BOPP matt film suitable for direct coating process and preparation method of BOPP matt film

Abstract

The invention relates to the field of matt films, in particular to a BOPP matt film suitable for a direct coating process and a preparation method of the BOPP matt film. The BOPP matt film suitable for the direct coating process comprises an upper surface layer, a middle core layer and a lower surface layer which are sequentially arranged, the upper surface layer is an extinction layer and comprises polypropylene random copolymer, 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 polypropylene random copolymer; the middle core layer comprises homo-polypropylene; and the lower surface layer comprises homo-polypropylene. According to the matt film, the roughness of the matt layer can be improved by optimizing the components of the matt layer, the problem of whitening'hard spots' on the surface of the matt film in a direct coating process is solved, and then the quality of a coated matt film product is improved, so that the appearance quality of products such as laminated paper, paper boxes and labels which are subsequently laminated is ensured.

Description

Technical Field

[0001] The present invention relates to the field of matting films, and particularly to a BOPP matting film applicable to a direct coating process and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene matting film (BOPP matting film) is usually a BOPP film with one matte side and one glossy side or both sides matte. It mainly achieves the matting effect by scattering light, which can improve the grade of printed outer packaging. Since the matting of the matting film gives a soft, fashionable and elegant high-class feeling and eliminates eye fatigue, the BOPP matting film is increasingly widely used in the packaging field, especially suitable for deep processing industries and fields such as coating and lamination. The main components of the matting layer of the BOPP matting film are random copolymer polypropylene and high-density polyethylene (HDPE). The microstructure of the matting layer is similar to a "sea-island" structure. Specifically, during the biaxial stretching process of film formation, when the random copolymer polypropylene is still in a relatively soft phase, the high-density polyethylene completes part or most of the crystallization to become a hard phase due to a faster crystallization rate and a higher crystallization temperature. Therefore, during the stretching process, the high-density polyethylene in the matting layer, as the hard phase, will protrude compared with the random copolymer polypropylene soft phase, thus forming a sea-island morphology with different degrees of coarsening.

[0003] The BOPP matting film products for functional coating mainly refer to BOPP films with one smooth side and one matte side. Common processing applications are as follows: ① Using the BOPP matting film as the base material, after coating anti-scratch oil on the matte side, through die stamping (usually a non-corona matting film or a glossy film) and UV curing, a scratch-resistant matting film product is formed; ② Using the coated matting film as the base material for the direct coating process, after coating anti-scratch oil on the matte side, coating is carried out on the surface of the matting layer of the film by using an anilox roll. After coating, it is passed through an oven for UV curing and then wound up to complete the entire anti-scratch process, and a scratch-resistant layer is formed on the surface of the matting layer. The completed coated product is laminated with paper, paper boxes or made into labels after coating or pre-coating an adhesive layer on the smooth side. However, white "pockmarks" often appear on the surface of the scratch-resistant matting film prepared by the direct coating process, thus affecting the appearance quality of subsequent products such as laminated paper, paper boxes and labels. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a BOPP matting film applicable to the direct coating process and a preparation method thereof. By optimizing the material composition of the matting layer, improving the roughness of the matting layer to solve the problem of white "pockmarks" appearing on the surface of the film after the direct coating process, and further improving the appearance quality of the coated matting film product to ensure the appearance quality of subsequent products such as laminated paper, paper boxes and labels after lamination.

[0005] A BOPP matte film applicable to the direct coating process, comprising a top surface layer, an intermediate 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 intermediate 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 molding process, the anti-scratch oil components in the direct coating process generally include acrylic resin, silica (with a particle size generally of 3-5 μm), and a dispersion aid. After coating the anti-scratch oil, the 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 cross-linked structure to achieve function 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, the silica in the anti-scratch oil cannot be effectively embedded 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 light scattering relationship, 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 a 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 for the crystallization of high-density polyethylene, making it easier for the HDPE molecular chains to aggregate around the modified hyperbranched polyester and form crystal nuclei. Therefore, the addition of the 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 the n-alkyl chain-modified hyperbranched polyester reduces the melt viscosity of high-density polyethylene. The lower melt viscosity is conducive to the flow and rearrangement of the HDPE molecular chains during the processing, promoting the increase in the thickness of the HDPE microcrystals, and is more beneficial to obtaining a higher-roughness extinction layer surface. When the addition amount of the 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 the 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 non-uniformity 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 bulging becomes more obvious, which easily leads to a poor combination between the hard phase of high-density polyethylene and the soft phase of random copolymer polypropylene in the matte layer. During the production process, the surface area of the bulging high-density polyethylene in the matte layer contacting 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 jelly-like substance. When the jelly-like substance accumulates to a certain extent, it will affect the film surface appearance quality and production smoothness. Therefore, on the basis of the above solution, to ensure the film surface appearance quality and production smoothness of the BOPP matte film itself, the present invention also adds a certain amount of maleic anhydride-styrene melt-grafted random copolymer polypropylene to the matte layer. The random copolymer polypropylene in the maleic anhydride-styrene melt-grafted random copolymer 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 between the hard phase of high-density polyethylene and the soft phase of random copolymer polypropylene, and making the bulging high-density polyethylene not easily separated from the soft phase by friction and fall off onto the pressure roller during the production process, thus ensuring the film surface appearance quality and production smoothness. Moreover, the cyclic rigid structure of styrene can improve the conformation of the random copolymer polypropylene molecular chain, making it more regularly arranged, which is beneficial to the formation of random copolymer polypropylene crystals. The branched chain structure of maleic anhydride-styrene melt-grafted random copolymer polypropylene is beneficial to increasing the crystallization temperature of the soft phase of random copolymer polypropylene, improving the hardness of the soft phase of random copolymer polypropylene wrapping the surface of the high-density polyethylene hard phase. Then, during the production process, when the matte layer contacts the pressure roller and is subjected to friction, the soft phase of random copolymer polypropylene wrapping 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 film surface appearance quality and production smoothness. When the addition amount of maleic anhydride-styrene melt-grafted random copolymer polypropylene is less than 5wt%, it cannot effectively protect the bulging high-density polyethylene from being rubbed off during the production process, affecting the production smoothness. When the addition amount of maleic anhydride-styrene melt-grafted random copolymer polypropylene is higher than 8wt%, excessive polar groups of maleic anhydride may over-crosslink with the soft phase of random copolymer polypropylene to form rigid microdomains, restricting the segment movement 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 maleic anhydride-styrene melt-grafted random copolymer polypropylene improves the roughness of the matte layer while ensuring the film surface appearance quality and production smoothness of the BOPP matte film itself, meeting the requirements of the subsequent direct coating process of the BOPP matte film product, improving the problem of "pockmarks" with whitening on the surface of the scratch-resistant matte film prepared by the direct coating process, and further improving the appearance quality of the coated matte 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 obtain a 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 of the n-alkyl chain modified hyperbranched polyester with the hard-phase high-density polyethylene and the crystallization performance of the hard-phase high-density polyethylene, and then 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%, it will overly restrict the movement of the high-density polyethylene molecular chain, 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.

[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 "pockmarks" 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 steric hindrance increases, resulting in the n-alkyl chain modified hyperbranched polyester being unable to effectively penetrate between the molecular chains of HDPE, leading to 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 "pockmarks" on the surface of the scratch-resistant matte film prepared by the direct coating process.

[0011] Furthermore, the maleic anhydride-styrene melt-grafted random copolymerized 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. Styrene-maleic anhydride copolymer is obtained by free radical copolymerization. Then, dicumyl peroxide is used as the initiator, and the styrene-maleic anhydride copolymer is grafted onto the random copolymerized polypropylene molecular chain by the melt-grafting method 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) 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 groups and random copolymerized polypropylene is reduced, affecting the grafting rate, resulting in too low a 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 random copolymerized polypropylene molecular chain, resulting in too high a grafting rate of maleic anhydride-styrene. Due to too many grafted chains, the voids between the molecular chains increase, reducing the mechanical strength of the film. The maleic anhydride-styrene melt-grafted random copolymerized polypropylene obtained within the above grafting rate range of the styrene-maleic anhydride copolymer has the best hardness and the best effect on improving the compatibility between the matte layer high-density polyethylene and random copolymerized polypropylene. The random copolymerized polypropylene used to prepare the maleic anhydride-styrene melt-grafted random copolymerized polypropylene is the same as the soft-phase random copolymerized 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 copolymer polypropylene is 7-9 g / 10 min. If the melt index of the maleic anhydride-styrene melt-grafted random copolymer polypropylene is lower than 7 g / 10 min, it is not conducive to the dispersion of the maleic anhydride-styrene melt-grafted random copolymer polypropylene in the soft-phase random copolymer polypropylene, affecting the heterogeneous nucleation of the soft-phase random copolymer polypropylene and being unfavorable for the improvement of the hardness of the soft-phase random copolymer polypropylene; if the melt index of the maleic anhydride-styrene melt-grafted random copolymer polypropylene is higher than 9 g / 10 min, the maleic anhydride-styrene melt-grafted random copolymer polypropylene accelerates the crystallization rate of the soft-phase random copolymer polypropylene, but the crystallinity decreases, which is also unfavorable for the improvement of the hardness of the soft-phase random copolymer polypropylene.

[0013] Further, the random copolymer polypropylene is a random ethylene-propylene copolymer; at 230 °C and a load of 2.16 kg, the melt index of the random copolymer 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 intermediate 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 copolymer polypropylene within the above melt index ranges is conducive to obtaining a BOPP matte film with good overall matte 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 intermediate 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 contamination of the guide roller, and at the same time increasing the haze and reducing 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: 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 conveys 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 through the runner and distributor. Step 2: Sheet casting: After being extruded from the die head, 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 rolls, starts longitudinal stretching, and then is shaped. Step 4: Transverse stretching: After the thick sheet that has undergone longitudinal stretching is preheated to a set temperature, transverse stretching is started, and then shaping and cooling treatments are carried out 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 a film roll with a specified width and length.

[0016] Furthermore, the melting and extrusion temperature of the upper surface layer: 200 - 260 °C; the melting and extrusion temperature 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.

[0017] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0018] Figure 1 It is a schematic structural diagram of the BOPP matte film applicable to the direct coating process described in Embodiments 1 - 3 of the present invention and the BOPP matte films described in Comparative Examples 1 - 10. Detailed Embodiments

[0019] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, 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 of 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 protected by the embodiments of the present application.

[0020] 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 dictates otherwise. It should also be understood that the term " / and" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0021] 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 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.

[0022] In addition, in the description of the present application, unless otherwise specified, " / and" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A / and B can 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.

[0023] 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.

[0024] A BOPP matte film suitable for direct coating process, comprising a top layer, a middle core layer, and a bottom layer arranged in sequence; the top layer is a matte layer, comprising random copolymer 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 copolymer polypropylene; the middle core layer comprises homopolypropylene; the bottom layer comprises homopolypropylene.

[0025] Further, the preparation method of the n-alkyl chain modified hyperbranched polyester is as follows: using p-toluenesulfonic acid as a catalyst, synthesizing hyperbranched polyester by reacting 2-carboxyethylphenylphosphinic acid and trimethylolpropane, and carrying out an esterification reaction between the obtained hyperbranched polyester and 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.

[0026] Further, the grafting rate of the saturated n-alkyl monohydric alcohol in the n-alkyl chain modified hyperbranched polyester is 60-80%.

[0027] Further, the degree of branching of the hyperbranched polyester is 0.6-0.8.

[0028] 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. A styrene-maleic anhydride copolymer is obtained through free radical copolymerization. Then, dicumyl peroxide is used as an initiator, and the styrene-maleic anhydride copolymer is grafted onto the molecular chain of random copolymerized polypropylene through a melt grafting method to form branches, thus 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.

[0029] 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.

[0030] 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.

[0031] Further, the middle core layer further includes 1 - 3 wt% antistatic agent, and the antistatic agent is a quaternary ammonium salt-based methacrylate copolymer. The lower surface layer further includes 0.1 - 0.5 wt% antiblocking agent, and the antiblocking agent is one or more of silica, talc powder, and calcium carbonate. The particle size of the antiblocking agent is 3 - 6 μm. To balance the surface layer thickness and peeling problem, it is preferably 4 - 5 μm.

[0032] 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.

[0033] A preparation method of the BOPP matte film applicable to the direct coating process includes the following steps: Step 1: Batching and Plasticization: Set the proportion of raw materials used in the control system of the biaxially stretched film production line. Then, the batching system automatically conveys the dried raw materials of each layer to the extruder according to the input proportion. After melting and plasticizing in the extruder, the melt enters the die head through the runner and distributor; Step 2: Sheet Casting: After being extruded from the die head, 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 rolls and 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, it starts transverse stretching, and then is shaped and cooled to obtain a multi-layer structure film; Step 5: Traction and Rewinding: The multi-layer structure film exiting the transverse stretching unit enters the traction unit. After thickness measurement and corona treatment, it enters the rewinding unit to obtain a master roll; Step 6: Slitting: The master roll that has undergone aging treatment is slit to obtain a film roll with a specified width and length.

[0034] Furthermore, the melting extrusion temperature of the upper surface layer: 200 - 260 °C; the melting 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.

[0035] The physical property indexes and their testing methods of the embodiments or comparative examples of the present invention are specifically as follows: The melt mass-flow rate (MFR) is measured according to GB / T3682-2018.

[0036] Powder accumulation on the longitudinal stretching compression roll: During production, after continuous production for 24 hours, measure the powder accumulation on the stretching compression roll in the longitudinal stretching area that contacts the matte layer. Judge by measuring the area of the powder accumulation on the width of the stretching compression roll (good effect: the area of the powder accumulation on the stretching compression roll is 0 - 20% (including 20%); general effect: the area of the powder accumulation on the stretching compression roll is 20 - 50% (including 50%); poor effect: the area of the powder accumulation on the stretching compression roll is > 50%)); The tensile strength is tested according to GB / T1040.3.

[0037] The glossiness test is carried out according to the standard of GB / T8807-1988.

[0038] The haze test is carried out according to GB / T2410-2008.

[0039] The roughness test is carried out in accordance with GB / T 6062-2009.

[0040] Appearance white dot situation of the BOPP matte film after direct coating process: Select a 1-square-meter sample, horizontally place the sample flat on the detection table with a black background (coating surface up, light surface 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 / 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.

[0041] In the following examples and comparative examples, the n-alkyl chain modified hyperbranched polyester is obtained by the esterification reaction of hyperbranched polyester and n-butanol.

[0042] Example 1 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 .

[0043] The preparation methods of the resins of each layer of the BOPP matte film applicable to the direct coating process in this example are as follows: Preparation of the resin of the upper surface layer 1: Take 40 wt% of random copolymerized 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 branching degree 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 copolymerized 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 resin of the upper surface layer 1.

[0044] Preparation of the resin of 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 of the middle core layer 2.

[0045] Preparation of the resin of the lower surface layer 3: 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 resin of the lower surface layer 3.

[0046] The preparation method of the BOPP matte film applicable to the direct coating process in this embodiment includes the following steps: 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 head through the runner and distributor; Sheet casting: After being extruded from the die head, the melt immediately contacts the cooling roll to form a thick sheet; Longitudinal stretching: The thick sheet is heated to the set temperature by multiple groups of preheating rolls, starts longitudinal stretching, and then is shaped; 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; 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; Slitting: The master roll that has undergone aging treatment is slit to obtain a film roll with a specified width and length.

[0047] The melting and extrusion temperature of the upper surface layer 1 is 235 °C; the melting and extrusion temperature of the middle core layer 2 is 250 °C; the melting and extrusion temperature of the lower surface layer 3 is 250 °C; in the process where the melt contacts the chill roll, the chill water and the temperature of the chill roll are 40 °C; the temperature of longitudinal stretching is 125 °C; the temperature of 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.

[0048] 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.

[0049] Example 2 This embodiment 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 .

[0050] The preparation method of the resins of each layer of the BOPP matte film applicable to the direct coating process in this embodiment is as follows: 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 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.

[0051] 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.

[0052] 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.

[0053] 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.

[0054] 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.

[0055] Example 3 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 .

[0056] 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: Preparation of the resin for the upper surface layer 1: Take 52 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), 40 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), 3 wt% of n-alkyl chain modified hyperbranched polyester (the degree of branching of the hyperbranched polyester is 0.8; the 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 copolymer polypropylene (with a melt index of 9 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of the styrene-maleic anhydride copolymer is 55%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] Comparative Example 1 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. The specific structure can be referred to Figure 1 .

[0062] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows: 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), 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 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.

[0063] 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.

[0064] 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 antiblocking agent (silica, particle size: 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0065] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0066] 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.

[0067] Comparative Example 2 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 .

[0068] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows: 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), 46 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), 1 wt% of n-alkyl chain modified hyperbranched polyester (branching degree of the hyperbranched polyester: 0.7; grafting rate of n-butanol in the n-alkyl chain modified hyperbranched polyester: 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; grafting rate of the styrene-maleic anhydride copolymer: 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0069] 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.

[0070] 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 anti-blocking agent (silica, particle size is 4.5 µm), mix them evenly to obtain the lower surface layer 3 resin.

[0071] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0072] 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.

[0073] Comparative Example 3 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 .

[0074] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows: Preparation of the upper surface layer 1 resin: Take 47 wt% of random copolymer polypropylene (melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 42 wt% of high-density polyethylene (melt index measured under the conditions of 190 °C and 2.16 kg is 15 g / 10 min), 5 wt% of n-alkyl chain modified hyperbranched polyester (branching degree 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 (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%), mix them evenly to obtain the upper surface layer 1 resin.

[0075] 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 antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), mix them evenly to obtain the middle core layer 2 resin.

[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 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 in this comparative example is the same as that in Example 1.

[0078] 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.

[0079] Comparative Example 4 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. The specific structure can be referred to Figure 1 .

[0080] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows: 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 40%), 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.

[0081] 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.

[0082] 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.

[0083] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0084] 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.

[0085] Comparative Example 5 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. The specific structure can be referred to Figure 1 .

[0086] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows: 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 90%), 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.

[0087] 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.

[0088] 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.

[0089] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0090] 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.

[0091] Comparative Example 6 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 .

[0092] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows: 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), 51 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 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.

[0093] 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.

[0094] 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.

[0095] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0096] 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.

[0097] Comparative Example 7 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, refer to Figure 1 。

[0098] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows: 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 styrene-maleic anhydride copolymer is 50%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0099] 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.

[0100] Preparation of the resin for the lower surface layer 3: Take 99.7 wt% of homopolypropylene (isotacticity of 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 anti-blocking agent (silica, particle size of 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

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

[0102] 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.

[0103] Comparative Example 8 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 .

[0104] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows: 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), 41 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 10 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.

[0105] 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.

[0106] 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.

[0107] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0108] 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.

[0109] Comparative Example 9 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 .

[0110] The preparation methods of the resins for each layer of the BOPP matting film in this comparative example are as follows: Preparation of the upper surface layer 1 resin: Take 47 wt% of random copolymer polypropylene (melt index measured under the conditions of 230 °C and 2.16 kg is 8 g / 10 min), 45 wt% of high-density polyethylene (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 (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%), mix them evenly to obtain the upper surface layer 1 resin.

[0111] 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.

[0112] 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.

[0113] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0114] 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.

[0115] Comparative Example 10 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 .

[0116] The preparation methods of the resins for each layer of the BOPP matte film in this comparative example are as follows: 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 60%), and mix them evenly to obtain the resin for the upper surface layer 1.

[0117] 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.

[0118] 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 anti-blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer 3.

[0119] The preparation method of the BOPP matte film in this comparative example is the same as that of Example 1.

[0120] 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.

[0121] 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 were used to prepare matte films with scratch-resistant layers according to the following direct coating process flow. Specifically: The scratch-resistant oil was uniformly transferred to the matte surface of the coated matte film by means of an anilox roll. The components of the scratch-resistant 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 a scratch-resistant layer of the film (with a thickness of 2-3 µm). The cured film is wound up after cooling, and finally, it is rewound, slit, and packaged according to requirements.

[0122] 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.

[0123] Table 1

[0124] Combined with the above performance test data, it can be seen that: In the upper surface layer of the BOPP matte film in Comparative Example 1, the n-alkyl chain-modified hyperbranched polyester is not added, so the roughening degree of the surface of the matte layer of the matte film cannot be improved, and the silica solid particle substances 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.

[0125] In the upper surface layer of the BOPP matte film in Comparative Example 2, the content of the n-alkyl chain-modified hyperbranched polyester added 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 are still a small part of the silica solid particle substances 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.

[0126] In the upper surface layer of the BOPP matte film in Comparative Example 3, the content of the n-alkyl chain-modified hyperbranched polyester added 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.

[0127] In the upper surface layer of the BOPP matte film in Comparative Example 4, the n-butanol grafting rate of the n-alkyl chain-modified hyperbranched polyester added is lower 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.

[0128] The grafting rate of n - alkyl chain - modified hyperbranched polyester with n - butanol added to the upper surface layer of the BOPP matte film in Comparative Example 5 is higher than 80%. The n - butanol chain segments restrict the movement of high - density polyethylene molecular chains, which is not conducive to the crystallization of high - density polyethylene and cannot increase the roughness of the matte layer. After coating, the BOPP matte film shows dense white "pockmarks" on the matte surface.

[0129] Maleic anhydride - styrene melt - grafted random copolymer polypropylene is not added to the upper surface layer of the BOPP matte film in Comparative Example 6. The protruding high - density polyethylene is rubbed during the production process and separated from the soft phase and falls onto the calender roll. The powder - accumulating area on the calender roll is > 50%, and there are many film breakages, which affect the smoothness of production.

[0130] The content of maleic anhydride - styrene melt - grafted random copolymer polypropylene added to the upper surface layer of the BOPP matte film in Comparative Example 7 is lower than 5wt%. It cannot effectively prevent the protruding high - density polyethylene from being rubbed off during the production process. The powder - accumulating area on the calender roll is between 20% and 50%, and there are many film breakages, which affect the smoothness of production.

[0131] The content of maleic anhydride - styrene melt - grafted random copolymer polypropylene added to the upper surface layer of the BOPP matte film in Comparative Example 8 is higher than 8wt%. The content of rigid groups in the grafted product is too high, resulting in the film becoming brittle, reducing the mechanical properties of the film, lowering the tensile strength of the film, and having many film breakages, which affect the smoothness of production.

[0132] The grafting rate of the styrene - maleic anhydride copolymer in the maleic anhydride - styrene melt - grafted random copolymer polypropylene added to the upper surface layer of the BOPP matte film in Comparative Example 9 is lower than 45%. The powder - accumulating area on the calender roll is > 50%, and there are many film breakages, which affect the smoothness of production.

[0133] The grafting rate of the styrene - maleic anhydride copolymer in the maleic anhydride - styrene melt - grafted random copolymer polypropylene added to the upper surface layer of the BOPP matte film in Comparative Example 10 is higher than 55%. Due to the excessive grafted chains, the voids between molecular chains increase, reducing the mechanical strength of the film and lowering the tensile strength of the film.

[0134] In the BOPP matte film applicable to the direct coating process of the present invention, 2-3 wt% of n-alkyl chain modified hyperbranched polyester is added to the upper surface layer. While ensuring good matte effect, it also improves the crystallization performance of high-density polyethylene, thereby increasing the surface roughness of the matte layer of the matte 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 matte layer, without excessive exposure on the surface of the anti-scratch layer, improving the problem of dense white "pockmarks" on the surface of the matte film after coating. In addition, 5-8 wt% 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 powder accumulation during the friction with the stretching roller, ensuring the appearance quality of the film surface and the smoothness of production, and meeting the requirements of subsequent processing. The above embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it cannot be understood as a limitation on 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 include these modifications and deformations.

Claims

1. A BOPP matte film suitable for direct coating process, characterized by: The invention comprises an upper surface layer, an intermediate core layer and a lower surface layer which are arranged in sequence; the upper surface layer is a matte layer, comprising random copolymerized polypropylene, 40-51wt% high-density polyethylene, 2-3wt% normal alkyl chain modified hyperbranched polyester and 5-8wt% maleic anhydride-styrene melt grafted random copolymerized polypropylene; the intermediate core layer comprises homopolymerized polypropylene; and the lower surface layer comprises homopolymerized polypropylene.

2. The BOPP matte film suitable for 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 prepare a 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.

3. The BOPP matte film suitable for direct coating process according to claim 2, characterized in that: The grafting rate of saturated n-alkyl monohydric alcohol in the n-alkyl chain modified hyperbranched polyester is 60-80%.

4. The BOPP matte film suitable for direct coating process according to claim 2, characterized in that: The branching degree of the hyperbranched polyester is 0.6-0.

8.

5. The BOPP matte film suitable for direct coating process according to claim 1, characterized in that: The maleic anhydride-styrene melt grafted random copolymer polypropylene is prepared by a melt grafting method, wherein styrene monomer and maleic anhydride monomer are added to a xylene solvent, azobisisobutylnitrile is used as an initiator, and a styrene-maleic anhydride copolymer is prepared by a free radical copolymerization method, and then dicumyl peroxide is used as an initiator, and the styrene-maleic anhydride copolymer is grafted onto the random copolymer polypropylene molecular chain by a melt grafting method to form a branched chain, thereby 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); and the grafting rate of the styrene-maleic anhydride copolymer is 45-55%.

6. The BOPP matte film suitable for direct coating process according to claim 1, characterized in that: At 230° C. and a load of 2.16 kg, the melt index of the maleic anhydride-styrene melt grafted random copolymer polypropylene is 7-9 g / 10 min.

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

8. The BOPP matte film suitable for direct coating process according to claim 1, characterized in that: The middle core layer also includes 1-3wt% antistatic agent; the lower surface layer also includes 0.1-0.5wt% anti-adhesive agent, the anti-adhesive agent is one or more of silicon dioxide, talcum powder, and calcium carbonate, and the particle size of the anti-adhesive agent is 3-6μm.

9. A method for preparing a BOPP matte film suitable for direct coating process according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: Batching and plasticization: The raw material usage ratio is set in the control system of the biaxial stretch film production line, and 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; Step 2: Slab casting: After being extruded through the die head, the melt immediately contacts the chilled roller to form a thick sheet; Step 3: longitudinal stretching: the thick sheet is heated to a set temperature by multiple sets of preheating rollers, and then longitudinal stretching is started, and then shaping is performed; Step 4: Transverse stretching: preheating the longitudinally stretched thick sheet to a set temperature, starting transverse stretching, and then performing shaping and cooling treatment to obtain a multi-layer structure film; Step 5: traction and reeling: the multi-layer film exiting the transverse stretching unit enters the traction unit, and after thickness measurement and corona treatment, enters the reeling unit to obtain a parent roll; Step 6: Slitting: Slitting the mother roll after aging treatment to obtain film rolls of specified width and length.

10. The method for preparing a BOPP matte film suitable for direct coating process according to claim 9, characterized in that: 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 where the melt contacts 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; the corona power factor of the upper surface layer is 20-25W·min / m.

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