A bio-based stiffening shrinkage masterbatch for BOPP cigarette film and its preparation method

Abstract

This invention discloses a bio-based stiffening and shrinkage masterbatch for BOPP cigarette films and its preparation method, belonging to the field of polymer material modification and biaxially oriented film technology. The masterbatch is composed of 30-55 parts of furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin, 0.5-3 parts of rare earth organic complex β-crystal nucleating agent, 3-8 parts of polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer, 35-60 parts of polypropylene grafted methyl methacrylate, and 0.2-0.8 parts of antioxidant. The resulting cigarette film has a longitudinal elastic modulus above 2100 MPa, a longitudinal heat shrinkage rate of 4.5%-8.5%, an MD / TD shrinkage rate difference below 2.5%, a haze below 1.8%, and a bio-based carbon content above 25%, achieving a synergistic improvement in high stiffness and controllable shrinkage, reducing the carbon footprint, and meeting the environmental protection and functional upgrade requirements of tobacco packaging.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification and biaxially oriented film technology, specifically to a bio-based stiffening shrinkage masterbatch for BOPP cigarette films and its preparation method. Background Technology

[0002] Biaxially oriented polypropylene (BOPP) film possesses excellent mechanical properties, high transparency, and good moisture resistance, making it widely used as the outer transparent packaging film for tobacco products, also known as cigarette film. The core performance requirements for BOPP cigarette film in the tobacco packaging industry include high stiffness and a suitable shrinkage rate. High stiffness ensures the cigarette pack maintains a firm shape and resists compression deformation, while a suitable heat shrinkage rate allows the film to adhere tightly to the cigarette pack surface after packaging, achieving a tight and secure packaging effect.

[0003] To meet the aforementioned performance requirements, existing technologies typically add stiffening components to the polypropylene matrix to increase the film modulus, while simultaneously adding shrinkage-regulating components to control heat shrinkage behavior. However, there is an inherent contradiction between stiffness and shrinkage performance: the addition of stiffening components often inhibits the relaxation behavior of polypropylene molecular chains during stretching and orientation, leading to a decrease in heat shrinkage rate; conversely, introducing low-modulus components to obtain a higher shrinkage rate reduces film stiffness. How to obtain a stable and controllable heat shrinkage rate while ensuring film stiffness has been a long-standing technical challenge in this field.

[0004] To address these contradictions, researchers attempted to add stiffening masterbatch and shrinkage functional masterbatch separately to polypropylene, balancing stiffness and shrinkage performance by independently controlling the dosage of each component. However, this approach has the following drawbacks: First, the simultaneous addition of multiple masterbatches complicates the batching process, making it difficult to control the consistency of component distribution between batches, resulting in large fluctuations in film performance. Second, compatibility differences exist between functional components in different masterbatches, easily leading to phase separation and causing quality problems such as increased film haze and the appearance of crystal points or white spots on the surface. Third, existing stiffening components are mainly hydrogenated petroleum resins (C5 and C9 hydrogenated resins), which are derived from fossil resources and have a high carbon footprint, failing to meet increasingly stringent environmental protection policies. Some studies have attempted to introduce bio-based materials such as polylactic acid and polyhydroxyalkanoates to reduce the carbon footprint, but these materials have low thermal decomposition temperatures (usually below 250°C), making them prone to thermal degradation during the melt extrusion and biaxial stretching processes of BOPP films, generating volatiles and gel particles, severely affecting the film's appearance quality and continuous production stability.

[0005] Therefore, in view of the above problems, the present invention provides a bio-based stiffening and shrinkage masterbatch for BOPP cigarette films and its preparation method, so as to solve the technical problems in the prior art that it is difficult to synergistically improve the stiffness and shrinkage performance of BOPP cigarette films, that the poor thermal stability of bio-based materials makes them unsuitable for high-temperature processing of BOPP, and that uneven dispersion of functional components leads to a decline in the optical quality of the film. Summary of the Invention

[0006] The purpose of this invention is to provide a bio-based stiffening and shrinkage masterbatch for BOPP cigarette films and its preparation method. By using furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin as a bio-based stiffening and shrinkage component, combined with rare earth organic complex β-crystal nucleating agents and bifunctional compatibility dispersants, and combining low-temperature pre-anchoring, ultrasonic-assisted pre-dispersion, gradient shear melt blending and high-pressure microporous atomization granulation, the stiffening, shrinkage regulation, nucleation and dispersion functions are integrated into a single masterbatch. This solves the technical problem of the difficulty in synergistically improving stiffness and shrinkage performance, while reducing the carbon footprint of the product and meeting the environmental protection and functional upgrade requirements of the tobacco packaging industry.

[0007] The objective of this invention is achieved through the following technical solution: A bio-based stiffening and shrinkage masterbatch for BOPP cigarette films is made from the following raw material components in parts by weight: 30-55 parts of furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin; 0.5-3 parts of rare earth organic complex β-crystal nucleating agent; 3-8 parts of polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer; 35-60 parts of polypropylene grafted methyl methacrylate; and 0.2-0.8 parts of antioxidant. The bio-based carbon content of the furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin is above 70%, and the maleic anhydride grafting rate of the polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer is 0.8%-1.5%, and the glycidyl methacrylate grafting rate is 0.5%-1.0%.

[0008] Preferably, the rigid structure of the furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin imparts a stiffening effect to polypropylene, and its copolyester segments undergo microphase relaxation during the heat setting stage to regulate shrinkage performance; the rare earth organic complex-type β-crystal nucleating agent is used to induce polypropylene to form β-crystals, achieving precise control of shrinkage performance; the polypropylene grafted with maleic anhydride-glycidyl methacrylate copolymer serves as a bifunctional compatibility dispersant, constructing a chemical bond network to solve interfacial compatibility issues; the polypropylene grafted with methyl methacrylate serves as a graft modification carrier, ensuring the processing fluidity of the masterbatch; and the antioxidant is used to inhibit thermal oxidative degradation.

[0009] Preferably, the furanyl aromatic-aliphatic copolyester is obtained by copolymerization of 2,5-furandicarboxylic acid, 1,4-butanediol and adipic acid, wherein 2,5-furandicarboxylic acid accounts for 50% to 70% of the total molar amount of the dicarboxylic acid; the softening point of the hydrogenated terpene resin is 115 to 135°C; the grafting modification is achieved through transesterification reaction, with a grafting rate of 5% to 15%.

[0010] Preferably, 2,5-furandicarboxylic acid is used as a bio-based monomer to reduce the carbon footprint, the softening point of the hydrogenated terpene resin is controlled at 115~135℃ to ensure compatibility and processability, and the grafting rate is controlled at 5%~15% to balance the stiffening effect and thermal stability.

[0011] Preferably, the rare earth organic complex β-crystal nucleating agent is a complex formed by lanthanum or cerium and an organic carboxylic acid, wherein the organic carboxylic acid is phthalic acid, naphthenic acid, or salicylic acid; the rare earth organic complex β-crystal nucleating agent further comprises an aryl amide compound, wherein the mass ratio of the rare earth organic complex to the aryl amide compound is 1:1.5~3, and the aryl amide compound is N,N'-dicyclohexyl terephthalamide or N,N'-dibenzoyl hexamethylenediamine.

[0012] Preferably, lanthanum or cerium complexes are used in combination with arylamides, and the two work synergistically to induce polypropylene to form β crystals. The β crystal content is controlled at 30% to 60%, which can reduce film haze compared with a single nucleating agent.

[0013] Preferably, the grafting rate of the polypropylene grafted with methyl methacrylate is 1% to 3%, the melt index is 8 to 15 g / 10 min, and the test conditions are 230℃ and 2.16 kg.

[0014] Preferably, the grafting rate is controlled at 1% to 3% to ensure compatibility, and the melt index is matched with the homopolymer polypropylene matrix to facilitate dispersion.

[0015] This application also provides a method for preparing the above-mentioned bio-based stiffening shrinkage masterbatch, comprising the following steps: S1, adding the furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin, the rare earth organic complex β-crystal nucleating agent, and 0.5%~2% of hydroxyethylated phosphatidylcholine by weight of both into a low-temperature reactor, and stirring at a constant temperature of 70~85℃ for 30~60 minutes under nitrogen protection to obtain a pre-anchored composite; S2, adding the polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer, the polypropylene grafted methyl methacrylate, and the pre-anchored composite obtained in step S1 together into an ultrasonic resonance mixer, and mixing at an ultrasonic frequency of 20~40kHz and an ultrasonic power density of 0.5~1.5W / cm². 2 S2. Treat the material at 50-65℃ for 10-25 minutes to obtain a pre-activated mixture; S3. Mix the pre-activated mixture obtained in step S2 with an antioxidant, and then feed it into a twin-screw extruder equipped with a screw element with an increasing shear gradient along the screw axis for melt blending extrusion. The length-to-diameter ratio of the twin-screw extruder is 48-60:1, and three shearing sections are set sequentially along the material conveying direction: the shearing rate of the first shearing section is 50-100 s. -1The length is 25% of the total screw length, and the temperature is 170~185℃; the shear rate of the second shearing section is 150~250s. -1 The length is 40% of the total screw length, and the temperature is 185~200℃; the shear rate of the third shearing section is 100~150s. -1 The length is 35% of the total screw length, the temperature is 200~215℃; the screw speed is 250~450rpm, and the total residence time of the material in the twin-screw extruder is 2~5 minutes; S4, the melt extruded in step S3 is filtered and sent to a high-pressure microporous atomizing granulation device. The melt is atomized into fine droplets through a microporous plate with a pore size of 0.3~0.8mm under a pressure of 1.5~3.0MPa. The droplets fall in a cooling tower with a height of 2.5~4.5 meters. During the fall, they pass through a low-temperature nitrogen cooling zone of 5~10℃ and a deep cryogenic nitrogen quenching zone of -5~0℃ in sequence, causing the droplets to solidify into spherical particles. After the particles are collected, they are placed in a vacuum drying oven at 40~50℃ and dried for 2~4 hours to obtain the bio-based stiffening shrinkage masterbatch.

[0016] Preferably, step S1 involves low-temperature pre-anchoring to pre-attach rare earth organic complex β-crystal nucleating agents to the furan ring conjugated structure surface of the furan-based aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin; step S2 involves ultrasonic-assisted pre-dispersion to promote uniform mixing of components and interfacial pre-reaction; step S3 involves gradient shearing to achieve nanoscale dispersion and interfacial reaction of each component; and step S4 involves high-pressure microporous atomization granulation to obtain spherical particles, improving flowability and dispersibility.

[0017] Preferably, the degree of hydroxyethylation of the hydroxyethylated phosphatidylcholine is 1.5 to 2.5; the inner wall of the low-temperature reactor is coated with a polytetrafluoroethylene anti-stick coating.

[0018] Preferably, the degree of hydroxyethylation is controlled at 1.5 to 2.5 to balance the hydrophilicity and oleophilicity, and the polytetrafluoroethylene anti-stick coating prevents material adhesion.

[0019] Preferably, in step S3, the shear gradient increasing distribution threaded element is composed of a forward conveying threaded block, a kneading block, and a reverse threaded block, wherein the staggered angle of the kneading block increases from 30° to 60° and then decreases to 45° along the material conveying direction.

[0020] Preferably, the staggered angle of the kneaded blocks is first increased and then decreased, first increasing the shear to break up the aggregates, and then decreasing the shear to prevent thermal degradation.

[0021] This application also provides a BOPP cigarette film, which is a three-layer co-extruded biaxially stretched structure, including an upper surface layer, a core layer and a lower surface layer. The core layer is composed of the following raw materials in parts by weight: 70-85 parts of homopolymer polypropylene, 15-30 parts of the above-mentioned bio-based stiffening shrinkage masterbatch, and 1-3 parts of antistatic agent masterbatch. The upper and lower surface layers are composed of the following raw materials in parts by weight: 85-95 parts of random copolymer polypropylene, 3-8 parts of slip agent masterbatch, and 2-5 parts of anti-blocking masterbatch.

[0022] Preferably, the masterbatch is added to the core layer to play a role in increasing stiffness and controlling shrinkage. The amount of masterbatch added is controlled at 15 to 30 parts to balance performance and film-forming properties. Slip agents and anti-blocking agents are added to the surface layer to ensure surface smoothness and opening performance.

[0023] Preferably, the BOPP smoke film has a thickness of 12~20μm, a longitudinal elastic modulus of 2100MPa or more, a longitudinal heat shrinkage rate of 4.5%~8.5%, a transverse heat shrinkage rate of 3.0%~6.0%, an absolute value of the difference between the longitudinal and transverse heat shrinkage rates of less than 2.5%, a haze of less than 1.8%, and a bio-based carbon content of more than 25%.

[0024] Preferably, the smoke film achieves a combination of high stiffness, uniform shrinkage, low haze, and high bio-based content at an ultra-thin thickness.

[0025] This application also provides a method for preparing the above-mentioned BOPP cigarette film, comprising the following steps: mixing the core layer raw material and each surface layer raw material separately and feeding them into their respective extruders, extruding them into a thick sheet through a three-layer co-extrusion die, and cooling and shaping it by a chilling roller; preheating the thick sheet at 120~130℃ and then stretching it longitudinally with a stretching ratio of 4.5~6.0 times and a stretching temperature of 130~150℃; then stretching it transversely with a stretching ratio of 8.0~10.0 times and a stretching temperature of 155~170℃; finally, heat-setting, cooling, corona treatment, winding and slitting are performed, wherein the heat-setting temperature is 160~175℃ and the time is 5~15 seconds.

[0026] Preferably, a higher longitudinal and transverse stretching ratio is used to enhance molecular chain orientation, and the heat setting temperature is controlled at 160~175℃ to retain suitable shrinkage properties.

[0027] Due to the application of the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. This invention achieves a synergistic improvement in the high stiffness and controllable shrinkage performance of BOPP cigarette film. The longitudinal elastic modulus of the cigarette film reaches more than 2100MPa, the longitudinal heat shrinkage rate is controlled at 4.5%~8.5%, the transverse heat shrinkage rate is controlled at 3.0%~6.0%, and the MD / TD shrinkage rate difference is controlled below 2.5%.

[0028] 2. This invention integrates stiffening, shrinkage control, nucleation, and dispersion functions into a single masterbatch, simplifying the tobacco film production process, simplifying the batching process, reducing performance fluctuations between batches, and increasing the yield to over 95%.

[0029] 3. This invention significantly reduces the carbon footprint of the product. The bio-based carbon content in the masterbatch is more than 35%, and the overall bio-based carbon content of the film is more than 25%, which significantly reduces carbon dioxide emissions compared with traditional petroleum resin-based smoke films.

[0030] 4. The smoke film prepared by this invention has excellent optical properties and processing adaptability. The haze of the film is controlled below 1.8%, the gloss is above 85%, and the thermal weight loss of the masterbatch at 230℃ is below 0.3%, which meets the requirements for continuous and stable production.

[0031] 5. The four-step preparation process adopted in this invention improves the dispersion uniformity of functional components and the flowability of the product. By low-temperature pre-anchoring, ultrasonic-assisted pre-dispersion, gradient shear melt blending and high-pressure microporous atomization granulation, spherical particles are obtained, which have better flowability and dispersion uniformity than traditional irregular columnar particles. Detailed Implementation

[0032] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific implementation schemes are now described in detail.

[0033] The present invention will be further described below with reference to embodiments, but the present invention is not limited to the following embodiments. The implementation conditions used in the embodiments can be further adjusted according to different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in the various embodiments of the present invention can be combined with each other as long as they do not conflict with each other.

[0034] Example 1

[0035] This embodiment provides a bio-based stiffening and shrinkage-reducing masterbatch for BOPP cigarette films, the raw material composition and weight parts of which are as follows: 45 parts of furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin; 1.5 parts of rare earth organic complex β-crystal nucleating agent; 5 parts of polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer; 48 parts of polypropylene grafted methyl methacrylate; 0.5 parts of antioxidant, of which antioxidant 1010 is 0.3 parts and antioxidant 168 is 0.2 parts.

[0036] The furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin has a bio-based carbon content of 72%. Its preparation method is as follows: using 2,5-furandicarboxylic acid, 1,4-butanediol, and adipic acid as raw materials, wherein 2,5-furandicarboxylic acid accounts for 60% of the total molar amount of the diacids, they undergo melt polycondensation under the catalysis of tetrabutyl titanate to obtain a PBF prepolymer; the PBF prepolymer is mixed with the hydrogenated terpene resin at a mass ratio of 1:3, and 0.5% organotin catalyst is added. The mixture undergoes transesterification at 200°C for 3.5 hours. After removing byproducts by vacuum distillation, the target product is obtained, with a grafting rate of 8%. The softening point of the hydrogenated terpene resin is 125°C.

[0037] The rare earth organic complex β-crystal nucleating agent is a complex system of lanthanum and phthalic acid and N,N'-dicyclohexylterephthalamide, with a mass ratio of 1:2.

[0038] The polypropylene-grafted maleic anhydride-glycidyl methacrylate copolymer has a maleic anhydride grafting rate of 1.2% and a glycidyl methacrylate grafting rate of 0.8%.

[0039] The grafting rate of the polypropylene grafted with methyl methacrylate was 2.1%, the melt index was 12 g / 10 min, and the test conditions were 230℃ and 2.16 kg.

[0040] The above-mentioned method for preparing bio-based stiffening shrinkage masterbatch for BOPP cigarette film includes the following steps: S1. The furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin, the rare earth organic complex β-crystal nucleating agent, and 1% by weight of hydroxyethylated phosphatidylcholine are added to a low-temperature reactor. Under nitrogen protection, the mixture is stirred at 78°C for 45 minutes to obtain a pre-anchored composite. The degree of hydroxyethylation of the hydroxyethylated phosphatidylcholine is 2.0, and the inner wall of the low-temperature reactor is coated with a polytetrafluoroethylene anti-stick coating.

[0041] S2. The polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer, the polypropylene grafted methyl methacrylate, and the pre-anchored composite obtained in step S1 are jointly added into an ultrasonic resonance mixer, and the mixture is subjected to an ultrasonic frequency of 30 kHz and an ultrasonic power density of 1.0 W / cm². 2 The mixture was treated at 58℃ for 18 minutes to obtain a pre-activated mixture.

[0042] S3. After mixing the pre-activated mixture obtained in step S2 with the antioxidant, the mixture is fed into a twin-screw extruder equipped with threaded elements that have an increasing shear gradient along the screw axial direction for melt blending and extrusion. The twin-screw extruder has a length-to-diameter ratio of 54:1 and is configured with three shearing zones along the material conveying direction: the shearing rate of the first shearing zone is 75 s.-1 The length is 25% of the total screw length, and the temperature is 178℃; the shear rate of the second shearing section is 200s. -1 The length is 40% of the total screw length, and the temperature is 192℃; the shear rate of the third shearing section is 125s. -1 The screw length is 35% of the total screw length, the temperature is 208℃, the screw speed is 350 rpm, and the total residence time of the material in the twin-screw extruder is 3.5 minutes. The shear gradient increasing distribution threaded element is composed of a forward conveying threaded block, a kneading block, and a reverse threaded block, wherein the staggered angle of the kneading block increases from 30° to 60° and then decreases to 45° along the material conveying direction.

[0043] S4. The melt extruded in step S3 is filtered and then fed into a high-pressure microporous atomization granulation device. The melt is atomized into fine droplets through a microporous plate with a pore size of 0.5 mm under a pressure of 2.2 MPa. The droplets fall in a cooling tower with a height of 3.5 meters. During the fall, they pass through a low-temperature nitrogen cooling zone of 8°C and a deep cryogenic nitrogen quenching zone of -3°C in sequence, causing the droplets to solidify into spherical particles. After the particles are collected, they are placed in a vacuum drying oven at 45°C and dried for 3 hours to obtain the bio-based stiffening shrinkage masterbatch MB-1.

[0044] This embodiment also provides a BOPP cigarette film, which is a three-layer co-extruded biaxially stretched structure, including an upper surface layer, a core layer and a lower surface layer.

[0045] The core layer raw material composition is: 78 parts homopolymer polypropylene, 20 parts of the above-mentioned masterbatch MB-1, and 2 parts of antistatic agent masterbatch. The homopolymer polypropylene has a melt index of 3.2 g / 10 min and an isotacticity of 97%.

[0046] The upper and lower surface layers are composed of: 91 parts random copolymer polypropylene, 5.5 parts slip agent masterbatch, and 3.5 parts anti-blocking masterbatch. The random copolymer polypropylene has a melt index of 6.5 g / 10 min and an ethylene content of 4%.

[0047] The above-mentioned BOPP cigarette film preparation method includes the following steps: the core layer raw material and each surface layer raw material are mixed separately and fed into their respective extruders, then extruded into a thick sheet through a three-layer co-extrusion die, and cooled and shaped by a chilling roller.

[0048] After preheating the thick sheet at 125℃, it is stretched longitudinally with a stretching ratio of 5.2 times and a stretching temperature of 140℃.

[0049] Subsequently, a transverse stretching was performed with a stretching ratio of 9.0 times and a stretching temperature of 162℃.

[0050] Finally, after heat setting, cooling, corona treatment, and winding and slitting, the BOPP smoke film with a thickness of 16μm, denoted as F-1, is obtained. The heat setting temperature is 168℃ and the time is 10 seconds.

[0051] Example 2 This embodiment is based on the above embodiment 1, and the similarities with embodiment 1 will not be repeated.

[0052] The difference between this embodiment and Example 1 is that in the formulation of masterbatch MB-2, the amount of furanyl aromatic-aliphatic copolyester grafted modified hydrogenated terpene resin is adjusted to 50 parts, the amount of rare earth organic complex β-crystal nucleating agent is adjusted to 2.0 parts, the amount of polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer is adjusted to 6 parts, the amount of polypropylene grafted methyl methacrylate is adjusted to 41 parts, and the amount of antioxidant is adjusted to 0.6 parts. Other preparation steps and cigarette film preparation conditions are the same as in Example 1, and the resulting cigarette film is designated as F-2.

[0053] Example 3 This embodiment is based on the above embodiment 1, and the similarities with embodiment 1 will not be repeated.

[0054] The difference between this embodiment and Example 1 is that in the formulation of masterbatch MB-3, the amount of furanyl aromatic-aliphatic copolyester grafted modified hydrogenated terpene resin is adjusted to 35 parts, the amount of rare earth organic complex β-crystal nucleating agent is adjusted to 1.0 part, the amount of polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer is adjusted to 4 parts, the amount of polypropylene grafted methyl methacrylate is adjusted to 59 parts, and the amount of antioxidant is adjusted to 0.4 parts. Other preparation steps and cigarette film preparation conditions are the same as in Example 1, and the resulting cigarette film is designated as F-3.

[0055] Comparative Example 1 This comparative example is based on Example 1 above, and the similarities with Example 1 will not be repeated.

[0056] The difference between this comparative example and Example 1 is that C5 hydrogenated petroleum resin is used instead of the furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin, while the dosage and other components in the preparation method are the same as in Example 1. The resulting masterbatch is designated MB-D1, and the resulting smoke film is designated D-1.

[0057] Comparative Example 2 This comparative example is based on Example 1 above, and the similarities with Example 1 will not be repeated.

[0058] The difference between this comparative example and Example 1 is that no rare earth organic complex β-crystal nucleating agent is added to the masterbatch; the missing amount is made up by polypropylene grafted with methyl methacrylate. The resulting masterbatch is designated MB-D2, and the resulting smoke film is designated D-2.

[0059] Comparative Example 3 This comparative example is based on Example 1 above, and the similarities with Example 1 will not be repeated.

[0060] The difference between this comparative example and Example 1 is that the low-temperature pre-anchoring treatment in step S1 and the ultrasonic-assisted pre-dispersion treatment in step S2 are omitted in the preparation method of the masterbatch. Instead, all raw material components are directly added to a high-speed mixer and mixed for 10 minutes, followed by direct melt blending and extrusion in step S3. The resulting masterbatch is denoted as MB-D3, and the resulting smoke film is denoted as D-3.

[0061] Comparative Example 4 This comparative example is based on Example 1 above, and the similarities with Example 1 will not be repeated.

[0062] The difference between this comparative example and Example 1 is that in the preparation method of the masterbatch, the twin-screw extruder in step S3 is a conventional screw combination without a shear gradient increasing distribution screw element, that is, the shear rate of the three shear sections is 120s. -1 The remaining conditions are the same as in Example 1. The resulting masterbatch is denoted as MB-D4, and the resulting smoke film is denoted as D-4.

[0063] The performance of the BOPP cigarette films prepared in the above embodiments and comparative examples was tested using the following methods: (1) Longitudinal elastic modulus: Tested according to GB / T1040.3-2006 standard, with a sample width of 15mm, a clamping distance of 100mm, and a tensile speed of 50mm / min.

[0064] (2) Longitudinal heat shrinkage rate and transverse heat shrinkage rate: The shrinkage rate was measured after heating in an oven at 120℃ for 5 minutes in accordance with GB / T10003-2008 standard.

[0065] (3) Haze: Tested according to GB / T2410-2008 standard.

[0066] (4) Gloss: Tested according to GB / T8807-1988 standard, with an incident angle of 45°.

[0067] (5) Bio-based carbon content of thin film: tested according to ASTM D6866 standard.

[0068] The test results are shown in Table 1.

[0069] Table 1

[0070] As shown in Table 1, the longitudinal elastic modulus of the BOPP cigarette films prepared in Examples 1 to 3 all exceeded 2100 MPa, with Example 2 showing the highest at 2360 MPa, a 26.2% increase compared to the 1870 MPa of Comparative Example 1 (traditional petroleum resin-based). Regarding heat shrinkage performance, the longitudinal heat shrinkage rate of Examples 1 to 3 ranged from 5.1% to 7.2%, and the transverse heat shrinkage rate ranged from 3.8% to 5.1%. The difference between MD and TD shrinkage rates was controlled below 2.5%, exhibiting uniform shrinkage characteristics. However, Comparative Example 2, lacking a β-crystal nucleating agent, had a significantly lower heat shrinkage rate (3.2% longitudinally and 2.5% transversely), failing to meet the requirements for cigarette film bonding and packaging.

[0071] In terms of optical performance, the haze of Examples 1 to 3 was all below 1.6%, with the lowest being 1.4%, and the gloss was all above 86%, with the highest being 88%, which was significantly better than the haze of 2.4% and the gloss of 81% of Comparative Example 1. This indicates that the bio-based stiffening shrinkage masterbatch of the present invention has good compatibility with the polypropylene matrix and no optical quality degradation caused by phase separation occurred.

[0072] Regarding the bio-based carbon content, the bio-based carbon content of the films in Examples 1 to 3 all reached more than 25%, with Example 2 reaching the highest at 31.2%. In contrast, Comparative Example 1, which used petroleum resin, had a bio-based carbon content of 0, demonstrating that the present invention effectively reduced the carbon footprint of the product.

[0073] In Comparative Examples 3 and 4, the low-temperature pre-anchoring and ultrasonic-assisted pre-dispersion treatments were omitted, and the gradient shear thread combination was not used. The haze (1.9%) and gloss (84%) of the films were worse than those of Example 1 (haze 1.5%, gloss 87%). The longitudinal elastic modulus (2180MPa, 2210MPa) and shrinkage uniformity of Comparative Examples 3 and 4 were also slightly lower than those of Example 1. This shows that the multi-stage synergistic preparation process of the present invention has a positive effect on improving the dispersion uniformity of the masterbatch and the overall performance of the film.

[0074] In summary, this invention employs a four-step preparation process—using furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin combined with rare earth organic complex β-crystal nucleating agents, low-temperature pre-anchoring, ultrasonic-assisted pre-dispersion, gradient shear melt blending, and high-pressure microporous atomization granulation—to achieve a BOPP tobacco film with a longitudinal elastic modulus exceeding 2100 MPa, a longitudinal thermal shrinkage rate controlled between 4.5% and 8.5%, an MD / TD shrinkage rate difference controlled below 2.5%, a haze controlled below 1.8%, and a film bio-based carbon content exceeding 25%. This achieves a synergistic improvement in high stiffness and controllable shrinkage performance, significantly reduces the carbon footprint, simplifies the production process, and fully meets the environmental protection and functional upgrade needs of the tobacco packaging industry.

[0075] The embodiments described above are merely illustrative of more specific and detailed implementations of the present invention, and should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A bio-based stiffening and shrinkage-enhancing masterbatch for BOPP cigarette film, characterized in that, It is made from the following raw material components in parts by weight: 30-55 parts of furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin; Rare earth organic complex β-crystal nucleating agent: 0.5-3 parts; 3-8 parts of polypropylene grafted with maleic anhydride-glycidyl methacrylate copolymer; 35-60 parts of polypropylene grafted with methyl methacrylate; Antioxidant 0.2~0.8 parts; The furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin has a bio-based carbon content of over 70%, and the maleic anhydride grafting rate of the polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer is 0.8%~1.5%, and the glycidyl methacrylate grafting rate is 0.5%~1.0%.

2. The bio-based stiffening shrinkage masterbatch according to claim 1, characterized in that, The furanyl aromatic-aliphatic copolyester is obtained by copolymerization of 2,5-furandicarboxylic acid, 1,4-butanediol and adipic acid, wherein 2,5-furandicarboxylic acid accounts for 50% to 70% of the total molar amount of the dicarboxylic acid; the softening point of the hydrogenated terpene resin is 115 to 135°C; the grafting modification is achieved through transesterification reaction, with a grafting rate of 5% to 15%.

3. The bio-based stiffening shrinkage masterbatch according to claim 1, characterized in that, The rare earth organic complex β-crystal nucleating agent is a complex formed by lanthanum or cerium and an organic carboxylic acid, wherein the organic carboxylic acid is phthalic acid, naphthenic acid or salicylic acid; the rare earth organic complex β-crystal nucleating agent also contains aryl amide compounds, wherein the mass ratio of the rare earth organic complex to the aryl amide compound is 1:1.5~3, and the aryl amide compound is N,N'-dicyclohexyl terephthalamide or N,N'-dibenzoyl hexamethylenediamine.

4. The bio-based stiffening shrinkage masterbatch according to claim 1, characterized in that, The grafting rate of the polypropylene grafted with methyl methacrylate is 1%~3%, the melt index is 8~15g / 10min, and the test conditions are 230℃ and 2.16kg.

5. A method for preparing a bio-based stiffening shrinkage masterbatch as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. The furanyl aromatic-aliphatic copolyester graft-modified hydrogenated terpene resin, the rare earth organic complex β-crystal nucleating agent, and 0.5%~2% of hydroxyethylated phosphatidylcholine by weight of both are added to a low-temperature reactor and stirred at 70~85℃ for 30~60 minutes under nitrogen protection to obtain a pre-anchored composite. S2. The polypropylene grafted maleic anhydride-glycidyl methacrylate copolymer, the polypropylene grafted methyl methacrylate, and the pre-anchored composite obtained in step S1 are jointly added into an ultrasonic resonance mixer, and the mixture is subjected to an ultrasonic frequency of 20~40kHz and an ultrasonic power density of 0.5~1.5W / cm². 2 The mixture is treated at 50-65℃ for 10-25 minutes to obtain a pre-activated mixture. S3. After mixing the pre-activated mixture obtained in step S2 with the antioxidant, the mixture is fed into a twin-screw extruder equipped with threaded elements that have an increasing shear gradient along the screw axial direction for melt blending and extrusion. The length-to-diameter ratio of the twin-screw extruder is 48~60:1, and three shearing zones are set sequentially along the material conveying direction: the shearing rate of the first shearing zone is 50~100s. -1 The length is 25% of the total screw length, and the temperature is 170~185℃; the shear rate of the second shearing section is 150~250s. -1 The length is 40% of the total screw length, and the temperature is 185~200℃; the shear rate of the third shearing section is 100~150s. -1 The length is 35% of the total screw length, the temperature is 200~215℃, the screw speed is 250~450rpm, and the total residence time of the material in the twin-screw extruder is 2~5 minutes; S4. The melt extruded in step S3 is filtered and then fed into a high-pressure microporous atomization granulation device. The melt is atomized into fine droplets through a microporous plate with a pore size of 0.3-0.8 mm under a pressure of 1.5-3.0 MPa. The droplets fall in a cooling tower with a height of 2.5-4.5 meters. During the fall, they pass through a low-temperature nitrogen cooling zone of 5-10°C and a deep cryogenic nitrogen quenching zone of -5-0°C in sequence, causing the droplets to solidify into spherical particles. After the particles are collected, they are placed in a vacuum drying oven at 40-50°C and dried for 2-4 hours to obtain the bio-based stiffening shrinkage masterbatch.

6. The preparation method according to claim 5, characterized in that, The degree of hydroxyethylation of the hydroxyethylated phosphatidylcholine is 1.5 to 2.5; the inner wall of the low-temperature reactor is coated with a polytetrafluoroethylene anti-stick coating.

7. The preparation method according to claim 5, characterized in that, In step S3, the shear gradient increasing distribution threaded element is composed of a forward conveying threaded block, a kneading block, and a reverse threaded block, wherein the staggered angle of the kneading block increases from 30° to 60° and then decreases to 45° along the material conveying direction.

8. A BOPP cigarette film, having a three-layer co-extruded biaxially oriented structure, comprising an upper surface layer, a core layer, and a lower surface layer, characterized in that, The core layer is composed of the following raw materials in parts by weight: 70-85 parts homopolymer polypropylene, 15-30 parts of the masterbatch described in claim 1, and 1-3 parts of antistatic agent masterbatch; the upper and lower surface layers are composed of the following raw materials in parts by weight: 85-95 parts random copolymer polypropylene, 3-8 parts slip agent masterbatch, and 2-5 parts anti-blocking masterbatch.

9. The BOPP cigarette film according to claim 8, characterized in that, The BOPP smoke film has a thickness of 12~20μm, a longitudinal elastic modulus of 2100MPa or more, a longitudinal heat shrinkage rate of 4.5%~8.5%, a transverse heat shrinkage rate of 3.0%~6.0%, an absolute value of the difference between the longitudinal and transverse heat shrinkage rates of less than 2.5%, a haze of less than 1.8%, and a bio-based carbon content of more than 25%.

10. A method for preparing a BOPP cigarette film according to claim 8 or 9, characterized in that, Includes the following steps: The core layer material and each surface layer material are mixed separately and fed into their respective extruders. They are then combined through a three-layer co-extrusion die and extruded into a thick sheet, which is then cooled and shaped by a chilling roller. After preheating the thick sheet at 120~130℃, it is longitudinally stretched with a stretching ratio of 4.5~6.0 times and a stretching temperature of 130~150℃. Then, a transverse stretching is performed with a stretching ratio of 8.0 to 10.0 times and a stretching temperature of 155 to 170°C. Finally, the product undergoes heat setting, cooling, corona treatment, and winding and slitting. The heat setting temperature is 160~175℃ and the time is 5~15 seconds.

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