispersed phase is evenly distributed in the island phase morphology to form a rough surface, thereby achieving a matte effect on the film surface. When a propylene-based copolymer with a high melting point and low crystallinity is added to the matte layer, the polyethylene continuous phase decreases in proportion, and the total crystallinity of the continuous phase also decreases. Therefore, during the biaxial stretching process of the matte film, the polypropylene dispersed phase, which is conducive to early crystallization and higher viscosity, is more likely to protrude from the surface of the matte layer during the biaxial stretching process, which is conducive to the formation of a rougher morphology in the matte layer.

[0111] From the data, it can be seen that as the amount of propylene copolymer added increases, the thermal shrinkage rate of BOPE matte film gradually increases. This is because the BOPE matte film accelerates the molecular chain orientation and crystallization during biaxial stretching. The biaxially stretched matte film is finally fixed in the transverse stretching zone, but the orientation of the polymer segment is an unstable state. The existence of stress in the polymer segment always has a tendency to return to random coils. This trend is particularly obvious at a certain heating temperature, and the thermal shrinkage ratio and the crystallinity of the material are mostly inversely proportional. Therefore, adding different proportions of propylene copolymers, although the matte effect of BOPE matte film is improved, the crystallinity of the system is reduced, and the stress in the amorphous zone is easily "thawed", so the thermal shrinkage increases, especially when the amount of propylene added increases to 35wt%, the amorphous zone gradually forms a regional continuous phase, and the thermal shrinkage increase will be greater. When the thermal shrinkage ratio exceeds 5%, the downstream manufacturers will have serious quality problems such as film surface curling and large overprint positioning deviation. Therefore, from the perspective of thermal shrinkage indicators, the proportion of propylene copolymer added should not exceed 30wt%. In addition, since the propylene-based copolymer is an elastomeric material with low crystallinity, the tensile strength of the BOPE matte film is reduced. Therefore, in order to ensure that the BOPE matte film has good mechanical strength, the proportion of propylene-based copolymer added is controlled within 30wt%.

[0112] It can also be concluded from the present invention that as the amount of high-melting-point, low-crystallization propylene-based copolymer added increases, the number of defects detected per 10,000 meters by the online detector gradually decreases. This is because the melting point of the propylene-based copolymer is 140°C, which is significantly higher than the melting point of the first linear low-density polyethylene in the matte layer, and higher than the longitudinal stretching preheating and stretching temperature. In high-speed production, the increase in high-melting-point components reduces the scalding of the low-melting-point components on the longitudinal stretching rollers, and reduces the generation of matte surface defects. At the same time, by comparing Example 2 and Example 3, it can be seen that the higher the melting point of the propylene-based copolymer, the fewer defects are detected on the matte surface. Therefore, the BOPE matte film of the invention can relatively adapt to higher production temperatures or higher speeds, and improve the utilization efficiency of the BOPE downstream industrial chain.

[0113] The above-mentioned embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and the present invention is also intended to include these modifications and modifications.

Claims

1. A BOPE matte film, characterized in that: It comprises a matte layer, a core layer and a lower surface layer which are arranged in sequence; the matte layer comprises 22-47.5wt% of a first metallocene linear low-density polyethylene, 38-48wt% of polypropylene and 10-30wt% of a propylene-based copolymer, wherein the propylene-based copolymer has a melting point of 140-160°C and a crystallinity of 5-10%, and is a propylene-1-butene copolymer, wherein the isotacticity of the propylene sequence is 90-93%, and the isotacticity of the 1-butene sequence is 87-90%; the core layer and the lower surface layer both comprise a second metallocene linear low-density polyethylene.

2. The BOPE matte film according to claim 1, characterized in that: The melt index of the first metallocene linear low-density polyethylene measured at 190° C. and 2.16 kg is 5-15 g / 10 min, and the melt index of the polypropylene measured at 230° C. and 2.16 kg is 0.1-5 g / 10 min.

3. The BOPE matte film according to claim 1, characterized in that: The melt index of the propylene-based copolymer measured at 230° C. and 2.16 kg is 5-10 g / 10 min.

4. The BOPE matte film according to claim 1, characterized in that: In the propylene-1-butene copolymer, the content of 1-butene is 15-35wt%.

5. The BOPE matte film according to claim 1, characterized in that: The matt layer further includes 0.3-0.5 wt % of an antioxidant, and the antioxidant includes antioxidant 1010 and antioxidant 168, and the ratio of the antioxidant 1010 to the antioxidant 168 is 1:

3.

6. The BOPE matte film according to claim 1, characterized in that: The melt index of the second metallocene linear low-density polyethylene measured at 190° C. and 2.16 kg is 3-10 g / 10 min.

7. The BOPE matte film according to claim 1, characterized in that: The core layer comprises 99-99.5wt% of a second metallocene linear low-density polyethylene and 0.5-1wt% of an antistatic agent masterbatch, the base resin of the antistatic agent masterbatch is the second metallocene linear low-density polyethylene, and the effective content of the antistatic agent in the antistatic agent masterbatch is 40wt%.

8. The BOPE matte film according to claim 1, characterized in that: The lower surface layer comprises 99-99.5 wt % of a second metallocene linear low-density polyethylene and 0.5-1 wt % of a silicon dioxide anti-blocking agent masterbatch.

9. A method for preparing a BOPE matte film according to any one of claims 1 to 8, characterized in that: The following steps are involved: The resin raw materials of each layer are weighed and mixed and then melt-extruded separately, wherein the matt layer extruder is a co-rotating twin-screw extruder, and the core layer and the lower surface layer are single-screw extruders. After the melt of each layer is extruded, it is merged into a thick sheet, and the thick sheet is cooled by a chilling roller and a chilling tank. The thick sheet is first preheated by longitudinal stretching at a preheating temperature of 125°C, and then stretched longitudinally at a longitudinal stretching multiple of 5 times and a longitudinal stretching temperature of 128°C, followed by longitudinal stretching and shaping. After longitudinal stretching and shaping, it is preheated by transverse stretching, and then stretched transversely at a transverse stretching multiple of 8 times and a transverse stretching temperature of 128°C. Then it is stretched transversely and shaped, and finally corona treatment is performed, and it is rolled and slit into finished film products.

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