A BOPP film with low-temperature heat-sealing performance and its preparation method

Abstract

The present invention relates to the field of BOPP films, specifically to a BOPP film with low-temperature heat-sealing properties and a preparation method thereof, which are used to address the problems of existing BOPP films, such as high heat-sealing temperatures and poor heat-sealing strength at low temperatures. By adding a modified polyolefin elastomer and optimizing its formulation and preparation method, the present invention enables the prepared BOPP film to achieve good heat-sealing effects even under low-temperature conditions, significantly reducing energy consumption during the packaging process and greatly improving packaging production efficiency. It also effectively increases the heat-sealing strength of the BOPP film, meeting the requirements of high-speed packaging production lines. Furthermore, by rationally designing the thickness ratio of the three-layer structure, the BOPP film has good processing properties and thermal stability. Furthermore, the preparation method of the BOPP film is simple in process and easy to operate, with good market prospects.

Description

Technical Field

[0001] The present invention relates to the field of BOPP films, in particular to a BOPP film with low-temperature heat-sealing performance and a preparation method thereof. Background Art

[0002] Biaxially oriented polypropylene (BOPP) film is widely used in the packaging industry due to its excellent physical properties, chemical stability, and processing performance. However, the heat-sealing temperature of traditional BOPP film is relatively high (typically 120-160°C). This high heat-sealing temperature not only increases energy consumption for packaging equipment but can also cause deformation and shrinkage of the film material during the heat-sealing process, impacting packaging quality and aesthetics. Furthermore, for heat-sensitive packaging contents, such as chocolate and candy, high-temperature heat sealing can adversely affect their quality.

[0003] Therefore, developing a BOPP film with low-temperature heat-sealing properties and a preparation method thereof has important practical significance. Summary of the Invention

[0004] In order to overcome the above technical problems, the purpose of the present invention is to provide a BOPP film with low-temperature heat-sealing performance and a preparation method thereof, which solves the problem that the existing BOPP film has high heat-sealing temperature and poor heat-sealing strength when heat-sealed at low temperatures.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A BOPP film with low-temperature heat-sealing properties, comprising a three-layer structure, from top to bottom, a heat-sealing layer, a core layer, and an anti-blocking layer;

[0007] The heat seal layer comprises the following components in mass ratio:

[0008] Metallocene polyethylene 75-85%, the balance is modified polyolefin elastomer;

[0009] The core layer includes the following components in mass ratio:

[0010] Antistatic masterbatch 1-3%, the balance is polypropylene homopolymer;

[0011] The anti-adhesion layer includes the following components in mass ratio:

[0012] Anti-blocking masterbatch 2-6%, the balance is polypropylene homopolymer;

[0013] Wherein, the modified polyolefin elastomer is prepared by the following steps:

[0014] Add polyolefin elastomer, low-temperature melting modifier, adhesion enhancer and antioxidant into a mixer, stir and mix for 20-30 minutes at a temperature of 70-80°C and a stirring rate of 800-1200 r / min, then add into an extruder, melt-extrude at a temperature of 130-140°C, and cool and granulate to obtain a modified polyolefin elastomer.

[0015] As a preferred embodiment of the present invention, the usage ratio of the polyolefin elastomer, the low-temperature melting modifier, the adhesion enhancer and the antioxidant is 60-70g: 5-11g: 2-6g: 0.5-1.5g.

[0016] As a preferred embodiment of the present invention, the polyolefin elastomer is Japan Mitsui DF840.

[0017] As a preferred embodiment of the present invention, the antioxidant is antioxidant 1010.

[0018] As a preferred embodiment of the present invention, the low-temperature melting modifier is prepared by the following steps:

[0019] Step a1: adding lauric acid to a three-necked flask equipped with a stirrer and a thermometer, stirring and reacting at a temperature of 70-75° C. and a stirring rate of 200-300 rpm for 20-30 minutes, then adding thionyl chloride and continuing to stir and react for 4-5 hours. After the reaction is completed, the reaction product is cooled to room temperature and then rotary evaporated to remove excess thionyl chloride to obtain a long-chain acyl chloride;

[0020] Step a2: L-ascorbic acid, pyridine and N, N-dimethylformamide are added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen protection is introduced. The reaction is stirred for 20-30 minutes at a temperature of 0-5 ° C and a stirring rate of 200-300 r / min, and then the long carbon chain acyl chloride is added dropwise while stirring. The dropwise addition rate is controlled to 1-2 drops / s. After the addition is completed, the temperature is raised to 35-40 ° C and the stirring reaction is continued for 15-20 hours. After the reaction is completed, the reaction product is cooled to room temperature and then added to methyl tert-butyl ether. After vacuum filtration, the filtrate is washed with hydrochloric acid solution and distilled water 3-5 times in sequence, and then dried with anhydrous magnesium sulfate. After vacuum filtration, the filtrate is rotary evaporated to remove the solvent, and then subjected to silica gel column chromatography with a mixed solvent to obtain a low-temperature melting modifier.

[0021] As a preferred embodiment of the present invention, the usage ratio of lauric acid and thionyl chloride in step a1 is 10 mmol:12-14 mmol.

[0022] As a preferred embodiment of the present invention, the usage ratio of the L-ascorbic acid, pyridine, N,N-dimethylformamide and long-chain acyl chloride in step a2 is 10 mmol:50-55 mmol:70-80 mL:40-45 mmol.

[0023] As a preferred embodiment of the present invention, the mass fraction of the hydrochloric acid solution in step a2 is 3-5%; the mixed solvent is a mixture of petroleum ether and ethyl acetate in a volume ratio of 8-10:1.

[0024] As a preferred embodiment of the present invention, the bonding enhancer is prepared by the following steps:

[0025] Pentaerythritol, isophorone diisocyanate, dibutyltin dilaurate and anhydrous acetone are added to a three-necked flask equipped with a stirrer, a thermometer and an air guide tube, and nitrogen is introduced for protection. The mixture is stirred and reacted at a temperature of 25-30°C and a stirring rate of 200-300 r / min for 20-30 minutes, and then the temperature is raised to 80-85°C and the stirring reaction is continued for 2-4 hours. After the reaction is completed, the reaction product is cooled to room temperature, and then the solvent is removed by rotary evaporation to obtain a bonding enhancer.

[0026] As a preferred embodiment of the present invention, the usage ratio of pentaerythritol, isophorone diisocyanate, dibutyltin dilaurate and anhydrous acetone is 10 mmol:40 mmol:0.03-0.05 g:70-80 mL.

[0027] As a preferred embodiment of the present invention, a method for preparing a BOPP film with low-temperature heat-sealing performance comprises the following steps:

[0028] Step 1: Weigh 75-85% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and mix the metallocene polyethylene and modified polyolefin elastomer evenly to obtain a heat seal layer raw material;

[0029] Step 2: Weigh 1-3% of the antistatic masterbatch and the remainder of the polypropylene homopolymer according to the mass ratio, and mix the antistatic masterbatch and the polypropylene homopolymer evenly to obtain the core layer raw material;

[0030] Step 3: Weigh 2-6% of the anti-blocking masterbatch and the remainder of the polypropylene homopolymer according to the mass ratio, and mix the anti-blocking masterbatch and the polypropylene homopolymer to obtain the raw material of the anti-blocking layer;

[0031] Step 4: Add the heat sealing layer raw material, the core layer raw material and the anti-sticking layer raw material to three different extruders respectively, melt them at a temperature of 230-250°C, and filter the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer and the anti-sticking layer, and extruded to form a three-layer composite casting sheet;

[0032] Step 5: Cool the three-layer composite casting sheet to 30-35°C with cooling water, then longitudinally stretch it at a temperature of 90-135°C, with a longitudinal stretch ratio of 4.9-5.5, and then transversely stretch it at a temperature of 150-175°C, with a transverse stretch ratio of 8-10 times to form a film. The film is corona treated at a power of 20-30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is harvested. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance.

[0033] As a preferred embodiment of the present invention, the thickness of the heat-sealing layer is 1.0-1.5 μm; the thickness of the core layer is 13-28 μm; and the thickness of the anti-adhesion layer is 0.6-1.0 μm.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] By adding a modified polyolefin elastomer and optimizing its formulation and preparation method, the present invention enables the prepared BOPP film to achieve excellent heat-sealing properties even at low temperatures, significantly reducing energy consumption during the packaging process and significantly improving packaging production efficiency. It also effectively enhances the heat-sealing strength of the BOPP film, meeting the requirements of high-speed packaging production lines. Furthermore, by rationally designing the thickness ratio of the three-layer structure, the BOPP film exhibits excellent processing properties and thermal stability. Furthermore, the preparation method of the BOPP film is simple and easy to operate, promising promising market prospects.

[0036] In the process of preparing BOPP film, a modified polyolefin elastomer is first prepared, and lauric acid is used for chlorination to obtain a long carbon chain acyl chloride. Then L-ascorbic acid and the long carbon chain acyl chloride react, and multiple hydroxyl groups on the L-ascorbic acid react with the acyl chloride groups on the long carbon chain acyl chloride, thereby introducing a large number of long carbon chains to obtain a low-temperature melting modifier. Then, pentaerythritol and isophorone diisocyanate are reacted to introduce multiple isocyanate groups to obtain a bonding enhancer. Finally, the polyolefin elastomer, the low-temperature melting modifier, the bonding enhancer and the antioxidant are blended to obtain a modified polyolefin elastomer; the polyolefin elastomer in the modified polyolefin elastomer is a low melting point polymer, which is added to a polypropylene homopolymer and mixed to impart BOPP film has good heat sealing performance and low-temperature heat sealing properties. The flexibility and large steric hindrance of the long carbon chain on the low-temperature melting modifier can weaken the interaction between polymer molecular chains, making the molecular chains more movable. At low temperatures, the enhanced mobility of the molecular chains makes the BOPP film more likely to bond during heat sealing, thereby further reducing the heat sealing temperature and improving the low-temperature heat sealing performance. The high reactivity of the isocyanate group on the bonding enhancer can chemically react with active hydrogen-containing groups (such as hydroxyl and amino groups) on the surface or inside the BOPP film to form chemical bonds, forming a three-dimensional cross-linked network structure. This chemical cross-linking greatly enhances the adhesion of the heat sealing interface, thereby improving the low-temperature heat sealing strength.

[0037] In summary, under the synergistic effect of polyolefin elastomer, low-temperature melt modifier and adhesion enhancer, the low-temperature heat sealing performance of BOPP film can be effectively enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] To facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0039] Figure 1 This is a schematic diagram of the structural principle of the BOPP film with low-temperature heat-sealing performance of the present invention. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0041] Example 1:

[0042] See also Figure 1As shown, this embodiment is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0043] Step S1: 10 mmol of lauric acid was added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture was stirred at 70° C. and a stirring rate of 200 r / min for 20 minutes. Then, 12 mmol of thionyl chloride was added and the stirring reaction was continued for 4 hours. After the reaction was completed, the reaction product was cooled to room temperature and then the excess thionyl chloride was removed by rotary evaporation to obtain a long-chain acyl chloride;

[0044] Step S2: 10mmol L-ascorbic acid, 50mmol pyridine and 70mL N, N-dimethylformamide were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen protection was introduced. The mixture was stirred for 20 minutes at a temperature of 0°C and a stirring rate of 200r / min. Then, 40mmol long carbon chain acyl chloride was added dropwise while stirring, and the dropping rate was controlled to 1 drop / s. After the addition was completed, the temperature was raised to 35°C and the stirring reaction was continued for 15 hours. After the reaction was completed, the reaction product was cooled to room temperature and then added to methyl tert-butyl ether. The mixture was then vacuum filtered and the filtrate was washed three times with a 3% hydrochloric acid solution and distilled water in sequence. The mixture was then dried over anhydrous magnesium sulfate and vacuum filtered. The filtrate was rotary evaporated to remove the solvent. The filtrate was then subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 8:1 to obtain a low-temperature melting modifier.

[0045] Step S3: 10 mmol of pentaerythritol, 40 mmol of isophorone diisocyanate, 0.03 g of dibutyltin dilaurate, and 70 mL of anhydrous acetone were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas guide tube, and nitrogen was introduced. The mixture was stirred at 25° C. and a stirring rate of 200 r / min for 20 minutes, and then the temperature was raised to 80° C. and the stirring reaction was continued for 2 hours. After the reaction was completed, the reaction product was cooled to room temperature and then rotary evaporated to remove the solvent to obtain a bonding enhancer;

[0046] Step S4: adding 60 g of a polyolefin elastomer (model Mitsui DF840 from Japan), 5 g of a low-temperature melt modifier, 2 g of an adhesion enhancer, and 0.5 g of an antioxidant 1010 to a mixer, stirring and mixing the mixture at a temperature of 70° C. and a stirring rate of 800 r / min for 20 min, then adding the mixture to an extruder, melt-extruded at a temperature of 130° C., and cooling and granulating the mixture to obtain a modified polyolefin elastomer;

[0047] Step S5: Weighing 75% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and uniformly mixing the metallocene polyethylene and the modified polyolefin elastomer to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 318BJ;

[0048] Step S6: Weighing 1% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4030 PP-HC; the polypropylene homopolymer is Huabei Petrochemical polypropylene HB28F;

[0049] Step S7: Weighing 2% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is Constant anti-blocking masterbatch AB6018PP; the polypropylene homopolymer is Huabei Petrochemical polypropylene HB28F;

[0050] Step S8: adding the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer raw material to three different extruders respectively, melting them at a temperature of 230° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer, and the anti-sticking layer, and extruded to form a three-layer composite casting sheet;

[0051] Step S9: The three-layer composite casting sheet is cooled to 30°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 90°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 150°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 20Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.0 μm, a core layer thickness of 13 μm, and an anti-blocking layer thickness of 0.6 μm.

[0052] Example 2:

[0053] See also Figure 1 As shown, this embodiment is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0054] Step S1: 10 mmol of lauric acid was added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture was stirred at 72° C. and a stirring rate of 250 r / min for 25 minutes. Then, 13 mmol of thionyl chloride was added and the stirring reaction was continued for 4.5 hours. After the reaction was completed, the reaction product was cooled to room temperature and then the excess thionyl chloride was removed by rotary evaporation to obtain a long-chain acyl chloride;

[0055] Step S2: 10mmol L-ascorbic acid, 52mmol pyridine and 75mL N, N-dimethylformamide were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen protection was introduced. The reaction was stirred for 25 minutes at a temperature of 3°C and a stirring rate of 250r / min. Then, 42mmol long carbon chain acyl chloride was added dropwise while stirring, and the drop rate was controlled to 1 drop / s. After the addition was completed, the temperature was raised to 38°C and the stirring reaction was continued for 18 hours. After the reaction was completed, the reaction product was cooled to room temperature and then added to methyl tert-butyl ether. The product was then vacuum filtered and the filtrate was washed 4 times with a 4% hydrochloric acid solution and distilled water in sequence. The product was then dried over anhydrous magnesium sulfate and vacuum filtered. The filtrate was rotary evaporated to remove the solvent. The product was then subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 9:1 to obtain a low-temperature melting modifier.

[0056] Step S3: 10 mmol of pentaerythritol, 40 mmol of isophorone diisocyanate, 0.04 g of dibutyltin dilaurate, and 75 mL of anhydrous acetone were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas guide tube, and nitrogen was introduced. The mixture was stirred at 28° C. and a stirring rate of 250 r / min for 25 minutes, and then the temperature was raised to 82° C. and the stirring was continued for 3 hours. After the reaction was completed, the reaction product was cooled to room temperature and then rotary evaporated to remove the solvent to obtain a bonding enhancer;

[0057] Step S4: adding 65 g of a polyolefin elastomer (model: Mitsui DF840, Japan), 8 g of a low-temperature melt modifier, 4 g of an adhesion enhancer, and 1 g of an antioxidant 1010 to a mixer, stirring and mixing them at a temperature of 75° C. and a stirring rate of 1000 r / min for 25 min, then adding the mixture to an extruder, melt-extruded at a temperature of 135° C., and cooling and granulating the mixture to obtain a modified polyolefin elastomer;

[0058] Step S5: Weighing 80% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and uniformly mixing the metallocene polyethylene and the modified polyolefin elastomer to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 318BJ;

[0059] Step S6: Weighing 2% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4030 PP-HC; the polypropylene homopolymer is Huabei Petrochemical polypropylene HB28F;

[0060] Step S7: Weighing 4% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is Constant anti-blocking masterbatch AB6018PP; the polypropylene homopolymer is Huabei Petrochemical polypropylene HB28F;

[0061] Step S8: adding the heat sealing layer raw material, the core layer raw material, and the anti-blocking layer raw material to three different extruders respectively, melting them at a temperature of 240° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-blocking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer, and the anti-blocking layer, and extruded to form a three-layer composite casting sheet;

[0062] Step S9: The three-layer composite casting sheet is cooled to 32°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 120°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 165°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 25Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.2μm, a core layer thickness of 21μm, and an anti-blocking layer thickness of 0.8μm.

[0063] Example 3:

[0064] See also Figure 1 As shown, this embodiment is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0065] Step S1: 10 mmol of lauric acid was added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture was stirred at 75° C. and a stirring rate of 300 r / min for 30 minutes. Then, 14 mmol of thionyl chloride was added and the stirring reaction was continued for 5 hours. After the reaction was completed, the reaction product was cooled to room temperature and then the excess thionyl chloride was removed by rotary evaporation to obtain a long-chain acyl chloride;

[0066] Step S2: 10mmol L-ascorbic acid, 55mmol pyridine and 80mL N, N-dimethylformamide were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen protection was introduced. The mixture was stirred for 30 minutes at a temperature of 5°C and a stirring rate of 300r / min. Then, 45mmol long carbon chain acyl chloride was added dropwise while stirring, and the dropwise acceleration rate was controlled to 2 drops / s. After the addition was completed, the temperature was raised to 40°C and the stirring reaction was continued for 20 hours. After the reaction was completed, the reaction product was cooled to room temperature and then added to methyl tert-butyl ether. The filtrate was then vacuum filtered and washed 5 times with 5% hydrochloric acid solution and distilled water in sequence. The filtrate was then dried over anhydrous magnesium sulfate and vacuum filtered. The filtrate was rotary evaporated to remove the solvent. The filtrate was then subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 10:1 to obtain a low-temperature melting modifier.

[0067] Step S3: 10 mmol of pentaerythritol, 40 mmol of isophorone diisocyanate, 0.05 g of dibutyltin dilaurate, and 80 mL of anhydrous acetone were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas guide tube, and nitrogen was introduced. The mixture was stirred at 30° C. and a stirring rate of 300 r / min for 30 minutes, and then the temperature was raised to 85° C. and the stirring reaction was continued for 4 hours. After the reaction was completed, the reaction product was cooled to room temperature and then rotary evaporated to remove the solvent to obtain a bonding enhancer;

[0068] Step S4: adding 70 g of a polyolefin elastomer of Japanese Mitsui DF840, 11 g of a low-temperature melt modifier, 6 g of an adhesion enhancer, and 1.5 g of an antioxidant 1010 to a mixer, stirring and mixing them at a temperature of 80° C. and a stirring rate of 1200 r / min for 30 min, then adding the mixture to an extruder, melt-extruded at a temperature of 140° C., and cooling and granulating the mixture to obtain a modified polyolefin elastomer;

[0069] Step S5: Weighing 85% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and uniformly mixing the metallocene polyethylene and the modified polyolefin elastomer to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 6218B;

[0070] Step S6: Weighing 3% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4084 PP-DC; the polypropylene homopolymer is Daqing Refining and Chemical T28FE polypropylene;

[0071] Step S7: Weighing 6% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is a silica AB905 anti-blocking agent; and the polypropylene homopolymer is a Daqing Refining and Chemical T28FE polypropylene;

[0072] Step S8: adding the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer raw material to three different extruders respectively, melting them at a temperature of 250° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer, and the anti-sticking layer, and extruded to form a three-layer composite casting sheet;

[0073] Step S9: The three-layer composite casting sheet is cooled to 35°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 135°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 175°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.5μm, a core layer thickness of 28μm, and an anti-blocking layer thickness of 1.0μm.

[0074] Comparative Example 1:

[0075] See also Figure 1 As shown, this comparative example is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0076] Step S1: Weighing 100% of metallocene polyethylene according to the mass ratio to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 6218B;

[0077] Step S2: Weighing 3% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4084 PP-DC; the polypropylene homopolymer is Daqing Refining and Chemical T28FE polypropylene;

[0078] Step S3: Weighing 6% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is a silica AB905 anti-blocking agent; and the polypropylene homopolymer is a Daqing Refining and Chemical T28FE polypropylene;

[0079] Step S4: adding the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer raw material to three different extruders respectively, melting them at a temperature of 250° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer, and the anti-sticking layer, and extruded to form a three-layer composite casting sheet;

[0080] Step S5: The three-layer composite casting sheet is cooled to 35°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 135°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 175°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.5μm, a core layer thickness of 28μm, and an anti-blocking layer thickness of 1.0μm.

[0081] Comparative Example 2:

[0082] See also Figure 1 As shown, this comparative example is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0083] Step S1: Weighing 85% of metallocene polyethylene and the balance of polyolefin elastomer (model: Mitsui DF840) according to a mass ratio, and uniformly mixing the metallocene polyethylene and the polyolefin elastomer (model: Mitsui DF840) to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 6218B;

[0084] Step S2: Weighing 3% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4084 PP-DC; the polypropylene homopolymer is Daqing Refining and Chemical T28FE polypropylene;

[0085] Step S3: Weighing 6% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is a silica AB905 anti-blocking agent; and the polypropylene homopolymer is a Daqing Refining and Chemical T28FE polypropylene;

[0086] Step S4: adding the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer raw material to three different extruders respectively, melting them at a temperature of 250° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer, and the anti-sticking layer, and extruded to form a three-layer composite casting sheet;

[0087] Step S5: The three-layer composite casting sheet is cooled to 35°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 135°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 175°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.5μm, a core layer thickness of 28μm, and an anti-blocking layer thickness of 1.0μm.

[0088] Comparative Example 3:

[0089] See also Figure 1 As shown, this comparative example is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0090] Step S1: 10 mmol of lauric acid was added to a three-necked flask equipped with a stirrer and a thermometer, and the mixture was stirred at 75° C. and a stirring rate of 300 r / min for 30 minutes. Then, 14 mmol of thionyl chloride was added and the stirring reaction was continued for 5 hours. After the reaction was completed, the reaction product was cooled to room temperature and then the excess thionyl chloride was removed by rotary evaporation to obtain a long-chain acyl chloride;

[0091] Step S2: 10mmol L-ascorbic acid, 55mmol pyridine and 80mL N, N-dimethylformamide were added to a three-necked flask equipped with a stirrer, a thermometer, an air guide tube and a constant pressure dropping funnel, and nitrogen protection was introduced. The mixture was stirred for 30 minutes at a temperature of 5°C and a stirring rate of 300r / min. Then, 45mmol long carbon chain acyl chloride was added dropwise while stirring, and the dropwise acceleration rate was controlled to 2 drops / s. After the addition was completed, the temperature was raised to 40°C and the stirring reaction was continued for 20 hours. After the reaction was completed, the reaction product was cooled to room temperature and then added to methyl tert-butyl ether. The filtrate was then vacuum filtered and washed 5 times with 5% hydrochloric acid solution and distilled water in sequence. The filtrate was then dried over anhydrous magnesium sulfate and vacuum filtered. The filtrate was rotary evaporated to remove the solvent. The filtrate was then subjected to silica gel column chromatography with a mixed solvent of petroleum ether and ethyl acetate in a volume ratio of 10:1 to obtain a low-temperature melting modifier.

[0092] Step S3: adding 70 g of a polyolefin elastomer of Japanese Mitsui DF840, 11 g of a low-temperature melt modifier, and 1.5 g of an antioxidant 1010 to a mixer, stirring and mixing them at a temperature of 80° C. and a stirring rate of 1200 r / min for 30 min, then adding the mixture to an extruder, melt-extruded at a temperature of 140° C., and cooling and granulating the mixture to obtain a modified polyolefin elastomer;

[0093] Step S4: Weighing 85% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and uniformly mixing the metallocene polyethylene and the modified polyolefin elastomer to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 6218B;

[0094] Step S5: Weighing 3% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4084 PP-DC; the polypropylene homopolymer is Daqing Refining and Chemical T28FE polypropylene;

[0095] Step S6: Weighing 6% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is a silica AB905 anti-blocking agent; and the polypropylene homopolymer is a Daqing Refining and Chemical T28FE polypropylene;

[0096] Step S7: adding the heat sealing layer raw material, the core layer raw material, and the anti-blocking layer raw material to three different extruders respectively, melting them at a temperature of 250° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-blocking layer molten materials are sequentially combined into a three-layer die according to the three-layer structure of the heat sealing layer, the core layer, and the anti-blocking layer, and extruded to form a three-layer composite casting sheet;

[0097] Step S8: The three-layer composite casting sheet is cooled to 35°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 135°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 175°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.5μm, a core layer thickness of 28μm, and an anti-blocking layer thickness of 1.0μm.

[0098] Comparative Example 4:

[0099] See also Figure 1 As shown, this comparative example is a method for preparing a BOPP film with low-temperature heat-sealing performance, comprising the following steps:

[0100] Step S1: 10 mmol of pentaerythritol, 40 mmol of isophorone diisocyanate, 0.05 g of dibutyltin dilaurate, and 80 mL of anhydrous acetone were added to a three-necked flask equipped with a stirrer, a thermometer, and a gas guide tube, and nitrogen was introduced for protection. The mixture was stirred at 30° C. and a stirring rate of 300 r / min for 30 minutes, and then the temperature was raised to 85° C. and the stirring reaction was continued for 4 hours. After the reaction was completed, the reaction product was cooled to room temperature and then rotary evaporated to remove the solvent to obtain a bonding enhancer;

[0101] Step S2: adding 70 g of a polyolefin elastomer (model Mitsui DF840 from Japan), 6 g of a bonding enhancer, and 1.5 g of an antioxidant 1010 to a mixer, stirring and mixing at a temperature of 80° C. and a stirring rate of 1200 r / min for 30 min, then adding the mixture to an extruder, melt-extruded at a temperature of 140° C., and cooling and granulating to obtain a modified polyolefin elastomer;

[0102] Step S3: Weighing 85% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and uniformly mixing the metallocene polyethylene and the modified polyolefin elastomer to obtain a heat seal layer raw material; the metallocene polyethylene is SABIC LLDPE 6218B;

[0103] Step S4: Weighing 3% of an antistatic masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the antistatic masterbatch and the polypropylene homopolymer to obtain a core layer raw material; the antistatic masterbatch is Constant AT 4084 PP-DC; the polypropylene homopolymer is Daqing Refining and Chemical T28FE polypropylene;

[0104] Step S5: Weighing 6% of an anti-blocking masterbatch and the remainder of a polypropylene homopolymer according to a mass ratio, and uniformly mixing the anti-blocking masterbatch and the polypropylene homopolymer to obtain a raw material for an anti-blocking layer; the anti-blocking masterbatch is a silica AB905 anti-blocking agent; and the polypropylene homopolymer is a Daqing Refining and Chemical T28FE polypropylene;

[0105] Step S6: adding the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer raw material to three different extruders respectively, melting them at a temperature of 250° C., and filtering the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material, and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer, and the anti-sticking layer, and extruded to form a three-layer composite casting sheet;

[0106] Step S7: The three-layer composite casting sheet is cooled to 35°C by cooling water, and then longitudinally stretched at a longitudinal stretching process temperature of 135°C with a longitudinal stretching ratio of 5, and then transversely stretched at a transverse stretching process temperature of 175°C with a transverse stretching ratio of 9 times to form a film. The film is subjected to corona treatment at a power of 30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is collected. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance, which has a heat sealing layer thickness of 1.5μm, a core layer thickness of 28μm, and an anti-blocking layer thickness of 1.0μm.

[0107] The BOPP films with low-temperature heat-sealability of Examples 1-3 and Comparative Examples 1-4 were tested under a heat-seal pressure of 0.2 MPa and a heat-seal time of 1 s to obtain the maximum heat-seal strength of the BOPP films with low-temperature heat-sealability. The lowest temperature at which the heat-seal strength reached ≥2 N / 15 mm was set as the starting heat-seal temperature.

[0108] The test results are shown in the following table:

[0109]

[0110] Referring to the data in the above table, based on the comparison between Examples 1-3 and Comparative Examples 1-4, it can be seen that the BOPP film with low-temperature heat-sealing performance of the present application has excellent heat-sealing strength and low-temperature heat-sealing performance.

[0111] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these 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 any one or more embodiments or examples.

[0112] The above contents are merely examples and explanations of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in similar ways. As long as they do not deviate from the invention or exceed the scope defined in this application, they should all fall within the scope of protection of the present invention.

Claims

1. A BOPP film with low-temperature heat-sealing properties, characterized in that: It includes three layers, from top to bottom: heat sealing layer, core layer and anti-adhesion layer; The heat seal layer comprises the following components in mass ratio: Metallocene polyethylene 75-85%, the balance is modified polyolefin elastomer; The core layer includes the following components in mass ratio: Antistatic masterbatch 1-3%, the balance is polypropylene homopolymer; The anti-adhesion layer includes the following components in mass ratio: Anti-blocking masterbatch 2-6%, the balance is polypropylene homopolymer; Wherein, the modified polyolefin elastomer is prepared by the following steps: Adding a polyolefin elastomer, a low-temperature melting modifier, an adhesion enhancer, and an antioxidant into a mixer, stirring and mixing them at a temperature of 70-80° C. and a stirring rate of 800-1200 r / min for 20-30 minutes, then adding the mixture into an extruder, melt-extruded at a temperature of 130-140° C., and cooling and granulating to obtain a modified polyolefin elastomer; The low-temperature melting modifier is prepared by the following steps: Step a1: stirring lauric acid for reaction, then adding thionyl chloride and continuing to stir the reaction. After the reaction is completed, the reaction product is cooled and then rotary evaporated to obtain a long-chain acyl chloride; Step a2: L-ascorbic acid, pyridine, and N,N-dimethylformamide are stirred for reaction, and then a long-chain acyl chloride is added dropwise while stirring. After the addition is complete, the stirring reaction is continued. After the reaction is completed, the reaction product is cooled and then added to methyl tert-butyl ether. The mixture is then vacuum filtered, the filtrate is washed and dried, and then vacuum filtered. The filtrate is rotary evaporated and then subjected to silica gel column chromatography using a mixed solvent to obtain a low-temperature melting modifier; the mixed solvent is a mixture of petroleum ether and ethyl acetate in a volume ratio of 8-10:1; The bonding enhancer is prepared by the following steps: Pentaerythritol, isophorone diisocyanate, dibutyltin dilaurate and anhydrous acetone are stirred for reaction. After the reaction is completed, the reaction product is cooled and then rotary evaporated to obtain a bonding enhancer.

2. The BOPP film with low-temperature heat-sealing performance according to claim 1, characterized in that: The usage ratio of the polyolefin elastomer, the low-temperature melting modifier, the adhesion enhancer and the antioxidant is 60-70g: 5-11g: 2-6g: 0.5-1.5g.

3. The BOPP film with low-temperature heat-sealing performance according to claim 1, characterized in that: The polyolefin elastomer is DF840; The antioxidant is antioxidant 1010.

4. The BOPP film with low-temperature heat-sealing performance according to claim 1, characterized in that: The usage ratio of the lauric acid and thionyl chloride in step a1 is 10 mmol:12-14 mmol.

5. The BOPP film with low-temperature heat-sealing performance according to claim 1, characterized in that: The usage ratio of the L-ascorbic acid, pyridine, N,N-dimethylformamide and long-chain acyl chloride in step a2 is 10 mmol:50-55 mmol:70-80 mL:40-45 mmol.

6. The BOPP film with low-temperature heat-sealing performance according to claim 1, characterized in that: The usage ratio of the pentaerythritol, isophorone diisocyanate, dibutyltin dilaurate and anhydrous acetone is 10 mmol: 40 mmol: 0.03-0.05 g: 70-80 mL.

7. A method for preparing a BOPP film with low-temperature heat-sealing properties according to any one of claims 1 to 6, characterized in that: The following steps are involved: Step 1: Weigh 75-85% of metallocene polyethylene and the remainder of modified polyolefin elastomer according to a mass ratio, and mix the metallocene polyethylene and modified polyolefin elastomer evenly to obtain a heat seal layer raw material; Step 2: Weigh 1-3% of the antistatic masterbatch and the remainder of the polypropylene homopolymer according to the mass ratio, and mix the antistatic masterbatch and the polypropylene homopolymer evenly to obtain the core layer raw material; Step 3: Weigh 2-6% of the anti-blocking masterbatch and the remainder of the polypropylene homopolymer according to the mass ratio, and mix the anti-blocking masterbatch and the polypropylene homopolymer to obtain the raw material of the anti-blocking layer; Step 4: Add the heat sealing layer raw material, the core layer raw material and the anti-sticking layer raw material to three different extruders respectively, melt them at a temperature of 230-250°C, and filter the molten materials through a 320-mesh filter. Then, the heat sealing layer raw material, the core layer raw material and the anti-sticking layer molten materials are sequentially combined into a three-layer die head according to the three-layer structure of the heat sealing layer, the core layer and the anti-sticking layer, and extruded to form a three-layer composite casting sheet; Step 5: Cool the three-layer composite casting sheet to 30-35°C with cooling water, then longitudinally stretch it at a temperature of 90-135°C, with a longitudinal stretch ratio of 4.9-5.5, and then transversely stretch it at a temperature of 150-175°C, with a transverse stretch ratio of 8-10 times to form a film. The film is corona treated at a power of 20-30Wmin / m 2 The corona treatment is carried out under the conditions of , and the mother roll film is harvested. The mother roll film is subjected to aging treatment, slitting and packaging to obtain a BOPP film with low-temperature heat sealing performance.

8. The method for preparing a BOPP film with low-temperature heat-sealing properties according to claim 7, characterized in that: The thickness of the heat-sealing layer is 1.0-1.5 μm; the thickness of the core layer is 13-28 μm; and the thickness of the anti-adhesion layer is 0.6-1.0 μm.

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