Anti-fog heat-sealable BOPET film and preparation method thereof

Abstract

The invention relates to the field of films, in particular to an anti-fog heat-sealable BOPET film and a preparation method thereof.The BOPET film is composed of an upper layer, a core layer and a lower layer, and the upper layer is composed of PETG, an anti-fog material and a silicon dioxide anti-blocking agent master batch; the core layer consists of a PET (Polyethylene Terephthalate) light material; and the lower layer is composed of PET and silicon dioxide master batch. Wherein the anti-fog material is prepared by taking acrylic resin, modified cellulose, modified chitosan and the like as main raw materials and an initiator, a solvent and the like as auxiliary materials through free radical polymerization. Cellulose and chitosan have anti-fogging performance, but are easy to absorb water and fall off when exposed outdoors for a long time, and the anti-fogging performance is greatly reduced, so that cellulose and chitosan are modified in the preparation process, and a large number of hydrophilic groups with an anti-fogging effect are introduced, so that the prepared modified cellulose and modified chitosan have excellent anti-fogging performance.

Description

Technical Field

[0001] This invention relates to the field of thin films, specifically to an anti-fog heat-sealable BOPET film and its preparation method. Background Technology

[0002] Biaxially oriented polyethylene terephthalate (BOPET) film holds an important position in the packaging industry due to its superior physical properties. It not only boasts high transparency, clearly displaying the contents of the package, but also possesses good mechanical strength, excellent dimensional stability, and superior chemical stability, characteristics that enable its widespread application.

[0003] However, in certain specific applications, especially when packaging moisture-sensitive items such as fresh food and medicine, BOPET film reveals two prominent problems: First, it is extremely prone to fogging, which seriously affects the visibility of the contents and makes it inconvenient for consumers to observe the product; second, ordinary BOPET film usually does not have heat-sealing properties. To achieve sealed packaging, an additional heat-sealing layer or other heat-sealing methods must be added, which undoubtedly increases packaging costs and also increases the complexity of the process.

[0004] Currently, while some anti-fog and heat-sealable film solutions have emerged in the market, BOPET films that simultaneously possess excellent anti-fog and heat-sealable properties remain relatively scarce. Although some heat-sealable films have achieved breakthroughs in heat-sealability through technologies such as copolymer modification, they have significant shortcomings in anti-fog performance. Either the anti-fog effect is short-lasting, or its effectiveness diminishes drastically in high humidity environments, making it difficult to meet the synergistic requirements of dual performance in practical applications.

[0005] Therefore, developing a BOPET film that combines excellent anti-fogging and heat-sealable properties is of great practical significance for improving packaging quality, reducing packaging costs, and simplifying packaging processes. Summary of the Invention

[0006] The purpose of this invention is to provide an anti-fog heat-sealable BOPET film and its preparation method.

[0007] The objective of this invention can be achieved through the following technical solutions: A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; Furthermore, the upper layer is composed of 80-85% PETG, 10-15% anti-fog material, and 5-10% silica opening agent masterbatch; the core layer is composed of 100% PET bright material; the lower layer is composed of 80-85% PET and 15-20% silica masterbatch; the thickness of the upper layer, core layer, and lower layer as a percentage of the total thickness is: upper layer 5-10%, core layer 80-90%, and lower layer 5-10%; the film thickness is 12-50 μm. Furthermore, the preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 220-285℃. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275-280℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 68-115℃, the stretching ratio is 3-4.1 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 99-116℃ and the stretching ratio is 3.8-4.0 times. (6) After corona treatment, traction and winding are performed.

[0008] Furthermore, the antifog material comprises the following raw materials in parts by weight: 50-60 parts hydroxyethyl acrylate, 30-40 parts methyl acrylate, 5-10 parts modified chitosan, 10-15 parts modified cellulose, 40-50 parts ethyl valerate, 1-2 parts N,N-methylenebisacrylamide, and 2-5 parts initiator.

[0009] Furthermore, the initiator is azobisisobutyronitrile or benzoyl peroxide.

[0010] Furthermore, the preparation method of the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, modified cellulose, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add the initiator to ethyl valerate and stir until homogeneous to obtain the initiator solution; Step 3: Take 20%-25% by weight of the premixed solution, heat it to 70-80℃, add 25%-30% by volume of the initiator solution, stir and react for 8-10 hours, then add the remaining premixed solution and initiator solution dropwise over 100-120 minutes. After the addition is complete, raise the temperature to 90-100℃ and react for 50-60 minutes. Then lower the temperature to 60-70℃, add N,N-methylenebisacrylamide, stir for 30-40 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifogging material.

[0011] Furthermore, the modified cellulose preparation method includes the following steps: Step 1: Add cellulose to an aqueous sodium hydroxide solution, stir at 50-60℃ for 1.5-2 hours, cool to room temperature, filter, and collect the filter cake; Step II: Add the filter cake to N,N-dimethylformamide and stir at room temperature for 30-40 minutes. Add the catalyst and 2-amino-3-butenoic acid, heat to 90-100℃, and maintain the temperature for reaction. After the reaction is completed, wash and dry to obtain modified cellulose.

[0012] Furthermore, in step I, the mass percentage of the sodium hydroxide aqueous solution is 20-25%.

[0013] Furthermore, in step II, the heat preservation reaction time is 12-14 hours.

[0014] The above technical solution involves first activating cellulose in an aqueous sodium hydroxide solution, where the hydroxyl groups in the cellulose react with the carboxyl groups in 2-amino-3-butenoic acid, resulting in modified cellulose containing unsaturated alkenyl groups and amino groups. Furthermore, the preparation method of the modified chitosan includes the following steps: Step A: Add chitosan to toluene and stir at room temperature to swell for 60-80 min. Add sodium hydroxide aqueous solution and stir at room temperature for 2-3 h. Heat to 60-70℃ and add 2-chloroacrylic acid in four portions, with an interval of 5-8 min each time. Stir the reaction for 3-4 h. After the reaction is complete, dry the product in a vacuum drying oven at 50-60℃ to obtain the chitosan intermediate. Step B: Add the chitosan intermediate to a solvent, add sorbitol and titanium dioxide, heat to 130-140℃ under nitrogen protection, stir for 2-3 hours, after the reaction is complete, remove the solvent under reduced pressure, and dry the product in an oven to obtain modified chitosan.

[0015] Further, in step B, the solvent is N,N-dimethyl sulfoxide.

[0016] Through the above technical solution, chitosan reacts with 2-chloroacrylic acid. The chitosan molecule has hydroxyl and amino groups, but oxygen has a higher electronegativity than nitrogen, so oxygen is more nucleophilic than ammonia. Since the primary alcohol group reacts faster than the secondary alcohol group, and the hydrogen atom on the secondary alcohol group may form a hydrogen bond with the lone pair of electrons on the amino group, nucleophilic substitution first occurs on the secondary alcohol group of chitosan, generating chitosan intermediates. The carboxyl group in the chitosan intermediate undergoes an esterification reaction with the hydroxyl group in sorbitol to obtain modified chitosan.

[0017] Furthermore, an anti-fog heat-sealable BOPET film is prepared using the above-described preparation method.

[0018] The beneficial effects of this invention are: (1) Cellulose itself can directly absorb water vapor, thus preventing it from condensing outside the matrix and achieving anti-fogging effect. However, its molecular chains may fall off when in contact with liquid water for a long time. In this invention, the nitrogen atom of the amino group in the modified cellulose has a lone pair of electrons, which can form hydrogen bonds with the hydrogen atoms in the water molecule, so that water vapor is adsorbed on the surface of cellulose and then distributed more evenly in the anti-fogging material through free radical polymerization, so that the prepared anti-fogging material has strong anti-fogging performance.

[0019] (2) In this invention, hydrophilic sorbitol is grafted onto the surface of chitosan. The hydroxyl groups in sorbitol can form strong hydrogen bonds with water molecules, which can quickly adsorb water vapor in the air and prevent water vapor from condensing in the form of small water droplets, thereby reducing light scattering and preventing fog formation. Finally, it is copolymerized with acrylates to make it uniformly dispersed in the system, so that the modified cellulose and modified chitosan in the anti-fog material have a synergistic anti-fog effect. Finally, through extrusion with the upper layer, core layer and lower layer materials, the prepared BOPET film has excellent anti-fog performance.

[0020] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is the infrared spectrum of the modified cellulose in this invention.

[0023] Figure 2 The images show the infrared spectra of chitosan, chitosan intermediates, and modified chitosan used in this invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0025] Example 1 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer accounts for 5% of the total thickness, respectively. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 21 μm.

[0026] The silicon content in the silica opening agent masterbatch is 6000 ppm.

[0027] The method for preparing the antifog material, by weight, includes the following components: 50 parts hydroxyethyl acrylate, 30 parts methyl acrylate, 5 parts modified chitosan, 10 parts modified cellulose, 40 parts ethyl valerate, 1 part N,N-methylenebisacrylamide, and 2 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, modified cellulose, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0028] The modified cellulose preparation method includes the following steps: Step 1: Add 2g of cellulose to 100ml of 20% sodium hydroxide aqueous solution, stir at 60℃ for 1.5h, cool to room temperature, filter, and collect the filter cake; Step II: Add the filter cake to 40 ml of N,N-dimethylformamide and stir at room temperature for 40 min. Add 0.08 g of p-toluenesulfonic acid and 1.5 g of 2-amino-3-butenoic acid, heat to 100 °C, react for 14 h, cool to room temperature, filter and collect the product, wash with 100 ml of deionized water, then wash with 80 ml of ethanol, and dry the washed product in an oven to obtain modified cellulose.

[0029] The modified cellulose was made into potassium bromide tablets, and infrared analysis was performed. The results are as follows: Figure 1 As shown, 3460cm -1 The absorption peak appearing at 3375 cm⁻¹ is a characteristic absorption peak of the hydroxyl groups in cellulose; -1 The absorption peak appearing at 3056 cm⁻¹ is a characteristic absorption peak of amino groups in modified cellulose; -1 The absorption peak appearing at 2910 cm⁻¹ is a characteristic absorption peak of the carbon-carbon double bond in modified cellulose; -1 The absorption peak appearing at 1725 cm⁻¹ is a characteristic absorption peak of alkyl groups in modified cellulose; -1 The peak appearing at this point is a characteristic absorption peak of the carbonyl group in the ester group of the modified cellulose.

[0030] The preparation method of the modified chitosan includes the following steps: Step A: Add 1g of chitosan to 50ml of toluene and stir at room temperature for 60 min to swell. Add 5ml of 30% sodium hydroxide aqueous solution and stir at room temperature for 2 h. Heat to 60℃ and divide 2g of 2-chloroacrylic acid into four equal portions. Add the mixture in four portions, with an interval of 5 min between each addition. Stir the mixture for 3 h after each addition. After the reaction is complete, add 20ml of deionized water to the reaction solution and adjust the pH to 7.0 with glacial acetic acid. Filter the mixture and wash the filter cake with 50ml of 70% ethanol aqueous solution and 30ml of anhydrous ethanol. Dry the obtained product in a vacuum drying oven at 50℃ to obtain the chitosan intermediate. Step B: Add 1g of chitosan intermediate to 50ml of N,N-dimethyl sulfoxide solvent, add 1.5g of sorbitol and 0.05g of p-toluenesulfonic acid, heat to 180℃ under nitrogen protection, stir and react for 4h. After the reaction is completed, remove the solvent under reduced pressure, place the product in an oven and dry to obtain modified chitosan.

[0031] Chitosan, chitosan intermediates, and modified chitosan were each prepared into potassium bromide tablets and subjected to infrared analysis. The results are as follows: Figure 2 As shown, 3400 cm in chitosan -1 The peak appearing at 2845 cm⁻¹ is the characteristic absorption peak of hydroxyl groups. -1 The absorption peak appearing at 3460 cm⁻¹ is a characteristic absorption peak of alkane; the absorption peak at 3460 cm⁻¹ in chitosan intermediates is a characteristic absorption peak of alkane. -1 The absorption peak appearing at 2880 cm⁻¹ is the characteristic absorption peak of hydroxyl groups; -1 The absorption peak appearing at 3075 cm⁻¹ is a characteristic absorption peak of alkane in 2-chloroacrylic acid; -1 The absorption peak at 1730 cm⁻¹ is a characteristic absorption peak of the carbon-carbon double bond in 2-chloroacrylic acid. -1 The absorption peak appearing at 3400 cm⁻¹ is the characteristic absorption peak of the carbonyl group in 2-chloroacrylic acid; the modified chitosan has an absorption peak at 3400 cm⁻¹. -1 The peak appearing at 2856 cm⁻¹ is the characteristic absorption peak of the hydroxyl group in sorbitol; -1 The absorption peak appearing at 1700 cm⁻¹ is a characteristic absorption peak of alkanes in sorbitol; -1 The absorption peak appearing at this point is a characteristic absorption peak of the carbonyl group.

[0032] Example 2 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer accounts for 5% of the total thickness, respectively. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 23 μm.

[0033] The method for preparing the antifog material, by weight, includes the following components: 51 parts hydroxyethyl acrylate, 32 parts methyl acrylate, 9 parts modified chitosan, 14 parts modified cellulose, 41 parts ethyl valerate, 1.2 parts N,N-methylenebisacrylamide, and 2.5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, modified cellulose, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0034] The preparation methods for the modified cellulose and modified chitosan are the same as in Example 1.

[0035] Example 3 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer accounts for 5% of the total thickness, respectively. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 22 μm.

[0036] The method for preparing the antifog material, by weight, includes the following components: 60 parts hydroxyethyl acrylate, 40 parts methyl acrylate, 10 parts modified chitosan, 15 parts modified cellulose, 50 parts ethyl valerate, 2 parts N,N-methylenebisacrylamide, and 5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, modified cellulose, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0037] The preparation methods for the modified cellulose and modified chitosan are the same as in Example 1.

[0038] Comparative Example 1 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer as a percentage of the total thickness is as follows: upper layer accounts for 5%, core layer accounts for 90%, and lower layer accounts for 5%. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 24 μm.

[0039] The method for preparing the antifog material, by weight, includes the following components: 51 parts hydroxyethyl acrylate, 32 parts methyl acrylate, 14 parts modified cellulose, 41 parts ethyl valerate, 1.2 parts N,N-methylenebisacrylamide, and 2.5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, and modified cellulose in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0040] The preparation method of the modified cellulose is the same as that in Example 1.

[0041] Comparative Example 2 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer as a percentage of the total thickness is as follows: upper layer accounts for 5%, core layer accounts for 90%, and lower layer accounts for 5%. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 25 μm.

[0042] The method for preparing the antifog material includes the following components by weight: 51 parts hydroxyethyl acrylate, 32 parts methyl acrylate, 9 parts modified chitosan, 41 parts ethyl valerate, 1.2 parts N,N-methylenebisacrylamide, and 2.5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0043] The preparation method of the modified chitosan is the same as that in Example 1.

[0044] Comparative Example 3 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer as a percentage of the total thickness is as follows: upper layer accounts for 5%, core layer accounts for 90%, and lower layer accounts for 5%. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 22 μm.

[0045] The method for preparing the antifog material, by weight, includes the following components: 51 parts hydroxyethyl acrylate, 32 parts methyl acrylate, 9 parts modified chitosan, 14 parts cellulose, 41 parts ethyl valerate, 1.2 parts N,N-methylenebisacrylamide, and 2.5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide and cellulose, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0046] The preparation method of the modified chitosan is the same as that in Example 1; The cellulose was purchased from Shanghai E. En Chemical Technology Co., Ltd., product number R197709.

[0047] Comparative Example 4 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer as a percentage of the total thickness is as follows: upper layer accounts for 5%, core layer accounts for 90%, and lower layer accounts for 5%. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 27 μm.

[0048] The method for preparing the antifog material includes the following components by weight: 51 parts hydroxyethyl acrylate, 32 parts methyl acrylate, 9 parts chitosan, 14 parts modified cellulose, 41 parts ethyl valerate, 1.2 parts N,N-methylenebisacrylamide, and 2.5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, and modified cellulose in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide and chitosan, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0049] The preparation method of the modified cellulose is the same as that in Example 1; The chitosan was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., product number C105800.

[0050] Comparative Example 5 A method for preparing an anti-fog heat-sealable BOPET film, wherein the BOPET film comprises an upper layer, a core layer and a lower layer; The upper layer consists of 80% PETG, 15% anti-fog material, and 5% silica opening agent masterbatch; the core layer consists of 100% PET bright material; and the lower layer consists of 85% PET and 15% silica masterbatch. The thickness of the upper layer, core layer, and lower layer as a percentage of the total thickness is as follows: upper layer accounts for 5%, core layer accounts for 90%, and lower layer accounts for 5%. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 280°C. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 80℃, the stretching ratio is 3.5 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 100℃ and the stretching ratio is 3.9 times. (6) After corona treatment, the film is pulled and wound up to obtain a heat-sealable anti-fog BOPET film with a thickness of 26 μm.

[0051] The method for preparing the antifog material includes the following components by weight: 51 parts hydroxyethyl acrylate, 32 parts methyl acrylate, 9 parts chitosan, 14 parts cellulose, 41 parts ethyl valerate, 1.2 parts N,N-methylenebisacrylamide, and 2.5 parts azobisisobutyronitrile. The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate and hydroxyethyl acrylate in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add azobisisobutyronitrile to ethyl valerate and stir until homogeneous to obtain an initiator solution; Step 3: Take 20% by weight of the premixed solution, heat it to 70℃, add 25% by volume of the initiator solution, stir and react for 8 hours, then add the remaining premixed solution and initiator solution dropwise over 100 minutes. After the addition is complete, raise the temperature to 90℃ and react for 50 minutes. Cool down to 60℃, add 1.5g of N,N-methylenebisacrylamide, chitosan and cellulose, stir for 30 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifog material.

[0052] Test case (1) The anti-fog heat-sealable BOPET film prepared in the examples and comparative examples was used to prepare test samples. The tensile strength and elongation at break of the film were tested according to the method of standard DIN 53455-6-5. The heat-sealing strength was tested according to the light industry standard QB / T 5076-2017.

[0053]

[0054] Based on the analysis of the above experimental data, it can be seen that the films prepared in the examples and comparative examples have good heat-sealing performance due to the addition of heat-sealing material PETG. The anti-fog heat-sealing BOPET films prepared in the examples and comparative examples of this invention have a thickness of 21-27 μm and excellent tensile strength and tensile strength at break, which meet the relevant film standards.

[0055] (2) The anti-fog heat-sealable BOPET films prepared in the examples and comparative examples were made into test samples and anti-fog tests were conducted in accordance with standard GB / T 31726-2015; the film gloss was tested in accordance with GB / T 8807-1988.

[0056]

[0057] Based on the experimental data above, compared with Comparative Example 1 and Example 2, the film prepared by adding modified cellulose achieves a level 2 anti-fogging effect. The modified cellulose plays a role in absorbing excess moisture under humid conditions, thereby giving the film an anti-fogging effect. Compared with Comparative Example 2 and Example 2, the film prepared by adding modified chitosan achieves a level 2 anti-fogging effect. The modified chitosan plays a role in absorbing excess moisture under humid conditions, thereby giving the film an anti-fogging effect. Compared with Example 2, the films prepared by Comparative Examples 3, 4, and 5 without the addition of modified chitosan and modified cellulose have anti-fogging levels of 2 and 3, respectively. Therefore, the modified cellulose and modified chitosan prepared in this invention have good anti-fogging performance. The films prepared in the examples and comparative examples all have good gloss.

[0058] (3) Prepare test samples using the anti-fogging heat-sealable BOPET films prepared in the examples and comparative examples, and conduct anti-fogging durability tests: Add 200 mL of water to a 250 mL beaker, cover the mouth of the beaker with the BOPET anti-fogging film prepared in the examples and comparative examples, place the beaker in a constant temperature water bath at 50°C, and observe the fogging of the BOPET anti-fogging film visually after 30 min; Add 500 mL of water to a 1000 mL beaker, cover the mouth of the beaker with the BOPET anti-fogging film prepared in the examples and comparative examples, and place the beaker on a heating plate. The water was boiled continuously for 30 minutes, and the fogging of the polyurethane anti-fog film was observed. Anti-fog durability: The BOPET anti-fog film provided in the above embodiments and comparative examples was pasted on the glass and placed in an open-air environment at room temperature (23±5℃ / 50%RH). The anti-fog performance of the BOPET anti-fog film was tested once a day for a total of 10 days until water droplets and fog appeared on 30% of the area of ​​the BOPET anti-fog film. The number of days was recorded. "√" represents passing the anti-fog durability test, and "×" represents water droplets or fog appearing on 30% or more of the area of ​​the polyurethane anti-fog film.

[0059]

[0060] Based on the above experimental data, analysis shows that, compared with Example 2, the anti-fogging durability and longevity of the film prepared by adding modified cellulose are reduced. Modified cellulose absorbs excess moisture under humid conditions and can remain stably in the film, making it less prone to falling off, thus achieving anti-fogging durability and longevity. Compared with Example 2, the anti-fogging durability and longevity of the film prepared by adding modified chitosan are reduced. Modified chitosan can absorb excess moisture under humid conditions and can remain stably in the film, making it less prone to falling off. Compared with Example 2, the anti-fogging durability and longevity of the films prepared by adding chitosan or cellulose in Comparative Examples 3, 4, and 5 are poor. Therefore, the modified cellulose and modified chitosan prepared in this invention have good anti-fogging function and are durable.

[0061] The above description is merely an example and illustration of the concept 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 concept of the invention or exceed the scope defined in the claims, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing an anti-fog, heat-sealable BOPET film, characterized in that, The BOPET film consists of an upper layer, a core layer, and a lower layer; The upper layer consists of 80-85% PETG, 10-15% anti-fog material, and 5-10% silica opening agent masterbatch; the core layer consists of 100% PET bright material; the lower layer consists of 80-85% PET and 15-20% silica masterbatch; the thickness of the upper, core, and lower layers as a percentage of the total thickness is: upper layer 5-10%, core layer 80-90%, and lower layer 5-10%; the film thickness is 12-50 μm. The preparation method of this anti-fog heat-sealable BOPET film includes the following steps: (1) Weigh the raw materials according to the proportions of each component in the upper layer, core layer, and lower layer; (2) The upper, core and lower layers of raw materials are fed into their respective extruders, mixed and melted and extruded at an extrusion temperature of 220-285℃. The main extruder is used for core layer extrusion, and the other two auxiliary extruders are used for upper and lower layer extrusion, respectively. (3) Each molten melt enters the die head separately. The die head temperature is set to 275-280℃. After they merge in the die head, they form a molten sheet through the die head opening and are then cast. (4) After the die head is cast, it enters the longitudinal stretching machine, the stretching temperature is 68-115℃, the stretching ratio is 3-4.1 times, and longitudinal stretching is performed; (5) After longitudinal stretching, it enters the transverse stretching machine. The transverse stretching temperature is 99-116℃ and the stretching ratio is 3.8-4.0 times. (6) After corona treatment, traction and winding are performed.

2. The method for preparing an anti-fog heat-sealable BOPET film according to claim 1, characterized in that, The anti-fog material comprises the following raw materials in parts by weight: 50-60 parts hydroxyethyl acrylate, 30-40 parts methyl acrylate, 5-10 parts modified chitosan, 10-15 parts modified cellulose, 40-50 parts ethyl valerate, 1-2 parts N,N-methylenebisacrylamide, and 2-5 parts initiator.

3. The method for preparing an anti-fog heat-sealable BOPET film according to claim 2, characterized in that, The initiator is azobisisobutyronitrile or benzoyl peroxide.

4. The method for preparing an anti-fog heat-sealable BOPET film according to claim 2, characterized in that, The method for preparing the anti-fog material includes the following steps: Step 1: Place ethyl acrylate, hydroxyethyl acrylate, modified cellulose, and modified chitosan in a reactor and stir until homogeneous to obtain a premixed solution; Step 2: Add the initiator to ethyl valerate and stir until homogeneous to obtain the initiator solution; Step 3: Take 20%-25% by weight of the premixed solution, heat it to 70-80℃, add 25%-30% by volume of the initiator solution, stir and react for 8-10 hours, then add the remaining premixed solution and initiator solution dropwise over 100-120 minutes. After the addition is complete, raise the temperature to 90-100℃ and react for 50-60 minutes. Then lower the temperature to 60-70℃, add N,N-methylenebisacrylamide, stir for 30-40 minutes, cool to room temperature, remove the solvent under reduced pressure, and dry to obtain the antifogging material.

5. The method for preparing an anti-fog heat-sealable BOPET film according to claim 2, characterized in that, The modified cellulose preparation method includes the following steps: Step 1: Add cellulose to an aqueous sodium hydroxide solution, stir at 50-60℃ for 1.5-2 hours, cool to room temperature, filter, and collect the filter cake; Step II: Add the filter cake to N,N-dimethylformamide and stir at room temperature for 30-40 minutes. Add p-toluenesulfonic acid and 2-amino-3-butenoic acid, heat to 90-100℃, and maintain the temperature for reaction. After the reaction is complete, wash and dry to obtain modified cellulose.

6. The method for preparing an anti-fog heat-sealable BOPET film according to claim 5, characterized in that, In step I, the mass percentage of the sodium hydroxide aqueous solution is 20-25%.

7. The method for preparing an anti-fog heat-sealable BOPET film according to claim 5, characterized in that, In step II, the heat preservation reaction time is 12-14 hours.

8. The method for preparing an anti-fog heat-sealable BOPET film according to claim 2, characterized in that, The preparation method of the modified chitosan includes the following steps: Step A: Chitosan is dissolved in toluene and stirred at room temperature for 60-80 min to swell. Sodium hydroxide aqueous solution is added and stirred at room temperature for 2-3 h. The mixture is then heated to 60-70℃. 2-Chloroacrylic acid is divided into four portions and added in four separate additions, with an interval of 5-8 min between each addition. The mixture is stirred and reacted for 3-5 h. After the reaction is complete, deionized water is added to the reaction solution, and the pH is adjusted to 7.0-7.5 with glacial acetic acid. The mixture is then filtered, and the filter cake is washed with 70-75% ethanol aqueous solution and anhydrous ethanol. The resulting product is dried in a vacuum drying oven at 50-60℃ to obtain the chitosan intermediate. Step B: Add the chitosan intermediate to a solvent, add sorbitol and p-toluenesulfonic acid, heat to 170-180℃ under nitrogen protection, stir and react for 4-5 hours. After the reaction is complete, remove the solvent under reduced pressure, and dry the product in an oven to obtain modified chitosan.

9. The method for preparing an anti-fog heat-sealable BOPET film according to claim 8, characterized in that, In step A, the sodium hydroxide aqueous solution has a mass fraction of 30-32%; in step B, the solvent is N,N-dimethyl sulfoxide.

10. A heat-sealable anti-fog BOPET film, characterized in that, It is prepared by the preparation method described in any one of claims 1-9.

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