Blue polyester film and method for producing the same

Abstract

The application discloses a blue polyester film and a preparation method thereof. The blue polyester film is obtained by co-extrusion of a surface layer solution and a core layer solution. The core layer solution comprises the following components by weight: 52-64 parts of modified polyester chips, 1-6 parts of blue master batch, 12-26 parts of tackifying recycled blue chips and 1-2 parts of dispersant. The modified polyester chips are polyester chips with a melting point of 210-230 DEG C. The polyester film prepared by the method has good color stability and small color difference between different batches.

Description

Technical Field

[0001] This application relates to the field of polyester materials, and in particular to a blue polyester film and a method for preparing the same. Background Technology

[0002] Polyester film is a film material made from polyethylene terephthalate (PET) through extrusion to form thick sheets, followed by biaxial stretching. Blue polyester film is a special type of polyester film produced by adding blue masterbatch. It can be used as an identification material in automated machines for recognizing and counting polyester films, significantly improving the efficiency of counting polyester films.

[0003] The formulation of blue polyester film is mainly achieved by adding a high concentration of blue masterbatch to transparent polyester chips. However, due to factors such as pigment dispersibility, particle size, and compatibility with polyester materials, there is a large color difference between different batches of blue polyester film. Summary of the Invention

[0004] To reduce the color difference problem of blue polyester film, this application provides a blue polyester film and its preparation method.

[0005] Firstly, a blue polyester film is obtained by co-extrusion of a surface melt and a core melt. The core melt, by weight, comprises the following components: 52-64 parts modified polyester chips, 1-6 parts blue masterbatch, 12-26 parts tackifying recycled blue chips, and 1-2 parts dispersant. The modified polyester chips are polyester chips with a melting point of 210-230°C.

[0006] By using low-melting-point polyester chips as the core layer melt material, the structural decomposition or agglomeration of pigments due to heating during core layer preparation is reduced, thus minimizing particle size increase and reducing color difference. Using viscous recycled blue chips as the core layer melt material allows for further recycling of waste materials, improving material utilization. Furthermore, during film preparation, color supersaturation affects pigment dispersion; adding viscous recycled blue chips reduces the use of masterbatch, improves pigment dispersion, and reduces color difference. Using low-melting-point polyester chips can decrease the film-forming properties and mechanical properties of the polyester film and easily cause pigment migration, leading to color difference during film preparation. By co-extruding the surface and core layer melts, the core layer is sandwiched in between, reducing pigment migration from the film interior to the surface and improving the film-forming properties and mechanical properties of the polyester film.

[0007] Preferably, the dispersant is a polyolefin elastomer or a polyethylene wax.

[0008] By adopting the above technical solutions, polyolefin elastomers can adjust the viscosity of the system and improve the extensibility and deformation capacity of polyester films, thereby improving the dispersion of pigments in polyester materials and reducing color differences; polyethylene wax can also improve the dispersion of pigments in polyester materials and reduce color differences.

[0009] Preferably, the pigment in the orchid masterbatch is phthalocyanine blue.

[0010] Typical, but not restrictive, phthalocyanine blue is selected from CI pigment blue 15:3.

[0011] By adopting the above technical solution and selecting phthalocyanine blue as the pigment in the blue masterbatch, phthalocyanine blue has good heat resistance and migration resistance. In this application, the color difference problem can be significantly improved by using the co-extrusion method of surface solution and core solution.

[0012] Preferably, the modified polyester chips, by weight, comprise the following raw materials: 50-83 parts terephthalic acid, 37-43 parts ethylene glycol, 2.7-10.8 parts 1,4-butanediol, 4.5-13.6 parts diethylene glycol, and 0.015-0.02 parts catalyst.

[0013] Typically, but not limitingly, the catalyst is one of antimony-based, germanium-based, and titanium-based catalysts.

[0014] By adopting the above technical solution, 1,4-butanediol, being an asymmetric structure, disrupts the original symmetrical structure of PET and increases the spacing between macromolecular chains, resulting in a looser molecular chain arrangement and reduced chain rigidity. This, in turn, increases the melt entropy of polyester and lowers its melting point. Furthermore, 1,4-butanediol possesses a flexible ethyl side chain, which enhances the fluidity of the molecular chains. Therefore, when 1,4-butanediol is used as a raw material for modified polyester chips, the melting point and viscosity of the modified polyester chips decrease, thereby reducing pigment thermal decomposition and agglomeration, and improving pigment dispersibility, thus reducing color difference. In addition, this application uses a co-extrusion process of surface solution and core solution. If the viscosity difference between the surface solution and the core solution is too large, it is easy to cause interface instability, making it difficult to form a uniform polyester film and easily causing color difference. This application uses 1,4-butanediol as a raw material, which not only lowers the melting point of the polyester material but also improves the fluidity of the material, that is, reduces the viscosity. By optimizing the viscosity between the surface solution and the core solution through the amount of 1,4-butanediol incorporation, the generation of color difference is further reduced.

[0015] Preferably, the method for preparing the modified polyester chips includes the following steps:

[0016] Terephthalic acid, ethylene glycol, 1,4-butanediol, diethylene glycol and catalyst are mixed and heated to 188-192℃ for esterification reaction for 4-5 hours. Then the temperature is adjusted to 280-290℃ for polycondensation reaction for 35-45 minutes to obtain modified polyester chips.

[0017] By adopting the above technical solution and optimizing the process parameters of modified polyester chips, the melting point of the obtained modified polyester chips is further reduced, and they have better fluidity.

[0018] Preferably, the tackified recycled blue chips are obtained by recycling through tackification technology, and the tackified recycled chips comprise the following materials in parts by weight: 46-82 parts of blue polyester film waste, 8-20 parts of ethylene glycol, 1-3 parts of chain extender and 0.01-0.02 parts of catalyst.

[0019] By adopting the above technical solution, 20-40% of blue polyester film waste will be generated during the production process of blue polyester film. This blue polyester film waste cannot be directly used to prepare polyester film by simply recycling it through granulation. After being treated with ethylene glycol and chain extender to increase its viscosity, it can be reused as a raw material for polyester film, reducing waste. At the same time, it reduces the oversaturation of pigments during the dispersion process, thereby reducing color difference.

[0020] Preferably, the method for preparing the thickened regenerated orchid slices includes the following steps:

[0021] Alcohololysis: Take ethylene glycol and blue polyester film waste, mix them, react at 60-70℃ for 40-60 min, and then melt-extrude to obtain the alcoholysis polyester melt;

[0022] Regeneration: Take the polyester melt after alcoholysis, add chain extender and catalyst, mix and carry out self-condensation reaction at 270-280℃, control the reaction time at 1-3h, and obtain viscous regenerated blue chips.

[0023] Typically, but not limitingly, the chain extender is terminal epoxy-based silicone oil, and the catalyst is one of antimony-based, germanium-based, and titanium-based catalysts.

[0024] By employing the above technical solution, the molecular weight and viscosity of blue polyester film waste are reduced through alcoholysis, improving the dispersibility of pigments in the recycled material and facilitating the regeneration of uniformly colored, viscous recycled blue chips. Further addition of chain extenders and catalysts allows for self-condensation polymerization, lengthening the molecular chains and reforming a stable molecular chain structure. This enhances the viscosity and ductility of the polyester material, improving the compatibility between the modified polyester chips and the blue masterbatch during core layer preparation, resulting in polyester films with smaller color differences.

[0025] Preferably, the surface melt is prepared by mixing optical polyester chips and anti-sticking masterbatch. The surface melt, by weight, includes the following components: 10-30 parts optical polyester chips and 1-2 parts anti-sticking masterbatch, wherein the anti-sticking masterbatch is a polyester masterbatch containing modified fumed silica.

[0026] By adopting the above technical solution, an anti-sticking masterbatch is added to the surface melt. This masterbatch contains silica powder, which improves the hydrophobicity of the surface film and reduces its surface energy. This reduces the adsorption of pigments from the core melt by the surface melt, thereby reducing color migration. Furthermore, the silica powder also improves the heat resistance of the surface melt, further enhancing the heat resistance of the blue polyester film, thus reducing pigment decomposition or agglomeration due to heat. In addition, during the co-extrusion process, the hydroxyl groups on the silica surface can form hydrogen bonds with the active groups on the pigment surface. Electrostatic attraction also exists between silica and pigment, creating an encapsulated adsorption layer that reduces pigment decomposition or agglomeration due to heat, thereby minimizing color difference.

[0027] Preferably, the anti-sticking masterbatch comprises, by weight, the following components: 1.2-4.6 parts modified fumed silica, 52-58 parts terephthalic acid, 40-44 parts ethylene glycol, 0.01-0.014 parts catalyst and 0.02-0.03 parts initiator, wherein the modified fumed silica is obtained by modifying fumed silica with dodecanol.

[0028] Typically, but not limitingly, the catalyst is one of antimony-based, germanium-based, and titanium-based catalysts.

[0029] By adopting the above technical solution, the number of surface hydroxyl groups in fumed silica is reduced after alcohol modification, thereby increasing the oleophilicity of fumed silica and improving the compatibility between fumed silica and polyester. At the same time, the surface steric hindrance of fumed silica is increased, reducing the agglomeration of fumed silica and further improving the dispersion of fumed silica in the surface solution. This improves the overall heat resistance of the blue polyester film and reduces migration, thereby reducing the generation of color difference.

[0030] Preferably, the method for preparing the anti-sticking masterbatch includes the following steps:

[0031] Alcohol modification: Take fumed silica and perform air jet milling. After taking it out, mix it with dodecanol, cosolvent and catalyst. React at 60-80℃ for 60-80 min. Wash and dry to obtain modified fumed silica.

[0032] Blending: Take terephthalic acid, ethylene glycol, modified fumed silica and initiator, mix them, and esterify at 180-200℃ for 3-5 hours. Then adjust the temperature to 280-290℃ and polycondensate for 35-45 minutes to obtain the anti-sticking masterbatch.

[0033] Typically, but not limitingly, xylene is used as the cosolvent, p-toluenesulfonic acid is used as the catalyst, and cobalt isooctanoate is used as the initiator.

[0034] By adopting the above technical solutions, airflow pulverization is used to reduce the particle size of fumed silica, improve the effect of fumed silica and the effect of alcohol modification, and optimize the process parameters for the preparation of anti-sticking masterbatch, which can significantly reduce the color difference problem of blue polyester film.

[0035] In summary, this application has the following beneficial effects:

[0036] 1. The film is obtained by co-extrusion of a surface melt and a core melt. The surface melt uses a polyester material with good heat resistance, while the core melt uses a polyester material with a lower melting point. This ensures that the resulting blue polyester film maintains good color uniformity while possessing good film-forming properties. Furthermore, the surface melt contains modified fumed silica. On one hand, the modified fumed silica improves the overall heat resistance of the polyester film and works synergistically with the modified polyester chips with a lower melting point to protect the substances in the core melt from thermal decomposition. On the other hand, it works with the pigments in the core melt to improve the stability and dispersibility of the pigments in the polyester film, reducing color differences caused by pigment agglomeration and migration.

[0037] 2. The polyester film prepared in this application has a more uniform dispersion of various substances and better compatibility between the surface solution and the core solution. Therefore, the blue polyester film prepared is more uniform, and the products from different production batches have closer mechanical properties. Detailed Implementation

[0038] The raw materials used in the examples and preparation examples are all commercially available and described in detail below. The present application will be further described in detail below with reference to the examples.

[0039] Preparation of modified polyester chips

[0040] Preparation Example 1-1: A modified polyester chip was prepared using the following steps:

[0041] Take 67g of terephthalic acid, 40g of ethylene glycol, 6.8g of 1,4-butanediol, 9g of diethylene glycol and 0.018g of antimony trioxide, mix them, heat to 190℃, and esterify for 4.5h. Then adjust the temperature to 285℃ and react in a vacuum environment for 40min to obtain modified polyester chips.

[0042] Preparation Examples 1-2: A modified polyester chip was prepared using the following steps:

[0043] Take 83g of terephthalic acid, 43g of ethylene glycol, 10.8g of 1,4-butanediol, 13.6g of diethylene glycol and 0.015g of antimony trioxide, mix them, heat to 192℃, and esterify for 5h. Then adjust the temperature to 290℃ and react in a vacuum environment for 45min to obtain modified polyester chips.

[0044] Preparation Examples 1-3: A modified polyester chip was prepared using the following steps:

[0045] Mix 50g terephthalic acid, 37g ethylene glycol, 2.7g 1,4-butanediol, 4.5g diethylene glycol and 0.02g antimony trioxide, heat to 188℃, and esterify for 4 hours. Then adjust the temperature to 280℃ and react in a vacuum environment for 35 minutes to obtain modified polyester chips.

[0046] Preparation Examples 1-4: A modified polyester chip, which differs from Preparation Example 1-1 in that 1,4-butanediol is replaced with an equal amount of diethylene glycol.

[0047] Preparation Examples 1-5: A modified polyester chip, which differs from Preparation Example 1-1 in that diethylene glycol is replaced with an equal amount of 1,4-butanediol.

[0048] Preparation Examples 1-6: A modified polyester chip was prepared by the following steps: 67g of terephthalic acid, 55.8g of ethylene glycol and 0.018g of antimony trioxide were mixed, heated to 190℃, and esterified for 4.5h. Then the temperature was adjusted to 285℃ and the reaction was carried out under vacuum for 40min to obtain the modified polyester chip.

[0049] Preparation of thickened regenerated orchid slices

[0050] Preparation Example 2-1, a type of thickened regenerated orchid slice, was prepared using the following steps:

[0051] Alcohololysis: Take 14g of ethylene glycol and 64g of blue polyester film waste, mix them, react at 65℃ for 50min, and then extrude them into a twin-screw extruder to obtain the alcoholysis polyester melt;

[0052] Regeneration: Take the polyester melt after alcoholysis, add 2g of terminal epoxy silicone oil and 0.015g of antimony trioxide, mix and carry out self-condensation reaction, react in a vacuum environment at 275℃ for 2h to obtain viscous regenerated blue chips.

[0053] Preparation Example 2-2, a type of thickened regenerated orchid slice, was prepared using the following steps:

[0054] Alcohololysis: Take 20g of ethylene glycol and 82g of blue polyester film waste, mix them, react at 70℃ for 60min, and then extrude them into a twin-screw extruder to obtain the alcoholysis polyester melt;

[0055] Regeneration: Take the polyester melt after alcoholysis, add 1g of terminal epoxy silicone oil and 0.01g of antimony trioxide, mix and carry out self-condensation reaction, react in a vacuum environment at 280℃ for 1h to obtain viscous regenerated blue chips.

[0056] Preparation Example 2-3, a type of thickened regenerated orchid slice, was prepared using the following steps:

[0057] Alcohololysis: Take 8g of ethylene glycol and 46g of blue polyester film waste, mix them, react at 60℃ for 40min, and then extrude them into a twin-screw extruder to obtain the alcoholysis polyester melt;

[0058] Regeneration: Take the polyester melt after alcoholysis, add 3g of terminal epoxy silicone oil and 0.02g of antimony trioxide, mix and carry out self-condensation reaction, react in a vacuum environment at 280℃ for 1h to obtain viscous regenerated blue chips.

[0059] Preparation Examples 2-4: A type of thickened regenerated orchid slice was prepared using the following steps:

[0060] Regeneration: Take 64g of blue polyester film waste, 14g of ethylene glycol, 2g of epoxy-terminated silicone oil and 0.015g of antimony trioxide, mix them, carry out self-condensation reaction, and react under vacuum at 275℃ for 2h to obtain viscous regenerated blue chips.

[0061] Preparation of anti-sticking masterbatch

[0062] Preparation Example 3-1, an anti-sticking masterbatch, was prepared using the following steps:

[0063] Alcohol modification: Take 10g of fumed silica and perform air jet milling. After classifying, obtain particles with a particle size of 10-18μm. Take them out and mix them with 8g of n-dodecyl alcohol, 20g of xylene and 0.5g of p-toluenesulfonic acid. React at 70℃ for 70min. Filter, wash and dry to obtain modified fumed silica.

[0064] Blending: Mix 55g terephthalic acid, 42g ethylene glycol, 2.9g modified fumed silica and 0.025g cobalt isooctanoate, esterify at 190℃ for 4h, then adjust the temperature to 285℃ and react in a vacuum environment for 40min to obtain an anti-sticking masterbatch.

[0065] Preparation Example 3-2, a modified anti-sticking masterbatch, was prepared using the following steps:

[0066] Alcohol modification: Take 12g of fumed silica and perform air jet milling. After classifying, obtain particles with a particle size of 10-18μm. Take them out and mix them with 10g of n-dodecyl alcohol, 20g of xylene and 0.4g of p-toluenesulfonic acid. React at 80℃ for 60min. Filter, wash and dry to obtain modified fumed silica.

[0067] Blending: Mix 58g terephthalic acid, 44g ethylene glycol, 4.6g modified fumed silica and 0.03g cobalt isooctanoate, esterify at 200℃ for 3h, then adjust the temperature to 290℃ and react in a vacuum environment for 35min to obtain anti-sticking masterbatch.

[0068] Preparation Example 3-3, an anti-sticking masterbatch, was prepared using the following steps:

[0069] Alcohol modification: Take 8g of fumed silica and perform air jet milling. After classifying, obtain particles with a particle size of 10-18μm. Take them out and mix them with 6g of n-dodecyl alcohol, 20g of xylene and 0.1g of p-toluenesulfonic acid. React at 70℃ for 80min. Filter, wash and dry to obtain modified fumed silica.

[0070] Blending: Mix 52g terephthalic acid, 40g ethylene glycol, 1.2g modified fumed silica and 0.02g cobalt isooctanoate, esterify at 180℃ for 5h, then adjust the temperature to 280℃ and react in a vacuum environment for 45min to obtain anti-sticking masterbatch.

[0071] Preparation Examples 3-4: An anti-sticking masterbatch was prepared using the following steps:

[0072] Blending: Mix 55g terephthalic acid, 42g ethylene glycol, 2.9g fumed silica and 0.025g cobalt isooctanoate, esterify at 190℃ for 4h, then adjust the temperature to 285℃ and react in a vacuum environment for 40min to obtain anti-sticking masterbatch.

[0073] Preparation Examples 3-5: An anti-sticking masterbatch was prepared using the following steps:

[0074] Surface modification: Take 10g of fumed silica and perform air jet milling. After classifying, obtain particles with a particle size of 10-18μm. Mix with 20g of anhydrous ethanol and add 8g of KH-581 (3-mercaptopropylmethyldiethoxysilane). React at 70℃ for 70min. Filter, wash and dry to obtain modified fumed silica.

[0075] Blending: Mix 55g terephthalic acid, 42g ethylene glycol, 2.9g modified fumed silica and 0.025g cobalt isooctanoate, esterify at 190℃ for 4h, then adjust the temperature to 285℃ and react in a vacuum environment for 40min to obtain an anti-sticking masterbatch. Example

[0076] Example 1: A blue polyester film, prepared by the following method:

[0077] Core layer melt: Take 58 kg of modified polyester chips, 3.5 kg of phthalocyanine blue BGS masterbatch, 19 kg of tackifying recycled blue chips and 1.5 kg of polyolefin elastomer, and melt them to obtain the core layer melt;

[0078] Surface melt: Take 20 kg of optical polyester chips and 1.5 kg of anti-sticking masterbatch, and melt them to obtain the surface melt;

[0079] Film making: The core layer melt and the surface layer melt are joined together by three layers of molds and cast into a sheet. After longitudinal stretching, transverse stretching and heat setting, a blue polyester film is obtained.

[0080] The thickness of the intermediate layer is controlled at 40%, and the thickness of the surface layer is 30% each. The melting temperature of the surface layer is 270℃, the melting temperature of the core layer is 245℃, the longitudinal stretching temperature is 100℃, and the stretching ratio is 4 times. The TD stretching temperature is 120℃, the stretching ratio is 4 times, and the heat setting temperature is 200℃.

[0081] In addition, the modified polyester chips were derived from Preparation Example 1-1, the tackified recycled polyester chips were derived from Preparation Example 2-1, and the anti-sticking masterbatch was derived from Preparation Example 3-1.

[0082] Example 2: A blue polyester film, prepared by the following method:

[0083] Core layer melt: Take 64 kg of modified polyester chips, 6 kg of phthalocyanine blue BGS masterbatch, 12 kg of tackifying recycled blue chips and 2 kg of polyolefin elastomer, and melt them to obtain the core layer melt;

[0084] Surface melt: Take 30 kg of optical polyester chips and 2 kg of anti-sticking masterbatch, and melt them to obtain the surface melt;

[0085] Film making: The core layer melt and the surface layer melt are joined together by three layers of molds and cast into a sheet. After longitudinal stretching, transverse stretching and heat setting, a blue polyester film is obtained.

[0086] The thickness of the intermediate layer is controlled to be 40%, and the thickness of the surface layer is 30% each. The melting temperature of the surface layer is 280℃, the melting temperature of the core layer is 250℃, the longitudinal stretching temperature is 125℃, and the stretching ratio is 4.5 times. The TD stretching temperature is 130℃, the stretching ratio is 4.5 times, and the heat setting temperature is 200℃.

[0087] In addition, the modified polyester chips were derived from Preparation Examples 1-2, the tackifying recycled polyester chips were derived from Preparation Example 2-2, and the anti-sticking masterbatch was derived from Preparation Example 3-2.

[0088] Example 3: A blue polyester film, prepared by the following method:

[0089] Core layer melt: Take 52 kg of modified polyester chips, 1 kg of Phthalocyanine Blue BGS masterbatch, 26 kg of tackifying recycled blue chips and 1 kg of polyolefin elastomer, and melt them to obtain the core layer melt;

[0090] Surface melt: Take 10 kg of optical polyester chips and 1 kg of anti-sticking masterbatch, and melt them to obtain the surface melt;

[0091] Film making: The core layer melt and the surface layer melt are joined together by three layers of molds and cast into a sheet. After longitudinal stretching, transverse stretching and heat setting, a blue polyester film is obtained.

[0092] The thickness of the intermediate layer is controlled to be 40%, and the thickness of the surface layer is 30% each. The melting temperature of the surface layer is 270℃, the melting temperature of the core layer is 245℃, the longitudinal stretching temperature is 80℃, and the stretching ratio is 3.5 times. The TD stretching temperature is 110℃, the stretching ratio is 4 times, and the heat setting temperature is 200℃.

[0093] In addition, the modified polyester chips were derived from Preparation Examples 1-3, the tackifying recycled polyester chips were derived from Preparation Examples 2-3, and the anti-sticking masterbatch was derived from Preparation Example 3-3.

[0094] Example 4, a blue polyester film, differs from Example 1 in that the modified polyester chips are derived from Preparation Examples 1-4.

[0095] Example 5, a blue polyester film, differs from Example 1 in that the modified polyester chips are derived from Preparation Examples 1-5.

[0096] Example 6, a blue polyester film, differs from Example 1 in that the tackified recycled blue chips are derived from Preparation Examples 2-4.

[0097] Example 7, a blue polyester film, differs from Example 1 in that the anti-sticking masterbatch is derived from preparation 3-4.

[0098] Example 8, a blue polyester film, differs from Example 1 in that the anti-sticking masterbatch is derived from preparation 3-5.

[0099] Example 9, a blue polyester film, differs from Example 1 in that the phthalocyanine blue BGS masterbatch is replaced with an equal amount of BASF phthalocyanine blue K6911D.

[0100] Comparative Example

[0101] Comparative Example 1, a blue polyester film, differs from Example 1 in that the modified polyester chips are derived from Preparation Examples 1-6.

[0102] Comparative Example 2, a blue polyester film, differs from Example 1 in that the tackifying recycled chips are replaced with an equal amount of modified polyester chips.

[0103] Comparative Example 3: A blue polyester film in which the surface melt is replaced by an equal amount of core melt.

[0104] Comparative Example 4: A blue polyester film, prepared by the following method:

[0105] (S1) 80 kg of optical polyester chips (ground to 0.3 μm), 10 kg of UV blocking masterbatch, 5 kg of phthalocyanine blue BGS masterbatch, and 4 kg of dispersant (a mixture of glycerol stearate and sulfonated modified polyvinyl alcohol prepared in Example 1 at a mass ratio of 1:5) are fed to the main extruder, melted, vacuumed, filtered, and enter the main melt pipeline. The melt temperature is about 280°C.

[0106] (S2) 80kg of optical polyester chips (ground to 0.3μm), 5kg of UV absorber UV360, and 0.2kg of antioxidant 1010 are fed into the auxiliary extruder, melted, vacuumed, filtered, and then enter the auxiliary melt pipeline. The melt temperature is about 265℃.

[0107] (S3) The melt from the main melt pipe and the auxiliary melt pipe are combined and co-extruded at a three-layer die. By controlling the metering pump, the thickness of the middle layer accounts for 60% of the total thickness, and the outer layers on both sides of the middle layer each account for about 20% of the total thickness. The three-layer co-extruded melt is cold-drum cast at 20°C, traction is performed, preheating is performed at 80°C, and then longitudinal stretching is performed at 105°C with a stretch ratio of 3.6 times. Then longitudinal stretching is performed at 120°C with a stretch ratio of 3.3 times. After biaxial stretching, high-temperature setting is performed at 220°C, flattening, static electricity removal, and winding to obtain the colored anti-aging biaxially oriented polyester film with a total thickness of 200μm, of which the thickness of the middle colored layer is 120μm, and the thickness of the transparent anti-UV layers on both sides of the middle layer is about 40μm each.

[0108] Performance testing

[0109] For the polyester films prepared in Examples 1-9 and Comparative Examples 1-4, six batches of samples were taken for performance testing, and the tests were performed in parallel for six times, and the average value was taken.

[0110] Experiment 0: Melting point test of modified polyester chips: The melting point of modified polyester chips was tested by differential scanning calorimetry, and the results are shown in Table 1.

[0111] Experiment 1: Haze test: The haze was tested according to the method of GB / T2410 "Determination of transmittance and haze of transparent plastics". The haze difference of different batches of samples was calculated and the absolute value was taken. The results are shown in Table 2.

[0112] Test 3: Tensile strength: The tensile properties of plastic films and sheets were tested according to ASTM D-882. The difference in tensile strength between different batches of samples was calculated and the absolute value was taken. The results are shown in Table 2.

[0113] Experiment 2: Color difference test: The color difference of the samples was measured with a colorimeter, and the color difference values ​​of different batches of samples were calculated. The absolute values ​​were taken, and the results are shown in Table 2.

[0114] Table 1: Melting point test results of modified polyester chips

[0115] Group Preparation Example 1-1 Preparation Examples 1-2 Preparation Examples 1-3 Preparation Examples 1-4 Preparation Examples 1-5 Preparation Examples 1-6 <![CDATA[T hm ]]> 211.2 214.6 213.7 222.5 226.8 242.8

[0116] Table 2: Test results of Examples 1-9 and Comparative Examples 1-4

[0117] Group Haze difference / % Difference in tensile strength (MD) / MPa △E Example 1 0.2 0.8 0.14 Example 2 0.26 1.2 0.19 Example 3 0.24 1.3 0.21 Example 4 0.46 2.3 0.39 Example 5 0.42 1.3 0.31 Example 6 0.65 1.2 0.44 Example 7 0.46 2.6 0.36 Example 8 0.38 2.2 0.27 Example 9 0.3 1.3 0.25 Comparative Example 1 1.12 3.5 1.07 Comparative Example 2 0.66 1.1 0.57 Comparative Example 3 2.19 4.4 3.1 Comparative Example 4 1.95 5.7 2.7

[0118] As can be seen from Examples 1-5 and Comparative Example 1, and Table 2, the blue polyester film obtained by co-extruding the surface melt and core melt using modified polyester chips with a lower melting point as the core layer exhibits small variations in haze, color difference, and tensile strength between different batches. This is because the core layer, as the color layer, melts at a lower temperature, which reduces pigment agglomeration and decomposition, thereby improving pigment dispersibility and further controlling the color and haze differences between different batches of polyester film. In addition, the core layer uses unmodified modified polyester material, which is melted at a lower temperature, resulting in a large difference in viscosity between the surface melt and the core melt, causing uneven dispersion of the polyester film and thus a large difference in tensile strength.

[0119] Combining Examples 1, 6-9, and Comparative Example 2 with Table 2, it can be seen that directly regenerating and thickening the recycled blue chips without alcoholysis, and modifying or not modifying the fumed silica in the anti-sticking masterbatch with a silane coupling agent, affects the color difference and haze difference of the blue polyester film. This is because the regenerated and thickened blue chips obtained after alcoholysis have better compatibility with the modified polyester chips and the blue masterbatch, and can produce a better dispersion effect on the pigments in the blue masterbatch, reducing the supersaturation of the pigments and further reducing the generation of color difference; fumed silica... After alcohol modification, the number of surface hydroxyl groups is reduced, improving the oleophilicity of fumed silica and thus enhancing its compatibility with polyester. Simultaneously, the surface steric hindrance of fumed silica is increased, reducing its agglomeration and further improving its dispersion in the surface solution. This enhances the overall heat resistance of the blue polyester film and reduces migration, thereby minimizing color difference. Furthermore, a synergistic effect exists between the anti-sticking masterbatch and the tackifying polyester film, further reducing color difference and stabilizing the tensile properties of different batches of the product.

[0120] As can be seen from Example 1, Comparative Examples 3-4, and Table 2, polyester films prepared solely using core layer solution extrusion exhibit significant color differences between batches and poor stability of tensile properties. This is because the present application actually employs a method of preparing a heat-resistant and migration-resistant material for the surface layer to protect the core layer, which serves as the colorant. This overcomes the technical obstacles of poor pigment dispersion in polyester when using heat-resistant and migration-resistant polyester, and pigment migration causing color differences when using polyester with good flowability. Furthermore, compared to conventional polyester films prepared by co-extrusion of surface layer solution and core layer solution, the modification of core layer polyester chips, the incorporation of anti-sticking masterbatch, and the modification of tackifying recycled blue chips in this application produce a synergistic effect, further reducing color differences and potential changes in tensile strength.

[0121] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A blue polyester film, characterized in that, It is obtained by co-extrusion of the surface melt and the core melt. The core melt, by weight, comprises the following components: 52-64 parts modified polyester chips, 1-6 parts blue masterbatch, 12-26 parts tackifying recycled blue chips, and 1-2 parts dispersant; wherein the modified polyester chips are polyester chips with a melting point of 210-230℃; and the modified polyester chips, by weight, comprise the following raw materials: 50-83 parts terephthalic acid, 37-43 parts ethylene glycol, 2.7-10.8 parts 1,4-butanediol, and 4.5 parts... -13.6 parts diethylene glycol and 0.015-0.02 parts catalyst; the tackifying recycled blue chips comprise the following materials in parts by weight: 46-82 parts blue polyester film waste, 8-20 parts ethylene glycol, 1-3 parts chain extender and 0.01-0.02 parts catalyst; the modified polyester chips are obtained by copolymerization of terephthalic acid, ethylene glycol, 1,4-butanediol and diethylene glycol; the tackifying recycled blue chips are obtained by alcoholysis regeneration of recycled blue polyester film waste; The surface melt, by weight, comprises the following components: 10-30 parts optical polyester chips and 1-2 parts anti-sticking masterbatch; the anti-sticking masterbatch, by weight, comprises the following components: 1.2-4.6 parts modified fumed silica, 52-58 parts terephthalic acid, 40-44 parts ethylene glycol, and 0.01-0.014 parts catalyst; the modified fumed silica is obtained by modifying fumed silica with dodecanol.

2. The blue polyester film according to claim 1, characterized in that, The pigment in the orchid masterbatch is phthalocyanine blue.

3. The blue polyester film according to claim 1, characterized in that, The method for preparing the modified polyester chips includes the following steps: Terephthalic acid, ethylene glycol, 1,4-butanediol, diethylene glycol and catalyst are mixed and heated to 188-192℃ for esterification reaction for 4-5 hours. Then the temperature is adjusted to 280-290℃ for polycondensation reaction for 35-45 minutes to obtain modified polyester chips.

4. The blue polyester film according to claim 1, characterized in that, The preparation method of the thickened regenerated orchid slices includes the following steps: Alcohololysis: Take ethylene glycol and blue polyester film waste, mix them, react at 60-70℃ for 40-60 min, and then melt and extrude to obtain the alcoholysis polyester melt; Regeneration: Take the polyester melt after alcoholysis, add chain extender and catalyst, mix, and carry out self-condensation reaction at 270-280℃. The reaction time is controlled at 1-3h to obtain viscous regenerated blue chips.

5. The blue polyester film according to claim 1, characterized in that, The method for preparing the anti-sticking masterbatch includes the following steps: Alcohol modification: Take fumed silica and perform air jet milling. After taking it out, mix it with dodecanol, cosolvent and catalyst. React at 60-80℃ for 60-80 min. Wash and dry to obtain modified fumed silica. Blending: Take terephthalic acid, ethylene glycol and modified fumed silica, mix them, and esterify them at 180-200℃ for 3-5 hours. Then adjust the temperature to 280-290℃ and polycondensate for 35-45 minutes to obtain the anti-sticking masterbatch.

6. A method for preparing a blue polyester film according to any one of claims 1-5, characterized in that, The following steps are used: Core layer melt: Modified polyester chips, blue masterbatch, viscous recycled blue chips and dispersant are melted to obtain core layer melt; Surface melt: Take optical polyester chips and anti-sticking masterbatch, and melt them to obtain the surface melt; Film making: The core melt and the surface melt are combined and cast into a sandwich-type sheet with the core melt as the middle layer. After longitudinal stretching, transverse stretching and heat setting, a blue polyester film is obtained.