A BOPP matte film applicable to direct coating process and its preparation method

Abstract

The present invention relates to the field of matte films, and particularly to a BOPP matte film suitable for direct coating process and a preparation method thereof. The BOPP matte film suitable for direct coating process described in the present invention comprises a top surface layer, an intermediate core layer, and a bottom surface layer arranged in sequence; the top surface layer is a matte layer, which comprises random copolymer polypropylene, 40-51 wt% of high-density polyethylene, 2-3 wt% of n-alkyl chain modified hyperbranched polyester, and 5-8 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene; the intermediate core layer comprises homopolypropylene; the bottom surface layer comprises homopolypropylene. By optimizing the components of the matte layer, the present invention can improve the roughness of the matte layer, which is beneficial to solving the problem of "pitting" with whitening on the film surface in the direct coating process, and further improving the quality of the matte film product after coating, so as to ensure the appearance quality of products such as laminated paper, paper boxes, and labels after subsequent lamination.

Description

Technical Field

[0001] The present invention relates to the field of matte films, in particular to a BOPP matte film suitable for a direct coating process and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene (BOPP) matte film (typically matte on one side and glossy on the other, or matte on both sides) achieves this matte effect primarily by scattering light, enhancing the quality of printed packaging. Because its matte effect creates a soft, stylish, and elegant look, while also reducing eye fatigue, BOPP matte film is increasingly used in the packaging industry, particularly in deep processing industries such as coating and laminating. The matte layer of BOPP film primarily consists of random copolymer polypropylene and high-density polyethylene (HDPE). The microstructure of this layer resembles an "islands-in-the-sea" structure. Specifically, during the biaxial stretching process, while the random copolymer polypropylene remains in a relatively soft phase, the HDPE, due to its faster crystallization rate and higher crystallization temperature, partially or fully crystallizes into a hard phase. Consequently, during the stretching process, the HDPE, as the hard phase, stands out from the soft phase of the random copolymer polypropylene, resulting in a coarsened, island-in-the-sea morphology.

[0003] BOPP matte film products used for functional coatings primarily refer to BOPP films with one glossy side and one matte side. Common processing applications include: ① Using BOPP matte film as the substrate, after applying anti-scratch oil to the matte side, the film is embossed with a stencil (typically a non-corona matte film or glossy film) and UV-cured to create a scratch-resistant matte film product; ② Direct coating is performed on the matte film substrate. After applying anti-scratch oil to the matte side, an anilox roller is used to coat the matte layer. After coating, the film is UV-cured in an oven and wound to complete the anti-scratch process, forming a scratch-resistant layer on the matte surface. The coated product is then coated or pre-coated with a glue layer on the glossy side before being laminated to paper, cartons, or labels. However, scratch-resistant matte films produced using direct coating often exhibit white "pitting" on the surface, which affects the appearance of subsequent laminated paper, cartons, and labels. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a BOPP matte film suitable for direct coating process and its preparation method, by optimizing the material composition of the matte layer and improving the roughness of the matte layer to improve the problem of white "pitting" on the surface of the film after the direct coating process, thereby improving the appearance quality of the matte film product after coating, so as to ensure the appearance quality of products such as laminated paper, paper boxes and labels after subsequent lamination.

[0005] A BOPP matte film suitable for direct coating process, comprising a top surface layer, a middle core layer, and a bottom surface layer arranged in sequence; the top surface layer is a matte layer, including random copolymerized polypropylene, 40-51 wt% high-density polyethylene, 2-3 wt% n-alkyl chain modified hyperbranched polyester, and 5-8 wt% maleic anhydride-styrene melt grafted random copolymerized polypropylene; the middle core layer includes homopolypropylene; the bottom surface layer includes homopolypropylene. Through the research of the inventor, it is found that different from the anti-scratch oil without silica in the plate film pressing process, the anti-scratch oil components in the direct coating process generally include acrylic resin, silica (the particle size is generally 3-5 um), and a dispersion aid. After coating the anti-scratch oil, silica is enriched on the surface of the coating and forms a microscopic concave-convex structure, forming a uniform rough surface. This coating not only enhances the matte effect but also improves the anti-scratch performance of the BOPP matte film through UV curing to form a crosslinked structure to achieve functional integration. However, due to the insufficient roughness of the matte surface of the currently conventionally produced BOPP matte film, when coating the anti-scratch oil, it is impossible to effectively embed the silica in the anti-scratch oil between the soft phase and the hard phase on the surface of the matte layer, and too much silica is exposed on the surface of the anti-scratch layer. When the area of the silica exposed on the surface of the anti-scratch layer is too large, due to the relationship of light scattering, visual white "pockmarks" will be formed, affecting the appearance quality of subsequent products such as laminated paper, paper boxes, and labels; and to form sufficient roughness in the matte layer, there needs to be sufficient difference between the protruding hard phase and the dispersed soft phase in the matte layer system.

[0006] According to the research findings of the inventors, adding a certain amount of hyperbranched polyester modified with n-alkyl chains to the extinction layer, on the one hand, the non-polarity of the n-alkyl chains in the n-alkyl chain-modified hyperbranched polyester has similar compatibility with the hard phases of high-density polyethylene and random copolymer polypropylene, and there is no problem of poor compatibility; on the other hand, the unique branched molecular structure of the modified hyperbranched polyester can form certain van der Waals force interactions with the HDPE molecular chains, affecting the movement and arrangement of the HDPE molecular chains, inducing the HDPE molecular chains to be arranged more orderly, and the modified hyperbranched polyester can serve as a heterogeneous nucleating agent in high-density polyethylene, providing nucleation sites for the crystallization of HDPE. Its branched structure can reduce the free energy barrier of high-density polyethylene crystallization, making it easier for HDPE molecular chains to aggregate around the modified hyperbranched polyester and form crystal nuclei. Therefore, the addition of n-alkyl chain-modified hyperbranched polyester can improve the crystallization performance of high-density polyethylene, making the crystals larger and more prominent after the crystallization of high-density polyethylene, thereby increasing the roughness of the extinction layer. At the same time, it can ensure its compatibility with other components of the extinction layer. In addition, the addition of n-alkyl chain-modified hyperbranched polyester reduces the melt viscosity of high-density polyethylene. The lower melt viscosity helps the HDPE molecular chains to flow and rearrange during the processing, promoting the increase in the thickness of the HDPE microcrystals, and is more conducive to obtaining an extinction layer surface with higher roughness. When the addition amount of n-alkyl chain-modified hyperbranched polyester is less than 2wt%, the crystallinity of high-density polyethylene itself is limited under the optimal process parameter adjustment, and the effect of improving the roughness of the extinction layer is not obvious, and it cannot be effectively applied to the direct coating process to prepare a scratch-resistant and extinction film product without white spots; when the addition amount of n-alkyl chain-modified hyperbranched polyester is higher than 3wt%, the n-alkyl chain-modified hyperbranched polyester will seriously interfere with the normal crystallization process of HDPE, affecting the crystallization rate and the unevenness of the crystal size, which is not conducive to obtaining an extinction layer with uniform roughness and is also not conducive to ensuring the mechanical properties of the film.

[0007] However, due to the increase in the crystallinity of high-density polyethylene, the protrusion becomes more obvious, which easily causes the poor combination of the high-density polyethylene hard phase and the random copolymerized polypropylene soft phase in the matting layer. During the production process, the surface area of the protruding high-density polyethylene in the matting layer in contact with the stretching roller is larger, and it is more likely to fall off during the friction process. The fallen high-density polyethylene will gradually accumulate on the pressure roller to form a layer of gel. When the gel accumulates to a certain extent, it will affect the appearance quality of the film surface and the smoothness of production. Therefore, on the basis of the above solution, to ensure the appearance quality of the BOPP matting film itself and the smoothness of production, the present invention also adds a certain amount of maleic anhydride-styrene melt-grafted random copolymerized polypropylene to the matting layer. The random copolymerized polypropylene in the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is fixed in the soft phase as an anchor point, while the polar groups of maleic anhydride (MAH) can interact with the non-polar segments in high-density polyethylene through hydrogen bonds to form an anchor structure, reducing the interfacial tension between the two phases, improving the compatibility of the high-density polyethylene hard phase and the random copolymerized polypropylene soft phase, and making the protruding high-density polyethylene not easily separated from the soft phase by friction and fall off onto the pressure roller during the production process, thereby ensuring the appearance quality of the film surface and the smoothness of production. Moreover, the cyclic rigid structure of styrene can improve the conformation of the random copolymerized polypropylene molecular chain, making it more regularly arranged, which is conducive to the formation of random copolymerized polypropylene crystals. The branched-chain structure of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is beneficial to increasing the crystallization temperature of the random copolymerized polypropylene soft phase and improving the hardness of the random copolymerized polypropylene soft phase wrapped on the surface of the high-density polyethylene hard phase. Then, during the production process, when the matting layer contacts the pressure roller and is subjected to friction, the random copolymerized polypropylene soft phase wrapped on the surface of the high-density polyethylene hard phase becomes hard, better protecting the high-density polyethylene soft phase from being directly contacted and separated from the soft phase by friction and falling off onto the pressure roller, ensuring the appearance quality of the film surface and the smoothness of production. When the addition amount of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is less than 5wt%, it cannot effectively protect the protruding high-density polyethylene from being rubbed off during the production process, affecting the smoothness of production. When the addition amount of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is higher than 8wt%, excessive polar groups of maleic anhydride may crosslink excessively with the random copolymerized polypropylene soft phase to form rigid microdomains, restricting the movement of chain segments and increasing the risk of film breakage during the biaxial stretching process of the film. The synergistic effect of the n-alkyl chain modified hyperbranched polyester and the maleic anhydride-styrene melt-grafted random copolymerized polypropylene improves the roughness of the matting layer while ensuring the appearance quality of the BOPP matting film itself and the smoothness of production, meets the requirements of the subsequent direct coating process of the BOPP matting film product, improves the problem of "pockmarks" with whitening on the surface of the scratch-resistant matting film prepared by the direct coating process, and further improves the appearance quality of the coated matting film product to ensure the appearance quality of the subsequent laminated products such as laminated paper, paper boxes, and labels.

[0008] Furthermore, the preparation method of the n-alkyl chain modified hyperbranched polyester is as follows: Using p-toluenesulfonic acid as a catalyst, 2-carboxyethylphenylphosphinic acid and trimethylolpropane are synthesized to prepare the hyperbranched polyester, and the obtained hyperbranched polyester is subjected to an esterification reaction with a saturated n-alkyl monohydric alcohol to obtain the n-alkyl chain modified hyperbranched polyester; the saturated n-alkyl monohydric alcohol includes one or more of n-butanol, n-pentanol, and n-hexanol. The above-mentioned saturated n-alkyl monohydric alcohol has a small steric hindrance and can form a more uniform dispersion with the high-density polyethylene matrix to promote heterogeneous nucleation. Moreover, the shorter alkyl chain on the one hand reduces the volume of the side groups of the n-alkyl chain modified hyperbranched polyester, reduces the hindrance to the movement of the high-density polyethylene main chain, improves the symmetry and flexibility of the molecular chain, makes the HDPE molecular chain easier to aggregate around the n-alkyl chain modified hyperbranched polyester and form crystal nuclei, and improves the crystallinity; on the other hand, it is more conducive to improving the compatibility of the n-alkyl chain modified hyperbranched polyester with other components of the matte layer.

[0009] Furthermore, the grafting rate of the saturated n-alkyl monohydric alcohol in the n-alkyl chain modified hyperbranched polyester is 60-80%. Setting the grafting rate of the saturated n-alkyl monohydric alcohol in the n-alkyl chain modified hyperbranched polyester within the above range is beneficial to improving the compatibility between the n-alkyl chain modified hyperbranched polyester and the hard-phase high-density polyethylene and the crystallization performance of the hard-phase high-density polyethylene, thereby improving the roughness of the matte layer. If the grafting rate is lower than 60%, the grafting rate of the saturated n-alkyl monohydric alcohol is too low, resulting in insufficient n-alkyl chain density on the surface of the hyperbranched polyester, and an effective physical entanglement effect cannot be formed with the high-density polyethylene. This weak interfacial interaction weakens the adhesion force between the two phases, and phase separation will occur between the n-alkyl chain modified hyperbranched polyester and the high-density polyethylene, which is not conducive to the crystallization of the high-density polyethylene, is not conducive to improving the roughness of the matte layer, and thus cannot effectively improve the problem of white "pitting" on the surface of the scratch-resistant matte film prepared by the direct coating process; if the grafting rate is higher than 80%, the movement of the high-density polyethylene molecular chain will be overly restricted, which is not conducive to the crystallization of the high-density polyethylene, is not conducive to improving the roughness of the matte layer, and thus cannot effectively improve the problem of white "pitting" on the surface of the film prepared by the direct coating process. [[ID=''5]]

[0010] Furthermore, the degree of branching of the hyperbranched polyester is 0.6 to 0.8. This degree of branching range helps the n-alkyl chain modified hyperbranched polyester molecules to better penetrate between the molecular chains of high-density polyethylene, thus playing a role in inducing crystallization; if the degree of branching of the hyperbranched polyester is lower than 0.6, the compatibility between the n-alkyl chain modified hyperbranched polyester and high-density polyethylene becomes poor, affecting the crystallization performance of high-density polyethylene, not conducive to high-density polyethylene obtaining a higher degree of crystallization, not conducive to improving the roughness of the matte layer, and thus unable to effectively improve the problem of white "pitting" on the surface of the scratch-resistant matte film prepared by the direct coating process; if the degree of branching of the hyperbranched polyester is higher than 0.8, the increased steric hindrance causes the n-alkyl chain modified hyperbranched polyester to be unable to effectively penetrate between the molecular chains of HDPE, resulting in poor dispersion in high-density polyethylene, and also not conducive to high-density polyethylene obtaining a higher degree of crystallization, not conducive to improving the roughness of the matte layer, and thus unable to effectively improve the problem of white "pitting" on the surface of the scratch-resistant matte film prepared by the direct coating process.

[0011] Furthermore, the maleic anhydride-styrene melt-grafted random copolymer polypropylene is prepared by the melt grafting method. Styrene monomer and maleic anhydride monomer are added to xylene solvent, and azobisisobutyronitrile is used as the initiator to obtain styrene-maleic anhydride copolymer through free radical copolymerization. Then, dicumyl peroxide is used as the initiator to graft the styrene-maleic anhydride copolymer onto the molecular chain of random copolymer polypropylene to form branches, obtaining the maleic anhydride-styrene melt-grafted random copolymer polypropylene; the molar ratio of the maleic anhydride monomer to the styrene monomer is (2:4) to (2:5); the grafting rate of the styrene-maleic anhydride copolymer is 45 to 55%. If the molar amount of maleic anhydride and styrene monomers is lower than 2:4, since the amount of monomers for the macromolecular free radical reaction between styrene group and random copolymer polypropylene is reduced, affecting the grafting rate, resulting in too low grafting rate of maleic anhydride-styrene, then the long-chain styrene-maleic anhydride copolymer and maleic anhydride functional groups are insufficient, and the improvement of the problem of accumulated glue on the pressure roller during the production process is not obvious; if the molar amount of maleic anhydride and styrene monomers is higher than 2:5, too much styrene monomer will damage the continuity of the molecular chain of random copolymer polypropylene, resulting in too high grafting rate of maleic anhydride-styrene. Due to the increased voids between molecular chains caused by too many grafted chains, the mechanical strength of the film is reduced. The maleic anhydride-styrene melt-grafted random copolymer polypropylene obtained within the above grafting rate range of the styrene-maleic anhydride copolymer has the best hardness and the best improvement effect on the compatibility between the high-density polyethylene and random copolymer polypropylene in the matte layer. The random copolymer polypropylene used to prepare the maleic anhydride-styrene melt-grafted random copolymer polypropylene is the same as the soft-phase random copolymer polypropylene in the matte layer.

[0012] Further, at 230 °C and a load of 2.16 kg, the melt index of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is 7-9 g / 10 min. If the melt index of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is lower than 7 g / 10 min, it is not conducive to the dispersion of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene in the soft-phase random copolymerized polypropylene, affecting the heterogeneous nucleation of the soft-phase random copolymerized polypropylene and being not conducive to the improvement of the hardness of the soft-phase random copolymerized polypropylene; if the melt index of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is higher than 9 g / 10 min, the maleic anhydride-styrene melt-grafted random copolymerized polypropylene accelerates the crystallization rate of the soft-phase random copolymerized polypropylene, but the crystallinity decreases, which is also not conducive to the improvement of the hardness of the soft-phase random copolymerized polypropylene.

[0013] Further, the random copolymerized polypropylene is a random ethylene-propylene copolymer; at 230 °C and a load of 2.16 kg, the melt index of the random copolymerized polypropylene is 6-10 g / 10 min; at 190 °C and a load of 2.16 kg, the melt index of the high-density polyethylene is 9-20 g / 10 min; the homopolypropylene in the middle core layer and the lower surface layer has a melt index of 3-8 g / 10 min at 230 °C and a load of 2.16 kg. Controlling the high-density polyethylene and random copolymerized polypropylene within the above melt index ranges is conducive to obtaining a BOPP matte film with good overall matting effect; controlling the homopolypropylene within the above melt index range is conducive to obtaining a BOPP matte film with excellent overall mechanical properties.

[0014] Further, the middle core layer further includes 1-3 wt% antistatic agent; the lower surface layer further includes 0.1-0.5 wt% anti-blocking agent, and the anti-blocking agent is one or more of silica, talc powder, and calcium carbonate, and the particle size of the anti-blocking agent is 3-6 μm. In order to balance the surface layer thickness and peeling problem, the anti-blocking agent is preferably 4-5 μm; adding an appropriate amount of anti-blocking agent to the lower surface layer is conducive to increasing the smoothness of the winding and unwinding of the matte film; if the content of the anti-blocking agent in the lower surface layer is lower than 0.1 wt%, it cannot play an effective anti-blocking role; if the content of the anti-blocking agent in the lower surface layer is higher than 0.5 wt%, the problem of anti-blocking agent peeling is likely to occur during the production process, resulting in pollution of the guide roller, and at the same time, it will increase the haze and reduce the gloss, affecting the appearance of the product.

[0015] A method for preparing a BOPP matte film suitable for the direct coating process includes the following steps:

[0016] Step 1: Batching and plasticization: The raw material usage ratio is set in the control system of the biaxial stretch film production line. Then the batching system automatically delivers the dried raw materials of each layer to the extruder according to the input ratio. After being melted and plasticized in the extruder, the melt enters the die head through the runner and distributor;

[0017] Step 2: Slab Casting: After extrusion through the die, the melt immediately contacts a chilled roller to form a thick sheet.

[0018] Step 3: Longitudinal stretching: The thick sheet is heated to the set temperature by multiple sets of preheating rollers, and then begins to be longitudinally stretched and then shaped;

[0019] Step 4: Transverse stretching: After preheating the longitudinally stretched thick sheet to a set temperature, transverse stretching is started, followed by shaping and cooling to obtain a multilayer film;

[0020] Step 5: Traction and Rewinding: The multi-layer film exiting the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, enters the rewinding unit to obtain a parent roll;

[0021] Step 6: Slitting: Slitting the aged mother roll to obtain film rolls of specified width and length.

[0022] Furthermore, the melt extrusion temperature of the upper surface layer is 200~260°C; the melt extrusion temperature of the middle core layer and the lower surface layer is 230~260°C; in the process of the melt contacting the chilled roller, the temperature of the chilled water and the chilled roller is 15~50°C; the temperature of the longitudinal stretching zone is 90~130°C; the temperature of the transverse stretching zone is 155~165°C; the longitudinal stretching ratio is 4.5~5.5 times; the transverse stretching ratio is 8~10 times; and the corona power factor of the upper surface layer is 20~25W·min / m.

[0023] For better understanding and implementation, the present invention is described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structures of the BOPP matte films suitable for direct coating process described in Examples 1 to 3 of the present invention and the BOPP matte films described in Comparative Examples 1 to 10. DETAILED DESCRIPTION

[0025] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the embodiments of the present application. It should be clear in the embodiments of the present application that the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the embodiments of the present application without creative efforts belong to the scope of protection of the embodiments of the present application.

[0026] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the embodiments of the present application. The singular forms "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0027] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all the embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0028] In addition, in the description of the present application, unless otherwise specified, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0029] It should be understood that the embodiments of the present application are not limited to the exact structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the embodiments of the present application is only limited by the appended claims.

[0030] A BOPP matte film applicable to the direct coating process, comprising a top layer, an intermediate core layer, and a bottom layer arranged in sequence; the top layer is a matte layer, comprising random copolymerized polypropylene, 40-51 wt% high-density polyethylene, 2-3 wt% n-alkyl chain modified hyperbranched polyester, and 5-8 wt% maleic anhydride-styrene melt-grafted random copolymerized polypropylene; the intermediate core layer comprises homopolypropylene; the bottom layer comprises homopolypropylene.

[0031] Further, the preparation method of the n-alkyl chain modified hyperbranched polyester is as follows: Using p-toluenesulfonic acid as a catalyst, 2-carboxyethylphenylphosphinic acid and trimethylolpropane are synthesized to prepare the hyperbranched polyester, and the obtained hyperbranched polyester is subjected to an esterification reaction with a saturated n-alkyl monohydric alcohol to obtain the n-alkyl chain modified hyperbranched polyester; the saturated n-alkyl monohydric alcohol includes one or more of n-butanol, n-pentanol, and n-hexanol.

[0032] Further, the grafting rate of the saturated n-alkyl monohydric alcohol in the n-alkyl chain modified hyperbranched polyester is 60-80%.

[0033] Further, the branching degree of the hyperbranched polyester is 0.6-0.8.

[0034] Further, the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is prepared by a melt-grafting method. Styrene monomer and maleic anhydride monomer are added to xylene solvent, and azobisisobutyronitrile is used as an initiator. Styrene-maleic anhydride copolymer is obtained by free radical copolymerization. Then, using dicumyl peroxide as an initiator, the styrene-maleic anhydride copolymer is grafted onto the molecular chain of random copolymerized polypropylene to form branches, obtaining the maleic anhydride-styrene melt-grafted random copolymerized polypropylene; the molar ratio of the maleic anhydride monomer to the styrene monomer fed is (2:4)-(2:5); the grafting rate of the styrene-maleic anhydride copolymer is 45-55%. The molar ratio of the maleic anhydride monomer to the styrene monomer fed is preferably 2:4. At this time, the maleic anhydride-styrene melt-grafted random copolymerized polypropylene can obtain a high grafting rate while ensuring the mechanical strength of the film.

[0035] Further, at 230 °C and a load of 2.16 kg, the melt index of the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is 7-9 g / 10min.

[0036] Further, the random copolymerized polypropylene is a random ethylene-propylene copolymer; at 230 °C and a load of 2.16 kg, the melt index of the random copolymerized polypropylene is 6-10 g / 10min; at 190 °C and a load of 2.16 kg, the melt index of the high-density polyethylene is 9-20 g / 10min; the homopolypropylene in the middle core layer and the lower surface layer has a melt index of 3-8 g / 10min at 230 °C and a load of 2.16 kg.

[0037] Further, the middle core layer further comprises 1-3 wt% antistatic agent, and the antistatic agent is a quaternary ammonium salt-based methacrylate copolymer; the lower surface layer further comprises 0.1-0.5 wt% anti-blocking agent, and the anti-blocking agent is one or more of silica, talcum powder, and calcium carbonate, and the particle size of the anti-blocking agent is 3-6 μm. To balance the surface layer thickness and peeling problem, it is preferably 4-5 μm.

[0038] Further, the total thickness of the BOPP matte film applicable to the direct coating process is 12-15 μm; the thickness of the upper surface layer is 1.8-2.2 μm, and the thickness of the lower surface layer is 0.8-1.2 μm.

[0039] A preparation method of the BOPP matte film applicable to the direct coating process comprises the following steps:

[0040] First step: batching and plasticizing: set the raw material usage ratio in the control system of the biaxially oriented film production line, and then the batching system automatically conveys the dried raw materials of each layer to the extruder according to the input ratio. After melting and plasticizing in the extruder, the melt enters the die head through the runner and the distributor;

[0041] Second step: casting: after being extruded from the die head, the melt immediately contacts the chill roll to form a thick sheet;

[0042] Third step: longitudinal stretching: the thick sheet is heated to the set temperature by multiple groups of preheating rolls, starts longitudinal stretching, and then is shaped;

[0043] Fourth step: transverse stretching: after preheating the thick sheet that has undergone longitudinal stretching to the set temperature, start transverse stretching, and then perform shaping and cooling treatments to obtain a multi-layer structure film;

[0044] Fifth step: traction and winding: the multi-layer structure film exiting the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain a master roll;

[0045] Sixth step: slitting: perform slitting treatment on the master roll that has undergone aging treatment to obtain a film roll with a specified width and length.

[0046] Further, the melting and extrusion temperature of the upper surface layer: 200-260 °C; the melting and extrusion temperatures of the middle core layer and the lower surface layer: 230-260 °C; in the process where the melt contacts the chill roll, the temperature of the chill water and the chill roll: 15-50 °C; the temperature in the longitudinal stretching zone: 90-130 °C; the temperature in the transverse stretching zone: 155-165 °C; the longitudinal stretching ratio: 4.5-5.5 times; the transverse stretching ratio: 8-10 times; the corona power factor of the upper surface layer: 20-25 W·min / m.

[0047] The physical property indexes and their testing methods of the embodiments or comparative examples of the present invention are specifically as follows:

[0048] The melt index (melt mass flow rate MFR) was measured according to GB / T3682-2018.

[0049] Powder accumulation on the longitudinal drawing and pressing rollers: During production, after continuous production for 24 hours, measure the powder accumulation on the drawing and pressing rollers in the longitudinal drawing area in contact with the matting layer. Judge by measuring the area of the powder accumulation on the width of the drawing and pressing rollers (good effect: the area of the powder accumulation on the drawing and pressing rollers is 0-20% (including 20%); general effect: the area of the powder accumulation on the drawing and pressing rollers is 20-50% (including 50%); poor effect: the area of the powder accumulation on the drawing and pressing rollers is >50%).

[0050] The tensile strength was tested according to GB / T1040.3.

[0051] The glossiness test was carried out according to the standard of GB / T8807-1988.

[0052] The haze test was carried out according to GB / T2410-2008.

[0053] The roughness test was carried out according to GB / T 6062-2009.

[0054] Appearance white dot situation of the BOPP matting film after direct coating process: Select a 1-square-meter sample, place the sample horizontally on the detection table with a black background (the coating surface facing up and the light surface facing down), observe the white dot situation on the film surface within 10 cm from the sample to the black background, mark the found white dots with a black oil-based pen, and then calculate the total number of white dots per square meter. If ≤20 dots per square meter, it is judged as qualified and can meet the appearance quality requirements of the product film surface after coating, otherwise it is unqualified.

[0055] In the following examples and comparative examples, the n-alkyl chain modified hyperbranched polyester was obtained by the esterification reaction of hyperbranched polyester and n-butanol.

[0056] Example 1

[0057] This example provides a BOPP matting film suitable for the direct coating process, including an upper surface layer 1, an intermediate core layer 2, and a lower surface layer 3 arranged in sequence. The specific structure can be referred to Figure 1 .

[0058] The preparation methods of the resins of each layer of the BOPP matting film suitable for the direct coating process in this example are as follows:

[0059] Preparation of the upper surface layer 1 resin: Take 40 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 50 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.6; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 60%), and 8 wt% of maleic anhydride-styrene melt grafted random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min; the grafting rate of the styrene-maleic anhydride copolymer is 45%), and mix them evenly to obtain the upper surface layer 1 resin.

[0060] Preparation of the middle core layer 2 resin: Take 99 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0061] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (the isotacticity is 96%, the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the lower surface layer 3 resin.

[0062] The preparation method of the BOPP matte film applicable to the direct coating process in this embodiment includes the following steps:

[0063] Batching and plasticization: Set the raw material usage ratio in the control system of the biaxially oriented film production line, and then the batching system automatically transports each layer of raw materials that have been dried to the extruder according to the input ratio. After melting and plasticizing in the extruder, the melt enters the die through the runner and the distributor;

[0064] Sheet casting: After being extruded from the die, the melt immediately contacts the cooling roll to form a thick sheet;

[0065] Longitudinal stretching: The thick sheet is heated to the set temperature by multiple groups of preheating rolls, starts longitudinal stretching, and then is shaped;

[0066] Transverse stretching: After preheating the thick sheet that has undergone longitudinal stretching to the set temperature, start transverse stretching, and then perform shaping and cooling treatment to obtain a multi-layer structure film;

[0067] Traction and winding: The multi-layer structure film exiting the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, it enters the winding unit to obtain a master roll;

[0068] Slitting: The aged master roll is slit to obtain film rolls with specified width and length.

[0069] The melting extrusion temperature of the upper surface layer 1 is 235 °C; the melting extrusion temperature of the middle core layer 2 is 250 °C; the melting extrusion temperature of the lower surface layer 3 is 250 °C; in the process where the melt contacts the chill roll, the temperature of the chilled water and the chill roll is 40 °C; the temperature for longitudinal stretching is 125 °C; the temperature for transverse stretching is 160 °C; the longitudinal stretching ratio is 5.3 times; the transverse stretching ratio is 8.5 times; the corona power factor of the upper surface layer 1 is 23.5 W·min / m.

[0070] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0071] Example 2

[0072] This example provides a BOPP matte film applicable to the direct coating process, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. The specific structure can be referred to Figure 1 .

[0073] The preparation methods of the resins for each layer of the BOPP matte film applicable to the direct coating process in this example are as follows:

[0074] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 45 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 70%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0075] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0076] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of an anti-blocking agent (silica, particle size is 4.5 µm), mix them evenly to obtain the lower surface layer 3 resin.

[0077] The preparation method of the BOPP matte film applicable to the direct coating process in this example is the same as that in Example 1.

[0078] The total thickness of the film is 12 µm, among which the upper surface layer 1 has a thickness of 1.8 µm, the middle core layer 2 has a thickness of 9.2 µm, and the lower surface layer 3 has a thickness of 1 µm.

[0079] Example 3

[0080] This example provides a BOPP matte film applicable to the direct coating process, which includes an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. The specific structure can be referred to Figure 1 .

[0081] The preparation methods of the resins for each layer of the BOPP matte film applicable to the direct coating process in this example are as follows:

[0082] Preparation of the upper surface layer 1 resin: Take 52 wt% of random copolymerized polypropylene (melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 40 wt% of high-density polyethylene (melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 3 wt% of a n-alkyl chain modified hyperbranched polyester (branching degree of the hyperbranched polyester is 0.8; grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 80%), and 5 wt% of maleic anhydride-styrene melt-grafted random copolymerized polypropylene (melt index measured under the conditions of 230 °C and 2.16 kg is 9 g / 10 min; grafting rate of the styrene-maleic anhydride copolymer is 55%), mix them evenly to obtain the upper surface layer 1 resin.

[0083] Preparation of the middle core layer 2 resin: Take 99 wt% of homopolypropylene (melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), mix them evenly to obtain the middle core layer 2 resin.

[0084] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of an anti-blocking agent (silica, particle size is 4.5 µm), mix them evenly to obtain the lower surface layer 3 resin.

[0085] The preparation method of the BOPP matte film applicable to the direct coating process in this embodiment is the same as that in Embodiment 1.

[0086] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0087] Comparative Example 1

[0088] This comparative example provides a BOPP matte film, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, refer to Figure 1 .

[0089] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows:

[0090] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymerized polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 47 wt% of high-density polyethylene (with a melt index of 15 g / 10 min measured under the conditions of 190 °C and 2.16 kg), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymerized polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0091] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0092] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0093] The preparation method of the BOPP matte film in this comparative example is the same as that in Embodiment 1.

[0094] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0095] Comparative Example 2

[0096] This comparative example provides a BOPP matte film, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, refer toFigure 1 。

[0097] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows:

[0098] Preparation of the upper surface layer 1 resin: Take 47 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 46 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 1 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 70%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the upper surface layer 1 resin.

[0099] Preparation of the middle core layer 2 resin: Take 99 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0100] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (the isotacticity is 96%, the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the lower surface layer 3 resin.

[0101] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0102] The total thickness of the film is 12 µm, wherein the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0103] Comparative Example 3

[0104] This comparative example provides a BOPP matting film, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 。

[0105] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows:

[0106] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymer polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 42 wt% of high-density polyethylene (with a melt index of 15 g / 10 min measured under the conditions of 190 °C and 2.16 kg), 5 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 70%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0107] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0108] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0109] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0110] The total thickness of the film is 12 µm, among which the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0111] Comparative Example 4

[0112] This comparative example provides a BOPP matte film, which includes an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0113] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows:

[0114] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymer polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 45 wt% of high-density polyethylene (with a melt index of 15 g / 10 min measured under the conditions of 190 °C and 2.16 kg), 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 40%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0115] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0116] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0117] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0118] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0119] Comparative Example 5

[0120] This comparative example provides a BOPP matte film, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0121] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows:

[0122] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymerized polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 45 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 90%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymerized polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0123] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0124] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (the isotacticity is 96%, and the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0125] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0126] The total thickness of the film is 12 µm, among which the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0127] Comparative Example 6

[0128] This comparative example provides a BOPP matte film, which includes an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0129] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows:

[0130] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymerized polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 51 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), and 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 70%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0131] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0132] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (isotacticity: 96%, with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 0.3 wt% of an anti-blocking agent (silica, particle size: 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0133] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0134] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0135] Comparative Example 7

[0136] This comparative example provides a BOPP matting film, which includes an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0137] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows:

[0138] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymer polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 48 wt% of high-density polyethylene (with a melt index of 15 g / 10 min measured under the conditions of 190 °C and 2.16 kg), 2 wt% of n-alkyl chain-modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain-modified hyperbranched polyester is 70%), and 3 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (with a melt index of 8 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of the styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0139] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (with a melt index of 3 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0140] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, melt index measured at 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of anti-blocking agent (silica, particle size is 4.5 µm), mix them evenly to obtain the lower surface layer 3 resin.

[0141] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0142] The total thickness of the film is 12 µm, among which the upper surface layer 1 has a thickness of 1.8 µm, the middle core layer 2 has a thickness of 9.2 µm, and the lower surface layer 3 has a thickness of 1 µm.

[0143] Comparative Example 8

[0144] This comparative example provides a BOPP matte film, which includes an upper surface layer 1, a middle core layer 2 and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0145] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows:

[0146] Preparation of the upper surface layer 1 resin: Take 47 wt% of random copolymerized polypropylene (melt index measured at 230 °C and 2.16 kg is 8 g / 10 min), 41 wt% of high-density polyethylene (melt index measured at 190 °C and 2.16 kg is 15 g / 10 min), 2 wt% of n-alkyl chain modified hyperbranched polyester (branching degree of hyperbranched polyester is 0.7; grafting rate of n-butanol in n-alkyl chain modified hyperbranched polyester is 70%), and 10 wt% of maleic anhydride-styrene melt-grafted random copolymerized polypropylene (melt index measured at 230 °C and 2.16 kg is 8 g / 10 min; grafting rate of styrene-maleic anhydride copolymer is 50%), mix them evenly to obtain the upper surface layer 1 resin.

[0147] Preparation of the middle core layer 2 resin: Take 99 wt% of homopolypropylene (melt index measured at 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), mix them evenly to obtain the middle core layer 2 resin.

[0148] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, melt index measured at 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of anti-blocking agent (silica, particle size is 4.5 µm), mix them evenly to obtain the lower surface layer 3 resin.

[0149] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0150] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0151] Comparative Example 9

[0152] This comparative example provides a BOPP matte film, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0153] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows:

[0154] Preparation of the resin for the upper surface layer 1: Take 47 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 45 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 70%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min; the grafting rate of the styrene-maleic anhydride copolymer is 35%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0155] Preparation of the resin for the middle core layer 2: Take 99 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0156] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (the isotacticity is 96%, and the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of antiblocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

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

[0158] The total thickness of the film is 12 µm, where the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0159] Comparative Example �10

[0160] This comparative example provides a BOPP matte film, including an upper surface layer 1, a middle core layer 2, and a lower surface layer 3 arranged in sequence. For the specific structure, please refer toFigure 1 。

[0161] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows:

[0162] Preparation of the upper surface layer 1 resin: Take 47 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 45 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 2 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.7; the grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester is 70%), and 6 wt% of maleic anhydride-styrene melt-grafted random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min; the grafting rate of the styrene-maleic anhydride copolymer is 60%), mix them evenly to obtain the upper surface layer 1 resin.

[0163] Preparation of the middle core layer 2 resin: Take 99 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), mix them evenly to obtain the middle core layer 2 resin.

[0164] Preparation of the lower surface layer 3 resin: Take 99.7 wt% of homopolypropylene (isotacticity is 96%, the melt index measured under the conditions of 230 °C and 2.16 kg is 3 g / 10 min) and 0.3 wt% of anti-blocking agent (silica, particle size is 4.5 µm), mix them evenly to obtain the lower surface layer 3 resin.

[0165] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0166] The total thickness of the film is 12 µm, among which the thickness of the upper surface layer 1 is 1.8 µm, the thickness of the middle core layer 2 is 9.2 µm, and the thickness of the lower surface layer 3 is 1 µm.

[0167] The BOPP matting films applicable to the direct coating process in Examples 1 to 3 and the BOPP matting films in Comparative Examples 1 to 10 were used to prepare the matting film with an anti-scratch layer according to the following direct coating process. Specifically: The anti-scratch oil was evenly transferred to the matting surface of the coated matting film by a gravure roll. The components of the anti-scratch oil (common grades are AR-2888 and HX-UV802) are generally acrylic resin, silica, and dispersion aids. After coating, it enters the hot air drying stage at a temperature of 100 - 120 °C for ultraviolet curing to form the anti-scratch layer (thickness is 2 - 3 µm) of the film. The cured film is wound up after cooling, and finally rewinding, slitting, and packaging are carried out according to requirements.

[0168] The performance test results of the BOPP matte films applicable to the direct coating process in Examples 1 to 3 and the BOPP matte films in Comparative Examples 1 to 10 are shown in Table 1 below.

[0169] Table 1

[0170]

[0171] Combined with the above performance test data, it can be seen that:

[0172] In the BOPP matte film of Comparative Example 1, no n-alkyl chain modified hyperbranched polyester is added to the upper surface layer, so the roughening degree of the surface of the matte layer of the matte film cannot be improved, and the silica solid particulate matter cannot be effectively hidden between the soft phase and the hard phase in the matte layer. After coating, the BOPP matte film shows dense white "pockmarks" on the matte surface.

[0173] In the BOPP matte film of Comparative Example 2, the content of the n-alkyl chain modified hyperbranched polyester added to the upper surface layer is less than 2 wt%, and the roughening degree of the surface of the matte layer of the matte film is not significantly improved. There is still a small part of the silica solid particulate matter that cannot be effectively hidden between the soft phase and the hard phase in the matte layer. After coating, the matte film shows dense white "pockmarks" on the matte surface.

[0174] In the BOPP matte film of Comparative Example 3, the content of the n-alkyl chain modified hyperbranched polyester added to the upper surface layer is higher than 3 wt%. The modified hyperbranched polyester interferes with the normal crystallization process of high-density polyethylene (HDPE), resulting in uneven crystallization rate and crystallization size, forming an irregular crystal structure, reducing the crystallinity of high-density polyethylene, leading to a decrease in the roughness of the matte layer and a reduction in the mechanical properties of the film, and making the transverse and longitudinal tensile strengths of the BOPP matte film lower.

[0175] In the BOPP matte film of Comparative Example 4, the n-butanol grafting rate of the n-alkyl chain modified hyperbranched polyester added to the upper surface layer is less than 60%. Phase separation occurs between the modified hyperbranched polyester and high-density polyethylene, which is not conducive to the crystallization of high-density polyethylene and cannot improve the roughness of the matte layer. After coating, the BOPP matte film shows dense white "pockmarks" on the matte surface.

[0176] In the BOPP matte film of Comparative Example 5, the n-butanol grafting rate of the n-alkyl chain modified hyperbranched polyester added to the upper surface layer is higher than 8%. The n-butanol chain segment restricts the movement of the high-density polyethylene molecular chain, which is not conducive to the crystallization of high-density polyethylene and cannot improve the roughness of the matte layer. After coating, the BOPP matte film shows dense white "pockmarks" on the matte surface.

[0177] In the upper surface layer of the BOPP matting film of Comparative Example 6, maleic anhydride-styrene melt grafted random copolymer polypropylene is not added. The protruding high-density polyethylene is rubbed during the production process and separated from the soft phase and falls off onto the calender roll. The powder accumulation area on the stretching calender roll > 50%, and there are many film breakages, affecting the smoothness of production.

[0178] In the upper surface layer of the BOPP matting film of Comparative Example 7, the content of maleic anhydride-styrene melt grafted random copolymer polypropylene added is less than 5wt%. It cannot effectively prevent the protruding high-density polyethylene from being rubbed and falling off during the production process. The powder accumulation area on the stretching calender roll is between 20% and 50%, and there are many film breakages, affecting the smoothness of production.

[0179] In the upper surface layer of the BOPP matting film of Comparative Example 8, the content of maleic anhydride-styrene melt grafted random copolymer polypropylene added is higher than 8wt%. The content of rigid groups in the grafted product is too much, resulting in the film becoming brittle, reducing the mechanical properties of the film, the tensile strength of the film becoming lower, and there are many film breakages, affecting the smoothness of production.

[0180] In the upper surface layer of the BOPP matting film of Comparative Example 9, the grafting rate of the styrene-maleic anhydride copolymer in the maleic anhydride-styrene melt grafted random copolymer polypropylene added is less than 45%. The powder accumulation area on the stretching calender roll > 50%, and there are many film breakages, affecting the smoothness of production.

[0181] In the upper surface layer of the BOPP matting film of Comparative Example 10, the grafting rate of the styrene-maleic anhydride copolymer in the maleic anhydride-styrene melt grafted random copolymer polypropylene added is higher than 55%. Due to too many grafted chains, the voids between molecular chains increase, reducing the mechanical strength of the film, and the tensile strength of the film becomes lower.

[0182] In the BOPP matting film applicable to the direct coating process of the present invention, 2-3wt% of n-alkyl chain modified hyperbranched polyester is added to the upper surface layer. While ensuring a good matting effect, it also improves the crystallization performance of high-density polyethylene, thereby improving the surface roughness of the matting layer of the matting film. The silica in the anti-scratch oil for the direct coating process can be effectively hidden between the soft phase and the hard phase in the matting layer, without being overly exposed on the surface of the anti-scratch layer, improving the problem of dense white "pockmarks" appearing on the surface of the matting film after coating. In addition, 5-8wt% of maleic anhydride-styrene melt grafted random copolymer polypropylene is added to the upper surface layer, improving the problem that the hard-phase high-density polyethylene is prone to falling off and accumulating powder during the process of contacting the stretching roll, ensuring the appearance quality of the film surface and the smoothness of production, and meeting the requirements of subsequent processing.

[0183] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to cover these modifications and deformations.

Claims

1. A BOPP matte film applicable to the direct coating process, characterized in that: It includes a top surface layer, an intermediate core layer, and a bottom surface layer arranged in sequence; the top surface layer is a matte layer and includes random copolymer polypropylene, 40wt% high-density polyethylene, 3wt% n-alkyl chain modified hyperbranched polyester, and 5wt% maleic anhydride-styrene melt-grafted random copolymer polypropylene; the intermediate core layer includes homopolypropylene; the bottom surface layer includes homopolypropylene; the grafting rate of saturated n-alkyl monohydric alcohol in the n-alkyl chain modified hyperbranched polyester is 80%, and the branching degree of the hyperbranched polyester is 0.8; at 230°C and under a load of 2.16 kg, the melt index of the maleic anhydride-styrene melt-grafted random copolymer polypropylene is 9 g / 10min; the maleic anhydride-styrene melt-grafted random copolymer polypropylene is prepared by a melt grafting method. Styrene monomer and maleic anhydride monomer are added to xylene solvent, and azobisisobutyronitrile is used as an initiator. Styrene-maleic anhydride copolymer is obtained by free radical copolymerization method. Then, using dicumyl peroxide as an initiator, the styrene-maleic anhydride copolymer is grafted onto the random copolymer polypropylene molecular chain by a melt grafting method to form a branched chain, and the maleic anhydride-styrene melt-grafted random copolymer polypropylene is obtained; the molar ratio of the maleic anhydride monomer to the styrene monomer in the feed is (2:4)~(2:5); the grafting rate of the styrene-maleic anhydride copolymer is 55%.

2. The BOPP matte film applicable to the direct coating process according to claim 1, characterized in that: The preparation method of the n-alkyl chain modified hyperbranched polyester is as follows: Using p-toluenesulfonic acid as a catalyst, 2-carboxyethylphenylphosphinic acid and trimethylolpropane are synthesized to obtain hyperbranched polyester, and the obtained hyperbranched polyester reacts with saturated n-alkyl monohydric alcohol by an esterification reaction to obtain the n-alkyl chain modified hyperbranched polyester; the saturated n-alkyl monohydric alcohol includes one or more of n-butanol, n-pentanol, and n-hexanol.

3. The BOPP matte film applicable to the direct coating process according to claim 1, characterized in that: The random copolymer polypropylene is a random ethylene-propylene copolymer; at 230°C and under a load of 2.16 kg, the melt index of the random copolymer polypropylene is 6~10 g / 10min; at 190°C and under a load of 2.16 kg, the melt index of the high-density polyethylene is 9~20 g / 10min; the homopolypropylene in the intermediate core layer and the bottom surface layer has a melt index of 3~8 g / 10min at 230°C and under a load of 2.16 kg.

4. The BOPP matte film applicable to the direct coating process according to claim 1, characterized in that: The intermediate core layer further includes 1~3wt% antistatic agent; the bottom surface layer further includes 0.1~0.5wt% anti-blocking agent, and the anti-blocking agent is one or more of silica, talcum powder, and calcium carbonate, and the particle size of the anti-blocking agent is 3~6μm.

5. A method for preparing a BOPP matte film applicable to the direct coating process according to any one of claims 1 to 4, characterized in that: It includes the following steps: The first step: batching and plasticizing: Set the raw material usage ratio in the control system of the biaxially oriented film production line, and then the batching system automatically transports the dried raw materials of each layer to the extruder according to the input ratio. After melting and plasticizing in the extruder, the melt enters the die through the runner and the distributor. The second step: casting sheet: After being extruded by the die, the melt immediately contacts the chill roll to form a thick sheet. Step 3: Longitudinal stretching: The thick sheet is heated to a set temperature by multiple groups of preheating rollers, starts longitudinal stretching, and then is shaped. Step 4: Transverse stretching: After preheating the thick sheet that has undergone longitudinal stretching to a set temperature, start transverse stretching, and then perform shaping and cooling treatments to obtain a multi-layer structure film. Step 5: Traction and winding: The multi-layer structure film exiting the transverse stretching unit enters the traction unit, undergoes thickness measurement and corona treatment, and then enters the winding unit to obtain a master roll. Step 6: Slitting: The master roll that has undergone aging treatment is slit to obtain film rolls with specified widths and lengths.

6. The preparation method of the BOPP matte film applicable to the direct coating process according to claim 5, characterized in that: The melting and extrusion temperature of the upper surface layer: 200~260 °C; the melting and extrusion temperatures of the intermediate core layer and the lower surface layer: 230~260 °C; in the process where the melt contacts the chill roll, the temperature of the chill water and the chill roll: 15~50 °C; the temperature in the longitudinal stretching zone: 90~130 °C; the temperature in the transverse stretching zone: 155~165 °C; the longitudinal stretching ratio: 4.5~5.5 times; the transverse stretching ratio: 8~10 times; the corona power factor of the upper surface layer: 20~25 W·min / m.

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