A retortable high transparency PET film and a method for preparing the same

Abstract

The application discloses a high-transparency PET film resistant to steaming and cooking 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, processing, coating and vacuum evaporation. The preparation of the filler comprises the following steps: coating cross-linked chitosan and adsorbing sodium carboxymethyl cellulose. The preparation of the high-barrier additive comprises the following steps: adsorbing magnesium citrate, adsorbing polyvinyl alcohol and adsorbing magnesium ions. The PET film prepared by the application has excellent resistance to steaming and cooking, high transparency, high barrier property and high flatness, does not need to use organic solvents in the preparation, and the coating in the PET film has strong bonding force and no defects on the surface.

Description

Technical Field

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

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

[0003] With the rapid development of the food industry, food packaging, as a key component in ensuring food safety and improving food quality, is facing increasingly stringent requirements. Corn, a typical carbohydrate food, is rich in protein, fat, vitamins, trace elements, and polysaccharides. Steaming is the simplest food processing method for corn, which also maintains its fresh and sweet taste and reduces nutrient loss. As living standards improve, people are increasingly concerned about retaining nutrients during food processing. Vacuum packaging corn using steamable materials not only maintains its fresh and sweet taste as much as possible during storage and cooking, minimizing nutrient loss, but is also convenient and fast, showing great market prospects.

[0004] If PET film is used directly as a retortable packaging material, it will not meet the barrier and retortability requirements due to its good airtightness and moderate moisture resistance. Therefore, a commonly used retort packaging material is to laminate PET film with other materials, specifically aluminum foil and cast polypropylene (CPP) film. This utilizes the excellent heat resistance, oil resistance, and mechanical strength of PET film and the excellent barrier and heat resistance of aluminum foil to produce a retort packaging material with excellent barrier properties, heat resistance, oil resistance, and mechanical strength. However, retort packaging made with aluminum foil is opaque, making it difficult to visually display the quality of the corn to consumers, which can easily reduce their purchasing desire.

[0005] One existing solution to this problem is to apply a high-barrier coating to PET film via a coating method, followed by a silica coating via vacuum evaporation. This results in a PET film with both high transparency and high barrier properties. Polyvinylidene chloride emulsion is a commonly used high-barrier coating material. To further enhance the barrier properties and retort resistance of the coating, hydrophobic inorganic fillers and other high-barrier materials are often added. The PET film prepared using the above-mentioned solution can simultaneously possess high transparency, high barrier properties, and retort resistance. However, the applicant discovered the following problems during experiments using this method: First, the solvent of the polyvinylidene chloride emulsion is water, and the hydrophobic inorganic filler has poor dispersibility in water, resulting in coating defects on the surface of the high-barrier coating and reduced flatness of the coated PET film. Second, the preparation of the hydrophobic inorganic filler generally requires the use of toxic organic solvents, such as toluene, which are prone to organic solvent residue problems. Third, the surface tension of the PET film is low, resulting in poor bonding with the high-barrier coating. Fourth, other high-barrier materials used mainly include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol and ethylene-vinyl alcohol copolymer contain hydroxyl groups, which form hydrogen bonds between the hydroxyl groups to build a hydrogen bond network, thereby achieving high barrier properties. However, the hydroxyl groups have poor water resistance, which will affect retort resistance. Summary of the Invention

[0006] In response to the shortcomings of the existing technology, the present invention provides a high-transparency PET film that is resistant to boiling and a preparation method thereof. The prepared PET film not only has excellent boiling resistance and high transparency, but also has high barrier properties and high flatness. No organic solvent is required in the preparation process. Moreover, the coating in the PET film has strong bonding strength and no surface defects.

[0007] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0008] A method for preparing a boiling-resistant high-transparency PET film, comprising: preparing a filler, preparing a high-barrier additive, preparing a coating liquid, treating, coating, and vacuum evaporating;

[0009] The preparation of the filler comprises: coating with cross-linked chitosan and adsorbing sodium carboxymethyl cellulose;

[0010] The coated cross-linked chitosan, the titanium dioxide, the acetic acid aqueous solution of chitosan are added into a reaction kettle, the stirring speed of the reaction kettle is controlled to 200-300 rpm, stirring is carried out for 20-30 min, the aqueous solution of glutaraldehyde is added dropwise, after the dropwise addition is completed, stirring is continuously carried out for 1-1.5 h, the reaction kettle is added into a centrifuge, and centrifugation is carried out at a centrifugal speed of 12000-13000 rpm for 30-35 min; the precipitate is taken out, washed with water, and dried to obtain the coated cross-linked chitosan titanium dioxide;

[0011] The amount ratio of the titanium dioxide, the acetic acid aqueous solution of chitosan and the aqueous solution of glutaraldehyde in the coated cross-linked chitosan is 200 g:2000-2200 mL:200-230 mL;

[0012] The dropwise addition speed of the aqueous solution of glutaraldehyde is 10-15 mL / min;

[0013] The titanium dioxide is anatase titanium dioxide, and the average particle size is 50 nm;

[0014] The preparation method of the acetic acid aqueous solution of chitosan is as follows: chitosan and an acetic acid aqueous solution are added into a reaction kettle, the stirring speed of the reaction kettle is controlled to 200-300 rpm, and stirring is carried out for 30-40 min to obtain the acetic acid aqueous solution of chitosan;

[0015] The amount ratio of chitosan and the acetic acid aqueous solution in the preparation of the acetic acid aqueous solution of chitosan is 9-10 g:1000-1050 mL;

[0016] The deacetylation degree of the chitosan is 90%;

[0017] The mass concentration of acetic acid in the acetic acid aqueous solution is 2%;

[0018] The mass concentration of glutaraldehyde in the aqueous solution of glutaraldehyde is 2%;

[0019] The adsorbed sodium carboxymethyl cellulose, sodium carboxymethyl cellulose and water are added into a reaction kettle, the stirring speed of the reaction kettle is controlled to 200-300 rpm, stirring is carried out for 20-30 min, the pH value is adjusted to 3.5-4 by adding an aqueous hydrochloric acid solution, the coated cross-linked chitosan titanium dioxide is added, and stirring is continuously carried out for 1-1.5 h; the reaction kettle is added into a centrifuge, and centrifugation is carried out at a centrifugal speed of 12000-13000 rpm for 30-35 min; the precipitate is taken out, dried, and the filler is obtained;

[0020] The amount ratio of sodium carboxymethyl cellulose, water and the coated cross-linked chitosan titanium dioxide in the adsorbed sodium carboxymethyl cellulose is 12-13 g:2000-2300 mL:200-210 g;

[0021] The molar concentration of hydrochloric acid in the aqueous hydrochloric acid solution is 1 mol / L.

[0022] The preparation of the high barrier additive comprises: adsorbing magnesium citrate, adsorbing polyvinyl alcohol, and adsorbing magnesium ions;

[0023] The magnesium citrate adsorption process comprises adding magnesium citrate and water into a reactor, controlling the stirring speed of the reactor to 200-300 rpm, stirring for 15-20 minutes, adding calcium stearate, continuing to stir for 30-40 minutes, adding into a centrifuge, centrifuging at a centrifugal speed of 10000-11000 rpm for 10-11 minutes, taking a precipitate, washing with water, and drying to obtain calcium stearate adsorbing magnesium citrate;

[0024] In the adsorbed magnesium citrate, the dosage ratio of magnesium citrate, water, and calcium stearate is 44-46 g:7500-8000 mL:200-210 g;

[0025] The average particle size of the calcium stearate is 100 nm;

[0026] The polyvinyl alcohol adsorption method comprises adding polyvinyl alcohol 2499 and water into a reactor, controlling the stirring speed of the reactor to 200-300 rpm, stirring for 25-30 minutes, adding calcium stearate adsorbed with magnesium citrate, continuing to stir for 30-40 minutes, adding into a centrifuge, centrifuging at a centrifugal speed of 10000-11000 rpm for 10-11 minutes, taking the precipitate, washing with water, and drying to obtain calcium stearate adsorbed with polyvinyl alcohol;

[0027] In the adsorbed polyvinyl alcohol, the dosage ratio of polyvinyl alcohol 2499, water, and calcium stearate for adsorbing magnesium citrate is 24-25g:8000-9000mL:205-215g;

[0028] The magnesium ion adsorption process includes adding magnesium chloride and water into a reactor, controlling the stirring speed of the reactor to 200-300 rpm, stirring for 25-30 minutes, adding calcium stearate adsorbed with polyvinyl alcohol, continuing to stir for 30-40 minutes, adding the mixture into a centrifuge, centrifuging at a centrifugal speed of 10000-11000 rpm for 10-11 minutes, taking the precipitate, washing it with water, and drying it to obtain a high barrier additive;

[0029] In the magnesium ion adsorption method, the ratio of magnesium chloride, water, and calcium stearate adsorbed with polyvinyl alcohol is 75-80 g: 8000-9000 mL: 210-217 g;

[0030] The coating liquid is prepared by adding polyvinylidene chloride emulsion, filler, and high barrier additive into a reactor, controlling the stirring speed of the reactor to 300-400 rpm, and stirring for 15-20 minutes to obtain a coating liquid;

[0031] In the coating solution, the mass ratio of polyvinylidene chloride emulsion, filler, and high barrier additive is 80-85:7-10:8-10;

[0032] The solid content of the polyvinylidene chloride emulsion is 38%;

[0033] The treatment involves pre-crystallizing and drying the polyester resin to obtain a treated polyester resin;

[0034] The pre-crystallization temperature is 160-180°C and the time is 25-30 minutes;

[0035] The drying temperature is 150-160°C and the drying time is 5-6 hours;

[0036] The coating comprises dividing the treated polyester resin into three parts as a raw material for layer A, a raw material for layer B, and a raw material for layer C, respectively adding the raw material for layer A, layer B, and layer C to a No. 1 twin-screw extruder, a single-screw extruder, and a No. 2 twin-screw extruder for melt extrusion, cooling and solidifying on a casting roll, longitudinally stretching, corona treatment, coating with a coating liquid, drying after coating, and transversely stretching to obtain a coated PET film;

[0037] During the coating, the mass ratio of the raw material of layer A, the raw material of layer B, and the raw material of layer C is 9-10:90-95:9-10;

[0038] In melt extrusion, the heating temperature of twin-screw extruder No. 1 and twin-screw extruder No. 2 is 256-265°C, and the heating temperature of single-screw extruder is 275-285°C;

[0039] The longitudinal stretching temperature is 75-80°C and the ratio is 3.2-3.4:1;

[0040] The coating amount of the coating liquid in the coating is 3.6-4g / m 2 ;

[0041] After coating, the drying temperature is 130-135°C and the drying time is 5-6 minutes;

[0042] The transverse stretching temperature is 115-120°C and the ratio is 4:1;

[0043] The vacuum evaporation is to add a layer of silicon dioxide to the coated side of the coated PET film by vacuum evaporation to obtain a highly transparent PET film that is resistant to boiling;

[0044] The thickness of the boiling-resistant high-transparency PET film is 12-15 μm.

[0045] A highly transparent PET film prepared by the above-mentioned preparation method.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] (1) The method for preparing a boiling-resistant high-transparency PET film of the present invention uses a filler and a high-barrier additive in the preparation. The preparation method of the filler includes coating cross-linked chitosan and adsorbing sodium carboxymethyl cellulose, wherein the coating cross-linked chitosan is to mix titanium dioxide and an acetic acid aqueous solution of chitosan, add glutaraldehyde for cross-linking, and coat a layer of cross-linked chitosan on the surface of the titanium dioxide to obtain titanium dioxide coated with cross-linked chitosan; the adsorption of sodium carboxymethyl cellulose is to utilize the fact that under acidic conditions, the amino groups in the cross-linked chitosan are protonated to carry a positive charge, and the carboxyl groups in the sodium carboxymethyl cellulose are negatively charged, and there is an electrostatic force between the cross-linked chitosan and the sodium carboxymethyl cellulose, and the sodium carboxymethyl cellulose is combined with the surface of the titanium dioxide coated with the 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, wherein the adsorption of magnesium citrate is to use a magnesium citrate aqueous solution to surface-treat calcium stearate, adsorb a layer of magnesium citrate on the surface of the calcium stearate, and obtain calcium stearate adsorbed with magnesium citrate; the adsorption of polyvinyl alcohol is to use a polyvinyl alcohol aqueous solution to surface-treat the calcium stearate adsorbed with magnesium citrate, and through the interaction between magnesium ions and polyvinyl alcohol, a layer of polyvinyl alcohol is adsorbed to obtain calcium stearate adsorbed with polyvinyl alcohol; the adsorption of magnesium ions is to use a magnesium chloride aqueous solution to surface-treat the calcium stearate adsorbed with polyvinyl alcohol, and continue to adsorb magnesium ions on the surface of the polyvinyl alcohol through the interaction between magnesium ions and polyvinyl alcohol to obtain the high-barrier additive. The 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 the titanium dioxide. The calcium stearate in the high-barrier additive can play a hydrophobic role. Magnesium citrate and polyvinyl alcohol can form a hydrophobic cross-linked network through hydrogen bonds. Polyvinyl alcohol can improve film-forming properties, thereby ensuring high barrier properties while improving retort resistance. The outermost magnesium ions can also act as a bridge, interacting with the sodium carboxymethyl cellulose on the filler surface, thereby forming a cross-linked network containing metal ions on the surface of the PET film, further improving retort resistance and smoothness.

[0048] (2) The PET film prepared by the method has excellent cooking resistance, high transparency, high barrier property and high flatness, does not need to use organic solvents in preparation, and has strong bonding force between the PET film and the coating layer, and no defects on the surface, specifically, the MD heat shrinkage rate (150℃, 30min) is 0.61-0.83%, the CD heat shrinkage rate (150℃, 30min) is 0-0.17%, the transparency is 89.4-90.1%, the haze is 3.20-3.43%, the water vapor transmission rate is 0.475-0.523g / (m 2 ·24h), and the oxygen transmission rate is 0.421-0.458cm 3 / (m 2 ·24h·0.1MPa); the static friction coefficient of the PET film before vacuum evaporation of the silicon dioxide layer, i.e. the PET film after coating, is 0.271-0.282, the dynamic friction coefficient is 0.224-0.235, the peeling strength is 31.2-33.4N / cm, and the surface is defect-free. DETAILED DESCRIPTION

[0049] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the specific embodiments of the present application will be described below.

[0050] Example 1

[0051] A preparation method of a cooking-resistant high-transparency PET film, specifically comprising:

[0052] 1. Preparation of filler:

[0053] (1) Coated cross-linked chitosan: 200g titanium dioxide, 2000mL chitosan acetic acid aqueous solution are added into a reaction kettle, the stirring speed of the reaction kettle is controlled to 200rpm, stirring is performed for 20min, 200mL glutaraldehyde aqueous solution is added dropwise, the dropwise adding speed is controlled to 10mL / min, after the dropwise adding is completed, stirring is continued for 1h, the product is added into a centrifuge, centrifugation is performed at a centrifugal speed of 12000rpm for 30min, the precipitate is taken out, washed with water, and dried to obtain coated cross-linked chitosan titanium dioxide;

[0054] The titanium dioxide is an anatase titanium dioxide, and the average particle size is 50nm;

[0055] The preparation method of the chitosan acetic acid aqueous solution is as follows: 9g chitosan, 1000mL acetic acid aqueous solution are added into a reaction kettle, the stirring speed of the reaction kettle is controlled to 200rpm, and stirring is performed for 30min to obtain the chitosan acetic acid aqueous solution;

[0056] The deacetylation degree of the chitosan is 90%;

[0057] The mass concentration of acetic acid in the acetic acid aqueous solution is 2%;

[0058] The mass concentration of glutaraldehyde in the glutaraldehyde aqueous solution is 2%;

[0059] (2) Adsorption of sodium carboxymethyl cellulose: 12 g of sodium carboxymethyl cellulose and 2000 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 200 rpm, and the mixture was stirred for 20 min. A hydrochloric acid solution was added to adjust the pH value to 3.5, 200 g of titanium dioxide coated with cross-linked chitosan was added, and the mixture was stirred for 1 h. The mixture was added to a centrifuge and centrifuged at 12000 rpm for 30 min. The precipitate was collected and dried to obtain a filler.

[0060] The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L;

[0061] 2. Preparation of high barrier additives:

[0062] (1) Adsorption of magnesium citrate: 44 g of magnesium citrate and 7500 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 200 rpm, and the stirring was continued for 15 min. 200 g of calcium stearate was added, and the stirring was continued for 30 min. The mixture was placed in a centrifuge and centrifuged at a centrifugal speed of 10000 rpm for 10 min. The precipitate was collected, washed with water, and dried to obtain calcium stearate adsorbing magnesium citrate.

[0063] The average particle size of the calcium stearate is 100 nm;

[0064] (2) Adsorption of polyvinyl alcohol: 24 g of polyvinyl alcohol 2499 and 8000 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 200 rpm, and the stirring was continued for 25 min. 205 g of calcium stearate adsorbed with magnesium citrate was added, and the stirring was continued for 30 min. The mixture was added to a centrifuge and centrifuged at a centrifugal speed of 10000 rpm for 10 min. The precipitate was collected, washed with water, and dried to obtain calcium stearate adsorbed with polyvinyl alcohol.

[0065] (3) Adsorption of magnesium ions: 75 g of magnesium chloride and 8000 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 200 rpm, and the mixture was stirred for 25 min. 210 g of calcium stearate adsorbed with polyvinyl alcohol was added, and the mixture was stirred for 30 min. The mixture was placed in a centrifuge and centrifuged at 10000 rpm for 10 min. The precipitate was collected, washed with water, and dried to obtain a high barrier additive.

[0066] 3. Prepare the coating solution: add polyvinylidene chloride emulsion, filler, and high barrier additive in a mass ratio of 80:7:8 into the reactor, control the stirring speed of the reactor to 300 rpm, and stir for 15 minutes to obtain the coating solution;

[0067] The solid content of the polyvinylidene chloride emulsion is 38%;

[0068] 4. Treatment: pre-crystallizing and drying the polyester resin to obtain treated polyester resin;

[0069] The pre-crystallization temperature is 160°C and the time is 25 minutes;

[0070] The drying temperature is 150°C and the drying time is 5 hours;

[0071] 5. Coating: The treated polyester resin is divided into three parts as the raw material of layer A, layer B and layer C. The raw material of layer A, layer B and layer C are added to the No. 1 twin-screw extruder, the single-screw extruder and the No. 2 twin-screw extruder for melt extrusion respectively. The heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder is controlled to be 256°C, and the heating temperature of the single-screw extruder is controlled to be 275°C. The sheets are cooled and solidified on the casting roller and longitudinally stretched. The longitudinal stretching temperature is controlled to be 75°C and the ratio is 3.2:1. The sheets are corona treated and coated with a coating liquid. The coating amount of the coating liquid is controlled to be 3.6g / m 2 After coating, the film was dried at 130°C for 5 minutes and then stretched transversely at a temperature of 115°C and a ratio of 4:1 to obtain a coated PET film.

[0072] The mass ratio of the raw materials of layer A, layer B and layer C is 9:90:9;

[0073] 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 highly transparent PET film that is resistant to boiling;

[0074] The thickness of the boiling-resistant high-transparency PET film is 15 μm.

[0075] This embodiment also provides a high-transparency PET film prepared by the aforementioned preparation method.

[0076] Example 2

[0077] A method for preparing a boiling-resistant high-transparency PET film, specifically comprising:

[0078] 1. Prepare filler:

[0079] (1) Coating cross-linked chitosan: 200 g of titanium dioxide and 2100 mL of chitosan in acetic acid aqueous solution were added to a reactor, the stirring speed of the reactor was controlled to 250 rpm, and the mixture was stirred for 25 min. 220 mL of glutaraldehyde aqueous solution was added dropwise at a dropping speed of 12 mL / min. After the addition was completed, the mixture was stirred for 1.5 h. The mixture was added to a centrifuge and centrifuged at 13,000 rpm for 32 min. The precipitate was collected, washed with water, and dried to obtain titanium dioxide coated with cross-linked chitosan.

[0080] The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm;

[0081] The preparation method of the chitosan acetic acid aqueous solution is as follows: 9.5 g of chitosan and 1020 mL of acetic acid aqueous solution are added to a reactor, the stirring speed of the reactor is controlled to 250 rpm, and the mixture is stirred for 35 minutes to obtain the chitosan acetic acid aqueous solution;

[0082] The deacetylation degree of the chitosan is 90%;

[0083] The mass concentration of acetic acid in the acetic acid aqueous solution is 2%;

[0084] The mass concentration of glutaraldehyde in the glutaraldehyde aqueous solution is 2%;

[0085] (2) Adsorption of sodium carboxymethyl cellulose: 12.5 g of sodium carboxymethyl cellulose and 2200 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 250 rpm, and the mixture was stirred for 25 min. A hydrochloric acid solution was added to adjust the pH value to 4, and 205 g of titanium dioxide coated with cross-linked chitosan was added. The mixture was stirred for 1.5 h, and the mixture was added to a centrifuge. The mixture was centrifuged at 13000 rpm for 32 min. The precipitate was collected and dried to obtain a filler.

[0086] The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L;

[0087] 2. Preparation of high barrier additives:

[0088] (1) Adsorption of magnesium citrate: 45 g of magnesium citrate and 7700 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 250 rpm, and the mixture was stirred for 18 min. 205 g of calcium stearate was added, and the mixture was stirred for 35 min. The mixture was placed in a centrifuge and centrifuged at 11000 rpm for 10 min. The precipitate was collected, washed with water, and dried to obtain calcium stearate adsorbing magnesium citrate.

[0089] The average particle size of the calcium stearate is 100 nm;

[0090] (2) Adsorption of polyvinyl alcohol: 24.5 g of polyvinyl alcohol 2499 and 8500 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 250 rpm, and the stirring was continued for 28 min. 210 g of calcium stearate adsorbed with magnesium citrate was added, and the stirring was continued for 35 min. The mixture was added to a centrifuge and centrifuged at a centrifugal speed of 11000 rpm for 10 min. The precipitate was collected, washed with water, and dried to obtain calcium stearate adsorbed with polyvinyl alcohol.

[0091] (3) Adsorption of magnesium ions: 77 g of magnesium chloride and 8500 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 250 rpm, and the mixture was stirred for 28 min. 215 g of calcium stearate adsorbed with polyvinyl alcohol was added, and the mixture was stirred for 35 min. The mixture was placed in a centrifuge and centrifuged at 11000 rpm for 10 min. The precipitate was collected, washed with water, and dried to obtain a high barrier additive.

[0092] 3. Prepare the coating solution: Add polyvinylidene chloride emulsion, filler, and high barrier additive in a mass ratio of 82:8:9 into a reactor, control the stirring speed of the reactor to 350 rpm, and stir for 18 minutes to obtain a coating solution;

[0093] The solid content of the polyvinylidene chloride emulsion is 38%;

[0094] 4. Treatment: pre-crystallizing and drying the polyester resin to obtain treated polyester resin;

[0095] The pre-crystallization temperature is 170°C and the time is 28 minutes;

[0096] The drying temperature is 155°C and the drying time is 5.5 hours;

[0097] 5. Coating: The treated polyester resin is divided into three parts as the raw material of layer A, layer B and layer C. The raw material of layer A, layer B and layer C are added to the No. 1 twin-screw extruder, the single-screw extruder and the No. 2 twin-screw extruder for melt extrusion respectively. The heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder is controlled to be 260°C, and the heating temperature of the single-screw extruder is controlled to be 280°C. The sheets are cooled and solidified on the casting roller and longitudinally stretched. The longitudinal stretching temperature is controlled to be 77°C and the ratio is 3.3:1. The sheets are corona treated and coated with a coating liquid. The coating amount of the coating liquid is controlled to be 3.8g / m 2 After coating, the film was dried at 132°C for 5.5 minutes and then stretched transversely at a temperature of 120°C and a ratio of 4:1 to obtain a coated PET film.

[0098] The mass ratio of the raw materials of layer A, layer B and layer C is 9.5:92:9.5;

[0099] 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 highly transparent PET film that is resistant to boiling;

[0100] The thickness of the boiling-resistant high-transparency PET film is 14 μm.

[0101] This embodiment also provides a high-transparency PET film prepared by the aforementioned preparation method.

[0102] Example 3

[0103] A method for preparing a boiling-resistant high-transparency PET film, specifically comprising:

[0104] 1. Prepare filler:

[0105] (1) Coating cross-linked chitosan: 200 g titanium dioxide and 2200 mL chitosan acetic acid aqueous solution were added to a reactor, the stirring speed of the reactor was controlled to 300 rpm, and the mixture was stirred for 30 min. 230 mL of glutaraldehyde aqueous solution was added dropwise at a dropping speed of 15 mL / min. After the addition was completed, the mixture was stirred for 1.5 h. The mixture was added to a centrifuge and centrifuged at 13,000 rpm for 35 min. The precipitate was collected, washed with water, and dried to obtain titanium dioxide coated with cross-linked chitosan.

[0106] The titanium dioxide is anatase titanium dioxide with an average particle size of 50 nm;

[0107] The preparation method of the chitosan acetic acid aqueous solution is as follows: 10g chitosan and 1050mL acetic acid aqueous solution are added into a reactor, the stirring speed of the reactor is controlled to 300rpm, and the mixture is stirred for 40min to obtain the chitosan acetic acid aqueous solution;

[0108] The deacetylation degree of the chitosan is 90%;

[0109] The mass concentration of acetic acid in the acetic acid aqueous solution is 2%;

[0110] The mass concentration of glutaraldehyde in the glutaraldehyde aqueous solution is 2%;

[0111] (2) Adsorption of sodium carboxymethyl cellulose: 13 g of sodium carboxymethyl cellulose and 2300 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 300 rpm, and the mixture was stirred for 30 min. A hydrochloric acid solution was added to adjust the pH value to 4, and 210 g of titanium dioxide coated with cross-linked chitosan was added. The mixture was stirred for 1.5 h, and the mixture was added to a centrifuge. The mixture was centrifuged at 13000 rpm for 35 min. The precipitate was collected and dried to obtain a filler.

[0112] The molar concentration of hydrochloric acid in the hydrochloric acid aqueous solution is 1 mol / L;

[0113] 2. Preparation of high barrier additives:

[0114] (1) Adsorption of magnesium citrate: 46 g of magnesium citrate and 8000 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 300 rpm, and the mixture was stirred for 20 min. 210 g of calcium stearate was added and the mixture was stirred for 40 min. The mixture was placed in a centrifuge and centrifuged at 11000 rpm for 11 min. The precipitate was collected, washed with water, and dried to obtain calcium stearate adsorbing magnesium citrate.

[0115] The average particle size of the calcium stearate is 100 nm;

[0116] (2) Adsorption of polyvinyl alcohol: 25 g of polyvinyl alcohol 2499 and 9000 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 300 rpm, and the mixture was stirred for 30 min. 215 g of calcium stearate adsorbed with magnesium citrate was added, and the mixture was stirred for 40 min. The mixture was placed in a centrifuge and centrifuged at 11000 rpm for 11 min. The precipitate was collected, washed with water, and dried to obtain calcium stearate adsorbed with polyvinyl alcohol.

[0117] (3) Adsorption of magnesium ions: 80 g of magnesium chloride and 9000 mL of water were added to a reactor, the stirring speed of the reactor was controlled to 300 rpm, and the mixture was stirred for 30 min. 217 g of calcium stearate adsorbed with polyvinyl alcohol was added, and the mixture was stirred for 40 min. The mixture was placed in a centrifuge and centrifuged at 11000 rpm for 11 min. The precipitate was washed with water and dried to obtain a high barrier additive.

[0118] 3. Prepare the coating solution: add polyvinylidene chloride emulsion, filler, and high barrier additive in a mass ratio of 85:10:10 into the reactor, control the stirring speed of the reactor to 400 rpm, and stir for 20 minutes to obtain the coating solution;

[0119] The solid content of the polyvinylidene chloride emulsion is 38%;

[0120] 4. Treatment: pre-crystallizing and drying the polyester resin to obtain treated polyester resin;

[0121] The pre-crystallization temperature is 180°C and the time is 30 minutes;

[0122] The drying temperature is 160°C and the drying time is 6 hours;

[0123] 5. Coating: The treated polyester resin is divided into three parts as the raw material of layer A, layer B and layer C. The raw material of layer A, layer B and layer C are added to the No. 1 twin-screw extruder, the single-screw extruder and the No. 2 twin-screw extruder for melt extrusion respectively. The heating temperature of the No. 1 twin-screw extruder and the No. 2 twin-screw extruder is controlled to be 265°C, and the heating temperature of the single-screw extruder is controlled to be 285°C. The sheets are cooled and solidified on the casting roller and longitudinally stretched. The longitudinal stretching temperature is controlled to be 80°C and the ratio is 3.4:1. The sheets are corona treated and coated with a coating liquid. The coating amount of the coating liquid is controlled to be 4g / m 2 After coating, the film was dried at 135°C for 6 minutes and then stretched transversely at a temperature of 120°C and a ratio of 4:1 to obtain a coated PET film.

[0124] The mass ratio of the raw materials of layer A, layer B and layer C is 10:95:10;

[0125] 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 highly transparent PET film that is resistant to boiling;

[0126] The thickness of the boiling-resistant high-transparency PET film is 12 μm.

[0127] This embodiment also provides a high-transparency PET film prepared by the aforementioned preparation method.

[0128] Comparative Example 1

[0129] On the basis of the technical solution of Example 1, the first step of preparing the filler is omitted, and in the third step of preparing the coating solution, anatase titanium dioxide with an average particle size of 50 nm is used as a mass substitute for the filler.

[0130] The remaining technical solutions are the same as those in Example 1.

[0131] The thickness of the retort-resistant high-transparency PET film obtained in this comparative example was 15 μm.

[0132] Comparative Example 2

[0133] On the basis of the technical solution of Example 1, the step (2) of adsorbing sodium carboxymethyl cellulose is omitted in the step (1) of preparing the filler, and the titanium dioxide coated with cross-linked chitosan obtained in the step (1) of coating cross-linked chitosan is used as the filler.

[0134] The remaining technical solutions are the same as those in Example 1.

[0135] The thickness of the retort-resistant high-transparency PET film obtained in this comparative example was 15 μm.

[0136] Comparative Example 3

[0137] On the basis of the technical solution of Example 1, the second step of preparing the high barrier additive is omitted, and in the third step of preparing the coating solution, calcium stearate with an average particle size of 100 nm is used as a filler substitute.

[0138] The remaining technical solutions are the same as those in Example 1.

[0139] The thickness of the retort-resistant high-transparency PET film obtained in this comparative example was 15 μm.

[0140] Comparative Example 4

[0141] On the basis of the technical solution of Example 1, in the second step of preparing the high barrier additive, 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.

[0142] The remaining technical solutions are the same as those in Example 1.

[0143] The thickness of the retort-resistant high-transparency PET film obtained in this comparative example was 15 μm.

[0144] Comparative Example 5

[0145] On the basis of the technical solution of Example 1, in the step of preparing the high barrier additive in step 2, step (3) of adsorbing magnesium ions is omitted, that is, the calcium stearate adsorbed with polyvinyl alcohol obtained in the step (2) of adsorbing polyvinyl alcohol is used as the high barrier additive.

[0146] The remaining technical solutions are the same as those in Example 1.

[0147] The thickness of the retort-resistant high-transparency PET film obtained in this comparative example was 15 μm.

[0148] Performance Test 1

[0149] The heat shrinkage (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. The test results are as follows:

[0150]

[0151] It can be seen from the above results that the heat shrinkage, transparency, haze, water vapor permeability and oxygen permeability of the high-transparency PET films prepared in Comparative Examples 1-5 are all worse than those in Example 1.

[0152] Performance Test 2

[0153] The static friction coefficient, dynamic friction coefficient, and peel strength of the coated PET films obtained in the fifth coating step in Examples 1-3 and Comparative Examples 1-5 were tested, and the surface defects were observed. The test results and observations are as follows:

[0154]

[0155] 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 higher than those in Example 1; the peel strength of the coated PET films prepared in Comparative Examples 1-3 is worse than that in Example 1; and there are still defects on the surface of the coated PET films prepared in Comparative Examples 1 and 3.

[0156] Finally, it should be noted that the above descriptions are merely 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 aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a boiling-resistant high-transparency PET film, characterized in that: include: Preparation of fillers, preparation of high barrier additives, preparation of coating liquid, treatment, coating, vacuum evaporation; The preparation of the filler comprises: coating with cross-linked chitosan and adsorbing sodium carboxymethyl cellulose; The cross-linked chitosan coating comprises mixing titanium dioxide and chitosan in an acetic acid aqueous solution, stirring, dropping a glutaraldehyde aqueous solution, continuing to stir after the addition is completed, centrifuging, taking a precipitate, washing it with water, and drying it to obtain titanium dioxide coated with cross-linked chitosan; The sodium carboxymethyl cellulose adsorption method comprises mixing sodium carboxymethyl cellulose and water, stirring, adjusting the pH value to 3.5-4, adding titanium dioxide coated with cross-linked chitosan, continuing to stir, centrifuging, taking a precipitate, and drying to obtain a filler; The preparation of the high barrier additive comprises: adsorbing magnesium citrate, adsorbing polyvinyl alcohol, and adsorbing magnesium ions; The magnesium citrate adsorption method comprises mixing magnesium citrate and water, stirring, adding calcium stearate, continuing stirring, centrifuging, taking a precipitate, washing it with water, and drying it to obtain calcium stearate adsorbing magnesium citrate; The polyvinyl alcohol adsorption method comprises mixing polyvinyl alcohol 2499 and water, stirring, adding calcium stearate adsorbed with magnesium citrate, continuing stirring, centrifuging, taking a precipitate, washing it with water, and drying it to obtain calcium stearate adsorbed with polyvinyl alcohol; The magnesium ion adsorption method comprises mixing magnesium chloride and water, stirring, adding calcium stearate adsorbed with polyvinyl alcohol, continuing to stir, centrifuging, taking a precipitate, washing with water, and drying to obtain a high barrier additive; The coating liquid is prepared by mixing polyvinylidene chloride emulsion, filler, and high barrier additive, and stirring to obtain the coating liquid; The treatment involves pre-crystallizing and drying the polyester resin to obtain a treated polyester resin; The coating comprises the following steps: dividing the treated polyester resin into three parts as a raw material for layer A, a raw material for layer B, and a raw material for layer C; adding the raw material for layer A, layer B, and layer C into a No. 1 twin-screw extruder, a single-screw extruder, and a No. 2 twin-screw extruder respectively for melt extrusion; cooling and solidifying the materials on a casting roller; longitudinally stretching the materials; performing a corona treatment; coating the materials with a coating liquid; drying the materials after coating; and transversely stretching the materials to obtain a coated PET film.

2. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: In the coated cross-linked chitosan, the ratio of titanium dioxide, chitosan acetic acid aqueous solution, and glutaraldehyde aqueous solution is 200g:2000-2200mL:200-230mL; The dropping speed 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 chitosan acetic acid aqueous solution comprises the following steps: mixing chitosan and acetic acid aqueous solution, and stirring to obtain the chitosan acetic acid aqueous solution; In the preparation of the chitosan acetic acid aqueous solution, the ratio of chitosan to acetic acid aqueous solution is 9-10 g: 1000-1050 mL; 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 glutaraldehyde aqueous solution is 2%.

3. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: In the sodium carboxymethyl cellulose adsorption, the usage ratio of sodium carboxymethyl cellulose, water, and titanium dioxide coated with cross-linked chitosan is 12-13 g: 2000-2300 mL: 200-210 g.

4. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: In the adsorbed 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 adsorbed polyvinyl alcohol, the dosage ratio of polyvinyl alcohol 2499, water, and calcium stearate for adsorbing magnesium citrate is 24-25g:8000-9000mL:205-215g; In the magnesium ion adsorption method, the dosage ratio of magnesium chloride, water, and calcium stearate for adsorbing polyvinyl alcohol is 75-80 g: 8000-9000 mL: 210-217 g.

5. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: In 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%.

6. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: In the process, the pre-crystallization temperature is 160-180°C and the time is 25-30 minutes; The drying temperature is 150-160° C. and the drying time is 5-6 hours.

7. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: During the coating, the mass ratio of the raw material of layer A, the raw material of layer B, and the raw material of layer C is 9-10:90-95:9-10; In melt extrusion, the heating temperature of twin-screw extruder No. 1 and twin-screw extruder No. 2 is 256-265°C, and the heating temperature of single-screw extruder is 275-285°C; The longitudinal stretching temperature is 75-80°C and the ratio is 3.2-3.4:1; The coating amount of the coating liquid in the coating is 3.6-4g / m 2 ; After coating, the drying temperature is 130-135°C and the drying time is 5-6 minutes; The temperature of the transverse stretching is 115-120° C., and the ratio is 4:

1.

8. The method for preparing a boiling-resistant high-transparency PET film according to claim 1, wherein: The vacuum evaporation is to add a layer of silicon dioxide to the coated side of the coated PET film by vacuum evaporation to obtain a highly transparent PET film that is resistant to boiling; The thickness of the cooking-resistant high-transparency PET film is 12-15 μm.

9. A highly transparent PET film prepared by the preparation method according to any one of claims 1 to 8.

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