CN110790968A

CN110790968A - Online coating type modified biaxially oriented polyester film and preparation method thereof

Info

Publication number: CN110790968A
Application number: CN201911128474.3A
Authority: CN
Inventors: 何志彪; 谢勇; 李明强; 黄亦迎; 郑邦鸿; 罗剑锋; 何燕霞; 陶宏伟; 招洛彬
Original assignee: DuPont Hongji Films Foshan Co Ltd
Current assignee: DuPont Hongji Films Foshan Co Ltd
Priority date: 2019-11-18
Filing date: 2019-11-18
Publication date: 2020-02-14
Anticipated expiration: 2039-11-18
Also published as: CN110790968B

Abstract

The invention provides an online coating type modified biaxially oriented polyester film and a preparation method and application thereof, wherein the modified biaxially oriented polyester film is provided with a coating on one side or two sides of a polyester base film, the coating is obtained by coating aqueous coating liquid on the surface of the polyester base film and then volatilizing and drying the coating, the aqueous coating liquid comprises aqueous resin, a curing agent, a surfactant, chitosan and a functional assistant, and the aqueous resin is obtained by copolymerizing the following monomers: vinylidene chloride, acrylic acid, alkyl (meth) acrylates, vinyl acetate and cellulose acrylate. The film provided by the invention has good barrier property after aluminizing, is particularly suitable for being used as a food packaging material, has high adhesion with an aluminum layer, has the peeling strength of more than 8.7N/25mm, does not generate dealumination even under high-temperature high-humidity conditions due to high aluminum layer fastness, greatly reduces fire safety hidden danger and harm to human bodies, and has obvious green and environment-friendly significance.

Description

Online coating type modified biaxially oriented polyester film and preparation method thereof

Technical Field

The invention belongs to the technical field of new materials, particularly relates to a plastic film, and more particularly relates to an online coating type modified biaxially oriented polyester film and a preparation method thereof.

Technical Field

The biaxially oriented polyester film (BOPET for short) has excellent comprehensive performance, high mechanical strength, good optical performance, wide use temperature, excellent barrier property, oil resistance, corrosion resistance and the like, so the biaxially oriented polyester film has wide application fields. The BOPET film is most commonly used in printing, laminating, vacuum aluminizing, and the like. In the field of packaging materials, the BOPET film has low water absorption rate and good water resistance, and is suitable for packaging foods with high water content. BOPET is prepared by taking amorphous polyester chip PET as a raw material through the processes of drying, melt extrusion, sheet casting and longitudinal and transverse stretching. Generally, when the ordinary biaxially oriented polyester film (BOPET) obtained according to the above process flow is not subjected to surface treatment, the surface properties such as printing, compounding and the like can meet the process requirements, and the method is widely applied in the industrial field. When BOPET is used for vacuum aluminum plating, the surface of a base material is required to be smooth and flat, and the thickness is required to be uniform; proper stiffness and friction coefficient; the surface tension is more than 40 mN/m; the heat property is good, and the heat radiation and condensation heat of the evaporation source can be resisted, and the effect under the high-humidity condition can be achieved. In order to further improve the bonding force between the vacuum aluminum-plated layer and the surface of the BOPET film and increase the adhesion fastness, the BOPET film is often subjected to surface treatment. The surface treatment method of the plastic film mainly comprises a corona treatment method and a coating method. The corona treatment method is common, but the corona method can generate aluminizing layer transfer when aluminizing, the main measure for preventing the back corona of the film is to adjust the pressure of a rubber compression roller before the corona treatment roller, the pressures at the two ends of the compression roller are consistent and proper, and then a strict dynamic and static balance test needs to be carried out before production, and very high requirements are provided for the operation conditions of the corona treatment roller and workers during production.

The coating method is one of the most effective measures. The coating method is to coat a layer of polymer solution, such as polyurethane, PVDF, PVOH, modified polyester and other polymer solutions, on the surface of the film.

However, the coating method of the market competitive products has the following defects: 1, the used solvent coating can remain and is unsafe for food packaging; 2, the surface improves the aluminizing binding force by greatly increasing the coating tension, but the two sides of the film are closely contacted and transferred due to the coating. The aluminum layer is easily reverse-adhered to the non-aluminum-plated surface after the film surface is coiled, namely, the phenomenon of reverse adhesion causes local dealumination to cause poor blocking effect; 3, the water resistance is poor after the aluminum-plated bag is made, and when the packaging bag is sterilized by high-temperature water vapor, the phenomenon that an aluminum layer is boiled or water bubbles fall off is generated, so that the blocking effect is poor or liquid food cannot be carried. The defects result in that the food packaging bag can not effectively ensure the freshness and quality preservation of the packaged food.

In the prior art, a polyester film capable of isolating water vapor is obtained by coating a barrier resin coating on the surface of a PET (polyethylene terephthalate) base material and then drying the PET base material, and CN103724646A discloses a polyester film with a polyester coating, which is obtained by coating a polyester adhesive on the surface of the base material after PET is subjected to fusion casting, longitudinal stretching to form a film, transverse stretching, drying, crosslinking, curing and heat setting. CN 105585726 a discloses a high-barrier polyester film, which is prepared by coating a high-barrier resin coating on one or both sides of a base film, melt-extruding, stretching in transverse and longitudinal directions, and heat-setting. CN 109232938A discloses an antirust polypropylene biaxially oriented film and a preparation method thereof, wherein a coating layer is coated on the surface of a substrate, a primer layer is arranged between the coating layer and the substrate, and the obtained biaxially oriented film has excellent water vapor barrier property.

However, in the methods in the above patents, the surface of the polyester substrate is coated with an aqueous emulsion of a certain resin material, specifically, the aqueous emulsion formed by forcibly dispersing the resin in water under the action of a surfactant is used as a coating layer, the aqueous emulsion is unstable in the subsequent process after coating, which may affect the performance of the obtained polyester film, and the dealumination phenomenon may occur in the subsequent vacuum aluminizing of the obtained BOPET product under the conditions of high heat and high humidity due to the low fastness of the aluminum layer, i.e., the barrier property of the material cannot be ensured, more importantly, the dealumination may adversely affect the health of the human body, and there is a scientific research report that the aluminum element may cause harm to the human body. Along with the development of medical science, people gradually recognize the harmfulness of aluminum, and the aluminum element is not only not needed by human bodies, but also has terrible harm to the human bodies. The world health organization formally identified aluminum as a food contaminant in 1989. When the content of aluminum element in human body is too high, the absorption of phosphorus, strontium, iron, calcium and other elements by intestinal tract can be affected. Insoluble aluminum phosphate is formed in the intestinal tract and is discharged out of the body along with feces, and phosphorus deficiency affects calcium absorption (insufficient calcium phosphate is generated), so that osteoporosis can be caused, and fracture is easy to occur. Excessive aluminum in vivo has adverse effects on central nervous system, digestive system, brain, liver, bone, kidney, cell, hematopoietic system, and immunologic function; meanwhile, the compound also can interfere acid-base balance in the body of the pregnant woman, so that ovaries are atrophied, the growth of a fetus is influenced, the metabolism of phosphorus and calcium of the body is influenced, and the like. Aluminum deposits in the brain and skin and accelerates the overall aging process of the human body, particularly obviously reducing the elasticity of the skin and increasing wrinkles. In recent years, it has been found that the occurrence of senile dementia is also related to the excessive intake of aluminum element in normal times.

At present, China pays great attention to food safety, and at present, higher requirements are put forward on food packaging materials, so that the production process of raw material biaxially oriented polyester films needs to be improved, the raw materials and products are required to be safe and non-toxic, the process needs to be green and environment-friendly, organic solvents and toxic resin products are not used as much as possible, and simultaneously, all performance indexes of the materials are ensured to meet the requirements.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides an online coating type modified biaxially oriented polyester film, which is characterized in that a coating is arranged on the surface of one side or two sides of a polyester base film, the coating is obtained by coating an aqueous coating liquid on the surface of the polyester base film and then volatilizing and drying the coating, the aqueous coating liquid comprises aqueous resin, a curing agent, a surfactant, chitosan and a functional auxiliary agent, and the aqueous resin is obtained by copolymerizing the following monomers: vinylidene chloride, acrylic acid, alkyl (meth) acrylates, vinyl acetate and cellulose acrylate.

In the preferred technical scheme of the invention, the weight ratio of the water-based resin, the curing agent, the surfactant, the chitosan and the functional auxiliary agent is 60-80:2-5:2-5:1-3: 3-8.

The aqueous coating liquid used in the invention is obtained by improving the formula of the PVDC aqueous emulsion, has the coating performance of the PVDC aqueous coating liquid, and meanwhile, the emulsion is stable, does not generate the layering demulsification phenomenon at high temperature, and is convenient for subsequent processing; meanwhile, the surface roughness of the polyester film is effectively reduced, and the surface roughness is uniform, so that the vacuum aluminized product is stable, and the phenomenon of dealumination can not occur under high temperature and high humidity.

The alkyl (meth) acrylate in the coating of the invention serves to increase the water solubility and barrier properties of the resin; the chitosan is rich in a large amount of hydroxyl and amino, and can react with acrylic acid, acrylic ester and vinyl acetate at high temperature under the action of a curing agent to generate a crosslinking effect, so that macromolecules of the water-based resin form a network structure, and the barrier property of the obtained film is further enhanced.

The thickness of the polyester-based film is 10-40 μm, preferably 20-40 μm; the thickness of the coating is 0.1-0.5 μm, preferably 0.2-0.4 μm.

In a preferred embodiment of the present invention, the aqueous resin is obtained by copolymerizing the following monomers in parts by weight in the presence of an initiator: 30-60 parts of vinylidene chloride, 20-30 parts of acrylic acid, 10-20 parts of (methyl) acrylic acid alkyl ester, 3-8 parts of vinyl acetate and 2-5 parts of cellulose acrylate.

Further preferably, the alkyl (meth) acrylate is preferably a compound of alkyl (meth) acrylate short-chain alkyl ester and long-chain alkyl (meth) acrylate according to a mass ratio of 10-18: 1-3, wherein the alkyl group in the alkyl (meth) acrylate short chain alkyl ester is a straight-chain alkyl group with an integer of 1-4 carbon atoms, and is specifically selected from methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate and butyl (meth) acrylate; the long-chain alkyl group in the long-chain alkyl (meth) acrylate is a branched or branched alkyl group having an integer of 8 to 16 carbon atoms, and may be specifically selected from decyl (meth) acrylate, dodecyl (meth) acrylate, tetradecyl (meth) acrylate, and hexadecyl (meth) acrylate.

The inventor unexpectedly discovers that when the alkyl (meth) acrylate is a compound of short-chain alkyl ester and long-chain alkyl ester, the alkyl (meth) acrylate can also play a certain role in dispersing, so that the stability of the aqueous coating liquid can be further enhanced, the coating of the polyester film after emulsion coating is more uniform and flat, the roughness uniformity of the polyester film after the coating is modified is improved while the surface roughness of the polyester film is reduced, the stability of the subsequent film after aluminizing is effectively enhanced, and the dealumination phenomenon can not occur even if the polyester film is used for a long time under the condition of high temperature and high humidity.

The initiator is not particularly limited, and any initiator conventionally used in addition polymerization in the art may be used, and examples thereof include, but are not limited to, potassium persulfate, ammonium persulfate, benzoyl peroxide, azobisisobutyronitrile. For safety reasons, it is preferred to use non-toxic inorganic peroxide initiator systems, i.e. potassium persulfate, ammonium persulfate, but other types of initiators should not be excluded from the scope of the present invention.

The amount of the initiator is 0.1 to 1 percent, preferably 0.2 to 0.5 percent of the total mass of the monomers.

The polymerization method is well known in the art, and bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, etc. can be used. Preferably, an emulsion polymerization mode is adopted, and an emulsion obtained by emulsion polymerization, a curing agent, a surfactant, chitosan and a functional auxiliary agent can be conveniently and directly used for preparing the aqueous coating liquid, wherein the using amount of the aqueous resin is calculated by the solid content of the emulsion after polymerization. The emulsion polymerization is performed by a seed emulsion polymerization method, which comprises the steps of preparing an initiator aqueous solution and a mixed monomer, mixing to prepare an emulsion, performing seed polymerization, performing emulsion polymerization, and adding a certain amount of water to make the solid content of the emulsion be 30-50% after the polymerization is finished.

The aqueous coating liquid is prepared by dispersing aqueous resin, a curing agent, chitosan and a functional auxiliary agent in water under the action of a surfactant in a container by a high-speed dispersing stirrer without the need of carrying out resin dispersion by an organic solvent. If an emulsion polymerization mode is adopted, a curing agent, chitosan, a functional assistant and the like can be directly dispersed in the emulsion obtained after polymerization, wherein the content of the water-based resin is calculated by the solid content of the emulsion obtained by polymerization.

The polyester substrate is selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), ethylene 2, 6-naphthalate (PEN), preferably polyethylene terephthalate (PET).

The curing agent is a cyanate ester containing compound, preferably a hydrophilic aliphatic isocyanate such as VPLS2319, VPLS2151 from bayer corporation.

The surfactant is selected from modified polydimethylsiloxanes such as BYK333, BYK345, BYK348 from BYK chemical, germany.

The functional auxiliary agent comprises a flatting agent, a defoaming agent and the like; the weight ratio of the leveling agent to the defoaming agent is 1-3: 1-3.

The defoamer is a silicone polyether copolymer, such as TEGO Foamex defoamer: 822,825 or TEGOAirex defoamer: 901W, 902W, 904W, 910, 916, 920.

The leveling agent is selected from modified polysiloxanes such as BYK-320, 322, 323, 325, 330 of Bick chemistry.

The functional assistant can also be an organosilicon leveling agent with defoaming property, such as BYK325 and EFKA-3785.

The aqueous coating liquid is prepared by dispersing aqueous resin, a curing agent, chitosan and a functional auxiliary agent in water under the action of a surfactant in a container by a high-speed dispersing stirrer without the need of carrying out resin dispersion by an organic solvent.

The aqueous resin is preferably an emulsion obtained by emulsion polymerization, wherein the aqueous resin content is calculated by the solid content of the emulsion obtained by polymerization.

The second purpose of the invention is to provide a preparation method of the modified biaxially oriented polyester film, which comprises the following steps: and carrying out melt extrusion on polyester, casting a sheet, longitudinally stretching, carrying out corona treatment, coating, transversely stretching, heat setting, cooling and rolling to obtain the modified biaxially oriented polyester film.

Wherein the melt extrusion is that after the polyester substrate is melted at the temperature of 300-320 ℃, the polyester melt is extruded from a die head through a metering pump, a filter and a melt line, and the extrusion speed is controlled at 20-35 r/min; the casting sheet is a cold drum casting sheet at the temperature of 10-20 ℃; the longitudinal stretching is that the casting sheet is preheated at 60-90 ℃ and then longitudinally stretched by 3.0-3.4 times at 100-120 ℃ on a longitudinal drawing machine, and the stretching speed is 10-20 m/min; the corona treatment is that the polyester film after longitudinal stretching is cooled to room temperature and then is subjected to corona; the coating is characterized in that an online coating machine is arranged between a longitudinal drawing Machine (MDO) and a transverse drawing machine (TDO), the aqueous coating liquid containing the aqueous resin is uniformly coated on one side or two sides of a polyester film subjected to longitudinal drawing, and the coating thickness is 1-4 mu m; the transverse stretching is to introduce the longitudinally stretched film into a heated transverse stretching roller group, and transverse stretching is carried out by 3.0-3.4 times at the temperature of 130-150 ℃ after preheating at the temperature of 105-120 ℃; the heat setting is carried out at the temperature of 220-240 ℃; and the cooling and rolling are carried out by gradually cooling to room temperature after heat setting, and the rolling tension is 200-400N, so that the modified biaxially-oriented polyester film is finally obtained. In the transverse stretching process, after the aqueous coating liquid coated on the surface of the polyester film is volatilized and dried, a uniform coating layer with the thickness of 0.1-0.5 μm, preferably 0.2-0.5 μm is left on the surface of the polyester film.

The third purpose of the invention is to provide the application of the biaxial stretching polyester film in food packaging materials, which is suitable for packaging high-heat water-containing food and high-oil salt liquid food, such as dairy products, coffee, hot drinks and snack packaging, can prolong the shelf life of the contents, and has good aroma retention property.

The invention has the following beneficial effects:

firstly, after the surface of the coating is coated, a layer of high molecular polymer with a net structure is left on the surface of the polyester film after the water of the aqueous resin solution is dried and volatilized in the stretching process.

The inventor unexpectedly discovers that the surface roughness of the polyester is greatly reduced after the polyester substrate is uniformly coated with the aqueous coating liquid as a coating layer, the adhesion between the film and an aluminum layer is high due to the treatment of the surface of the film, and the peeling strength is more than 8.7N/25 mm; due to the high fastness of the aluminum layer, the aluminum removing phenomenon can not occur even under the conditions of high heat and high humidity.

After the modified biaxially-oriented polyester film provided by the invention is subjected to vacuum aluminizing, the fire-fighting potential safety hazard and the harm to a human body are greatly reduced, and the modified biaxially-oriented polyester film has obvious green and environment-friendly significance.

The modified biaxially oriented polyester film provided by the invention has good water resistance and temperature resistance, excellent air and water vapor barrier performance, and only slightly reduced air and water vapor barrier performance under high-temperature and high-humidity conditions, is suitable for water cooking sterilization after bag making, and is particularly suitable for the field of food packaging for containing high-heat water content.

Fifth, the modified biaxially oriented polyester provided by the invention has the advantages of simple preparation method, easily available raw materials and excellent comprehensive performance, greatly reduces the fire safety hidden danger and the harmfulness to human body under the condition of higher and higher quality requirement environment, especially the safety requirement, is provided by modern food packaging, has obvious green and environmental protection significance, and is biaxially oriented polyester with market competitiveness.

Drawings

FIG. 1 is a graph showing the change in peel strength between the aluminum-plated layer and the modified biaxially oriented polyester film of example 1 after aluminum plating and the biaxially oriented polyester films of comparative examples 1 and 2 under high temperature and high humidity conditions.

Detailed Description

The technical content of the invention is further explained below with reference to specific embodiments. However, the present invention is not limited to the following examples. Unless otherwise defined, all terms of art used hereinafter have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present invention.

The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified. Unless otherwise specified, "parts" in the examples are parts by weight, and the percentages are mass percentages.

Preparation examplePreparation of aqueous coating liquid

Preparation example 1

1) The formulation of the emulsion polymerization was as follows: 60 parts of vinylidene chloride, 30 parts of acrylic acid, 15 parts of methyl methacrylate, 3 parts of dodecyl acrylate, 6 parts of vinyl acetate, 3 parts of cellulose acrylate, 0.3 part of potassium persulfate and 1.8 parts of emulsifier OP-10, carrying out emulsion polymerization according to the following steps to obtain an emulsion, and finally adding a certain amount of water to enable the solid content of the emulsion to be about 40 wt%. The specific operation is as follows:

a. preparing a solution: accurately weighing an initiator potassium persulfate in the formula, and then weighing 1.5 parts of deionized water to prepare an initiator aqueous solution; preparing a mixed monomer: accurately weighing monomers in the formula, and stirring for 2 hours to prepare a monomer mixture; preparing an emulsifier aqueous solution: weighing an emulsifier, dissolving the emulsifier in 2-5 parts of deionized water, adding water to 50 parts, and dispersing for 2 hours to prepare an emulsifier aqueous solution;

b. seed polymerization: washing the reaction kettle with deionized water for 1-5 times, sequentially adding 100 parts of deionized water and about 10% of the emulsion obtained in the step a into the reaction kettle, uniformly stirring, sealing, emptying after pressure test is carried out and gas leakage is avoided, vacuumizing to 0.1MPa, placing about 10% of the mixed monomer prepared in the step a into a feeder, and sucking the mixed monomer into the reaction kettle by utilizing the vacuum degree in the reaction kettle to ensure that the pressure in the reaction kettle is normal pressure; starting stirring at the stirring speed of 500rpm, and carrying out cold stirring for 10 min; slowly adding about 10% of initiator solution, heating to 55 ℃ for reaction, and finishing the polymerization of the seed emulsion when the reaction material is changed from milky white to translucent with blue halo;

c. emulsion polymerization: and continuously adding the rest monomer emulsion, the emulsifier aqueous solution and the initiator, keeping the adding speed unchanged, heating to 70 ℃ for reaction for 8 hours, adding triethylamine to adjust the pH value to 8-8.5 after the reaction is finished, filtering, adding a proper amount of water to obtain the aqueous resin emulsion with the solid content of about 40 wt%, cooling and discharging.

2) Preparing an aqueous coating liquid: and (2) taking 160 parts of the emulsion obtained in the step 1), adding 3 parts of a curing agent VPLS2319, 5 parts of a surfactant BYK333, 3 parts of chitosan, 2 parts of a defoaming agent TEGO Foamex 825 and 2 parts of a flatting agent BYK-325 into the emulsion, and dispersing the mixture into emulsion under high-speed stirring to obtain the aqueous coating liquid.

Preparation example 2

The preparation steps are the same as those of preparation example 1, except that the amount of chitosan used in the preparation of the aqueous coating solution of step 2) is changed to 1 part.

Preparation example 3

The preparation procedure was the same as in preparation example 1, except that in the preparation of the aqueous coating solution in step 2), the amount of chitosan was changed to 5 parts.

Preparation example 4

The preparation steps are the same as those of preparation example 1, except that the amount of the cellulose acrylate in the monomer formula is changed to 5 parts during the emulsion polymerization in step 1).

Preparation example 5

The preparation steps are the same as those of preparation example 1, except that in the step 1) of emulsion polymerization, the amount of methyl methacrylate in the monomer formula is changed to 17 parts, and the amount of dodecyl acrylate is changed to 1 part.

Preparation example 6

The procedure was the same as in preparation example 5, except that lauryl acrylate was changed to cetyl acrylate in the monomer formulation.

Preparation example 7

The procedure was as in preparation example 1, except that the amount of methyl methacrylate used in the monomer formulation was changed to 18 parts, and lauryl acrylate was not added.

Comparative preparation example 1

The procedure was as in preparation example 1, except that no vinyl acetate was added to the monomer formulation during the emulsion polymerization.

Comparative preparation example 2

The procedure was as in preparation example 1, except that no cellulose acrylate was added to the monomer formulation during the emulsion polymerization.

Comparative preparation example 3

The preparation procedure was the same as in preparation example 1, except that chitosan was not added in the preparation of the aqueous coating solution in step 2).

And (3) testing the heat resistance stability of the aqueous coating liquid obtained in the preparation example, specifically, taking a proper amount of emulsion sample in a weighing bottle, covering the weighing bottle, standing the weighing bottle in an oven at 80 ℃ for 24 hours until the emulsion is free of layering, oil floating and emulsion breaking, and then showing that the emulsion is stable, wherein the results are shown in the following table 1:

TABLE 1

Sample (I)	Preparation example 1	Preparation example 2	Preparation example 3	Preparation example 4	Preparation example 5
						Phenomenon(s)	Stabilization	Stabilization	Stabilization	Stabilization	Micro-floating oil
Sample (I)	Preparation example 6	Preparation example 7	Comparative preparation example 1	Comparative preparation example 2	Comparative preparation example 3
						Phenomenon(s)	Stabilization	Micro-floating oil	A little bleaching oil	Demulsification stratification	Stabilization

The data in table 1 show that the aqueous coating liquid obtained by the invention does not generate phenomena such as layering and demulsification for a long time at high temperature, and can keep good stability after being coated on a polyester film, so that a uniform coating is finally obtained, the affinity and stability between a polyester base film and the coating are ensured, and the stable and uniform coating formed by volatilization and drying of the aqueous coating liquid in the subsequent stretching process is facilitated.

ExamplesPreparation of modified biaxially oriented polyester

Example 1

Putting PET polyester into a double-screw extruder, extruding the PET polyester through a metering pump, a filter and a melt line by a die head, wherein the specific working conditions are that the length-diameter ratio of a screw of the extruder is 32, the rotating speed of the screw is controlled at 500 revolutions per minute, the rotating speed of a granulator is 600 revolutions per minute, the extrusion speed is controlled at 30r/min, and the processing temperature is divided into four sections: i, 280 +/-5 ℃; II, 290 ℃ plus or minus 5 ℃; III, at the temperature of 300 +/-5 ℃; IV, at 305 +/-5 ℃; cooling the polyester chip on a cold drum with the surface temperature of 15-20 ℃ to cast the chip; guiding the obtained cast sheet into a heated longitudinal drawing roller group, longitudinally drawing along the length direction, controlling the temperature of a preheating roller at about 80 ℃, the drawing temperature at about 110 ℃, the drawing ratio at 3.3 times and the drawing speed at 20m/min in the preheating process, and cooling to room temperature for corona treatment after drawing; uniformly coating the aqueous coating liquid obtained in the preparation example 1 on two sides of the longitudinally stretched polyester film by using an online coating machine, wherein the coating thickness is about 2 mu m, introducing the polyester film coated with the aqueous coating liquid into a heated transverse stretching roller set, and transversely stretching the polyester film at 150 ℃ by 3.3 times by preheating at 110 ℃; and (3) after the obtained biaxially oriented polyester film is subjected to heat setting at 240 ℃, gradually cooling to room temperature for cooling and rolling, wherein the rolling tension is 200-400N, and finally the modified biaxially oriented polyester film is obtained, wherein the thickness of the PET base film is 22 mu m, and the thickness of the coating is 0.3 mu m.

Example 2

The modified biaxially oriented polyester film was finally obtained by uniformly coating both sides of the longitudinally oriented polyester film with the aqueous coating solution obtained in preparation example 2 in the same manner as in example 1 to a coating thickness of about 2 μm, wherein the PET base film had a thickness of 22 μm and the coating thickness was 0.3. mu.m.

Example 3

The modified biaxially oriented polyester film was finally obtained by uniformly coating both sides of the longitudinally oriented polyester film with the aqueous coating solution obtained in preparation example 3 at a coating thickness of about 2 μm in the same manner as in example 1, wherein the thickness of the PET base film was 22 μm and the coating thickness was 0.3. mu.m.

Example 4

The modified biaxially oriented polyester film was finally obtained by uniformly coating both sides of the longitudinally oriented polyester film with the aqueous coating solution obtained in preparation example 4 at a coating thickness of about 2 μm in the same manner as in example 1, wherein the thickness of the PET base film was 22 μm and the coating thickness was 0.3. mu.m.

Example 5

The modified biaxially oriented polyester film was finally obtained by uniformly coating both sides of the longitudinally oriented polyester film with the aqueous coating solution obtained in preparation example 5 in the same manner as in example 1 to a coating thickness of about 2 μm, wherein the PET base film had a thickness of 22 μm and the coating thickness was 0.3. mu.m.

Example 6

The modified biaxially oriented polyester film was finally obtained by uniformly coating both sides of the longitudinally oriented polyester film with the aqueous coating solution obtained in preparation example 6 in the same manner as in example 1 to a coating thickness of about 2 μm, wherein the PET base film had a thickness of 22 μm and the coating thickness was 0.3. mu.m.

Example 7

The modified biaxially oriented polyester film was finally obtained by uniformly coating both sides of the longitudinally oriented polyester film with the aqueous coating solution obtained in preparation example 7 at a coating thickness of about 2 μm in the same manner as in example 1, wherein the thickness of the PET base film was 22 μm and the coating thickness was 0.3. mu.m.

Example 8

The other procedure was the same as in example 1 except that the aqueous coating solution was uniformly coated on both sides of the longitudinally stretched polyester film to a coating thickness of about 3 μm. Finally obtaining the modified biaxially oriented polyester film, wherein the thickness of the PET base film is 22 mu m, and the thickness of the coating is 0.4 mu m.

Comparative example 1

The other steps were the same as in example 1 except that after the longitudinal stretching, the transverse stretching was directly carried out without coating with an aqueous coating solution to finally obtain a PET polyester film without a coating layer and having a thickness of about 22 μm.

Comparative example 2

The other steps were the same as in example 1, 150 parts of a commercially available PVDC aqueous coating solution (L905A from Asahi chemical Co., Ltd., Japan) having a solid content of 40% was uniformly coated on both sides of the longitudinally stretched polyester film to a coating thickness of about 2 μm, to finally obtain a biaxially stretched polyester film in which the PET base film had a thickness of 22 μm and the coating thickness was 0.3. mu.m.

Comparative example 3

The other steps were the same as in example 1, and the aqueous coating solution obtained in comparative preparation example 1 was uniformly coated on both sides of the longitudinally stretched polyester film to a coating thickness of about 2 μm to finally obtain a biaxially stretched polyester film in which the thickness of the PET base film was 22 μm and the coating thickness was 0.3. mu.m.

Comparative example 4

The other steps were the same as in example 1, and the aqueous coating solution obtained in comparative preparation example 2 was uniformly coated on both sides of the longitudinally stretched polyester film to a coating thickness of about 2 μm to finally obtain a biaxially stretched polyester film in which the thickness of the PET base film was 22 μm and the coating thickness was 0.3. mu.m.

Comparative example 5

The other steps were the same as in example 1, and the aqueous coating solution obtained in comparative preparation example 3 was uniformly coated on both sides of the longitudinally stretched polyester film to a coating thickness of about 2 μm to finally obtain a biaxially stretched polyester film in which the thickness of the PET base film was 22 μm and the coating thickness was 0.3. mu.m.

Application example 1Performance testing of biaxially oriented polyester films

The biaxially oriented polyester films obtained in examples and comparative examples were subjected to the following property tests, and the results are shown in Table 2

a) Tensile strength and elongation at break: testing according to ASTM D882 standard.

b) Surface roughness test reference, test with reference to German standard DIN4768/DIN4771, was carried out 5 times in total, and the results were expressed as mean values. + -. standard deviation. c) Testing the thermal shrinkage rate: heat shrinkage the samples were heated at 150 ℃ for 20 minutes according to GB/T169581-2008. The length in the transverse and longitudinal directions thereof was measured using an amplifier, and from the measurement results, the heat shrinkage of each sample was calculated according to the following formula (I),

heat shrinkage (%) (length before heating-length after heating)/length before heating formula (I)

d) And (3) testing high-temperature resistance: testing according to UL 746B standard

TABLE 2

As can be seen from the data in Table 1, various performance indexes of the modified biaxially oriented polyester film obtained by the invention meet the requirements of food packaging materials. Meanwhile, the invention adopts the specific monomer to combine emulsion polymerization, and the prepared aqueous coating liquid prepared by the aqueous resin forms a coating after the polyester film is coated, thus greatly reducing the surface roughness of the polyester film, having good roughness uniformity and small standard deviation, having good reprocessing performance in the subsequent process, strengthening the combination with aluminum in the subsequent vacuum aluminum plating process, and avoiding the phenomenon of reverse adhesion and local dealumination.

Application example 2Preparation and application of aluminized biaxially-oriented polyester film

The operation and conditions of vacuum aluminizing of the biaxially oriented polyester film are known in the art, and specifically, the biaxially oriented polyester film obtained in the examples and the comparative examples is carried out in a vacuum aluminizing machine, vacuumizing is carried out until the vacuum degree is below 0.1Pa, an evaporation boat is opened and heated, the heating temperature is 1800-2000 ℃, then an aluminum wire is started for conveying, equipment is started for winding to the speed of 2.5m/s, evaporation is started, the change of the thickness of the micro-coating of the aluminized film is measured on line, the aluminizing is stopped when the thickness of the aluminized layer is controlled to be about 10nm, and cooling, vacuumizing and evaporation are finished.

After the modified biaxially oriented polyester is subjected to vacuum aluminizing, the surface of the material has no cracks, is rich in metallic luster, has good water vapor isolation performance, does not generate phenomena such as dealumination and the like under the conditions of high temperature and high humidity, avoids potential safety hazards of possible aluminum elements to human bodies, and can ensure the quality and aroma of foods, hot drinks and the like as a packaging material.

Meanwhile, as the water-based resin obtained by copolymerizing a plurality of specific monomers is adopted and is prepared into the water-based coating liquid to be used as the coating material of the polyester film, the stability between the coating and the polyester basal film is good; meanwhile, the emulsion of the water-based resin is used as a coating material, so that the surface roughness of the polyester film can be greatly reduced, the phenomena of dealumination and the like of the obtained polyester film under the conditions of high temperature and high humidity after vacuum aluminizing are avoided, and the quality of food and the like is guaranteed.

The following performance tests were performed on the modified biaxially oriented polyester after vacuum aluminizing, and the results are shown in table 3 below:

oxygen transmission amount: GB-T19789-.

Water vapor transmission amount: GBT 21529-.

The peel strength was carried out according to the GB8808-1988 standard.

Whether or not to dealuminate was determined by heat sealing a resin film (thickness 3 about microns) of a copolymer of ethylene and acrylic acid (DuPont EAA669, U.S.A., thickness about 3 microns) at 90 deg.C under 2MPa for 10 seconds to peel off the EAA and see if the aluminum layer had been transferred to the EAA film.

TABLE 3

As can be seen from the data in Table 2, the modified biaxially oriented polyester film provided by the invention has excellent barrier property after vacuum aluminizing. And because the surface roughness of the polyester film is low, and the roughness is uniform step by step, the local dealumination phenomenon under high temperature and high humidity can not occur, the polyester film is particularly suitable for being used as a food packaging material, the potential health safety hazard possibly caused by dealumination is avoided, and the defect that the barrier property is poor under the condition of high heat and high humidity is also avoided.

The tendency of the peel strength of the aluminum layer of the aluminized post-modified biaxially oriented polyester film of example 1 to change with time under 100 ℃ water vapor (RH 90%) was also carried out. The results are shown in FIG. 1.

As can be seen from fig. 1, after the modified biaxially oriented polyester film provided by the invention is vacuum aluminized, even if the film is placed under high temperature and high humidity conditions for a long time (more than 4 weeks), the peeling strength between the film and an aluminum layer is hardly reduced, and the polyester film in comparative example 1 is not subjected to coating treatment, has weak bonding force after aluminizing and is easy to peel; the biaxially oriented film of the conventional commercial PVDC coating in comparative example 2, which has a high initial peel strength but a greatly reduced peel strength with time under high temperature and high humidity conditions, is used as a food packaging material, and may undergo a dealumination phenomenon under heating conditions in food materials and hot drinks, thereby posing a safety hazard to human health.

The applicant states that the present invention is illustrated by the above examples to show specific reagents, equipment and process flows of the present invention, but the present invention is not limited to the above specific reagents, equipment and process flows, i.e. it does not mean that the present invention must rely on the above reagents, equipment and process flows to be carried out. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. The on-line coating type modified biaxially oriented polyester film is characterized in that a coating is arranged on one surface or two surfaces of a polyester base film, the coating is obtained by coating an aqueous coating liquid on the surface of the polyester base film and then volatilizing and drying the coating, the aqueous coating liquid comprises aqueous resin, a curing agent, a surfactant, chitosan and a functional assistant, and the water-soluble resin is obtained by copolymerizing the following monomers: vinylidene chloride, acrylic acid, alkyl (meth) acrylates, vinyl acetate and cellulose acrylate.

2. The polyester film according to claim 1, wherein the weight ratio of the water-based resin, the curing agent, the surfactant, the chitosan and the functional assistant is 60-80:2-5:2-5:1-3: 3-8.

3. The polyester film according to claim 1, wherein the thickness of the polyester-based film is 10 to 40 μm, preferably 20 to 40 μm; the thickness of the coating is 0.1-0.5 μm, preferably 0.2-0.4 μm.

4. The polyester film according to claim 1, wherein the aqueous resin is obtained by copolymerizing monomers comprising, in parts by weight: 30-60 parts of vinylidene chloride, 20-30 parts of acrylic acid, 10-20 parts of (methyl) acrylic acid alkyl ester, 3-8 parts of vinyl acetate and 2-5 parts of cellulose acrylate.

5. The polyester film according to claim 4, wherein the alkyl (meth) acrylate is a mixture of an alkyl (meth) acrylate short-chain alkyl ester and a (meth) acrylate long-chain alkyl ester in a mass ratio of 10 to 18: 1-3, wherein the exercise alkyl in the alkyl (meth) acrylate short-chain alkyl ester is a straight-chain alkyl with an integer of 1-4 carbon atoms; the long-chain alkyl in the long-chain alkyl (meth) acrylate is a branched or branched alkyl group having an integer of 8 to 16 carbon atoms.

6. The polyester film according to claim 4, wherein the polymerization is carried out by bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization; preferably, the emulsion polymerization is carried out, and the solid content of the emulsion is controlled to be 30-50% after the polymerization is finished.

7. The polyester film according to claim 1, wherein the material of the polyester-based film is selected from the group consisting of polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and ethylene 2, 6-naphthalate (PEN).

8. A process for producing a modified biaxially oriented polyester film according to any one of claims 1 to 7, which comprises the steps of: and carrying out melt extrusion on polyester, casting a sheet, longitudinally stretching, carrying out corona treatment, coating, transversely stretching, heat setting, cooling and rolling to obtain the modified biaxially oriented polyester film.

9. The method according to claim 8, wherein the melt extrusion is performed by melting the polyester substrate at 320 ℃ under 300 ℃, and then extruding the polyester melt from the die head through a metering pump, a filter and a melt line, wherein the extrusion speed is controlled to be 20-35 r/min; the casting sheet is a cold drum casting sheet at the temperature of 10-20 ℃; the longitudinal stretching is that the casting sheet is preheated at 60-90 ℃ and then longitudinally stretched by 3.0-3.4 times at 100-120 ℃ on a longitudinal drawing machine, and the stretching speed is 10-20 m/min; the corona treatment is that the polyester film after longitudinal stretching is cooled to room temperature and then is subjected to corona; the coating is characterized in that an online coating machine is arranged between a longitudinal drawing Machine (MDO) and a transverse drawing machine (TDO), the aqueous coating liquid containing the aqueous resin is uniformly coated on one side or two sides of a polyester film subjected to longitudinal drawing, and the coating thickness is 1-4 mu m; the transverse stretching is to introduce the longitudinally stretched film into a heated transverse stretching roller group, and transverse stretching is carried out by 3.0-3.4 times at the temperature of 130-150 ℃ after preheating at the temperature of 105-120 ℃; the heat setting is carried out at the temperature of 220-240 ℃; and the cooling and rolling are carried out by gradually cooling to room temperature after heat setting, and the rolling tension is 200-400N, so that the modified biaxially-oriented polyester film is finally obtained. In the transverse stretching process, after the aqueous coating liquid coated on the surface of the polyester film is volatilized and dried, a uniform coating layer with the thickness of 0.1-0.5 μm, preferably 0.2-0.5 μm is left on the surface of the polyester film.

10. Use of the modified biaxially oriented polyester film according to any one of claims 1 to 7 for food packaging materials.