A peel-resistant, easy-to-print, high-strength BOPP pearlescent film and its preparation method

Abstract

This invention relates to a peel-resistant, easily printable, high-strength BOPP pearlescent film and its preparation method, belonging to the field of pearlescent film technology. The peel-resistant, easily printable, high-strength BOPP pearlescent film of this invention comprises, in sequence, an upper surface layer, a lower surface layer, a core layer, a lower surface layer, and a bottom surface layer; both the upper and lower surface layers comprise homopolymer polypropylene and 2-10 wt% dicumyl peroxide premix, the dicumyl peroxide premix comprising homopolymer polypropylene and 45-55 wt% dicumyl peroxide; the core layer comprises homopolymer polypropylene and 10-20 wt% modified calcium carbonate filler masterbatch; the modified calcium carbonate filler masterbatch comprises homopolymer polypropylene and 55-65 wt% modified calcium carbonate; the modified calcium carbonate is obtained by modifying 95-97 wt% calcium carbonate with 3-5 wt% linolenic acid. This film, while ensuring a good pearlescent effect, features strong interlayer bonding, ease of printing, and high mechanical strength.

Description

Technical Field

[0001] This invention relates to the field of pearlescent film technology, and in particular to a peel-resistant, easy-to-print, high-strength BOPP pearlescent film and its preparation method. Background Technology

[0002] In biaxially oriented polypropylene (BOPP) pearlescent films, the pearlescent effect is typically achieved by adding calcium carbonate. During biaxial stretching, the difference in mechanical strength between calcium carbonate and polypropylene creates numerous tiny cavities around the calcium carbonate. These cavities cause light entering the film to be reflected or interfered with, thus giving the film a pearlescent luster. Utilizing the pearlescent effect of BOPP pearlescent films, manufacturers can produce a wide variety of labels and flexibly overlay their brand image onto them.

[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 contain appropriate functional additives depending on product requirements. Because calcium carbonate and the polypropylene in the core layer have significantly different properties, to accommodate high-speed film production, calcium carbonate masterbatch is usually prepared first. Then, during film production, the calcium carbonate masterbatch is added to the extruder in a specific ratio, undergoing multi-layer co-extrusion to obtain a thick sheet, which is subsequently biaxially stretched to form the BOPP pearlescent film.

[0004] However, due to the special biaxial stretching process of BOPP pearlescent films, tiny voids inevitably form around the calcium carbonate in the core layer. These voids become mechanically weak points in the film. Therefore, how to improve the mechanical strength at these voids while ensuring the dispersion of calcium carbonate is a problem worthy of research.

[0005] Furthermore, BOPP pearlescent film is frequently used in the labeling industry, and its surface printability is crucial to the market acceptance of the final product. However, to improve the dispersion of calcium carbonate, existing BOPP pearlescent films typically incorporate a significant 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 printability. Therefore, improving the printability of BOPP pearlescent film is also an important issue. Summary of the Invention

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

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film, comprising an upper surface layer, a secondary surface layer, a core layer, a secondary surface layer, and a lower surface layer arranged sequentially; the upper surface layer comprises homopolymer polypropylene and 5-10 wt% modified silica filler masterbatch; the modified silica filler masterbatch comprises homopolymer polypropylene and 15-25 wt% modified silica; the modified silica is obtained by modifying silica with maleic anhydride, wherein the amount of maleic anhydride is 1-3 wt% of silica; the secondary surface layer... Both the top and bottom layers comprise homopolymer polypropylene and 2-10 wt% dicumyl peroxide premix, wherein the dicumyl peroxide premix comprises homopolymer polypropylene and 45-55 wt% dicumyl peroxide; the core layer comprises homopolymer polypropylene and 10-20 wt% modified calcium carbonate filler masterbatch; the modified calcium carbonate filler masterbatch comprises homopolymer polypropylene and 55-65 wt% 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.

[0009] The peel-resistant, printable, high-strength BOPP pearlescent film of the present invention incorporates dicumyl peroxide into the upper and lower surface layers, and calcium carbonate modified with linolenic acid into the core layer. During multilayer co-extrusion, the dicumyl peroxide decomposes at the co-extrusion processing temperature to generate free radicals. At the interfaces between the upper and lower surface layers and the core layer, these free radicals contact the linolenic acid in the core layer, initiating a bonding reaction (polymerization reaction) of the unsaturated double bonds in the linolenic acid to form linolenic acid oligomers. One end of the carboxyl group in the linolenic acid oligomer is bonded to calcium carbonate, while the other end is wrapped around the upper or lower surface layer. This establishes chemical bonds between the core layer and both the upper and lower surface layers, which is beneficial for improving the interlayer bonding strength between the core layer and both the upper and lower surface layers. Furthermore, the polymerization of linolenic acid to form linolenic acid oligomers significantly reduces the content of linolenic acid monomers in the core layer, greatly decreasing the possibility of low-molecular-weight linolenic acid monomers migrating to the film surface. This greatly improves the problem of traditional low-molecular-weight substances coating modified calcium carbonate easily migrating to the film surface, negatively impacting the film's printing performance. It should also be noted that this invention uses linolenic acid to modify calcium carbonate. Linolenic acid itself has a certain molecular chain length and good thermal stability, making it less prone to premature polymerization during the modification process of the modified calcium carbonate and the preparation of the modified calcium carbonate filler masterbatch. This prevents premature polymerization of linolenic acid, which would render it ineffective during multilayer co-extrusion. It should also be noted that the peel-resistant, easily printable, high-strength BOPP pearlescent film of this invention incorporates dicumyl peroxide in the form of the dicumyl peroxide premix in the upper and lower surface layers, facilitating uniform dispersion of dicumyl peroxide in these layers. Similarly, the core layer incorporates modified calcium carbonate in the form of modified calcium carbonate filler masterbatch, further facilitating uniform dispersion of the modified calcium carbonate within the core layer.

[0010] Because the free radicals generated by dicumyl peroxide are highly reactive 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, this invention adds 2-10 wt% dicumyl peroxide premix to the upper and lower surface layers and controls the content of the dicumyl peroxide premix to be 45-55 wt% dicumyl peroxide (the amount of dicumyl peroxide added is much higher than that in conventional polymerization). At the same time, no chain terminator is specifically added to the upper and lower surface layers to prevent the molecular weight of the linolenic acid oligomers formed by the polymerization of linolenic acid from being too low, so as not to play a role in improving the interlayer bonding force. If the amount of dicumyl peroxide premix added to the core layer is too low and / or the content of dicumyl peroxide in the dicumyl peroxide premix is ​​too low, the number of free radicals formed during the production of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film will be small, resulting in low initiation efficiency. If the amount of dicumyl peroxide premix added to the core layer is too high and / or the content of dicumyl peroxide in the dicumyl peroxide premix is ​​too high, too many molecular chain initiation sites will be formed during the production of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film, causing the linolenic acid monomer to polymerize only to form linolenic acid oligomers with too low a molecular weight, which cannot exert the characteristics of "high molecular weight" (i.e., the linolenic acid oligomer molecular chains are too short to effectively combine with the previous and next surface layers, and the linolenic acid oligomers with too low a molecular weight are easy to migrate to the film surface, affecting the printing performance).

[0011] Furthermore, to further improve the printability of the upper surface of the film, the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of the present invention also incorporates 5-10 wt% modified silica filler masterbatch into the upper surface layer. The modified silica filler masterbatch comprises homopolymer polypropylene and 15-25 wt% modified silica; the modified silica is obtained by modifying silica with maleic anhydride. Adding modified silica in the form of modified silica filler masterbatch to the upper surface layer facilitates the uniform dispersion of the modified silica within the upper surface layer. Maleic anhydride-modified silica was selected. By chemically modifying the silica with maleic anhydride and grafting polar functional groups onto the silica surface, the modified silica can both adsorb ink through its porous structure and chemically bond with the ink through the grafted polar functional groups. This improves the ink adhesion to the upper surface, ensuring excellent printability and making the upper surface suitable for printing. If the amount of modified silica filler masterbatch added is too low, the printability of the upper surface will not be effectively improved; if the amount added is too high, the uniform dispersion of the modified silica in the upper surface will be hindered, thus affecting the appearance quality of the film.

[0012] The peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this invention features an linolenic acid oligomer formed after polymerization under the action of free radicals generated by dicumyl peroxide. This oligomer forms a network structure between the calcium carbonate in the core layer, the homopolymer polypropylene in the core layer, and the homopolymer polypropylene of the upper or lower surface layer. This effectively improves the mechanical strength of the "cavities" formed by the calcium carbonate during biaxial stretching, and also enhances the interlayer bonding between the core layer and the upper and lower surface layers, thus mitigating interlayer peeling. Furthermore, the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this invention incorporates specific modified silica in the upper surface layer, enhancing the ink adsorption capacity of the upper surface. This, combined with the advantage that the linolenic acid oligomer formed by the polymerization of linolenic acid does not easily migrate to the film surface (i.e., the synergistic effect of the linolenic acid oligomer does not negatively impact the printability of the film surface compared to traditional low-molecular-weight substances coating modified calcium carbonate), makes the upper surface easy to print on, improving its printability.

[0013] Further, the preparation method of the dicumyl peroxide premix is ​​as follows: Homopolymer polypropylene and dicumyl peroxide are added to a high-speed mixer according to a specified ratio, the mixing temperature is 30-50℃, and the mixture is stirred 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 homopolymer polypropylene of the upper and lower surface layers, dicumyl peroxide and homopolymer polypropylene are mixed in a high-speed mixer according to a specified ratio, the mixing temperature is 30-50℃, and the mixture is stirred for 5-15 minutes to obtain the dicumyl peroxide premix. The dicumyl peroxide premix is ​​then added to the upper and lower surface layers in a specific ratio, which helps to improve the dispersibility of dicumyl peroxide in the upper and lower surface layers. Preferably, the dicumyl peroxide premix comprises 50 wt% homopolymer polypropylene and 50 wt% dicumyl peroxide; the homopolymer polypropylene 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.

[0014] Further, 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 at a mixing temperature of 80-100°C for 15-25 minutes to obtain the modified calcium carbonate. During the mixing process of calcium carbonate and linolenic acid, the linolenic acid reacts fully with the calcium carbonate, causing the linolenic acid to coat the surface of the calcium carbonate, thereby preparing 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 into a high-speed mixer and mixing at a mixing temperature of 90°C for 20 minutes to obtain the modified calcium carbonate. The reasons for choosing linolenic acid to modify calcium carbonate in this invention are as follows: 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 polymerize under the action of diisopropylbenzene peroxide to form linolenic acid oligomers. This allows calcium carbonate to 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 at the "cavities" formed by calcium carbonate. Moreover, the formation of linolenic acid oligomers does not have the problem of negatively affecting the printability of the film surface due to the traditional low-molecular-weight substance coating modification of calcium carbonate. Third, linolenic acid itself has a certain molecular chain length, good thermal stability, and is not prone to premature polymerization during the modification process, making it suitable for multilayer co-extrusion.

[0015] Furthermore, the average particle size D50 of the calcium carbonate is 1-2 μm. Selecting calcium carbonate with an average particle size D50 of 1-2 μm (without surface modification) ensures that the prepared modified calcium carbonate, when added to the core layer as a modified calcium carbonate filler masterbatch, can be uniformly dispersed in the core layer, which is beneficial for improving the uniformity of the pearlescent effect of the peel-resistant, printable, high-strength BOPP pearlescent film. If calcium carbonate with an excessively large average particle size is selected, its high addition amount will result in it occupying a significant portion of the film. This prevents the matrix resin (homogeneous polypropylene) in the core layer from forming a continuous phase with sufficient mechanical strength, leading to insufficient mechanical strength of the film and making it difficult to meet the performance requirements of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film after label manufacturing. Conversely, if calcium carbonate with an excessively small average particle size is selected, dispersion in the homopolymer polypropylene of the core layer becomes difficult, and excessive calcium carbonate agglomeration can cause production disruptions and uneven pearlescent effects in the product. Furthermore, if the calcium carbonate particle size is too small, it is difficult for it to form large-sized cavities, resulting in an unsatisfactory pearlescent effect in the peel-resistant, easy-to-print, high-strength BOPP pearlescent film.

[0016] Further, the preparation method of the modified calcium carbonate filler masterbatch is as follows: homopolymer polypropylene and modified calcium carbonate are added to a twin-screw extruder according to the formula, heated and melt-extruded, and then granulated to obtain the modified calcium carbonate masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 210-230℃, the screw speed is 350-450rpm, and the modified calcium carbonate is side-fed. Preferably, the modified calcium carbonate masterbatch comprises 40wt% homopolymer polypropylene and 60wt% modified calcium carbonate, and the homopolymer polypropylene and modified calcium carbonate are added to a twin-screw extruder according to the formula, heated and melt-extruded, and then granulated to obtain the modified calcium carbonate filler masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 220℃, the screw speed is 400rpm, and the modified calcium carbonate is side-fed.

[0017] Further, the preparation method of the modified silica is as follows: silica is added to toluene to form a solution, and then maleic anhydride is added to the solution, wherein the amount of maleic anhydride added is 1-3 wt% of the silica; the reaction is carried out at 90-110°C for 20-40 minutes under a nitrogen atmosphere; after the reaction is completed, the solution is cooled, filtered, and the product is dried to obtain maleic anhydride modified silica, i.e., the modified silica. Preferably, the preparation method of the modified silica is as follows: silica is added to toluene to form a solution, and then maleic anhydride is added, wherein the amount of maleic anhydride added is 2 wt% of the silica; the above solution is reacted at 100°C for 30 minutes under a nitrogen atmosphere; after the reaction is completed, the solution is cooled, filtered, and the product is dried to obtain maleic anhydride modified silica, i.e., the modified silica.

[0018] Furthermore, the silica is silica synthesized by the gel method. The function of the silica on the upper surface is to absorb ink. The silica synthesized by the gel method has a porous surface structure and a high oil absorption value.

[0019] 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 usually 2-4 μm, silica with an average particle size D50 of 5-7 μm is selected for modification. This allows the modified silica, when added to the upper surface layer as modified silica filler masterbatch, to partially protrude from the upper surface layer, effectively adsorbing ink. If the silica particle size is small, it is easily completely encapsulated by the matrix resin (homopolymer polypropylene) and difficult to expose on the upper surface layer, resulting in ineffective ink adsorption during printing on the upper surface layer, which is not conducive to promoting the full spread of ink on the upper surface layer. If the silica particle size is too large, it will form excessively large protrusions on the upper surface layer, affecting the film quality and posing a risk of film breakage during the biaxial stretching production of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film.

[0020] Further, the preparation method of the modified silica-filled masterbatch is as follows: homopolymer polypropylene and modified silica are added to a twin-screw extruder according to the formula, heated and melted and extruded, and then granulated to obtain the modified silica-filled masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 210-230℃, the screw speed is 200-300rpm, and the modified silica is side-fed. Preferably, the modified silica-filled masterbatch comprises 80wt% homopolymer polypropylene and 20wt% modified silica, and the homopolymer polypropylene and modified silica are added to a twin-screw extruder according to the formula, heated and melted and extruded, and then granulated to obtain the modified silica-filled masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 220℃, the screw speed is 250rpm, and the modified silica is side-fed.

[0021] Furthermore, the lower surface layer comprises copolymer polypropylene or homopolymer polypropylene.

[0022] Furthermore, the melt flow index of the homopolymer polypropylene in the upper surface layer, the homopolymer polypropylene in the modified silica-filled masterbatch, the homopolymer polypropylene in the upper and lower surface layers, the homopolymer polypropylene in the dicumyl peroxide premix, the homopolymer polypropylene in the core layer, the homopolymer polypropylene in the modified calcium carbonate-filled masterbatch, and the homopolymer polypropylene in the lower surface layer are all 2-4 g / 10 min (230℃, 2.16 kg). Using homopolymer polypropylene within the above melt flow index range ensures efficient operation of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film during the production process, and also helps improve the compatibility of the components within the film layer and between film layers.

[0023] The present invention also provides a method for preparing any of the above-mentioned peel-resistant and easy-to-print high-strength BOPP pearlescent films, comprising the following steps: according to the proportion of each layer of raw materials, the raw materials are mixed and weighed and fed into each layer extruder. After multi-layer co-extrusion through a die, the film is cast and chilled into a thick sheet using the flat film method. The thick sheet is then stretched into a biaxially oriented film by a simultaneous longitudinal and transverse biaxial stretching method. After shaping, the film is subjected to corona treatment, and then wound, aged, slit, and packaged into the finished product, namely the peel-resistant and easy-to-print high-strength BOPP pearlescent film.

[0024] Furthermore, the melt extrusion temperature of the lower surface layer is 220-240℃, the melt extrusion temperature of the upper and lower surface layers is 160-180℃, and the melt extrusion temperature of the core layer is 200-220℃; the temperature of the quenching roller during quenching is 50-80℃; the temperature during biaxial stretching is 100-120℃, and the ratio of longitudinal stretching to transverse stretching is 4-5 times.

[0025] Compared to existing technologies:

[0026] The peel-resistant, easy-to-print, high-strength BOPP pearlescent film of this invention not only ensures a good pearlescent effect but also features strong interlayer adhesion, ease of printing, and high strength. While maintaining a good pearlescent effect through "cavitation," this invention improves the mechanical strength at the "cavities" in the film and enhances the interlayer adhesion between the upper surface layer, core layer, and lower surface layer, effectively mitigating interlayer peeling in practical applications (e.g., after label manufacturing). Furthermore, by adding specific modified silica to the upper surface layer of the film, this invention enhances the ink adsorption capacity of the upper surface. Combined with the advantage that linoleic acid oligomers do not negatively impact the printability of the film surface due to traditional low-molecular-weight modified calcium carbonate coating, the resulting peel-resistant, easy-to-print, high-strength BOPP pearlescent film's upper surface is easy to print on and suitable for label manufacturing. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film of the present invention. Detailed Implementation

[0028] The present invention is further illustrated below with reference to specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, unless otherwise specified, are generally performed under conventional conditions in the art or as recommended by the manufacturer; the raw materials and reagents used, unless otherwise specified, are all commercially available from the conventional market. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention are within the scope of protection claimed by the present invention.

[0029] In the following embodiments or comparative examples:

[0030] Modified silica-filled masterbatch: comprising 80 wt% homopolymer polypropylene and 20 wt% modified silica; wherein, the modified silica is prepared by adding silica (synthesized by 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, the amount of maleic anhydride added being 2 wt% of silica; the above solution is reacted at 100°C for 30 minutes under a nitrogen atmosphere, after the reaction is completed, the solution is cooled, filtered and dried to obtain maleic anhydride-modified silica, i.e., the modified silica; the modified silica-filled masterbatch is prepared by adding homopolymer polypropylene and modified silica to a twin-screw extruder according to the ratio, heating and melting extrusion, and then granulating to obtain the modified silica-filled masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 220°C, the screw speed is 250 rpm, and the modified silica is side-fed.

[0031] Dicumyl peroxide premix: comprising 50 wt% dicumyl peroxide and 50 wt% homopolymer polypropylene; the preparation method of the dicumyl peroxide premix is ​​as follows: the homopolymer polypropylene and dicumyl peroxide are mixed in a high-speed mixer according to the ratio, the mixing temperature is 40°C, and after mixing for 10 minutes, the dicumyl peroxide premix is ​​obtained.

[0032] Modified calcium carbonate filler masterbatch: comprising 40 wt% homopolymer polypropylene and 60 wt% modified calcium carbonate; wherein the modified calcium carbonate is prepared by adding 95 parts by weight of raw calcium carbonate powder (average particle size D50 is 1 μm) and 5 parts by weight of linolenic acid into a high-speed mixer and mixing at 90°C for 20 minutes to obtain the modified calcium carbonate; the modified calcium carbonate masterbatch is prepared by adding homopolymer polypropylene and modified calcium carbonate into a twin-screw extruder according to the formula, heating and melting extrusion, and then granulating to obtain the modified calcium carbonate filler masterbatch, wherein the processing temperature in the twin-screw extruder is set to 220°C, the screw speed is 400 rpm, and the modified calcium carbonate is side-fed.

[0033] Ordinary calcium carbonate filler masterbatch: 40 wt% homopolymer polypropylene and 60 wt% conventional calcium carbonate; wherein, the conventional calcium carbonate is prepared by adding 97 parts by weight of raw calcium carbonate powder (average particle size D50 of 1 μm) 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 homopolymer polypropylene and conventional calcium carbonate to a twin-screw extruder according to the formula, heating and melting extrusion, and then granulating to obtain the ordinary calcium carbonate filler masterbatch, wherein in the twin-screw extruder, the processing temperature is set to 220°C, the screw speed is 400 rpm, and conventional calcium carbonate is side-fed.

[0034] The melt index of the above homopolymer polypropylene, as well as the homopolymer polypropylene of the upper surface layer, upper sub-surface layer, core layer, lower sub-surface layer and lower surface layer, is 3 g / 10 min (melt index measurement conditions are 230℃ and 2.16 kg).

[0035] Example 1

[0036] This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Please refer to [link / reference]. Figure 1 It includes, in sequence, an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a lower sub-surface layer 4, and a lower surface layer 5; wherein the composition and content of each layer are as follows:

[0037] Top layer 1: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch;

[0038] Top layer 2: 90 wt% homopolymer polypropylene and 10 wt% dicumyl peroxide premix;

[0039] Core layer 3: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch;

[0040] Next surface layer 4: has the same components and content as the previous surface layer in this embodiment;

[0041] Bottom layer 5: 100wt% homopolymer polypropylene.

[0042] This embodiment also provides a method for preparing a peel-resistant, easy-to-print, high-strength BOPP pearlescent film, including the following steps: according to the ratio of raw materials for each layer, the raw materials are mixed and weighed and fed into each layer extruder. After multi-layer co-extrusion through a die, the film is cast and then chilled into a thick sheet using the flat film method. The thick sheet is then stretched in both longitudinal and transverse directions to form a biaxially stretched film. After shaping, it is subjected to corona treatment, and then wound, aged, cut, and packaged into the finished product, namely the peel-resistant, easy-to-print, high-strength BOPP pearlescent film.

[0043] The melt extrusion temperature of the lower surface layer is 230°C, the melt extrusion temperature of the upper and lower surface layers is 170°C, and the melt extrusion temperature of the core layer is 210°C. The quench roller temperature is 70°C, the biaxial stretching temperature is 110°C, and the ratio of longitudinal stretching to transverse stretching is 5 times.

[0044] In this embodiment, the total thickness of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film is 60 μm, of which 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 are both 7 μm, and the thickness of the lower surface layer 5 is 2 μm.

[0045] Example 2

[0046] This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Please refer to [link / reference]. Figure 1 It includes, in sequence, an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a lower sub-surface layer 4, and a lower surface layer 5; wherein the composition and content of each layer are as follows:

[0047] Top layer 1: 90wt% homopolymer polypropylene and 10wt% modified silica filler masterbatch;

[0048] Top layer 2: 90 wt% homopolymer polypropylene and 10 wt% dicumyl peroxide premix;

[0049] Core layer 3: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch;

[0050] Next surface layer 4: has the same components and content as the previous surface layer in this embodiment;

[0051] Bottom layer 5: 100wt% homopolymer polypropylene.

[0052] The preparation method of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film in this embodiment is the same as that in Example 1.

[0053] The total thickness and the thickness of each layer of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film in this embodiment are the same as those in Embodiment 1.

[0054] Example 3

[0055] This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Please refer to [link / reference]. Figure 1 It includes, in sequence, an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a lower sub-surface layer 4, and a lower surface layer 5; wherein the composition and content of each layer are as follows:

[0056] Top layer 1: 92wt% homopolymer polypropylene and 8wt% modified silica filler masterbatch;

[0057] Previous surface layer 2: 98 wt% homopolymer polypropylene and 2 wt% dicumyl peroxide premix;

[0058] Core layer 3: 90wt% homopolymer polypropylene and 10wt% modified calcium carbonate filler masterbatch;

[0059] Next surface layer 4: has the same components and content as the previous surface layer in this embodiment;

[0060] Bottom layer 5: 100wt% homopolymer polypropylene.

[0061] The preparation method of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film in this embodiment is the same as that in Example 1.

[0062] The total thickness and the thickness of each layer of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film in this embodiment are the same as those in Embodiment 1.

[0063] Example 4

[0064] This embodiment provides a peel-resistant, easy-to-print, high-strength BOPP pearlescent film. Please refer to [link / reference]. Figure 1 It includes, in sequence, an upper surface layer 1, an upper sub-surface layer 2, a core layer 3, a lower sub-surface layer 4, and a lower surface layer 5; wherein the composition and content of each layer are as follows:

[0065] Top layer 1: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch;

[0066] Previous surface layer 2: 94 wt% homopolymer polypropylene and 6 wt% dicumyl peroxide premix;

[0067] Core layer 3: 85wt% homopolymer polypropylene and 15wt% modified calcium carbonate filler masterbatch;

[0068] Next surface layer 4: has the same components and content as the previous surface layer in this embodiment;

[0069] Bottom layer 5: 100wt% homopolymer polypropylene.

[0070] The preparation method of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film in this embodiment is the same as that in Example 1.

[0071] The total thickness and the thickness of each layer of the peel-resistant, easy-to-print, high-strength BOPP pearlescent film in this embodiment are the same as those in Embodiment 1.

[0072] Comparative Example 1

[0073] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer arranged sequentially; wherein the components and contents of each layer are as follows:

[0074] Top layer: 100wt% homopolymer polypropylene;

[0075] Top layer: 90 wt% homopolymer polypropylene and 10 wt% dicumyl peroxide premix;

[0076] Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch;

[0077] Next surface layer: The same composition and content as the previous surface layer in this comparative example;

[0078] Bottom layer: 100wt% homopolymer polypropylene.

[0079] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0080] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0081] Comparative Example 2

[0082] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer arranged sequentially; wherein the components and contents of each layer are as follows:

[0083] Top layer: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch;

[0084] Previous surface layer: 100wt% homopolymer polypropylene;

[0085] Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch;

[0086] Next surface layer: The same composition and content as the previous surface layer in this comparative example;

[0087] Bottom layer: 100wt% homopolymer polypropylene.

[0088] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0089] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0090] Comparative Example 3

[0091] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer arranged sequentially; wherein the components and contents of each layer are as follows:

[0092] Top layer: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch;

[0093] Top layer: 90 wt% homopolymer polypropylene and 10 wt% dicumyl peroxide premix;

[0094] Core layer: 80wt% homopolymer polypropylene and 20wt% ordinary calcium carbonate filler masterbatch;

[0095] Next surface layer: The same composition and content as the previous surface layer in this comparative example;

[0096] Bottom layer: 100wt% homopolymer polypropylene.

[0097] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0098] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0099] Comparative Example 4

[0100] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer arranged sequentially; wherein the components and contents of each layer are as follows:

[0101] Top layer: 100wt% homopolymer polypropylene;

[0102] Previous surface layer: 100wt% homopolymer polypropylene;

[0103] Core layer: 80wt% homopolymer polypropylene and 20wt% ordinary calcium carbonate filler masterbatch;

[0104] Next surface layer: The same composition and content as the previous surface layer in this comparative example;

[0105] Bottom layer: 100wt% homopolymer polypropylene.

[0106] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0107] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0108] Comparative Example 5

[0109] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer arranged sequentially; wherein the components and contents of each layer are as follows:

[0110] Top layer: 95wt% homopolymer polypropylene and 5wt% modified silica filler masterbatch;

[0111] Top layer: 85 wt% homopolymer polypropylene and 15 wt% dicumyl peroxide premix;

[0112] Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch;

[0113] Next surface layer: The same composition and content as the previous surface layer in this comparative example;

[0114] Bottom layer: 100wt% homopolymer polypropylene.

[0115] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0116] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0117] Comparative Example 6

[0118] This comparative example provides a BOPP pearlescent film, comprising an upper surface layer, an upper secondary surface layer, a core layer, a lower secondary surface layer, and a lower surface layer arranged sequentially; wherein the components and contents of each layer are as follows:

[0119] Top layer: 85wt% homopolymer polypropylene and 15wt% modified silica filler masterbatch;

[0120] Top layer: 90 wt% homopolymer polypropylene and 10 wt% dicumyl peroxide premix;

[0121] Core layer: 80wt% homopolymer polypropylene and 20wt% modified calcium carbonate filler masterbatch;

[0122] Next surface layer: The same composition and content as the previous surface layer in this comparative example;

[0123] Bottom layer: 100wt% homopolymer polypropylene.

[0124] The preparation method of the BOPP pearlescent film in this comparative example is the same as that in Example 1.

[0125] The total thickness and the thickness of each layer of the BOPP pearlescent film in this comparative example are the same as those in Example 1.

[0126] Performance Evaluation

[0127] The following performance evaluations were performed 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:

[0128] (1) Film surface quality: Randomly select a 50×50cm area of ​​the finished film and observe the surface defects such as crystal points, bright spots, and protrusions with the naked eye. Record the total number; if the number is <5, it is rated as excellent; if the number is <10, it is rated as good; if the number is <15, it is rated as medium; other situations are rated as poor.

[0129] (2) Interlayer bonding strength: Apply 3M 810 tape to the surface of the film (either the upper or lower surface). Use a 2kg roller to roll back and forth 6 times without applying any extra force. Finally, pull up the tape at a 60° angle and observe whether the film delamination occurs. If there is no delamination, it is rated as excellent. If there is delamination and the delamination area accounts for less than 10% of the total tape bonding area, it is rated as good. If there is delamination and the delamination area accounts for less than 30% of the total tape bonding area, it is rated as average. Other situations are rated as poor.

[0130] (3) Surface dyne value: The surface dyne value of the upper surface layer of the film is used to evaluate the printing performance.

[0131] (4) Tensile strength: According to GB / T 1040.3, the transverse tensile strength and longitudinal tensile strength of the film are tested.

[0132] (5) Whiteness and transmittance: Whiteness is tested according to GB / T 2913 and transmittance is tested according to GB / T 2410. The pearlescent effect is evaluated by these two tests.

[0133] Please refer to Table 1 for the performance evaluation results:

[0134] Table 1 Performance evaluation results of the thin films of Examples 1-4 and Comparative Examples 1-6

[0135]

[0136] As can be seen from the performance evaluation results in Table 1, the peel-resistant, easy-to-print, high-strength BOPP pearlescent films of Examples 1-4 of the present invention, while ensuring good pearlescent effect, have excellent film surface quality, excellent interlayer bonding force and mechanical strength, and good printability.

[0137] The BOPP pearlescent film of Comparative Example 1 did not have modified silica filler masterbatch added to its upper surface layer. As a result, the surface dyne value of the upper surface layer of Comparative Example 1 was low, the ink adsorption effect was poor, and the printing applicability was poor.

[0138] In Comparative Example 2, no dicumyl peroxide premix was added to either the upper or lower surface layer of the BOPP pearl film. As a result, the linolenic acid in the core layer of the BOPP pearl film in Comparative Example 2 could not polymerize to form linolenic acid oligomers with a certain molecular weight. Consequently, the interlayer bonding of the BOPP pearl film in Comparative Example 2 was poor, and the linolenic acid in the core layer easily migrated to the surface of the upper surface layer, resulting in a lower dyne value on the surface of the upper surface layer, poor ink adsorption, and poor printability.

[0139] Compared with the BOPP pearlescent film of Comparative Example 3, the addition of ordinary calcium carbonate filler masterbatch to the core layer resulted in poor film surface quality, poor interlayer bonding, and poor mechanical strength. The low molecular weight stearic acid in the core layer easily migrated to the surface of the upper layer, resulting in a lower dyne value on the surface of the upper layer, poor ink adsorption effect, and poor printability.

[0140] Compared with the BOPP pearlescent film of Comparative Example 4, no modified silica filler masterbatch was added to the upper surface layer, no dicumyl peroxide premix was added to the upper and lower surface layers, and ordinary calcium carbonate filler masterbatch was added to the core layer. The BOPP pearlescent film of Comparative Example 4 had poor film surface quality, poor interlayer bonding, and poor mechanical strength. The low molecular weight stearic acid in the core layer easily migrated to the surface of the upper surface layer, resulting in a lower dyne value of the upper surface layer, poor ink adsorption effect, and poor printability.

[0141] In Comparative Example 5, the BOPP pearlescent film contained excessive amounts of dicumyl peroxide premix in both the upper and lower surface layers. During production, this resulted in the formation of too many molecular chain initiation sites, causing the linolenic acid monomers to polymerize only into linolenic acid oligomers with excessively low molecular weights. Consequently, the BOPP pearlescent film of Comparative Example 5 exhibited generally poor film surface quality, weak interlayer adhesion, and poor mechanical strength. Furthermore, the low-molecular-weight linolenic acid oligomers also migrated to the upper surface, leading to a lower dyne value on the upper surface, resulting in poor ink adsorption and limited printability.

[0142] In Comparative Example 6, the BOPP pearlescent film had excessive modified silica filler masterbatch added to the upper surface layer, which resulted in the modified silica not being evenly dispersed on the upper surface layer, leading to poor film appearance quality and adverse effects on the overall mechanical strength of the film.

[0143] 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 peel-resistant, easy-to-print, high-strength BOPP pearlescent film, characterized in that: This includes the top layer, the next top layer, the core layer, the next bottom layer, and the bottom layer, arranged in sequence. The upper surface layer comprises homopolymer polypropylene and 5-10 wt% modified silica filler masterbatch; the modified silica filler masterbatch comprises homopolymer polypropylene and 15-25 wt% modified silica; the modified silica is obtained by modifying silica with maleic anhydride. Both the upper and lower surface layers comprise homopolymer polypropylene and 2-10 wt% dicumyl peroxide premix, wherein the dicumyl peroxide premix comprises homopolymer polypropylene and 45-55 wt% dicumyl peroxide. The core layer comprises homopolymer polypropylene and 10-20 wt% modified calcium carbonate filler masterbatch; the modified calcium carbonate filler masterbatch comprises homopolymer polypropylene and 55-65 wt% 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.

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: homopolymer polypropylene and dicumyl peroxide are added to a high-speed mixer according to the ratio and mixed at a mixing temperature of 30-50℃ 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 at a mixing temperature of 80-100℃ 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 filler masterbatch is prepared by adding homopolymer polypropylene and modified calcium carbonate into a twin-screw extruder according to the formula, heating and melting extrusion, and then granulating to obtain the modified calcium carbonate filler masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 210-230℃, the screw speed is 350-450rpm, 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 1-3 wt% 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 the modified silica.

7. The peel-resistant, easy-to-print, high-strength BOPP pearlescent film according to claim 6, characterized in that: The silica is silica synthesized by the gel method, and the average particle size D50 of the silica 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 homopolymer polypropylene and modified silica into a twin-screw extruder according to the ratio, heating and melting extrusion, and then granulating to obtain the modified silica filler masterbatch; wherein, in the twin-screw extruder, the processing temperature is set to 210-230℃, the screw speed is 200-300rpm, 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 homopolymer polypropylene in the upper surface layer, the homopolymer polypropylene in the modified silica-filled masterbatch, the homopolymer polypropylene in the upper and lower surface layers, the homopolymer polypropylene in the dicumyl peroxide premix, the homopolymer polypropylene in the core layer, and the homopolymer polypropylene in the modified calcium carbonate-filled masterbatch all have a melt index of 2-4 g / 10 min under the test conditions of 230°C and 2.16 kg.

10. A method for preparing a peel-resistant, easily printable, high-strength BOPP pearlescent film as described in any one of claims 1-9, characterized in that: Includes the following steps: According to the proportion of raw materials for each layer, the raw materials are mixed and then fed into the extruders of each layer by weighing. After multi-layer co-extrusion through the die head, the film is cast and then chilled into a thick sheet using the flat film method. The thick sheet is then stretched in both longitudinal and transverse directions to form a biaxially oriented film. After shaping, it is subjected to corona treatment, and then wound, aged, slit, and packaged into finished products.

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