A biaxially oriented polypropylene matt film and a method for producing the same

Abstract

The present application relates to the field of film, particularly to a kind of biaxially oriented polypropylene matt film and its preparation method, biaxially oriented polypropylene matt film includes matt layer, core layer and lower surface layer arranged in sequence, matt layer includes copolymer polypropylene, 50-55wt% high density polyethylene, 1-3wt% polyethylene glycol monomethyl ether grafting polystyrene and 2-5wt% terephthalic acid diethylene glycol grafting polypropylene, core layer and lower surface layer all include homopolymer polypropylene.The biaxially oriented polypropylene matt film described in the present application, by optimizing the composition of matt layer material, on the one hand, improve the sliding performance of the surface of matt layer, reduce the friction between matt layer and external object;On the other hand, optimize the thermal conductivity of matt layer as a whole, accelerate the heat transfer from contact point to other areas, synergistically improve the phenomenon of "scratch", "wear" on the surface of matt layer due to the friction with external object.

Description

Technical Field

[0001] This invention relates to the field of films, and in particular to a biaxially oriented polypropylene matte film and its preparation method. Background Technology

[0002] Biaxially oriented polypropylene matte film (BOPP matte film) is usually a BOPP film with one matte and one glossy or both matte sides. It mainly achieves its matte effect by scattering light, which can enhance the grade of printed packaging. Because the matte effect of the film gives people a soft, fashionable and elegant high-end feeling and eliminates eye fatigue, BOPP matte film is increasingly widely used in the packaging field, especially suitable for coating, lamination and other deep processing industries and fields.

[0003] Currently, considering production costs and the achieved matting effect, commercially available BOPP matting films primarily incorporate polyolefin matting masterbatches. These masterbatches utilize the phase separation that occurs during biaxial stretching between two polyolefin polymers with different crystallization rates and temperatures. The polymer with the faster crystallization rate protrudes, forming a rough, uneven matting layer, thus achieving the matting effect. In common matting masterbatch systems, the continuous phase is typically random copolymer polypropylene (ethylene-propylene copolymer or ethylene-propylene-butadiene copolymer), and the dispersed phase is generally high-density polyethylene. Following the principle of soft-encapsulating-hard, during biaxial stretching, the high-density polyethylene (hard phase) is mostly encapsulated by the random copolymer polypropylene (soft phase).

[0004] Because random copolymer polypropylene has low crystallinity and insufficient yield strength, resulting in insufficient material hardness, BOPP matte film produced from this matte masterbatch system often suffers from scratches and wear during product transportation due to friction between film rolls, between film rolls and bubble wrap, and even between laminated boxes and cartons. This seriously affects the packaging appearance quality of consumer products in the end market.

[0005] Invention patent CN202410410594.7 discloses a BOPP matte film and its preparation method. This method replaces part of the random copolymer polypropylene with block copolymer polypropylene in the matte layer, and simultaneously adds a certain proportion of cyclic olefin block polymers to the matte layer. While maintaining the matte effect, this improves the overall hardness and yield strength of the matte layer material, thereby reducing scratches and damage to the film matte layer under dynamic and static friction. However, while this method improves the overall hardness and yield strength of the matte layer and enhances its wear resistance through "intramolecular rigid segment reinforcement" by adding block copolymer polypropylene and cyclic olefin block polymers, it also restricts the movement of polypropylene molecular chains, hindering the plastic deformation of the film. In processing applications requiring bending, this can easily lead to cracking at the bending point, affecting the appearance quality of packaged products. Wear resistance is the material's ability to resist surface damage or material detachment under repeated contact, friction, sliding, and other mechanical actions. Summary of the Invention

[0006] Based on this, the purpose of the present invention is to provide a biaxially oriented polypropylene matte film and its preparation method. By optimizing the composition of the matte layer material, on the one hand, the sliding performance of the matte layer surface is improved, and the friction between the matte layer and external objects is reduced; on the other hand, the overall thermal conductivity of the matte layer is optimized, and the heat is transferred from the contact point to other areas, thereby synergistically improving the phenomenon of "scratches" and "wear" on the surface of the matte layer due to friction with external objects.

[0007] The technical solution of the present invention is achieved in the following ways:

[0008] A biaxially oriented polypropylene matte film includes a matte layer, a core layer, and a lower surface layer arranged sequentially. The matte layer comprises copolymer polypropylene, 50-55 wt% high-density polyethylene, 1-3 wt% polyethylene glycol monomethyl ether grafted polystyrene, and 2-5 wt% diethylene terephthalate grafted polypropylene. The core layer and the lower surface layer both comprise homopolymer polypropylene.

[0009] Through extensive practical experience, the inventors discovered that the quality problems of "scratches" and "wear" that occur in subsequent processing applications of matte finishes are primarily due to insufficient sliding performance of the matte finish. The high friction between the matte finish and external objects makes it more prone to "scratches" after friction. Secondly, the mechanical energy generated during friction is converted into heat energy at the friction contact point. This heat energy accumulates at the contact point and cannot be transferred, causing "wear" at the contact point. The apparent phenomenon is the appearance quality problem of "scratches" and "wear" on the matte surface. Therefore, improving the sliding performance of the matte finish surface and reducing the concentrated energy accumulation during sliding through rapid energy dissipation can reduce damage to the surface of the matte finish.

[0010] This application improves the sliding properties of the matte layer by adding polyethylene glycol monomethyl ether (PEG)-grafted polystyrene (PPE). The ether bonds in PEG-grafted PPE have high rotational freedom and good flexibility, causing PEG segments to tend to migrate and accumulate on the film surface. The ether bonds (-O-) in the PEG-grafted PPE molecular structure can form weak interactions with water molecules in the air, creating a very thin layer of water molecules on the matte layer surface, forming a stable boundary lubrication film. When the BOPP matte film slides relative to other objects, it significantly reduces the coefficient of friction, thereby reducing resistance during sliding. Furthermore, the styrene groups have good compatibility with the copolymerized polypropylene matrix in the matte layer, acting as a "bridge" between the PEG segments and the matrix, stably anchoring the PEG segments to the matte layer surface. This anchoring effect ensures the durability of the lubrication effect. Meanwhile, the presence of styrene groups also allows polyethylene glycol monomethyl ether-grafted polystyrene to be uniformly dispersed in the matte layer, further improving the consistency of surface lubrication effect.

[0011] If the amount of polyethylene glycol monomethyl ether (PEG) grafted polystyrene is less than 1 wt%, the PEG segments cannot effectively cover the surface of the matte layer to form an effective lubricating layer. This results in mechanical interlocking dominating the friction between the matte layer and the external object during subsequent processing, failing to effectively guarantee lubrication. Mechanical interlocking refers to the physical adhesion force generated at the micro or nano scale due to the irregular roughening effect of the matte surface and the uneven surface of the external object, resulting in interlocking and engagement. If the amount of PEG grafted polystyrene is greater than 3 wt%, the excessive PEG segments are rich in ether bonds, forming strong hydrogen bonds with water molecules in the air. The film surface is covered with a tightly bound layer of water molecules. However, the highly hydrophilic PEG segments and their polar groups are incompatible with inks and adhesives, leading to decreased adhesion and affecting subsequent processing.

[0012] This application also adds a ladder-shaped diethylene terephthalate-grafted polypropylene to the matte layer. This polypropylene has two main polypropylene chains. Firstly, the two main chains improve compatibility with copolymerized polypropylene, thus enhancing the compatibility of the diethylene terephthalate-grafted polypropylene in the matrix. Secondly, the rigid benzene ring structure in the diethylene terephthalate-grafted polypropylene can absorb some mechanical energy during friction through the bending and rotation of the molecular chains, converting it into heat energy that diffuses away. Thirdly, high-density polyethylene typically has a large spherulite structure with distinct interfaces between the spherulites, while the ladder-shaped diethylene terephthalate-grafted polypropylene... The polar ester group in high-density polyethylene (HDPE) has a high electronegativity of carbonyl oxygen (C=O), which can act as a hydrogen bond acceptor. After corona treatment, the H group of HDPE carries a partial positive charge and can form a weak hydrogen bond with the carbonyl oxygen of the ester group. This type of hydrogen bond enhances the interaction at the polymer interface through a cumulative effect, inducing a more ordered arrangement of HDPE molecular chains. This reduces the interfacial free energy for the formation of polymer embryos and lowers the activation energy for nucleation. As a result, HDPE can accelerate the crystallization rate, reduce the spherulite size, refine the size of HDPE grains and make their distribution more uniform, improve the thermal conductivity of HDPE, and promote the rapid diffusion of heat at friction contact points. When the matte layer of BOPP matte film comes into contact with other objects during subsequent application and processing, high-density polyethylene is the raised phase in the matte layer, which is the main contact point with the external object. The polar ester groups of diethylene terephthalate grafted polypropylene help to improve the thermal conductivity (heat conduction ability) of high-density polyethylene, accelerating the transfer of heat from the heat source at the contact point to the heat dissipation area. When the matte layer slides and rubs against the external object, the mechanical energy generated at the contact point of high-density polyethylene is converted into heat energy. Due to the increased thermal conductivity, the heat energy is quickly transferred to the surroundings, reducing the damage caused by the concentration of heat at the contact point, thereby reducing damage to the surface of the matte layer and helping to resist damage to the matte layer by external forces.

[0013] If the amount of diethylene terephthalate-grafted polypropylene added is less than 2 wt%, it reduces the directional alignment of the high-density polyethylene (HDPE) molecular chains, resulting in insufficient grain size refinement and an inability to effectively improve the thermal conductivity of HDPE, which is detrimental to improving the sliding performance of the matte layer. If the amount of diethylene terephthalate-grafted polypropylene added is greater than 5 wt%, the presence of a large number of heterogeneous polar and rigid groups restricts the movement of HDPE molecular chains, causing localized increases in film rigidity, increasing the risk of film breakage, and affecting production smoothness.

[0014] Furthermore, the lubricating film formed by polyethylene glycol monomethyl ether grafted polystyrene primarily provides lubrication on the surface of the matte layer, reducing intermolecular friction. Meanwhile, diethylene terephthalate grafted polypropylene also reduces friction by improving the crystallinity of high-density polyethylene, decreasing intermolecular adhesion and the actual contact area. The synergistic effect of these two components optimizes the surface morphology of the matte layer, reducing surface roughness and defects, resulting in smoother sliding. Moreover, the flexible segments of polyethylene glycol monomethyl ether grafted polystyrene act as bridges and buffers between the crystalline regions promoted by diethylene terephthalate grafted polypropylene, regulating intermolecular interactions. This ensures both the rigid support provided by the crystalline regions and the lubricating and compliant properties of the flexible segments, allowing for better coordinated movement between molecules during sliding, thus synergistically improving the sliding performance of the matte layer surface.

[0015] On the other hand, the styrene portion of polyethylene glycol monomethyl ether grafted polystyrene exhibits good compatibility with high-density polyethylene (HDPE) and copolymer polypropylene, effectively improving the compatibility between HDPE and copolymer polypropylene in the matting layer, reducing defects caused by poor compatibility. Furthermore, the grafted structure creates microphase separation in the matting layer, increasing surface roughness and contributing to a better matting effect. Meanwhile, the polar branched ester groups of diethylene terephthalate grafted polypropylene form hydrogen bonds with HDPE molecular chains, inducing a more ordered arrangement of HDPE molecular chains, lowering their crystallization free energy barrier, and making it easier for HDPE molecular chains to aggregate and form nuclei around the diethylene terephthalate grafted polypropylene. This nucleation effect makes the crystallization of HDPE more uniform, refines the grain structure, improves the roughness and crystallinity of the matting layer, and synergistically enhances the matting effect. Simultaneously, it helps reduce intermolecular adhesion and the actual contact area, thereby reducing friction.

[0016] Further, the preparation method of polyethylene glycol monomethyl ether grafted polystyrene includes the following steps: polyethylene glycol monomethyl ether undergoes an etherification reaction with p-chloromethylstyrene, causing the polyethylene glycol monomethyl ether segments to be linked to methylstyrene via ether bonds, obtaining a polyethylene glycol monomethyl ether macromonomer; the polyethylene glycol monomethyl ether macromonomer and a styrene small molecule monomer are mixed at a mass ratio of (1.2-5.0):1; and under the action of benzoyl peroxide initiator, the styrene groups on the polyethylene glycol monomethyl ether macromonomer undergo free radical copolymerization with the styrene small molecule monomer at a reaction temperature of 70-85℃. The reaction time is 12-24 hours to obtain polyethylene glycol monomethyl ether grafted polystyrene with a polystyrene backbone and polyethylene glycol monomethyl ether as a branch chain. The weight-average molecular weight of the polyethylene glycol monomethyl ether is 2000-5000. When the molecular weight of the polyethylene glycol monomethyl ether is below 2000, it is easily soluble in the organic phase and has poor compatibility with the hydrophobic polystyrene backbone, resulting in poor contact at the reaction interface and reducing the grafting rate. When the molecular weight of the polyethylene glycol monomethyl ether is above 5000, the long polyethylene glycol monomethyl ether chain segments have excessive steric hindrance, hindering the active end groups from approaching the reaction sites on the polystyrene backbone and affecting the grafting rate.

[0017] Furthermore, the grafting rate of polyethylene glycol monomethyl ether (PEG) in the PEG-grafted polystyrene is 10-15%. When the PEG grafting rate in the PEG-grafted polystyrene is 10-15%, the matte layer exhibits the best sliding performance and can significantly improve the wear resistance of the matte layer. If the grafting rate of polyethylene glycol monomethyl ether (PEG) in polystyrene is less than 10%, the number of PEG methyl ether segments is insufficient to form a continuous and complete lubricating layer on the surface of the matte layer. This increases the probability that the high-density polyethylene and copolymer polypropylene components on the surface of the film will directly contact external objects during subsequent processing, resulting in insufficient sliding performance of the matte layer and failing to improve its wear resistance. If the grafting rate of PEG methyl ether in polystyrene is greater than 15%, the PEG methyl ether segments will form "micro-droplet" precipitates on the surface of the matte layer. These precipitates will affect the printing or coating process, causing missing prints or white spots, further affecting the appearance quality of the paper-plastic product.

[0018] Furthermore, the diethylene terephthalate-grafted polypropylene is prepared by a melt grafting method. Under the action of benzoyl peroxide initiator, diethylene terephthalate forms diradicals, which can undergo a grafting reaction with the two polypropylene backbones to obtain the diethylene terephthalate-grafted polypropylene in a ladder-like shape. Preferably, the polypropylene used to prepare the diethylene terephthalate-grafted polypropylene is a copolymer polypropylene, which includes a random ethylene-propylene copolymer.

[0019] Furthermore, the grafting rate of diethylene terephthalate in the terephthalate-grafted polypropylene is 3-5%. At this rate, the energy dissipation effect of the matte layer is optimal, effectively reducing the coefficient of friction and wear, and helping to resist external forces from damaging the surface. If the grafting rate of terephthalate in the terephthalate-grafted polypropylene is less than 3%, the degree of ordering of the high-density polyethylene molecular chains is insufficient, which is not conducive to forming an effective heat conduction path, failing to effectively improve the thermal conductivity of high-density polyethylene, affecting the efficiency of energy dissipation, and hindering the improvement of the sliding performance of the matte layer. If the grafting rate of terephthalate in the terephthalate-grafted polypropylene is greater than 5 wt%, the terephthalate-grafted polypropylene itself becomes too rigid, which is not conducive to improving the sliding performance of the matte layer, nor is it conducive to the growth of high-density polyethylene crystals, causing a decrease in the crystallinity of high-density polyethylene, affecting the matte effect of the matte surface, and may also cause a local increase in the rigidity of the film, increasing the risk of film breakage and affecting production smoothness.

[0020] Furthermore, under test conditions of 230℃ and 2.16kg, the melt index of the diethylene terephthalate-grafted polypropylene was measured to be 6-8 g / 10min.

[0021] Furthermore, the melt index of the homopolymer polypropylene was measured to be 5-7 g / 10 min under test conditions of 230°C and 2.16 kg, the melt index of the high-density polyethylene was measured to be 8-15 g / 10 min under test conditions of 190°C and 2.16 kg, and the melt index of the copolymer polypropylene was measured to be 7-9 g / 10 min under test conditions of 230°C and 2.16 kg, wherein the copolymer polypropylene includes random ethylene-propylene copolymer.

[0022] Furthermore, the core layer further includes 1-3 wt% of an antistatic agent, and the lower surface layer further includes 0.1-0.5 wt% of an anti-blocking agent. The antistatic agent includes a quaternary ammonium salt-based methacrylate copolymer antistatic agent, and the anti-blocking agent includes one or more of silica, talc, and calcium carbonate. The particle size of the anti-blocking agent is 3-6 μm. Adding an appropriate amount of anti-blocking agent to the lower surface layer helps to increase the smoothness of the matte film during winding and unwinding. If the content of the anti-blocking agent in the lower surface layer is less than 0.1 wt%, it will not have an effective anti-blocking effect. If the content of the anti-blocking agent is greater than 0.5 wt%, the anti-blocking agent is prone to falling off during the production process, resulting in contamination of the guide rollers, increasing haze and reducing gloss, thus affecting the appearance of the product. To balance the surface layer thickness and the problem of falling off, the particle size of the anti-blocking agent is preferably 4-5 μm.

[0023] Furthermore, the thickness of the matte layer is 1.8-2.2 μm, the thickness of the lower surface layer is 0.8-1.2 μm, and the total thickness of the biaxially oriented polypropylene matte film is 12-15 μm.

[0024] The present invention also provides a method for preparing any of the above-mentioned biaxially oriented polypropylene matte films, comprising the following steps: mixing the dried raw materials of each layer according to the formula and feeding them into each extruder; after melting and plasticizing, the melt enters the die head for co-extrusion through the flow channel and distributor; the melt extruded from the die head contacts the cooling roller to form a thick sheet; after the thick sheet is preheated, it is first stretched longitudinally and then stretched transversely; after thickness measurement and corona treatment, it is wound up to obtain a master roll; after aging treatment, the master roll is slit to obtain the biaxially oriented polypropylene matte film.

[0025] Furthermore, the melt extrusion temperature of the matte layer is 200-260℃, the melt extrusion temperature of the core layer and the lower surface layer is 230-260℃, the temperature of the cooling roller is 15-50℃, the longitudinal stretching temperature is 90-130℃, the longitudinal stretching ratio is 4.5-5.5, the transverse stretching temperature is 155-165℃, the transverse stretching ratio is 8-10, and the corona power factor of the matte layer is 20-25 W·min / m.

[0026] To better understand and implement this invention, the invention will be described in detail below. Detailed Implementation

[0027] It should be understood that the described embodiments are merely some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of the embodiments of this application.

[0028] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0029] The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims. In the description of this application, it should be understood that the terms "first," "second," "third," etc., are used only to distinguish similar objects and are not necessarily used to describe a specific order or sequence, nor should they be construed as indicating or implying relative importance. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0030] Furthermore, in the description of this application, unless otherwise stated, "multiple" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0031] It should be understood that the embodiments of this application are not limited to the precise structures already described above, and various modifications and changes can be made without departing from their scope. The scope of the embodiments of this application is limited only by the appended claims.

[0032] This invention provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The matte layer comprises copolymer polypropylene, 50-55 wt% high-density polyethylene, 1-3 wt% polyethylene glycol monomethyl ether grafted polystyrene, and 2-5 wt% diethylene terephthalate grafted polypropylene. Both the core layer and the lower surface layer comprise homopolymer polypropylene.

[0033] Furthermore, the preparation method of the polyethylene glycol monomethyl ether grafted polystyrene includes the following steps:

[0034] Polyethylene glycol monomethyl ether (PEG) is reacted with p-chloromethylstyrene to link PEG segments to methylstyrene via ether bonds, yielding a PEG macromonomer. The PEG macromonomer is then mixed with a styrene small monomer at a mass ratio of (1.2-5.0):1. Under the action of benzoyl peroxide initiator, the styrene groups on the PEG macromonomer undergo free radical copolymerization with the styrene small monomer. The reaction temperature is 70-85℃, and the reaction time is 12-24 hours, resulting in PEG-grafted polystyrene with a polystyrene backbone and PEG-PEG as the side chain.

[0035] Furthermore, the grafting rate of polyethylene glycol monomethyl ether in the polyethylene glycol monomethyl ether-grafted polystyrene is 10-15%.

[0036] Furthermore, the ethylene terephthalate-grafted polypropylene is prepared by melt grafting. Under the action of benzoyl peroxide initiator, ethylene terephthalate forms diradicals, which undergo a grafting reaction with the two polypropylene backbones to obtain the ethylene terephthalate-grafted polypropylene in a ladder shape. Specifically, in a twin-screw extruder, 84.5-90.95 wt% polypropylene, 9-15 wt% ethylene terephthalate, and 0.05-0.5 wt% dicumyl peroxide initiator are weighed in proportion, and reactive melt extrusion is used. The twin-screw extruder temperature is set at 170–190℃, the screw speed is set at 100–300 rpm, and the residence time is approximately 10–15 minutes. In this process, firstly, diethylene terephthalate forms diethylene terephthalate diradicals under the action of an initiator, and then undergoes a grafting reaction with the two polypropylene backbones, ultimately forming a ladder-shaped diethylene terephthalate-grafted polypropylene.

[0037] Furthermore, the grafting rate of diethylene terephthalate in the diethylene terephthalate-grafted polypropylene is 3-5%.

[0038] Furthermore, under test conditions of 230℃ and 2.16kg, the melt index of the diethylene terephthalate-grafted polypropylene was measured to be 6-8 g / 10min.

[0039] Furthermore, the melt index of the homopolymer polypropylene was measured to be 5-7 g / 10 min under test conditions of 230°C and 2.16 kg, the melt index of the high-density polyethylene was measured to be 8-15 g / 10 min under test conditions of 190°C and 2.16 kg, and the melt index of the copolymer polypropylene was measured to be 7-9 g / 10 min under test conditions of 230°C and 2.16 kg, wherein the copolymer polypropylene includes random ethylene-propylene copolymer.

[0040] Furthermore, the core layer further includes 1-3 wt% of an antistatic agent, and the lower surface layer further includes 0.1-0.5 wt% of an anti-blocking agent. The antistatic agent includes a quaternary ammonium salt-based methacrylate copolymer antistatic agent, and the anti-blocking agent includes one or more of silica, talc, and calcium carbonate. The particle size of the anti-blocking agent is 3-6 μm.

[0041] Furthermore, the thickness of the matte layer is 1.8-2.2 μm, the thickness of the lower surface layer is 0.8-1.2 μm, and the total thickness of the biaxially oriented polypropylene matte film is 12-15 μm.

[0042] The present invention also provides a method for preparing any of the above-mentioned biaxially oriented polypropylene matte films, comprising the following steps: mixing the dried raw materials of each layer according to the formula and feeding them into each extruder; after melting and plasticizing, the melt enters the die head for co-extrusion through the flow channel and distributor; the melt extruded from the die head contacts the cooling roller to form a thick sheet; after the thick sheet is preheated, it is first stretched longitudinally and then stretched transversely; after thickness measurement and corona treatment, it is wound up to obtain a master roll; after aging treatment, the master roll is slit to obtain the biaxially oriented polypropylene matte film.

[0043] Furthermore, the melt extrusion temperature of the matte layer is 200-260℃, the melt extrusion temperature of the core layer and the lower surface layer is 230-260℃, the temperature of the cooling roller is 15-50℃, the longitudinal stretching temperature is 90-130℃, the longitudinal stretching ratio is 4.5-5.5, the transverse stretching temperature is 155-165℃, the transverse stretching ratio is 8-10, and the corona power factor of the matte layer is 20-25 W·min / m.

[0044] The physical properties and testing methods of the embodiments or comparative examples of the present invention are as follows:

[0045] Melt flow index (MFR) is determined according to GB / T3682.1-2018.

[0046] Surface tension was tested according to GB / T14216-2008.

[0047] The coefficient of friction was tested according to GB / T10006-2021.

[0048] The haze test was conducted according to GB / T2410-2008.

[0049] Glossiness was tested according to GB / T8807-1988.

[0050] The abrasion resistance test was conducted according to GB / T454-2020. Specifically, a GM-339 alcohol-rubber abrasion tester was used, with a 200g rubber head, to rub back and forth 50 times, and the friction of the matte layer was observed.

[0051] Tensile strength was tested according to GB / T1040.3-2006.

[0052] The antistatic agent in this embodiment is a quaternary ammonium salt-based methacrylate copolymer antistatic agent, and the antiblocking agent is silica with a particle size of 4.5 μm.

[0053] It should be noted that the proportions mentioned in the embodiments or comparative examples of the present invention are all weight percentages. The components and contents of each layer in the embodiments and comparative examples of the present invention are shown in Table 1 below.

[0054] Table 1

[0055]

[0056] Example 1

[0057] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0058] Preparation of matte layer resin: 55wt% high-density polyethylene (melt index of 13g / 10min measured at 190℃ and 21.6kg), 39wt% copolymer polypropylene (melt index of 8g / 10min measured at 230℃ and 2.16kg), 1wt% polyethylene glycol monomethyl ether grafted polystyrene (polyethylene glycol monomethyl ether grafting rate of 10%) and 5wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min measured at 230℃ and 2.16kg; diethylene terephthalate grafting rate of 3%) were mixed evenly to obtain matte layer resin.

[0059] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0060] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0061] The method for preparing the BOPP film in this embodiment includes the following steps:

[0062] Ingredients and plasticizing: The raw material usage ratio is set in the control system of the biaxial stretch film production line. Then the batching system will automatically deliver the dried raw materials to the extruder according to the input ratio. After melting and plasticizing in the extruder, the melt enters the die head through the flow channel and distributor.

[0063] Cast sheet: After being extruded through the die, the molten material immediately contacts the cooling roller to form a thick sheet;

[0064] Longitudinal stretching: The thick sheet is heated to a set temperature by multiple sets of preheating rollers, and then longitudinal stretching begins, followed by shaping;

[0065] Lateral stretching: After the thick sheet that has been stretched longitudinally is preheated to the set temperature, lateral stretching begins. After lateral stretching, it undergoes shaping and cooling processes.

[0066] Traction and winding: The multi-layered film exiting the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain the master roll;

[0067] Slitting: The mother roll that has undergone aging treatment is slitted to obtain a film roll of specified width and length.

[0068] The melt extrusion temperature of the matte layer is 235℃; the melt extrusion temperature of the core layer is 250℃; the melt extrusion temperature of the lower surface layer is 250℃; the temperature of the quench water and quench roller when the melt contacts the cooling roller is 40℃; the longitudinal stretching temperature is 125℃; the transverse stretching temperature is 160℃; the longitudinal stretching ratio is 5.3 times; the transverse stretching ratio is 8.5 times; and the corona power factor of the matte layer is 23.5 W·min / m.

[0069] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0070] Example 2

[0071] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0072] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 44wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 13%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 4%) were mixed evenly to obtain matte layer resin.

[0073] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0074] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0075] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0076] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0077] Example 3

[0078] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0079] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 45wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), 3wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 15%) and 2wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 5%) were mixed evenly to obtain matte layer resin.

[0080] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0081] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0082] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0083] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0084] Comparative Example 1

[0085] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0086] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 46wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; diethylene terephthalate grafting rate of 4%) were mixed evenly to obtain matte layer resin.

[0087] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0088] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0089] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0090] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0091] Comparative Example 2

[0092] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0093] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 45.5wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), 0.5wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 13%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 4%) were mixed evenly to obtain matte layer resin.

[0094] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0095] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0096] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0097] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0098] Comparative Example 3

[0099] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0100] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min measured at 190℃ and 21.6kg), 42wt% copolymer polypropylene (melt index of 8g / 10min measured at 230℃ and 2.16kg), 4wt% polyethylene glycol monomethyl ether grafted polystyrene (polyethylene glycol monomethyl ether grafting rate of 13%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min measured at 230℃ and 2.16kg; diethylene terephthalate grafting rate of 4%) were mixed evenly to obtain matte layer resin.

[0101] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0102] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0103] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0104] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0105] Comparative Example 4

[0106] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0107] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 48wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), and 2wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 13%) were mixed evenly to obtain matte layer resin.

[0108] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0109] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0110] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0111] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0112] Comparative Example 5

[0113] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0114] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min measured at 190℃ and 21.6kg), 47wt% copolymer polypropylene (melt index of 8g / 10min measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (polyethylene glycol monomethyl ether grafting rate of 13%) and 1wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min measured at 230℃ and 2.16kg; diethylene terephthalate grafting rate of 4%) were mixed evenly to obtain matte layer resin.

[0115] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0116] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0117] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0118] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0119] Comparative Example 6

[0120] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0121] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 42wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 13%) and 6wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 4%) were mixed evenly to obtain matte layer resin.

[0122] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0123] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0124] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0125] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0126] Comparative Example 7

[0127] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0128] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 44wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 5%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 4%) were mixed evenly to obtain matte layer resin.

[0129] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0130] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0131] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0132] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0133] Comparative Example 8

[0134] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0135] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min measured at 190℃ and 21.6kg), 44wt% copolymer polypropylene (melt index of 8g / 10min measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (polyethylene glycol monomethyl ether grafting rate of 17%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min measured at 230℃ and 2.16kg; diethylene terephthalate grafting rate of 4%) were mixed evenly to obtain matte layer resin.

[0136] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0137] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0138] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0139] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0140] Comparative Example 9

[0141] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0142] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min measured at 190℃ and 21.6kg), 44wt% copolymer polypropylene (melt index of 8g / 10min measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 13%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 2%) were mixed evenly to obtain matte layer resin.

[0143] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0144] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0145] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0146] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0147] Comparative Example 10

[0148] This embodiment provides a biaxially oriented polypropylene matte film, comprising a matte layer, a core layer, and a lower surface layer arranged sequentially. The preparation method of each resin layer of the biaxially oriented polypropylene matte film in this embodiment includes the following steps:

[0149] Preparation of matte layer resin: 50wt% high-density polyethylene (melt index of 13g / 10min was measured at 190℃ and 21.6kg), 44wt% copolymer polypropylene (melt index of 8g / 10min was measured at 230℃ and 2.16kg), 2wt% polyethylene glycol monomethyl ether grafted polystyrene (grafting rate of polyethylene glycol monomethyl ether was 13%) and 4wt% diethylene terephthalate grafted polypropylene (melt index of 7g / 10min was measured at 230℃ and 2.16kg; grafting rate of diethylene terephthalate was 7%) were mixed evenly to obtain matte layer resin.

[0150] Core layer resin preparation: 99wt% homopolymer polypropylene (melt index of 6g / 10min was measured at 230℃ and 2.16kg) and 1wt% antistatic agent (quaternary ammonium salt methacrylate copolymer antistatic agent) were mixed evenly to obtain core layer resin.

[0151] Preparation of the lower surface resin: 99.7 wt% homopolymer polypropylene (isotacticity of 96%, melt index of 6 g / 10 min measured at 230℃ and 2.16 kg) and 0.3 wt% antiblocking agent (silica, particle size of 4.5 μm) were mixed evenly to obtain the lower surface resin.

[0152] The preparation method of the biaxially oriented polypropylene matte film in this embodiment is the same as that in Example 1, so it will not be described again.

[0153] The total thickness of the film is 12µm, of which the thickness of the matting layer is 1.8µm and the thickness of the lower surface layer is 1µm.

[0154] The performance test and composite effect test results of the biaxially oriented polypropylene matte films of Examples 1-3 and Comparative Examples 1-10 are shown in Table 2 below.

[0155] Table 2

[0156]

[0157] As can be seen from the above performance test data, the improved sliding performance of Embodiments 1-3 of the present invention enhances the sliding properties of the BOPP matte film surface, reduces the friction between the matte layer and external objects, and accelerates the transfer of heat from the contact point to other areas by optimizing the thermal conductivity (heat conduction ability) of high-density polyethylene. When the matte layer slides relative to other objects, the mechanical energy generated at the contact point is converted into heat energy. Due to the improved thermal conductivity of high-density polyethylene, the heat energy is quickly transferred to the surroundings, reducing the damage caused by the concentration of heat at the contact point. By reducing the actual contact area and the rapid loss of energy after contact, the two work together to reduce the concentrated energy accumulation during the sliding process, thereby reducing damage to the surface of the matte layer. This improves the phenomenon of "scratches" and "wear" on the surface of the matte layer due to friction during relative movement, avoids seriously affecting the packaging appearance quality of consumer products in the end market, and ensures that the BOPP matte film meets the requirements of high-speed automated production.

[0158] Comparative Example 1: Biaxially oriented polypropylene matte film. Without the addition of polyethylene glycol monomethyl ether grafted polystyrene to the matte layer, the surface of the matte layer lacks a lubricating layer formed by polyethylene glycol monomethyl ether segments. As a result, it cannot effectively reduce the coefficient of friction and thus reduce the resistance during sliding, and the matte layer exhibits severe wear.

[0159] In Comparative Example 2, the biaxially oriented polypropylene matte film had too little polyethylene glycol monomethyl ether grafted polystyrene added to the matte layer. The polyethylene glycol monomethyl ether segments could not effectively cover the lubricating layer formed by the matte layer, resulting in mechanical meshing as the dominant friction between the matte layer and the external object in subsequent processing. This could not effectively guarantee the lubrication effect, and the matte layer showed obvious wear.

[0160] In Comparative Example 3, the biaxially oriented polypropylene matte film had an excessively high content of polyethylene glycol monomethyl ether grafted polystyrene in the matte layer. This resulted in a large migration of polyethylene glycol monomethyl ether segments to the film surface. While this improved the sliding properties of the matte layer, the excessive polyethylene glycol monomethyl ether segments, rich in ether bonds, formed strong hydrogen bonds with water molecules in the air. The film surface was covered by a tightly bound layer of water molecules. Furthermore, the highly hydrophilic polyethylene glycol monomethyl ether segments and their polar groups were incompatible with inks and adhesives, leading to decreased adhesion and affecting subsequent processing.

[0161] Comparative Example 4: Biaxially oriented polypropylene matte film without added diethylene terephthalate-grafted polypropylene in the matte layer; when the matte layer slides relative to other objects, the mechanical energy generated at the contact point is converted into heat energy. The heat cannot be transferred to the surroundings in a low efficiency, and the heat concentration at the contact point causes damage, resulting in obvious wear of the matte layer.

[0162] In Comparative Example 5, the biaxially oriented polypropylene matte film had an excessively low content of diethylene terephthalate-grafted polypropylene in the matte layer. This reduced the directional alignment of the high-density polyethylene molecular chains, resulting in insufficient grain size refinement and an inability to effectively improve the thermal conductivity of high-density polyethylene. Consequently, the efficiency of heat dissipation generated by friction was affected, and the matte layer exhibited significant wear.

[0163] In Comparative Example 6, the biaxially oriented polypropylene matte film had an excessively high content of diethylene terephthalate-grafted polypropylene in the matte layer. Due to the presence of a large number of heterogeneous polar and rigid groups, the movement of high-density polyethylene molecular chains was restricted, resulting in increased local rigidity of the film, which increased the risk of film breakage and prevented the formation of effective and good sliding performance, thus affecting the smoothness of production.

[0164] In Comparative Example 7, the biaxially oriented polypropylene matte film exhibited an excessively low grafting rate of polyethylene glycol monomethyl ether (PEG) into polystyrene, resulting in insufficient PEG monomethyl ether segments to form a continuous and complete lubricating layer on the matte film surface. During subsequent processing, the increased likelihood of direct contact between the high-density polyethylene and copolymer polypropylene components on the film surface and external objects led to insufficient sliding performance of the matte layer, failing to improve its wear resistance and resulting in significant wear.

[0165] In Comparative Example 8, the biaxially oriented polypropylene matte film showed an excessively high grafting rate of polyethylene glycol monomethyl ether (PEG) in the polystyrene grafted with PEG. PEG monomethyl ether segments formed "microdroplet-like" precipitates on the surface of the matte layer. These precipitates affected the surface tension, leading to printing or coating processes that resulted in missing prints or white spots, further impacting the appearance quality of the paper-plastic products.

[0166] In Comparative Example 9, the biaxially oriented polypropylene matte film had a low grafting rate of diethylene terephthalate in the polypropylene grafted with diethylene terephthalate, resulting in insufficient ordering of the high-density polyethylene molecular chains. This hindered the formation of an effective heat conduction pathway, failed to effectively improve the thermal conductivity of high-density polyethylene, affected energy dissipation efficiency, and was detrimental to improving the sliding performance of the matte layer. The matte layer also exhibited significant wear.

[0167] In Comparative Example 10, the biaxially oriented polypropylene matting film had an excessively high grafting rate of diethylene terephthalate in the diethylene terephthalate-grafted polypropylene. The rigid structure in the diethylene terephthalate-grafted polypropylene interfered with the growth of high-density polyethylene crystals, reducing the crystallinity of high-density polyethylene and affecting the matting effect of the matting surface.

[0168] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and the present invention also intends to include these modifications and variations.

Claims

1. A biaxially oriented polypropylene matte film, characterized in that, It includes a matte layer, a core layer and a bottom layer arranged in sequence. The matte layer includes copolymer polypropylene, 50-55 wt% high-density polyethylene, 1-3 wt% polyethylene glycol monomethyl ether grafted polystyrene and 2-5 wt% diethylene terephthalate grafted polypropylene. The core layer and the bottom layer both include homopolymer polypropylene. The grafting rate of polyethylene glycol monomethyl ether in the polyethylene glycol monomethyl ether-grafted polystyrene is 10-15%. The preparation method of the polyethylene glycol monomethyl ether-grafted polystyrene includes the following steps: polyethylene glycol monomethyl ether undergoes an etherification reaction with p-chloromethylstyrene, so that the polyethylene glycol monomethyl ether chain segment is linked to methylstyrene through ether bonds to obtain polyethylene glycol monomethyl ether macromonomer; the polyethylene glycol monomethyl ether macromonomer and styrene small molecule monomer are mixed at a mass ratio of (1.2-5.0):1; under the action of benzoyl peroxide initiator, the styrene groups on the polyethylene glycol monomethyl ether macromonomer undergo free radical copolymerization with the styrene small molecule monomer; the reaction temperature is 70-85℃ and the reaction time is 12-24 hours to obtain the polyethylene glycol monomethyl ether-grafted polystyrene with polystyrene main chain and polyethylene glycol monomethyl ether as branch chain; The grafting rate of diethylene terephthalate in the terephthalate-grafted polypropylene is 3-5%. The terephthalate-grafted polypropylene is prepared by melt grafting, in which diethylene terephthalate forms diradicals under the action of benzoyl peroxide initiator, which then undergo a grafting reaction with the two polypropylene backbones to obtain the terephthalate-grafted polypropylene in the form of a ladder shape.

2. The biaxially oriented polypropylene matte film according to claim 1, characterized in that, The melt index of the diethylene terephthalate-grafted polypropylene was measured to be 6-8 g / 10 min under test conditions of 230℃ and 2.16 kg.

3. The biaxially oriented polypropylene matte film according to claim 1, characterized in that, The melt index of the homopolymer polypropylene was measured to be 5-7 g / 10 min under test conditions of 230℃ and 2.16 kg; the melt index of the high-density polyethylene was measured to be 8-15 g / 10 min under test conditions of 190℃ and 2.16 kg; and the melt index of the copolymer polypropylene was measured to be 7-9 g / 10 min under test conditions of 230℃ and 2.16 kg. The copolymer polypropylene includes random ethylene-propylene copolymer.

4. The biaxially oriented polypropylene matte film according to claim 1, characterized in that, The core layer also includes 1-3 wt% of an antistatic agent; the lower surface layer also includes 0.1-0.5 wt% of an anti-blocking agent.

5. A method for preparing a biaxially oriented polypropylene matte film as described in any one of claims 1 to 4, characterized in that, Includes the following steps: After drying, the raw materials of each layer are mixed and fed into each extruder according to the formula. After melting and plasticizing, the melt enters the die head for co-extrusion through the flow channel and distributor. The melt extruded from the die head contacts the cooling roller to form a thick sheet. After the thick sheet is preheated, it is first stretched longitudinally and then stretched transversely. After thickness measurement and corona treatment, it is wound up to obtain a master roll. After aging treatment, the master roll is slit to obtain the biaxially oriented polypropylene matte film.

6. The method for preparing biaxially oriented polypropylene matte film according to claim 5, characterized in that, The melt extrusion temperature of the matte layer is 200-260℃, the melt extrusion temperature of the core layer and the lower surface layer is 230-260℃, the temperature of the cooling roller is 15-50℃, the longitudinal stretching temperature is 90-130℃, the longitudinal stretching ratio is 4.5-5.5, the transverse stretching temperature is 155-165℃, the transverse stretching ratio is 8-10, and the corona power factor of the matte layer is 20-25 W·min / m.

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