A highly transparent flexible barrier film and its preparation method

Abstract

The present invention belongs to the technical field of composite laminated films, and particularly relates to a high-transparency flexible barrier film and a preparation method thereof. The barrier film in the present invention includes a three-layer structure of a first surface layer, a core layer, and a second surface layer, all of which use polyester as the matrix material and have good flexibility, light transmittance, and barrier properties. Among them, the raw materials of the first surface layer and the second surface layer include carbon nanotube / POSS modified polyester. During the preparation of the modified polyester, a fluorinated dibasic acid and polyethylene glycol are introduced. The introduction of fluorine elements can improve the hydrophobic property of the polyester, and the introduction of the oleophobic polyether segment can improve the oleophobic property of the polyester, so that the surface layer structure of the composite film material has the properties of hydrophobicity and oleophobicity, is not easily contaminated, and has the effect of self-cleaning; the introduction of carbon nanotube / POSS can improve the barrier properties of the modified polyester and PET, and at the same time can improve the flexibility of the film material.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite laminated films, and particularly relates to a highly transparent flexible barrier film and a preparation method thereof. Background Art

[0002] Photovoltaics (solar photovoltaic power generation system) is a new type of power generation system that uses the photovoltaic effect of semiconductor materials in solar cells to directly convert solar radiation energy into electrical energy. Photovoltaic panel components include flexible photovoltaic panels and rigid photovoltaic panels. Among them, flexible photovoltaic panels are widely used due to their advantages of light weight, flexibility, and durability. However, precisely because they can be bent and folded, higher requirements are imposed on the encapsulation technology and encapsulation materials. The encapsulation materials not only require good light transmittance and barrier properties, but also need to have good flexibility to meet the bending and folding changes of flexible photovoltaic panels without damaging the encapsulation structure.

[0003] Polyester materials, such as PET (polyethylene terephthalate) films, are widely used in flexible photovoltaic encapsulation due to their good flexibility, light transmittance, and barrier properties. Chinese Patent CN113844146B discloses a preparation method of a blended polyester resin, which consists of masterbatch I composed of six components: pure PET resin, polyethylene terephthalate - 1,4 - cyclohexanedimethanol ester, polybutylene terephthalate, N,N'-ethylenebisstearamide, 1,2 - dimethylpyridinium iodide, and polyester wax dispersant, and masterbatch II composed of four components: pure PET resin, polyethylene terephthalate - 1,4 - cyclohexanedimethanol ester, polybutylene terephthalate, and polyester wax dispersant. Masterbatch I and pure PET resin are used as raw materials for layers A and C, and masterbatch II and pure PET resin are used as raw materials for layer B. Through three - layer co - extrusion and biaxial stretching, a BOPET film with high light transmittance, good slipperiness, and good antistatic performance is prepared. However, the problems of poor toughness and easy brittleness of PET films have not been solved, and the barrier performance also needs to be improved. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the present invention provides a highly transparent flexible barrier film to solve the problems of the barrier performance and flexibility of PET - based barrier films in the prior art that need to be improved.

[0005] To achieve the above - mentioned purpose, the technical solution adopted by the present invention is as follows:

[0006] A preparation method of a highly transparent flexible barrier film includes the following steps:

[0007] Step 1: Prepare carbon nanotube / POSS - modified polyester and carbon nanotube / POSS - modified PET;

[0008] Among them, the carbon nanotube / POSS - modified polyester is prepared through the following steps:

[0009] (1) Dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, polyethylene glycol, and catalyst 1 are mixed, nitrogen is introduced, and a reaction is carried out. After the reaction is completed, a stabilizer and catalyst 2 are added, and the reaction continues. After the reaction ends, the reaction mixture is discharged, cooled, and pelletized to obtain a modified polyester;

[0010] (2) The modified polyester and carbon nanotube-grafted POSS are melt-blended, extruded, cooled, and pelletized to obtain carbon nanotube / POSS-modified polyester;

[0011] Among them, the carbon nanotube / POSS-modified PET is prepared by the following steps:

[0012] PET (polyethylene terephthalate) and carbon nanotube-grafted POSS are melt-blended, extruded, cooled, and pelletized to obtain carbon nanotube / POSS-modified PET;

[0013] Step two: Prepare a polyester film sheet;

[0014] The carbon nanotube / POSS-modified polyester and PET are mixed as the first surface layer raw material and the second surface layer raw material;

[0015] The carbon nanotube / POSS-modified PET and PET are mixed as the core layer raw material;

[0016] According to the setting of the three-layer structure of the first surface layer / core layer / second surface layer, the first surface layer raw material, the core layer raw material, and the second surface layer raw material are respectively melted to obtain the first surface layer melt, the core layer melt, and the second surface layer melt. The first surface layer melt, the core layer melt, and the second surface layer melt are converged and extruded in a die head, cooled and solidified to obtain a polyester film sheet;

[0017] Step three: Prepare a high-transparency flexible barrier film;

[0018] The polyester film sheet is stretched and shaped to obtain a high-transparency flexible barrier film.

[0019] Preferably, in the first step: when preparing the modified polyester, the molar ratio of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol is 1:(1.2 - 1.4):(0.1 - 0.3):(0.05 - 0.2), the addition amount of catalyst 1 is 0.015% - 0.03% of the total mass of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol, the addition amount of the stabilizer is 0.02% - 0.04% of the total mass of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol, the addition amount of catalyst 2 is 0.02% - 0.04% of the total mass of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol, the reaction conditions are reacting at 240 - 260 °C and 250 kPa for 3 - 5 h, and the conditions for the continued reaction are reacting at 260 - 280 °C and 20 - 60 Pa for 2 - 4 h.

[0020] Preferably, the polyethylene glycol includes at least one of polyethylene glycol 200 (PEG - 200) and polyethylene glycol 400 (PEG - 400);

[0021] The fluorinated dibasic acid includes at least one of 2,2 - difluoromalonic acid and 2,2 - difluorosuccinic acid;

[0022] The catalyst 1 includes tetrabutyl titanate;

[0023] The stabilizer includes triethyl phosphate;

[0024] The catalyst 2 includes antimony trioxide.

[0025] Preferably, in the first step: when preparing carbon nanotube / POSS - modified polyester, the mass ratio of the modified polyester to carbon nanotube - grafted POSS is 100:(0.5 - 2), and the melting temperature is 265 - 280 °C.

[0026] Preferably, in the first step: when preparing carbon nanotube / POSS - modified PET, the mass ratio of PET to carbon nanotube - grafted POSS is 100:(0.5 - 2), and the melting temperature is 265 - 280 °C.

[0027] Preferably, in the first step: the carbon nanotube - grafted POSS used for preparing carbon nanotube / POSS - modified polyester and carbon nanotube / POSS - modified PET is the same;

[0028] The carbon nanotube - grafted POSS is prepared from epoxy - POSS and amino - modified carbon nanotubes, and the preparation method includes the following steps:

[0029] S1. Mix isopropanol, tetramethylammonium hydroxide, and deionized water. While stirring, add dropwise an isopropanol solution of γ-glycidoxypropyltrimethoxysilane (silane coupling agent KH560). After the addition is complete, stir. After the stirring is completed, remove isopropanol by vacuum distillation, add toluene, and react. After the reaction ends, purify to obtain epoxy POSS (cage-like oligosilsesquioxane).

[0030] S2. Dissolve epoxy POSS in toluene, add amino-modified carbon nanotubes, and react. After the reaction ends, filter and dry to obtain carbon nanotube-grafted POSS.

[0031] Preferably, in S1, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, the isopropanol solution of γ-glycidoxypropyltrimethoxysilane, and toluene is (325 - 365):(3.2 - 3.6):(28 - 32):(180 - 190):(370 - 400). The dropping time of the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is 1 - 2 h, the stirring condition is stirring at room temperature for 8 - 10 h, and the reaction condition is reflux reaction at 105 - 115 °C for 6 - 10 h. The isopropanol solution of γ-glycidoxypropyltrimethoxysilane is prepared by mixing γ-glycidoxypropyltrimethoxysilane and isopropanol in a mass ratio of (130 - 135):(50 - 55).

[0032] Preferably, in S2, the mass ratio of epoxy POSS, toluene, and amino-modified carbon nanotubes is 267.2:(800 - 1200):(26 - 28), and the reaction condition is sealed reaction at 55 - 65 °C for 8 - 12 h.

[0033] Preferably, the amino-modified carbon nanotubes are prepared through the following steps:

[0034] Dissolve FeSO4·7H2O in deionized water, adjust the pH value to 2.5 - 3.5, add carbon nanotubes, ultrasonically disperse, then add dropwise an aqueous hydrogen peroxide solution, stir, filter, wash, and dry to obtain hydroxylated carbon nanotubes.

[0035] Among them, the mass ratio of FeSO4·7H2O, deionized water, carbon nanotubes, and the aqueous hydrogen peroxide solution is 50:250:4:300, and the stirring condition is stirring at room temperature for 24 h.

[0036] Add the hydroxylated carbon nanotubes to ethyl acetate, ultrasonically disperse, then add γ-aminopropyltriethoxysilane (silane coupling agent KH550), react. After the reaction ends, filter, wash, and dry to obtain amino-modified carbon nanotubes.

[0037] Among them, the mass ratio of hydroxylated carbon nanotubes, ethyl acetate, and γ-aminopropyltriethoxysilane is 4:200:20, and the reaction conditions are reflux reaction at 65-75°C for 5-7 hours.

[0038] Preferably, the aqueous hydrogen peroxide solution is a 30wt% aqueous hydrogen peroxide solution.

[0039] Preferably, in the second step: the mass ratio of carbon nanotube / POSS-modified polyester to PET in the first surface layer raw material is the same as that of carbon nanotube / POSS-modified polyester to PET in the second surface layer raw material, and the mass ratio of carbon nanotube / POSS-modified polyester to PET is (25-45):100;

[0040] The mass ratio of carbon nanotube / POSS-modified PET to PET in the core layer raw material is (20-40):100.

[0041] Preferably, the PET in the second step is the same as the PET used to prepare carbon nanotube / POSS-modified PET in the first step.

[0042] Preferably, the melting temperature of the first surface layer raw material is 265-280°C, the melting temperature of the first core layer raw material is 265-280°C, and the melting temperature of the second surface layer raw material is 265-280°C;

[0043] The die head temperature is 270-285°C.

[0044] Preferably, in the third step: the stretch setting sequentially includes longitudinal stretch setting and transverse stretch setting;

[0045] The longitudinal stretch setting includes preheating at 75-85°C, longitudinal stretching at 90-120°C, the stretching ratio is 3.5-4.5 times, the stretching strength is 280-300 MPa, and after longitudinal stretching, heat setting is carried out, the setting temperature is 165-180°C, and the setting time is 2-5 s;

[0046] The transverse stretch setting includes preheating at 95-105°C, transverse stretching at 110-130°C, the stretching ratio is 3-4 times, the stretching strength is 260-285 MPa, and after longitudinal stretching, heat setting is carried out, the setting temperature is 175-185°C, and the setting time is 2-3 s.

[0047] The present invention also discloses a highly transparent flexible barrier film prepared by using the preparation method of the highly transparent flexible barrier film as described above.

[0048] Compared with the prior art, the beneficial effects of the present invention are:

[0049] In the present invention, polyester is used as the matrix material for preparing the composite film material, which has good flexibility, light transmittance and barrier properties. The composite film material comprises a three-layer structure, namely a first surface layer, a core layer and a second surface layer. The modified polyester in the raw materials of the first surface layer and the second surface layer is prepared by esterification reaction and polycondensation reaction of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid and polyethylene glycol. The introduction of fluorine element can improve the hydrophobic property of polyester, and the introduction of hydrophilic polyether chain segments can improve the oleophobic property of polyester, so that the surface layer structure of the composite film material has hydrophobic and oleophobic properties, the film material is not easily contaminated, and has the effect of self-cleaning of the surface layer. In addition, the introduction of flexible polyether chains can also improve the flexibility of the polyester molecular chain.

[0050] As a nano-modified material with a hybrid structure, POSS acts synergistically with carbon nanotubes to effectively enhance the toughness of the polyester-based film material. The modified polyester in the raw materials of the first surface layer and the second surface layer is modified by grafting POSS with carbon nanotubes to obtain carbon nanotube / POSS modified polyester, which can effectively improve the toughness of the modified polyester. Similarly, the carbon nanotube / POSS modified PET in the core layer raw material is prepared by reacting PET with carbon nanotubes grafted with POSS, which can effectively improve the toughness of PET, and the prepared composite film material has good toughness.

[0051] The POSS in the present invention is prepared by hydrolysis and condensation of γ-glycidyl ether oxypropyltrimethoxysilane under alkaline conditions and contains multiple epoxy groups. By reacting part of the epoxy groups with the amino groups on the surface of amino-modified carbon nanotubes, chemical bonding between POSS and carbon nanotubes is achieved to obtain carbon nanotubes grafted with POSS. The carbon nanotubes grafted with POSS then undergo ring-opening reactions with the hydroxyl or carboxyl groups at both ends of the modified polyester and PET molecules through the remaining epoxy groups in the molecule to form a chemical cross-linking structure, connecting the carbon nanotubes grafted with POSS to the polyester molecular chain with stable chemical bonds, significantly improving the interfacial bonding force between POSS, carbon nanotubes and polyester molecules, and further improving the compatibility between POSS, carbon nanotubes and polyester materials. Under stress, the carbon nanotube / POSS inorganic core at the cross-linking points can induce plastic deformation of the surrounding matrix and induce crazes to prevent crack propagation, thereby enhancing the toughness of the composite film material.

[0052] As a toughening material, carbon nanotubes have good light transmittance while enhancing the toughness of the film material. Within an appropriate addition range, the addition of POSS does not significantly affect the light transmittance of the film material. Therefore, the addition of carbon nanotubes grafted with POSS has little effect on the light transmittance of the composite film material, and through the bonding effect between carbon nanotubes grafted with POSS and polyester molecules, the problem of light transmittance decrease caused by the aggregation of carbon nanotubes and POSS can be effectively prevented.

[0053] Finally, due to the introduction of fluorine elements in the surface layer structure of the film, the adsorption and diffusion of water molecules by the film material can be reduced, improving the barrier performance of the film material. Moreover, the introduction of carbon nanotube-grafted POSS on the polyester matrix forms a maze effect, which can extend the diffusion path of water vapor and further improve the barrier performance of the film material. Brief Description of the Drawings

[0054] Figure 1 It is a process flow chart for the preparation of the high-transparency flexible barrier film in the present invention;

[0055] Figure 2 It is a bar chart of the light transmittance measurement results of the high-transparency flexible barrier films prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention;

[0056] Figure 3 It is a bar chart of the barrier performance measurement results of the high-transparency flexible barrier films prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention;

[0057] Figure 4 It is a bar chart of the tensile performance measurement results of the high-transparency flexible barrier films prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention;

[0058] Figure 5 It is a bar chart of the hydrophobic and oleophobic performance measurement results of the high-transparency flexible barrier films prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention;

[0059] Figure 6 It is an infrared spectrum diagram of carbon nanotube-grafted POSS prepared in Example 1 of the present invention;

[0060] Figure 7 It is an infrared spectrum diagram of epoxy POSS prepared in Example 1 of the present invention;

[0061] Figure 8 It is an infrared spectrum diagram of amino-modified carbon nanotubes prepared in Example 1 of the present invention. Detailed Description of the Invention

[0062] Examples

[0063] This example discloses a method for preparing a high-transparency flexible barrier film, which includes the following steps:

[0064] Step 1: Prepare carbon nanotube / POSS-modified polyester and carbon nanotube / POSS-modified PET;

[0065] Among them, the carbon nanotube / POSS-modified polyester is prepared by the following steps:

[0066] (1)Mix dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, PEG-200, and tetrabutyl titanate, introduce nitrogen gas, and react at 240 °C and 250 kPa for 5 h. After the reaction is completed, add triethyl phosphate and antimony trioxide, and react at 260 °C and 60 Pa for 4 h. After the reaction ends, discharge the reaction mixture in a strand shape into cold water, cool, and pelletize to obtain the modified polyester;

[0067] Among them, the molar ratio of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200 is 1:1.2:0.1:0.05. The addition amount of tetrabutyl titanate is 0.015% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200. The addition amount of triethyl phosphate is 0.02% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200. The addition amount of antimony trioxide is 0.02% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200.

[0068] (2)Melt-blend the modified polyester and carbon nanotube-grafted POSS. The mass ratio of the modified polyester to carbon nanotube-grafted POSS is 100:0.5, the melting temperature is 265 °C, extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified polyester;

[0069] Among them, the carbon nanotube / POSS-modified PET is prepared by the following steps:

[0070] Melt-blend PET and carbon nanotube-grafted POSS. The mass ratio of PET to carbon nanotube-grafted POSS is 100:0.5, the melting temperature is 265 °C, extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified PET;

[0071] Among them, the carbon nanotube-grafted POSS used for preparing the carbon nanotube / POSS-modified polyester and the carbon nanotube / POSS-modified PET is the same.

[0072] The carbon nanotube-grafted POSS is prepared from epoxy POSS and amino-modified carbon nanotubes. The preparation method includes the following steps:

[0073] S1. Mix isopropanol, tetramethylammonium hydroxide, and deionized water. While stirring at a speed of 300 r / min, dropwise add an isopropanol solution of γ-glycidoxypropyltrimethoxysilane. The dropping time of the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is 1 h. After the dropping is completed, stir at room temperature and a stirring speed of 300 r / min for 8 h. After the stirring is completed, under a vacuum of -0.095 MPa and at a temperature of 60 °C, distill off isopropanol under reduced pressure. Add toluene and reflux at a temperature of 105 °C for 10 h. After the reaction is completed, filter, wash the filtrate with saturated sodium chloride solution until the pH value is 7, add anhydrous sodium sulfate and dry overnight. Under a vacuum of -0.095 MPa and at a temperature of 80 °C, distill off toluene under reduced pressure to obtain epoxy POSS;

[0074] It can be seen from Figure 7 that the characteristic absorption peaks of aliphatic -CH2- introduced in the γ-glycidoxypropyltrimethoxysilane molecule are at 2865 cm -1 and 2795 cm -1 . The characteristic absorption peak of Si-C introduced in the γ-glycidoxypropyltrimethoxysilane molecule is at 1235 cm -1 . The characteristic absorption peak of Si-O-Si formed by the condensation of silanols between γ-glycidoxypropyltrimethoxysilane molecules is at 1105 cm -1 . The characteristic absorption peak of the epoxy group introduced in the γ-glycidoxypropyltrimethoxysilane molecule is at 920 cm -1 ;

[0075] Among them, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, the isopropanol solution of γ-glycidoxypropyltrimethoxysilane, and toluene is 325:3.2:28:180:370; the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is prepared by mixing γ-glycidoxypropyltrimethoxysilane and isopropanol at a mass ratio of 130:50;

[0076] S2. Dissolve epoxy POSS in toluene, add amino-modified carbon nanotubes. The mass ratio of epoxy POSS, toluene, and amino-modified carbon nanotubes is 267.2:800:26. Seal and react at a temperature of 55 °C for 12 h. After the reaction is completed, filter to remove toluene and unreacted epoxy POSS, and place it in a vacuum drying oven at 50 °C for 24 h to obtain carbon nanotube-grafted POSS;

[0077] It can be seen from Figure 6 that the characteristic absorption peak of the N-H bond of the secondary amine obtained by the reaction of the epoxy group in the POSS molecule with the amino group on the amino-modified carbon nanotubes is at 3425 cm -1 . The characteristic absorption peaks at 2895 cm -1 and 2785 cm-1 This is the characteristic absorption peak of the aliphatic -CH2- in the γ - glycidoxypropyltrimethoxysilane molecule at 1380 cm -1 This is the characteristic absorption peak of the C - N bond in the γ - aminopropyltriethoxysilane molecule grafted on the surface of the amino - modified carbon nanotubes at 1125 cm -1 This is the characteristic absorption peak of Si - O - Si in the POSS molecule at 905 cm -1 This is the characteristic absorption peak of the epoxy group in the POSS molecule;

[0078] Among them, the amino - modified carbon nanotubes are prepared by the following steps:

[0079] Dissolve FeSO4·7H2O in deionized water, adjust the pH value to 3 with 1 mol / L sulfuric acid aqueous solution, add carbon nanotubes, ultrasonically disperse for 30 min at a frequency of 50 kHz, then dropwise add 30 wt% hydrogen peroxide aqueous solution. The mass ratio of FeSO4·7H2O, deionized water, carbon nanotubes, and 30 wt% hydrogen peroxide aqueous solution is 50:250:4:300. Stir at room temperature for 24 h, filter, wash with deionized water until the filtrate is neutral, and dry in a vacuum drying oven at 50 °C for 24 h to obtain hydroxylated carbon nanotubes;

[0080] Add the hydroxylated carbon nanotubes into ethyl acetate, ultrasonically disperse for 30 min at a frequency of 50 kHz, then add γ - aminopropyltriethoxysilane. The mass ratio of hydroxylated carbon nanotubes, ethyl acetate, and γ - aminopropyltriethoxysilane is 4:200:20. Reflux and react at 65 °C for 6 h. After the reaction is completed, filter, wash away the unreacted γ - aminopropyltriethoxysilane with ethyl acetate, and dry in a vacuum drying oven at 50 °C for 24 h to obtain amino - modified carbon nanotubes;

[0081] From Figure 8 it can be seen that at 3490 cm -1 and 3270 cm -1 are the two characteristic absorption peaks of N - H of primary amine in the γ - aminopropyltriethoxysilane molecule, and at 2810 cm -1 is the characteristic absorption peak of C - H on the methylene group in the γ - aminopropyltriethoxysilane molecule, at 1405 cm -1 is the characteristic absorption peak of C - N in the γ - aminopropyltriethoxysilane molecule, and at 1080 cm -1 is the characteristic absorption peak of C - O - Si formed by the condensation reaction of the hydroxyl group obtained by the hydrolysis of the siloxane on the γ - aminopropyltriethoxysilane molecule and the hydroxyl group on the surface of the hydroxylated carbon nanotubes;

[0082] Step two: Prepare the polyester film;

[0083] Mix carbon nanotube / POSS modified polyester with PET as the first surface layer raw material and the second surface layer raw material;

[0084] The mass ratio of carbon nanotube / POSS modified polyester to PET in the first surface layer raw material is the same as that in the second surface layer raw material, and the mass ratio of carbon nanotube / POSS modified polyester to PET is 25:100;

[0085] Mix carbon nanotube / POSS modified PET with PET at a mass ratio of 20:100 as the core layer raw material;

[0086] Among them, the PET is the same as the PET used to prepare carbon nanotube / POSS modified PET in step one;

[0087] According to the three-layer structure of the first surface layer / core layer / second surface layer, melt the first surface layer raw material, the core layer raw material, and the second surface layer raw material respectively to obtain the first surface layer melt, the core layer melt, and the second surface layer melt. The melting temperature of the first surface layer raw material is 265°C, the melting temperature of the first core layer raw material is 265°C, and the melting temperature of the second surface layer raw material is 265°C. Converge and extrude the first surface layer melt, the core layer melt, and the second surface layer melt in the die head. The die head temperature is 270°C, and cool and solidify to obtain a polyester film sheet.

[0088] Step three: Stretch and shape the polyester film sheet to obtain a high-transparency flexible barrier film;

[0089] Among them, the stretch shaping includes longitudinal stretch shaping and transverse stretch shaping in sequence;

[0090] Longitudinal stretch shaping: Preheat at 80°C, perform longitudinal stretching at 110°C, the stretching ratio is 4 times, the stretching strength is 280 MPa, perform heat setting after longitudinal stretching, the setting temperature is 170°C, and the setting time is 5 s;

[0091] Transverse stretch shaping: Preheat at 100°C, perform transverse stretching at 120°C, the stretching ratio is 3.5 times, the stretching strength is 280 MPa, perform heat setting after longitudinal stretching, the setting temperature is 180°C, and the setting time is 2.5 s;

[0092] The thickness of the high-transparency flexible barrier film is 25 μm, including a first surface layer, a core layer, and a second surface layer, and the thickness ratio of the first surface layer, the core layer, and the second surface layer is 5:15:5. Example

[0093] This example discloses a preparation method of a high-transparency flexible barrier film, including the following steps:

[0094] Step 1: Prepare carbon nanotube / POSS modified polyester and carbon nanotube / POSS modified PET;

[0095] Among them, the carbon nanotube / POSS modified polyester is prepared by the following steps:

[0096] (1) Mix dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, PEG-400, and tetrabutyl titanate, introduce nitrogen, and react at 260 °C and 250 kPa for 3 h. After the reaction is completed, add triethyl phosphate and antimony trioxide, and react at 280 °C and 20 Pa for 2 h. After the reaction ends, discharge the reaction mixture in a strand shape into cold water, cool, and pelletize to obtain the modified polyester;

[0097] Among them, the molar ratio of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-400 is 1:1.4:0.3:0.2, the addition amount of tetrabutyl titanate is 0.03% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-400, the addition amount of triethyl phosphate is 0.04% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-400, and the addition amount of antimony trioxide is 0.04% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-400.

[0098] (2) Melt-blend the modified polyester with carbon nanotube-grafted POSS. The mass ratio of the modified polyester to carbon nanotube-grafted POSS is 100:2, the melting temperature is 280 °C, extrude, cool, and pelletize to obtain the carbon nanotube / POSS modified polyester;

[0099] Among them, the carbon nanotube / POSS modified PET is prepared by the following steps:

[0100] Melt-blend PET with carbon nanotube-grafted POSS. The mass ratio of PET to carbon nanotube-grafted POSS is 100:2, the melting temperature is 280 °C, extrude, cool, and pelletize to obtain the carbon nanotube / POSS modified PET;

[0101] Among them, the carbon nanotube-grafted POSS used for preparing the carbon nanotube / POSS modified polyester and the carbon nanotube / POSS modified PET is the same.

[0102] The carbon nanotube-grafted POSS is prepared from epoxy POSS and amino-modified carbon nanotubes. The preparation method includes the following steps:

[0103] S1. Mix isopropanol, tetramethylammonium hydroxide, and deionized water. While stirring at a speed of 300 r / min, add an isopropanol solution of γ-glycidoxypropyltrimethoxysilane dropwise. The dropping duration of the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is 2 h. After the addition is complete, stir at a speed of 300 r / min at room temperature for 10 h. After the stirring is completed, under a vacuum of -0.095 MPa and at a temperature of 60 °C, distill off isopropanol under reduced pressure. Add toluene and reflux at a temperature of 115 °C for 6 h. After the reaction is completed, filter, wash the filtrate with saturated sodium chloride solution until the pH value reaches 7, add anhydrous sodium sulfate and dry overnight. Under a vacuum of -0.095 MPa and at a temperature of 80 °C, distill off toluene under reduced pressure to obtain epoxy POSS;

[0104] Among them, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, the isopropanol solution of γ-glycidoxypropyltrimethoxysilane, and toluene is 365:3.6:32:190:400; the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is prepared by mixing γ-glycidoxypropyltrimethoxysilane and isopropanol at a mass ratio of 135:55.

[0105] S2. Dissolve epoxy POSS in toluene, add amino-modified carbon nanotubes. The mass ratio of epoxy POSS, toluene, and amino-modified carbon nanotubes is 267.2:1200:28. Seal and react at a temperature of 65 °C for 8 h. After the reaction is completed, filter to remove toluene and unreacted epoxy POSS, and place it in a vacuum drying oven at 50 °C for 24 h to obtain carbon nanotube-grafted POSS;

[0106] Among them, the preparation method of the amino-modified carbon nanotubes is the same as that in Example 1.

[0107] Step 2. Prepare a polyester film sheet;

[0108] Mix carbon nanotube / POSS-modified polyester and PET as the first surface layer raw material and the second surface layer raw material;

[0109] The mass ratio of carbon nanotube / POSS-modified polyester to PET in the first surface layer raw material is the same as that in the second surface layer raw material. The mass ratio of carbon nanotube / POSS-modified polyester to PET is 45:100;

[0110] Mix carbon nanotube / POSS-modified PET and PET at a mass ratio of 40:100 as the core layer raw material;

[0111] Among them, the PET is the same as the PET used to prepare carbon nanotube / POSS-modified PET in Step 1;

[0112] According to the setting of the three-layer structure of the first surface layer / core layer / second surface layer, the raw materials of the first surface layer, the core layer, and the second surface layer are respectively melted to obtain the first surface layer melt, the core layer melt, and the second surface layer melt. The melting temperature of the first surface layer raw material is 280 °C, the melting temperature of the first core layer raw material is 280 °C, and the melting temperature of the second surface layer raw material is 280 °C. The first surface layer melt, the core layer melt, and the second surface layer melt are converged and extruded in a die head. The die head temperature is 285 °C, and after cooling and solidification, a polyester film sheet is obtained.

[0113] Step 3: Stretch and shape the polyester film sheet to obtain a high-transparency flexible barrier film;

[0114] Among them, the stretching and shaping sequentially include longitudinal stretching and shaping and transverse stretching and shaping;

[0115] The specific stretching and shaping process is the same as that in Example 1;

[0116] The thickness of the high-transparency flexible barrier film is 25 μm, and it includes a first surface layer, a core layer, and a second surface layer. The thickness ratio of the first surface layer, the core layer, and the second surface layer is 5:15:5.

[0117] Example 3

[0118] This example discloses a preparation method of a high-transparency flexible barrier film, including the following steps:

[0119] Step 1: Prepare carbon nanotube / POSS modified polyester and carbon nanotube / POSS modified PET;

[0120] Among them, the carbon nanotube / POSS modified polyester is prepared by the following steps:

[0121] (1) Mix dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid, PEG-200, and tetrabutyl titanate, introduce nitrogen, and react at 245 °C and 250 kPa for 4.5 h. After the reaction is completed, add triethyl phosphate and antimony trioxide, and react at 265 °C and 50 Pa for 3.5 h. After the reaction ends, discharge the reaction mixture in a strand shape into cold water, cool, and pelletize to obtain modified polyester;

[0122] Among them, the molar ratio of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid, and PEG-200 is 1:1.25:0.15:0.1. The addition amount of tetrabutyl titanate is 0.02% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid, and PEG-200. The addition amount of triethyl phosphate is 0.025% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid, and PEG-200. The addition amount of antimony trioxide is 0.025% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid, and PEG-200.

[0123] (2) Melt-blend the modified polyester and carbon nanotube-grafted POSS. The mass ratio of the modified polyester to carbon nanotube-grafted POSS is 100:1. The melting temperature is 270 °C. Extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified polyester.

[0124] Among them, the carbon nanotube / POSS-modified PET is prepared through the following steps:

[0125] Melt-blend PET and carbon nanotube-grafted POSS. The mass ratio of PET to carbon nanotube-grafted POSS is 100:1. The melting temperature is 270 °C. Extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified PET.

[0126] Among them, the carbon nanotube-grafted POSS used for preparing carbon nanotube / POSS-modified polyester and carbon nanotube / POSS-modified PET is the same.

[0127] The carbon nanotube-grafted POSS is prepared from epoxy POSS and amino-modified carbon nanotubes. The preparation method includes the following steps:

[0128] S1. Mix isopropanol, tetramethylammonium hydroxide, and deionized water. Dropwise add the isopropanol solution of γ-glycidoxypropyltrimethoxysilane at a stirring speed of 300 r / min. The dropping time of the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is 1.5 h. After the addition is completed, stir at a stirring speed of 300 r / min at room temperature for 9 h. After the stirring is completed, under a vacuum of -0.095 MPa and at a temperature of 60 °C, distill off isopropanol under reduced pressure. Add toluene and reflux at a temperature of 110 °C for 8 h. After the reaction is completed, filter. Wash the filtrate with saturated sodium chloride solution until the pH value is 7. Add anhydrous sodium sulfate and dry overnight. Under a vacuum of -0.095 MPa and at a temperature of 80 °C, distill off toluene under reduced pressure to obtain epoxy POSS.

[0129] Among them, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, isopropanol solution of γ-glycidoxypropyltrimethoxysilane, and toluene is 340:3.4:30:183:380; the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is prepared by mixing γ-glycidoxypropyltrimethoxysilane and isopropanol at a mass ratio of 132:51.

[0130] S2. Dissolve epoxy POSS in toluene, add amino-modified carbon nanotubes. The mass ratio of epoxy POSS, toluene, and amino-modified carbon nanotubes is 267.2:950:26.5. React under sealed conditions at 60 °C for 10 h. After the reaction, filter to remove toluene and unreacted epoxy POSS, and place it in a vacuum drying oven at 50 °C for 24 h to obtain carbon nanotube-grafted POSS;

[0131] Among them, the preparation method of the amino-modified carbon nanotubes is the same as that in Example 1.

[0132] Step 2. Prepare a polyester film sheet;

[0133] Mix carbon nanotube / POSS-modified polyester with PET as the first surface layer raw material and the second surface layer raw material;

[0134] The mass ratio of carbon nanotube / POSS-modified polyester to PET in the first surface layer raw material is the same as that of carbon nanotube / POSS-modified polyester to PET in the second surface layer raw material. The mass ratio of carbon nanotube / POSS-modified polyester to PET is 30:100;

[0135] Mix carbon nanotube / POSS-modified PET and PET at a mass ratio of 25:100 as the core layer raw material;

[0136] Among them, the PET is the same as the PET used to prepare carbon nanotube / POSS-modified PET in Step 1;

[0137] According to the setting of the three-layer structure of the first surface layer / core layer / second surface layer, melt the first surface layer raw material, core layer raw material, and second surface layer raw material respectively to obtain the first surface layer melt, core layer melt, and second surface layer melt. The melting temperature of the first surface layer raw material is 270 °C, the melting temperature of the first core layer raw material is 270 °C, and the melting temperature of the second surface layer raw material is 270 °C. Converge and extrude the first surface layer melt, core layer melt, and second surface layer melt in the die head. The die head temperature is 275 °C, and cool and solidify to obtain a polyester film sheet.

[0138] Step 3. Stretch and shape the polyester film sheet to obtain a high-transparency flexible barrier film;

[0139] Among them, the stretching and shaping includes longitudinal stretching and shaping and transverse stretching and shaping in sequence;

[0140] The specific stretching and setting process is the same as that in Example 1;

[0141] The thickness of the high light-transmissive flexible barrier film is 25 μm, which includes a first surface layer, a core layer and a second surface layer, and the thickness ratio of the first surface layer, the core layer and the second surface layer is 5:15:5.

[0142] Example 4

[0143] This example discloses a preparation method of a high light-transmissive flexible barrier film, which includes the following steps:

[0144] Step 1, prepare carbon nanotube / POSS modified polyester and carbon nanotube / POSS modified PET;

[0145] Among them, the carbon nanotube / POSS modified polyester is prepared by the following steps:

[0146] (1) Mix dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid, PEG-400 and tetrabutyl titanate, introduce nitrogen, and react at 255 °C and 250 kPa for 3.5 h. After the reaction is completed, add triethyl phosphate and antimony trioxide, and react at 275 °C and 30 Pa for 2.5 h. After the reaction ends, discharge the reaction mixture in a strand shape into cold water, cool, and pelletize to obtain modified polyester;

[0147] Among them, the molar ratio of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid and PEG-400 is 1:1.35:0.25:0.15, the addition amount of tetrabutyl titanate is 0.025% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid and PEG-400, the addition amount of triethyl phosphate is 0.035% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid and PEG-400, and the addition amount of antimony trioxide is 0.035% of the total mass of dimethyl terephthalate, ethylene glycol, 2,2-difluorosuccinic acid and PEG-400.

[0148] (2) Melt-blend the modified polyester with carbon nanotube-grafted POSS, and the mass ratio of the modified polyester to carbon nanotube-grafted POSS is 100:1.5. The melting temperature is 275 °C, extrude, cool, and pelletize to obtain carbon nanotube / POSS modified polyester;

[0149] Among them, the carbon nanotube / POSS modified PET is prepared by the following steps:

[0150] Melt-blend PET with carbon nanotube-grafted POSS, and the mass ratio of PET to carbon nanotube-grafted POSS is 100:1.5. The melting temperature is 275 °C, extrude, cool, and pelletize to obtain carbon nanotube / POSS modified PET;

[0151] Among them, the carbon nanotubes grafted with POSS used for preparing carbon nanotube / POSS modified polyester and carbon nanotube / POSS modified PET are the same.

[0152] The carbon nanotubes grafted with POSS are prepared from epoxy POSS and amino modified carbon nanotubes, and the preparation method includes the following steps:

[0153] S1. Mix isopropanol, tetramethylammonium hydroxide, and deionized water, and dropwise add an isopropanol solution of γ-glycidoxypropyltrimethoxysilane at a stirring speed of 300 r / min. The dropping time of the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is 1.5 h. After the dropping is completed, stir at a stirring speed of 300 r / min at room temperature for 9 h. After the stirring is completed, under a vacuum of -0.095 MPa and at a temperature of 60 °C, distill off isopropanol under reduced pressure. Add toluene, and reflux and react at a temperature of 110 °C for 8 h. After the reaction is completed, filter, wash the filtrate with saturated sodium chloride solution until the pH value is 7, add anhydrous sodium sulfate and dry overnight, and under a vacuum of -0.095 MPa and at a temperature of 80 °C, distill off toluene under reduced pressure to obtain epoxy POSS;

[0154] Among them, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, the isopropanol solution of γ-glycidoxypropyltrimethoxysilane, and toluene is 355:3.4:30:186:390; the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is prepared by mixing γ-glycidoxypropyltrimethoxysilane and isopropanol at a mass ratio of 134:52.

[0155] S2. Dissolve epoxy POSS in toluene, add amino modified carbon nanotubes. The mass ratio of epoxy POSS, toluene, and amino modified carbon nanotubes is 267.2:1100:27.5, and react in a sealed manner at a temperature of 60 °C for 10 h. After the reaction is completed, filter to remove toluene and unreacted epoxy POSS, and place it in a vacuum drying oven at 50 °C and dry for 24 h to obtain carbon nanotubes grafted with POSS;

[0156] Among them, the preparation method of amino modified carbon nanotubes is the same as that in Example 1.

[0157] Step two: Prepare polyester film sheets;

[0158] Mix carbon nanotube / POSS modified polyester and PET as the first surface layer raw material and the second surface layer raw material;

[0159] The mass ratio of carbon nanotube / POSS modified polyester to PET in the first surface layer raw material is the same as that of carbon nanotube / POSS modified polyester to PET in the second surface layer raw material, and the mass ratio of carbon nanotube / POSS modified polyester to PET is 40:100;

[0160] Mix carbon nanotube / POSS modified PET and PET at a mass ratio of 35:100 as the core layer raw material;

[0161] Among them, the PET is the same as the PET used to prepare carbon nanotube / POSS modified PET in step one;

[0162] According to the setting of the three-layer structure of the first surface layer / core layer / second surface layer, melt the first surface layer raw material, the core layer raw material, and the second surface layer raw material respectively to obtain the first surface layer melt, the core layer melt, and the second surface layer melt. The melting temperature of the first surface layer raw material is 270 °C, the melting temperature of the first core layer raw material is 270 °C, and the melting temperature of the second surface layer raw material is 270 °C. Converge and extrude the first surface layer melt, the core layer melt, and the second surface layer melt in the die head. The die head temperature is 275 °C, and cool and solidify to obtain a polyester film sheet.

[0163] Step three: Stretch and shape the polyester film sheet to obtain a high light-transmitting flexible barrier film;

[0164] Among them, the stretching and shaping sequentially include longitudinal stretching and shaping and transverse stretching and shaping;

[0165] The specific stretching and shaping process is the same as that in Example 1;

[0166] The thickness of the high light-transmitting flexible barrier film is 25 μm, including a first surface layer, a core layer, and a second surface layer, and the thickness ratio of the first surface layer, the core layer, and the second surface layer is 5:15:5.

[0167] Comparative Example 1

[0168] This comparative example discloses a method for preparing a high light-transmitting flexible barrier film, including the following steps:

[0169] Step one: Prepare carbon nanotube modified polyester and carbon nanotube modified PET;

[0170] Among them, the carbon nanotube modified polyester is prepared by the following steps:

[0171] (1) Mix dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, PEG-200, and tetrabutyl titanate, introduce nitrogen, react at 240 °C and 250 kPa for 5 h. After the reaction is completed, add triethyl phosphate and antimony trioxide, and react at 260 °C and 60 Pa for 4 h. After the reaction ends, discharge the reaction mixture in a strand shape into cold water, cool, and pelletize to obtain modified polyester;

[0172] Among them, the molar ratio of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200 is 1:1.2:0.1:0.05. The addition amount of tetrabutyl titanate is 0.015% of the sum of the masses of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200. The addition amount of triethyl phosphate is 0.02% of the sum of the masses of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200. The addition amount of antimony trioxide is 0.02% of the sum of the masses of dimethyl terephthalate, ethylene glycol, 2,2-difluoromalonic acid, and PEG-200.

[0173] (2) Melt-blend the modified polyester with epoxy-modified carbon nanotubes. The mass ratio of the modified polyester to the epoxy-modified carbon nanotubes is 100:0.05. The melting temperature is 265°C. Extrude, cool, and pelletize to obtain carbon nanotube-modified polyester;

[0174] Among them, the carbon nanotube-modified PET is prepared by the following steps:

[0175] Melt-blend PET with epoxy-modified carbon nanotubes. The mass ratio of PET to the epoxy-modified carbon nanotubes is 100:0.05. The melting temperature is 265°C. Extrude, cool, and pelletize to obtain carbon nanotube-modified PET;

[0176] Among them, the epoxy-modified carbon nanotubes used for preparing the carbon nanotube-modified polyester and the carbon nanotube-modified PET are the same;

[0177] Among them, the epoxy-modified carbon nanotubes are prepared by the following steps:

[0178] Dissolve FeSO4·7H2O in deionized water. Adjust the pH value to 3 with 1 mol / L sulfuric acid aqueous solution. Add carbon nanotubes. After ultrasonic dispersion at a frequency of 50 kHz for 30 min, dropwise add 30 wt% hydrogen peroxide aqueous solution. The mass ratio of FeSO4·7H2O, deionized water, carbon nanotubes, and 30 wt% hydrogen peroxide aqueous solution is 50:250:4:300. Stir at room temperature for 24 h. Filter, wash with deionized water until the filtrate is neutral, and place in a vacuum drying oven at 50°C for drying for 24 h to obtain hydroxylated carbon nanotubes;

[0179] The hydroxylated carbon nanotubes were added to ethyl acetate and ultrasonically dispersed for 30 min at a frequency of 50 kHz. Then, γ-glycidoxypropyltrimethoxysilane was added. The mass ratio of hydroxylated carbon nanotubes, ethyl acetate, and γ-glycidoxypropyltrimethoxysilane was 4:200:20. The mixture was refluxed at 65 °C for 6 h. After the reaction, it was filtered, and the unreacted γ-glycidoxypropyltrimethoxysilane was washed away with ethyl acetate. Then it was placed in a vacuum drying oven at 50 °C and dried for 24 h to obtain epoxy-modified carbon nanotubes.

[0180] Step 2: Prepare a polyester film sheet.

[0181] The carbon nanotube-modified polyester and PET were mixed as the first surface layer raw material and the second surface layer raw material.

[0182] The mass ratio of carbon nanotube-modified polyester to PET in the first surface layer raw material was the same as that in the second surface layer raw material, and the mass ratio of carbon nanotube-modified polyester to PET was 25:100.

[0183] The carbon nanotube-modified PET and PET were mixed at a mass ratio of 20:100 as the core layer raw material.

[0184] Among them, the PET was the same as the PET used to prepare the carbon nanotube-modified PET in Step 1.

[0185] According to the three-layer structure setting of the first surface layer / core layer / second surface layer, the first surface layer raw material, the core layer raw material, and the second surface layer raw material were melted respectively to obtain the first surface layer melt, the core layer melt, and the second surface layer melt. The melting temperature of the first surface layer raw material was 265 °C, the melting temperature of the first core layer raw material was 265 °C, and the melting temperature of the second surface layer raw material was 265 °C. The first surface layer melt, the core layer melt, and the second surface layer melt were converged and extruded in a die head. The die head temperature was 270 °C, and then it was cooled and solidified to obtain a polyester film sheet.

[0186] Step 3: Stretch and shape the polyester film sheet to obtain a high-transparency flexible barrier film.

[0187] Among them, the stretching and shaping included longitudinal stretching and shaping and transverse stretching and shaping in sequence.

[0188] Longitudinal stretching and shaping: Preheat at 80 °C, perform longitudinal stretching at 110 °C, the stretching ratio is 4 times, the stretching strength is 280 MPa. After longitudinal stretching, perform heat setting, the setting temperature is 170 °C, and the setting time is 5 s.

[0189] Transverse stretching and setting: Preheat at 100°C, perform transverse stretching at 120°C with a stretching ratio of 3.5 times and a stretching strength of 280 MPa. After longitudinal stretching, perform heat setting at 180°C for 2.5 s;

[0190] The thickness of the high-transparency flexible barrier film is 25 μm, including a first surface layer, a core layer, and a second surface layer, and the thickness ratio of the first surface layer, the core layer, and the second surface layer is 5:15:5.

[0191] Comparative Example 2

[0192] This comparative example discloses a preparation method of a high-transparency flexible barrier film, including the following steps:

[0193] Step 1: Prepare carbon nanotube / POSS-modified PET;

[0194] Melt-blend PET with carbon nanotube-grafted POSS, with the mass ratio of PET to carbon nanotube-grafted POSS being 100:0.5, a melting temperature of 265°C, extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified PET.

[0195] The carbon nanotube-grafted POSS is prepared from epoxy POSS and amino-modified carbon nanotubes, and the preparation method includes the following steps:

[0196] S1: Mix isopropanol, tetramethylammonium hydroxide, and deionized water, and dropwise add an isopropanol solution of γ-glycidoxypropyltrimethoxysilane at a stirring speed of 300 r / min. The dropping time of the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is 1 h. After dropping, stir at room temperature and a stirring speed of 300 r / min for 8 h. After stirring, under a vacuum of -0.095 MPa and at a temperature of 60°C, distill off isopropanol under reduced pressure. Add toluene and reflux at 105°C for 10 h. After the reaction, filter, wash the filtrate with saturated sodium chloride solution until the pH value is 7, add anhydrous sodium sulfate and dry overnight, and under a vacuum of -0.095 MPa and at a temperature of 80°C, distill off toluene under reduced pressure to obtain epoxy POSS;

[0197] Among them, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, the isopropanol solution of γ-glycidoxypropyltrimethoxysilane, and toluene is 325:3.2:28:180:370; the isopropanol solution of γ-glycidoxypropyltrimethoxysilane is prepared by mixing γ-glycidoxypropyltrimethoxysilane and isopropanol at a mass ratio of 130:50.

[0198] S2. Dissolve epoxy-POSS in toluene, add amino-modified carbon nanotubes. The mass ratio of epoxy-POSS, toluene, and amino-modified carbon nanotubes is 267.2:800:26. React under sealing at 55 °C for 12 h. After the reaction, filter to remove toluene and unreacted epoxy-POSS, and place it in a vacuum drying oven at 50 °C for drying for 24 h to obtain carbon nanotube-grafted POSS;

[0199] Among them, the preparation method of the amino-modified carbon nanotubes is the same as that in Example 1.

[0200] Step 2. Prepare a polyester film sheet;

[0201] Mix carbon nanotube / POSS-modified PET and PET, and use them as the first surface layer raw material, core layer raw material, and second surface layer raw material respectively;

[0202] The mass ratio of carbon nanotube / POSS-modified PET to PET in the first surface layer raw material is the same as that of carbon nanotube / POSS-modified PET to PET in the second surface layer raw material. The mass ratio of carbon nanotube / POSS-modified PET to PET is 25:100;

[0203] The mass ratio of carbon nanotube / POSS-modified PET to PET in the core layer raw material is 20:100;

[0204] Among them, the PET is the same as the PET used to prepare the carbon nanotube / POSS-modified PET in Step 1;

[0205] According to the setting of the three-layer structure of the first surface layer / core layer / second surface layer, melt the first surface layer raw material, core layer raw material, and second surface layer raw material respectively to obtain the first surface layer melt, core layer melt, and second surface layer melt. The melting temperature of the first surface layer raw material is 265 °C, the melting temperature of the first core layer raw material is 265 °C, and the melting temperature of the second surface layer raw material is 265 °C. Converge and extrude the first surface layer melt, core layer melt, and second surface layer melt in the die head. The die head temperature is 270 °C, and cool and solidify to obtain a polyester film sheet.

[0206] Step 3. Stretch and shape the polyester film sheet to obtain a high-transparency flexible barrier film;

[0207] Among them, the stretching and shaping includes longitudinal stretching and shaping and transverse stretching and shaping in sequence;

[0208] Longitudinal stretching and shaping: Preheat at 80 °C, perform longitudinal stretching at 110 °C, the stretching ratio is 4 times, the stretching strength is 280 MPa, and perform heat setting after longitudinal stretching. The setting temperature is 170 °C, and the setting time is 5 s;

[0209] Transverse stretching and setting: Preheat at 100 °C, perform transverse stretching at 120 °C, with a stretching ratio of 3.5 times and a stretching strength of 280 MPa. After longitudinal stretching, perform heat setting at 180 °C for 2.5 s;

[0210] The thickness of the high-transparency flexible barrier film is 25 μm, and it includes a first surface layer, a core layer, and a second surface layer. The thickness ratio of the first surface layer, the core layer, and the second surface layer is 5:15:5.

[0211] In the above examples and comparative examples: PEG-200 and PEG400 were both purchased from Hai'an Petrochemical Factory, Jiangsu Province. PEG-200 is a colorless transparent liquid, with hydroxyl value (mgKOH / g): 534 - 590, and molecular weight of 190 - 210. PEG-400 is a colorless transparent liquid, with hydroxyl value (mgKOH / g): 567 - 295, and molecular weight of 380 - 420; PET is transparent PET plastic particles, purchased from Ningbo Jianxing Plastic Co., Ltd., grade: WK801, melting point: 243 ± 2 °C; carbon nanotubes were purchased from Jiaxing Bona New Materials Co., Ltd., product number: NACO-CNTs-1, tube length: 5 - 15 μm, tube diameter: 7 - 15 nm.

[0212] Test Example

[0213] Perform performance tests on the high-transparency flexible barrier films prepared in Examples 1 - 4 and Comparative Examples 1 - 2:

[0214] Light transmittance performance test: Refer to the standard GB / T2410 - 2008 "Determination of Light Transmittance and Haze of Transparent Plastics" to measure the light transmittance of the film. The measurement results are shown in Table 1:

[0215] ;

[0216] As can be seen from Table 1, the film materials prepared in the present invention have good light transmittance. The present invention uses polyester as the matrix material for preparing the composite film material, which has good light transmittance. The addition of carbon nanotubes and POSS does not significantly affect the light transmittance of the film material. Compared with Example 1, in Comparative Example 1, POSS was not introduced. In Comparative Example 2, the raw materials for the first surface layer, the second surface layer, and the core layer were all carbon nanotube / POSS modified PET and PET, and fluorine elements and hydrophilic polyether segments were not introduced, which did not significantly affect the light transmittance of the film material.

[0217] (2) Barrier performance test: Refer to the standard GB / T21529 - 2008 "Determination of Water Vapor Transmission Rate of Plastic Films and Sheets - Electrolytic Sensor Method" to measure the water vapor transmission rate of the film. The measurement results are shown in Table 2:

[0218] ;

[0219] As can be seen from Table 2, the film material prepared by the present invention has good barrier properties. The present invention uses polyester as the matrix material for preparing the composite film material, which has good barrier properties. The introduction of fluorine element in the surface layer raw material can reduce the adsorption and diffusion of water molecules by the film material. The introduction of carbon nanotube grafted POSS on the polyester matrix forms a maze effect, which can extend the diffusion path of water vapor and improve the barrier properties of the film material. Compared with Example 1, in Comparative Example 1, POSS was not introduced, the maze effect was weakened, and the barrier properties were reduced. In Comparative Example 2, the carbon nanotube / POSS modified polyester in the first surface layer raw material and the second surface layer raw material was replaced with carbon nanotube / POSS modified PET, that is, fluorine element was not introduced, the adsorption and diffusion of water molecules were enhanced, and the barrier properties were also reduced.

[0220] (3)Tensile properties: The elongation at break of the film was measured with reference to the standard ASTM D-882. The measurement results are shown in Table 3:

[0221] ;

[0222] As can be seen from Table 3, the film material prepared by the present invention has good tensile properties. In the present invention, when preparing the modified polyester, the introduced flexible polyether chain can improve the flexibility of the polyester molecular chain; the introduction of carbon nanotube grafted POSS can also improve the toughness of the modified polyester and PET. The composite film material has good toughness and high elongation at break. Compared with Example 1, in Comparative Example 1, POSS was not introduced, and the toughening performance was reduced; in Comparative Example 2, the carbon nanotube / POSS modified polyester in the first surface layer raw material and the second surface layer raw material was replaced with carbon nanotube / POSS modified PET, that is, the flexible polyether chain was not introduced, and the toughening performance was also reduced.

[0223] (4)Hydrophobic and oleophobic property test: The contact angle of the film material was measured. The droplet method was used for the test. A specimen of 0.5 cm × 1 cm was taken and spread on a glass slide. 5 μL of water was dropped on the film surface, and the water contact angle was measured by a contact angle measuring instrument JC2000A. The test was carried out 3 times and the average value was taken; the water was replaced with diiodomethane, and the above test method was repeated to measure the diiodomethane contact angle. The test results are shown in Table 4:

[0224] ;

[0225] As can be seen from Table 4, the membrane material prepared by the present invention has good hydrophobic and oleophobic properties. The modified polyester in the surface layer raw material introduces hydrophobic fluorine elements and oleophobic polyether segments, making the surface layer structure of the composite membrane material have hydrophobic and oleophobic properties, thus having the effect of self-cleaning of the surface layer. Compared with Example 1, in Comparative Example 2, the carbon nanotube / POSS modified polyester in the first surface layer raw material and the second surface layer raw material was replaced with carbon nanotube / POSS modified PET, that is, fluorine elements and polyether segments were not introduced, and both the hydrophobic property and the oleophobic property decreased significantly.

[0226] Although the embodiments of the present invention have been shown and described, those of ordinary skill in the art can understand that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a highly transparent flexible barrier film, characterized in that, It includes the following steps: Step 1: Prepare carbon nanotube / POSS-modified polyester and carbon nanotube / POSS-modified PET; Among them, the carbon nanotube / POSS-modified polyester is prepared by the following steps: (1) Mix dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, polyethylene glycol, and catalyst 1, introduce nitrogen, react. After the reaction is completed, add a stabilizer and catalyst 2, and continue to react. After the reaction ends, discharge the reaction mixture, cool, and pelletize to obtain the modified polyester; Among them, the molar ratio of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol is 1:(1.2 - 1.4):(0.1 - 0.3):(0.05 - 0.2). The addition amount of catalyst 1 is 0.015% - 0.03% of the total mass of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol. The addition amount of the stabilizer is 0.02% - 0.04% of the total mass of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol. The addition amount of catalyst 2 is 0.02% - 0.04% of the total mass of dimethyl terephthalate, ethylene glycol, fluorinated dibasic acid, and polyethylene glycol. The reaction conditions are to react at 240 - 260 °C and 250 kPa for 3 - 5 h. The conditions for the continued reaction are to react at 260 - 280 °C and 20 - 60 Pa for 2 - 4 h; The polyethylene glycol includes at least one of polyethylene glycol 200 and polyethylene glycol 400; The fluorinated dibasic acid includes at least one of 2,2-difluoromalonic acid and 2,2-difluorosuccinic acid; The catalyst 1 includes tetrabutyl titanate; The stabilizer includes triethyl phosphate; The catalyst 2 includes antimony trioxide; (2) Melt-blend the modified polyester with carbon nanotube-grafted POSS, extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified polyester; Among them, the carbon nanotube / POSS-modified PET is prepared by the following steps: Melt-blend PET with carbon nanotube-grafted POSS, extrude, cool, and pelletize to obtain carbon nanotube / POSS-modified PET; The carbon nanotube-grafted POSS used for preparing carbon nanotube / POSS-modified polyester and carbon nanotube / POSS-modified PET is the same; The carbon nanotube-grafted POSS is prepared from epoxy POSS and amino-modified carbon nanotubes. The preparation method includes the following steps: S1: Mix isopropanol, tetramethylammonium hydroxide, and deionized water, dropwise add an isopropanol solution of γ-glycidoxypropyltrimethoxysilane under stirring. After the addition is completed, stir. After the stirring is completed, remove isopropanol by vacuum distillation, add toluene, react. After the reaction ends, purify to obtain epoxy POSS; Among them, the mass ratio of isopropanol, tetramethylammonium hydroxide, deionized water, isopropanol solution of γ-glycidyletheroxypropyltrimethoxysilane, and toluene is (325 - 365):(3.2 - 3.6):(28 - 32):(180 - 190):(370 - 400). The dropping time of the isopropanol solution of γ-glycidyletheroxypropyltrimethoxysilane is 1 - 2 h, the stirring condition is stirring at room temperature for 8 - 10 h, and the reaction condition is reflux reaction at a temperature of 105 - 115 °C for 6 - 10 h; the isopropanol solution of γ-glycidyletheroxypropyltrimethoxysilane is prepared by mixing γ-glycidyletheroxypropyltrimethoxysilane and isopropanol in a mass ratio of (130 - 135):(50 - 55); S2. Dissolve epoxy-POSS in toluene, add amino-modified carbon nanotubes, react, after the reaction ends, filter and dry to obtain carbon nanotubes grafted with POSS; Among them, the mass ratio of epoxy-POSS, toluene, and amino-modified carbon nanotubes is 267.2:(800 - 1200):(26 - 28), and the reaction condition is sealed reaction at a temperature of 55 - 65 °C for 8 - 12 h; Step two. Prepare a polyester film sheet; Mix carbon nanotubes / POSS-modified polyester and PET as the first surface layer raw material and the second surface layer raw material; Mix carbon nanotubes / POSS-modified PET and PET as the core layer raw material; According to the setting of the three-layer structure of the first surface layer / core layer / second surface layer, melt the first surface layer raw material, the core layer raw material, and the second surface layer raw material respectively to obtain the first surface layer melt, the core layer melt, and the second surface layer melt. Converge and extrude the first surface layer melt, the core layer melt, and the second surface layer melt in a die head, and cool and solidify to obtain a polyester film sheet; Step three. Prepare a high-transparency flexible barrier film; Perform stretching and shaping on the polyester film sheet to obtain a high-transparency flexible barrier film.

2. The preparation method of a highly transparent flexible barrier film according to claim 1, characterized in that, In the above step one: when preparing carbon nanotubes / POSS-modified polyester, the mass ratio of modified polyester to carbon nanotubes grafted with POSS is 100:(0.5 - 2), and the melting temperature is 265 - 280 °C.

3. The preparation method of a highly light-transmissive flexible barrier film according to claim 1, characterized in that, In the above step one: when preparing carbon nanotubes / POSS-modified PET, the mass ratio of PET to carbon nanotubes grafted with POSS is 100:(0.5 - 2), and the melting temperature is 265 - 280 °C.

4. The preparation method of a highly transparent flexible barrier film according to claim 1, characterized in that, The preparation of the amino-modified carbon nanotubes includes the following steps: Dissolve FeSO4·7H2O in deionized water, adjust the pH value to 2.5 - 3.5, add carbon nanotubes, after ultrasonic dispersion, dropwise add an aqueous hydrogen peroxide solution, stir, filter, wash, and dry to obtain hydroxylated carbon nanotubes; Among them, the mass ratio of FeSO4·7H2O, deionized water, carbon nanotubes, and aqueous hydrogen peroxide solution is 50:250:4:300, and the stirring condition is stirring at room temperature for 24 h; Add the hydroxylated carbon nanotubes to ethyl acetate, after ultrasonic dispersion, add γ-aminopropyltriethoxysilane, react, after the reaction ends, filter, wash, and dry to obtain amino-modified carbon nanotubes; Among them, the mass ratio of hydroxylated carbon nanotubes, ethyl acetate, and γ-aminopropyltriethoxysilane is 4:200:20, and the reaction conditions are reflux reaction at 65 - 75 °C for 5 - 7 h.

5. The preparation method of a highly light-transmissive flexible barrier film according to claim 1, characterized in that, In the second step: the mass ratio of carbon nanotube / POSS-modified polyester to PET in the first surface layer raw material is the same as that in the second surface layer raw material, and the mass ratio of carbon nanotube / POSS-modified polyester to PET is (25 - 45):100; The mass ratio of carbon nanotube / POSS-modified PET to PET in the core layer raw material is (20 - 40):100; The melting temperature of the first surface layer raw material is 265 - 280 °C, the melting temperature of the core layer raw material is 265 - 280 °C, and the melting temperature of the second surface layer raw material is 265 - 280 °C; The die head temperature is 270 - 285 °C.

6. The preparation method of a highly light-transmissive flexible barrier film according to claim 1, wherein In the third step: the stretching and setting includes longitudinal stretching and setting and transverse stretching and setting in sequence; The longitudinal stretching and setting includes preheating at 75 - 85 °C, longitudinal stretching at 90 - 120 °C with a stretching ratio of 3.5 - 4.5 times, and heat setting at 165 - 180 °C for 2 - 5 s after longitudinal stretching; The transverse stretching and setting includes preheating at 95 - 105 °C, transverse stretching at 110 - 130 °C with a stretching ratio of 3 - 4 times, and heat setting at 175 - 185 °C for 2 - 3 s after transverse stretching.

7. A highly transparent flexible barrier film prepared by using the preparation method of the highly transparent flexible barrier film according to any one of claims 1 - 6.

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