Preparation method of high-barrier fresh-keeping film for food fresh-keeping packaging

Abstract

The invention discloses a preparation method of a high-barrier fresh-keeping film for food fresh-keeping packaging, belongs to the technical field of fresh-keeping film processing, and aims to solve the technical problem that the barrier property of a high-barrier fresh-keeping film to water vapor and oxygen and the tensile property of the high-barrier fresh-keeping film in the prior art need to be further improved. The preparation method comprises the following steps: adding barrier layer mixed particles, bonding layer mixed particles and a supporting layer material into a multi-layer co-extrusion extruder, carrying out melt extrusion, injecting into a multi-layer co-extrusion film machine, and carrying out blow molding to obtain the high-barrier-property preservative film which is compounded by five layers, namely a supporting layer, a bonding layer, a barrier layer, a bonding layer and a supporting layer from top to bottom, according to the invention, modified graphene is added into composite polyester of the barrier layer for modification, and waterborne polyurethane added with modified polysiloxane is prepared to obtain the bonding layer, so that the tensile property and the barrier property to water vapor and oxygen of the preservative film are further improved.

Description

Technical Field

[0001] The invention relates to the technical field of food fresh-keeping film preparation, and in particular to a method for preparing a high-barrier fresh-keeping film used for food fresh-keeping packaging. Background Art

[0002] Food is very easy to spoil during storage, transportation and sales, and food packaging can protect food from contamination by microorganisms. It is an indispensable part of food processing, storage and transportation. Among them, food cling film prevents food from being contaminated by microorganisms and delays the spoilage process by isolating air, moisture and the external environment. In addition to traditional transparent cling film, some special cling film can also add antibacterial agents, antioxidants, and even regulate gas exchange to further enhance the preservation effect.

[0003] In the prior art, the main materials for making cling film include polyethylene, polyamide, polyurethane and polyvinyl alcohol. Although the gas barrier capacity of cling film made of these materials is good, it is still far behind that of high-barrier cling film. The oxygen permeability and water vapor permeability of cling film need to be further improved, which is difficult to meet people's daily needs for food preservation and environmental friendliness.

[0004] In addition, high-barrier cling film is usually used to wrap and preserve fresh food ingredients, which requires the cling film to have good tensile properties. However, traditional high-barrier cling film has poor tensile properties. When using high-barrier cling film to wrap fresh food ingredients, the cling film is often torn. The tensile properties of high-barrier cling film need to be further improved.

[0005] In view of the technical defects in this aspect, a solution is now proposed. Summary of the invention

[0006] The object of the present invention is to provide a method for preparing a high-barrier cling film for food fresh-keeping packaging, so as to solve the technical problem that the oxygen permeability, water vapor permeability and tensile properties of the food cling film in the prior art need to be further improved.

[0007] The object of the present invention can be achieved by the following technical scheme: A method for preparing a high-barrier cling film for food fresh-keeping packaging comprises the following steps:

[0008] S1, adding the composite polyester and auxiliary additives into a twin-screw extruder for melt extrusion, and after cooling, adding them into a single-screw granulator for cutting to obtain barrier layer mixed granules;

[0009] S2, placing polyurethane prepolymer, triethylamine, deionized water and amino-terminated polysiloxane in a three-necked bottle, heating to 30-40°C, stirring for 1-1.5 hours, heating and curing, and then melt-extruded in a twin-screw extruder, and after cooling, adding to a single-screw granulator for cutting to obtain bonding layer mixed particles;

[0010] S3. Add barrier layer mixed particles, bonding layer mixed particles and support layer materials into a multi-layer co-extrusion extruder, melt extrude, inject into a multi-layer co-extrusion film machine, and undergo inflation molding to obtain a high-barrier cling film composed of five layers from top to bottom, namely support layer 1, bonding layer 1, barrier layer 1, bonding layer 2 and support layer 2.

[0011] Further, in step S1, the weight ratio of the composite polyester to the auxiliary additive is 10-15:3.5-7, the auxiliary material is composed of a plasticizer, a dispersant, an antioxidant and an antioxidant in a dosage ratio of 1g:1g:1g:1g, the plasticizer is one or more of tributyl citrate, trioctyl citrate, acetyl tributyl citrate and trioctyl acetyl citrate; the dispersant is one or more of zinc stearate, calcium stearate, magnesium stearate and cadmium stearate; the antioxidant is one or more of antioxidant DPPD, antioxidant PPD and antioxidant H one or more; the antioxidant is one or more of butylated hydroxyanisole, dibutyl hydroxytoluene, and tert-butylhydroquinone; in step S2, the amount ratio of polyurethane prepolymer, triethylamine, deionized and amino-terminated polysiloxane is 1-2g:1-1.5mL:10-15mL:0.5-1g; in step S3, the supporting layer material is nylon 6, and the temperatures of the six temperature sections of the multilayer co-extruder from the feed end to the discharge end are 110°C, 170°C, 225°C, 225°C, 225°C, and 225°C respectively.

[0012] Furthermore, in step S1, the method for preparing the composite polyester comprises the following steps:

[0013] A1. Place terephthalic acid, 1,4-butanediol, 1,6-hexanedioic acid and tetrabutyltitanium bromide in a twin-screw extruder in a nitrogen atmosphere, heat to 180-200° C., stir for 2-3 hours, melt extrude and granulate to obtain poly(butylene terephthalate-adipate);

[0014] A2. Add polybutylene adipate terephthalate, L-polylactic acid and modified graphene into a twin-screw extruder, melt-extrude and granulate to obtain a composite resin.

[0015] Furthermore, in step A1, the usage ratio of phthalic acid, 1,4-butanediol, 1,6-hexanedioic acid and tetrabutyltitanium bromide is 1.5-2g:2-3g:1.5-2g:0.5-1g; in step A2, the usage ratio of polybutylene adipate terephthalate, left-handed polylactic acid and modified graphene is 7-10g:3-4g:0.5-1g.

[0016] Furthermore, the preparation method of the modified graphene is:

[0017] B1. Disperse the graphene and ethanol solution in a three-necked flask, add ammonia water to adjust the pH value of the system to 8-9, and obtain a mixed alkali solution;

[0018] B2. Evenly mix the ethyl orthosilicate solution and KH-560, slowly drip into the mixed alkali solution, heat to 60-80°C, stir and reflux for 12h, and post-treat to obtain modified graphene.

[0019] Furthermore, in step B1, the ethanol solution is composed of ethanol and purified water in a volume ratio of 90-95:5-10, the ratio of graphene to the ethanol solution is 0.1g:10mL, and the tetraethyl orthosilicate solution in step B2 is composed of tetraethyl orthosilicate and ethanol in a volume ratio of 1:2.5, and the amount ratio of the tetraethyl orthosilicate solution to KH-560 is 10-15mL:1-1.5g. The post-treatment includes: cooling the refluxed solution to room temperature, centrifuging and precipitating, washing the precipitate with ethanol and water 1-2 times in sequence and then draining it, transferring the filter cake to a dryer at a temperature of 100-120°C for drying, and vacuum drying to constant weight to obtain modified graphene.

[0020] Furthermore, in step S2, the preparation method of the polyurethane prepolymer is: placing polycarbonate diol in a three-necked flask heated to 70-100° C., protecting with nitrogen, stirring at a speed of 300-400 r / min for 40-50 min, then adding 1,4-butanediol, isophorone diisocyanate, N-methylpyrrolidone and functional auxiliary materials, stirring for 0.5-1 h, and obtaining a polyurethane prepolymer.

[0021] Furthermore, the dosage ratio of the polycarbonate diol, 1,4-butanediol, isophorone diisocyanate, N-methylpyrrolidone and functional auxiliary materials is 1-2g:1-1.5g:0.5-2g:10-20mL:0.5-1g, and the functional auxiliary materials are composed of a plasticizer, a catalyst and a chain extender in a dosage ratio of 1-3g:0.5-1g:2-5g, the plasticizer is dibutyl phthalate, and the chain extender is dihydroxymethyl propionic acid.

[0022] Furthermore, the dimethylolpropionic acid solution is prepared by dimethylolpropionic acid and N-methylpyrrolidone in a dosage ratio of 1-2g:10-20mL, the dosage ratio of the polycarbonate diol, 1,4-butanediol, isophorone diisocyanate, N-methylpyrrolidone and functional auxiliary materials is 1-2g:1-1.5g:0.5-2g:10-20mL:0.5-1g, the functional auxiliary materials are composed of a plasticizer, a catalyst and a chain extender in a dosage ratio of 1-3g:0.5-1g:2-5g, the plasticizer is dibutyl phthalate, the catalyst is dibutyl tin dilaurate, and the chain extender is dimethylolpropionic acid.

[0023] The present invention has the following beneficial effects:

[0024] 1. When preparing a high-barrier cling film for food preservation packaging, the present invention adds barrier layer mixed particles, adhesive layer mixed particles and support layer materials into a multi-layer co-extruder, melts and extrudes, injects into a multi-layer co-extrusion film machine, and undergoes inflation molding to obtain a high-barrier cling film having five layers from top to bottom, namely, support layer 1, adhesive layer 1, barrier layer 1, adhesive layer 2 and support layer 2; the amino-terminated polysiloxane introduced into the adhesive layer contains Si-O bonds, which are polar bonds and have certain ionicity and free rotation. This property enables the entire siloxane molecular chain to rotate freely around the Si-O bond and has flexibility. At the same time, the intermolecular force of siloxane molecules is not strong, so that it has a smaller surface energy and a weaker surface tension, provides more cross-linking sites, and can well undergo intermolecular polymerization with the hydroxyl group and the carboxyl group in the barrier layer, thereby increasing the intermolecular force and making the cross-linking between the adhesive layer and the barrier layer tighter, thereby improving the gas barrier and water vapor barrier properties of the cling film and reducing the oxygen permeability and water vapor permeability.

[0025] 2. The barrier layer of the cling film prepared by the present invention undergoes esterification reaction and polymerization reaction when preparing poly(butylene adipate terephthalate), generating block and branched polymers, making the polyester molecular chains closer, reducing the free volume, reducing the gas diffusion resistance, and reducing the oxygen permeability; the left-handed polylactic acid itself has strong crystallinity, and its molecular chains form an ordered and dense arrangement structure in the solid state, which reduces the water vapor permeability of the cling film and enhances the tensile strength and toughness of the cling film; the siloxy group in the modified graphene can form chemical bonds with the carboxyl and hydroxyl groups in poly(butylene adipate terephthalate) and the left-handed polylactic acid, thereby improving the compactness of the composite polyester molecules, improving the interface compatibility, and improving the tensile strength and toughness of the cling film; and the poly(butylene adipate terephthalate) is an aromatic and aliphatic copolymer with good biodegradability and a wide source of raw materials, thereby reducing the cost and pollution of the cling film.

[0026] 3. When preparing the polyurethane adhesive layer, the present invention selects low molecular weight polycarbonate diol as the soft segment. Compared with general polyester polyols, the polycarbonate diol contains a large number of carbonate bonds in the molecule and has higher cohesive energy, which further improves the tensile strength of the cling film. In addition, the polyurethane molecule contains an aliphatic ring structure, which enhances the interaction ability within the molecule and makes the synthesized polyurethane adhesive have excellent hydrolysis resistance, wear resistance and oxidation resistance. The carboxyl group in the hydrophilic chain extender dimethylol propionic acid can react with the hydrogen ions of water to form hydrogen bonds, which improves the cohesive force between the polyurethane molecular segments and further improves the hydrophobicity and tensile strength of the cling film. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] The nylon P6 used in the present invention is made by Dongguan Wanshixin Plastic Raw Materials Co., Ltd., with a specification of 25KG and a model of P6-G50 HMNC003;

[0029] The amino-terminated polysiloxane used in the present invention is obtained from Wuhan Huaxiang Kejie Biotechnology Co., Ltd. and has a molecular weight of 1,000.

[0030] The L-polylactic acid used in the present invention is obtained from Wuhan Smik Biotechnology Co., Ltd., with an active ingredient content of 99%, a molecular weight of 100,000, and a CAS number of 26811-96-1;

[0031] The polycarbonate diol used in the present invention is obtained from Wuhan Lanabai Pharmaceutical Chemical Co., Ltd., with an active ingredient content of 99%, a molecular weight of 1000, and a CAS number of 24937-06-2.

[0032] Example 1

[0033] The method for preparing the high barrier cling film for food fresh-keeping packaging of this embodiment comprises the following steps:

[0034] S1. Preparation of barrier layer mixed particles

[0035] Weigh: 1 g of graphene and 100 mL of ethanol solution are placed in a three-necked flask for dispersion, and ammonia water is added to adjust the pH of the system to 8 to obtain a mixed alkali solution;

[0036] Weigh: 1 mL of tetraethyl orthosilicate, 2.5 mL of ethanol and 0.4 g of KH-560, mix well, slowly drip into the mixed alkali solution, heat to 60-80°C, stir and reflux for 12 hours, and post-treat to obtain modified graphene;

[0037] Weigh: 6 g of terephthalic acid, 8 g of 1,4-butanediol, 6 g of 1,6-hexanodioic acid and 2 g of tetrabutyltitanium bromide, place in a twin-screw extruder in a nitrogen atmosphere, heat to 180-200° C., stir for 2-3 hours, melt extrude, and granulate to obtain poly(butylene terephthalate-adipate);

[0038] Weigh: 14 g of poly (butylene adipate terephthalate), 6 g of L-polylactic acid and 1 g of modified graphene, add them into a twin-screw extruder, melt extrude and granulate to obtain a composite resin;

[0039] Weigh: 50g of composite polyester and 17.5g of auxiliary additives are added into a twin-screw extruder for melt extrusion, and after cooling, they are added into a single-screw granulator for cutting to obtain barrier layer mixed granules;

[0040] S2. Preparation of bonding layer mixed particles

[0041] Weigh: 5 g of polycarbonate diol, 7.5 g of 1,4-butanediol, 2.5 g of isophorone diisocyanate, 50 mL of N-methylpyrrolidone and 2.5 g of functional auxiliary materials, place in a three-necked flask heated to 80° C., protect with nitrogen, stir at a speed of 350 r / min for 1 h to obtain a polyurethane prepolymer;

[0042] Weigh: put 2g of polyurethane prepolymer, 2mL of triethylamine, 20mL of deionized water and 1g of terminal amino polysiloxane in a three-necked bottle, heat to 30-40°C, stir for 1-1.5h, heat and cure, melt and extrude in a twin-screw extruder, add to a single-screw granulator for cutting after cooling, and obtain bonding layer mixed particles.

[0043] S3. Prepare cling film

[0044] The barrier layer mixed particles, bonding layer mixed particles and support layer materials are added into a multi-layer co-extrusion extruder, the temperatures of the six temperature sections from the feed end to the discharge end are 110°C, 170°C, 225°C, 225°C, 225°C, 225°C, the spindle speed is set to 20r / min, melt extrusion is injected into a multi-layer co-extrusion film machine, and after inflation molding, a high-barrier cling film is obtained which is a five-layer composite of support layer one, bonding layer two, barrier layer one, bonding layer two and support layer two from top to bottom.

[0045] Example 2

[0046] The method for preparing the high barrier cling film for food fresh-keeping packaging of this embodiment comprises the following steps:

[0047] S1. Preparation of barrier layer mixed particles

[0048] Weigh: 1.2 g of graphene and 120 mL of ethanol solution are placed in a three-necked flask for dispersion, and ammonia water is added to adjust the pH of the system to 8 to obtain a mixed alkali solution;

[0049] Weigh: 1.1 mL of tetraethyl orthosilicate, 3 mL of ethanol and 0.6 g of KH-560, mix well, slowly drip into the mixed alkali solution, heat to 60-80°C, stir and reflux for 12 hours, and post-treat to obtain modified graphene;

[0050] Weigh: 6.5 g of terephthalic acid, 8.9 g of 1,4-butanediol, 7.0 g of 1,6-hexanediol and 2.2 g of tetrabutyltitanium bromide, place in a twin-screw extruder in a nitrogen atmosphere, heat to 180-200° C., stir for 2-3 hours, melt extrude, and granulate to obtain poly(butylene terephthalate-adipate);

[0051] Weigh: 14.2 g of poly(butylene adipate terephthalate), 6.1 g of L-polylactic acid and 1 g of modified graphene, add them into a twin-screw extruder, melt extrude and granulate to obtain a composite resin;

[0052] Weigh: 52g of composite polyester and 18.3g of auxiliary additives are added into a twin-screw extruder for melt extrusion, and after cooling, they are added into a single-screw granulator for cutting to obtain barrier layer mixed granules;

[0053] S2. Preparation of bonding layer mixed particles

[0054] Weigh: 5.4 g of polycarbonate diol, 8.2 g of 1,4-butanediol, 3.1 g of isophorone diisocyanate, 54 mL of N-methylpyrrolidone and 3.1 g of functional auxiliary materials, place in a three-necked flask heated to 80° C., protect with nitrogen, stir at a speed of 350 r / min for 1 h to obtain a polyurethane prepolymer;

[0055] Weigh: put 2.3g of polyurethane prepolymer, 3mL of triethylamine, 24mL of deionized water and 1g of terminal amino polysiloxane in a three-necked bottle, heat to 30-40°C, stir for 1-1.5h, heat and cure, melt and extrude in a twin-screw extruder, add to a single-screw granulator for cutting after cooling, and obtain bonding layer mixed particles.

[0056] S3. Prepare cling film

[0057] The barrier layer mixed particles, bonding layer mixed particles and support layer materials are added into a multi-layer co-extrusion extruder, the temperatures of the six temperature sections from the feed end to the discharge end are 110°C, 170°C, 225°C, 225°C, 225°C, 225°C, the spindle speed is set to 20r / min, melt extrusion is injected into a multi-layer co-extrusion film machine, and after inflation molding, a high-barrier cling film is obtained which is a five-layer composite of support layer one, bonding layer two, barrier layer one, bonding layer two and support layer two from top to bottom.

[0058] Example 3

[0059] The method for preparing the high barrier cling film for food fresh-keeping packaging of this embodiment comprises the following steps:

[0060] S1. Preparation of barrier layer mixed particles

[0061] Weigh: 1.5 g of graphene and 150 mL of ethanol solution are placed in a three-necked flask for dispersion, and ammonia water is added to adjust the pH of the system to 9 to obtain a mixed alkali solution;

[0062] Weigh: 2 mL of tetraethyl orthosilicate, 3 mL of ethanol and 0.8 g of KH-560, mix them evenly, drip them into the mixed alkali solution at a rate of 1.5 mL / min, heat to 60-80°C, stir and reflux for 12 h, and post-treat to obtain modified graphene;

[0063] Weigh: 7 g of terephthalic acid, 9.1 g of 1,4-butanediol, 7.2 g of 1,6-hexanodioic acid and 2.5 g of tetrabutyltitanium bromide, place in a twin-screw extruder in a nitrogen atmosphere, heat to 180-200° C., stir for 2-3 h, melt extrude, and granulate to obtain poly(butylene terephthalate-adipate);

[0064] Weigh: 14.5 g of poly(butylene adipate terephthalate), 6.5 g of L-polylactic acid and 1.5 g of modified graphene, add them into a twin-screw extruder, melt extrude and granulate to obtain a composite resin;

[0065] Weigh: 54g of composite polyester and 19.3g of auxiliary additives are added to a twin-screw extruder for melt extrusion. After cooling, they are added to a single-screw granulator for cutting to obtain barrier layer mixed granules.

[0066] S2. Preparation of bonding layer mixed particles

[0067] Weigh: 6.1 g of polycarbonate diol, 8.7 g of 1,4-butanediol, 3.5 g of isophorone diisocyanate, 58 mL of N-methylpyrrolidone and 3.5 g of functional auxiliary materials, place in a three-necked flask heated to 80° C., protect with nitrogen, stir at a speed of 350 r / min for 1 h to obtain a polyurethane prepolymer;

[0068] Weigh: put 2.5g of polyurethane prepolymer, 4mL of triethylamine, 26mL of deionized water and 1.5g of terminal amino polysiloxane in a three-necked bottle, heat to 30-40°C, stir for 1-1.5h, heat and cure, melt and extrude in a twin-screw extruder, add to a single-screw granulator for cutting after cooling, and obtain bonding layer mixed particles.

[0069] S3. Prepare cling film

[0070] The barrier layer mixed particles, bonding layer mixed particles and support layer materials are added into a multi-layer co-extrusion extruder, the temperatures of the six temperature sections from the feed end to the discharge end are 110°C, 170°C, 225°C, 225°C, 225°C, 225°C, the spindle speed is set to 20r / min, melt extrusion is injected into a multi-layer co-extrusion film machine, and after inflation molding, a high-barrier cling film is obtained which is a five-layer composite of support layer one, bonding layer two, barrier layer one, bonding layer two and support layer two from top to bottom.

[0071] Comparative Example 1

[0072] The difference between this comparative example and Example 1 is that step S1 is eliminated, and the barrier layer mixed particles of step S1 are replaced by an equal amount of mixed particles consisting of poly(butylene terephthalate adipate) and poly(lactic acid) in a weight ratio of 1:1.

[0073] Comparative Example 2

[0074] The difference between this comparative example and Example 1 is that step S2 is eliminated, and the bonding layer mixed particles in step S2 are replaced by an equal amount of polyurethane prepolymer particles.

[0075] Comparative Example 3

[0076] The difference between this comparative example and Example 1 is that no modified graphene is added in step S1.

[0077] Performance Testing:

[0078] The oxygen permeability and water vapor permeability of the high barrier cling film samples prepared in Examples 1-3 and Comparative Examples 1-3 were measured with reference to the standard GB / T 40266-2021 "General Rules for Quality of Oxide Barrier Transparent Plastic Composite Films and Bags for Food Packaging";

[0079] The tensile strength and elongation at break of the high barrier cling film samples prepared in Examples 1-3 and Comparative Examples 1-3 were measured with reference to the standard GB / T 528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber". The specific test results are shown in Table 1:

[0080] Table 1-Performance test data of each sample

[0081]

[0082]

[0083] Data Analysis:

[0084] The data in Table 1 are compared and analyzed. The oxygen permeability of the cling film prepared by the present invention is reduced to 0.11 cm 3 ·(m 2 ·24h·0.1MPa) -1 , the water vapor transmission rate is reduced to 0.06g·(m 2 24h) -1 , the tensile strength reached 32.1MPa, and the elongation at break reached 260.0%;

[0085] By comparing the data of Example 3 and Comparative Example 1, it can be found that the oxygen permeability of the cling film is significantly increased, indicating that in the reaction process of preparing polybutylene adipate terephthalate, the alcohol compound and the acid compound undergo esterification reaction and polymerization reaction to generate block and branched polymers, making the molecular chains closer, the free volume smaller, and the gas diffusion resistance smaller, thereby reducing the oxygen permeability; by comparing the data of Example 3 and Comparative Example 1, it can be found that the water vapor permeability of the cling film is significantly increased, indicating that the left-handed polylactic acid has strong crystallinity, which makes its molecular chain form an orderly arrangement structure in the solid state, and the crystalline structure is relatively dense, making it difficult for water vapor to pass through the film layer, and having low water vapor permeability;

[0086] By comparing the data of Example 3 and Comparative Example 2, it can be found that the tensile strength and elongation at break of the cling film are significantly reduced, indicating that the binder uses a low molecular weight polycarbonate diol as the soft segment. Compared with general polyester polyols, its molecule contains a large number of carbonate bonds and has a higher cohesive energy, which makes the synthesized polyurethane adhesive have a high mechanical strength, thereby improving the tensile strength and elongation at break of the cling film;

[0087] By comparing the data of Example 3 and Comparative Example 3, it can be found that the oxygen permeability, tensile strength and elongation at break of the cling film are significantly reduced, indicating that in the barrier layer, the siloxy group in the modified graphene can form chemical bonds with the carboxyl group and hydroxyl group in poly(butylene adipate terephthalate) and poly(lactic acid), thereby improving the compactness of the composite polyester molecules, improving the interfacial compatibility, and improving the oxygen permeability, tensile strength and toughness of the cling film;

[0088] The present invention is to prepare a high-barrier cling film for food preservation packaging by co-extruding a barrier layer, an adhesive layer and a support layer, which not only effectively improves the barrier performance of the cling film to water vapor and oxygen, but also improves its tensile performance.

[0089] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0090] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0091] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a high barrier cling film for food fresh-keeping packaging, characterized in that: The following steps are involved: S1, adding the composite polyester and auxiliary additives into a twin-screw extruder for melt extrusion, and after cooling, adding them into a single-screw granulator for cutting to obtain barrier layer mixed granules; S2, placing polyurethane prepolymer, triethylamine, deionized water and amino-terminated polysiloxane in a three-necked bottle, heating to 30-40°C, stirring for 1-1.5 hours, heating and curing, and then melt-extruded in a twin-screw extruder, and after cooling, adding to a single-screw granulator for cutting to obtain bonding layer mixed particles; S3. Add barrier layer mixed particles, bonding layer mixed particles and support layer materials into a multi-layer co-extrusion extruder, melt extrude, inject into a multi-layer co-extrusion film machine, and undergo inflation molding to obtain a high-barrier cling film composed of five layers from top to bottom, namely support layer 1, bonding layer 1, barrier layer 1, bonding layer 2 and support layer 2.

2. The method for preparing a high barrier cling film for food fresh-keeping packaging according to claim 1, characterized in that: In step S1, the weight ratio of the composite polyester and the auxiliary additive is 10-15:3.5-7; in step S2, the amount ratio of the polyurethane prepolymer, triethylamine, deionized water and terminal amino polysiloxane is 1-2g:1-1.5mL:10-15mL:0.5-1g; in step S3, the support layer material is nylon 6, and the temperatures of the six temperature zones from the feed end to the discharge end of the multilayer co-extruder are 110°C, 170°C, 225°C, 225°C, 225°C, 225°C, and the spindle speed of the multilayer co-extruder is 20r / min.

3. The method for preparing a high barrier cling film for food fresh-keeping packaging according to claim 1, characterized in that: In step S1, the method for preparing the composite polyester comprises the following steps: A1. Place terephthalic acid, 1,4-butanediol, 1,6-hexanedioic acid and tetrabutyltitanium bromide in a twin-screw extruder in a nitrogen atmosphere, heat to 180-200° C., stir for 2-3 hours, melt extrude and granulate to obtain poly(butylene terephthalate-adipate); A2. Add polybutylene adipate terephthalate, L-polylactic acid and modified graphene into a twin-screw extruder, melt-extrude and granulate to obtain a composite resin.

4. The method for preparing a high barrier cling film for food fresh-keeping packaging according to claim 3, characterized in that: In step A1, the amount ratio of phthalic acid, 1,4-butanediol, 1,6-hexanedioic acid and tetrabutyltitanium bromide is 1.5-2g:2-3g:1.5-2g:0.5-1g; in step A2, the amount ratio of polybutylene terephthalate adipate, left-handed polylactic acid and modified graphene is 7-10g:3-4g:0.5-1g.

5. The method for preparing the high barrier cling film for food fresh-keeping packaging according to claim 3, characterized in that: The preparation method of the modified graphene is: B1. Disperse the graphene and ethanol solution in a three-necked flask, add ammonia water to adjust the pH of the system to 8-9, and obtain a mixed alkali solution. B2. Evenly mix the ethyl orthosilicate solution and KH-560, slowly drip into the mixed alkali solution, heat to 60-80°C, stir and reflux for 12h, and post-treat to obtain modified graphene.

6. The method for preparing the high barrier cling film for food fresh-keeping packaging according to claim 5, characterized in that: In step B1, the ethanol solution is composed of ethanol and purified water in a volume ratio of 90-95:5-10, the amount ratio of the graphene and the ethanol solution is 0.1g:10mL, the tetraethyl orthosilicate solution in step B2 is composed of tetraethyl orthosilicate and ethanol in a volume ratio of 1:2.5, the amount ratio of the tetraethyl orthosilicate solution and KH-560 is 10-15mL:1-1.5g, and the post-treatment includes: cooling the refluxed solution to room temperature, centrifuging and precipitating, washing the precipitate with ethanol and water 1-2 times in sequence and then draining, transferring the filter cake to a drying machine at a temperature of 100-120°C for drying, and vacuum drying to constant weight to obtain modified graphene.

7. The method for preparing a high barrier cling film for food fresh-keeping packaging according to claim 1, characterized in that: In step S2, the preparation method of the polyurethane prepolymer is as follows: polycarbonate diol is placed in a three-necked flask heated to 70-100° C., protected by nitrogen, stirred at a speed of 300-400 r / min for 40-50 min, and then 1,4-butanediol, isophorone diisocyanate, N-methylpyrrolidone and functional auxiliary materials are added, and stirred for 0.5-1 h to obtain a polyurethane prepolymer.

8. The method for preparing a high barrier cling film for food fresh-keeping packaging according to claim 7, characterized in that: The dosage ratio of the polycarbonate diol, 1,4-butanediol, isophorone diisocyanate, N-methylpyrrolidone and functional auxiliary materials is 1-2g:1-1.5g:0.5-2g:10-20mL:0.5-1g. The functional auxiliary materials are composed of a plasticizer, a catalyst and a chain extender in a dosage ratio of 1-3g:0.5-1g:2-5g. The plasticizer is dibutyl phthalate, the catalyst is dibutyl tin dilaurate, and the chain extender is dihydroxymethyl propionic acid.

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