A BOPP pearlescent film and its preparation method

Abstract

This invention relates to the field of pearlescent films, and particularly to a BOPP pearlescent film and its preparation method. The pearlescent film comprises, sequentially arranged, an upper surface layer, a lower surface layer, a core layer, a lower sub-surface layer, and a lower surface layer; the lower surface layer comprises 5-15 wt% maleic anhydride-grafted ethylene-octene copolymer A; the core layer comprises homopolymer polypropylene, 25-40 wt% pearlescent masterbatch, and 5-10 wt% maleic anhydride-grafted ethylene-octene copolymer B; the pearlescent masterbatch comprises 65-75 wt% modified heavy calcium carbonate and homopolymer polypropylene; the modified heavy calcium carbonate is obtained by coating the heavy calcium carbonate with an organic coating agent containing epoxy-functionalized titanate, with the coating amount being 1.5-2.0 wt% of the heavy calcium carbonate. This invention improves the dispersibility of heavy calcium carbonate in the pearlescent masterbatch, alleviates difficulties in film breakage and repair, and reduces interlayer separation problems during pearlescent film production, reduces ink droplet detachment during printing, and improves the production efficiency and packaging quality of pearlescent films.

Description

Technical Field

[0001] This invention relates to the field of pearlescent films, and in particular to a BOPP pearlescent film and its preparation method. Background Technology

[0002] BOPP pearlescent film is an opaque film with a white luster, widely used in labeling, food packaging, and other industries. During the production of pearlescent film, the pearlescent masterbatch contains a high proportion of calcium carbonate. Since calcium carbonate is an inorganic substance, its adhesion to polypropylene is relatively low. Under external force, countless cavities are formed between the calcium carbonate and polypropylene. When light enters these cavities, interference occurs. The multi-layered interference light has refraction and scattering effects, ultimately creating the pearlescent effect.

[0003] However, when pearlescent masterbatch is added to the core layer of the film, it creates numerous pores during production and stretching, deteriorating the film's mechanical properties, particularly tensile strength. This leads to frequent film breakage during production, resulting in difficulties in re-molding and prolonged repair times. Especially when pearlescent film is used as a label film, the poor bonding between calcium carbonate and polypropylene due to the high calcium carbonate content in the core layer makes the core layer and sub-surface layer prone to delamination under external tearing. Furthermore, to achieve better dispersibility, current pearlescent masterbatches often selectively incorporate migratable low-molecular-weight dispersants as coating modifiers, such as silane coupling agents and surface dispersants, when coating inorganic powders. However, these coating agents inevitably have negative effects; the low-molecular-weight components migrate to the film surface, affecting surface tension and causing frequent or pinpoint peeling of downstream surface inks, severely impacting the appearance quality of the packaging and further limiting the production and use of BOPP pearlescent film. Summary of the Invention

[0004] To address the aforementioned problems, the present invention aims to optimize the formulation of BOPP pearlescent film and its pearlescent masterbatch. This is achieved through three optimizations: 1) coating the heavy calcium carbonate in the pearlescent masterbatch with epoxy-functionalized titanate; 2) adding a certain amount of maleic anhydride-grafted ethylene-octene copolymer B to the core layer; and 3) adding maleic anhydride-grafted ethylene-octene copolymer A to the upper and lower surface components. These three synergistic effects improve the interfacial bonding strength between calcium carbonate and polypropylene, and enhance the dispersibility of heavy calcium carbonate in the pearlescent masterbatch within the core layer, thereby improving the overall BOPP formulation. The tensile strength of the P film improves the problem of easy film breakage and difficulty in repair during high-speed production of BOPP pearl film; secondly, the optimized formula of BOPP pearl film results in very few low molecular weight precipitates on the film surface, ensuring a clean film surface and reducing the phenomenon of pinpoint peeling off of downstream surface printing ink, thereby improving the production efficiency and packaging quality of BOPP pearl film; thirdly, it enhances the interfacial bonding force between the core layer and the sub-surface layer, improving the problem of interlayer separation that easily occurs when the film is torn by external force.

[0005] The BOPP matte film of the present invention is achieved through the following detailed technical solutions:

[0006] A BOPP pearlescent film includes an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially.

[0007] The upper surface layer comprises binary random copolymer polypropylene; the lower surface layer comprises homopolymer polypropylene.

[0008] Both the upper and lower surface layers comprise homopolymer polypropylene and 5-15 wt% maleic anhydride-grafted ethylene-octene copolymer A; in the maleic anhydride-grafted ethylene-octene copolymer A, the grafting rate of maleic anhydride is 0.8-1.0%, and the octene content in the ethylene-octene copolymer segments is 20-25 wt%.

[0009] The core layer comprises homopolymer polypropylene, 25-40 wt% pearlescent masterbatch, and 5-10 wt% maleic anhydride-grafted ethylene-octene copolymer B; in the maleic anhydride-grafted ethylene-octene copolymer B, the grafting rate of maleic anhydride is 1.2-1.5%, and the octene content in the ethylene-octene copolymer segments is 10-15 wt%; the pearlescent masterbatch comprises 65-75 wt% modified heavy calcium carbonate and homopolymer polypropylene; the modified heavy calcium carbonate is obtained by coating heavy calcium carbonate with an organic coating agent, the organic coating agent comprising epoxy-functionalized titanate, and the amount of epoxy-functionalized titanate used is controlled to be 1.5-2.0 wt% of the heavy calcium carbonate.

[0010] This invention creatively selects heavy calcium carbonate coated with epoxy-functionalized titanate as pearlescent masterbatch and adds it to the core layer of a BOPP pearlescent film. Unlike traditional coating modifiers such as silane coupling agents, titanate coupling agents (such as monoalkoxy titanate coupling agents), stearic acid, and surface dispersants, the maleic anhydride groups of maleic anhydride-grafted ethylene-octene copolymer B in the core layer undergo a ring-opening reaction with the active epoxy groups of the epoxy-functionalized titanate to form more stable chemical bonds. This reaction chemically anchors the maleic anhydride-grafted ethylene-octene copolymer B to the surface of the epoxy-functionalized titanate-treated modified heavy calcium carbonate, enhancing the interfacial bonding strength between the inorganic and organic phases. At the same time, the long chain segments of the ethylene-octene copolymer are physically entangled with the homopolymer polypropylene molecular chain segments of the core layer, further enhancing the interfacial bonding and increasing the interaction force between the modified heavy calcium carbonate and the homopolymer polypropylene of the core layer. This is more conducive to force transmission during stretching, effectively reducing film breakage during high-speed production of BOPP pearlescent film and improving the production efficiency of pearlescent film. Furthermore, the organic chains of titanate reduce the polarity of the surface of heavy calcium carbonate, and the modified coating of epoxy-functionalized titanate reduces the generation of low surface tension migrants without reducing the surface tension. This effectively improves the problem of peeling or pinpoint peeling of downstream surface ink printing, thus improving the packaging quality of pearlescent film. If the amount of epoxy-functionalized titanate used is less than 1.5 wt% of heavy calcium carbonate, the coating rate of heavy calcium carbonate is low, and the heavy calcium carbonate is prone to agglomeration and poor dispersion. If the amount of epoxy-functionalized titanate used is more than 2.0 wt% of heavy calcium carbonate, the cost increases, and the organic coating agent is prone to forming multilayer coatings on the surface of heavy calcium carbonate, which may lead to interparticle adhesion and poor dispersibility.

[0011] The BOPP pearlescent film of this invention employs a differential design: the octene content of maleic anhydride-grafted ethylene-octene copolymer B in the core layer is lower than that of maleic anhydride-grafted ethylene-octene copolymer A in the sub-layer, while the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer B is higher than that of maleic anhydride-grafted ethylene-octene copolymer A. This results in higher hardness of the core layer, making it less prone to collapse of the ethylene-octene copolymer segments at the pore formation points during stretching, thus preventing a decline in the foaming effect of the pearlescent film. This also avoids the problem of decreased film mechanical properties caused by the need to add more modified heavy calcium carbonate at the same density. Simultaneously, more maleic anhydride groups can react with the active epoxy groups on the surface of the modified heavy calcium carbonate to improve the dispersibility of the modified heavy calcium carbonate and the interfacial stress between it and the core layer matrix polypropylene resin, reducing phase separation within the core layer and enhancing anti-delamination ability. If the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer B is less than 1.2 wt%, the effect of maleic anhydride-grafted ethylene-octene copolymer B on improving the dispersibility and core layer interfacial stress of modified heavy calcium carbonate is weak. If the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer B exceeds 1.5 wt%, too many maleic anhydride groups form polar microregions in the core layer, causing phase separation between homopolymer polypropylene and maleic anhydride-grafted ethylene-octene copolymer B in the core layer and adjacent upper and lower sub-surface layers. At the same time, the high grafting rate enhances the polarity of the ethylene-octene copolymer molecular chain, increases the rigidity of the chain segment, and reduces the flexibility, making it difficult to spread and entangle on the surface of pearlescent masterbatch. The number of hydroxyl groups (-OH) on the surface of calcium carbonate is limited and unevenly distributed. When polar maleic anhydride groups are close to the surface of calcium carbonate, some groups cannot effectively contact the -OH sites due to spatial crowding. Therefore, it will also reduce the reactivity of maleic anhydride groups with the polar groups of inorganic powder calcium carbonate. If the octene content of the ethylene-octene copolymer in maleic anhydride-grafted ethylene-octene copolymer B is less than 10 wt%, the rigidity of the ethylene-octene copolymer segments increases and the elasticity decreases. The compatibility between the rigid segments and the homopolymer polypropylene matrix of the core layer deteriorates, and the elastic buffering of the rigid segments at the interface is insufficient, which is not conducive to improving interlayer separation. If the octene content of the ethylene-octene copolymer in maleic anhydride-grafted ethylene-octene copolymer B is higher than 15 wt%, the ethylene-octene copolymer segments are relatively too soft, and the tensile strength and modulus of the ethylene-octene copolymer decrease. It is difficult to effectively transfer stress to the pearlescent masterbatch matrix interface, which is not conducive to the stretching and pore-forming effect of calcium carbonate in the core layer, and ultimately affects the pearlescent effect of the pearlescent film.

[0012] The maleic anhydride-grafted ethylene-octene copolymer B, with a higher octene content in the sub-layer, can better entangle with the homopolymer polypropylene segments in the core layer. In this invention, 5-15 wt% maleic anhydride-grafted ethylene-octene copolymer A is added to both the upper and lower sub-layers. The maleic anhydride groups of the maleic anhydride-grafted ethylene-octene copolymer A in the sub-layer can undergo a ring-opening reaction with the active groups of the functionalized titanate on the surface of the modified heavy calcium carbonate in the core layer, realizing an interlayer interlocking structure. The long chains of the ethylene-octene copolymer in both the core and sub-layers can physically entangle with the homopolymer polypropylene segments in the adjacent layers, forming an interlayer "interlocking structure". Furthermore, the non-polar properties of the ethylene-octene copolymer segments match those of the homopolymer polypropylene matrix, forming a smooth polar gradient and alleviating interlayer interface stress. Under the above-mentioned synergistic effect of the two layers, the problem of film breakage during pearlescent film production and delamination during downstream production and use can be effectively improved. If the amount of maleic anhydride-grafted ethylene-octene copolymer A added in the sub-surface layer is less than 5 wt%, the content of ethylene-octene copolymer groups and maleic anhydride groups is too low, and the effect on improving the interlayer compatibility between the sub-surface layer and the core layer is not significant. If the amount of maleic anhydride-grafted ethylene-octene copolymer A added in the sub-surface layer is greater than 15 wt%, the excessive maleic anhydride groups will form local high polarity regions, which will reduce the compatibility with the non-polar segments of polypropylene in the sub-surface layer and adjacent layers, causing phase separation. At the same time, excessive ethylene-octene copolymer will lead to a decrease in the tensile properties of BOPP pearl film material, which is not conducive to the processing and production of BOPP pearl film, and will also significantly increase the production material cost of pearl film. If the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer A in the sub-surface layer is less than 0.8%, it cannot effectively improve the interlayer bonding ability between the core layer and the sub-surface layer. If the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer A in the sub-surface layer is greater than 1.0%, the excessively high grafting rate will cause the maleic anhydride groups to form polar microregions in the sub-surface layer, leading to phase separation of polypropylene and maleic anhydride-grafted ethylene-octene copolymer A in the sub-surface layer and adjacent layers, resulting in a decrease in the mechanical properties of the pearlescent film. If the octene content in the ethylene-octene copolymer segments of maleic anhydride-grafted ethylene-octene copolymer A in the sub-surface layer is less than 20 wt%, the rigidity of the ethylene-octene copolymer segments is enhanced, the elasticity is reduced, and the compatibility between the hard segments and the homopolymer polypropylene matrix of the sub-surface layer deteriorates, resulting in the inability of maleic anhydride-grafted ethylene-octene copolymer A to disperse in the homopolymer polypropylene matrix. If the octene content in the ethylene-octene copolymer segments of maleic anhydride-grafted ethylene-octene copolymer A in the subsurface layer is higher than 25 wt%, the ethylene-octene copolymer segments become excessively flexible, resulting in a significant decrease in melt strength and a lower glass transition temperature (Tg). This will cause an increase in thermal shrinkage of the subsurface layer, leading to uneven thickness. At the same time, if the ethylene-octene copolymer segments are too soft, the modulus of the subsurface layer will decrease, and stress will be absorbed by elastic buffers at the interface, weakening the stress transfer between the modified heavy calcium carbonate in the core layer and the subsurface layer.

[0013] Furthermore, the organic coating agent is formed by uniformly mixing the epoxy-functionalized titanate and anhydrous ethanol in a mass ratio of 1:4.

[0014] Furthermore, the preparation method of the epoxy-functionalized titanate includes the following steps:

[0015] (1) At room temperature, tetraisopropoxide titanium and glycidyl ether were dissolved in tetrahydrofuran (THF) at a molar ratio of 1:1. After mixing evenly, 0.3 mol% Lewis acid catalyst stannous chloride was added and stirred evenly to obtain a mixed solution for later use.

[0016] (2) Under the protection of inert argon gas, the temperature of the mixture is controlled at 48°C in a water bath and the mixture is stirred for 3.5 hours;

[0017] (3) After the mixture is cooled to room temperature, it is transferred to a rotary evaporator to remove tetrahydrofuran (THF) and the byproduct isopropanol from the mixture;

[0018] (4) The eluent was purified by silica gel column chromatography and vacuum dried to obtain a transparent liquid epoxy-functionalized titanate; the eluent consisted of ethyl acetate and petroleum ether in a mass ratio of 1:3.

[0019] Furthermore, the particle size D50 of the heavy calcium carbonate is 0.9~1.3μm. If the particle size D50 of the heavy calcium carbonate is less than 0.9μm, the small particle size results in a large specific surface area, making powder dispersion difficult and prone to agglomeration. This can lead to increased membrane breakage due to inorganic matter clogging the filter screen during pearlescent film production. If the particle size D50 of the modified heavy calcium carbonate exceeds 1.3μm, its particle size is too large, resulting in large foamed pores at the same stretching ratio, a significant decrease in film density, a decrease in the proportion of pearlescent masterbatch added to the core layer, an increase in the proportion of homopolymer polypropylene added, and an increase in film production costs.

[0020] Furthermore, the coating process for the modified heavy calcium carbonate includes the following steps:

[0021] (1) Place the heavy calcium carbonate powder in a high-speed mixer at 105°C and stir and dry for half an hour, controlling the moisture content of the heavy calcium carbonate powder to be ≤0.5wt%;

[0022] (2) An organic coating agent is obtained by uniformly mixing epoxy-functionalized titanate and anhydrous ethanol at a mass ratio of 1:4;

[0023] (3) The temperature of the high-speed mixer is controlled at 70°C, and the organic coating agent is evenly sprayed onto the heavy calcium carbonate powder being stirred in the high-speed mixer through a high-pressure atomizing nozzle;

[0024] (4) Heat the high-speed mixer to 90°C and set the rotation speed to 1000 rpm, so that the heavy calcium carbonate powder and the organic coating agent in the high-speed mixer are continuously mixed for 15 to 20 minutes.

[0025] (5) After mixing, cool down to below 40°C, and sieve through a 300-mesh sieve to remove agglomerated powder particles, and obtain the coated modified heavy calcium carbonate.

[0026] Furthermore, at 230℃ and a load of 2.16 kg, the melt index of the pearlescent masterbatch is 5~15 g / 10 min. When the melt index of the pearlescent masterbatch is below 5 g / 10 min, its fluidity is poor, which is not conducive to the dispersion of the pearlescent masterbatch in the core layer, and the extrusion pressure is high; if the melt index is above 15 g / 10 min, under the high filling of the pearlescent masterbatch, the overall fluidity difference between the core layer and other layers is large, which can easily cause uneven film thickness and reduce the mechanical strength of the film.

[0027] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted ethylene-octene copolymer A in the upper and lower sub-layers is 5~10 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted ethylene-octene copolymer B in the core layer is 5~15 g / 10 min. If the melt index of the maleic anhydride-grafted ethylene-octene copolymer A is lower than 5 g / 10 min, since the sub-layer is produced by a single-screw extruder, the ability of the low melt index maleic anhydride-grafted ethylene-octene copolymer A to wet and disperse in the homopolymer polypropylene phase decreases, which is not conducive to the effective dispersion of polar maleic anhydride groups, reduces the effective contact between maleic anhydride groups and the pearlescent masterbatch in the core layer, and the effect on improving the interlayer compatibility between the sub-layer and the core layer is not significant. If the melt index of maleic anhydride-grafted ethylene-octene copolymer A is higher than 10 g / 10 min, the viscosity difference between the maleic anhydride-grafted ethylene-octene copolymer A and the homopolymer polypropylene melt in the subsurface layer is too large, which is not conducive to the uniform dispersion of the two phases during the extrusion process of a single screw extruder, leading to problems such as interfacial delamination or uneven thickness. When the melt index of maleic anhydride-grafted ethylene-octene copolymer B is lower than 5 g / 10 min, its flowability is poor, which is not conducive to its wetting and dispersion on the surface of the pearlescent masterbatch, thus having insufficient effect on improving the compatibility of homopolymer polypropylene and pearlescent masterbatch in the core layer. If the melt index of maleic anhydride-grafted ethylene-octene copolymer B is higher than 10 g / 10 min, the mechanical strength of maleic anhydride-grafted ethylene-octene copolymer B decreases, which will reduce the mechanical properties of the pearlescent film.

[0028] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the binary random copolymer polypropylene in the upper surface layer is 5~10 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the homopolymer polypropylene in the upper sub-surface layer, the lower sub-surface layer, the core layer, and the lower surface layer is 2.8~3.6 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the homopolymer polypropylene in the pearlescent masterbatch is 5~10 g / 10 min.

[0029] Further, the preparation method of the pearlescent masterbatch is as follows: 65-75 wt% of the modified heavy calcium carbonate and 25-35 wt% of homopolymer polypropylene are fed into a twin-screw extruder with a length-to-diameter ratio of 60:1 by a loss-in-weight weighing system for melt extrusion. At the same time, a vacuum is drawn at the end to remove volatiles. The extruded melt is then stretched, pelletized, and dried to obtain the pearlescent masterbatch. The extrusion temperature is 200-230℃.

[0030] A method for preparing the above-mentioned BOPP pearlescent film: Five layers of raw materials are mixed evenly by a feeder and then fed into a screw extruder. After each layer of raw materials is melted and plasticized, it is metered by a metering pump. The melts extruded by each extruder are combined into a film sheet by a T-die. The film sheet is cooled by a chilling roller and enters a chilling water tank. After passing through a water blowing chamber, it is stretched 4.5 to 5.2 times longitudinally, and then stretched 7.5 to 8.5 times transversely. After biaxial stretching, the film is corona treated after shaping, and then wound, aged, slit, and packaged into finished products.

[0031] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0032] Figure 1 These are schematic diagrams of the BOPP pearlescent films described in Examples 1-4 and Comparative Examples 1-10 of the present invention. Detailed Implementation

[0033] The terminology used in the embodiments of this application is for the purpose of describing specific embodiments only and is not intended to limit the embodiments of this application. It should be understood in this application that the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. 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.

[0034] 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.

[0035] A BOPP pearlescent film includes an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a bottom surface layer arranged sequentially.

[0036] The upper surface layer comprises binary random copolymer polypropylene; the lower surface layer comprises homopolymer polypropylene.

[0037] Both the upper and lower surface layers comprise homopolymer polypropylene and 5-15 wt% maleic anhydride-grafted ethylene-octene copolymer A; in the maleic anhydride-grafted ethylene-octene copolymer A, the grafting rate of maleic anhydride is 0.8-1.0%, and the octene content in the ethylene-octene copolymer segments is 20-25 wt%.

[0038] The core layer comprises homopolymer polypropylene, 25-40 wt% pearlescent masterbatch, and 5-10 wt% maleic anhydride-grafted ethylene-octene copolymer B; in the maleic anhydride-grafted ethylene-octene copolymer B, the grafting rate of maleic anhydride is 1.2-1.5%, and the octene content in the ethylene-octene copolymer segments is 10-15 wt%; the pearlescent masterbatch comprises 65-75 wt% modified heavy calcium carbonate and homopolymer polypropylene; the modified heavy calcium carbonate is obtained by coating heavy calcium carbonate with an organic coating agent, the organic coating agent comprising epoxy-functionalized titanate, and the amount of epoxy-functionalized titanate used is controlled to be 1.5-2.0 wt% of the heavy calcium carbonate.

[0039] Furthermore, the organic coating agent is formed by uniformly mixing the epoxy-functionalized titanate and anhydrous ethanol in a mass ratio of 1:4.

[0040] Furthermore, the preparation method of the epoxy-functionalized titanate includes the following steps:

[0041] (1) At room temperature, tetraisopropoxide titanium and glycidyl ether were dissolved in tetrahydrofuran (THF) at a molar ratio of 1:1. After mixing evenly, 0.3 mol% Lewis acid catalyst stannous chloride was added and stirred evenly to obtain a mixed solution for later use.

[0042] (2) Under the protection of inert argon gas, the temperature of the mixture is controlled at 48°C in a water bath and the mixture is stirred for 3.5 hours;

[0043] (3) After the mixture is cooled to room temperature, it is transferred to a rotary evaporator to remove tetrahydrofuran (THF) and the byproduct isopropanol from the mixture;

[0044] (4) The eluent was purified by silica gel column chromatography and vacuum dried to obtain a transparent liquid epoxy-functionalized titanate; the eluent consisted of ethyl acetate and petroleum ether in a mass ratio of 1:3.

[0045] Furthermore, the particle size D50 of the modified heavy calcium carbonate is 0.9~1.3μm.

[0046] Furthermore, the coating process for the modified heavy calcium carbonate includes the following steps:

[0047] (1) Place the heavy calcium carbonate powder in a high-speed mixer at 105°C and stir and dry for half an hour, controlling the moisture content of the heavy calcium carbonate powder to be ≤0.5wt%;

[0048] (2) An organic coating agent is obtained by uniformly mixing epoxy-functionalized titanate and anhydrous ethanol at a mass ratio of 1:4;

[0049] (3) The temperature of the high-speed mixer is controlled at 70°C, and the organic coating agent is evenly sprayed onto the heavy calcium carbonate powder being stirred in the high-speed mixer through a high-pressure atomizing nozzle;

[0050] (4) Heat the high-speed mixer to 90°C and set the rotation speed to 1000 rpm, so that the heavy calcium carbonate powder and the organic coating agent in the high-speed mixer are continuously mixed for 15 to 20 minutes.

[0051] (5) After mixing, cool down to below 40°C, and sieve through a 300-mesh sieve to remove agglomerated powder particles, and obtain the coated modified heavy calcium carbonate.

[0052] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the pearlescent masterbatch is 5~15 g / 10 min.

[0053] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted ethylene-octene copolymer A in the upper and lower surface layers is 5~10 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted ethylene-octene copolymer B in the core layer is 5~15 g / 10 min.

[0054] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the binary random copolymer polypropylene in the upper surface layer is 5~10 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the homopolymer polypropylene in the upper sub-surface layer, the lower sub-surface layer, the core layer, and the lower surface layer is 2.8~3.6 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the homopolymer polypropylene in the pearlescent masterbatch is 5~10 g / 10 min.

[0055] The preparation method of the pearlescent masterbatch of the above-mentioned BOPP pearlescent film is as follows: 65~75wt% of the modified heavy calcium carbonate and 25~35wt% of homopolymer polypropylene are fed into a twin-screw extruder with a length-to-diameter ratio of 60:1 by loss weighing and melt extrusion. At the same time, vacuum is drawn at the end to remove volatiles. The extruded melt is stretched, pelletized and dried to obtain the pearlescent masterbatch. The extrusion temperature is 200~230℃.

[0056] A method for preparing the above-mentioned BOPP pearlescent film: Five layers of raw materials are mixed evenly by a feeder and then fed into a screw extruder. After each layer of raw materials is melted and plasticized, it is metered by a metering pump. The melts extruded by each extruder are combined into a film sheet by a T-die. The film sheet is cooled by a chilling roller and enters a chilling water tank. After passing through a water blowing chamber, it is stretched 4.5 to 5.2 times longitudinally, and then stretched 7.5 to 8.5 times transversely. After biaxial stretching, the film is corona treated after shaping, and then wound, aged, slit, and packaged into finished products.

[0057] Furthermore, the core layer also includes 0.5~1wt% antistatic masterbatch.

[0058] Furthermore, the lower surface layer also includes 0.5~1wt% anti-adhesion masterbatch; the anti-adhesion masterbatch includes silicon dioxide.

[0059] Furthermore, the total thickness of the BOPP pearlescent film is 30~70μm, wherein the thickness of the upper surface layer and the lower surface layer is 1~2μm, and the thickness of the upper sub-surface layer and the lower sub-surface layer is 4~6μm.

[0060] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. All percentages mentioned in the following embodiments or comparative examples are by weight. The components, contents, and characteristics of each layer in the embodiments and comparative examples of the present invention are shown in Table 1 below.

[0061] Table 1

[0062]

[0063] To better demonstrate the effects of the present invention, the melt index of the homopolymer polypropylene in the upper, lower, core, and lower layers of the examples and comparative examples is 3.3 g / 10 min (230°C, 2.16 kg), the melt index of the homopolymer polypropylene of the pearlescent masterbatch in the core layer is 5 g / 10 min, and the particle size D50 of the modified heavy calcium carbonate powder of the pearlescent masterbatch in the examples and comparative examples is 0.95 μm.

[0064] Example 1

[0065] This embodiment provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a lower secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0066] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0067] The upper surface layer 2 and the lower surface layer 4 comprise 95 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 5 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 0.8%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0068] The core layer 3 comprises 59 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 9.5 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 5 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.2%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0069] The coating process for modified heavy calcium carbonate described in this embodiment includes the following steps:

[0070] (1) First, the heavy calcium carbonate powder with a particle size D50 of 0.95 μm is pre-dried, and then the heavy calcium carbonate powder is placed in a high-speed mixer at 105℃ and stirred and dried for half an hour, controlling the moisture content of the heavy calcium carbonate powder to be ≤0.5 wt%;

[0071] (2) An organic coating agent is obtained by uniformly mixing epoxy-functionalized titanate and anhydrous ethanol at a mass ratio of 1:4;

[0072] (3) The temperature of the high-speed mixer is controlled at 70°C. The organic coating agent is evenly sprayed onto the heavy calcium carbonate powder being stirred in the high-speed mixer through a high-pressure atomizing nozzle. The amount of epoxy-functionalized titanate used is controlled to be 1.5 wt% of the heavy calcium carbonate.

[0073] (4) Heat the high-speed mixer to 90°C and set the rotation speed to 1000 rpm. Mix the heavy calcium carbonate powder and the organic coating agent in the high-speed mixer for 15 minutes to allow the epoxy-functionalized titanate in the organic coating agent to fully react with the surface of the heavy calcium carbonate to obtain modified heavy calcium carbonate powder.

[0074] (5) After mixing, cool down to below 40°C to avoid overheating and decomposition of epoxy groups. Use a 300-mesh sieve to remove agglomerated powder particles and obtain the coated modified heavy calcium carbonate.

[0075] The pearlescent masterbatch preparation method described in this embodiment is as follows: 70wt% of the modified heavy calcium carbonate and 30wt% of homopolymer polypropylene (with a melt index of 5g / 10min measured at 230℃ and 2.16kg) are fed into a twin-screw extruder with a length-to-diameter ratio of 60:1 via a loss-in-weight weigher for melt extrusion (extrusion temperature 230℃, production filter screen 300 mesh, extruder speed 600rpm). At the same time, a vacuum is drawn at the end to remove volatiles. The extruded melt is then stretched, underwater pelletized and dried to obtain the pearlescent masterbatch.

[0076] The preparation method of the BOPP pearlescent film in this embodiment is as follows: Five layers of raw materials are mixed evenly by a feeder and then fed into a screw extruder. After each layer of raw materials is melted and plasticized, it is metered by a metering pump. The melt extruded from each extruder is transported through a narrow channel to a T-die to form a film sheet (the core layer extrusion temperature is 250°C, and the extrusion temperature of the other layers is 245°C). The film sheet is cooled by a chilling roller and enters a chilling water tank. After passing through a water blowing chamber, it enters a longitudinal stretching zone (preheating zone 138°C, stretching zone 135°C) for 5 times longitudinal stretching and shaping. Then it enters a transverse stretching zone (preheating zone 170°C, stretching zone 166°C) for 8 times transverse stretching. After biaxial stretching, the film is corona treated after shaping, then wound, aged, cut according to specifications, and packaged into finished products.

[0077] In this embodiment, the total thickness of the BOPP pearlescent film is 50 μm, wherein the thickness of the upper surface layer 1 is 2 μm, the thickness of the upper secondary surface layer 2 and the lower secondary surface layer 4 is 6.0 μm, the thickness of the core layer 3 is 34.5 μm, and the thickness of the lower surface layer 5 is 1.5 μm.

[0078] Example 2

[0079] This embodiment provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a lower secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0080] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0081] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 0.8%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0082] The core layer 3 comprises 59 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 9.5 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 5 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.2%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0083] The coating process for modified heavy calcium carbonate described in this embodiment is the same as in Embodiment 1.

[0084] The method for preparing pearlescent masterbatch in this embodiment is the same as in Embodiment 1.

[0085] The preparation method of the BOPP pearlescent film in this embodiment is the same as that in Embodiment 1.

[0086] The total thickness and the thickness of each layer of the BOPP pearlescent film in this embodiment are the same as in Embodiment 1.

[0087] Example 3

[0088] This embodiment provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a lower secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0089] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0090] The upper surface layer 2 and the lower surface layer 4 comprise 85 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 15 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0091] The core layer 3 comprises 54 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 10 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.2%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0092] The coating process of the modified heavy calcium carbonate described in this embodiment is the same as that in embodiment 1, except that in step (3), the amount of epoxy functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0093] The method for preparing pearlescent masterbatch in this embodiment is the same as in Embodiment 1.

[0094] The preparation method of the BOPP pearlescent film in this embodiment is the same as that in Embodiment 1.

[0095] The total thickness and the thickness of each layer of the BOPP pearlescent film in this embodiment are the same as in Embodiment 1.

[0096] Example 4

[0097] This embodiment provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a lower secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0098] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0099] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0100] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.3 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0101] The coating process of the modified heavy calcium carbonate described in this embodiment is the same as that in embodiment 1, except that in step (3), the amount of epoxy functionalized titanate used is controlled to be 2.0 wt% of the heavy calcium carbonate.

[0102] The method for preparing pearlescent masterbatch in this embodiment is the same as in Embodiment 1.

[0103] The preparation method of the BOPP pearlescent film in this embodiment is the same as that in Embodiment 1.

[0104] The total thickness and the thickness of each layer of the BOPP pearlescent film in this embodiment are the same as in Embodiment 1.

[0105] Comparative Example 1

[0106] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0107] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0108] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 0.5%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0109] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0110] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0111] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0112] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0113] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0114] Comparative Example 2

[0115] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0116] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0117] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0118] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 0.9%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0119] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0120] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0121] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0122] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0123] Comparative Example 3

[0124] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0125] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0126] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0127] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.1 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0128] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy functionalized titanate used is controlled to be 2.4 wt% of the heavy calcium carbonate.

[0129] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0130] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0131] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0132] Comparative Example 4

[0133] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0134] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0135] The upper surface layer 2 and the lower surface layer 4 comprise 80 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 20 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0136] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0137] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0138] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0139] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0140] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0141] Comparative Example 5

[0142] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0143] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0144] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0145] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 5.0 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0146] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy functionalized titanate used is controlled to be 0.8 wt% of the heavy calcium carbonate.

[0147] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0148] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0149] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0150] Comparative Example 6

[0151] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0152] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0153] The upper surface layer 2 and the lower surface layer 4 comprise 97 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 3 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0154] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0155] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0156] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0157] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0158] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0159] Comparative Example 7

[0160] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0161] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0162] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.2%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0163] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0164] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0165] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0166] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0167] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0168] Comparative Example 8

[0169] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0170] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0171] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0172] The core layer 3 comprises 56 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 8 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.8%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0173] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0174] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0175] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0176] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0177] Comparative Example 9

[0178] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0179] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0180] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0181] The core layer 3 comprises 61 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 3 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0182] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0183] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0184] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0185] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0186] Comparative Example 10

[0187] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer 1, an upper secondary surface layer 2, a core layer 3, a secondary secondary surface layer 4, and a lower surface layer 5 arranged sequentially. For details, please refer to [reference needed]. Figure 1 .

[0188] The upper surface layer 1 comprises binary random copolymer polypropylene (melt index of 7.5 g / 10 min measured at 230°C and 2.16 kg). The lower surface layer 5 comprises 99 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg) and 1 wt% anti-blocking masterbatch (containing 10 wt% silica with a silica particle size D50 of 4.5 μm).

[0189] The upper surface layer 2 and the lower surface layer 4 comprise 90 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230 °C and 2.16 kg) and 10 wt% maleic anhydride-grafted ethylene-octene copolymer A (octene content in the ethylene-octene copolymer segment is 22 wt%; maleic anhydride grafting rate is 1.0%; melt index of 8 g / 10 min measured at 230 °C and 2.16 kg).

[0190] The core layer 3 comprises 49 wt% homopolymer polypropylene (melt index of 3.3 g / 10 min measured at 230°C and 2.16 kg), 35 wt% pearlescent masterbatch (melt index of 8.6 g / 10 min measured at 230°C and 2.16 kg), 1 wt% antistatic masterbatch, and 15 wt% maleic anhydride-grafted ethylene-octene copolymer B (octene content in the ethylene-octene copolymer segment is 15 wt%; maleic anhydride grafting rate is 1.5%; melt index of 8 g / 10 min measured at 230°C and 2.16 kg).

[0191] The coating process of the modified heavy calcium carbonate described in this comparative example is the same as that in Example 1, except that in step (3), the amount of epoxy-functionalized titanate used is controlled to be 1.7 wt% of the heavy calcium carbonate.

[0192] The pearlescent masterbatch preparation method described in this comparative example is the same as that in Example 1.

[0193] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0194] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as in Example 1.

[0195] The following tests were conducted on the performance of the BOPP pearlescent films and their contained pearlescent masterbatches described in Examples 1-4 and the BOPP pearlescent films and their contained pearlescent masterbatches described in Comparative Examples 1-10:

[0196] Pearl masterbatch FPV value test: Filtration pressure value (FPV) testing is a standard for evaluating the dispersion performance of inorganic fillers. A certain amount of sample is extruded, and the FPV value is calculated based on the pressure difference and filling ratio. The unit of FPV value is (Bar / g). The worse the dispersibility, the larger the pressure difference, and the higher the corresponding FPV value, and vice versa. The testing instrument used is a commercially available FPV pressure filter tester with an extrusion temperature of 230℃, a 1800-mesh filter screen, and a 1kg pearl masterbatch test sample. In this invention, FPV = (P1 - P0) / m, where P0 is the pressure before filtration using the 1800-mesh filter screen, P1 is the pressure after filtration using the 1800-mesh filter screen, and m is the content of inorganic filler. In this comparative example and embodiment, the BOPP pearl membrane is filled with 70wt% modified heavy calcium carbonate, therefore m is taken as 700g. During the pressure filter test, the equipment automatically stops when the test pressure exceeds 250 bar.

[0197] The mechanical properties of the thin film were tested in accordance with the GB / T1040.3-2006 standard.

[0198] The light transmittance of the film was tested according to GB / T2410-2008.

[0199] Thin film delamination test method:

[0200] 1. Applying the tape: Apply 3M 610 tape (length ≥ 75mm) evenly to the white film test area, and then roll it back and forth 3 times with a standard pressure roller (2kg);

[0201] 2. Setting time: After the tape is applied, let it stand for 60-90 seconds to eliminate the instantaneous viscoelastic effect;

[0202] 3. Peeling operation: Peel manually at a constant speed at a 180° angle;

[0203] 4. Observe the delamination area and calculate the area percentage (delamination area / tape coverage area × 100%).

[0204] 5. Delamination evaluation.

[0205]

[0206] The filtration pressure test results of the BOPP pearlescent films described in Examples 1-4 and the pearlescent masterbatches of Comparative Examples 1-10 are shown in Table 2 below. The performance test results of the BOPP pearlescent films described in Examples 1-4 and the BOPP pearlescent films of Comparative Examples 1-10 are shown in Table 3 below.

[0207] Table 2

[0208]

[0209] Table 3

[0210]

[0211] Table 2 shows the results of organic modification of heavy calcium carbonate powder. With increasing use of epoxy-functionalized titanate modifier, the filtration pressure value of the pearlescent masterbatch decreased significantly. In Comparative Example 5, when the amount of epoxy-functionalized titanate was only 0.8 wt% of the heavy calcium carbonate, the amount was too low to effectively coat and modify the high specific surface area of ​​the heavy calcium carbonate. This low coating rate led to increased agglomeration of the heavy calcium carbonate powder, affecting its dispersion in polypropylene. During pearlescent membrane production, the filter screen pressure was high, and the weak bonding between the calcium carbonate agglomerates and the matrix exacerbated stress concentration, becoming a weak point for membrane rupture under high-speed biaxial stretching. Simultaneously, due to the agglomeration and poor dispersibility of the heavy calcium carbonate, the force transmission between the pearlescent masterbatch and the polypropylene melt in the core layer was weakened, resulting in poor flowability and even die lip clogging. Furthermore, pressure over-limit tripping occurred during pressure filtration testing. The data in Table 3 also demonstrate that the improved dispersibility of modified heavy calcium carbonate enhances the smoothness of pearlescent film production and reduces the number of film breakages. Therefore, increasing the amount of epoxy-functionalized titanate increases the degree of modification of heavy calcium carbonate coating, thereby reducing agglomeration and improving the compatibility between heavy calcium carbonate and polypropylene. However, for the pearlescent masterbatch in Comparative Example 3, when the amount of epoxy-functionalized titanate exceeds 2.0 wt% of heavy calcium carbonate, the excess epoxy-functionalized titanate forms a multilayer coating on the surface of heavy calcium carbonate, which in turn causes interparticle adhesion, leading to powder bridging and agglomeration, affecting the production efficiency of the pearlescent masterbatch. Simultaneously, unreacted free titanate migrates to the interface, forming a weak boundary layer. The residual titanate decomposes at high temperatures (>250℃), increasing the release of small molecule products and other adverse effects. Therefore, considering the processing stability of the masterbatch, product quality, and cost-effectiveness, this invention controls the amount of epoxy-functionalized titanate treatment between 1.5 and 2.0 wt% of heavy calcium carbonate.

[0212] To reduce the cost of BOPP film, this invention fills the core layer of the film with a high proportion of pearlescent masterbatch. As shown in Table 3, different addition ratios of maleic anhydride-grafted ethylene-octene copolymer in the upper and lower surface layers and the core layer, different maleic anhydride grafting rates, and different amounts of epoxy-functionalized titanate in the organic coating agent of the pearlescent masterbatch all have different effects on the physical properties and delamination effect of the pearlescent film. Since the amount of epoxy-functionalized titanate in Comparative Example 5 is only 0.8 wt% of the heavy calcium carbonate, the pearlescent masterbatch in Comparative Example 5 has poor dispersion, fewer functionalized groups on the surface of the modified heavy calcium carbonate that can react with the maleic anhydride-grafted ethylene-octene copolymer, and fewer anchor points for chemical bond forces. Therefore, the film in Comparative Example 5 exhibits the worst force transmission between the modified heavy calcium carbonate and the PP matrix under biaxial stretching. Furthermore, due to the high agglomeration and relatively large particle size of the modified heavy calcium carbonate, the pearlescent film exhibits the best stretching and foaming effect. This higher foaming efficiency results in lower density and the lowest elongation at break. From Examples 1 to 3, as the content of maleic anhydride-grafted ethylene-octene copolymer A in the upper and lower surface layers increases, or its grafting rate increases, the degree of contact reaction between the maleic anhydride groups and the epoxy-functionalized titanate on the surface of the modified heavy calcium carbonate at the interface between the sub-surface layer and the core layer increases. This results in increased tensile strength and decreased delamination area of ​​the film. This is because the maleic anhydride groups can react with the functionalized modified heavy calcium carbonate, and the ethylene-octene copolymer segments can entangle with the PP segments in the core layer. Under this dual synergy, the content of maleic anhydride-grafted ethylene-octene copolymer A in the sub-surface layer has a more significant effect on improving the pearlescent delamination effect. Comparing the data from Examples 2 and 4, it can be seen that Example 4 uses a higher amount of epoxy-functionalized titanate, and the grafting rate of maleic anhydride-grafted ethylene-octene copolymer B in the core layer is also higher. The highly active epoxy-functionalized titanate reacts more fully with the maleic anhydride in the core layer and the sub-surface layer, resulting in a better anti-delamination effect in Example 4. In Comparative Example 4, the maleic anhydride-grafted ethylene-octene copolymer A content was highest in the upper and lower layers, resulting in more complete bonding with the PP or modified heavy calcium carbonate in the core layer and a relatively low delamination area. In Comparative Example 1, the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer A in the upper and lower layers was low, and in Comparative Example 2, the maleic anhydride grafting rate of maleic anhydride-grafted ethylene-octene copolymer B in the core layer was also low. Similarly, there was a lack of sufficient maleic anhydride groups to react with the epoxy-functionalized titanate. Therefore, the delamination area ratios of Comparative Example 1 and Comparative Example 2 were both higher. Furthermore, the low maleic anhydride grafting rate in the core layer of Comparative Example 2 also affected the dispersion of modified heavy calcium carbonate in the core layer. It can be observed that the film production smoothness of Comparative Example 2 was worse than that of Comparative Example 1.Comparative Example 7 significantly increased the maleic anhydride grafting rate of ethylene-octene copolymer A in the upper and lower surface layers, while Comparative Example 8 significantly increased the maleic anhydride grafting rate of ethylene-octene copolymer B in the core layer. The delamination area ratio decreased significantly. However, the excessively high maleic anhydride grafting rate resulted in unreacted and agglomerated maleic anhydride regions becoming highly polar microregions. The poor compatibility between polar and non-polar microregions led to no foaming in the stretched maleic anhydride polar microregions of the core layer, resulting in inconsistent light transmittance and large thickness deviations in certain areas. In Comparative Example 3, the highest amount of epoxy-functionalized titanate was used, leading to excessive coating and multiple coatings. The chemical bonds and tensile forces generated between maleic anhydride and functionalized titanate were not effectively transferred to the surface of the modified heavy calcium carbonate. Therefore, the delamination area of ​​Comparative Example 3 was higher than that of Example 4. The maleic anhydride content in the upper and lower layers of Comparative Examples 4 and 6 differed significantly, indicating that a higher maleic anhydride content resulted in better anti-delamination performance. This suggests that the chemical and physical interactions between the maleic anhydride-grafted ethylene-octene copolymer A in the upper and lower layers and the modified heavy calcium carbonate in the core layer were more effective in combating delamination. However, in Comparative Example 4, the excessive addition of maleic anhydride-grafted ethylene-octene copolymer in the upper and lower layers actually increased the thermal shrinkage rate, causing the film to shrink excessively after heating, thus affecting the appearance quality of the products produced in subsequent processing. The maleic anhydride-grafted ethylene-octene copolymer B content in the core layers of Comparative Examples 9 and 10 differed significantly. In Comparative Example 9, the addition of maleic anhydride-grafted ethylene-octene copolymer B in the core layer was less than 5 wt%, reducing the chemical interaction between the maleic anhydride groups and the modified heavy calcium carbonate. This decreased the dispersion effect of the modified heavy calcium carbonate and reduced its compatibility with PP, resulting in relatively poor production smoothness. However, in Comparative Example 10, the amount of maleic anhydride-grafted ethylene-octene copolymer B added to the core layer exceeded 10wt%. The unreacted polar groups had a large difference in compatibility with non-polar PP, and there was no foaming effect under stretching, resulting in color differences in the film appearance, which affected the packaging performance and the smoothness of downstream ink printing.

[0213] 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 BOPP pearlescent film, characterized in that: This includes the upper surface layer, the upper sub-surface layer, the core layer, the lower sub-surface layer, and the bottom surface layer, which are arranged sequentially. The upper surface layer comprises binary random copolymer polypropylene; the lower surface layer comprises homopolymer polypropylene. Both the upper and lower surface layers comprise homopolymer polypropylene and 5-15 wt% maleic anhydride-grafted ethylene-octene copolymer A; in the maleic anhydride-grafted ethylene-octene copolymer A, the grafting rate of maleic anhydride is 0.8-1.0%, and the octene content in the ethylene-octene copolymer segments is 20-25 wt%. The core layer comprises homopolymer polypropylene, 25-40 wt% pearlescent masterbatch, and 5-10 wt% maleic anhydride-grafted ethylene-octene copolymer B; in the maleic anhydride-grafted ethylene-octene copolymer B, the grafting rate of maleic anhydride is 1.2-1.5%, and the octene content in the ethylene-octene copolymer segments is 10-15 wt%; the pearlescent masterbatch comprises 65-75 wt% modified heavy calcium carbonate and homopolymer polypropylene; the modified heavy calcium carbonate is obtained by coating heavy calcium carbonate with an organic coating agent, the organic coating agent comprising epoxy-functionalized titanate, and the amount of epoxy-functionalized titanate used is controlled to be 1.5-2.0 wt% of the heavy calcium carbonate.

2. The BOPP pearlescent film according to claim 1, characterized in that: The organic coating agent is formed by uniformly mixing the epoxy-functionalized titanate and anhydrous ethanol in a mass ratio of 1:

4.

3. The BOPP pearlescent film according to claim 1, characterized in that: The preparation method of the epoxy-functionalized titanate includes the following steps: (1) At room temperature, tetraisopropoxide titanium and glycidyl ether are dissolved in tetrahydrofuran at a molar ratio of 1:

1. After mixing evenly, 0.3 mol% Lewis acid catalyst stannous chloride is added and stirred evenly to obtain a mixed solution for later use. (2) Under the protection of inert argon gas, the temperature of the mixture is controlled at 40~50℃ in a water bath and the mixture is stirred for 3~4 hours; (3) After the mixture is cooled to room temperature, it is transferred to a rotary evaporator to remove tetrahydrofuran (THF) and the byproduct isopropanol from the mixture; (4) The eluent was purified by silica gel column chromatography and vacuum dried to obtain a transparent liquid epoxy-functionalized titanate; the eluent consisted of ethyl acetate and petroleum ether in a mass ratio of 1:

3.

4. The BOPP pearlescent film according to claim 1, characterized in that: The modified heavy calcium carbonate has a particle size D50 of 0.9~1.3μm.

5. The BOPP pearlescent film according to claim 1, characterized in that: The coating process for the modified heavy calcium carbonate includes the following steps: (1) Place the heavy calcium carbonate powder in a high-speed mixer at 105°C and stir and dry for half an hour, controlling the moisture content of the heavy calcium carbonate powder to be ≤0.5wt%; (2) An organic coating agent is obtained by uniformly mixing epoxy-functionalized titanate and anhydrous ethanol at a mass ratio of 1:4; (3) The temperature of the high-speed mixer is controlled at 60~70℃, and the organic coating agent is evenly sprayed onto the heavy calcium carbonate powder being stirred in the high-speed mixer through a high-pressure atomizing nozzle; (4) Heat the high-speed mixer to 80~90℃ and set the speed to 800~1200rpm, so that the heavy calcium carbonate powder and the organic coating agent in the high-speed mixer are continuously mixed for 15~20 minutes; (5) After mixing, cool down to below 40°C, and sieve through a 300-mesh sieve to remove agglomerated powder particles, and obtain the coated modified heavy calcium carbonate.

6. The BOPP pearlescent film according to claim 1, characterized in that: At 230℃ and a load of 2.16kg, the melt index of the pearlescent masterbatch is 5~15g / 10min.

7. The BOPP pearlescent film according to claim 1, characterized in that: At 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted ethylene-octene copolymer A in the upper and lower surface layers is 5~10 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the maleic anhydride-grafted ethylene-octene copolymer B in the core layer is 5~15 g / 10 min.

8. The BOPP pearlescent film according to claim 1, characterized in that: At 230℃ and a load of 2.16 kg, the melt index of the binary random copolymer polypropylene in the upper surface layer is 5~10 g / 10 min; at 230℃ and a load of 2.16 kg, the melt index of the homopolymer polypropylene in the upper sub-surface layer, the lower sub-surface layer, the core layer, and the lower surface layer is 2.8~3.6 g / 10 min; at 230℃ and a load of 2.16 kg, the melt index of the homopolymer polypropylene in the pearlescent masterbatch is 5~10 g / 10 min.

9. The BOPP pearlescent film according to any one of claims 1 to 8, characterized in that: The pearlescent masterbatch is prepared as follows: 65-75 wt% of the modified heavy calcium carbonate and 25-35 wt% of homopolymer polypropylene are fed into a twin-screw extruder with a length-to-diameter ratio of 60:1 via a loss-in-weight weighing system for melt extrusion. At the same time, a vacuum is drawn at the end to remove volatiles. The extruded melt is then stretched, pelletized, and dried to obtain the pearlescent masterbatch. The extrusion temperature is 200-230℃.

10. A method for preparing a BOPP pearlescent film according to any one of claims 1 to 9, characterized in that: The five layers of raw materials are mixed evenly by a feeder and then fed into a screw extruder. After each layer of raw materials is melted and plasticized, it is metered by a metering pump. The melts extruded by each extruder are combined into a thin film sheet at a T-die. The film sheet is cooled by a chilling roller and then enters a chilling water tank. After passing through a water blowing chamber, it is stretched 4.5 to 5.2 times longitudinally, and then stretched 7.5 to 8.5 times transversely. After biaxial stretching, the film is corona treated after setting, and then wound, aged, slit, and packaged into finished products.

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