BOPP (biaxially-oriented polypropylene) matt film for smooth inner printing and preparation method of BOPP matt film

Abstract

The invention relates to the field of matt films, in particular to a BOPP (biaxially-oriented polypropylene) matt film for smooth inner printing and a preparation method of the BOPP matt film. The BOPP matt film for smooth inner printing comprises an upper surface matt layer, a middle core layer and a lower surface smooth layer which are sequentially arranged, the upper surface layer comprises high-density polyethylene and polypropylene random copolymer; the middle core layer is prepared from homo-polypropylene and 5 to 10 weight percent of poly (p-vinylphenol) grafted polypropylene; the smooth surface layer of the lower surface layer comprises polypropylene random copolymer and 30-40wt% of styrene-maleic anhydride copolymer melt-grafted polypropylene random copolymer. According to the BOPP matt film for smooth surface inner printing and the preparation method of the BOPP matt film, the thickness uniformity of the BOPP matt film and the surface tension performance of the smooth surface are improved by optimizing the material components of the middle core layer and the lower surface smooth surface layer, and the printing requirement of smooth surface inner printing of BOPP matt film products and the high-speed automatic production requirement of the BOPP matt film products are met.

Description

Technical Field

[0001] The present invention relates to the field of matte films, and particularly to a BOPP matte film for printing on the glossy side and a preparation method thereof. Background Art

[0002] A BOPP matte film is usually a BOPP film with one matte side and one glossy side or both sides matte. It mainly achieves the matte effect by scattering light, which can enhance the grade of printed outer packaging. Since the matte effect of the matte film gives a soft, fashionable and elegant high-class feeling and eliminates eye fatigue, the BOPP matte film is increasingly widely used in the packaging field, especially suitable for deep processing industries and fields such as coating and laminating. Usually, most applications of BOPP matte film products are printed on the matte side. However, for some relatively high-end processing applications, the matte film products are required to meet the requirements of printing on the glossy side: taking the BOPP matte film as the base material, after printing the required pattern on the glossy side, ① applying PE glue by curtain coating on the printed glossy side and then laminating with foam cotton to make wallpaper; or ② laminating with paper, paper box or making labels after applying an immediate coating or pre-coated adhesive layer on the printed glossy side. This application method belongs to internal printing. The purpose is to print the required pattern on the glossy side of the BOPP matte film. After laminating it on paper or paper box, it can protect the ink without applying UV varnish or laminating other films again.

[0003] However, there are the following problems in the actual application process. When some downstream terminals use water-based ink for printing on the glossy side, there will be a problem that the water-based ink adheres poorly, resulting in the separation of the ink on the wallpaper products, laminated paper, and paper box from the BOPP base material, affecting the finished product effect; moreover, when the BOPP matte film base material is applied to the internal printing application scenario, there are often problems such as position deviation and inaccurate overprinting of the pattern printing, affecting the printing effect. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide a BOPP matte film for printing on the glossy side and a preparation method thereof. By optimizing the material components of the middle core layer and the lower surface glossy layer, on the one hand, the thickness uniformity of the BOPP matte film is improved, and the problems of position deviation and inaccurate overprinting of the pattern printing on the glossy side are improved. On the other hand, the adhesion between the glossy layer and the ink is enhanced, and the problem of poor adhesion of water-based ink is improved, meeting the printing application requirements of the glossy layer internal printing of BOPP matte film products.

[0005] The BOPP matte film of the present invention is achieved through the following detailed technical solutions: A BOPP matting film for inside printing on the glossy surface, comprising a top surface matting layer, an intermediate core layer, and a bottom surface glossy layer arranged in sequence; the top surface matting layer comprises high-density polyethylene and random copolymer polypropylene; the intermediate core layer comprises homopolypropylene and 5-10 wt% of poly(p-vinylphenol) grafted polypropylene; the bottom surface glossy layer comprises random copolymer polypropylene and 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene.

[0006] Through the research of the inventor, it is found that the reason for the poor adhesion between the water-based ink and the glossy layer is that the non-polarity of the polypropylene in the glossy layer cannot form effective chemical bonding or physical adsorption with the polar resin in the water-based ink; and the main reasons for the printing effect problems such as the position deviation and inaccurate overprinting of the pattern printing are the insufficient thickness uniformity of the BOPP matting film substrate. Different application scenarios have different requirements for the thickness uniformity of the BOPP matting film substrate. For example, the thickness of the conventional water-based glue coating is generally 2-3 µm, but when the BOPP matting film substrate is applied to the inside printing application scenario, full-color printing is usually carried out on the glossy surface, and the thickness of the ink printing is generally 1-1.5 µm, with higher requirements for the thickness uniformity of the substrate. The BOPP matting film for inside printing on the glossy surface of the present invention has a three-layer structure, and the intermediate core layer is the main reflection layer of the film mechanical properties and the main provider of thickness uniformity. In the conventional homopolypropylene core layer, the molecular weight distribution of homopolypropylene is relatively wide, the chain entanglement density of the high molecular weight chain segments is high, the orientation resistance is large during the biaxial stretching process, the local stretching rate decreases, resulting in uneven molecular chain orientation, while the low molecular weight chain segments have strong fluidity in the amorphous region and are prone to preferentially respond to the tensile stress to form local high-orientation regions. Different molecular weight chain segments respond differently during the biaxial stretching process, forming local stress concentration and density gradient, thus causing thickness deviation; in addition, the remaining amorphous chain segments after biaxial stretching will undergo secondary crystallization (the crystallinity increases by 3-5%) during the aging treatment process, and the dynamic volume change caused by the relaxation and retraction of the amorphous region chain segments will affect the thickness uniformity; therefore, the conventional homopolypropylene cannot meet the requirements for the thickness uniformity of the BOPP matting film substrate in the inside printing application on the glossy surface.

[0007] In a BOPP matting film for smooth surface internal printing of the present invention, 5-10 wt% of poly(4-vinylphenol) grafted polypropylene is added to the homopolypropylene in the middle core layer. Since the main chain of the poly(4-vinylphenol) grafted polypropylene is polypropylene, it has good compatibility with the homopolypropylene in the middle core layer, so that the 4-vinylphenol branches are evenly dispersed in the homopolypropylene. Moreover, the polar hydroxyl groups in the 4-vinylphenol branches of the poly(4-vinylphenol) grafted polypropylene interact with the molecular chains of the homopolypropylene through dipole interaction, partially destroying the entanglement network of the high molecular weight chain segments in the homopolypropylene, reducing the entanglement density and the orientation resistance during the stretching process. The rigid benzene ring groups in the 4-vinylphenol branches, due to the rigid support of the molecular chains, inhibit the excessive flow of the low molecular weight chain segments in the homopolypropylene through steric hindrance effects, restricting the excessive relaxation of the low molecular weight chain segments. Specifically, on the one hand, the entanglement of the high molecular weight chain segments is reduced, and on the other hand, the excessive relaxation of the low molecular weight chain segments is restricted, narrowing the difference in the stretching rates of the high molecular weight chain segments and the low molecular weight chain segments, making the molecular chain orientation more uniform, which is beneficial to improving the thickness uniformity of the middle core layer of the BOPP matting film. In addition, the polar hydroxyl groups in the 4-vinylphenol branches form dynamic physical crosslinks with the chain segments in the amorphous region of the homopolypropylene, restricting the relaxation and secondary crystallization of the amorphous chain segments of the homopolypropylene. After the movement of the chain segments in the amorphous region is restricted, the amplitude of the thickness fluctuation during the post-treatment process is significantly reduced, which is also beneficial to improving the thickness uniformity of the BOPP matting film. If the addition amount of the poly(4-vinylphenol) grafted polypropylene is less than 5 wt%, due to the insufficient content of the 4-vinylphenol branches, the rigid benzene ring groups and hydrogen bond interactions cannot effectively restrict the molecular chain movement and optimize the orientation movement of the molecular chains during stretching, and the overall thickness uniformity of the BOPP matting film cannot be improved; if the addition amount of the poly(4-vinylphenol) grafted polypropylene is higher than 10 wt%, due to the excessive physical crosslinking points of the network caused by the rigid benzene ring groups and hydrogen bond interactions of the 4-vinylphenol branches, the brittleness of the BOPP matting film will be too high, increasing the risk of film breakage during the biaxial stretching process and affecting the smoothness of production.

[0008] In addition, for a BOPP matte film for internal printing on a smooth surface of the present invention, 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is added to the lower surface light layer. The matrix resin of the graft polymer, the random copolymer polypropylene in the main chain, has good compatibility with the homopolymer polypropylene in the lower surface light layer, enabling the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene to be effectively dispersed in the lower surface light layer. The styrene group in the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene has a rigid benzene ring structure. On the one hand, the rigid benzene ring structure has a certain steric hindrance. Through the rigid support of the molecular chain, it hinders the movement of the molecular chain of the copolymer polypropylene, enabling the melt to maintain better rheological stability during the stretching process. Moreover, the rigid benzene ring group can inhibit the melt fracture caused by local stress concentration during the stretching of the random copolymer polypropylene melt in the lower surface light layer, maintaining the uniformity of the film thickness, which is beneficial to improving the thickness uniformity of the lower surface light layer and synergistically improving the thickness uniformity of the intermediate layer, and a BOPP matte film with good overall thickness uniformity and high persistence of surface tension on the lower surface light layer can be obtained, which can improve the printing performance of the substrate and meet the application requirements of internal printing of downstream BOPP matte films. On the other hand, it is beneficial to slow down the attenuation rate of surface tension and improve the persistence of the surface tension of the light layer after corona treatment. Moreover, the polar group in maleic anhydride can form an effective bond with the polar resin in the water-based ink, making the ink easier to adhere to the lower surface of the BOPP matte film and more firmly adhered after attachment, effectively improving the printing performance of the lower surface light layer. If the addition amount of the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is less than 30 wt%, due to the insufficient maleic anhydride group and benzene ring rigid group, the printing performance of the lower surface light layer and the effect of synergistically improving the thickness uniformity of the core layer are not obvious. If the addition amount of the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is higher than 40 wt%, excessive maleic anhydride polar groups crosslink with the random copolymer polypropylene to form rigid microdomains and benzene ring rigid groups, overly restricting the movement of the chain segments and increasing the risk of film breakage.

[0009] In addition, poly(p-vinylphenol) grafted polypropylene added to the intermediate core layer, due to the grafted poly(p-vinylphenol) branches on the main chain and the phenolic hydroxyl group located at the end of the branch, and due to the polarity difference between the phenolic hydroxyl group and the hydrophobic homopolymer polypropylene main chain, the phenolic hydroxyl group will extend towards the surface of the polar lower surface light layer (printing surface). Synergistically with the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene added to the lower surface light layer, hydroxyl groups and anhydride groups with stronger polarity are enriched on the lower surface light layer (printing surface). These groups will form effective chemical bonding or physical adsorption with the polar resin in the water-based ink during the printing process, further improving the printing performance of the light layer of the BOPP matte film substrate.

[0010] Further, the preparation method of the poly(4-vinylphenol) grafted polypropylene is as follows: using benzoyl peroxide as an initiator, adding homopolypropylene and 4-vinylphenol into a mixer, and preparing the poly(4-vinylphenol) grafted polypropylene through a melt grafting process; the grafting rate of the 4-vinylphenol is 35-40%. The poly(4-vinylphenol) grafted polypropylene within the above grafting rate range of the 4-vinylphenol has the best effect on improving the molecular chain orientation of the core layer of the BOPP matte film, and the thickness uniformity of the obtained BOPP matte film substrate is the best, which can effectively cooperate with the lower surface light layer to improve the surface tension of the printing surface of the BOPP matte film and further improve the printing performance of the inside printing on the smooth surface of the BOPP matte film. If the grafting rate of the 4-vinylphenol is lower than 35%, due to insufficient grafted branches, the 4-vinylphenol branches cannot effectively narrow the difference in the stretching rates of the high molecular weight chain segments and the low molecular weight chain segments of the homopolypropylene, which is not conducive to the more uniform orientation of the homopolypropylene molecular chains, and there are not enough phenolic hydroxyl groups extending to the lower surface light layer, resulting in insufficient improvement in the surface tension of the lower surface light layer; if the grafting rate of the 4-vinylphenol branches is higher than 40%, the excessive aggregation of the branches will exacerbate the formation of physical crosslinks and cause crystallization defects, increasing the risk of film breakage during the biaxial stretching process of the film and affecting the smoothness of production.

[0011] Furthermore, the styrene-maleic anhydride copolymer 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 the styrene-maleic anhydride copolymer is prepared by a free radical copolymerization method, and then dicumyl peroxide is used as an initiator to graft the styrene-maleic anhydride copolymer onto the random copolymer polypropylene molecular chain by a melt grafting method; the content of the styrene monomer in the styrene-maleic anhydride copolymer is 4-5 mol%; and the grafting rate of the styrene-maleic anhydride copolymer is 45-55%. During the grafting process of random copolymer polypropylene with styrene-maleic anhydride copolymer, the maleic anhydride group will induce the degradation of homopolypropylene molecules, while the styrene monomer can inhibit the degradation, so that the styrene-maleic anhydride copolymer is effectively grafted onto the main chain of the random copolymer polypropylene. Therefore, the above-mentioned styrene monomer content range is conducive to obtaining a styrene-maleic anhydride copolymer with a high grafting rate while ensuring the mechanical strength of the film; if the content of the styrene monomer is lower than 4 mol%, the amount of the monomer that the styrene group reacts with the random copolymer polypropylene to generate macromolecular free radicals is too small, which affects the grafting rate of the styrene-maleic anhydride copolymer and is not conducive to solving the problem of decreased mechanical strength caused by degradation of the random copolymer polypropylene; if the content of the styrene monomer is higher than 5 mol%, too much styrene monomer will destroy the continuity of the molecular chain of the random copolymer polypropylene, resulting in decreased mechanical strength of the film. The BOPP matte film prepared by melt grafting random copolymerization of styrene-maleic anhydride copolymer with polypropylene within the above-mentioned grafting rate range has the best thickness uniformity and printing performance; if the grafting rate of styrene-maleic anhydride copolymer is lower than 45%, due to insufficient polar groups in maleic anhydride and styrene functional groups, the lower surface glossy layer of the BOPP matte film cannot effectively combine with the polar groups in the water-based ink to form a strong printing layer, and cannot effectively cooperate with the middle core layer to improve the thickness uniformity of the film; if the grafting rate of styrene-maleic anhydride copolymer is higher than 55%, when the grafting rate is too high, the excessive rigid structure of the benzene ring in the side chain leads to stress concentration, increasing the risk of film breakage and affecting the smoothness of production.

[0012] Furthermore, at 230°C and a load of 2.16kg, the melt index of the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is 7-9g / 10min. If the melt index is lower than 7g / 10min, the resistance of the melt of the lower surface smooth layer will increase when passing through the die head, which will easily cause pressure fluctuations, resulting in uneven thickness of the lower surface smooth layer and thus affecting the thickness uniformity of the BOPP matte film substrate; if the melt index is higher than 9g / 10min, it is not conducive to the uniform dispersion of the styrene-maleic anhydride side chain in the styrene-maleic anhydride copolymer in the random copolymer polypropylene, and stress concentration problems will easily occur during the biaxial stretching process, resulting in film breakage and affecting the smoothness of production.

[0013] Further, at 230°C and a load of 2.16 kg, the melt index of the poly(vinylphenol) grafted polypropylene is 7 - 11 g / 10 min. When the melt index is lower than 7 g / 10 min, the rigid benzene ring groups in the poly(vinylphenol) grafted polypropylene are unevenly dispersed in the homopolypropylene of the middle core layer, and stress concentration is likely to occur during the biaxial stretching process, resulting in film breakage and affecting the smoothness of production. When the melt index is higher than 11 g / 10 min, the melt viscosity of the homopolypropylene in the middle core layer will be reduced, leading to poor thickness uniformity due to insufficient melt strength during the biaxial stretching process, affecting the internal printing performance of the BOPP matte film substrate.

[0014] Further, at 190°C and a load of 21.6 kg, the melt index of the high-density polyethylene is 9 - 20 g / 10 min; the random copolymerized polypropylene of the upper surface matte layer and the lower surface glossy layer is a random ethylene-propylene copolymer, and at 230°C and a load of 2.16 kg, the melt index is 6 - 10 g / 10 min; at 230°C and a load of 2.16 kg, the melt index of the homopolypropylene is 3 - 8 g / 10 min.

[0015] Further, the middle core layer further includes 1 - 3 wt% of an antistatic agent; the lower surface glossy layer further includes 0.1 - 0.5 wt% of an anti-blocking agent, and the anti-blocking agent is one or more of silica, talcum powder, and calcium carbonate. Adding an appropriate amount of anti-blocking agent to the lower surface glossy layer is beneficial to improving the smoothness of winding and unwinding of the matte film. If the content of the anti-blocking agent in the lower surface layer is less than 0.1 wt%, it cannot play an effective anti-blocking role. If the content of the anti-blocking agent is higher than 0.5 wt%, problems such as shedding of the anti-blocking agent are likely to occur during production, resulting in contamination of the guide rollers, and at the same time, it will increase the haze and reduce the glossiness, affecting the appearance of the product. To balance the surface layer thickness and shedding problems, the particle size is preferably 4 - 5 µm.

[0016] Further, the total thickness of the glossy internal printing BOPP matte film is 12 - 15 µm; the thickness of the upper surface matte layer is 1.8 - 2.2 µm, and the thickness of the lower surface glossy layer is 0.8 - 1.2 µm.

[0017] A method for preparing a glossy internal printing BOPP matte film includes the following steps: The first step: batching and plasticizing: Set the raw material usage ratio in the control system of the biaxial stretching 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 distributor. The second step: casting: After being extruded from 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, it starts transverse stretching, and then is shaped and cooled. Step 5: Traction and winding: The multi-layer structured 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.

[0018] Furthermore, the melting and extrusion temperature of the upper surface matte layer is 200 - 260 °C; the melting and extrusion temperatures of the middle core layer and the lower surface glossy layer are 230 - 260 °C; in the process where the melt contacts the chill roll, the temperature of the chill water and the chill roll is 15 - 50 °C; the temperature in the longitudinal stretching zone is 90 - 130 °C, and the temperature in the transverse stretching zone is 155 - 165 °C; the longitudinal stretching ratio is 4.5 - 5.5 times, and the transverse stretching ratio is 8 - 10 times; the corona power factor of the upper surface matte layer is 20 - 25 W·min / m.

[0019] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0020] Figure 1 It is a schematic structural diagram of a BOPP matte film. Detailed Embodiments

[0021] 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 without creative efforts based on the embodiments in the embodiments of the present application belong to the scope protected by the embodiments of the present application.

[0022] 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. The singular forms of "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" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0023] Different application scenarios have different requirements for the thickness uniformity of the BOPP matte film substrate. For example, the thickness of conventional aqueous glue coating is generally 2 - 3 µm, and the requirement for the thickness uniformity index of the BOPP film substrate in conventional aqueous glue coating applications is ≤2.0%; while the thickness of ink printing is generally 1 - 1.5 µm, and the requirement for the thickness uniformity index of the BOPP film substrate in reverse printing applications is ≤1.5%, with higher requirements for the thickness uniformity of the substrate.

[0024] A BOPP matte film for reverse printing on the glossy side comprises a top surface matte layer, a middle core layer, and a bottom surface glossy layer arranged in sequence; the top surface layer comprises 40 - 55 wt% high-density polyethylene and 45 - 60 wt% random copolymer polypropylene; the middle core layer comprises homopolypropylene and 5 - 10 wt% poly(4-vinylphenol) grafted polypropylene; the bottom surface glossy layer comprises random copolymer polypropylene and 30 - 40 wt% styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene.

[0025] Further, the preparation method of the poly(4-vinylphenol) grafted polypropylene is to add homopolypropylene and 4-vinylphenol into a kneader with benzoyl peroxide as an initiator, and prepare the poly(4-vinylphenol) grafted polypropylene through a melt grafting process; the grafting rate of the 4-vinylphenol is 35 - 40%.

[0026] Further, the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is prepared by a melt grafting method. Styrene monomer and maleic anhydride monomer are added to xylene solvent, and styrene-maleic anhydride copolymer is obtained through free radical copolymerization with azobisisobutyronitrile as an initiator. Then, with dicumyl peroxide as an initiator, the styrene-maleic anhydride copolymer is grafted onto the molecular chain of random copolymer polypropylene through a melt grafting method; the content of the styrene monomer in the styrene-maleic anhydride copolymer is 4 - 5 mol%; the grafting rate of the styrene-maleic anhydride copolymer is 45 - 55%.

[0027] Further, at 230 °C and a load of 2.16 kg, the melt index of the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is 7 - 9 g / 10 min.

[0028] Further, at 230 °C and a load of 2.16 kg, the melt index of the poly(4-vinylphenol) grafted polypropylene is 7 - 11 g / 10 min.

[0029] Further, at 190 °C and a load of 21.6 kg, the melt index of the high-density polyethylene is 9 - 20 g / 10 min; the random copolymer polypropylene in the upper surface matte layer and the lower surface glossy layer is a random ethylene-propylene copolymer, and at 230 °C and a load of 2.16 kg, the melt index is 6 - 10 g / 10 min; at 230 °C and a load of 2.16 kg, the melt index of the homopolypropylene is 3 - 8 g / 10 min.

[0030] Further, the intermediate core layer further includes 1 - 3 wt% of an antistatic agent, and the antistatic agent is a quaternary ammonium salt-based methacrylate copolymer antistatic agent; the lower surface glossy layer further includes 0.1 - 0.5 wt% of an anti-blocking agent, and the anti-blocking agent is one or more of silica, talcum powder, and calcium carbonate, with a particle size of 3 - 6 µm.

[0031] Further, the total thickness of the glossy inside-printed BOPP matte film is 12 - 15 µm; the thickness of the upper surface matte layer is 1.8 - 2.2 µm, and the thickness of the lower surface glossy layer is 0.8 - 1.2 µm.

[0032] A method for preparing a glossy inside-printed BOPP matte film includes the following steps: 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 head through the runner and the distributor; Second step: Casting: After being extruded from the die head, the melt immediately contacts the chill roll to form a thick sheet; 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; 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; Fifth step: Traction and winding: The multi-layer structured 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; Sixth step: Slitting: The master roll that has undergone aging treatment is slit to obtain a film roll with a specified width and length.

[0033] Furthermore, the melting and extrusion temperature of the upper surface matting layer is 200~260°C; the melting and extrusion temperatures of the middle core layer and the lower surface smooth layer are 230~260°C; in the process where the melt contacts the chill roll, the temperature of the chill water and the chill roll is 15~50°C; the temperature of the longitudinal stretching zone is 90~130°C, and the temperature of the transverse stretching zone is 155~165°C; the longitudinal stretching ratio is 4.5~5.5 times, and the transverse stretching ratio is 8~10 times; the corona power factor of the upper surface matting layer is 20~25 W·min / m.

[0034] The physical property indexes and their testing methods of the embodiments or comparative examples of the present invention are specifically as follows: The melt index (melt mass flow rate MFR) is measured according to GB / T3682-2018.

[0035] Surface tension situation: The surface tension is tested according to GB / T14216-2008.

[0036] The antistatic agent is a quaternary ammonium salt-based methacrylate copolymer antistatic agent.

[0037] The anti-blocking agent is silicon dioxide with a particle size of 4.5 µm.

[0038] Tensile strength: It is tested according to GB / T1040.3-2006.

[0039] Calculation method of the thickness uniformity index (TUI): Formula: TUI = standard deviation (SD) / average thickness ( ) × 100%.

[0040] Standard deviation (SD):

[0041] The standard deviation (SD) reflects the dispersion degree of the film thickness data.

[0042] Average thickness ( ) is the arithmetic mean of the film thickness.

[0043] Among them, Xi is the thickness value of each measurement point, and n is the number of measurement points.

[0044] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described. The component and content ratios of each layer in the following embodiments and comparative examples of the present invention are shown in Table 1 below. The said ratios in the embodiments or comparative examples of the present invention are all in weight percentages. The characteristics of some components of each layer in the embodiments and comparative examples of the present invention are shown in Table 2 below.

[0045] Table 1

[0046] Table 2

[0047] Example 1 This example provides a BOPP matte film for inside printing on the smooth side, which includes a top surface matte layer 1, an intermediate core layer 2, and a bottom surface smooth layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0048] The preparation method of the resins for each layer of the BOPP matte film for inside printing on the smooth side in this example includes the following steps: Preparation of the resin for the top surface matte layer 1: Take 40 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 21.6 kg is 14 g / 10 min) and 60 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), and mix them evenly to obtain the resin for the top surface matte layer 1.

[0049] Preparation of the resin for the intermediate core layer 2: Take 94 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 5 g / 10 min), 5 wt% of poly(4-vinylphenol) grafted polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 9 g / 10 min; the grafting rate of 4-vinylphenol is 35%), and 1 wt% of antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the intermediate core layer 2.

[0050] Preparation of the resin for the bottom surface smooth layer 3: Take 69.7 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), 30 wt% of styrene-maleic anhydride copolymer 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 styrene-maleic anhydride copolymer is 45%; the content of styrene monomer in styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% of antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin for the bottom surface smooth layer 3.

[0051] The preparation method of the BOPP matte film for inside printing on the smooth side in this example includes the following steps: Batching and plasticizing: Set the raw material usage ratio in the control system of the biaxial stretching film production line, and then the batching system automatically conveys the dried raw materials for 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 chill roll to form a thick sheet; Longitudinal stretching: The thick sheet is heated to a set temperature by multiple groups of preheating rollers, starts longitudinal stretching, and then is shaped. 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. 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 film rolls with specified widths and lengths.

[0052] The melting extrusion temperature of the upper surface matte 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 glossy 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 in the longitudinal stretching zone is 125°C, and the temperature in the transverse stretching zone is 160°C; the longitudinal stretching ratio is 5.3 times, and the transverse stretching ratio is 8.5 times; the corona power factor of the upper surface matte layer 1 is 23.5 W·min / m.

[0053] The total thickness of the film is 12 µm, where the thickness of the upper surface matte 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 glossy layer 3 is 1 µm.

[0054] Example 2 This example provides a BOPP matte film for offset printing on the smooth side, which includes an upper surface matte layer 1, a middle core layer 2, and a lower surface glossy layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0055] The preparation method of the resins for each layer of the BOPP matte film for offset printing on the smooth side in this example includes the following steps: Preparation of the resin for the upper surface matte layer 1: Take 45 wt% high-density polyethylene (the melt index measured under the conditions of 190°C and 21.6 kg is 14 g / 10 min) and 55 wt% random copolymer polypropylene (the melt index measured under the conditions of 230°C and 2.16 kg is 7 g / 10 min), and mix them evenly to obtain the resin for the upper surface matte layer 1.

[0056] Preparation of the resin for the middle core layer 2: Take 91 wt% homopolypropylene (the melt index measured under the conditions of 230°C and 2.16 kg is 5 g / 10 min), 8 wt% poly(4-vinylphenol) grafted polypropylene (the melt index measured under the conditions of 230°C and 2.16 kg is 9 g / 10 min; the grafting rate of 4-vinylphenol is 37%), and 1 wt% antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0057] Preparation of the lower surface smooth layer 3 resin: Take 64.7 wt% of random copolymerized polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 35 wt% of styrene - maleic anhydride copolymer melt - grafted random copolymerized polypropylene (with a melt index of 7 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%; the content of styrene monomer in the styrene - maleic anhydride copolymer is 4 mol%), and 0.3 wt% of an anti - blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the lower surface smooth layer 3 resin.

[0058] The preparation method of the BOPP matte film for smooth surface internal printing in this example is the same as that in Example 1.

[0059] The total thickness of the film is 12 µm, where the thickness of the upper surface matte 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 smooth layer 3 is 1 µm.

[0060] Example 3 This example provides a BOPP matte film for smooth surface internal printing, which includes an upper surface matte layer 1, a middle core layer 2, and a lower surface smooth layer 3 arranged in sequence. The specific structure can be referred to Figure 1 .

[0061] The preparation method of the resins for each layer of the BOPP matte film for smooth surface internal printing in this example includes the following steps: Preparation of the upper surface matte layer 1 resin: Take 50 wt% of high - density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg) and 50 wt% of random copolymerized polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the upper surface matte layer 1 resin.

[0062] Preparation of the middle core layer 2 resin: Take 89 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 10 wt% of poly(p - vinylphenol) - grafted 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 p - vinylphenol is 40%), and 1 wt% of an antistatic agent (quaternary ammonium salt - based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0063] Preparation of the lower surface smooth layer 3 resin: Take 59.7 wt% of homopolypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene (with a melt index of 7 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%; the content of styrene monomer in the styrene-maleic anhydride copolymer is 5 mol%), and 0.3 wt% of an anti-blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the lower surface smooth layer 3 resin.

[0064] The preparation method of the smooth surface inside-printing BOPP matting film in this example is the same as that in Example 1.

[0065] The total thickness of the film is 12 µm, where the thickness of the upper surface matting 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 smooth layer 3 is 1 µm.

[0066] Comparative Example 1 This comparative example provides a BOPP matting film, which includes an upper surface matting layer 1, a middle core layer 2, and a lower surface smooth layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0067] The preparation method of the resins for each layer of the BOPP matting film in this comparative example includes the following steps: Preparation of the upper surface matting layer 1 resin: Take 45 wt% of high-density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg) and 55 wt% of random copolymerized polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the upper surface matting layer 1 resin.

[0068] Preparation of the middle core layer 2 resin: Take 99 wt% of homopolypropylene (with a melt index of 5 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 middle core layer 2 resin.

[0069] Preparation of the lower surface light surface layer 3 resin: Take 64.7 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), 35 wt% of styrene-maleic anhydride copolymer 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 50%; the content of styrene monomer in the styrene-maleic anhydride copolymer is 4 mol%) and 0.3 wt% of an anti-blocking agent (silica, particle size of 4.5 µm), and mix them evenly to obtain the lower surface light surface layer 3 resin.

[0070] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0071] The total thickness of the film is 12 µm, wherein the thickness of the upper surface matte 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 light surface layer 3 is 1 µm.

[0072] Comparative Example 2 This comparative example provides a BOPP matte film, which includes an upper surface matte layer 1, a middle core layer 2, and a lower surface light surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0073] The preparation method of the resin for each layer of the BOPP matte film in this comparative example includes the following steps: Preparation of the upper surface matte layer 1 resin: Take 45 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 21.6 kg is 14 g / 10 min) and 55 wt% of random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), and mix them evenly to obtain the upper surface matte layer 1 resin.

[0074] Preparation of the middle core layer 2 resin: Take 96 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 5 g / 10 min), 3 wt% of poly(p-vinylphenol) grafted polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 9 g / 10 min; the grafting rate of p-vinylphenol is 37%) and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0075] Preparation of the lower surface light surface layer 3 resin: Take 64.7 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 35 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene (with a melt index of 7 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%; the content of styrene monomer in the styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% of an anti-blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the lower surface light surface layer 3 resin.

[0076] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0077] The total thickness of the film is 12 µm, where the thickness of the upper surface matting 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 light surface layer 3 is 1 µm.

[0078] Comparative Example 3 This comparative example provides a BOPP matting film, which includes an upper surface matting layer 1, a middle core layer 2, and a lower surface light surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0079] The preparation method of the resins for each layer of the BOPP matting film in this comparative example includes the following steps: Preparation of the upper surface matting layer 1 resin: Take 45 wt% of high-density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg), 55 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the upper surface matting layer 1 resin.

[0080] Preparation of the middle core layer 2 resin: Take 84 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 15 wt% of poly(p-vinylphenol) grafted 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 p-vinylphenol is 37%), and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0081] Preparation of the lower surface smooth layer 3 resin: Take 64.7 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 35 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene (with a melt index of 7 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%; the content of styrene monomer in the styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% of an anti-blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the lower surface smooth layer 3 resin.

[0082] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0083] The total thickness of the film is 12 µm, among which the thickness of the upper surface matting 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 smooth layer 3 is 1 µm.

[0084] Comparative Example 4 This comparative example provides a BOPP matting film, which includes an upper surface matting layer 1, a middle core layer 2, and a lower surface smooth layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0085] The preparation method of the resins of each layer of the BOPP matting film in this comparative example includes the following steps: Preparation of the upper surface matting layer 1 resin: Take 45 wt% of high-density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg), 55 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the upper surface matting layer 1 resin.

[0086] Preparation of the middle core layer 2 resin: Take 91 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 8 wt% of poly(4-vinylphenol) grafted 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 4-vinylphenol is 30%), and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0087] Preparation of the lower surface light-facing layer 3 resin: Take 64.7 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 35 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene (with a melt index of 7 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%; the content of styrene monomer in the styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% of an anti-blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the lower surface light-facing layer 3 resin.

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

[0089] The total thickness of the film is 12 µm, where the thickness of the upper surface matte 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 light-facing layer 3 is 1 µm.

[0090] Comparative Example 5 This comparative example provides a BOPP matte film, which includes an upper surface matte layer 1, a middle core layer 2, and a lower surface light-facing layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 。

[0091] The preparation method of the resin for each layer of the BOPP matte film in this comparative example includes the following steps: Preparation of the upper surface matte layer 1 resin: Take 45 wt% of high-density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg) and 55 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the upper surface matte layer 1 resin.

[0092] Preparation of the middle core layer 2 resin: Take 91 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 8 wt% of poly(p-vinylphenol) grafted 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 p-vinylphenol is 45%), and 1 wt% of an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the middle core layer 2 resin.

[0093] Preparation of the lower surface smooth layer 3 resin: Take 64.7 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 35 wt% of styrene - maleic anhydride copolymer melt - grafted random copolymer polypropylene (with a melt index of 7 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%; the content of styrene monomer in the styrene - maleic anhydride copolymer is 4 mol%), and 0.3 wt% of an anti - blocking agent (silica, with a particle size of 4.5 µm), mix them evenly to obtain the lower surface smooth layer 3 resin.

[0094] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0095] The total thickness of the film is 12 µm, where the thickness of the upper surface matte 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 smooth layer 3 is 1 µm.

[0096] Comparative Example 6 This comparative example provides a BOPP matte film, which includes an upper surface matte layer 1, a middle core layer 2, and a lower surface smooth layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0097] The preparation method of the resins for each layer of the BOPP matte film in this comparative example includes the following steps: Preparation of the upper surface matte layer 1 resin: Take 45 wt% of high - density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg) and 55 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), mix them evenly to obtain the upper surface matte layer 1 resin.

[0098] Preparation of the middle core layer 2 resin: Take 91 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 8 wt% of poly(p - vinylphenol) - grafted 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 p - vinylphenol is 37%), 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.

[0099] Preparation of the lower surface smooth layer 3 resin: Take 99.7 wt% of random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg) and 0.3 wt% of an anti - blocking agent (silica, with a particle size of 4.5 µm), mix them evenly to obtain the lower surface smooth layer 3 resin.

[0100] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0101] The total thickness of the film is 12 µm, where the thickness of the upper surface matte 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 glossy layer 3 is 1 µm.

[0102] Comparative Example 7 This comparative example provides a BOPP matte film, which includes an upper surface matte layer 1, a middle core layer 2, and a lower surface glossy layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0103] The preparation method of the resins for each layer of the BOPP matte film in this comparative example includes the following steps: Preparation of the resin for the upper surface matte layer 1: Take 45 wt% high-density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg) and 55 wt% random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the resin for the upper surface matte layer 1.

[0104] Preparation of the resin for the middle core layer 2: Take 91 wt% homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 8 wt% poly(4-vinylphenol) grafted 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 4-vinylphenol is 37%), and 1 wt% antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0105] Preparation of the resin for the lower surface glossy layer 3: Take 79.7 wt% random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 20 wt% styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of styrene-maleic anhydride copolymer is 50%; the content of styrene monomer in styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% anti-blocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the resin for the lower surface glossy layer 3.

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

[0107] The total thickness of the film is 12 µm, where the thickness of the upper surface matte 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 glossy layer 3 is 1 µm.

[0108] Comparative Example 8 This comparative example provides a BOPP matte film, which includes an upper surface matte layer 1, an intermediate core layer 2, and a lower surface glossy layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0109] The preparation method of the resins of each layer of the BOPP matte film in this comparative example includes the following steps: Preparation of the resin of the upper surface matte layer 1: Take 45 wt% high-density polyethylene (the melt index measured under the conditions of 190 °C and 21.6 kg is 14 g / 10 min), and 55 wt% random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), and mix them evenly to obtain the resin of the upper surface matte layer 1.

[0110] Preparation of the resin of the intermediate core layer 2: Take 91 wt% homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 5 g / 10 min), 8 wt% poly(4-vinylphenol) grafted polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 9 g / 10 min; the grafting rate of 4-vinylphenol is 37%), and 1 wt% antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin of the intermediate core layer 2.

[0111] Preparation of the resin of the lower surface glossy layer 3: Take 49.7 wt% homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), 50 wt% styrene-maleic anhydride copolymer 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 styrene-maleic anhydride copolymer is 50%; the content of styrene monomer in styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% anti-blocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin of the lower surface glossy layer 3.

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

[0113] The total thickness of the film is 12 µm, wherein the thickness of the upper surface matte layer 1 is 1.8 µm, the thickness of the intermediate core layer 2 is 9.2 µm, and the thickness of the lower surface glossy layer 3 is 1 µm.

[0114] Comparative Example 9 This comparative example provides a BOPP matte film, which includes an upper surface matte layer 1, an intermediate core layer 2, and a lower surface glossy layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0115] The preparation method of the resins for each layer of the BOPP matting film in this comparative example includes the following steps: Preparation of the resin for the upper surface matting layer 1: Take 45 wt% of high-density polyethylene (the melt index measured under the conditions of 190 °C and 21.6 kg is 14 g / 10 min), and 55 wt% of random copolymerized polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), and mix them evenly to obtain the resin for the upper surface matting layer 1.

[0116] Preparation of the resin for the middle core layer 2: Take 91 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 5 g / 10 min), 8 wt% of poly(4-vinylphenol)-grafted polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 9 g / 10 min; the grafting rate of 4-vinylphenol is 37%), 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.

[0117] Preparation of the resin for the lower surface glossy layer 3: Take 64.7 wt% of homopolypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), 35 wt% of styrene-maleic anhydride copolymer 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 styrene-maleic anhydride copolymer is 40%; the content of styrene monomer in styrene-maleic anhydride copolymer is 4 mol%), 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 glossy layer 3.

[0118] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0119] The total thickness of the film is 12 µm, wherein the thickness of the upper surface matting 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 glossy layer 3 is 1 µm.

[0120] Comparative Example 10 This comparative example provides a BOPP matting film, which includes an upper surface matting layer 1, a middle core layer 2, and a lower surface glossy layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0121] The preparation method of the resins for each layer of the BOPP matting film in this comparative example includes the following steps: Preparation of the resin for the upper surface matting layer 1: Take 45 wt% of high-density polyethylene (with a melt index of 14 g / 10 min measured under the conditions of 190 °C and 21.6 kg) and 55 wt% of random copolymerized polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), and mix them evenly to obtain the resin for the upper surface matting layer 1.

[0122] Preparation of the resin for the middle core layer 2: Take 91 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 8 wt% of poly(4-vinylphenol) grafted 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 4-vinylphenol is 37%), 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.

[0123] Preparation of the resin for the lower surface glossy layer 3: Take 64.7 wt% of homopolypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 35 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg; the grafting rate of styrene-maleic anhydride copolymer is 60%; the content of styrene monomer in styrene-maleic anhydride copolymer is 4 mol%), 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 glossy layer 3.

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

[0125] The total thickness of the film is 12 µm, among which the thickness of the upper surface matting 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 glossy layer 3 is 1 µm.

[0126] The performance test results of the glossy inside-printed BOPP matting films in Examples 1 to 3 and the BOPP matting films in Comparative Examples 1 to 9 are shown in Table 3 below.

[0127] Table 3

[0128] Combined with the above performance test data, it can be seen that the glossy inside-printed BOPP matting films in Examples 1 to 3 of the present invention have good thickness uniformity and high corona durability, effectively improving the printing performance of the substrate, meeting the application requirements of downstream inside printing of BOPP matting films, and conforming to the requirements of high-speed automated production of BOPP matting films.

[0129] For the BOPP matting film of Comparative Example 1, poly(p-vinylphenol) grafted polypropylene is not added to the middle core layer, which cannot effectively optimize the molecular chain orientation and the chain segment relaxation of secondary crystallization during the stretching process of homopolypropylene, and cannot improve the overall thickness uniformity of the BOPP matting film substrate.

[0130] For the BOPP matting film of Comparative Example 2, the content of poly(p-vinylphenol) grafted polypropylene added to the middle core layer is too low. Due to the insufficient content of p-vinylphenol branches, it is impossible to effectively restrict the molecular chain movement by the benzene ring rigid groups and hydrogen bond interactions and optimize the orientation movement of the molecular chain during stretching, and it is impossible to effectively improve the overall thickness uniformity of the BOPP matting film.

[0131] For the BOPP matting film of Comparative Example 3, the content of poly(p-vinylphenol) grafted polypropylene added to the middle core layer is too high. Due to the excessive benzene ring rigid groups of the p-vinylphenol branches and the physical crosslinking points of the hydrogen bond network, the brittleness of the BOPP matting film is too high, and there are many film-breaking phenomena during the biaxial stretching process, which affects the smoothness of production.

[0132] For the BOPP matting film of Comparative Example 4, the grafting rate of p-vinylphenol in the poly(p-vinylphenol) grafted polypropylene added to the middle core layer is too low. Due to the insufficient grafted p-vinylphenol branches, it is impossible to significantly optimize the molecular chain orientation of the homopolypropylene in the middle core layer, nor can it effectively restrict the amorphous chain segments and secondary crystallization of the homopolypropylene. The thickness uniformity index is significantly higher than that of Examples 1 to 3; and the content of phenolic hydroxyl groups extending to the lower surface light layer is low, and it is impossible to effectively improve the internal printing performance of the lower surface light layer in cooperation with the styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene. The surface tension and persistence of the printed surface are slightly worse than those of Examples 1 to 3.

[0133] For the BOPP matting film of Comparative Example 5, the grafting rate of p-vinylphenol in the poly(p-vinylphenol) grafted polypropylene added to the middle core layer is too high. The excessive aggregation of branches intensifies the physical crosslinking to form crystal defects, and there are many film-breaking phenomena during the biaxial stretching process, which affects the smoothness of production.

[0134] For the BOPP matting film of Comparative Example 6, styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene is not added to the lower surface light layer. The surface tension and persistence of the lower surface light layer are much lower than those of Examples 1 to 3, the printing performance is poor, and the improvement effect on the thickness uniformity of the film is much worse than that of Examples 1 to 3.

[0135] For the BOPP matte film of Comparative Example 7, although styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene was added to the lower surface glossy layer, the surface tension and persistence were slightly improved compared with Comparative Example 6. However, the content of maleic anhydride groups and benzene ring rigid groups was too low. On the one hand, it could not form an effective bond with the polar resin in the water-based ink. On the other hand, it was not conducive to slowing down the surface tension decay rate, resulting in insufficient improvement in the surface tension and persistence of the printed surface of the lower surface glossy layer, and poor printing performance.

[0136] For the BOPP matte film of Comparative Example 8, the content of styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene added to the lower surface glossy layer was too high. Excessive maleic anhydride polar groups crosslinked excessively with random copolymerized polypropylene to form rigid microdomains and benzene ring rigid groups, restricting the movement of chain segments, resulting in many film-breaking phenomena and affecting the smoothness of production.

[0137] For the BOPP matte film with improved printing performance of Comparative Example 9, the grafting rate of the styrene-maleic anhydride copolymer in the styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene added to the lower surface was too low, and the polar groups in maleic anhydride and styrene functional groups were insufficient. The lower surface glossy layer of the BOPP matte film could not effectively combine with the polar groups in the water-based ink, was not conducive to slowing down the surface tension decay rate to form a firm printing layer, and could not effectively improve the thickness uniformity of the film.

[0138] For the BOPP matte film of Comparative Example 10, the grafting rate of the styrene-maleic anhydride copolymer in the styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene added to the lower surface glossy layer was too high. Due to too many grafted chains, the voids between molecular chains increased, reducing the mechanical strength of the film and significantly decreasing the tensile strength of the film.

[0139] A BOPP matte film for smooth-surface internal printing of the present invention optimizes the orientation and secondary crystallization chain relaxation during the stretching of homopolypropylene in the middle core layer by adding 5-10 wt% of poly(p-vinylphenol) grafted polypropylene to the middle core layer; adds 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene to the lower surface glossy layer, and together with the phenolic hydroxyl groups in the poly(p-vinylphenol) grafted polypropylene in the middle core layer, improves the binding performance with the polar resin in the water-based ink. Using the rigid benzene ring structure of the styrene group slows down the surface tension decay rate and inhibits the melt fracture caused by local stress concentration during the stretching of the random copolymerized polypropylene melt in the lower surface glossy layer; the two together improve the overall thickness uniformity of the BOPP matte film substrate, meet the requirement of the thickness uniformity index of the BOPP film substrate for smooth-surface internal printing applications ≤ 1.5%, and effectively improve the smooth-surface printing performance of the substrate, meeting the application requirements of downstream BOPP matte film internal printing.

[0140] 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 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 cover these modifications and variations.

Claims

1. A BOPP matte film for printing on the smooth inner surface, characterized in that: It includes a top surface matting layer, an intermediate core layer, and a bottom surface glossy layer arranged in sequence; the top surface matting layer includes high-density polyethylene and random copolymer polypropylene; the intermediate core layer includes homopolypropylene and 5-10 wt% of poly(4-vinylphenol) grafted polypropylene; the bottom surface glossy layer includes random copolymer polypropylene and 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted onto random copolymer polypropylene.

2. The BOPP matting film for inner printing with smooth surface according to claim 1, wherein: The preparation method of the poly(4-vinylphenol) grafted polypropylene is to use benzoyl peroxide as an initiator, add homopolypropylene and 4-vinylphenol to a kneader, and prepare the poly(4-vinylphenol) grafted polypropylene through a melt grafting process; the grafting rate of 4-vinylphenol is 35-40%.

3. The BOPP matte film for inner printing on smooth surface according to claim 1, characterized in that: The styrene-maleic anhydride copolymer melt-grafted onto random copolymer polypropylene is prepared by a melt grafting method. Add styrene monomer and maleic anhydride monomer to xylene solvent, use azobisisobutyronitrile as an initiator, and obtain the styrene-maleic anhydride copolymer through free radical copolymerization. Then, use dicumyl peroxide as an initiator and graft the styrene-maleic anhydride copolymer onto the molecular chain of random copolymer polypropylene through a melt grafting method; the content of styrene monomer in the styrene-maleic anhydride copolymer is 4-5 mol%; the grafting rate of the styrene-maleic anhydride copolymer is 45-55%.

4. The BOPP matting film for inner printing with smooth surface according to claim 1, wherein: At 230 °C and a load of 2.16 kg, the melt index of the styrene-maleic anhydride copolymer melt-grafted onto random copolymer polypropylene is 7-9 g / 10 min.

5. The BOPP matte film for smooth inner printing according to claim 1, characterized in that: At 230 °C and a load of 2.16 kg, the melt index of the poly(4-vinylphenol) grafted polypropylene is 7-11 g / 10 min.

6. The BOPP matte film for smooth inner printing according to claim 1, wherein: At 190 °C and a load of 21.6 kg, the melt index of the high-density polyethylene is 9-20 g / 10 min; the random copolymer polypropylene in the top surface matting layer and the bottom surface glossy layer is a random ethylene-propylene copolymer, and at 230 °C and a load of 2.16 kg, the melt index is 6-10 g / 10 min; at 230 °C and a load of 2.16 kg, the melt index of the homopolypropylene is 3-8 g / 10 min.

7. The BOPP matte film for inner printing on smooth surface according to claim 1, characterized in that: The intermediate core layer further includes 1-3 wt% of an antistatic agent; the bottom surface glossy layer further includes 0.1-0.5 wt% of an antiblocking agent, and the antiblocking agent is one or more of silica, talc, and calcium carbonate.

8. The BOPP matte film for smooth inner printing according to any one of claims 1 to 7, characterized in that: The total thickness of the glossy surface internal printing BOPP matting film is 12-15 µm; the thickness of the top surface matting layer is 1.8-2.2 µm, and the thickness of the bottom surface glossy layer is 0.8-1.2 µm.

9. A preparation method of a smooth-surface inner-printed BOPP matte film as described in any one of claims 1 to 8, 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 biaxial stretching 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. The second step: 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 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; 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.

10. The preparation method of the BOPP matting film for inside printing on smooth surface according to claim 9, characterized in that: The melting and extrusion temperature of the upper surface matte layer is 200 - 260 °C; the melting and extrusion temperatures of the middle core layer and the lower surface glossy layer are 230 - 260 °C; in the process where the melt contacts the chill roll, the temperature of the chill water and the chill roll is 15 - 50 °C; the temperature in the longitudinal stretching zone is 90 - 130 °C, and the temperature in the transverse stretching zone is 155 - 165 °C; the longitudinal stretching ratio is 4.5 - 5.5 times, and the transverse stretching ratio is 8 - 10 times; the corona power factor of the upper surface matte layer is 20 - 25 W·min / m.

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