A BOPP matte film for inner printing on smooth surface and its preparation method

Abstract

The present invention relates to the field of matte films, and particularly to a BOPP matte film for inside printing on the glossy surface and a preparation method thereof. The BOPP matte film for inside printing on the glossy surface according to the present invention comprises a top surface matte layer, an intermediate core layer, and a bottom surface glossy layer which are arranged in sequence; the top surface layer comprises high-density polyethylene and random copolymer polypropylene; the intermediate core layer comprises homopolypropylene and 5-10 wt% of poly(4-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. The present invention provides a BOPP matte film for inside printing on the glossy surface and a preparation method thereof. By optimizing the material compositions of the intermediate core layer and the bottom surface glossy layer, the thickness uniformity of the BOPP matte film and the surface tension performance of the glossy surface are improved, meeting the printing requirements for inside printing on the glossy surface of the BOPP matte film product and the requirements for high-speed automated production.

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 lamination. Usually, most applications of BOPP matte film products are printed on the matte side. However, for some relatively high-end processing applications, it is required that the matte film product can 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 coating PE glue on the printed glossy side and then laminating with foam cotton to make wallpaper; or ② immediately coating or pre-coating an adhesive layer on the printed glossy side and then laminating with paper, paper box or making labels. This application method belongs to inside printing, aiming 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.

[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 does not adhere firmly, resulting in the separation of the ink of the wallpaper product, 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 application scenario of inside printing, there are often problems such as deviation in the printing position of the pattern and inaccurate overprinting, 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 deviation in the printing position of the pattern on the glossy side and inaccurate overprinting 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 inside printing of BOPP matte film products.

[0005] The BOPP matte film of the present invention is realized through the following detailed technical solutions:

[0006] A BOPP matte film for reverse printing on the glossy side, comprising a top surface matte layer, an intermediate core layer, and a bottom surface glossy layer arranged in sequence; the top surface matte layer comprises high-density polyethylene and random copolymer polypropylene; the intermediate core layer comprises homopolypropylene and 5-10 wt% of poly(4-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.

[0007] Through research by the inventors, it was 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 printing effect problems such as position deviation and inaccurate overprinting of the pattern are the insufficient thickness uniformity of the BOPP matte film substrate. Different application scenarios have different requirements for the thickness uniformity of the BOPP matte film substrate. For example, the thickness of conventional water-based glue coating is generally 2-3 µm, but when the BOPP matte film substrate is applied to the reverse printing application scenario, full-surface printing is usually carried out on the glossy side, 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 matte film for reverse printing on the glossy side of the present invention has a three-layer structure, and the intermediate core layer is the main layer reflecting the mechanical properties of the film and the main layer providing the thickness uniformity. In a conventional homopolypropylene core layer, the molecular weight distribution of homopolypropylene is relatively wide, the chain entanglement density of 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 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 residual amorphous chain segments after biaxial stretching will undergo secondary crystallization (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, conventional homopolypropylene cannot meet the requirements for the thickness uniformity of the BOPP matte film substrate in reverse printing applications on the glossy side.

[0008] In a homopolypropylene of the middle core layer of a BOPP matte film for smooth-surface internal printing, 5-10 wt% of poly(4-vinylphenol) grafted polypropylene is added. Since the main chain of poly(4-vinylphenol) grafted polypropylene is polypropylene, it has good compatibility with the homopolypropylene in the middle core layer, enabling the 4-vinylphenol branches to be evenly dispersed in the homopolypropylene. Moreover, the polar hydroxyl groups in the 4-vinylphenol branches of poly(4-vinylphenol) grafted polypropylene interact with the molecular chains of the homopolypropylene through dipole interactions, partially disrupting the entanglement network of high-molecular-weight chain segments in the homopolypropylene, reducing the entanglement density and the orientation resistance during the stretching process. The benzene ring rigid groups in the 4-vinylphenol branches, due to the rigid support of the molecular chains, inhibit the excessive flow of low-molecular-weight chain segments in the homopolypropylene through steric hindrance effects, restricting the excessive relaxation of low-molecular-weight chain segments. Specifically, on the one hand, the entanglement of high-molecular-weight chain segments is reduced, and on the other hand, the excessive relaxation of low-molecular-weight chain segments is restricted, narrowing the difference in the stretching rates of high-molecular-weight and low-molecular-weight chain segments, making the molecular chain orientation more uniform and facilitating the improvement of the thickness uniformity of the middle core layer of the BOPP matte 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 amorphous region chain segments is restricted, the amplitude of thickness fluctuations during the post-treatment process is significantly reduced, which also contributes to the improvement of the thickness uniformity of the BOPP matte film. If the addition amount of poly(4-vinylphenol) grafted polypropylene is less than 5 wt%, due to the insufficient content of 4-vinylphenol branches, the benzene ring rigid 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 matte film cannot be improved. If the addition amount of poly(4-vinylphenol) grafted polypropylene is higher than 10 wt%, due to the excessive benzene ring rigid groups and hydrogen bond interactions of the 4-vinylphenol branches resulting in too many physical crosslinking points in the network, the brittleness of the BOPP matte film will be too high, increasing the risk of film breakage during the biaxial stretching process and affecting the smoothness of production.

[0009] In addition, in the lower surface light layer of a matte BOPP film of the present invention, 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is added. The random copolymer polypropylene in the main chain of the grafted polymer has good compatibility with the matrix resin 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. A matte BOPP 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 reverse printing of the downstream matte BOPP film. 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 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 effect on the printing performance of the lower surface light layer and synergistically improving the thickness uniformity of the core layer is 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.

[0010] In addition, the 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, polar hydroxyl and anhydride groups 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 film substrate.

[0011] Furthermore, 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 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 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 upper and lower surface glossy layers to improve the surface tension of the printing surface of the BOPP matte film and further improve the printing performance of the BOPP matte film with reverse printing on the glossy surface. 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 between 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 upper and lower surface glossy layers, resulting in insufficient improvement in the surface tension of the upper and lower surface glossy layers; 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 cross-links and cause crystallization defects, increasing the risk of film breakage during the biaxial stretching process and affecting the smoothness of production.

[0012] Furthermore, the styrene-maleic anhydride copolymer is melt-grafted onto random copolymerized polypropylene by a melt grafting method, wherein styrene monomer and maleic anhydride monomer are added to a xylene solvent, and azobisisobutyronitrile is used as an initiator to obtain the styrene-maleic anhydride copolymer by a free radical copolymerization method. Then, dicumyl peroxide is used as an initiator to graft the styrene-maleic anhydride copolymer onto the random copolymerized 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 styrene-maleic anhydride copolymer onto random copolymerized polypropylene, the maleic anhydride groups will induce degradation of the homopolypropylene molecules. However, the styrene monomer can inhibit the degradation, allowing the styrene-maleic anhydride copolymer to be effectively grafted onto the main chain of the random copolymerized 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 styrene monomer content is less than 4 mol%, the amount of monomer available for the styrene groups to react with the random copolymerized polypropylene to form 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 reduced mechanical strength caused by degradation of the random copolymerized polypropylene. If the styrene monomer content is higher than 5 mol%, the excessive styrene monomer will destroy the continuity of the random copolymerized polypropylene molecular chain, resulting in a reduction in the 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 and styrene functional groups in maleic anhydride, the lower surface glossy layer of the BOPP matte film cannot effectively combine with the polar groups in the water-based ink, cannot 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%, because when the grafting rate is too high, the excessive rigid structure of the benzene ring in the side chain leads to stress concentration, increases the risk of film breakage, and affects production smoothness.

[0013] Furthermore, at 230°C and a load of 2.16 kg, the melt index of the styrene-maleic anhydride copolymer melt-grafted onto the random copolymerized polypropylene is 7-9 g / 10 min. If the melt index is lower than 7 g / 10 min, the resistance of the lower surface smooth layer melt passing through the die is increased, which can easily cause pressure fluctuations, resulting in uneven thickness of the lower surface smooth layer and affecting the thickness uniformity of the BOPP matte film substrate. If the melt index is higher than 9 g / 10 min, the styrene-maleic anhydride side chains in the styrene-maleic anhydride copolymer are not uniformly dispersed in the random copolymerized polypropylene, and stress concentration is likely to occur during biaxial stretching, causing film breakage and affecting smooth production.

[0014] Further, at 230°C and under a load of 2.16 kg, the melt index of the poly(vinylphenol) grafted polypropylene is 7 - 11 g / 10 min. If 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; if 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 during the biaxial stretching process due to insufficient melt strength, and affecting the reverse printing performance of the BOPP matte film substrate.

[0015] Further, at 190°C and under a load of 21.6 kg, the melt index of the high-density polyethylene is 9 - 20 g / 10 min; the random copolymer polypropylene of the upper surface matte layer and the lower surface glossy layer is a random ethylene-propylene copolymer, and at 230°C and under a load of 2.16 kg, the melt index is 6 - 10 g / 10 min; at 230°C and under a load of 2.16 kg, the melt index of the homopolypropylene is 3 - 8 g / 10 min.

[0016] 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 antiblocking agent, and the antiblocking agent is one or more of silica, talcum powder, and calcium carbonate. Adding an appropriate amount of antiblocking 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 antiblocking agent in the lower surface layer is lower than 0.1 wt%, it cannot play an effective antiblocking role; if the content of the antiblocking agent is higher than 0.5 wt%, problems such as shedding of the antiblocking agent are likely to occur during production, resulting in contamination of the guide rollers, and at the same time increasing the haze and reducing the gloss, affecting the appearance of the product; in order to balance the surface layer thickness and shedding problems, the particle size is preferably 4 - 5 µm.

[0017] Further, the total thickness of the glossy reverse-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.

[0018] A method for preparing a glossy reverse-printing BOPP matte film includes the following steps:

[0019] 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 through the runner and the distributor;

[0020] Step 2: Sheet casting: After being extruded from the die head, the melt immediately contacts the chill roll to form a thick sheet.

[0021] 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.

[0022] Step 4: Transverse stretching: After the thick sheet that has undergone longitudinal stretching is preheated to a set temperature, it starts transverse stretching, and then is shaped and cooled.

[0023] Step 5: 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.

[0024] Step 6: Slitting: The master roll that has undergone aging treatment is slit to obtain a film roll with a specified width and length.

[0025] Further, 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 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 matting layer is 20 - 25 W·min / m.

[0026] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of a BOPP matting film. Detailed Embodiments

[0028] 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 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.

[0029] 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 "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.

[0030] 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.

[0031] A BOPP matte film for reverse printing on a glossy surface comprises a top surface matte layer, an intermediate 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 intermediate core layer comprises homopolypropylene, 5 - 10 wt% poly(4 - vinylphenol) grafted polypropylene; the bottom surface glossy layer comprises random copolymer polypropylene, 30 - 40 wt% styrene - maleic anhydride copolymer melt - grafted random copolymer polypropylene.

[0032] Further, 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 poly(4 - vinylphenol) grafted polypropylene through a melt - grafting process; the grafting rate of the 4 - vinylphenol is 35 - 40%.

[0033] Further, the styrene - maleic anhydride copolymer melt - grafted 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 styrene - maleic anhydride copolymer through free - radical copolymerization. Then, use dicumyl peroxide as an initiator and graft the styrene - maleic anhydride copolymer onto the random copolymer polypropylene molecular chain 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%.

[0034] 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.

[0035] 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.

[0036] 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 of the upper surface extinction 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.

[0037] Further, the middle core layer further comprises 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 comprises 0.1 - 0.5 wt% of an anti-blocking agent, and the anti-blocking agent is one or more of silica, talc powder, and calcium carbonate, with a particle size of 3 - 6 µm.

[0038] Further, the total thickness of the glossy inside-printed BOPP extinction film is 12 - 15 µm; the thickness of the upper surface extinction layer is 1.8 - 2.2 µm, and the thickness of the lower surface glossy layer is 0.8 - 1.2 µm.

[0039] A preparation method of a glossy inside-printed BOPP extinction film comprises the following steps:

[0040] 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 flow channel and the distributor;

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

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

[0043] The 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;

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

[0045] The sixth step: slitting: The master roll that has undergone aging treatment is subjected to slitting treatment to obtain a film roll with a specified width and length.

[0046] 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 chill water and the temperature of the chill roll are 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 matte layer is 20~25 W·min / m.

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

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

[0049] Surface tension condition: The surface tension is tested according to GB / T14216-2008.

[0050] The antistatic agent is a quaternary ammonium salt-based methacrylate copolymer antistatic agent.

[0051] The anti-blocking agent is silica, and the particle size is 4.5 µm.

[0052] Tensile strength: It is tested according to GB / T1040.3-2006.

[0053] Calculation method of the thickness uniformity index (TUI):

[0054] Formula: TUI = standard deviation (SD) / average thickness ( ) × 100%.

[0055] Standard deviation (SD):

[0056]

[0057] The standard deviation (SD) reflects the dispersion degree of the film thickness data.

[0058] Average thickness ( ): The arithmetic mean of the film thickness.

[0059] Among them, Xi is the thickness value of each measurement point, and n is the number of measurement points.

[0060] Next, in combination with the embodiments of the present invention, the technical solutions in the embodiments of the present invention will be described clearly and completely. 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 weight percentages. The characteristics of some components in each layer of the embodiments and comparative examples of the present invention are shown in Table 2 below.

[0061] Table 1

[0062]

[0063] Table 2

[0064]

[0065] Example 1

[0066] This example provides a BOPP matte film for smooth interior printing, which includes a top surface matte layer 1, an intermediate core layer 2, and a bottom surface smooth layer 3 arranged in sequence. The specific structure can be referred to Figure 1 .

[0067] The preparation method of the resin for each layer of the BOPP matte film for smooth interior printing in this example includes the following steps:

[0068] Preparation of the resin for the top surface matte layer 1: Take 40 wt% high-density polyethylene (the melt index measured at 190 °C and 21.6 kg is 14 g / 10 min), and 60 wt% random copolymer polypropylene (the melt index measured at 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.

[0069] Preparation of the resin for the intermediate core layer 2: Take 94 wt% homopolypropylene (the melt index measured at 230 °C and 2.16 kg is 5 g / 10 min), 5 wt% poly(p-vinylphenol) grafted polypropylene (the melt index measured at 230 °C and 2.16 kg is 9 g / 10 min; the grafting rate of p-vinylphenol is 35%), and 1 wt% antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the intermediate core layer 2.

[0070] Preparation of the lower surface light surface layer 3 resin: Take 69.7 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), 30 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 45%; 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.

[0071] The preparation method of the smooth surface internal printing BOPP matte film in this example includes the following steps:

[0072] Batching and plasticization: Set the raw material usage ratio in the control system of the biaxially oriented film production line, and then the batching system automatically 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;

[0073] Sheet casting: After being extruded from the die head, the melt immediately contacts the chill roll to form a thick sheet;

[0074] Longitudinal stretching: The thick sheet is heated to the set temperature by multiple groups of preheating rolls, starts longitudinal stretching, and then is shaped;

[0075] Transverse stretching: After preheating the thick sheet that has undergone longitudinal stretching to the set temperature, start transverse stretching, and then perform shaping and cooling treatment;

[0076] 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;

[0077] Slitting: The master roll that has undergone aging treatment is slit to obtain a film roll with a specified width and length.

[0078] The melting and extrusion temperature of the upper surface matte 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 light 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 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.

[0079] The total thickness of the film is 12 µm, among which 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.

[0080] Example 2

[0081] This example provides a BOPP matte film for interior 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 .

[0082] The preparation method of the resins for each layer of the BOPP matte film for interior printing on the smooth side in this example includes the following steps:

[0083] Preparation of the resin for the top 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 top surface matte layer 1.

[0084] Preparation of the resin for 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(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% antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the intermediate core layer 2.

[0085] Preparation of the resin for the bottom surface smooth layer 3: Take 64.7 wt% random copolymer polypropylene (the melt index measured under the conditions of 230 °C and 2.16 kg is 7 g / 10 min), 35 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 the styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% antiblocking agent (silica, particle size is 4.5 µm), and mix them evenly to obtain the resin for the bottom surface smooth layer 3.

[0086] The preparation method of the BOPP matte film for interior printing on the smooth side in this example is the same as that in Example 1.

[0087] The total thickness of the film is 12 µm, wherein the thickness of the top 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 bottom surface smooth layer 3 is 1 µm.

[0088] Example 3

[0089] This embodiment provides a BOPP matte film for offset printing on the smooth side, which includes an upper surface matte layer 1, an intermediate core layer 2, and a lower surface smooth layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0090] The preparation method of the resins for each layer of the BOPP matte film for offset printing on the smooth side in this embodiment includes the following steps:

[0091] Preparation of the resin for the upper surface matte layer 1: 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 resin for the upper surface matte layer 1.

[0092] Preparation of the resin for the intermediate core layer 2: 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 resin for the intermediate core layer 2.

[0093] Preparation of the resin for the lower surface smooth layer 3: 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 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 antiblocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the resin for the lower surface smooth layer 3.

[0094] The preparation method of the BOPP matte film for offset printing on the smooth side in this embodiment is the same as that in Example 1.

[0095] The total thickness of the film is 12 µm, among which 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 smooth layer 3 is 1 µm.

[0096] Comparative Example 1

[0097] 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 smooth layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0098] The preparation method of the resins for each layer of the BOPP matting film in this comparative example includes the following steps:

[0099] 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 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 matting layer 1.

[0100] Preparation of the resin for the middle core layer 2: 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 antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0101] Preparation of the resin for the lower surface glossy layer 3: 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 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.

[0102] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0103] 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.

[0104] Comparative Example 2

[0105] 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 .

[0106] The preparation method of the resins for each layer of the BOPP matting film in this comparative example includes the following steps:

[0107] 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.

[0108] Preparation of the resin for the middle core layer 2: Take 96 wt% of homopolypropylene (with a melt index of 5 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 3 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.

[0109] Preparation of the resin for the lower surface glossy layer 3: Take 64.7 wt% of random copolymerized polypropylene (with a melt index of 7 g / 10 min measured under the conditions of 2,30 °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 50%; 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.

[0110] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0111] 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.

[0112] Comparative Example 3

[0113] 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 .

[0114] The preparation method of the resin for each layer of the BOPP matting film in this comparative example includes the following steps:

[0115] Preparation of the resin for the upper surface matte 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 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.

[0116] Preparation of the resin for the middle core layer 2: 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(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.

[0117] Preparation of the resin for the lower surface glossy layer 3: 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 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 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.

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

[0119] The total thickness of the film is 12 µm, among which 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.

[0120] Comparative Example 4

[0121] 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. The specific structure can be referred to Figure 1 .

[0122] The preparation method of the resin for each layer of the BOPP matte film in this comparative example includes the following steps:

[0123] 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 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 matting layer 1.

[0124] 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 30%), 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.

[0125] Preparation of the resin for the lower surface glossy layer 3: 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 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 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.

[0126] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0127] 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 glossy layer 3 is 1 µm.

[0128] Comparative Example 5

[0129] 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 .

[0130] The preparation method of the resin for each layer of the BOPP matting film in this comparative example includes the following steps:

[0131] 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.

[0132] 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 45%), 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.

[0133] Preparation of the resin for the lower surface glossy layer 3: 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 styrene-maleic anhydride copolymer is 50%; 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.

[0134] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0135] 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.

[0136] Comparative Example 6

[0137] 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 .

[0138] The preparation method of the resin for each layer of the BOPP matting film in this comparative example includes the following steps:

[0139] 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.

[0140] 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 an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0141] Preparation of the resin for the lower surface glossy layer 3: Take 99.7 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) and 0.3 wt% of an 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.

[0142] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0143] 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.

[0144] Comparative Example 7

[0145] 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 .

[0146] The preparation method of the resin for each layer of the BOPP matting film in this comparative example includes the following steps:

[0147] 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.

[0148] 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 an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0149] Preparation of the resin for the lower surface layer and smooth surface layer 3: Take 79.7 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), 20 wt% of random copolymer polypropylene melt-grafted with styrene-maleic anhydride copolymer (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 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 resin for the lower surface layer and smooth surface layer 3.

[0150] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0151] The total thickness of the film is 12 µm, wherein the thickness of the upper surface layer 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 layer and smooth surface layer 3 is 1 µm.

[0152] Comparative Example 8

[0153] This comparative example provides a BOPP matting film, which includes an upper surface layer matting layer 1, a middle core layer 2, and a lower surface layer and smooth surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0154] The preparation method of the resin for each layer of the BOPP matting film in this comparative example includes the following steps:

[0155] Preparation of the resin for the upper surface layer 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 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 layer matting layer 1.

[0156] 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 an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0157] Preparation of the resin for the lower surface layer and smooth surface layer 3: Take 49.7 wt% of homopolypropylene (with a melt index of 7 g / 10 min measured under the conditions of 230 °C and 2.16 kg), 50 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 resin for the lower surface layer and smooth surface layer 3.

[0158] The preparation method of the BOPP matting film in this comparative example is the same as that in Example 1.

[0159] The total thickness of the film is 12 µm, among which the thickness of the upper surface layer 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 layer and smooth surface layer 3 is 1 µm.

[0160] Comparative Example 9

[0161] This comparative example provides a BOPP matting film, which includes an upper surface layer matting layer 1, a middle core layer 2, and a lower surface layer and smooth surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0162] The preparation method of the resin for each layer of the BOPP matting film in this comparative example includes the following steps:

[0163] Preparation of the resin for the upper surface layer 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 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 layer matting layer 1.

[0164] 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 an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0165] Preparation of the resin for the lower surface layer and smooth surface 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 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 40%; the content of styrene monomer in the styrene-maleic anhydride copolymer is 4 mol%), and 0.3 wt% of an antiblocking agent (silica, with a particle size of 4.5 µm), and mix them evenly to obtain the resin for the lower surface layer and smooth surface layer 3.

[0166] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0167] The total thickness of the film is 12 µm, among which the thickness of the upper surface layer 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 layer and smooth surface layer 3 is 1 µm.

[0168] Comparative Example 10

[0169] This comparative example provides a BOPP matte film, which includes an upper surface layer matte layer 1, a middle core layer 2, and a lower surface layer and smooth surface layer 3 arranged in sequence. For the specific structure, please refer to Figure 1 .

[0170] The preparation method of the resin for each layer of the BOPP matte film in this comparative example includes the following steps:

[0171] Preparation of the resin for the upper surface layer matte 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 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 layer matte layer 1.

[0172] 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 an antistatic agent (quaternary ammonium salt-based methacrylate copolymer antistatic agent), and mix them evenly to obtain the resin for the middle core layer 2.

[0173] Preparation of the resin for the lower surface smooth 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 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 60%; 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 resin for the lower surface smooth layer 3.

[0174] The preparation method of the BOPP matte film in this comparative example is the same as that in Example 1.

[0175] The total thickness of the film is 12 µm, among which 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.

[0176] The performance test results of the BOPP matte films for smooth surface internal printing in Examples 1 to 3 and the BOPP matte films in Comparative Examples 1 to 9 are shown in Table 3 below.

[0177] Table 3

[0178]

[0179] Combined with the above performance test data, it can be seen that the BOPP matte films for smooth surface internal printing 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 BOPP matte film internal printing, and conforming to the requirements of high-speed automated production of BOPP matte films.

[0180] For the BOPP matte film in Comparative Example 1, poly(4-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 matte film substrate.

[0181] For the BOPP matting film of Comparative Example 2, the content of poly(4-vinylphenol)-grafted polypropylene added to the middle core layer is too low. Due to the insufficient content of 4-vinylphenol side chains, the rigid benzene ring groups and hydrogen bond interactions cannot effectively restrict the movement of molecular chains and optimize the orientation movement of molecular chains during stretching, and thus cannot effectively improve the overall thickness uniformity of the BOPP matting film.

[0182] For the BOPP matting film of Comparative Example 3, the content of poly(4-vinylphenol)-grafted polypropylene added to the middle core layer is too high. Due to the excessive rigid benzene ring groups of 4-vinylphenol side chains and physical crosslinking points in 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.

[0183] For the BOPP matting film of Comparative Example 4, the grafting rate of 4-vinylphenol in the poly(4-vinylphenol)-grafted polypropylene added to the middle core layer is too low. Due to the insufficient grafted 4-vinylphenol side chains, the molecular chain orientation of the homopolypropylene in the middle core layer cannot be significantly optimized, and the amorphous chain segments and secondary crystallization of the homopolypropylene cannot be effectively restricted. The thickness uniformity index is significantly higher than that of Examples 1 to 3; moreover, the content of phenolic hydroxyl groups extending to the lower surface light layer is low, and it cannot synergistically improve the internal printing performance of the lower surface light layer with styrene-maleic anhydride copolymer-grafted random copolymer polypropylene. The surface tension and durability of the printed surface are slightly worse than those of Examples 1 to 3.

[0184] For the BOPP matting film of Comparative Example 5, the grafting rate of 4-vinylphenol in the poly(4-vinylphenol)-grafted polypropylene added to the middle core layer is too high. The excessive aggregation of side chains intensifies physical crosslinking and forms crystallization defects, and there are many film-breaking phenomena during the biaxial stretching process, which affects the smoothness of production.

[0185] For the BOPP matting film of Comparative Example 6, styrene-maleic anhydride copolymer-grafted random copolymer polypropylene is not added to the lower surface light layer. The surface tension and durability 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 far less than that of Examples 1 to 3.

[0186] For the BOPP matting film of Comparative Example 7, although styrene-maleic anhydride copolymer-grafted random copolymer polypropylene is added to the lower surface light layer, the surface tension and durability are slightly improved compared with Comparative Example 6. However, the content of maleic anhydride groups and rigid benzene ring groups is too low. On the one hand, it cannot form an effective bond with the polar resin in the water-based ink, and on the other hand, it is not conducive to slowing down the attenuation rate of surface tension. The improvement effect on the surface tension and durability of the printed surface of the lower surface light layer is insufficient, and the printing performance is poor.

[0187] For the BOPP matting film of Comparative Example 8, the content of the styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene added in the lower surface light layer is too high. Excessive polar groups of maleic anhydride react with random copolymerized polypropylene to form rigid microdomains and benzene ring rigid groups, restricting the movement of chain segments, resulting in many film breakage phenomena and affecting the smoothness of production.

[0188] For the BOPP matting 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 in the lower surface layer is too low, and the polar groups in maleic anhydride and styrene functional groups are insufficient. The lower surface light layer of the BOPP matting film cannot effectively combine with the polar groups in the water-based ink, which is not conducive to slowing down the surface tension decay rate to form a firm printing layer, and cannot effectively improve the thickness uniformity of the film.

[0189] For the BOPP matting 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 in the lower surface light layer is too high. Due to the increase in the voids between molecular chains caused by excessive grafted chains, the mechanical strength of the film is reduced, and the tensile strength of the film is significantly reduced.

[0190] A BOPP matting film for smooth-surface inside printing of the present invention optimizes the orientation and segment relaxation of the homopolypropylene during stretching in the middle core layer by adding 5-10 wt% of poly(p-vinylphenol) grafted polypropylene in the middle core layer; adding 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymerized polypropylene in the lower surface light layer, and together with the phenolic hydroxyl groups in the poly(p-vinylphenol) grafted polypropylene in the middle core layer, improve the binding performance with the polar resin in the water-based ink, and use the rigid benzene ring structure of the styrene group to slow down the surface tension decay rate and inhibit the melt fracture caused by local stress concentration during stretching of the random copolymerized polypropylene melt in the lower surface light layer; the two together improve the overall thickness uniformity of the BOPP matting film substrate, meet the requirement of the thickness uniformity index of the BOPP film substrate for smooth-surface inside printing applications ≤ 1.5%, effectively improve the smooth-surface printing performance of the substrate, and meet the application requirements of downstream BOPP matting film inside printing.

[0191] The above embodiments only represent several implementation manners of the present invention, and their descriptions are relatively specific and detailed, but should not be construed as limiting 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 changes and modifications.

Claims

1. A BOPP matte film for inner printing with smooth 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, and the grafting rate of 4-vinylphenol in the poly(4-vinylphenol) grafted polypropylene is 35-40%; the bottom surface glossy layer includes random copolymer polypropylene and 30-40 wt% of styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene, and the grafting rate of styrene-maleic anhydride copolymer in the styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is 45-55%.

2. The BOPP matte film for smooth inner printing 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 into a mixer, and prepare the poly(4-vinylphenol) grafted polypropylene through a melt grafting process.

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

4. 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 styrene-maleic anhydride copolymer melt-grafted random copolymer polypropylene is 7-9 g / 10 min.

5. The BOPP matte film for smooth inner printing according to claim 1, wherein: 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 matting film for inside printing on smooth surface according to claim 1, characterized in that: 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 smooth inner printing according to claim 1, wherein: 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 matting 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 BOPP matte film for printing on the smooth inner surface 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 biaxially oriented film production line, and then the batching system automatically transports the dried raw materials of each layer to the extruder according to the input ratio. After melting and plasticizing in the extruder, the melt enters the die through the runner and the distributor; 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, 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, and after thickness measurement and corona treatment, 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.

10. The preparation method of the BOPP matte film for smooth inner printing 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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