Process for the preparation of a high heat seal strength flexible bopp film

Abstract

The application relates to the field of BOPP films, in particular to a preparation method of a high-heat-seal-strength flexible BOPP film, which is used for solving the problems of low heat seal strength of the existing BOPP film and poor protection performance of the BOPP film on the content after the BOPP film is made into a packaging bag; the high-heat-seal-strength flexible BOPP film comprises a four-layer structure, and the four layers are a heat seal layer, a secondary upper surface layer, a core layer and an anti-sticking layer from top to bottom; the preparation method adds sorbitol derivatives and long-chain modifiers into the raw materials of the heat seal layer, so that the prepared high-heat-seal-strength flexible BOPP film has excellent heat seal strength, effectively enhances the stability and sealing effect of the BOPP film in the heat seal process, improves the sealing performance and leakage prevention performance of the packaging product, prolongs the shelf life of the product, and makes the product perform well in various complex packaging applications and adapt to the packaging requirements of various different products.

Description

Technical Field

[0001] This invention relates to the field of BOPP film, specifically to a method for preparing a high heat-sealing strength and flexible BOPP film. Background Technology

[0002] Polypropylene resin is plasticized and extruded through multiple extruders, then aggregated into a coat hanger-shaped die to form a sheet. This sheet is then stretched in both longitudinal and transverse directions to produce biaxially oriented polypropylene film, or BOPP film for short. Due to its high mechanical strength and physical stability, it is widely used in the packaging of food, pharmaceuticals, and daily necessities. However, ordinary heat-sealable BOPP film has low heat-seal strength, less than 2.5 N / 15 mm, resulting in poor protection of the contents in packaging bags, and in some cases, even breakage.

[0003] Therefore, developing a method for preparing a high heat-sealing strength and flexible BOPP film is of significant practical importance. To address the aforementioned technical shortcomings, a solution is proposed. Summary of the Invention

[0004] In order to overcome the above-mentioned technical problems, the purpose of this invention is to provide a method for preparing a high heat-sealing strength and flexible BOPP film, which solves the problem that the existing BOPP film has low heat-sealing strength and poor protection performance of the contents after being made into packaging bags.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] In a first aspect, this application provides a method for preparing a high heat-sealing strength and flexible BOPP film, comprising the following steps:

[0007] Step 1: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer, and the anti-stick layer are added to four different extruders and melted at a temperature of 180-250℃. The molten material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer, and the anti-stick layer are then extruded sequentially in a four-layer die to obtain a four-layer composite film.

[0008] Step 2: Cool the four-layer composite film to 30-35℃ with cooling water, then stretch it longitudinally at a longitudinal stretching temperature of 85-145℃ with a longitudinal stretching ratio of 4.5-5.5. Then stretch it transversely at a transverse stretching temperature of 150-175℃ with a transverse stretching ratio of 8-10. After corona treatment, the master roll film is obtained. After aging treatment, the master roll film is slit to obtain a high heat-sealing strength flexible BOPP film.

[0009] In a preferred embodiment of the present invention, the thickness of the heat-sealing layer is 0.5-1.0 μm.

[0010] In a preferred embodiment of the present invention, the thickness of the secondary upper surface layer is 0.5-0.8 μm.

[0011] In a preferred embodiment of the present invention, the thickness of the core layer is 13-25 μm.

[0012] In a preferred embodiment of the present invention, the thickness of the anti-stick layer is 0.5-1.0 μm.

[0013] In a preferred embodiment of the present invention, the high heat-sealing strength and flexibility BOPP film comprises a four-layer structure, which, from top to bottom, consists of a heat-sealing layer, a second upper surface layer, a core layer, and an anti-sticking layer.

[0014] In a preferred embodiment of the present invention, the heat-sealing layer comprises the following raw materials in parts by weight:

[0015] The mixture consists of 10-15 parts of octene copolymerized linear low-density polyethylene, 5-15 parts of metallocene polyethylene, 55-80 parts of ternary copolymerized polypropylene, 1-5 parts of sorbitol derivatives, and 4-8 parts of multi-chain modifiers.

[0016] In a preferred embodiment of the present invention, the secondary upper surface layer comprises the following raw materials in parts by weight:

[0017] 80-85 parts of ternary copolymer polypropylene, 10-15 parts of POE, and 2-5 parts of antistatic masterbatch.

[0018] In a preferred embodiment of the present invention, the core layer comprises the following raw materials in parts by weight:

[0019] 97-98 parts homopolymer polypropylene, 1-2 parts antistatic masterbatch, and 0.5-1 parts slip masterbatch.

[0020] In a preferred embodiment of the present invention, the anti-stick layer comprises the following raw materials in parts by weight:

[0021] 96-98 parts of homopolymer polypropylene and 2-4 parts of anti-blocking masterbatch.

[0022] In a preferred embodiment of the present invention, the octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B.

[0023] In a preferred embodiment of the present invention, the metallocene polyethylene is SABIC LLDPE 318BJ.

[0024] In a preferred embodiment of the present invention, the ternary copolymer polypropylene is Yanshan Petrochemical F5606.

[0025] In a preferred embodiment of the present invention, the POE is Dow POE 7467.

[0026] In a preferred embodiment of the present invention, the antistatic masterbatch is Constance AT 4190 PP.

[0027] In a preferred embodiment of the present invention, the homopolymer polypropylene is HB28F from North China Petrochemical.

[0028] In a preferred embodiment of the present invention, the slip masterbatch is Constance SL 5068 PP.

[0029] In a preferred embodiment of the present invention, the anti-blocking masterbatch is Constance AB 6019 PP.

[0030] In a preferred embodiment of the present invention, the sorbitol derivative is prepared by the following steps:

[0031] Sorbitol, isophorone diisocyanate, dibutyltin dilaurate, and N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas was introduced for protection, and the mixture was stirred at 0-5℃ and 200-300 r / min for 10-20 min. Then, the temperature was raised to 40-50℃ and the mixture was stirred for another 8-10 h. After the reaction was completed, the product was cooled to room temperature, and the solvent was removed by rotary evaporation to obtain the sorbitol derivative.

[0032] In a preferred embodiment of the present invention, the ratio of sorbitol, isophorone diisocyanate, dibutyltin dilaurate, and N,N-dimethylformamide is 10 mmol: 45-55 mmol: 0.02-0.04 g: 40-50 mL.

[0033] In a preferred embodiment of the present invention, the multi-chain modifier is prepared by the following steps:

[0034] Step a1: Citric acid, n-decyl alcohol, p-toluenesulfonic acid, and toluene are added to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Nitrogen gas is introduced for protection. The mixture is stirred for 20-30 minutes at a temperature of 20-25℃ and a stirring rate of 200-300 r / min. Then, the temperature is raised to 120-130℃ and the mixture is stirred for another 3-4 hours. After the reaction is completed, the reaction product is cooled to room temperature. The pH is then adjusted to 7-7.5 with sodium hydroxide solution. The product is then washed 2-3 times with distilled water. Finally, the solvent is removed by rotary evaporation to obtain the hydroxyl polychain compound.

[0035] Step a2: Add the hydroxyl multi-chain compound, 1,6-dibromohexane, potassium carbonate, and dimethyl sulfoxide to a three-necked flask equipped with a stirrer, thermometer, and gas delivery tube. Purge with nitrogen for protection and stir the reaction at 20-25°C and 200-300 r / min for 20-30 min. Then raise the temperature to 50-60°C and continue stirring for 3-4 h. After the reaction is complete, cool the reaction product to room temperature and pour it into distilled water. Then extract with chloroform 2-3 times, combine the extracts and dry them with anhydrous magnesium sulfate. Then filter under vacuum and remove the solvent by rotary evaporation to obtain the multi-chain modifier.

[0036] In a preferred embodiment of the present invention, the ratio of citric acid, n-decyl alcohol, p-toluenesulfonic acid and toluene in step a1 is 10 mmol: 35-40 mmol: 0.05-0.1 g: 50-60 mL.

[0037] In a preferred embodiment of the present invention, the sodium hydroxide solution in step a1 has a mass fraction of 8-10%.

[0038] In a preferred embodiment of the present invention, the ratio of the hydroxyl polychain compound, 1,6-dibromohexane, potassium carbonate and dimethyl sulfoxide in step a2 is 20 mmol: 10 mmol: 30-35 mmol: 60-70 mL.

[0039] Compared with the prior art, the beneficial effects of the present invention are:

[0040] This invention discloses a method for preparing a high heat-sealable strength flexible BOPP film. The method involves melting the raw materials for the heat-sealable layer, the upper second-layer layer, the core layer, and the anti-stick layer separately, then combining and extruding them to obtain a four-layer composite film. The four-layer composite film is then cooled and stretched to obtain the high heat-sealable strength flexible BOPP film. This preparation method, by adding sorbitol derivatives and multi-chain modifiers to the raw materials of the heat-sealable layer, results in a high heat-sealable strength flexible BOPP film with excellent heat-sealable strength. This effectively enhances the stability and sealing effect of the BOPP film during the heat-seal process, improves the sealing and leak-proof performance of packaged products, extends the shelf life of the products, and enables it to perform excellently in various complex packaging applications, adapting to the packaging needs of a variety of different products.

[0041] In the preparation of high heat-sealing strength and flexibility BOPP film, a sorbitol derivative was first prepared. This involved the reaction of sorbitol and isophorone diisocyanate. Sorbitol contains multiple hydroxyl groups that react with the isocyanate groups on isophorone diisocyanate, thereby introducing a large number of isocyanate groups to obtain the sorbitol derivative. This sorbitol derivative has a large number of isocyanate groups in its molecular structure. These isocyanate groups are highly reactive and can react with hydroxyl and amino groups in the BOPP film to form stable chemical bonds and rapidly create a rich cross-linked network structure, thus significantly improving the heat-sealing strength of the BOPP film.

[0042] In the process of preparing a high heat-sealing strength and flexible BOPP film, a multi-chain modifier was also prepared. This modifier utilizes a reaction between citric acid and n-decanol, where the carboxyl group on citric acid undergoes an esterification reaction with the hydroxyl group on n-decanol, introducing multiple long carbon chains to obtain a hydroxyl multi-chain compound. Then, using this hydroxyl multi-chain compound and 1,6-dibromohexane, the hydroxyl group on the hydroxyl multi-chain compound reacts with the bromine atom on 1,6-dibromohexane to form a multi-chain modifier with multiple carbon chains at both ends. This multi-chain modifier contains a large number of long carbon chains in its molecular structure. These long carbon chains have a lower glass transition temperature and good fluidity. During heat sealing, these long carbon chains melt first and migrate to the interface between the two films, reducing the activation energy of polymer chain movement. This makes it easier for molecules at the heat-sealing interface to interpenetrate and diffuse, forming stronger intermolecular bonds. Furthermore, the long carbon chains can diffuse and entangle with each other, further forming a cross-linked network structure, thereby significantly improving the heat-sealing strength of the BOPP film. Attached Figure Description

[0043] To facilitate understanding by those skilled in the art, the present invention will be further described below with reference to the accompanying drawings.

[0044] Figure 1 This is a schematic diagram of the structure of the high heat-sealing strength and flexibility BOPP film of the present invention.

[0045] Figure 2 This is a schematic diagram showing the test results of the heat-sealing strength performance of the high heat-sealing strength and flexibility BOPP film of the present invention. Detailed Implementation

[0046] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Example 1, please refer to Figure 1 As shown, this embodiment is a method for preparing a high heat-sealing strength and flexible BOPP film, including the following steps:

[0048] Step s1: 10 mmol of sorbitol, 45 mmol of isophorone diisocyanate, 0.02 g of dibutyltin dilaurate and 40 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 0 °C and 200 r / min for 10 min. Then the temperature was raised to 40 °C and the mixture was stirred for 8 h. After the reaction was completed, the reaction product was cooled to room temperature and the solvent was removed by rotary evaporation to obtain the sorbitol derivative.

[0049] Step s2: 10 mmol citric acid, 35 mmol n-decyl alcohol, 0.05 g p-toluenesulfonic acid and 50 mL toluene were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 20 °C and 200 r / min for 20 min. Then the temperature was raised to 120 °C and the mixture was stirred for 3 h. After the reaction was completed, the reaction product was cooled to room temperature. The pH was then adjusted to 7 with 8% sodium hydroxide solution. The product was washed twice with distilled water and the solvent was removed by rotary evaporation to obtain the hydroxyl polychain compound.

[0050] Step s3: 20 mmol of hydroxyl multi-chain compound, 10 mmol of 1,6-dibromohexane, 30 mmol of potassium carbonate and 60 mL of dimethyl sulfoxide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 20 °C and 200 r / min for 20 min. Then the temperature was raised to 50 °C and the mixture was stirred for 3 h. After the reaction was completed, the reaction product was cooled to room temperature and poured into distilled water. The product was then extracted twice with chloroform. The extracts were combined and dried with anhydrous magnesium sulfate. The product was then filtered under vacuum and the solvent was removed by rotary evaporation to obtain the multi-chain modifier.

[0051] Step s4: Weigh out 10 parts by weight of octene copolymer linear low-density polyethylene, 5 parts by weight of metallocene polyethylene, 55 parts by weight of ternary copolymer polypropylene, 1 part by weight of sorbitol derivative, and 4 parts by weight of multi-chain modifier to obtain the raw material for the heat-sealing layer; wherein, the octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B; the metallocene polyethylene is SABIC LLDPE 318BJ; and the ternary copolymer polypropylene is Yanshan Petrochemical F5606.

[0052] Step s5: Weigh 80 parts of ternary copolymer polypropylene, 10 parts of POE and 2 parts of antistatic masterbatch according to the weight ratio to obtain the raw material for the second upper surface layer; wherein, the POE is Dow POE 7467 from the United States.

[0053] Step s6: Weigh 97 parts by weight of homopolymer polypropylene, 1 part by weight of antistatic masterbatch and 0.5 parts by weight of slip masterbatch to obtain the raw materials for the core layer; wherein, the homopolymer polypropylene is Huabei Petrochemical HB28F; the antistatic masterbatch is Constance AT4190 PP; and the slip masterbatch is Constance SL 5068 PP.

[0054] Step s7: Weigh 96 parts of homopolymer polypropylene and 2 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the anti-blocking layer; wherein, the anti-blocking masterbatch is Constance AB 6019 PP;

[0055] Step s8: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are added to four different extruders and melted at a temperature of 230°C. The melted material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are then extruded in sequence through a four-layer die to obtain a four-layer composite film.

[0056] Step s9: The four-layer composite film is cooled to 30°C with cooling water, and then longitudinally stretched at a stretching roller temperature of 120°C with a longitudinal stretching ratio of 4.5. Then, it is transversely stretched at a stretching zone temperature of 153°C with a transverse stretching ratio of 8. After corona treatment, a master roll film is obtained. The master roll film is then slit after aging treatment to obtain a high heat-sealing strength flexible BOPP film with a heat-sealing layer thickness of 0.8μm, a secondary upper surface layer thickness of 0.6μm, a core layer thickness of 20μm, and an anti-stick layer thickness of 0.8μm.

[0057] Example 2, please refer to Figure 1 As shown, this embodiment is a method for preparing a high heat-sealing strength and flexible BOPP film, including the following steps:

[0058] Step s1: 10 mmol of sorbitol, 50 mmol of isophorone diisocyanate, 0.03 g of dibutyltin dilaurate and 45 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 3 °C and 250 r / min for 15 min. Then the temperature was raised to 45 °C and the mixture was stirred for 9 h. After the reaction was completed, the product was cooled to room temperature and the solvent was removed by rotary evaporation to obtain the sorbitol derivative.

[0059] Step s2: 10 mmol citric acid, 38 mmol n-decyl alcohol, 0.08 g p-toluenesulfonic acid and 55 mL toluene were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 22 °C and 250 r / min for 25 min. Then the temperature was raised to 125 °C and the mixture was stirred for 3.5 h. After the reaction was completed, the reaction product was cooled to room temperature. The pH was then adjusted to 7 with 9% sodium hydroxide solution. The product was washed twice with distilled water and the solvent was removed by rotary evaporation to obtain the hydroxyl polychain compound.

[0060] Step s3: 20 mmol of hydroxyl multi-chain compound, 10 mmol of 1,6-dibromohexane, 33 mmol of potassium carbonate and 65 mL of dimethyl sulfoxide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 22 °C and 250 r / min for 25 min. Then the temperature was raised to 55 °C and the mixture was stirred for 3.5 h. After the reaction was completed, the reaction product was cooled to room temperature and poured into distilled water. The product was then extracted twice with chloroform. The extracts were combined and dried with anhydrous magnesium sulfate. The product was then filtered under vacuum and the solvent was removed by rotary evaporation to obtain the multi-chain modifier.

[0061] Step s4: Weigh out 12 parts by weight of octene copolymer linear low-density polyethylene, 10 parts by weight of metallocene polyethylene, 70 parts by weight of ternary copolymer polypropylene, 3 parts by weight of sorbitol derivative, and 6 parts by weight of multi-chain modifier to obtain the raw material for the heat-sealing layer; wherein, the octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B; the metallocene polyethylene is SABIC LLDPE 318BJ; and the ternary copolymer polypropylene is Yanshan Petrochemical F5606.

[0062] Step s5: Weigh 82 parts of ternary copolymer polypropylene, 12 parts of POE and 3.5 parts of antistatic masterbatch according to the weight ratio to obtain the raw material for the second upper surface layer; wherein, the POE is Dow POE 7467 from the United States.

[0063] Step s6: Weigh 97.5 parts by weight of homopolymer polypropylene, 1.5 parts by weight of antistatic masterbatch and 0.8 parts by weight of slip masterbatch to obtain the raw materials for the core layer; wherein, the homopolymer polypropylene is Huabei Petrochemical HB28F; the antistatic masterbatch is Constance AT 4190 PP; and the slip masterbatch is Constance SL 5068 PP.

[0064] Step s7: Weigh 97 parts of homopolymer polypropylene and 3 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the anti-blocking layer; wherein, the anti-blocking masterbatch is Constance AB 6019 PP;

[0065] Step s8: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are added to four different extruders and melted at a temperature of 220°C. The melted material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are then extruded in sequence through a four-layer die to obtain a four-layer composite film.

[0066] Step s9: The four-layer composite film is cooled to 32°C with cooling water, and then longitudinally stretched at a stretching roller temperature of 118°C with a longitudinal stretching ratio of 5. Then, it is transversely stretched at a stretching zone temperature of 154°C with a transverse stretching ratio of 9. After corona treatment, a master roll film is obtained. The master roll film is then slit after aging treatment to obtain a high heat-sealing strength flexible BOPP film with a heat-sealing layer thickness of 0.8μm, a secondary upper surface layer thickness of 0.6μm, a core layer thickness of 20μm, and an anti-stick layer thickness of 0.8μm.

[0067] Example 3, please refer to Figure 1 As shown, this embodiment is a method for preparing a high heat-sealing strength and flexible BOPP film, including the following steps:

[0068] Step s1: 10 mmol of sorbitol, 55 mmol of isophorone diisocyanate, 0.04 g of dibutyltin dilaurate and 50 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 5 °C and 300 r / min for 20 min. Then the temperature was raised to 50 °C and the mixture was stirred for 10 h. After the reaction was completed, the reaction product was cooled to room temperature and the solvent was removed by rotary evaporation to obtain the sorbitol derivative.

[0069] Step s2: 10 mmol citric acid, 40 mmol n-decyl alcohol, 0.1 g p-toluenesulfonic acid and 60 mL toluene were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 25 °C and 300 r / min for 30 min. Then the temperature was raised to 130 °C and the mixture was stirred for 4 h. After the reaction was completed, the reaction product was cooled to room temperature. The pH was then adjusted to 7.5 with 10% sodium hydroxide solution. The product was washed three times with distilled water. The solvent was then removed by rotary evaporation to obtain the hydroxyl polychain compound.

[0070] Step s3: 20 mmol of hydroxyl multi-chain compound, 10 mmol of 1,6-dibromohexane, 35 mmol of potassium carbonate and 70 mL of dimethyl sulfoxide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 25 °C and 300 r / min for 30 min. Then the temperature was raised to 60 °C and the mixture was stirred for 4 h. After the reaction was completed, the reaction product was cooled to room temperature and poured into distilled water. The product was then extracted three times with chloroform. The extracts were combined and dried with anhydrous magnesium sulfate. The product was then filtered under vacuum and the solvent was removed by rotary evaporation to obtain the multi-chain modifier.

[0071] Step s4: Weigh out 15 parts by weight of octene copolymer linear low-density polyethylene, 15 parts by weight of metallocene polyethylene, 80 parts by weight of ternary copolymer polypropylene, 5 parts by weight of sorbitol derivative, and 8 parts by weight of multi-chain modifier to obtain the raw material for the heat-sealing layer; wherein, the octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B; the metallocene polyethylene is SABIC LLDPE 318BJ; and the ternary copolymer polypropylene is Yanshan Petrochemical F5606.

[0072] Step s5: Weigh 85 parts of ternary copolymer polypropylene, 15 parts of POE and 5 parts of antistatic masterbatch according to the weight ratio to obtain the raw material for the second upper surface layer; wherein, the POE is Dow POE 7467 from the United States.

[0073] Step s6: Weigh 98 parts of homopolymer polypropylene, 2 parts of antistatic masterbatch, and 1 part of slip masterbatch according to the weight ratio to obtain the raw materials for the core layer; wherein, the homopolymer polypropylene is Huabei Petrochemical HB28F; the antistatic masterbatch is Constance AT 4190PP; and the slip masterbatch is Constance SL 5068 PP.

[0074] Step s7: Weigh 98 parts of homopolymer polypropylene and 4 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the anti-blocking layer; wherein, the anti-blocking masterbatch is Constance AB 6019 PP;

[0075] Step s8: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are added to four different extruders and melted at a temperature of 250°C. The molten material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are then extruded in sequence through a four-layer die to obtain a four-layer composite film.

[0076] Step s9: The four-layer composite film is cooled to 35°C with cooling water, and then longitudinally stretched in the stretching zone at a roller temperature of 105°C with a longitudinal stretching ratio of 5.5. Then, it is transversely stretched in the stretching zone at a temperature of 156°C with a transverse stretching ratio of 10. After corona treatment, a master roll film is obtained. The master roll film is then slit after aging treatment to obtain a high heat-sealing strength flexible BOPP film with a heat-sealing layer thickness of 0.8μm, a secondary upper surface layer thickness of 0.6μm, a core layer thickness of 20μm, and an anti-stick layer thickness of 0.8μm.

[0077] Comparative Example 1:

[0078] Please see Figure 1 As shown, this comparative example illustrates a method for preparing a common BOPP heat-sealable film, comprising the following steps:

[0079] Step s1: Weigh 98 parts of ternary copolymer polypropylene and 2 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the heat-sealing layer; wherein, the ternary copolymer polypropylene is Yanshan Petrochemical F5606; and the anti-blocking masterbatch is Constance AB 6056PPR.

[0080] Step s2: Weigh 97 parts of ternary copolymer polypropylene and 3 parts of antistatic masterbatch according to the weight ratio to obtain the raw material for the second upper surface layer;

[0081] Step s3: Weigh 98 parts of homopolymer polypropylene, 2 parts of antistatic masterbatch, and 1 part of slip masterbatch according to the weight ratio to obtain the raw materials for the core layer; wherein, the homopolymer polypropylene is Huabei Petrochemical HB28F; the antistatic masterbatch is Constance AT 4190PP; and the slip masterbatch is Constance SL 5068 PP.

[0082] Step s4: Weigh 98 parts of homopolymer polypropylene and 4 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the anti-blocking layer; wherein, the anti-blocking masterbatch is Constance AB 6019 PP;

[0083] Step s5: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are added to four different extruders and melted at a temperature of 240°C. The melted material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are then extruded in sequence through a four-layer die to obtain a four-layer composite film.

[0084] Step s6: The four-layer composite film is cooled to 35°C with cooling water, and then longitudinally stretched at 125°C in the stretching zone of the longitudinal stretching process, with a longitudinal stretching ratio of 5.5. Then, it is transversely stretched at 156°C in the stretching zone of the transverse stretching process, with a transverse stretching ratio of 10. After corona treatment, a master roll film is obtained. The master roll film is then slit after aging treatment to obtain a high heat-sealing strength flexible BOPP film with a heat-sealing layer thickness of 0.8μm, a secondary upper surface layer thickness of 0.6μm, a core layer thickness of 20μm, and an anti-stick layer thickness of 0.8μm.

[0085] Comparative Example 2:

[0086] Please see Figure 1 As shown, this comparative example illustrates a method for preparing a high heat-sealing strength and flexible BOPP film, comprising the following steps:

[0087] Step s1: 10 mmol of sorbitol, 55 mmol of isophorone diisocyanate, 0.04 g of dibutyltin dilaurate and 50 mL of N,N-dimethylformamide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 5 °C and 300 r / min for 20 min. Then the temperature was raised to 50 °C and the mixture was stirred for 10 h. After the reaction was completed, the reaction product was cooled to room temperature and the solvent was removed by rotary evaporation to obtain the sorbitol derivative.

[0088] Step s2: Weigh out 15 parts by weight of octene copolymer linear low-density polyethylene, 15 parts by weight of metallocene polyethylene, 80 parts by weight of ternary copolymer polypropylene, and 5 parts by weight of sorbitol derivative to obtain the raw materials for the heat-sealing layer; wherein, the octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B; the metallocene polyethylene is SABIC LLDPE 318BJ; and the ternary copolymer polypropylene is Yanshan Petrochemical F5606.

[0089] Step s3: Weigh 85 parts of ternary copolymer polypropylene, 15 parts of POE and 5 parts of antistatic masterbatch according to the weight ratio to obtain the raw material for the second upper surface layer; wherein, the POE is Dow POE 7467 from the United States.

[0090] Step s4: Weigh 98 parts of homopolymer polypropylene, 2 parts of antistatic masterbatch, and 1 part of slip masterbatch according to the weight ratio to obtain the raw materials for the core layer; wherein, the homopolymer polypropylene is Huabei Petrochemical HB28F; the antistatic masterbatch is Constance AT 4190PP; and the slip masterbatch is Constance SL 5068 PP.

[0091] Step s5: Weigh 98 parts of homopolymer polypropylene and 4 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the anti-blocking layer; wherein, the anti-blocking masterbatch is Constance AB 6019 PP;

[0092] Step s6: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are added to four different extruders and melted at a temperature of 240°C. The melted material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are then extruded in sequence through a four-layer die to obtain a four-layer composite film.

[0093] Step s7: The four-layer composite film is cooled to 35°C with cooling water, and then longitudinally stretched in the stretching zone at a roller temperature of 120°C with a longitudinal stretching ratio of 5.4. Then, it is transversely stretched in the stretching zone at a temperature of 153°C with a transverse stretching ratio of 10. After corona treatment, a master roll film is obtained. The master roll film is then slit after aging treatment to obtain a high heat-sealing strength flexible BOPP film with a heat-sealing layer thickness of 0.8μm, a secondary upper surface layer thickness of 0.6μm, a core layer thickness of 20μm, and an anti-stick layer thickness of 0.8μm.

[0094] Comparative Example 3:

[0095] Please see Figure 1 As shown, this comparative example illustrates a method for preparing a high heat-sealing strength and flexible BOPP film, comprising the following steps:

[0096] Step s1: 10 mmol citric acid, 40 mmol n-decyl alcohol, 0.1 g p-toluenesulfonic acid and 60 mL toluene were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 25 °C and 300 r / min for 30 min. Then the temperature was raised to 130 °C and the mixture was stirred for 4 h. After the reaction was completed, the reaction product was cooled to room temperature. The pH was then adjusted to 7.5 with 10% sodium hydroxide solution. The product was washed three times with distilled water. The solvent was then removed by rotary evaporation to obtain the hydroxyl polychain compound.

[0097] Step s2: 20 mmol of hydroxyl multi-chain compound, 10 mmol of 1,6-dibromohexane, 35 mmol of potassium carbonate and 70 mL of dimethyl sulfoxide were added to a three-necked flask equipped with a stirrer, thermometer and gas delivery tube. Nitrogen gas was introduced for protection. The mixture was stirred at 25 °C and 300 r / min for 30 min. Then the temperature was raised to 60 °C and the mixture was stirred for 4 h. After the reaction was completed, the reaction product was cooled to room temperature and poured into distilled water. The product was then extracted three times with chloroform. The extracts were combined and dried with anhydrous magnesium sulfate. The product was then filtered under vacuum and the solvent was removed by rotary evaporation to obtain the multi-chain modifier.

[0098] Step s3: Weigh out 15 parts by weight of octene copolymer linear low-density polyethylene, 15 parts by weight of metallocene polyethylene, 80 parts by weight of ternary copolymer polypropylene, and 8 parts by weight of multi-chain modifier to obtain the raw materials for the heat-sealing layer; wherein, the octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B; the metallocene polyethylene is SABIC LLDPE 318BJ; and the ternary copolymer polypropylene is Yanshan Petrochemical F5606.

[0099] Step s4: Weigh 85 parts of ternary copolymer polypropylene, 15 parts of POE and 5 parts of antistatic masterbatch according to the weight ratio to obtain the raw material for the second upper surface layer; wherein, the POE is Dow POE 7467 from the United States.

[0100] Step s5: Weigh 98 parts of homopolymer polypropylene, 2 parts of antistatic masterbatch, and 1 part of slip masterbatch according to the weight ratio to obtain the raw materials for the core layer; wherein, the homopolymer polypropylene is Huabei Petrochemical HB28F; the antistatic masterbatch is Constance AT 4190PP; and the slip masterbatch is Constance SL 5068 PP.

[0101] Step s6: Weigh 98 parts of homopolymer polypropylene and 4 parts of anti-blocking masterbatch according to the weight ratio to obtain the raw materials for the anti-blocking layer; wherein, the anti-blocking masterbatch is Constance AB 6019 PP;

[0102] Step s7: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are added to four different extruders and melted at a temperature of 230°C. The melted material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer and the anti-stick layer are then extruded in sequence through a four-layer die to obtain a four-layer composite film.

[0103] Step s8: The four-layer composite film is cooled to 35°C with cooling water, and then longitudinally stretched at a roller temperature of 119°C in the longitudinal stretching process with a longitudinal stretching ratio of 5.5. Then, it is transversely stretched at a temperature of 154°C in the transverse stretching process with a transverse stretching ratio of 10. After corona treatment, a master roll film is obtained. The master roll film is then slit after aging treatment to obtain a high heat-sealing strength flexible BOPP film with a heat-sealing layer thickness of 0.8μm, a secondary upper surface layer thickness of 0.6μm, a core layer thickness of 20μm, and an anti-stick layer thickness of 0.8μm.

[0104] Performance testing

[0105] The high heat-sealing strength and flexibility BOPP films of Examples 1-3 and Comparative Examples 1-3 were heat-sealed for 1 second under a heat-sealing pressure of 180 kPa and a heat-sealing temperature of 135°C. The heat-sealing strength was then tested, and the results are as follows: Figure 2 As shown.

[0106] See Figure 2 Based on the comparison between Examples 1-3 and Comparative Examples 1-3, it can be seen that adding sorbitol derivatives and multi-chain modifiers to the heat-sealing layer of high heat-sealing strength flexible BOPP film can significantly improve the heat-sealing strength, and the BOPP film finally prepared has high heat-sealing strength.

[0107] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0108] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing a high heat-sealing strength and flexible BOPP film, characterized in that, Includes the following steps: Step 1: The raw materials for the heat-sealing layer, the second upper surface layer, the core layer, and the anti-stick layer are added to four different extruders and melted at a temperature of 180-250℃. The molten material is then filtered through a 320-mesh filter. The heat-sealing layer, the second upper surface layer, the core layer, and the anti-stick layer are then extruded sequentially in a four-layer die to obtain a four-layer composite film. Step 2: Cool the four-layer composite film to 30-35℃ with cooling water, then stretch it longitudinally at a longitudinal stretching temperature of 85-145℃ with a longitudinal stretching ratio of 4.5-5.5, and then stretch it transversely at a transverse stretching temperature of 150-175℃ with a transverse stretching ratio of 8-10. After corona treatment, the master roll film is obtained. After aging treatment, the master roll film is cut to obtain a high heat-sealing strength flexible BOPP film. The heat-sealing layer comprises the following raw materials in parts by weight: 10-15 parts of octene copolymerized linear low-density polyethylene, 5-15 parts of metallocene polyethylene, 55-80 parts of ternary copolymerized polypropylene, 1-5 parts of sorbitol derivative, and 4-8 parts of multi-chain modifier. The sub-top layer comprises the following raw materials in parts by weight: 80-85 parts of ternary copolymer polypropylene, 10-15 parts of POE, and 2-5 parts of antistatic masterbatch; The core layer comprises the following components in the indicated mass ratio: 97-98 parts homopolymer polypropylene, 1-2 parts antistatic masterbatch, and 0.5-1 parts slip masterbatch; The anti-stick layer comprises the following components in the indicated mass ratio: 96-98 parts of homopolymer polypropylene and 2-4 parts of anti-blocking masterbatch; The sorbitol derivative was prepared by the following steps: Sorbitol, isophorone diisocyanate, dibutyltin dilaurate and N,N-dimethylformamide were stirred and reacted. After the reaction was completed, the reaction product was cooled and then rotary evaporated to obtain the sorbitol derivative. The multi-chain modifier is prepared by the following steps: Step a1: Citric acid, n-decyl alcohol, p-toluenesulfonic acid and toluene were stirred and reacted. After the reaction was completed, the reaction product was cooled, and then the pH was adjusted with sodium hydroxide solution. After washing and rotary evaporation, hydroxyl polychain compounds were obtained. Step a2: The hydroxyl multi-chain compound, 1,6-dibromohexane, potassium carbonate, and dimethyl sulfoxide are stirred and reacted. After the reaction is completed, the reaction product is cooled and then poured into distilled water. The product is then extracted, dried, and then vacuum filtered. The filtrate is then rotary evaporated to obtain the multi-chain modifier. The ratio of the hydroxyl multi-chain compound, 1,6-dibromohexane, potassium carbonate, and dimethyl sulfoxide in step a2 is 20 mmol: 10 mmol: 30-35 mmol: 60-70 mL.

2. The method for preparing a high heat-sealing strength and flexible BOPP film according to claim 1, characterized in that, The thickness of the heat-sealing layer is 0.5-1.0 μm; The thickness of the secondary upper surface layer is 0.5-0.8 μm; The thickness of the core layer is 13-25 μm; The thickness of the anti-stick layer is 0.5-1.0 μm.

3. The method for preparing a high heat-sealing strength and flexible BOPP film according to claim 1, characterized in that, The high heat-sealing strength and flexibility BOPP film comprises a four-layer structure, consisting of a heat-sealing layer, a second upper surface layer, a core layer, and an anti-sticking layer from top to bottom.

4. The method for preparing a high heat-sealing strength and flexible BOPP film according to claim 1, characterized in that, The octene copolymer linear low-density polyethylene is DOWLEX™ LLDPE NG 2049B; The metallocene polyethylene is SABIC LLDPE 318BJ; The ternary copolymer polypropylene is Yanshan Petrochemical F5606; The POE is Dow POE 7467; The antistatic masterbatch is Constance AT 4190 PP; The homopolymer polypropylene is North China Petrochemical HB28F; The slip masterbatch is Constance SL 5068 PP; The anti-blocking masterbatch is Constance AB 6019 PP.

5. The method for preparing a high heat-sealing strength and flexible BOPP film according to claim 1, characterized in that, The ratio of sorbitol, isophorone diisocyanate, dibutyltin dilaurate, and N,N-dimethylformamide is 10 mmol: 45-55 mmol: 0.02-0.04 g: 40-50 mL.

6. The method for preparing a high heat-sealing strength and flexible BOPP film according to claim 1, characterized in that, In step a1, the ratio of citric acid, n-decyl alcohol, p-toluenesulfonic acid, and toluene is 10 mmol: 35-40 mmol: 0.05-0.1 g: 50-60 mL; the mass fraction of the sodium hydroxide solution is 8-10%.

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