Ultrathin high-speed packaging biaxially oriented polypropylene film and preparation method thereof

Abstract

The invention belongs to the technical field of packaging materials, and particularly relates to an ultrathin high-speed packaging biaxially oriented polypropylene film and a preparation method thereof. The polypropylene film comprises an extrusion layer I, an extrusion layer II, a core layer, an extrusion layer III and an extrusion layer IV which are sequentially connected from outside to inside. The sealing temperature of the polypropylene film is lower than 90 DEG C, and the sealing requirement of a high-speed packaging machine can be met; the bending modulus of the film exceeds 1800 Mpa, and the high-speed film feeding requirement of a packaging machine is met; meanwhile, the advantages of low friction, high transparency, low shrinkage and the like are realized.

Description

Technical Field

[0001] This invention relates to the field of packaging materials technology, and in particular to an ultra-thin, high-speed packaging biaxially oriented polypropylene film and its preparation method. Background Technology

[0002] Driven by the upgrading and development of the consumer market, the packaging industry for snack foods and consumer goods is also showing growth, with online consumption showing particularly significant growth. Therefore, the packaging industry for products such as disposable straws, chopsticks, spoons and forks, ready-to-eat seaweed, cartoon cards, and books is trending towards ultra-thin, high-speed, and functional designs. Reducing plastic use in packaging is a mainstream direction for achieving carbon peaking and compliance with carbon emission standards. Traditional membrane materials face the following challenges: ultra-thinness (film thickness of 10-25μm or even lower); high speed (lower coefficient of friction (COF) and higher elastic modulus (tear resistance and dimensional stability); and functionalization (barrier properties against oxygen and water vapor).

[0003] Traditional heat-sealable films have a starting temperature of 125-134℃, which is high and results in a long heat-sealing time. They also have a flexural modulus of 1250-1350 MPa and a material thickness of more than 22 μm, which cannot meet the needs of high-speed packaging. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides an ultra-thin, high-speed packaging biaxially oriented polypropylene film and its preparation method. The polypropylene film has a sealing temperature below 90°C, which meets the sealing requirements of high-speed packaging machines. The film's flexural modulus exceeds 1800 MPa, meeting the requirements of high-speed film feeding in packaging machines. It also has advantages such as low friction, high transparency, and low shrinkage.

[0005] To achieve one of the objectives of this invention, the following technical solution is adopted: An ultra-thin, high-speed packaging biaxially oriented polypropylene film, comprising, from the outside to the inside, an extruded layer I, an extruded layer II, a core layer, an extruded layer III, and an extruded layer IV; the extruded layer I is a heat-sealing layer, and the extruded layer IV is a corona-electrode layer; the extruded layer I is composed of 30-50 parts by weight of ternary copolymer polypropylene I, 50-70 parts by weight of polybutene, and 3-6 parts by weight of an opening agent; the extruded layer II is composed of 40-60 parts by weight of ternary copolymer polypropylene II and 40-60 parts by weight of homopolymer polypropylene I; the core layer is composed of 98 parts by weight of homopolymer polypropylene II and 2 parts by weight of antistatic masterbatch; the extruded layer III is composed of 100 parts by weight of homopolymer polypropylene II; and the extruded layer IV is composed of 83 parts by weight of homopolymer polypropylene I, 15 parts by weight of ternary copolymer polypropylene I, and 2 parts by weight of anti-blocking masterbatch.

[0006] Preferably, the thickness of extruded layer I is 1.0um-1.5um; the thickness of extruded layer II is 0.5um-1.0um, ensuring that the overall gloss (haze) of the film material meets the standards; the thickness of the core layer is 7um-11um, which is a key layer to ensure that the biaxial film does not break during stretching, and to ensure heat resistance, creep resistance, flatness and slippage during subsequent high-speed packaging; the thickness of extruded layer III is 0.5-1.0um, and the co-extrusion of extruded layer III and core layer further enhances the overall strength and modulus of the film, as well as good gloss (haze) and processing performance; the thickness of extruded layer IV is 0.5um-1.0um.

[0007] Preferably, the total thickness of the polypropylene film is 10µm-14µm.

[0008] Preferably, the ternary copolymer polypropylene I is grade F8005 produced by Maoming Petrochemical Company, with a Vicat softening temperature of 134℃, exhibiting good heat-sealing and composite properties; the polybutene is grade F0410 produced by Zhenhai Refining & Chemical Company, with an MFR (230℃, 2.16kg) of 8.0g / 10min, a density of 0.9g / cm³, and a melting temperature of 90℃; the opening agent is grade AB6364 produced by Constance Chemical Company; and the ternary copolymer polypropylene II is grade FS305 produced by Lihe Zhixin Company, with an MFR (230℃, 2.16kg) of 5.7g / 10min, a density of 0.9g / cm³, and a Vicat softening temperature of 134℃. The melting point is 119℃; the grade of homopolymer polypropylene I is F03T produced by Anqing Baiju Company, with an MFR (230℃, 2.5kg) of 3.0g / 10min, a Vicat softening point of 150℃, and a density of 0.9g / cm³; the grade of homopolymer polypropylene II is FH0403 produced by Fushun Petrochemical Company, with an MFR (230℃, 2.16kg) of 3.0g / 10min; the grade of antistatic masterbatch is AT4021 produced by Constance Company; the grade of anti-blocking masterbatch is AB6264 produced by Constance Company, which can be uniformly distributed after stretching and has good temperature resistance, meeting the requirements for preventing adhesion in subsequent processing.

[0009] To achieve the second objective of this invention, this invention provides a method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film, comprising the following steps: S1. Melt extrusion: Each layer of raw material is fed into the corresponding extruder and melted by heating. The melt-extruded material is then extruded through a T-die to form a five-layer composite sheet. S2. Stretching and winding: The composite sheet is stretched longitudinally and laterally in sequence, and then trimmed, corona treated and wound in sequence. S3. Curing and Shaping: After the steel roller is wound up, it is suspended on a curing rack and kept at an ambient temperature of 50℃ and a humidity of <50%RH for 48-72 hours. Finally, it is cut to obtain biaxially oriented polypropylene film.

[0010] Preferably, in step S1, the extrusion temperature of extruded layer I is 235°C, the extrusion temperature of extruded layer II is 245°C, the extrusion temperature of core layer is 245°C, the extrusion temperature of extruded layer III is 235°C, and the extrusion temperature of extruded layer IV is 235°C.

[0011] Preferably, in step S1, the screw speed is 25-55 r / min; the extrusion rate of the composite sheet is 4.5 tons / hour.

[0012] Preferably, in step S2, the longitudinal stretching is divided into 24 preheating rollers, 6 stretching rollers, and 6 shaping rollers; the temperature of the 24 preheating rollers is 110℃-130℃, the temperature of the 6 stretching rollers is 150℃-160℃, and the temperature of the 6 shaping rollers is 150-160℃; the longitudinal stretching gap is 122-125mm; and the stretching ratio is 3.5-4.5 times.

[0013] Preferably, in step S2, the width of the longitudinally stretched membrane is 1000mm-1100mm; the transverse stretching is divided into three sections, including a preheating section, a heat-setting section, and a natural transition section. The temperature of the preheating section is 130-150℃, the temperature of the heat-setting section is 155-160℃, the temperature of the natural transition section is 60-70℃, and the stretching ratio is 8-9 times.

[0014] Preferably, in step S2, during the winding process, the gap between the winding stationary roller and the tension roller is 5-6 mm, the initial winding tension is 300 N / m, the winding tension taper curve is 80%, the initial contact roller pressure is 68 N / m, and the clamping force taper curve is 92%.

[0015] The advantages of this invention compared to the prior art are as follows: 1) The present invention has a lower initial sealing temperature, which can ensure the heat sealing effect under high-speed production conditions, and has a higher modulus to ensure that the film material is not easily broken under high-speed operation. At the same time, it meets the high challenges of film smoothness, appearance and forming effect under high-speed packaging conditions of different packaging machines.

[0016] 2) The polypropylene film of this invention has a sealing temperature of less than 90°C, which can meet the sealing requirements of high-speed packaging machines; the film modulus exceeds 1800 MPa, which meets the requirements of high-speed film feeding in packaging machines; and it also has the advantages of low friction, high transparency, and low shrinkage.

[0017] 3) Through a unique raw material formulation design, the raw materials in each layer work synergistically to keep the film's initial sealing temperature below 90°C, which is far superior to the initial sealing temperature of traditional heat-sealing films and can meet the heat-sealing requirements under high-speed packaging conditions.

[0018] 4) The film body of this invention is made of high-stiffness, high-modulus polypropylene material, with a flexural modulus exceeding 1800 MPa, a tensile strength exceeding 160 MPa, and an elongation at break of approximately 180%. It exhibits higher toughness and tensile strength during high-speed packaging production, and is less prone to tearing or breakage compared to ordinary heat-sealable films. Its low friction, high transparency, and low shrinkage characteristics allow it to adapt to higher processing speeds, increasing packaging efficiency by more than 30% compared to traditional heat-sealable films. While possessing high modulus, low initial sealing temperature, and ultra-thin thickness, all raw material particles are domestically produced, resulting in exceptional cost-effectiveness. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0020] A method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film includes the following steps: S1. Raw material preparation: Weigh the raw material resin for each layer, feed it into the designated and corresponding storage tanks, and set the feeding ratio for automatic feeding.

[0021] S2. Melt Extrusion: The raw materials for each layer are fed into their respective extruders and melted by heating. During extrusion, parameters such as temperature, pressure, and screw speed are strictly controlled to ensure uniform extrusion. Specifically, the extrusion temperature for layer I (heat-sealing layer) is 235℃, for layer II it is 245℃, for the core layer it is 245℃, for layer III it is 235℃, and for layer IV (corona layer) it is 235℃. The screw speed is adjusted within the range of 25-55 r / min based on the characteristics of the raw materials for each layer and the required extrusion volume.

[0022] S3. Casting: The five-layer co-extrusion rate is controlled at 4.5 tons / hour, and the traction roller speed is 5% higher than that of ordinary polyolefin materials. The materials of each layer after melt extrusion are extruded through a T-die to form a multi-layer composite sheet. During the casting process, a rapid cooling roller is used to quickly cool the sheet. The temperature of cooling water tank 1 is 45℃, and the temperature of cooling water tank 2 is 40℃. The liquid level of cooling water tank 1 is simultaneously lowered by 10cm to solidify the sheet and ensure the uniformity and stability of the internal structure of the sheet, thus avoiding the resin from absorbing water and reacting.

[0023] S4. Longitudinal Stretching: The cast sheet is then subjected to longitudinal and transverse stretching sequentially. Longitudinal stretching consists of 24 preheating rollers (temperature set at 110℃-130℃), 6 stretching rollers (temperature set at 150℃-160℃), and 6 setting rollers (temperature set at 150-160℃). The stretching gap setting was specifically explored and locked in at 122-125mm, with uniform stretching being the best result, corresponding to a stretching ratio of 3.5-4.5 times.

[0024] S5. Transverse Stretching: After longitudinal stretching, the width of the film is 1000mm-1100mm. The stretching is divided into three sections: the preheating section is set at 130-150℃, the heat setting section at 155-160℃, and the natural transition section at 60-70℃, with a stretching ratio of 8-9 times. By precisely controlling the stretching temperature and ratio, the polypropylene molecular chains are arranged in an orderly manner in both the longitudinal and transverse directions, thereby improving the film's strength, transparency, and barrier properties.

[0025] S6. Winding process: After transverse stretching, edge trimming and corona treatment are performed sequentially; based on the high modulus and high gloss characteristics of high barrier film, the gap between the winding stationary roller and the tension roller is set to 5-6mm, the initial winding tension is 300N / m, the winding tension taper curve is 80%, the initial contact roller pressure is 68N / m, and the clamping force taper curve is 92%. The winding process is crucial for the flatness and stress release of ultra-thin film materials.

[0026] S7. Curing and Shaping: After the steel roller is coiled, it is suspended on a curing rack and kept at an ambient temperature of 50℃ and a humidity of <50%RH for 48-72 hours. It is then cut into pieces according to the required specifications.

[0027] Example 1 Biaxially oriented polypropylene film 1 was prepared using the above preparation method, and the formulation of each layer was designed as follows: Extruded layer I (heat-sealing layer): consists of 45% ternary copolymer polypropylene I (brand name F8005), 55% polybutene (brand name F0410), and 5% opening agent (brand name AB6364), with a layer thickness of 1.0 μm. Extrusion layer II: consists of 50% ternary copolymer polypropylene I (grade F8005) and 50% homopolymer polypropylene I (grade F03T), with a layer thickness of 0.5µm; Core layer: consists of 98% homopolymer polypropylene II (grade FH0403) and 2% antistatic masterbatch (grade AT4021), with a layer thickness of 7µm; Extrusion layer III: consists of 100% homopolymer polypropylene II (grade FH0403) with a layer thickness of 1.0 μm; Extruded layer IV (corona layer): comprising 80% homopolymer polypropylene I (grade F03T), 20% ternary copolymer polypropylene I (grade F8005), and 2% anti-blocking masterbatch (grade AB6264), with a layer thickness of 0.5µm.

[0028] The preparation process parameters of the biaxially oriented polypropylene film 1 are shown in Table 1 below: Table 1

[0029] Example 2 Biaxially oriented polypropylene film 2 was prepared using the above preparation method, and the formulation of each layer was designed as follows: Extruded layer I (heat-sealing layer): consists of 55% ternary copolymer polypropylene I (brand name F8005), 40% polybutene (brand name F0410), and 5% opening agent (brand name AB6364), with a layer thickness of 1.5µm. Extrusion layer II: consists of 60% ternary copolymer polypropylene I (grade F8005) and 40% homopolymer polypropylene I (grade F03T), with a layer thickness of 0.6 μm. Core layer: consists of 98% homopolymer polypropylene II (grade FH0403) and 2% antistatic masterbatch (grade AT4021), with a layer thickness of 10.5µm; Extrusion layer III: consists of 100% homopolymer polypropylene II (grade FH0403) with a layer thickness of 0.8 μm; Extruded layer IV (corona layer): comprising 83% homopolymer polypropylene I (grade F03T), 15% ternary copolymer polypropylene I (grade F8005), and 2% anti-blocking masterbatch (grade AB6264), with a layer thickness of 0.6µm.

[0030] The preparation process parameters of the biaxially oriented polypropylene film 2 are shown in Table 2 below: Table 2

[0031] Comparative Example 1 Comparative Example 1 uses imported heat-sealing material and process, and other conditions are the same as in Example 1, to produce a traditional BOPP heat-sealing film.

[0032] The biaxially oriented polypropylene films 1-2 prepared in Examples 1 and 2, as well as the traditional BOPP heat-sealing film, were subjected to performance tests. The results are shown in Table 3 below. Table 3

[0033] As shown in Table 3 above, the film prepared in Comparative Example 1 has a tensile strength of 150 MPa, an elongation at break of 154%, a sealing temperature of 125℃, and a heat-sealing strength of 2.5 N / 15 mm at 125℃. The independent five-layer copolymer design in Example 1, with each resin layer performing a different function, ensures good processing capabilities at low temperatures. A comparison of Examples 1 and 2 with Comparative Example 1 clearly demonstrates that the ultra-thin, high-speed packaging biaxially oriented polypropylene film material prepared by this invention, through unique raw material formulation design and processing methods, not only has a lower sealing temperature and better heat-sealing effect compared to traditional BOPP heat-sealing films, but also higher tensile strength, lower friction, and lower cost, contributing to the development of the industry.

Claims

1. An ultra-thin, high-speed packaging biaxially oriented polypropylene film, characterized in that: The polypropylene film comprises, from the outside to the inside, an extruded layer I, an extruded layer II, a core layer, an extruded layer III, and an extruded layer IV connected sequentially. The extruded layer I is a heat-sealing layer, and the extruded layer IV is a corona-electrode layer. The extruded layer I consists of 30-50 parts by weight of ternary copolymer polypropylene I, 50-70 parts by weight of polybutene, and 3-6 parts by weight of an opening agent. The extruded layer II consists of 40-60 parts by weight of ternary copolymer polypropylene II and 40-60 parts by weight of homopolymer polypropylene I. The core layer consists of 98 parts by weight of homopolymer polypropylene II and 2 parts by weight of an antistatic masterbatch. The extruded layer III consists of 100 parts by weight of homopolymer polypropylene II. The extruded layer IV consists of 83 parts by weight of homopolymer polypropylene I, 15 parts by weight of ternary copolymer polypropylene I, and 2 parts by weight of an anti-blocking masterbatch.

2. The ultra-thin high-speed packaging biaxially oriented polypropylene film according to claim 1, characterized in that: The thickness of the extruded layer I is 1.0um-1.5um; the thickness of the extruded layer II is 0.5um-1.0um; the thickness of the core layer is 7um-11um; the thickness of the extruded layer III is 0.5-1.0um; and the thickness of the extruded layer IV is 0.5um-1.0um.

3. The ultra-thin high-speed packaging biaxially oriented polypropylene film according to claim 1, characterized in that: The total thickness of the polypropylene film is 10µm-14µm.

4. The ultra-thin high-speed packaging biaxially oriented polypropylene film according to claim 1, characterized in that: The grade of the ternary copolymer polypropylene I is F8005 produced by Maoming Petrochemical Company; the grade of the polybutene is F0410 produced by Zhenhai Refining & Chemical Company; the grade of the opening agent is AB6364 produced by Constance Chemical Company; the grade of the ternary copolymer polypropylene II is FS305 produced by Lihe Zhixin Company; the grade of the homopolymer polypropylene I is F03T produced by Anqing Baiju Company; the grade of the homopolymer polypropylene II is FH0403 produced by Fushun Petrochemical Company; the grade of the antistatic masterbatch is AT4021 produced by Constance Chemical Company; and the grade of the anti-blocking masterbatch is AB6264 produced by Constance Chemical Company.

5. A method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Melt extrusion: Each layer of raw material is fed into the corresponding extruder and melted by heating. The melt-extruded material is then extruded through a T-die to form a five-layer composite sheet. S2. Stretching and winding: The composite sheet is stretched longitudinally and laterally in sequence, and then trimmed, corona treated and wound in sequence. S3. Curing and Shaping: After the steel roller is wound up, it is suspended on a curing rack and kept at an ambient temperature of 50℃ and a humidity of <50%RH for 48-72 hours. Finally, it is cut to obtain biaxially oriented polypropylene film.

6. The method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film according to claim 5, characterized in that: In step S1, the extrusion temperature of layer I is 235°C, the extrusion temperature of layer II is 245°C, the extrusion temperature of the core layer is 245°C, the extrusion temperature of layer III is 235°C, and the extrusion temperature of layer IV is 235°C.

7. The method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film according to claim 5, characterized in that: In step S1, the screw speed is 25-55 r / min; the extrusion rate of the composite sheet is 4.5 tons / hour.

8. The method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film according to claim 5, characterized in that: In step S2, the longitudinal stretching is divided into 24 preheating rollers, 6 stretching rollers, and 6 shaping rollers; the temperature of the 24 preheating rollers is 110℃-130℃, the temperature of the 6 stretching rollers is 150℃-160℃, and the temperature of the 6 shaping rollers is 150-160℃; the longitudinal stretching gap is 122-125mm; and the stretching ratio is 3.5-4.5 times.

9. The method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film according to claim 5, characterized in that: In step S2, the width of the longitudinally stretched membrane is 1000mm-1100mm; the transverse stretching is divided into three sections, including a preheating section, a heat setting section, and a natural transition section. The temperature of the preheating section is 130-150℃, the temperature of the heat setting section is 155-160℃, the temperature of the natural transition section is 60-70℃, and the stretching ratio is 8-9 times.

10. The method for preparing an ultrathin, high-speed packaging biaxially oriented polypropylene film according to claim 5, characterized in that: In step S2, during the winding process, the gap between the winding stationary roll and the tension roll is 5-6 mm, the initial winding tension is 300 N / m, the winding tension taper curve is 80%, the initial contact roll pressure is 68 N / m, and the clamping force taper curve is 92%.

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