Anti-stripping easy-to-print high-strength BOPP (biaxially-oriented polypropylene) pearlized film and preparation method thereof

Abstract

The invention relates to an anti-stripping easy-to-print high-strength BOPP pearlized film and a preparation method thereof, and belongs to the technical field of pearlized films. The anti-stripping easy-to-print high-strength BOPP pearlized film comprises an upper surface layer, an upper sub-surface layer, a core layer, a lower sub-surface layer and a lower surface layer which are arranged in sequence, each of the upper secondary surface layer and the lower secondary surface layer comprises homo-polypropylene and 2-10wt% of dicumyl peroxide premix, and the dicumyl peroxide premix comprises homo-polypropylene and 45-55wt% of dicumyl peroxide; the core layer comprises homo-polypropylene and 10-20wt% of modified calcium carbonate filled master batch; the modified calcium carbonate filled master batch comprises homo-polypropylene and 55-65wt% of modified calcium carbonate; the modified calcium carbonate is obtained by modifying 95-97 parts by weight of calcium carbonate with 3-5 parts by weight of linolenic acid. The film has the characteristics of high interlayer binding force, easiness in printing and high mechanical strength on the basis of ensuring that a good pearlescent effect is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of pearlescent films, in particular to a peeling-resistant, easy-to-print, high-strength BOPP pearlescent film and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene (BOPP) pearlescent film is typically imparted with a pearlescent effect by adding calcium carbonate. During biaxial stretching, the difference in mechanical strength between the calcium carbonate and polypropylene creates numerous tiny cavities around the calcium carbonate. These cavities reflect or interfere with light entering the film, imparting a pearlescent sheen to the film. This pearlescent effect allows manufacturers to create a wide variety of labels and flexibly incorporate product branding.

[0003] Existing BOPP pearlescent films are typically designed with a three- or five-layer structure. Calcium carbonate is added to the core layer of the BOPP pearlescent film, while other layers incorporate functional additives based on product requirements. Due to the significant differences in properties between calcium carbonate and the polypropylene in the core layer, a calcium carbonate masterbatch is typically prepared to accommodate high-speed film production. This masterbatch is then added to the extruder in a specific proportion during film production. This multi-layer co-extrusion process creates a thick sheet, which is then biaxially stretched to form the BOPP pearlescent film.

[0004] However, due to the unique biaxial stretching process used in BOPP pearlescent film, tiny voids inevitably form around the calcium carbonate in the core layer. These voids become mechanically weak points in the film. Therefore, how to ensure the dispersion of calcium carbonate while also improving the mechanical strength of these voids is a question worth studying.

[0005] Furthermore, BOPP pearlescent film is often used in the labeling industry, and its surface printing performance is crucial to the market acceptance of the final product. However, to improve the dispersion of calcium carbonate, existing BOPP pearlescent films often incorporate a large amount of low-molecular-weight dispersants and coupling agents in the core layer. These low-molecular-weight substances (such as stearic acid) easily migrate to the surface of the BOPP pearlescent film, often negatively impacting its surface printing performance. Therefore, improving the printability of BOPP pearlescent film is a key issue. Summary of the Invention

[0006] Based on this, the object of the present invention is to provide a peel-resistant, easy-to-print, high-strength BOPP pearlescent film and a preparation method thereof. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film can improve the mechanical strength (i.e., high strength) at the "holes" of the film while ensuring a good pearlescent effect. At the same time, it can also improve the interlayer bonding force (i.e., peel-resistance) between the core layer and the upper and lower surface layers. This effectively improves the interlayer peeling phenomenon of the film in practical applications (for example, after being made into labels) and is also conducive to improving the printability of the film (i.e., easy printing).

[0007] To achieve the above object, the present invention adopts the following technical solutions: The present invention provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; the upper surface layer comprises homopolypropylene and 5-10wt% modified silica filler masterbatch; the modified silica filler masterbatch comprises homopolypropylene and 15-25wt% modified silica; the modified silica is obtained by modifying silica with maleic anhydride, wherein the amount of maleic anhydride is 1-3wt% of the silica; the upper sub-surface layer comprises a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; the upper sub-surface layer comprises homopolypropylene and 5-10wt% modified silica filler masterbatch; the modified silica filler masterbatch comprises homopolypropylene and 15-25wt% modified silica; the modified silica is obtained by modifying silica with maleic anhydride, wherein the amount of maleic anhydride is 1-3wt% of the silica; the upper sub-surface layer comprises a core layer, a sub-surface layer, and a lower surface layer ... The surface layer and the subsurface layer both include homopolypropylene and 2-10 wt% dicumyl peroxide premix, wherein the dicumyl peroxide premix includes homopolypropylene and 45-55 wt% dicumyl peroxide; the core layer includes homopolypropylene and 10-20 wt% modified calcium carbonate filler masterbatch; the modified calcium carbonate filler masterbatch includes homopolypropylene and 55-65 wt% modified calcium carbonate; the modified calcium carbonate is obtained by modifying 95-97 wt parts of calcium carbonate with 3-5 wt parts of linolenic acid.

[0008] The anti-stripping, easy-to-print, high-strength BOPP pearlescent film of the present invention is prepared by adding dicumyl peroxide to the upper surface layer and the lower surface layer, and simultaneously adding calcium carbonate modified with linolenic acid to the core layer. When the multi-layer co-extruded BOPP film is produced, the dicumyl peroxide decomposes at the co-extrusion processing temperature to generate free radicals. At the interface between the upper surface layer and the core layer, and at the interface between the lower surface layer and the core layer, the free radicals generated by the decomposition of the dicumyl peroxide contact the linolenic acid in the core layer, triggering a bonding reaction (polymerization reaction) of the unsaturated double bonds on the linolenic acid in the core layer to form linolenic acid oligomers. One end of the carboxyl group in the linolenic acid oligomer is bonded to the calcium carbonate, and the other end is entangled in the upper surface layer or the lower surface layer, so that chemical bonds are established between the core layer and the upper surface layer, as well as between the lower surface layer, thereby improving the interlayer bonding strength between the core layer and the upper surface layer, as well as between the core layer and the lower surface layer. Furthermore, the polymerization of linolenic acid to form linolenic acid oligomers significantly reduces the content of linolenic acid monomers in the core layer, greatly reducing the likelihood of low-molecular-weight linolenic acid monomers migrating to the film surface. This significantly improves the problem of conventional low-molecular-weight substances coating modified calcium carbonate, which then easily migrate to the film surface and negatively impact the film's printing properties. Furthermore, it should be noted that the present invention uses linolenic acid to modify calcium carbonate. Linolenic acid itself has a certain molecular chain length and good thermal stability, making it less likely to polymerize prematurely during the modification process and preparation of the modified calcium carbonate filler masterbatch. This prevents premature polymerization of linolenic acid, which could render it ineffective during multi-layer coextrusion. It should be noted that in the present invention's peel-resistant, easily printable, high-strength BOPP pearlescent film, the addition of dicumyl peroxide in the form of a dicumyl peroxide premix to the upper and lower surface layers facilitates uniform dispersion of dicumyl peroxide in the upper and lower surface layers. The addition of modified calcium carbonate in the form of a modified calcium carbonate filler masterbatch to the core layer facilitates uniform dispersion of the modified calcium carbonate in the core layer.

[0009] Since the free radicals generated by dicumyl peroxide are highly active and easily quenched, in order to ensure that the linolenic acid oligomers formed by the polymerization of linolenic acid can reach a certain molecular weight, the present invention adds 2-10wt% of dicumyl peroxide premix to the upper surface layer and the lower surface layer and controls the dicumyl peroxide premix to contain 45-55wt% of dicumyl peroxide (the amount of dicumyl peroxide added is much higher than that of conventional polymerization). At the same time, no chain terminator is specifically added to the upper surface layer and the lower surface layer to prevent the molecular weight of the linolenic acid oligomers formed by the polymerization of linolenic acid from being too low, thereby failing to play a role in improving the interlayer bonding strength. If the amount of the dicumyl peroxide premix added to the core layer is too low and / or the content of the dicumyl peroxide in the dicumyl peroxide premix is ​​too low, the number of free radicals formed during the production of the anti-stripping, easy-to-print, high-strength BOPP pearlescent film is small and the initiation efficiency is low; if the amount of the dicumyl peroxide premix added to the core layer is too high and / or the content of the dicumyl peroxide in the dicumyl peroxide premix is ​​too high, too many molecular chain initiation points will be formed during the production of the anti-stripping, easy-to-print, high-strength BOPP pearlescent film, so that the linolenic acid monomers can only polymerize to form linolenic acid oligomers with too low a molecular weight, which cannot exert the characteristics of "polymer" (i.e., the molecular chain of the linolenic acid oligomer is too short to effectively combine with the upper surface layer and the lower surface layer, and the linolenic acid oligomers with too low a molecular weight easily migrate to the film surface and affect the printing performance).

[0010] To further enhance the printability of the film's top surface, the anti-peeling, easy-to-print, high-strength BOPP pearlescent film of the present invention incorporates 5-10 wt% of a modified silica filler masterbatch into the top surface. The masterbatch comprises homopolypropylene and 15-25 wt% of modified silica, obtained by modifying silica with maleic anhydride. Adding the modified silica as a masterbatch to the top surface facilitates uniform dispersion of the modified silica throughout the layer. By selecting silica modified with maleic anhydride and chemically modifying the silica with maleic anhydride and grafting polar functional groups onto the silica surface, the modified silica can both absorb ink through the porous structure of the silica itself and chemically bond with the ink through the polar functional groups grafted onto the silica surface, thereby improving the ink's adhesion to the upper surface, fully ensuring the printing performance of the upper surface, and further ensuring the printability of the upper surface. If the amount of modified silica filler masterbatch added is too low, the printing performance of the upper surface cannot be effectively improved. If the amount of modified silica filler masterbatch added is too high, it is not conducive to the uniform dispersion of the modified silica in the upper surface, thereby affecting the appearance quality of the film.

[0011] The anti-stripping, easy-to-print, high-strength BOPP pearlescent film of the present invention has linolenic acid in the core layer anchored to the calcium carbonate via carboxyl groups. Linolenic acid oligomers formed after polymerization under the action of free radicals generated by dicumyl peroxide form a network structure between the calcium carbonate in the core layer and the homopolypropylene in the core layer, the upper surface layer, or the lower surface layer. This effectively improves the mechanical strength of the "voids" formed in the calcium carbonate during biaxial stretching, while also enhancing the interlayer bonding between the core layer and the upper surface layer and the lower surface layer, thereby alleviating interlayer peeling. Furthermore, the anti-stripping, easy-to-print, high-strength BOPP pearlescent film of the present invention incorporates specific modified silica in the upper surface layer to enhance the ink adsorption capacity of the upper surface layer. This synergistically enhances the advantage that the linolenic acid oligomers formed by the polymerization of linolenic acid are less likely to migrate to the film surface (i.e., the linolenic acid oligomers do not have the negative impact on the printing performance of the film surface caused by conventional low-molecular-weight substances coating the modified calcium carbonate). This makes the upper surface layer easier to print, thereby improving the printability of the upper surface layer.

[0012] Furthermore, the preparation method of the dicumyl peroxide premix is ​​as follows: homopolypropylene and dicumyl peroxide are added to a high-speed mixer according to a ratio, mixed at a temperature of 30-50°C, and mixed for 5-15 minutes to obtain the dicumyl peroxide premix. Dicumyl peroxide is a solid powder. To facilitate uniform mixing of dicumyl peroxide in the homopolypropylene of the upper and lower surface layers, dicumyl peroxide and homopolypropylene are mixed in a high-speed mixer according to a ratio, mixed at a temperature of 30-50°C, and mixed for 5-15 minutes to obtain the dicumyl peroxide premix; the dicumyl peroxide premix is ​​then added to the upper and lower surface layers according to a specific ratio, which helps to improve the dispersibility of the dicumyl peroxide in the upper and lower surface layers. Preferably, the dicumyl peroxide premix comprises 50 wt% homopolypropylene and 50 wt% dicumyl peroxide; homopolypropylene and dicumyl peroxide are added to a high-speed mixer according to the ratio and mixed at a mixing temperature of 40° C. for 10 minutes to obtain the dicumyl peroxide premix.

[0013] Furthermore, the modified calcium carbonate is prepared by adding 95-97 parts by weight of calcium carbonate and 3-5 parts by weight of linolenic acid to a high-speed mixer, mixing at a mixing temperature of 80-100°C for 15-25 minutes to obtain the modified calcium carbonate. During the mixing process of the calcium carbonate and linolenic acid, the linolenic acid fully reacts with the calcium carbonate, coating the surface of the calcium carbonate with the linolenic acid, thereby obtaining the modified calcium carbonate. Preferably, the modified calcium carbonate is prepared by adding 95 parts by weight of calcium carbonate (bare powder) and 5 parts by weight of linolenic acid to a high-speed mixer, mixing at a mixing temperature of 90°C for 20 minutes to obtain the modified calcium carbonate. The reasons why linolenic acid is selected to modify calcium carbonate in the present invention are: first, linolenic acid contains carboxyl groups, which can react with the hydroxyl groups on the surface of calcium carbonate, thereby effectively coating the calcium carbonate; second, linolenic acid contains unsaturated double bonds, which can be polymerized under the action of diisopropylbenzene peroxide to form linolenic acid oligomers, so that calcium carbonate can form chemical bonds with the core layer, the upper surface layer or the lower surface layer through the linolenic acid oligomers, thereby improving the interlayer bonding force of the film and the mechanical strength of the "holes" formed by calcium carbonate, and the formation of linolenic acid oligomers does not have the problem of negative impact on the printing performance of the film surface layer caused by traditional low-molecular substances coating modified calcium carbonate; third, linolenic acid itself has a certain molecular chain length and good thermal stability, is not easy to polymerize prematurely during the modification process, and can be suitable for multi-layer co-extrusion.

[0014] Furthermore, the calcium carbonate has an average particle size D50 of 1-2 μm. Selecting unmodified calcium carbonate with an average particle size D50 of 1-2 μm allows the prepared modified calcium carbonate to be evenly dispersed in the core layer after being added to the core layer as a modified calcium carbonate filler masterbatch, thereby improving the uniformity of the pearlescent effect of the anti-peeling, easy-to-print, high-strength BOPP pearlescent film. If calcium carbonate with an excessively large average particle size is selected, the high amount of calcium carbonate added will cause it to occupy a large portion of the film, preventing the matrix resin (homopolypropylene) in the core layer from forming a continuous phase with sufficient mechanical strength. This in turn results in insufficient mechanical strength of the film, making it difficult to meet the application performance requirements of the anti-peeling, easy-to-print, high-strength BOPP pearlescent film after it is subsequently made into a label. If calcium carbonate with an excessively small average particle size is selected, on the one hand, it becomes difficult to disperse in the homopolypropylene in the core layer, and excessive calcium carbonate agglomeration will cause production problems and uneven pearlescent effect of the product. On the other hand, if the calcium carbonate particle size is too small, it is difficult for the calcium carbonate to form large pores, resulting in an unsatisfactory pearlescent effect of the anti-peeling, easy-to-print, high-strength BOPP pearlescent film.

[0015] Furthermore, the preparation method of the modified calcium carbonate filling masterbatch is as follows: homopolypropylene and modified calcium carbonate are added to a twin-screw extruder according to a ratio, heated and melted, and then granulated to obtain the modified calcium carbonate masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 210-230°C, the screw speed is 350-450rpm / min, and the modified calcium carbonate is side-fed. Preferably, the modified calcium carbonate masterbatch comprises 40wt% homopolypropylene and 60wt% modified calcium carbonate, and homopolypropylene and modified calcium carbonate are added to a twin-screw extruder according to a ratio, heated and melted, and then granulated to obtain the modified calcium carbonate filling masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 220°C, the screw speed is 400rpm / min, and the modified calcium carbonate is side-fed.

[0016] Furthermore, the preparation method of the modified silica is as follows: adding silica to toluene to form a solution, then adding maleic anhydride to the solution, wherein the amount of maleic anhydride added is 1-3wt% of the silica; reacting at 90-110°C for 20-40 minutes under a nitrogen atmosphere, after the reaction is completed, filtering and drying the product after the solution is cooled to obtain maleic anhydride-modified silica, that is, the modified silica. Preferably, the preparation method of the modified silica is as follows: adding silica to toluene to form a solution, then adding maleic anhydride, wherein the amount of maleic anhydride added is 2wt% of the silica; the above solution is reacted at 100°C for 30 minutes under a nitrogen atmosphere, after the reaction is completed, filtering and drying the product after the solution is cooled to obtain maleic anhydride-modified silica, that is, the modified silica.

[0017] Furthermore, the silicon dioxide is synthesized by the gel method. The function of the silicon dioxide on the upper surface is to absorb ink. The surface of the silicon dioxide synthesized by the gel method has a porous structure and a high oil absorption value.

[0018] Furthermore, the average particle size D50 of the silica is 5-7 μm. Considering that the thickness of the upper surface layer of BOPP pearlescent film is typically 2-4 μm, silica with an average particle size D50 of 5-7 μm is selected for modification. This allows the prepared modified silica to be added to the upper surface layer in the form of a modified silica filler masterbatch, where the silica therein can partially protrude from the surface of the upper surface layer, effectively adsorbing ink. If the silica particle size is small, the silica is easily completely encapsulated by the matrix resin (homopolypropylene) and is difficult to expose from the upper surface layer, resulting in an inability to effectively adsorb ink when printing on the upper surface layer, which is not conducive to promoting the full spreading of ink on the upper surface layer. If the silica particle size is too large, the silica will form excessively large protrusions on the upper surface layer, affecting the film surface quality and creating a risk of film breakage during the biaxial stretching production of the anti-peeling, easy-to-print, high-strength BOPP pearlescent film.

[0019] Furthermore, the modified silica filler masterbatch is prepared by adding homopolypropylene and modified silica to a twin-screw extruder according to a ratio, heating and melt-extruding, and then granulating to obtain the modified silica filler masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 210-230°C, the screw speed is 200-300rpm / min, and the modified silica is side-fed. Preferably, the modified silica filler masterbatch comprises 80wt% homopolypropylene and 20wt% modified silica, and the homopolypropylene and modified silica are added to a twin-screw extruder according to a ratio, heating and melt-extruding, and then granulating to obtain the modified silica filler masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 220°C, the screw speed is 250rpm / min, and the modified silica is side-fed.

[0020] Furthermore, the lower surface layer comprises copolymerized polypropylene or homopolymerized polypropylene.

[0021] Furthermore, the homopolypropylene in the upper surface layer, the homopolypropylene in the modified silica filler masterbatch, the homopolypropylene in the upper and lower surface layers, the homopolypropylene in the dicumyl peroxide premix, the homopolypropylene in the core layer, the homopolypropylene in the modified calcium carbonate filler masterbatch, and the homopolypropylene in the lower surface layer all have a melt index of 2-4 g / 10 min (230°C, 2.16 kg). Using homopolypropylene within this melt index range ensures efficient production of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film and improves compatibility among film components and between film layers.

[0022] The present invention also provides a method for preparing any of the above-mentioned anti-peeling, easy-to-print, high-strength BOPP pearlescent films, comprising the following steps: mixing the raw materials according to the ratio of the raw materials of each layer, feeding them into the extruders of each layer through a metering scale, and after multi-layer co-extrusion through the die head, casting the sheets according to the flat film method and then quenching them into thick sheets. The thick sheets are subjected to a synchronous biaxial stretching method in the longitudinal and transverse directions to form a biaxially stretched film, which is corona treated after shaping, and then wound, aged, slit, and packaged into the finished product, i.e., the anti-peeling, easy-to-print, high-strength BOPP pearlescent film.

[0023] Furthermore, the melt extrusion temperature of the lower surface layer is 220-240°C, the melt extrusion temperature of the upper surface layer and the lower surface layer are both 160-180°C, and the melt extrusion temperature of the core layer is 200-220°C; the temperature of the chilling roller during chilling is 50-80°C; the temperature during biaxial stretching is 100-120°C, and the ratios of longitudinal stretching and transverse stretching are both 4-5 times.

[0024] Compared with existing technologies: The anti-peeling, easy-to-print, high-strength BOPP pearlescent film of the present invention not only ensures a good pearlescent effect but also has the characteristics of high interlayer bonding, ease of printing, and high strength. While ensuring a good pearlescent effect through "cavitation," the anti-peeling, easy-to-print, high-strength BOPP pearlescent film of the present invention improves the mechanical strength of the film's "cavities" while also improving the interlayer bonding between the upper surface layer, the core layer, and the lower surface layer, effectively improving the interlayer peeling phenomenon that occurs with the anti-peeling, easy-to-print, high-strength BOPP pearlescent film in practical applications (e.g., after being made into labels). The anti-peeling, easy-to-print, high-strength BOPP pearlescent film of the present invention also enhances the ink adsorption capacity of the upper surface layer of the anti-peeling, easy-to-print, high-strength BOPP pearlescent film by adding specific modified silica to the upper surface layer of the film. This synergistic effect of linolenic acid oligomers eliminates the negative impact on the printing performance of the film surface layer caused by conventional low-molecular-weight substances coated with modified calcium carbonate. This makes the upper surface layer of the resulting anti-peeling, easy-to-print, high-strength BOPP pearlescent film easy to print and suitable for making labels. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic structural diagram of the anti-peeling, easy-to-print, high-strength BOPP pearlescent film of the present invention. DETAILED DESCRIPTION

[0026] The present invention is further described below with reference to the examples. These examples are intended to illustrate the present invention only and are not intended to limit the scope of the present invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally based on conventional conditions in the art or the conditions recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from conventional markets. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention fall within the scope of protection claimed in the present invention.

[0027] In the following examples or comparative examples: A modified silica filler masterbatch comprises 80 wt% homopolypropylene and 20 wt% modified silica. The modified silica is prepared by adding silica (synthesized by a gel method, with an average particle size D50 of 5 μm) to toluene to form a solution, and then adding maleic anhydride to the solution in an amount equal to 2 wt% of the silica. The solution is reacted at 100°C for 30 minutes under a nitrogen atmosphere. After the reaction, the solution is cooled, filtered, and the product is dried to obtain maleic anhydride-modified silica, i.e., the modified silica. The modified silica filler masterbatch is prepared by adding homopolypropylene and modified silica according to a ratio into a twin-screw extruder, heating, melting, and extruding, and then granulating to obtain the modified silica filler masterbatch. The twin-screw extruder is set at a processing temperature of 220°C, a screw speed of 250 rpm / min, and side-feeding the modified silica.

[0028] A dicumyl peroxide premix comprises 50 wt% dicumyl peroxide and 50 wt% homopolypropylene. The dicumyl peroxide premix is ​​prepared by mixing homopolypropylene and dicumyl peroxide in a high-speed mixer according to a ratio at a mixing temperature of 40° C. for 10 minutes to obtain the dicumyl peroxide premix.

[0029] Modified calcium carbonate filler masterbatch: includes 40wt% homopolypropylene and 60wt% modified calcium carbonate; the modified calcium carbonate is prepared by adding 95 parts by weight of bare calcium carbonate powder (average particle size D50: 1μm) and 5 parts by weight of linolenic acid into a high-speed mixer and mixing at a mixing temperature of 90°C for 20 minutes to obtain the modified calcium carbonate; the modified calcium carbonate masterbatch is prepared by adding homopolypropylene and modified calcium carbonate according to a ratio into a twin-screw extruder, heating and melt-extruding, and then granulating to obtain the modified calcium carbonate filler masterbatch, wherein the processing temperature in the twin-screw extruder is set at 220°C, the screw speed is set at 400rpm / min, and the modified calcium carbonate is side-fed.

[0030] Ordinary calcium carbonate filler masterbatch: 40wt% homopolypropylene and 60wt% conventional calcium carbonate. The conventional calcium carbonate is prepared by adding 97 parts by weight of bare calcium carbonate powder (average particle size D50: 1μm) and 3 parts by weight of stearic acid to a high-speed mixer, setting the temperature to 60°C, and mixing for 20 minutes to obtain the conventional calcium carbonate. The ordinary calcium carbonate filler masterbatch is prepared by adding homopolypropylene and conventional calcium carbonate according to the ratio into a twin-screw extruder, heating and melt-extruding, and then granulating to obtain the ordinary calcium carbonate filler masterbatch. The twin-screw extruder is set at a processing temperature of 220°C, a screw speed of 400rpm / min, and side-feeding conventional calcium carbonate.

[0031] The melt index of the homopolypropylene and the homopolypropylene of the upper surface layer, upper sub-surface layer, core layer, sub-surface layer and lower surface layer is 3 g / 10 min (melt index measurement conditions are 230° C., 2.16 kg).

[0032] Example 1 This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Figure 1 , comprising an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a sub-surface layer 4 and a lower surface layer 5 arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer 1: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch; Upper surface layer 2: 90 wt% homopolypropylene and 10 wt% dicumyl peroxide premix; Core layer 3: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch; Subsurface layer 4: the same composition and content as the previous surface layer of this embodiment; Lower surface layer 5: 100wt% homopolymer polypropylene.

[0033] This embodiment also provides a method for preparing a peel-resistant, easy-to-print, high-strength BOPP pearlescent film, comprising the following steps: mixing the raw materials according to the ratio of the raw materials for each layer, feeding the raw materials into the extruders for each layer through a metering scale, co-extruding the raw materials through the die head, casting the film into a thick sheet according to the flat film method, and then chilling the thick sheet into a biaxially oriented film by a synchronous biaxial stretching method in the longitudinal and transverse directions. After shaping, the film is corona treated, and then rolled, aged, slit, and packaged into the finished product, i.e., the peel-resistant, easy-to-print, high-strength BOPP pearlescent film.

[0034] The melt extrusion temperature of the lower surface layer was 230° C., the melt extrusion temperature of the upper and lower surface layers was 170° C., and the melt extrusion temperature of the core layer was 210° C. The chill roll temperature was 70° C., the biaxial stretching temperature was 110° C., and the longitudinal and transverse stretching ratios were both 5 times.

[0035] The total thickness of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment is 60 μm, of which the upper surface layer 1 is 2 μm thick, the upper surface layer 2 and the lower surface layer 4 are both 7 μm thick, and the lower surface layer 5 is 2 μm thick.

[0036] Example 2 This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Figure 1 , comprising an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a sub-surface layer 4 and a lower surface layer 5 arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer 1: 90wt% homopolymer polypropylene and 10wt% modified silica filler masterbatch; Upper surface layer 2: 90 wt% homopolypropylene and 10 wt% dicumyl peroxide premix; Core layer 3: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch; Subsurface layer 4: the same composition and content as the previous surface layer of this embodiment; Lower surface layer 5: 100wt% homopolymer polypropylene.

[0037] The preparation method of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment is the same as that of Example 1.

[0038] The total thickness and thickness of each layer of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment are the same as those of Example 1.

[0039] Example 3 This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Figure 1 , comprising an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a sub-surface layer 4 and a lower surface layer 5 arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer 1: 92wt% homopolymer polypropylene and 8wt% modified silica filler masterbatch; Upper surface layer 2: 98 wt% homopolypropylene and 2 wt% dicumyl peroxide premix; Core layer 3: 90wt% homopolymer polypropylene and 10wt% modified calcium carbonate filler masterbatch; Subsurface layer 4: the same composition and content as the previous surface layer of this embodiment; Lower surface layer 5: 100wt% homopolymer polypropylene.

[0040] The preparation method of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment is the same as that of Example 1.

[0041] The total thickness and thickness of each layer of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment are the same as those of Example 1.

[0042] Example 4 This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Figure 1 , comprising an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a sub-surface layer 4 and a lower surface layer 5 arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer 1: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch; Upper surface layer 2: 94 wt% homopolypropylene and 6 wt% dicumyl peroxide premix; Core layer 3: 85wt% homopolymer polypropylene and 15wt% modified calcium carbonate filler masterbatch; Subsurface layer 4: the same composition and content as the previous surface layer of this embodiment; Lower surface layer 5: 100wt% homopolymer polypropylene.

[0043] The preparation method of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment is the same as that of Example 1.

[0044] The total thickness and thickness of each layer of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this embodiment are the same as those of Example 1.

[0045] Comparative Example 1 This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer: 100wt% homopolymer polypropylene; Upper surface layer: 90wt% homopolypropylene and 10wt% dicumyl peroxide premix; Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch; The next surface layer: the components and contents are the same as those of the previous surface layer of this comparative example; Lower surface layer: 100wt% homopolymer polypropylene.

[0046] The preparation method of the BOPP pearlescent film of this comparative example is the same as that of Example 1.

[0047] The total thickness and thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0048] Comparative Example 2 This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch; Upper surface layer: 100wt% homopolymer polypropylene; Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch; The next surface layer: the components and contents are the same as those of the previous surface layer of this comparative example; Lower surface layer: 100wt% homopolymer polypropylene.

[0049] The preparation method of the BOPP pearlescent film of this comparative example is the same as that of Example 1.

[0050] The total thickness and thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0051] Comparative Example 3 This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch; Upper surface layer: 90wt% homopolypropylene and 10wt% dicumyl peroxide premix; Core layer: 80wt% homopolymer polypropylene and 20wt% ordinary calcium carbonate filler masterbatch; The next surface layer: the components and contents are the same as those of the previous surface layer of this comparative example; Lower surface layer: 100wt% homopolymer polypropylene.

[0052] The preparation method of the BOPP pearlescent film of this comparative example is the same as that of Example 1.

[0053] The total thickness and thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0054] Comparative Example 4 This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer: 100wt% homopolymer polypropylene; Upper surface layer: 100wt% homopolymer polypropylene; Core layer: 80wt% homopolymer polypropylene and 20wt% ordinary calcium carbonate filler masterbatch; The next surface layer: the components and contents are the same as those of the previous surface layer of this comparative example; Lower surface layer: 100wt% homopolymer polypropylene.

[0055] The preparation method of the BOPP pearlescent film of this comparative example is the same as that of Example 1.

[0056] The total thickness and thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0057] Comparative Example 5 This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch; Upper surface layer: 85wt% homopolypropylene and 15wt% dicumyl peroxide premix; Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch; The next surface layer: the components and contents are the same as those of the previous surface layer of this comparative example; Lower surface layer: 100wt% homopolymer polypropylene.

[0058] The preparation method of the BOPP pearlescent film of this comparative example is the same as that of Example 1.

[0059] The total thickness and thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0060] Comparative Example 6 This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer, and a lower surface layer arranged in sequence; wherein the components and contents of each layer are as follows: Upper surface layer: 85wt% homopolymer polypropylene and 15wt% modified silica filler masterbatch; Upper surface layer: 90wt% homopolypropylene and 10wt% dicumyl peroxide premix; Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch; The next surface layer: the components and contents are the same as those of the previous surface layer of this comparative example; Lower surface layer: 100wt% homopolymer polypropylene.

[0061] The preparation method of the BOPP pearlescent film of this comparative example is the same as that of Example 1.

[0062] The total thickness and thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0063] Performance evaluation The following performance evaluations were conducted on the peel-resistant, easy-to-print, high-strength BOPP pearlescent films of Examples 1-4 and the BOPP pearlescent films of Comparative Examples 1-6: (1) Film surface quality: Randomly select a 50×50 cm area of ​​the finished film product and visually observe the surface defects such as crystal points, bright spots, and protrusions, and record the total number; if the number is less than 5, it is rated as excellent; if the number is less than 10, it is rated as good; if the number is less than 15, it is rated as medium; otherwise, it is rated as poor.

[0064] (2) Interlayer bonding strength: Use 3M 810 tape to stick on the surface of the film (either the upper surface or the lower surface), use a 2kg roller to move back and forth 6 times without applying additional force, and finally pull up the tape at a 60° angle to observe whether the film has delamination; no delamination is rated as excellent; if there is delamination, the delamination area accounts for less than 10% of the total area of ​​the tape, which is rated as good; if there is delamination, the delamination area accounts for less than 30% of the total area of ​​the tape, which is rated as medium; other cases are rated as poor.

[0065] (3) Surface dyne value: The surface dyne value of the upper surface layer of the test film is used to evaluate printing performance.

[0066] (4) Tensile strength: According to GB / T 1040.3, the transverse tensile strength and longitudinal tensile strength of the film are tested.

[0067] (5) Whiteness and light transmittance: Whiteness is tested according to GB / T 2913, and light transmittance is tested according to GB / T 2410. These two tests are used to evaluate the pearlescent effect.

[0068] Please refer to Table 1 for the performance evaluation results: Table 1 Performance evaluation results of the films of Examples 1-4 and Comparative Examples 1-6

[0069] Referring to the performance evaluation results in Table 1, it can be seen that the peel-resistant, easy-to-print, high-strength BOPP pearlescent films of Examples 1-4 of the present invention have excellent film surface quality, excellent interlayer bonding force and mechanical strength, and good printing applicability while ensuring a good pearlescent effect.

[0070] The BOPP pearlescent film of Comparative Example 1 does not have modified silica filler masterbatch added to the upper surface layer. The surface dyne value of the upper surface layer of Comparative Example 1 is low, the adsorption effect on ink is poor, and the printing applicability is poor.

[0071] In the BOPP pearlescent film of Comparative Example 2, no dicumyl peroxide premix is ​​added to the upper surface layer and the lower surface layer. The linolenic acid in the core layer of the BOPP pearlescent film of Comparative Example 2 cannot be polymerized to form linolenic acid oligomers with a certain molecular weight. The interlayer bonding strength of the BOPP pearlescent film of Comparative Example 2 is poor, and the linolenic acid in the core layer easily migrates to the surface of the upper surface layer, resulting in a lower dyne value of the upper surface layer, poor adsorption effect on ink, and poor printing applicability.

[0072] The BOPP pearlescent film of Comparative Example 3 has ordinary calcium carbonate filler masterbatch added to the core layer. The BOPP pearlescent film of Comparative Example 3 has poor film surface quality, poor interlayer bonding force, and poor mechanical strength. The low molecular weight stearic acid in the core layer easily migrates to the surface of the upper surface layer, resulting in a lower dyne value on the surface of the upper surface layer, poor adsorption effect on ink, and poor printing applicability.

[0073] The BOPP pearlescent film of Comparative Example 4 does not add modified silica filler masterbatch in the upper surface layer, does not add dicumyl peroxide premix in the upper and lower surface layers, and adds ordinary calcium carbonate filler masterbatch in the core layer. The BOPP pearlescent film of Comparative Example 4 has poor film surface quality, poor interlayer bonding, and poor mechanical strength. The low molecular weight stearic acid in the core layer easily migrates to the surface of the upper surface layer, resulting in a low dyne value on the surface of the upper surface layer, poor adsorption effect on ink, and poor printing applicability.

[0074] In the BOPP pearlescent film of Comparative Example 5, too much dicumyl peroxide premix is ​​added to the upper surface layer and the lower surface layer. During the production process, too many molecular chain initiation points are formed, so that the linolenic acid monomer can only be polymerized to form linolenic acid oligomers with too low a molecular weight. The BOPP pearlescent film of Comparative Example 5 has average film surface quality, average interlayer bonding strength, and poor mechanical strength. In addition, the linolenic acid oligomers with too low a molecular weight will also migrate to the surface of the upper surface layer, resulting in a low dyne value on the surface of the upper surface layer, poor adsorption effect on ink, and poor printing suitability.

[0075] In the BOPP pearlescent film in Comparative Example 6, excessive modified silica filler masterbatch was added to the upper surface layer, resulting in the inability to evenly disperse the modified silica in the upper surface layer. This resulted in poor appearance quality of the film and also had an adverse effect on the overall mechanical strength of the film.

[0076] The above-described embodiments merely represent several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, and the present invention is intended to encompass such modifications and variations.

Claims

1. A peel-resistant, easy-to-print, high-strength BOPP pearlescent film, characterized by: It includes an upper surface layer, an upper sub-surface layer, a core layer, a sub-surface layer and a lower surface layer which are arranged in sequence; The upper surface layer includes homopolypropylene and 5-10 wt% modified silica filler masterbatch; the modified silica filler masterbatch includes homopolypropylene and 15-25 wt% modified silica; the modified silica is obtained by modifying silica with maleic anhydride; The upper surface layer and the lower surface layer both comprise homopolypropylene and 2-10 wt% dicumyl peroxide premix, and the dicumyl peroxide premix comprises homopolypropylene and 45-55 wt% dicumyl peroxide; The core layer includes homopolypropylene and 10-20wt% modified calcium carbonate filling masterbatch; the modified calcium carbonate filling masterbatch includes homopolypropylene and 55-65wt% modified calcium carbonate; the modified calcium carbonate is obtained by modifying 95-97wt parts of calcium carbonate with 3-5wt parts of linolenic acid.

2. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 1, characterized in that: The preparation method of the dicumyl peroxide premix is ​​as follows: homopolymerized polypropylene and dicumyl peroxide are added into a high-speed mixer according to a ratio and mixed at a mixing temperature of 30-50° C. for 5-15 minutes to obtain the dicumyl peroxide premix.

3. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 1, characterized in that: The modified calcium carbonate is prepared by adding 95-97 parts by weight of calcium carbonate and 3-5 parts by weight of linolenic acid into a high-speed mixer and mixing them at a mixing temperature of 80-100° C. for 15-25 minutes to obtain the modified calcium carbonate.

4. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 3, characterized in that: The average particle size D50 of the calcium carbonate is 1-2 μm.

5. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 1, characterized in that: The modified calcium carbonate filling masterbatch is prepared by adding homopolypropylene and modified calcium carbonate into a twin-screw extruder according to a ratio, heating and melting the mixture, and then granulating the mixture to obtain the modified calcium carbonate filling masterbatch; wherein, in the twin-screw extruder, the processing temperature is set at 210-230° C., the screw speed is set at 350-450 rpm / min, and the modified calcium carbonate is side-fed.

6. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 1, characterized in that: The modified silica is prepared by adding silica to toluene to form a solution, then adding maleic anhydride to the solution, wherein the amount of maleic anhydride added is 1-3wt% of the silica; reacting at 90-110°C for 20-40 minutes under a nitrogen atmosphere, and after the reaction is completed, filtering and drying the product after cooling the solution to obtain the modified silica.

7. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 6, characterized in that: The silicon dioxide is synthesized by a gel method, and the average particle size D50 of the silicon dioxide is 5-7 μm.

8. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 1, characterized in that: The modified silica filler masterbatch is prepared by adding homopolypropylene and modified silica into a twin-screw extruder according to a ratio, heating and melting the mixture for extrusion, and then granulating the mixture to obtain the modified silica filler masterbatch. The processing temperature of the twin-screw extruder is set at 210-230°C, the screw speed is set at 200-300 rpm / min, and the modified silica is side-fed.

9. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 1, characterized in that: The homopolypropylene in the upper surface layer, the homopolypropylene in the modified silica filler masterbatch, the homopolypropylene in the upper surface layer and the lower surface layer, the homopolypropylene in the dicumyl peroxide premix, the homopolypropylene in the core layer, and the homopolypropylene in the modified calcium carbonate filler masterbatch all have a melt index of 2-4 g / 10 min under test conditions of 230° C. and 2.16 kg.

10. A method for preparing the peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to any one of claims 1 to 9, characterized in that: The following steps are involved: According to the ratio of raw materials for each layer, the raw materials are mixed and fed into the extruder of each layer through a metering scale. After multi-layer co-extrusion through the die head, the film is cast into a thick sheet according to the flat film method, and then chilled into a thick sheet. The thick sheet is made into a biaxially oriented film by the synchronous biaxial stretching method in the longitudinal and transverse directions. After shaping, it is corona treated, and then it is wound, aged, slit, and packaged into a finished product.

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