Cooking-resistant high-transparency PET (Polyethylene Terephthalate) film and preparation method thereof

Abstract

The invention discloses a cooking-resistant high-transparency PET (polyethylene terephthalate) film and a preparation method thereof, and belongs to the technical field of PET films, the preparation method comprises the following steps: preparing a filler, preparing a high-barrier additive, preparing a coating liquid, treating, coating and carrying out vacuum evaporation; the preparation of the filler comprises the following steps: coating cross-linked chitosan, and adsorbing sodium carboxymethyl cellulose; the step of preparing the high-barrier-property additive comprises the steps of adsorbing magnesium citrate, adsorbing polyvinyl alcohol and adsorbing magnesium ions. The prepared PET film not only has excellent boiling resistance and high transparency, but also has high barrier property and high flatness, an organic solvent does not need to be used in the preparation process, the binding force of a coating in the PET film is strong, and the surface of the PET film does not have defects.

Description

Technical Field

[0001] The present invention relates to the technical field of PET films, and particularly relates to a high-transparency PET film resistant to cooking and a preparation method thereof. Background Art

[0002] PET (polyethylene terephthalate) film is a commonly used packaging film, which has excellent transparency, heat resistance, cold resistance, oil resistance, and also has excellent mechanical strength. It is widely used in industries such as packaging, printing, electronics, medical, and automotive.

[0003] With the rapid development of the food industry, as a key link in ensuring food safety and improving food quality, the requirements for food packaging are also getting higher and higher. As a typical carbohydrate food, corn is rich in protein, fat, vitamins, trace elements, and polysaccharides. For corn, cooking is the simplest food processing method, which can also maintain the sweet and fresh taste of corn and reduce the loss of nutrients. With the improvement of living standards, people are increasingly concerned about the retention of nutrients in food processing. Vacuum packaging of corn with cookable materials can not only maintain the sweet and fresh taste of corn as much as possible during storage and cooking of corn, reduce the loss of nutrients, but also be convenient and fast, having a large market prospect.

[0004] If directly using PET film as a cookable packaging material, due to the good airtightness and medium moisture resistance of PET film, it cannot meet the requirements for barrier properties and cookability of cookable packaging materials. Therefore, the commonly used cookable packaging materials at present are to compound other materials on PET film, specifically to compound aluminum foil and CPP (cast polypropylene) film on PET film, using the excellent heat resistance, oil resistance, and mechanical strength of PET film, and the excellent barrier properties and heat resistance of aluminum foil, so as to prepare a cookable packaging material with excellent barrier properties, heat resistance, oil resistance, and mechanical strength. However, the cookable packaging material prepared from aluminum foil is opaque, it is difficult to visually display the quality of corn to consumers, and it is easy to reduce the purchasing desire of consumers.

[0005] In view of the above problems, one of the existing solutions is to add a coating with high barrier properties to the PET film by means of coating, and then add a silica coating by means of vacuum evaporation, so as to obtain a PET film with high transparency and high barrier properties. Among them, the commonly used coating material with high barrier properties is polyvinylidene chloride emulsion. In order to further improve the barrier properties and retort resistance of the coating, hydrophobic inorganic fillers and other high-barrier materials are also added. The PET film prepared by the above solution can simultaneously have high transparency, high barrier properties and retort resistance. However, the applicant found the following problems when conducting experiments according to this method: First, the solvent of the polyvinylidene chloride emulsion is water, and the hydrophobic inorganic fillers have poor dispersibility in water, resulting in easy coating defects on the surface of the coating with high barrier properties, and also reducing the flatness of the coated PET film; Second, in the preparation of the hydrophobic inorganic fillers, toxic organic solvents such as toluene are generally required, and there is an easy problem of residual organic solvents; Third, the surface tension of the PET film is low, and the bonding force with the coating with high barrier properties is poor; Fourth, the other high-barrier materials used mainly include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc. Polyvinyl alcohol and ethylene-vinyl alcohol copolymer contain hydroxyl groups, and hydrogen bonds are formed between the hydroxyl groups to construct a hydrogen bond network, so as to achieve high barrier properties. However, the hydroxyl groups have poor water resistance and will affect the retort resistance. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention provides a retort-resistant high-transparency PET film and a preparation method thereof. The prepared PET film not only has excellent retort resistance and high transparency, but also has high barrier properties and high flatness. Organic solvents are not required in the preparation, and the coating in the PET film has strong bonding force and no surface defects.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows: A preparation method of a retort-resistant high-transparency PET film, comprising: preparing fillers, preparing high-barrier additives, preparing coating liquids, treating, coating, and vacuum evaporating; The preparation of the fillers includes: coating and crosslinking chitosan, and adsorbing sodium carboxymethyl cellulose; For the coating and crosslinking chitosan, titanium dioxide and an acetic acid aqueous solution of chitosan are added to a reaction kettle, the stirring speed of the reaction kettle is controlled to 200-300 rpm, stirred for 20-30 min, an aqueous solution of glutaraldehyde is added dropwise, and after the addition is completed, stirring is continued for 1-1.5 h, then put into a centrifuge and centrifuged at a centrifugal speed of 12000-13000 rpm for 30-35 min. Take the precipitate, wash it with water, and dry it to obtain titanium dioxide coated with crosslinked chitosan; In the coated crosslinked chitosan, the dosage ratio of titanium dioxide, acetic acid aqueous solution of chitosan, and glutaraldehyde aqueous solution is 200 g: 2000 - 2200 mL: 200 - 230 mL; The dropping rate of the glutaraldehyde aqueous solution is 10 - 15 mL / min; The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm; The preparation method of the acetic acid aqueous solution of chitosan is to add chitosan and acetic acid aqueous solution into a reaction kettle, control the stirring speed of the reaction kettle to 200 - 300 rpm, and stir for 30 - 40 min to obtain the acetic acid aqueous solution of chitosan; In the preparation of the acetic acid aqueous solution of chitosan, the dosage ratio of chitosan to acetic acid aqueous solution is 9 - 10 g: 1000 - 1050 mL; The degree of deacetylation of the chitosan is 90%; The mass concentration of acetic acid in the acetic acid aqueous solution is 2%; The mass concentration of glutaraldehyde in the glutaraldehyde aqueous solution is 2%; For the adsorption of sodium carboxymethylcellulose, add sodium carboxymethylcellulose and water into a reaction kettle, control the stirring speed of the reaction kettle to 200 - 300 rpm, stir for 20 - 30 min, add hydrochloric acid aqueous solution to adjust the pH value to 3.5 - 4, add titanium dioxide coated with crosslinked chitosan, continue to stir for 1 - 1.5 h, add it to a centrifuge, centrifuge at a speed of 12000 - 13000 rpm for 30 - 35 min, take the precipitate, dry it to obtain the filler; In the adsorption of sodium carboxymethylcellulose, the dosage ratio of sodium carboxymethylcellulose, water, and titanium dioxide coated with crosslinked chitosan is 12 - 13 g: 2000 - 2300 mL: 200 - 210 g; The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L; The preparation of the high-barrier additive includes: adsorption of magnesium citrate, adsorption of polyvinyl alcohol, and adsorption of magnesium ions; For the adsorption of magnesium citrate, add magnesium citrate and water into a reaction kettle, control the stirring speed of the reaction kettle to 200 - 300 rpm, stir for 15 - 20 min, add calcium stearate, continue to stir for 30 - 40 min, add it to a centrifuge, centrifuge at a speed of 10000 - 11000 rpm for 10 - 11 min, take the precipitate, wash it with water and then dry it to obtain calcium stearate adsorbed with magnesium citrate; In the adsorption of magnesium citrate, the dosage ratio of magnesium citrate, water, and calcium stearate is 44 - 46 g: 7500 - 8000 mL: 200 - 210 g; The average particle size of the calcium stearate is 100 nm; Regarding the adsorption of polyvinyl alcohol, add polyvinyl alcohol 2499 and water into the reaction kettle, control the stirring speed of the reaction kettle to 200 - 300 rpm, stir for 25 - 30 min, add calcium stearate adsorbed with magnesium citrate, continue to stir for 30 - 40 min, add it into the centrifuge, centrifuge at a speed of 10000 - 11000 rpm for 10 - 11 min, take the precipitate, wash it with water, and then dry it to obtain calcium stearate adsorbed with polyvinyl alcohol; In the adsorbed polyvinyl alcohol, the dosage ratio of polyvinyl alcohol 2499, water, and calcium stearate adsorbed with magnesium citrate is 24 - 25 g: 8000 - 9000 mL: 205 - 215 g; Regarding the adsorption of magnesium ions, add magnesium chloride and water into the reaction kettle, control the stirring speed of the reaction kettle to 200 - 300 rpm, stir for 25 - 30 min, add calcium stearate adsorbed with polyvinyl alcohol, continue to stir for 30 - 40 min, add it into the centrifuge, centrifuge at a speed of 10000 - 11000 rpm for 10 - 11 min, take the precipitate, wash it with water, and then dry it to obtain a high-barrier additive; In the adsorption of magnesium ions, the dosage ratio of magnesium chloride, water, and calcium stearate adsorbed with polyvinyl alcohol is 75 - 80 g: 8000 - 9000 mL: 210 - 217 g; Regarding the preparation of the coating solution, add polyvinylidene chloride emulsion, filler, and high-barrier additive into the reaction kettle, control the stirring speed of the reaction kettle to 300 - 400 rpm, stir for 15 - 20 min to obtain the coating solution; In the preparation of the coating solution, the mass ratio of polyvinylidene chloride emulsion, filler, and high-barrier additive is 80 - 85: 7 - 10: 8 - 10; The solid content of the polyvinylidene chloride emulsion is 38%; Regarding the treatment, pre-crystallize and dry the polyester resin to obtain the treated polyester resin; The temperature of the pre-crystallization is 160 - 180 °C, and the time is 25 - 30 min; The temperature of the drying is 150 - 160 °C, and the time is 5 - 6 h; Regarding the coating, divide the treated polyester resin into three parts as the raw materials for layer A, layer B, and layer C. Add the raw materials for layer A, layer B, and layer C into the No. 1 twin-screw extruder, single-screw extruder, and No. 2 twin-screw extruder respectively for melt extrusion, cool and solidify on the casting roller, conduct longitudinal stretching, conduct corona treatment, coat with the coating solution, dry after coating, conduct transverse stretching to obtain the coated PET film; In the coating, the mass ratio of the raw materials for layer A, layer B, and layer C is 9 - 10: 90 - 95: 9 - 10; In melt extrusion, the heating temperatures of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder are 256 - 265 °C, and the heating temperature of the single-screw extruder is 275 - 285 °C; The temperature of the longitudinal stretching is 75 - 80 °C, and the magnification is 3.2 - 3.4:1; In the coating, the coating amount of the coating liquid is 3.6 - 4 g / m 2 ; When drying is carried out after coating, the drying temperature is 130 - 135 °C, and the time is 5 - 6 min; The temperature of the transverse stretching is 115 - 120 °C, and the magnification is 4:1; In the vacuum evaporation coating, a layer of silicon dioxide is added to the coated side of the coated PET film through vacuum evaporation coating to obtain a high-transparency PET film resistant to cooking; The thickness of the high-transparency PET film resistant to cooking is 12 - 15 μm.

[0008] A high-transparency PET film prepared by the foregoing preparation method.

[0009] Compared with the prior art, the beneficial effects of the present invention are: (1)The preparation method of the high - transparency PET film resistant to cooking uses fillers and high - barrier additives in the preparation. The preparation method of the fillers includes coating cross - linked chitosan and adsorbing sodium carboxymethylcellulose. Among them, coating cross - linked chitosan is to mix titanium dioxide with an acetic acid aqueous solution of chitosan, then add glutaraldehyde for cross - linking, and coat a layer of cross - linked chitosan on the surface of titanium dioxide to obtain titanium dioxide coated with cross - linked chitosan; adsorbing sodium carboxymethylcellulose is that under acidic conditions, the amino group in cross - linked chitosan will be protonated and carry a positive charge, the carboxyl group in sodium carboxymethylcellulose carries a negative charge, and there is an electrostatic force between cross - linked chitosan and sodium carboxymethylcellulose, so sodium carboxymethylcellulose is combined on the surface of titanium dioxide coated with cross - linked chitosan to obtain the filler. The preparation method of the high - barrier additive includes adsorbing magnesium citrate, adsorbing polyvinyl alcohol, and adsorbing magnesium ions. Among them, adsorbing magnesium citrate is to use an aqueous solution of magnesium citrate to perform surface treatment on calcium stearate, and adsorb a layer of magnesium citrate on the surface of calcium stearate to obtain calcium stearate adsorbed with magnesium citrate; adsorbing polyvinyl alcohol is to use an aqueous solution of polyvinyl alcohol to perform surface treatment on calcium stearate adsorbed with magnesium citrate, and adsorb a layer of polyvinyl alcohol through the interaction between magnesium ions and polyvinyl alcohol to obtain calcium stearate adsorbed with polyvinyl alcohol; adsorbing magnesium ions is to use an aqueous solution of magnesium chloride to perform surface treatment on calcium stearate adsorbed with polyvinyl alcohol, and continue to adsorb magnesium ions on the surface of polyvinyl alcohol through the interaction between magnesium ions and polyvinyl alcohol to obtain the high - barrier additive. Titanium dioxide in the filler can act as a filler while avoiding affecting transparency, and the cross - linked chitosan on its surface can improve the hydrophobicity of titanium dioxide; calcium stearate in the high - barrier additive can play a hydrophobic role, a hydrophobic cross - linked network can be formed between magnesium citrate and polyvinyl alcohol through hydrogen bonds, and polyvinyl alcohol can improve film - forming properties, so as to ensure high barrier properties while improving cooking resistance. The outermost magnesium ions can also play a bridging role and have an interaction with sodium carboxymethylcellulose on the surface of the filler, so as to form a cross - linked network containing metal ions on the surface of the PET film, further improving cooking resistance and flatness; (2)The PET film prepared by the present invention not only has excellent cooking resistance and high transparency, but also has high barrier properties and high flatness. It does not require the use of organic solvents in the preparation, and the bonding strength between the PET film and the coating in the PET film is strong, and there are no defects on the surface. Specifically, the MD thermal shrinkage rate (150 °C, 30 min) is 0.61 - 0.83%, the CD thermal shrinkage rate (150 °C, 30 min) is 0 - 0.17%, the transparency is 89.4 - 90.1%, the haze is 3.20 - 3.43%, the water vapor transmission rate is 0.475 - 0.523 g / (m 2 •24 h), and the oxygen transmission rate is 0.421 - 0.458 cm 3 / (m 2•24h•0.1MPa); The static friction coefficient of the PET film before vacuum evaporation of the silica layer, i.e., the coated PET film, is 0.271 - 0.282, the dynamic friction coefficient is 0.224 - 0.235, the peel strength is 31.2 - 33.4 N / cm, and the surface has no defects. Detailed implementation manners

[0010] In order to have a clearer understanding of the technical features, objectives, and effects of the present invention, the detailed implementation manners of the present invention are now described.

[0011] Example 1 A method for preparing a high-transparency PET film resistant to cooking, specifically as follows: 1. Prepare the filler: (1) Coated crosslinked chitosan: Add 200 g of titanium dioxide and 2000 mL of an acetic acid aqueous solution of chitosan to the reaction kettle, control the stirring speed of the reaction kettle to 200 rpm, stir for 20 min, dropwise add 200 mL of an aqueous glutaraldehyde solution, control the dropping speed to 10 mL / min, continue to stir for 1 h after the dropping is completed, add it to the centrifuge, centrifuge at a speed of 12000 rpm for 30 min, take the precipitate, wash it with water, and dry it to obtain titanium dioxide coated with crosslinked chitosan; The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm; The method for preparing the acetic acid aqueous solution of chitosan is: Add 9 g of chitosan and 1000 mL of an acetic acid aqueous solution to the reaction kettle, control the stirring speed of the reaction kettle to 200 rpm, and stir for 30 min to obtain the acetic acid aqueous solution of chitosan; The deacetylation degree of the chitosan is 90%; The mass concentration of acetic acid in the acetic acid aqueous solution is 2%; The mass concentration of glutaraldehyde in the aqueous glutaraldehyde solution is 2%; (2) Adsorb sodium carboxymethylcellulose: Add 12 g of sodium carboxymethylcellulose and 2000 mL of water to the reaction kettle, control the stirring speed of the reaction kettle to 200 rpm, stir for 20 min, add hydrochloric acid aqueous solution to adjust the pH value to 3.5, add 200 g of titanium dioxide coated with crosslinked chitosan, continue to stir for 1 h, add it to the centrifuge, centrifuge at a speed of 12000 rpm for 30 min, take the precipitate, and dry it to obtain the filler; The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L; 2. Prepare the high-barrier additive: (1)Adsorb magnesium citrate: Add 44 g of magnesium citrate and 7500 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 200 rpm, stir for 15 min, add 200 g of calcium stearate, continue to stir for 30 min, add it into the centrifuge, centrifuge at a speed of 10000 rpm for 10 min, take the precipitate, wash it with water, and dry it to obtain calcium stearate adsorbed with magnesium citrate; The average particle size of the calcium stearate is 100 nm; (2)Adsorb polyvinyl alcohol: Add 24 g of polyvinyl alcohol 2499 and 8000 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 200 rpm, stir for 25 min, add 205 g of calcium stearate adsorbed with magnesium citrate, continue to stir for 30 min, add it into the centrifuge, centrifuge at a speed of 10000 rpm for 10 min, take the precipitate, wash it with water, and dry it to obtain calcium stearate adsorbed with polyvinyl alcohol; (3)Adsorb magnesium ions: Add 75 g of magnesium chloride and 8000 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 200 rpm, stir for 25 min, add 210 g of calcium stearate adsorbed with polyvinyl alcohol, continue to stir for 30 min, add it into the centrifuge, centrifuge at a speed of 10000 rpm for 10 min, take the precipitate, wash it with water, and dry it to obtain a high-barrier additive; 3. Prepare the coating solution: Add polyvinylidene chloride emulsion, filler, and high-barrier additive into the reaction kettle according to a mass ratio of 80:7:8, control the stirring speed of the reaction kettle to 300 rpm, and stir for 15 min to obtain the coating solution; The solid content of the polyvinylidene chloride emulsion is 38%; 4. Treatment: Pre-crystallize and dry the polyester resin to obtain the treated polyester resin; The temperature of the pre-crystallization is 160 °C and the time is 25 min; The temperature of the drying is 150 °C and the time is 5 h; 5. Coating: Divide the treated polyester resin into three parts as the raw materials for layer A, layer B, and layer C. Add the raw materials for layer A, layer B, and layer C into the No. 1 twin-screw extruder, single-screw extruder, and No. 2 twin-screw extruder respectively for melt extrusion. Control the heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder to 256 °C, and the heating temperature of the single-screw extruder to 275 °C. Cool and solidify on the casting roll, conduct longitudinal stretching, control the temperature of the longitudinal stretching to 75 °C, and the magnification to 3.2:1. Conduct corona treatment, and use the coating solution for coating. Control the coating amount of the coating solution in the coating to 3.6 g / m 2, after coating, it is dried at 130 °C for 5 min, and then subjected to transverse stretching. The temperature of transverse stretching is 115 °C and the magnification is 4:1 to obtain the coated PET film; The mass ratio of the raw materials of layer A, layer B, and layer C is 9:90:9; 6. Vacuum evaporation coating: A layer of silica layer is added to the coated side of the coated PET film by vacuum evaporation coating to obtain a high-transparency PET film with retort resistance; The thickness of the high-transparency PET film with retort resistance is 15 μm.

[0012] This example also provides a high-transparency PET film prepared by the foregoing preparation method.

[0013] Example 2 A preparation method of a high-transparency PET film with retort resistance, specifically: 1. Preparation of filler: (1) Coated crosslinked chitosan: Add 200 g of titanium dioxide and 2100 mL of acetic acid aqueous solution of chitosan to the reaction kettle, control the stirring speed of the reaction kettle to 250 rpm, stir for 25 min, dropwise add 220 mL of glutaraldehyde aqueous solution, control the dropping speed to 12 mL / min, continue to stir for 1.5 h after the dropping is completed, add it to the centrifuge, centrifuge at a speed of 13000 rpm for 32 min, take the precipitate, wash it with water, and dry it to obtain titanium dioxide coated with crosslinked chitosan; The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm; The preparation method of the acetic acid aqueous solution of chitosan is: Add 9.5 g of chitosan and 1020 mL of acetic acid aqueous solution to the reaction kettle, control the stirring speed of the reaction kettle to 250 rpm, and stir for 35 min to obtain the acetic acid aqueous solution of chitosan; The degree of deacetylation of the chitosan is 90%; The mass concentration of acetic acid in the acetic acid aqueous solution is 2%; The mass concentration of glutaraldehyde in the glutaraldehyde aqueous solution is 2%; (2) Adsorbing sodium carboxymethylcellulose: Add 12.5 g of sodium carboxymethylcellulose and 2200 mL of water to the reaction kettle, control the stirring speed of the reaction kettle to 250 rpm, stir for 25 min, add hydrochloric acid aqueous solution to adjust the pH value to 4, add 205 g of titanium dioxide coated with crosslinked chitosan, continue to stir for 1.5 h, add it to the centrifuge, centrifuge at a speed of 13000 rpm for 32 min, take the precipitate, and dry it to obtain the filler; The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L; 2. Preparation of high-barrier additive: (1)Adsorb magnesium citrate: Add 45 g of magnesium citrate and 7700 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 250 rpm, stir for 18 min, add 205 g of calcium stearate, continue to stir for 35 min, add it into the centrifuge, centrifuge at a speed of 11000 rpm for 10 min, take the precipitate, wash it with water and then dry it to obtain calcium stearate adsorbed with magnesium citrate; The average particle size of the calcium stearate is 100 nm; (2)Adsorb polyvinyl alcohol: Add 24.5 g of polyvinyl alcohol 2499 and 8500 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 250 rpm, stir for 28 min, add 210 g of calcium stearate adsorbed with magnesium citrate, continue to stir for 35 min, add it into the centrifuge, centrifuge at a speed of 11000 rpm for 10 min, take the precipitate, wash it with water and then dry it to obtain calcium stearate adsorbed with polyvinyl alcohol; (3)Adsorb magnesium ions: Add 77 g of magnesium chloride and 8500 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 250 rpm, stir for 28 min, add 215 g of calcium stearate adsorbed with polyvinyl alcohol, continue to stir for 35 min, add it into the centrifuge, centrifuge at a speed of 11000 rpm for 10 min, take the precipitate, wash it with water and then dry it to obtain a high-barrier additive; 3. Prepare the coating liquid: Add the polyvinylidene chloride emulsion, filler, and high-barrier additive into the reaction kettle according to a mass ratio of 82:8:9, control the stirring speed of the reaction kettle to 350 rpm, and stir for 18 min to obtain the coating liquid; The solid content of the polyvinylidene chloride emulsion is 38%; 4. Treatment: Pre-crystallize and dry the polyester resin to obtain the treated polyester resin; The temperature of the pre-crystallization is 170 °C and the time is 28 min; The temperature of the drying is 155 °C and the time is 5.5 h; 5. Coating: Divide the treated polyester resin into three parts as the raw materials for layer A, layer B, and layer C. Add the raw materials for layer A, layer B, and layer C into the No. 1 twin-screw extruder, single-screw extruder, and No. 2 twin-screw extruder respectively for melt extrusion. Control the heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder to 260 °C, and the heating temperature of the single-screw extruder to 280 °C. Cool and solidify on the casting roller, perform longitudinal stretching, control the temperature of the longitudinal stretching to 77 °C, the magnification to 3.3:1, perform corona treatment, and use the coating liquid for coating. Control the coating amount of the coating liquid in the coating to 3.8 g / m 2, after coating, it is dried at 132 °C for 5.5 min, and then subjected to transverse stretching at a temperature of 120 °C and a magnification of 4:1 to obtain the coated PET film; The mass ratio of the raw material of layer A, the raw material of layer B, and the raw material of layer C is 9.5:92:9.5; 6. Vacuum evaporation: A layer of silicon dioxide is added to the coated side of the coated PET film by vacuum evaporation to obtain a high-transparency PET film resistant to retorting; The thickness of the high-transparency PET film resistant to retorting is 14 μm.

[0014] This embodiment also provides a high-transparency PET film prepared by the foregoing preparation method.

[0015] Example 3 A preparation method of a high-transparency PET film resistant to retorting, specifically: 1. Preparation of filler: (1) Coated crosslinked chitosan: Add 200 g of titanium dioxide and 2200 mL of an acetic acid aqueous solution of chitosan to the reaction kettle, control the stirring speed of the reaction kettle to 300 rpm, stir for 30 min, dropwise add 230 mL of an aqueous glutaraldehyde solution, control the dropping speed to 15 mL / min, continue stirring for 1.5 h after the dropping is completed, add it to the centrifuge, centrifuge at a speed of 13000 rpm for 35 min, take the precipitate, wash it with water, and dry it to obtain titanium dioxide coated with crosslinked chitosan; The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm; The preparation method of the acetic acid aqueous solution of chitosan is: Add 10 g of chitosan and 1050 mL of acetic acid aqueous solution to the reaction kettle, control the stirring speed of the reaction kettle to 300 rpm, and stir for 40 min to obtain the acetic acid aqueous solution of chitosan; The degree of deacetylation of the chitosan is 90%; The mass concentration of acetic acid in the acetic acid aqueous solution is 2%; The mass concentration of glutaraldehyde in the aqueous glutaraldehyde solution is 2%; (2) Adsorbing sodium carboxymethylcellulose: Add 13 g of sodium carboxymethylcellulose and 2300 mL of water to the reaction kettle, control the stirring speed of the reaction kettle to 300 rpm, stir for 30 min, adjust the pH value to 4 by adding hydrochloric acid aqueous solution, add 210 g of titanium dioxide coated with crosslinked chitosan, continue stirring for 1.5 h, add it to the centrifuge, centrifuge at a speed of 13000 rpm for 35 min, take the precipitate, and dry it to obtain the filler; The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L; 2. Preparation of high-barrier additive: (1) Adsorb magnesium citrate: Add 46 g of magnesium citrate and 8000 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 300 rpm, stir for 20 min, add 210 g of calcium stearate, continue to stir for 40 min, add it into the centrifuge, centrifuge at a speed of 11000 rpm for 11 min, take the precipitate, wash it with water and then dry it to obtain calcium stearate adsorbed with magnesium citrate; The average particle size of the calcium stearate is 100 nm; (2) Adsorb polyvinyl alcohol: Add 25 g of polyvinyl alcohol 2499 and 9000 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 300 rpm, stir for 30 min, add 215 g of calcium stearate adsorbed with magnesium citrate, continue to stir for 40 min, add it into the centrifuge, centrifuge at a speed of 11000 rpm for 11 min, take the precipitate, wash it with water and then dry it to obtain calcium stearate adsorbed with polyvinyl alcohol; (3) Adsorb magnesium ions: Add 80 g of magnesium chloride and 9000 mL of water into the reaction kettle, control the stirring speed of the reaction kettle to 300 rpm, stir for 30 min, add 217 g of calcium stearate adsorbed with polyvinyl alcohol, continue to stir for 40 min, add it into the centrifuge, centrifuge at a speed of 11000 rpm for 11 min, take the precipitate, wash it with water and then dry it to obtain a high-barrier additive; 3. Prepare the coating solution: Add polyvinylidene chloride emulsion, filler, and high-barrier additive into the reaction kettle according to a mass ratio of 85:10:10, control the stirring speed of the reaction kettle to 400 rpm, and stir for 20 min to obtain the coating solution; The solid content of the polyvinylidene chloride emulsion is 38%; 4. Treatment: Pre-crystallize and dry the polyester resin to obtain the treated polyester resin; The temperature of the pre-crystallization is 180 °C and the time is 30 min; The temperature of the drying is 160 °C and the time is 6 h; 5. Coating: Divide the treated polyester resin into three parts as the raw materials for layer A, layer B, and layer C. Add the raw materials for layer A, layer B, and layer C into the No. 1 twin-screw extruder, single-screw extruder, and No. 2 twin-screw extruder respectively for melt extrusion. Control the heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder to 265 °C, and the heating temperature of the single-screw extruder to 285 °C. Cool and solidify on the casting roller, conduct longitudinal stretching, control the temperature of the longitudinal stretching to 80 °C, and the magnification to 3.4:1. Conduct corona treatment, and use the coating solution for coating. Control the coating amount of the coating solution in the coating to 4 g / m 2, after coating, it is dried at 135 °C for 6 min, and then subjected to transverse stretching at a temperature of 120 °C and a magnification of 4:1 to obtain the coated PET film; The mass ratio of the raw materials of layer A, layer B, and layer C is 10:95:10; 6. Vacuum evaporation: A layer of silica layer is added to the coated side of the coated PET film by vacuum evaporation to obtain a high-transparency PET film resistant to retorting; The thickness of the high-transparency PET film resistant to retorting is 12 μm.

[0016] This example also provides a high-transparency PET film prepared by the aforementioned preparation method.

[0017] Comparative Example 1 On the basis of the technical solution of Example 1, the first-step preparation of the filler step is omitted, and in the third-step preparation of the coating solution step, anatase titanium dioxide with an average particle size of 50 nm is used to replace the addition of the filler in equal mass.

[0018] The remaining technical solutions are the same as those of Example 1.

[0019] The thickness of the high-transparency PET film resistant to retorting obtained in this comparative example is 15 μm.

[0020] Comparative Example 2 On the basis of the technical solution of Example 1, in the first-step preparation of the filler step, the adsorption of sodium carboxymethyl cellulose in the second step is omitted, that is, the titanium dioxide coated with crosslinked chitosan obtained in the first-step coating crosslinked chitosan step is used as the filler.

[0021] The remaining technical solutions are the same as those of Example 1.

[0022] The thickness of the high-transparency PET film resistant to retorting obtained in this comparative example is 15 μm.

[0023] Comparative Example 3 On the basis of the technical solution of Example 1, the second-step preparation of the high-barrier additive step is omitted, and in the third-step preparation of the coating solution step, calcium stearate with an average particle size of 100 nm is used to replace the addition of the filler in equal mass.

[0024] The remaining technical solutions are the same as those of Example 1.

[0025] The thickness of the high-transparency PET film resistant to retorting obtained in this comparative example is 15 μm.

[0026] Comparative Example 4 On the basis of the technical solution of Example 1, in the step of preparing the high-barrier additive in the second step, step (2) of adsorbing polyvinyl alcohol and step (3) of adsorbing magnesium ions are omitted, that is, the calcium stearate adsorbed with magnesium citrate obtained in step (1) of adsorbing magnesium citrate is used as the high-barrier additive.

[0027] The remaining technical solutions are the same as those of Example 1.

[0028] The thickness of the high-transparency PET film with resistance to retort obtained in this comparative example is 15 μm.

[0029] Comparative Example 5 On the basis of the technical solution of Example 1, in the step of preparing the high-barrier additive in the second step, step (3) of adsorbing magnesium ions is omitted, that is, the calcium stearate adsorbed with polyvinyl alcohol obtained in step (2) of adsorbing polyvinyl alcohol is used as the high-barrier additive.

[0030] The remaining technical solutions are the same as those of Example 1.

[0031] The thickness of the high-transparency PET film with resistance to retort obtained in this comparative example is 15 μm.

[0032] Performance Test 1 The thermal shrinkage rate (150 °C, 30 min), transparency, haze, water vapor transmission rate, and oxygen transmission rate of the high-transparency PET films prepared in Examples 1-3 and Comparative Examples 1-5 were tested, and the test results are as follows:

[0033] It can be seen from the above results that the thermal shrinkage rate, transparency, haze, water vapor transmission rate, and oxygen transmission rate of the high-transparency PET films prepared in Comparative Examples 1-5 are all worse than those of Example 1.

[0034] Performance Test 2 The static friction coefficient, dynamic friction coefficient, and peel strength of the coated PET films obtained in the fifth coating step of Examples 1-3 and Comparative Examples 1-5 were tested, and whether there are defects on the surface was observed. The test results and observation results are as follows:

[0035] It can be seen from the above results that the static friction coefficient and dynamic friction coefficient of the coated PET films prepared in Comparative Examples 1-5 are both higher than those of Example 1; the peel strength of the coated PET films prepared in Comparative Examples 1-3 is worse than that of Example 1; there are also defects on the surfaces of the coated PET films prepared in Comparative Example 1 and Comparative Example 3.

[0036] Finally, it should be noted that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a high-transparency PET film resistant to cooking, characterized in that, Including: Preparing filler, preparing high-barrier additive, preparing coating solution, treating, coating, vacuum evaporation; The preparation of the filler includes: coating crosslinked chitosan and adsorbing sodium carboxymethyl cellulose; The preparation of the high-barrier additive includes: adsorbing magnesium citrate, adsorbing polyvinyl alcohol, and adsorbing magnesium ions.

2. The preparation method of the high transparency PET film resistant to cooking according to claim 1, characterized in that, For the coating crosslinked chitosan, after mixing titanium dioxide and an acetic acid aqueous solution of chitosan, stirring, dropping glutaraldehyde aqueous solution, continuing to stir after the dropping is completed, centrifuging, taking the precipitate, washing with water, and drying, titanium dioxide coated with crosslinked chitosan is obtained; In the coating crosslinked chitosan, the dosage ratio of titanium dioxide, acetic acid aqueous solution of chitosan, and glutaraldehyde aqueous solution is 200 g: 2000 - 2200 mL: 200 - 230 mL; The dropping rate of the glutaraldehyde aqueous solution is 10 - 15 mL / min; The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm; The preparation method of the acetic acid aqueous solution of chitosan is to mix chitosan and acetic acid aqueous solution and stir to obtain the acetic acid aqueous solution of chitosan; In the preparation of the acetic acid aqueous solution of chitosan, the dosage ratio of chitosan to acetic acid aqueous solution is 9 - 10 g: 1000 - 1050 mL; The degree of deacetylation of the chitosan is 90%; The mass concentration of acetic acid in the acetic acid aqueous solution is 2%; The mass concentration of glutaraldehyde in the glutaraldehyde aqueous solution is 2%.

3. The preparation method of the high transparency PET film resistant to cooking according to claim 1, characterized in that, For the adsorption of sodium carboxymethyl cellulose, after mixing sodium carboxymethyl cellulose and water, stirring, adjusting the pH value to 3.5 - 4, adding titanium dioxide coated with crosslinked chitosan, continuing to stir, centrifuging, taking the precipitate, and drying, the filler is obtained; In the adsorption of sodium carboxymethyl cellulose, the dosage ratio of sodium carboxymethyl cellulose, water, and titanium dioxide coated with crosslinked chitosan is 12 - 13 g: 2000 - 2300 mL: 200 - 210 g.

4. The preparation method of the high transparency PET film resistant to cooking according to claim 1, characterized in that, For the adsorption of magnesium citrate, after mixing magnesium citrate and water, stirring, adding calcium stearate, continuing to stir, centrifuging, taking the precipitate, washing with water, and drying, calcium stearate adsorbed with magnesium citrate is obtained; For the adsorption of polyvinyl alcohol, after mixing polyvinyl alcohol 2499 and water, stirring, adding calcium stearate adsorbed with magnesium citrate, continuing to stir, centrifuging, taking the precipitate, washing with water, and drying, calcium stearate adsorbed with polyvinyl alcohol is obtained; For the adsorption of magnesium ions, after mixing magnesium chloride and water, stirring, adding calcium stearate adsorbed with polyvinyl alcohol, continuing to stir, centrifuging, taking the precipitate, washing with water, and drying, the high-barrier additive is obtained.

5. The preparation method of the high-transparency PET film resistant to cooking according to claim 1, characterized in that, In the adsorption of magnesium citrate, the dosage ratio of magnesium citrate, water, and calcium stearate is 44 - 46 g: 7500 - 8000 mL: 200 - 210 g; The average particle size of the calcium stearate is 100 nm; In the adsorption of polyvinyl alcohol, the dosage ratio of polyvinyl alcohol 2499, water, and calcium stearate adsorbed with magnesium citrate is 24 - 25 g: 8000 - 9000 mL: 205 - 215 g; In the adsorption of magnesium ions, the dosage ratio of magnesium chloride, water, and calcium stearate adsorbed with polyvinyl alcohol is 75 - 80 g: 8000 - 9000 mL: 210 - 217 g.

6. The preparation method of the high-transparency PET film resistant to cooking according to claim 1, characterized in that, To prepare the coating liquid, a polyvinylidene chloride emulsion, a filler, and a high-barrier additive are mixed and then stirred to obtain the coating liquid; In the preparation of the coating liquid, the mass ratio of the polyvinylidene chloride emulsion, the filler, and the high-barrier additive is 80-85:7-10:8-10; The solid content of the polyvinylidene chloride emulsion is 38%.

7. The preparation method of the high transparency PET film resistant to cooking according to claim 1, characterized in that, For the treatment, the polyester resin is pre-crystallized and dried to obtain the treated polyester resin; The temperature of the pre-crystallization is 160-180°C, and the time is 25-30 min; The temperature of the drying is 150-160°C, and the time is 5-6 h.

8. The preparation method of the high transparency PET film resistant to cooking according to claim 1, characterized in that, For the coating, the treated polyester resin is divided into three parts as the raw materials for layer A, layer B, and layer C. The raw materials for layer A, layer B, and layer C are respectively added into a No. 1 twin-screw extruder, a single-screw extruder, and a No. 2 twin-screw extruder for melt extrusion, cooled and solidified on a casting roll, longitudinally stretched, corona-treated, coated with the coating liquid, dried after coating, and transversely stretched to obtain the coated PET film; In the coating, the mass ratio of the raw materials for layer A, layer B, and layer C is 9-10:90-95:9-10; In the melt extrusion, the heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder is 256-265°C, and the heating temperature of the single-screw extruder is 275-285°C; The temperature of the longitudinal stretching is 75-80°C, and the magnification is 3.2-3.4:1; The coating amount of the coating liquid during coating is 3.6 - 4 g / m 2 ; When drying is carried out after coating, the drying temperature is 130-135°C, and the time is 5-6 min; The temperature of the transverse stretching is 115-120°C, and the magnification is 4:

1.

9. The preparation method of the high-transparency PET film resistant to cooking according to claim 1, characterized in that, For the vacuum evaporation coating, a layer of silicon dioxide is added to the coating side of the coated PET film by vacuum evaporation coating to obtain a high-transparency PET film resistant to retorting; The thickness of the high-transparency PET film resistant to retorting is 12-15 μm.

10. A high-transparency PET film prepared by the preparation method according to any one of claims 1-9.

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