Multilayer barrier film and preparation method and application thereof

Abstract

The invention relates to the field of films, and discloses a multilayer barrier film and a preparation method and application thereof, the multilayer barrier film takes a surface layer as a base layer, a middle layer at least comprises a barrier layer and a bonding layer, and the base layer is arranged in a manner that the bonding layer is bonded with the barrier layer; wherein the barrier layer contains polyglycolic acid with multimodal molecular weight distribution; and the bonding layer contains a polyglycolic acid block copolymer. The multilayer barrier film provided by the invention has high barrier performance, heat sealing strength and interlayer peel strength.

Description

Technical Field

[0001] The present invention relates to the field of thin film technology, and in particular to a multilayer barrier film and a preparation method and application thereof. Background Art

[0002] The levels of gases like oxygen and carbon dioxide significantly impact the quality of food and pharmaceutical storage. Therefore, high-barrier plastic packaging materials can effectively extend the shelf life and expiration date of these products. However, currently available high-barrier packaging films are still not fully biodegradable, contributing to the "white pollution" problem. Therefore, the development of fully biodegradable barrier packaging films has become a recent research hotspot.

[0003] Among currently known resins, polyglycolic acid (PGA, also known as polyglycolide or polyglycolic acid) not only possesses excellent biodegradability but also exceptional gas barrier properties. PGA's oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) are lower than those of common barrier materials such as ethylene vinyl alcohol copolymer (EVOH), polyvinylidene chloride (PVDC), polyethylene terephthalate (PET), and polyamide (PA). Its oxygen and water vapor barrier performance is 100 times greater than that of PET, and its barrier properties are less affected by ambient temperature.

[0004] However, existing PGA also has many disadvantages, such as low molecular weight and low melt strength at processing temperature, which makes it difficult to directly obtain thin films from pure PGA through the film blowing method. At the same time, the shortcomings of PGA itself, such as easy hydrolysis and poor toughness, make it difficult to use a single-layer PGA film directly. Therefore, considering the service life and mechanical properties, PGA is only used as a barrier layer, and the outer layer adopts a matrix resin with certain water-blocking and toughness as the base layer. In addition, because PGA is a highly polar polymer with high crystallinity, it has poor compatibility with other resins. When directly compounded with the base layer, the bonding performance is poor. The resulting film will delaminate and cannot meet the requirements of practical applications. Therefore, a bonding layer is usually required to improve the interlayer bonding.

[0005] CN101945749A (Kureha Co., Ltd., January 12, 2011) discloses a polyglycolic acid-based multilayer film. The method for preparing this multilayer film involves first obtaining a sequentially biaxially stretched monolayer polyglycolic acid film and then using this as a substrate to prepare a multilayer film. First, PGA has a high melting point, high crystallinity, and poor heat-sealing properties. Therefore, without a bonding layer, a PGA layer is difficult to bond to other layers. Second, the process of first preparing a monolayer film and then laminating it into a multilayer film is prone to residual oxygen and water vapor between the layers. PGA itself is easily hydrolyzed, resulting in a short lifespan for the multilayer film obtained using this process. Finally, because the melt strength of the PGA used is low, the PGA film is obtained by a casting method, which also requires biaxial stretching and multilayer lamination. This method requires significant equipment investment, low production efficiency, and high production costs.

[0006] CN115433383B (Nantong University, 2022.09.05) discloses a biodegradable multilayer polylactic acid barrier film and its preparation method. The invention first obtains CDA g PDLA graft copolymer by grafting D-lactide and diacetyl cellulose, and then prepares a multilayer barrier film using polylactic acid and CDA g PDLA as raw materials. However, since the barrier function of the invention is polylactic acid, the water vapor permeability is 39.81~45.13g / (m 2 ·24h), oxygen permeability is 178.56~358.65cm 3 / (m 2 ·24h·0.1MPa), the barrier property is still poor and it is difficult to meet the application fields that require high barrier.

[0007] CN115891365A (Wanhua Chemical Group Co., Ltd., October 27, 2022) discloses a degradable barrier film with antibacterial properties and controllable degradation rate and its preparation method. The PGA barrier layer in this invention is not pure PGA, but a blend containing other degradable resins. Therefore, its oxygen barrier performance is not as good as pure PGA, and its oxygen permeability is as low as 12cm 3 / (m 2 · 24h · 0.1MPa). In addition, the actual thickness of the resulting film and the interlayer adhesion are not disclosed. Due to the poor compatibility between PGA and other biodegradable resins, the adhesion between the PGA layer and other layers in the preparation of multilayer films is poor. Generally, a special adhesive layer is required to improve the interlayer peeling force to meet practical requirements.

[0008] CN116512721A (China Shenhua Coal-to-Liquid Chemical Co., Ltd., 2023.05.19) discloses a high-barrier PBAT / PGA multilayer composite film. Since not only pure PGA is used as the barrier layer, but also the outer layer and adhesive layer also use a PBAT / PGA blend with a high PGA content, it has good barrier properties. However, due to the problem of fast hydrolysis rate of PGA, when the outer layer itself contains PGA, the resulting multilayer film will also have a faster hydrolysis rate, which in turn affects its lifespan. At the same time, PGA and polymers such as PBAT have poor compatibility, and the bonding effect is also average when it is prepared into an adhesive layer only by simple blending. In addition, the multilayer film of this invention is made by casting rather than blow molding. Compared with the casting process, blow molding has the advantages of higher production efficiency, lower equipment investment, lower material loss, etc., and has a lower cost, which is more suitable for large-scale industrial amplification.

[0009] In summary, while polyglycolic acid (PGA) possesses the best gas barrier properties of all biodegradable plastics, making it a preferred material for applications requiring high barrier properties, PGA itself suffers from inherent issues such as low melt strength, poor heat sealability, susceptibility to hydrolysis, and poor compatibility (adhesion) with other biodegradable plastics. This makes the coextrusion of PGA with other biodegradable plastics in multi-layer blown film production very difficult and lacks practicality and versatility. Summary of the Invention

[0010] The purpose of the present invention is to overcome the problems of low melt strength, poor heat sealing, easy hydrolysis, compatibility (adhesion) with other biodegradable plastics and difficulty in film blowing of PGA films in the prior art, and to provide a multilayer barrier film and its preparation method and application. The film has excellent barrier properties, interlayer peel strength and heat sealing strength.

[0011] In order to achieve the above-mentioned objectives, the first aspect of the present invention provides a multilayer barrier film, wherein the surface layer is a base layer, the middle layer includes at least a barrier layer and an adhesive layer, and the base layer is arranged by bonding the barrier layer to the adhesive layer; wherein the barrier layer contains polyglycolic acid with a multimodal molecular weight distribution; and the adhesive layer contains a polyglycolic acid block copolymer.

[0012] A second aspect of the present invention provides a method for preparing the multilayer barrier film of the present invention, comprising: co-extruding a blend containing a degradable resin as a base layer, a blend containing polyglycolic acid with a multimodal molecular weight distribution as a barrier layer, and a blend containing a polyglycolic acid block copolymer as a tie layer, or extruding them separately, followed by a step including film formation.

[0013] The third aspect of the present invention provides applications of the multi-layer barrier film of the present invention in food packaging bags, agricultural films, medical packaging, and electronic fields.

[0014] Through the above technical solution, the base layer, barrier layer and adhesive layer of the multi-layer barrier film are designed in the present invention. The base layer has good physical and mechanical properties, molding and processing performance, and heat sealing properties, and can extend the functional life of the barrier layer. At the same time, the adhesive layer containing the polyglycolic acid block copolymer, the base layer containing the degradable resin, and the barrier layer containing the polyglycolic acid with a multimodal molecular weight distribution have better physical volume expansion, which can better increase the adhesion of the multi-layer barrier film and improve the interlayer peel strength, so that the multi-layer barrier film of the present invention has high barrier performance, heat sealing strength and interlayer peel strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a GPC curve diagram of the polyglycolic acid particles in Example 1, Example 4, and Comparative Example 2;

[0016] Figure 2 This is a flow chart of preparing a composite film in a multi-layer co-extrusion blown film preparation device with a uniaxial stretching device;

[0017] Figure 3 This is a flow chart of preparing a composite film in a multi-layer co-extrusion cast film preparation device with a uniaxial stretching device;

[0018] Figure 4 Schematic diagram of the structure of the fully biodegradable composite membrane in Example 1.

[0019] Description of Reference Numerals

[0020] 10a, 10b, 10c: Hoppers 20a, 20b, 20c: Single-screw extruders

[0021] 30a, 30b, 30c: melt pumps 40a: feed pipe

[0022] 40b: Coextrusion distributor 50a: Film blowing die

[0023] 50b: air ring 50c: casting die

[0024] 60: Herringbone splint 70a: Clamp roller

[0025] 80: Unidirectional stretching device 90: Winding roller

[0026] 01a: Membrane vesicle 01b: Precursor membrane

[0027] 01c: Film after stretching DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0029] The testing methods for the physicochemical parameters and other characteristics of the polymers / products of the present invention are as follows:

[0030] The melt strength of the present invention can be tested using conventional testing methods in the art, for example, on a Rosand RH7 high-pressure capillary rheometer from Malvern Panalytical, China. The test is performed using a Haul Off model (diameter: 2.0 mm, length: 20 mm), a barrel push rod downward speed of 15 mm / min, a test temperature of 235°C, an initial draw-down speed of 3 mm / min, a final draw-down speed of 50 mm / min, and a ramp-up time of 3 minutes.

[0031] The melt flow rate of the present invention can be tested by conventional testing methods in the art, for example, on a CEAST MF20 melt flow rate tester from Instron Corporation of the United States, with a test temperature of 230° C., a load of 2.16 kg, and a preheating time of 4 minutes.

[0032] The weight-average molecular weight, number of molecular weight distribution peaks, molecular weight distribution index and other parameters of each polymer in the present invention can be detected by gel permeation chromatography (GPC). Those skilled in the art can choose a visual testing method, for example: the testing instrument is a PL-GPC50 gel permeation chromatograph produced by Angilent, USA, and the processing software is GPCoffline. During the test, the mobile phase is hexafluoroisopropanol containing 5 mmol / L sodium trifluoroacetate, the flow rate is 1 mL / min, the column temperature is 40°C, the injection volume is 100 μL, the standard sample is PMMA, and the sample concentration is 1 mg / mL.

[0033] The number of layers and thickness of each layer in the present invention can be measured and characterized by photographing a cross-section of the multilayer film using an optical microscope or a scanning electron microscope, specifically a Japanese HIROX KH-1300M 3D video microscope. The film is then secured with a homemade film fixture and cut with a blade. The cross-section is then observed at a magnification of 400x, and the thickness is measured using the software's built-in measurement tool.

[0034] The interlayer peel strength of the multilayer barrier film of the present invention was tested according to Method A in GB 8808-1988. The multilayer film was cut into strips 15 mm wide and 200 mm long. After peeling off a section by 50 mm, a tensile test was performed on an Instron 3344 material testing machine. The unpeeled section formed a T-shape in the direction of stretching, and the stretching rate was 300 mm / min.

[0035] The heat sealing strength of the multi-layer barrier film of the present invention refers to QB / T2358-1998, with a sample width of 15 mm, a clamp spacing of 50 mm, and a test speed of 300 mm / min.

[0036] The oxygen barrier properties of the multi-layer barrier film of the present invention were tested using a MOCON OX-TRAN Model 2 / 22 oxygen transmission rate tester, specifically in accordance with international standard ISO 15105-2. Film samples were cut using a circular sampler and their thickness was measured. High-vacuum sealant was applied along the sealing ring on one side of the sample, and the sample was secured in a test chamber. The test temperature was 23°C and the relative humidity (RH) was 65%.

[0037] The water vapor barrier properties of the multilayer barrier film of the present invention were tested using a MOCON PERMATRAN-W Model 3 / 61 water vapor transmission rate tester, in accordance with the international standard ISO 15106-2, using an infrared detector method. Circular film samples were taken with a sampler and their thickness measured. The test temperature was 38°C, the humidity was 90%, and the pressure was 1 standard atmosphere (atm). The test lasted for 24 hours.

[0038] As used herein, the term "degradable" refers to biodegradability (i.e., the ability to biodegrade), specifically referring to degradation of a material due to biological activity. This ecological term is readily understood by those skilled in the art. According to a preferred embodiment of the present invention, the multi-layer barrier film obtained by the present invention exhibits a relative biodegradability of no less than 90%, in accordance with national standard GB / T 1010-2021.

[0039] A first aspect of the present invention provides a multilayer barrier film, wherein the surface layer is a base layer, the intermediate layer includes at least a barrier layer and an adhesive layer, and the base layer is bonded to the barrier layer by the adhesive layer; wherein the barrier layer contains polyglycolic acid with a multimodal molecular weight distribution; and the adhesive layer contains a polyglycolic acid block copolymer.

[0040] The multilayer barrier film of the present invention has excellent water vapor barrier properties and oxygen barrier properties, and the polyglycolic acid block copolymer contained in the adhesive layer has physical compatibility with the degradable resin and the multimodal molecular weight distribution polyglycolic acid, so that the layers have high interlayer peel strength. At the same time, the multilayer barrier film also has excellent heat sealing strength.

[0041] According to a preferred embodiment of the present invention, the multimodal molecular weight distribution polyglycolic acid is a homogeneous continuous phase. Using the above embodiment, the multilayer barrier film has high barrier properties and heat sealing strength.

[0042] The homogeneous continuous phase in the present invention means that the volume proportion of its main phase is not less than 95%, preferably not less than 99%, and its phase structure is continuous. The phase structure can be measured by methods well known in the art, for example: after the sample is quenched at low temperature, its cross section is observed by scanning electron microscopy.

[0043] According to a preferred embodiment of the present invention, the multimodal molecular weight distribution polyglycolic acid comprises a polyglycolic acid graft copolymer and a polyglycolic acid homopolymer. Using this embodiment, the multilayer barrier film exhibits performance far superior to films prepared using conventional polyglycolic acid blends containing a discontinuous polyglycolic acid phase.

[0044] According to a preferred embodiment of the present invention, the main chain of the polyglycolic acid graft copolymer comprises: a grafting structural unit represented by formula (I1); optionally a polyvinyl alcohol structural unit represented by formula (I2); optionally a polyethylene structural unit represented by formula (I3); optionally a polyvinyl acetate structural unit represented by formula (I4);

[0045]

[0046] The side chain of the polyglycolic acid graft copolymer contains a glycolic acid structural unit as shown in formula (I5),

[0047]

[0048] In the present invention, * in the structural unit or structural segment represents a connection site. For example, in the polyglycolic acid graft copolymer, the grafting structural unit represented by formula (I1) and the glycolic acid structural unit represented by formula (I5) are connected through the connection sites represented by their respective *.

[0049] In the present invention, "optionally" means that it may be contained or not contained depending on the purpose of the present invention.

[0050] The barrier film according to the present invention using the above-described embodiment has excellent barrier properties and further excellent adhesion between layers.

[0051] According to a preferred embodiment of the present invention, the sum of the number x of grafting structural units, the number y2 of polyvinyl alcohol structural units, and the number y1 of polyethylene structural units z and / or polyvinyl acetate structural units is not less than 50, preferably 50 to 6000, and more preferably 200 to 2500.

[0052] In the present invention, the sum of x+y1+y2+z is generally the degree of polymerization of the main chain, which can be calculated by the number average molecular weight of the raw material providing the main chain structure, and the ratio of the polyethylene structural unit to the polyvinyl alcohol structural unit is calculated by the integrated area of the corresponding peak of the nuclear magnetic hydrogen spectrum.

[0053] According to the present invention, as long as the purpose of the present invention can be achieved, the selection range of the value of m is relatively wide. In a preferred embodiment of the present invention, the number m of glycolic acid structural units is not less than 50, preferably 50 to 1000.

[0054] In the present invention, m = (number average molecular weight of the polyglycolic acid graft copolymer - number average molecular weight of the raw material providing the backbone of the polyglycolic acid graft copolymer) / (x * molecular weight of the glycolic acid structural unit). If the polyglycolic acid having the multimodal molecular weight distribution of the present invention is obtained directly and consists entirely of polyglycolic acid graft copolymers, it can be first fully hydrolyzed, the initiator collected, the structure analyzed, and then tested using the above method. According to the examples described below, calculations show that the m values of the resulting polymers are all greater than 50.

[0055] According to a preferred embodiment of the present invention, the ratio of z to x+y1+y2+z is 0% to 50%.

[0056] According to a preferred embodiment of the present invention, the ratio of y1 to x+y1+y2 is 0% to 32%.

[0057] In the present invention, when z is 0, that is, the main chain of the polyglycolic acid graft copolymer does not contain polyethylene structural units, preferably when z is 0, the proportion of y1 to the sum of x+y1+y2 is 0.1% to 32%.

[0058] In the present invention, when z is not 0, that is, the main chain of the polyglycolic acid graft copolymer contains polyethylene structural units, the ratio of z to x+y1+y2+z is preferably 1% to 50%, preferably 20% to 45%, and the ratio of y1 to the sum of x+y1+y2 is preferably 0.1% to 6%.

[0059] According to the present invention, the structure of the main chain of the polyglycolic acid graft copolymer of the present invention can be random, block, or alternating. The specific form of the main chain is related to the raw materials and / or polymerization method of the structural units, and is generally random. In an exemplary embodiment, the general structural formula of the polyglycolic acid graft copolymer is shown in formula (I):

[0060]

[0061] According to the present invention, it can be understood that, in formula (I), when y1 is 0, the main chain of the polyglycolic acid graft copolymer is an ethylene-vinyl alcohol copolymer segment; when z is 0, the main chain of the polyglycolic acid graft copolymer is a polyvinyl alcohol segment; the above x+y1+y2+z is the degree of polymerization of the ethylene-vinyl alcohol copolymer and / or polyvinyl alcohol, which can be calculated by the number average molecular weight of the ethylene-vinyl alcohol copolymer and / or polyvinyl alcohol.

[0062] According to a preferred embodiment of the present invention, the polyglycolic acid homopolymer contains: glycolic acid structural units, and co-initiator structural units provided by a small molecule co-initiator containing hydroxyl or amino groups.

[0063] According to a preferred embodiment of the present invention, the number of glycolic acid structural units in the polyglycolic acid homopolymer is 50 to 5000, for example, 50, 100, 500, 1500, 2000, 3000, 4000, 5000, and any interval consisting of any two of the above values.

[0064] According to a preferred embodiment of the present invention, the coinitiator structural unit is as shown in formula (III),

[0065]

[0066] In formula (II1), M1, M2, ..., M i Each is an imino group, a secondary amino group or an ether bond, R is H or an alkane group or an aromatic hydrocarbon group with a molecular weight of 14 to 1000 g / mol; i is an integer not less than 1, preferably an integer between 1 and 6, for example, it can be 1, 2, 3, 4, 5, or 6.

[0067] According to a more preferred embodiment of the present invention, the general structural formula of the polyglycolic acid homopolymer is as shown in formula (II),

[0068]

[0069] In formula (II), n1, n2, ..., n i The sum is the number of glycolic acid structural units in the polyglycolic acid homopolymer, i, M1, M2, ..., M i The definitions of R are the same as those in formula (III).

[0070] In the present invention, n1, n2, ..., n i The sum of the values can be calculated by dividing the number average molecular weight of the polyglycolic acid homopolymer in the GPC results by the molecular weight of the repeating unit of the glycolic acid structural unit. According to the embodiments of the present invention, after calculation, n1, n2, ..., n i The sum of the values is greater than 100.

[0071] According to a preferred embodiment of the present invention, relative to 100 parts by mass of polyglycolic acid segments The multimodal molecular weight distribution polyglycolic acid contains 0.001 to 10 parts by weight of the main chain Contains 0.001 to 10 parts by mass Coinitiator structural unit.

[0072] According to a preferred embodiment of the present invention, relative to 100 parts by mass of polyglycolic acid segments The multimodal molecular weight distribution polyglycolic acid contains 0.01 to 1 parts by mass of the main chain Contains 0.01 to 1 parts by mass Coinitiator structural unit.

[0073] The various structural units / segments in the present invention can be detected using conventional methods in the art, or can be calculated based on the feed ratio of raw materials.

[0074] According to a preferred embodiment of the present invention, the content of the polyglycolic acid graft copolymer in the multimodal molecular weight distribution polyglycolic acid is 0.1% to 80% by mass, preferably 1% to 30% by mass.

[0075] According to a preferred embodiment of the present invention, in the polyglycolic acid having a multimodal molecular weight distribution, the content of the polyglycolic acid homopolymer is 20% to 99.9% by mass, preferably 70% to 99% by mass.

[0076] According to the present invention, multimodal molecular weight distribution polyglycolic acid means that the polyglycolic acid has multiple molecular weights with different molecular weights, each molecular weight corresponding to a peak. In a preferred embodiment, the multimodal molecular weight distribution polyglycolic acid contains 2 to 4 peaks, for example, 2, 3 or 4 peaks.

[0077] According to a preferred embodiment of the present invention, the weight-average molecular weight of the polyglycolic acid graft copolymer is 500,000 to 10 million g / mol, for example, it can be 500,000 g / mol, 1 million g / mol, 2 million g / mol, 3 million g / mol, 4 million g / mol, 4 million g / mol, 5 million g / mol, 6 million g / mol, 8 million g / mol, 10 million g / mol, and any interval range consisting of any two of the above values, preferably 1 million to 6 million g / mol.

[0078] According to a preferred embodiment of the present invention, the molecular weight polydispersity index of the polyglycolic acid graft copolymer is 1.01 to 3.0, for example, it can be 1.01, 1.1, 1.3, 1.5, 2.0, 2.3, 2.5, 3.0, and any interval range consisting of any two of the above values, preferably 1.05 to 1.5.

[0079] According to a preferred embodiment of the present invention, the weight-average molecular weight of the polyglycolic acid homopolymer is 50,000 to 350,000 g / mol, for example, 50,000 g / mol, 80,000 g / mol, 100,000 g / mol, 120,000 g / mol, 150,000 g / mol, 170,000 g / mol, 190,000 g / mol, 200,000 g / mol, 250,000 g / mol, 350,000 g / mol, and any interval range consisting of any two of the above values, preferably 100,000 to 200,000 g / mol.

[0080] According to a preferred embodiment of the present invention, the molecular weight polydispersity index of the polyglycolic acid homopolymer is 1 to 3, for example, it can be 1, 1.1, 1.4, 1.5, 1.6, 2.0, 2.3, 2.5, 2.9, 3.0, and any interval range consisting of any two of the above values, preferably 1.4 to 2.9.

[0081] According to a preferred embodiment of the present invention, the weight average molecular weight of the multimodal molecular weight distribution polyglycolic acid is 200,000 to 1.5 million g / mol, for example, it can be 200,000 g / mol, 250,000 g / mol, 270,000 g / mol, 300,000 g / mol, 400,000 g / mol, 500,000 g / mol, 800,000 g / mol, 1 million g / mol, 1.5 million g / mol, and any interval range consisting of any two of the above values, preferably 250,000 to 500,000 g / mol.

[0082] According to a preferred embodiment of the present invention, the molecular weight distribution index of the multimodal molecular weight distribution polyglycolic acid is 1.5 to 20.0, 1.5, 1.8, 2.0, 2.1, 3.1, 3.5, 4.0, 6.0, 8.0, 10.0, 12.5, 14.0, 15.0, 180, 19.5, 20.0, and any interval range consisting of any two of the above values, preferably 2.0 to 3.5.

[0083] According to a preferred embodiment of the present invention, the melt flow rate of the multimodal molecular weight distribution polyglycolic acid at 230°C / 2.16kg is not higher than 20.0g / 10min, preferably 0.5-10.0g / 10min, for example, it can be 0.5g / 10min, 1g / 10min, 2g / 10min, 3g / 10min, 4g / 10min, 5.5g / 10min, 6g / 10min, 7g / 10min, 8g / 10min, 9g / 10min, 9.9g / 10min, 10g / 10min, and any interval range consisting of any two of the above values.

[0084] According to a preferred embodiment of the present invention, the melt strength of the multimodal molecular weight distribution polyglycolic acid at 235°C is not less than 4 cN, preferably not less than 8 cN, for example, it can be 8 cN, 10 cN, 15 cN, 18 cN, 20 cN, 25 cN, and any interval range consisting of any two of the above values.

[0085] The multimodal molecular weight distribution polyglycolic acid in the present invention can be prepared by copolymerization. Preferably, the raw materials used in the preparation method can provide the corresponding structural units and structural segments of the polyglycolic acid graft copolymer and polyglycolic acid homopolymer in the multimodal molecular weight distribution polyglycolic acid.

[0086] According to a preferred embodiment of the present invention, the method for preparing the multimodal molecular weight distribution polyglycolic acid comprises: in the presence of a catalyst and optionally an antioxidant, providing a polyvinyl alcohol structural unit The monomers, ethylene-vinyl alcohol copolymer (and / or polyvinyl alcohol) and optionally a small molecule co-initiator are melt polymerized to obtain a multimodal molecular weight distribution polyglycolic acid.

[0087] According to a preferred embodiment of the present invention, when preparing polyglycolic acid with multimodal molecular weight distribution, the monomer is selected from at least one of methyl glycolate, glycolic acid and glycolide; more preferably glycolide.

[0088] According to a preferred embodiment of the present invention, the small molecule co-initiator is selected from a small molecule substance containing hydroxyl or amino groups with a boiling point greater than 160°C. Preferably, the molecular weight of the small molecule co-initiator is not greater than 1000 g / mol, preferably 60-300 g / mol. The small molecule co-initiators that can be listed include: aniline, benzylamine, p-phenylenediamine, m-phenylenediamine, hexamethylenediamine, dodecanediamine, phenol, hydroquinone, resorcinol, benzyl alcohol, ethylene glycol, butanediol, glycerol, serinol, pentaerythritol, leucinol, sorbitol, xylitol, and amino acids.

[0089] According to the present invention, when preparing polyglycolic acid with a multimodal molecular weight distribution, the catalyst can be used as long as it can achieve melt polymerization, and its specific type is not particularly limited. For example, the catalyst includes a compound or mixture based on at least one element of Sn, Bi, Mg, Al, Ca, Fe, Mn, Ti and Zn, such as dibutyltin oxide, stannous chloride, dibutyltin dilaurate, stannous octoate, bismuth trioxide, zinc acetate, etc.

[0090] According to the present invention, when preparing a multimodal molecular weight distribution polyglycolic acid, the specific selection of the type and amount of each raw material can be selected according to the amount of each segment / structural unit in the multimodal molecular weight distribution polyglycolic acid. Preferably, the amount of the ethylene-vinyl alcohol copolymer (and / or polyvinyl alcohol) is 0.001 to 10 parts by mass, preferably 0.01 to 1 part, relative to 100 parts of the monomer; preferably, the content of the ethylene segment in the ethylene-vinyl alcohol copolymer is 25 to 50 mol%, for example, 25 mol%, 35 mol%, 45 mol%, or 50 mol%. Preferably, the degree of polymerization of the ethylene-vinyl alcohol copolymer is 50 to 6000, preferably 300. ~2000, for example, it can be 300, 600, 1200, 1500, 2000; preferably, the melt flow rate of the ethylene-vinyl alcohol copolymer at 190°C / 2.16kg is 0.1-50g / 10min; the alcoholysis degree of polyvinyl alcohol is a known parameter of the raw material factory, and can also be detected by various detection methods in the field such as nuclear magnetic resonance and near infrared. Preferably, the alcoholysis degree of polyvinyl alcohol is 68% to 100%, for example, 68%, 70%, 88%, 95%, 99%, 100%; preferably, the amount of the small molecule co-initiator is 0.001 to 10 parts by mass relative to 100 parts of the monomer, preferably 0.01 to 1 part.

[0091] According to the present invention, when preparing polyglycolic acid with multimodal molecular weight distribution, the amount of catalyst used is preferably an amount that is conducive to the smooth progress of melt polymerization, preferably, by mass, relative to 100 parts of monomer, the amount of the catalyst used is 0.005 to 1 part, preferably 0.01 to 0.2 parts.

[0092] According to the present invention, when preparing polyglycolic acid with a multimodal molecular weight distribution, an antioxidant is optionally added, which means that an antioxidant may be added or not. Preferably, the amount of the antioxidant is 0 to 2 parts by mass, preferably 0.01 to 1 part by mass, relative to 100 parts of monomer (phr).

[0093] In the present invention, when preparing polyglycolic acid with a multimodal molecular weight distribution, the conditions of melt polymerization are not particularly limited as long as the purpose of the present invention can be achieved. The preferred melt polymerization temperature is 160 to 250°C, preferably 200 to 240°C; the preferred melt polymerization time is 0.5 to 60 minutes, preferably 1 to 10 minutes.

[0094] The melt polymerization in the present invention can be carried out in a conventional melt mixing device in the art, such as a kettle reactor, a tubular reactor (such as a single-screw extruder, a multi-screw extruder and a reciprocating single-screw extruder), an internal mixer, a Farrel continuous mixer, a Banbury mixer, etc. The melt polymerization can be carried out in a single melt mixing device or in multiple identical or different melt mixing devices.

[0095] According to a preferred embodiment of the present invention, the conditions for melt polymerization in a twin-screw extruder, preferably in a twin-screw extruder, include: a temperature of 160 to 250° C., preferably 200 to 240° C.; and / or a residence time of 0.5 to 60 min, preferably 1 to 10 min; and / or a screw speed of 5 to 300 rpm, preferably 40 to 150 rpm; and / or an aspect ratio of 30 to 80, preferably 40 to 70.

[0096] According to a preferred embodiment of the present invention, the polyglycolic acid block copolymer comprises polyglycolic acid structural units and polyester structural units. The polyglycolic acid block copolymer comprising polyglycolic acid structural units and polyester structural units in the aforementioned embodiment can achieve improved physical compatibility with the degradable resin and polyglycolic acid with a multimodal molecular weight distribution, thereby further enhancing the barrier properties, interlayer peel strength, and heat seal strength of the multilayer barrier film.

[0097] In the present invention, the specific content of the polyglycolic acid structural unit and the polyester structural unit in the polyglycolic acid block copolymer is not particularly limited. Preferably, the mass ratio of the polyglycolic acid structural unit to the polyester structural unit is 2:8 to 9:1, for example, 2:8, 3:7, 4:6, 5:5, 6:4, 7:3, 8:2, 9:1, and any range consisting of any two of the above values, preferably 4:6 to 8:2. The mass ratio here is calculated based on the feed ratio corresponding to the structural unit.

[0098] The polyester structural unit in the present invention refers to the structural unit provided by polyester, wherein the polyester can be unmodified polyester, or can be alcoholysis-modified polyester and / or chain-extended modified polyester, wherein the purpose of alcoholysis includes reducing the molecular weight of the polyester, and the purpose of chain-extending modification includes increasing the molecular weight of the polyester.

[0099] In the present invention, the polyester structural unit refers to the structural unit provided by polyester, which may include unmodified polyester, alcoholysis-modified polyester structural unit, and may also include chain-extended modified polyester, wherein the alcoholysis-modified polyester is obtained by alcoholysis of polyester, and the alcoholysis method is a conventional method in the art. Preferably, the method for obtaining the alcoholysis-modified polyester includes: alcoholyzing the polyester in the presence of an alcoholysis catalyst and ethylene glycol.

[0100] In the present invention, the alcoholysis catalyst can be an alcoholysis catalyst commonly used in the art, such as a zinc-based catalyst, specifically zinc acetate. Preferably, the mass ratio of the alcoholysis catalyst to the polyester is (1-5):100, and preferably the mass ratio of ethylene glycol to the polyester is (0.1-10):100, preferably (0.5-2):100.

[0101] In the present invention, alcoholysis is preferably carried out in a screw extruder (e.g., a parallel co-rotating twin-screw extruder). Preferred alcoholysis conditions include: a temperature of 140 to 200° C., preferably 150 to 195° C.; after the alcoholysis is completed, the alcoholysis-modified polyester can be obtained by cooling, crushing, and drying.

[0102] The chain-extended modified polyester is obtained by chain-extending polyester with a chain extender. The chain-extending modification method is a conventional method in the art. The preferred method for obtaining the chain-extended modified polyester includes: chain-extending the polyester in the presence of a chain extender (e.g., an epoxy chain extender or an isocyanate chain extender).

[0103] According to a preferred embodiment of the present invention, the polyester structural unit includes at least one of a polybutylene terephthalate-co-adipate structural unit, a polybutylene terephthalate-co-succinate structural unit, a polybutylene succinate structural unit, a polybutylene succinate-adipate structural unit, a polylactic acid structural unit, a polypropylene carbonate structural unit, and a polyhydroxyalkanoate structural unit. The multilayer barrier film according to this embodiment has improved barrier properties, interlayer peel strength, and heat seal strength.

[0104] According to a more preferred embodiment of the present invention, the polyglycolic acid block copolymer includes at least one of a diblock or multiblock copolymer of polyglycolic acid and polybutylene terephthalate-co-adipate, a diblock or multiblock copolymer of polyglycolic acid and polybutylene terephthalate-co-succinate, a diblock or multiblock copolymer of polyglycolic acid and polylactic acid, and a diblock or multiblock copolymer of polyglycolic acid and polypropylene carbonate. The multilayer barrier film according to the aforementioned embodiment has improved barrier properties, interlayer peel strength, and heat seal strength.

[0105] In the present invention, in order to further improve the comprehensive properties of the barrier film, such as mechanical properties, a chain extender may be added to the blend for preparing the adhesive layer. Preferably, in the adhesive layer, the amount of the chain extender is generally 0 to 0.5 parts by mass based on 100 parts by mass of the polyglycolic acid block copolymer. When the amount is 0 parts by mass, it means that no chain extender is added.

[0106] In the present invention, in order to further increase the life of the barrier film, an antioxidant may be added to the adhesive layer. In the adhesive layer, the amount of antioxidant is generally 0 to 0.5 parts by mass based on 100 parts by mass of the polyglycolic acid block copolymer. When it is 0 parts by mass, it means that no antioxidant is added.

[0107] In the present invention, in order to further increase the stability of the barrier film, a stabilizer may be added to the adhesive layer. In the adhesive layer, the amount of the stabilizer is generally 0 to 1 part by mass based on 100 parts by mass of the polyglycolic acid block copolymer. When the amount is 0 part by mass, it means that no stabilizer is added.

[0108] In the present invention, in order to further increase the hydrolysis resistance of the barrier film, an anti-hydrolysis agent may be added to the adhesive layer. In the adhesive layer, the amount of the anti-hydrolysis agent is generally 0 to 1 part by mass based on 100 parts by mass of the polyglycolic acid block copolymer. When it is 0 parts by mass, it means that no anti-hydrolysis agent is added.

[0109] The polyglycolic acid block copolymer of the present invention can be obtained commercially or homemade. During the preparation process, auxiliary agents such as chain extenders, antioxidants, light stabilizers, and anti-hydrolysis agents can be added as needed to ensure that the corresponding auxiliary agents are present in the adhesive layer. In one embodiment, the preparation method of the polyglycolic acid block copolymer comprises: in the presence of a copolymerization catalyst, glycolide and a comonomer (including but not limited to at least one of polybutylene succinate, polybutylene adipate, polybutylene succinate-co-adipate, polybutylene terephthalate-co-adipate, polybutylene terephthalate-co-succinate, polylactic acid and its copolymerized derivatives, polypropylene carbonate and its copolymerized derivatives, polycaprolactone and its copolymerized derivatives, polyhydroxyalkanoates and its copolymerized derivatives, starch and its derivatives, cellulose and its derivatives, and protein polymers) are melt-blended, followed by extrusion, cooling, and pelletizing.

[0110] When preparing the polyglycolic acid block copolymer, additives such as antioxidants, stabilizers, and anti-hydrolysis agents may be added as needed.

[0111] In the present invention, when preparing the glycolic acid block copolymer, the copolymerization catalyst can be a conventional catalyst in the art that can promote the smooth progress of the copolymerization reaction, preferably including a compound or mixture based on at least one element of Sn, Bi, Mg, Al, Ca, Fe, Mn, Ti and Zn, such as dibutyltin oxide, stannous chloride, dibutyltin dilaurate, stannous octoate, bismuth trioxide, zinc acetate, etc.

[0112] According to the present invention, when preparing the glycolic acid block copolymer, the mass ratio of glycolide to comonomer is 2:8 to 9:1, preferably 4:6 to 8:2.

[0113] According to the present invention, when preparing glycolic acid block copolymers, the amount of copolymerization catalyst used is selected to promote melt blending to form the corresponding polyglycolic acid block copolymer. Preferably, the amount of copolymerization catalyst used is 0.005 to 1 part by mass, preferably 0.01 to 0.2 parts by mass, relative to 100 parts of glycolide.

[0114] According to the present invention, when preparing the glycolic acid block copolymer, melt blending can be carried out in a conventional melt mixing device in the art (e.g., a twin-screw extruder, the diameter and aspect ratio of the twin-screw extruder can be selected as needed, for example, the screw diameter is 50 to 52 mm, and the aspect ratio is 50 to 60).

[0115] According to the present invention, when preparing glycolic acid block copolymers, the melt blending conditions can be selected to be conducive to the production of block copolymers. Preferably, the melt blending temperature is 140°C to 250°C; and the melt blending reaction time is preferably 0.5 to 60 minutes, preferably 1 to 10 minutes.

[0116] According to the present invention, when a twin-screw extruder is used as a melt mixing device to prepare glycolic acid block copolymer, the preferred feeding rate is 10-30 kg / h; the preferred screw speed is 5-300 rpm, preferably 40-150 rpm.

[0117] According to the present invention, when preparing the glycolic acid block copolymer, melt blending is not limited to being performed using a twin-screw extruder, but can also be performed using an internal mixer or other device.

[0118] According to a preferred embodiment of the present invention, the base layer contains a degradable resin.

[0119] In the present invention, the base layer mainly plays the role of protecting the barrier layer. In order to better improve the barrier performance of the barrier layer, according to a preferred embodiment of the present invention, the water vapor transmission coefficient of the base layer is not more than 20000g·μm / (m 2 ·day·atm).

[0120] According to a preferred embodiment of the present invention, the base resin providing the polyester structural unit is the same as the degradable resin in the base layer. The multi-layer barrier film of the aforementioned embodiment has better interlayer peeling strength and heat sealing strength.

[0121] According to a preferred embodiment of the present invention, the degradable resin is selected from degradable polyester resin.

[0122] According to a more preferred embodiment of the present invention, the blend comprises any one or more of polybutylene succinate, polybutylene adipate, polybutylene succinate-co-adipate, polybutylene terephthalate-co-adipate, polybutylene terephthalate-co-succinate, polybutylene terephthalate-co-adipate, polyethylene terephthalate-co-succinate, polylactic acid, polypropylene carbonate, polyhydroxyalkanoate and thermoplastic starch.

[0123] In the present invention, when the degradable polyester resin is a blend of multiple different types, the content of the degradable polyester resin of each component in the blend is not particularly limited.

[0124] According to a preferred embodiment of the present invention, the degradable polyester resin at least includes polybutylene terephthalate-co-adipate and / or polybutylene terephthalate-co-succinate.

[0125] According to a more preferred embodiment of the present invention, the degradable polyester resin is polybutylene terephthalate-co-adipate.

[0126] According to a more preferred embodiment of the present invention, the degradable polyester resin is selected from a blend of polybutylene terephthalate-co-adipate and polylactic acid. As long as the purpose of the present invention can be achieved, the content of polybutylene terephthalate-co-adipate and polylactic acid in the blend is not particularly limited. Preferably, the mass ratio of polybutylene terephthalate-co-adipate to polylactic acid is (0.5-10):1, for example, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 6:1, 8:1, 10:1, and any interval consisting of any two of the above values, preferably (1.5-4:1).

[0127] According to a more preferred embodiment of the present invention, the degradable polyester resin is selected from a blend of polybutylene terephthalate-co-adipate and polypropylene carbonate. As long as the purpose of the present invention can be achieved, the content of polybutylene terephthalate-co-adipate and polypropylene carbonate in the blend is not particularly limited. Preferably, the mass ratio of polybutylene terephthalate-co-adipate and polypropylene carbonate is (0.5-10):1, for example, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 6:1, 8:1, 10:1, and any interval consisting of any two of the above values, preferably (1.5-4:1).

[0128] According to a more preferred embodiment of the present invention, the degradable polyester resin is selected from a blend of polybutylene succinate and polylactic acid. As long as the purpose of the present invention can be achieved, the content of polybutylene succinate and polylactic acid in the blend is not particularly limited. Preferably, the mass ratio of polybutylene succinate to polylactic acid is (0.5-10):1, for example, 0.5:1, 1:1, 1.5:1, 2:1, 3:1, 4:1, 6:1, 8:1, 10:1, and any interval consisting of any two of the above values, preferably (1.5-4):1.

[0129] According to a more preferred embodiment of the present invention, the degradable polyester resin is selected from a blend of polybutylene terephthalate-co-adipate, polypropylene carbonate, and polylactic acid. As long as the purpose of the present invention can be achieved, the content of polybutylene terephthalate-co-adipate, polypropylene carbonate, and polylactic acid in the blend is not particularly limited.

[0130] According to the present invention, in order to further improve the mechanical properties of the barrier film, the base layer contains a chain extender. In the base layer, the amount of the chain extender is generally 0.1 to 1 part by mass based on 100 parts by mass of the degradable resin.

[0131] According to the present invention, in order to further increase the openness and water barrier properties of the barrier film, the base layer contains an inorganic filler. In the base layer, based on 100 parts by mass of the degradable resin, the amount of the inorganic filler is generally 0 to 10 parts by mass. When the amount of the inorganic filler is generally 0 parts by mass, it means that no inorganic filler is used.

[0132] According to the present invention, in order to further increase the UV resistance of the barrier film, the base layer contains a light stabilizer. In the base layer, the amount of the light stabilizer is generally 0 to 1 part by mass based on 100 parts by mass of the degradable resin. When the amount of the light stabilizer is generally 0 part by mass, it means that no light stabilizer is used.

[0133] According to the present invention, in order to further improve the overall performance of the barrier film, the base layer contains a dispersant. In the base layer, based on 100 parts by mass of the biodegradable resin, the amount of the dispersant is generally 0 to 1 part by mass. When the amount of the dispersant is generally 0 part by mass, it means that no dispersant is used.

[0134] In the present invention, in order to further increase the life of the barrier film, an antioxidant may be added to the base layer. In the base layer, the amount of antioxidant is generally 0 to 0.5 parts by mass based on 100 parts by mass of the degradable resin. When it is 0 parts by mass, it means that no antioxidant is added.

[0135] In the present invention, in order to further increase the hydrolysis resistance of the barrier film, an anti-hydrolysis agent may be added to the base layer. In the base layer, the amount of the anti-hydrolysis agent is generally 0 to 1 part by mass based on 100 parts by mass of the degradable resin. When it is 0 parts by mass, it means that no anti-hydrolysis agent is added.

[0136] According to the present invention, the chain extender can be a raw material in the art that can react with the polyglycolic acid block copolymer, including but not limited to epoxy chain extenders (for example, (polymethyl methacrylate / glycidyl methacrylate) copolymer, JONCRYLADR 4468, chain extender ADR 4370), isocyanate chain extenders (for example, phenylene diisocyanate (TDI), isophorone diisocyanate (IPDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), hexamethylene diisocyanate (HDI), lysine diisocyanate (LDI)), anhydride chain extenders, and amine chain extenders.

[0137] According to the present invention, the inorganic filler can be any conventional choice in the art, including but not limited to silicon dioxide, talc, calcium sulfate, montmorillonite, diatomaceous earth, kaolin, wollastonite, calcium carbonate, mica, and bentonite.

[0138] The light stabilizer used in the present invention can be a conventional light stabilizer in the art, including but not limited to salicylate light stabilizers, benzoate light stabilizers, benzophenone light stabilizers, benzotriazole light stabilizers, triazine light stabilizers, substituted acrylonitrile light stabilizers, oxamide light stabilizers, organic nickel complex light stabilizers and hindered amine light stabilizers. Specific examples of light stabilizers include light stabilizer SEED, ultraviolet absorber VSU, ultraviolet absorber UV-120, light stabilizer HA-10, light stabilizer 622, hindered amine light stabilizer HS-944, and light stabilizer LQ-783.

[0139] The dispersant used in the present invention can be a conventional choice in the art, and the dispersant is selected from at least one of oleamide, erucamide, stearamide, natural paraffin, and ethylene bisstearamide (EBS).

[0140] The antioxidant used in the present invention may be a conventional antioxidant in the art, and the present invention has no special limitation thereto. In the embodiments of the present invention, antioxidant 1010 and / or antioxidant 626 are used as illustrative antioxidants, but are not limited thereto.

[0141] The anti-hydrolysis agent used in the present invention may be any conventional anti-hydrolysis agent in the art, and the present invention has no particular limitation thereto, including but not limited to N,N'-bis(2,6-diisopropylphenyl)carbodiimide and polycarbodiimide.

[0142] In the present invention, the "surface layer" refers to the film layers on the upper and lower surfaces of the multilayer barrier film, and the intermediate layer refers to all film layers arranged between the upper and lower surfaces. The arrangement order of the multilayer barrier film in this application can be base layer / adhesive layer / barrier layer / adhesive layer / base layer, or base layer / adhesive layer / barrier layer / adhesive layer / base layer / adhesive layer / barrier layer / adhesive layer / base layer, or other methods.

[0143] According to the present invention, as long as the purpose of the present invention can be achieved, the thickness of each film layer in the barrier film of the present invention is not particularly limited.

[0144] According to a preferred embodiment of the present invention, the thickness of a single layer of the barrier layer is preferably 1 to 50 μm, preferably 5 to 40 μm;

[0145] According to a preferred embodiment of the present invention, the thickness of each single layer of the base layer is 4 to 90 μm, preferably 20 to 75 μm.

[0146] According to a preferred embodiment of the present invention, the thickness of a single layer of the adhesive layer is 0.5 to 35 μm, preferably 3 to 30 μm.

[0147] According to a preferred embodiment of the present invention, the total thickness of the multi-layer barrier film is 10 to 300 μm, preferably 15 to 250 μm.

[0148] The multi-layer barrier film of the present invention has excellent sealing strength. Preferably, the heat sealing strength of the multi-layer barrier film is not less than 3.5 N / 15 mm, preferably not less than 5.0 N / 15 mm.

[0149] The multilayer barrier film of the present invention has excellent interlayer peeling strength. Preferably, the interlayer peeling strength of the multilayer barrier film is not less than 1.5 N / 15 mm, and more preferably not less than 2.5 N / 15 mm.

[0150] The multilayer barrier film of the present invention has excellent barrier properties. Preferably, the multilayer barrier film has an oxygen transmission rate of no more than 6 cm at 23±0.5°C and a relative humidity of 65%±5%. 3 / (m 2 ·day·atm), preferably no larger than 2cm 3 / (m 2 ·day·atm); preferably, the multilayer barrier film has an oxygen permeability coefficient of not more than 1500cm at 23±0.5°C and a relative humidity of 65%±5%. 3 μm / (m 2 ·day·atm), preferably not more than 500cm 3 μm / (m 2 ·day·atm); preferably, the water vapor transmission rate of the multilayer barrier film is not more than 30g / (m 2 ·day·atm), preferably not more than 15g / (m 2·day·atm); preferably, the water vapor permeability coefficient of the multilayer barrier film is not greater than 2000g·μm / (m 2 ·day·atm), preferably not more than 1500g·μm / (m 2 ·day·atm).

[0151] A second aspect of the present invention provides a method for preparing the multilayer barrier film of the present invention, comprising: co-extruding a blend containing a degradable resin as a base layer, a blend containing polyglycolic acid with a multimodal molecular weight distribution as a barrier layer, and a blend containing a polyglycolic acid block copolymer as a tie layer, or extruding them separately, followed by a step including film formation.

[0152] In the present invention, the various film layers are arranged, using a blend containing a degradable resin to prepare the base layer, using a blend containing polyglycolic acid with a multimodal molecular weight distribution to prepare the barrier layer, and using a blend containing a polyglycolic acid block copolymer to prepare the adhesive layer. The barrier film finally prepared has excellent barrier properties, as well as excellent interlayer peel strength and heat seal strength.

[0153] In the present invention, the film forming method can be conventional in the art, preferably blown film or cast film; blown film uses a blown film mold, and cast film uses a cast film mold. Single-screw extrusion film blowing machines suitable for the present invention include film blowing machines of various designs, such as the single-screw extrusion film blowing machine model E30P from Dr. Collin, Germany.

[0154] According to the present invention, existing films using PGA as a matrix resin cannot be prepared by the blown film forming method. The inventors have discovered that the barrier layer in the present invention contains polyglycolic acid with a multimodal molecular weight distribution, and blown film forming can also be used to form a multilayer barrier film with better overall performance. In order to improve production efficiency and reduce equipment investment and material loss, the preferred film forming method of the present invention is blown film forming.

[0155] In the present invention, when extrusion is performed separately, the film layers formed after the film formation of each layer of material are heat-pressed to obtain a multi-layer barrier film; the conditions for each extrusion include: melting, compression and then extrusion.

[0156] In the present invention, when multiple layers are co-extruded, the blends of the corresponding film layers are melted and compressed separately and then extruded through a co-extrusion distributor according to the required structure and thickness of the multi-layer barrier film.

[0157] In the present invention, after film blowing or casting, the film can be cooled and wound up, preferably stretched before winding up, to finally obtain the corresponding film product, that is, after film blowing or casting, cooling, stretching, and winding up are performed to finally prepare the corresponding film product. Cooling, stretching, and winding up are conventional methods in the art. For example, stretching is to orient the film in one or more directions to further improve the orientation degree and reduce the thickness of the film. Specifically, the film can be heated to a temperature lower than the melting point of one or more polymers in the film (higher than the glass transition temperature) by heating with guide rollers. The heated temperature enables the film to be continuously and controllably stretched. The gradually increasing speed of adjacent rollers serves to stretch the film. Some guide rollers can also be used as preheating rollers. The guide rollers can be multiple guide rollers (for example, from 5 to 8), which gradually stretch the film in the machine direction (MD) and thin the film. The specific number of guide rollers can be selected as needed and is related to the desired stretching ratio and the stretching degree between each roller. During stretching, the heated "softened" film can be stretched step by step by guide rollers rotating at different speeds to stretch the film in the machine direction (MD). Direction) to a desired stretch ratio. Additionally, various additional potential processing and / or finishing steps, such as slitting, treatment, perforation, graphic printing, or lamination, may be performed on the film having other layers without departing from the spirit and scope of the present invention. In the present invention, the conditions for preparing the composite film are not particularly limited as long as the objectives of the present invention can be achieved. For example, during film blowing, a gas such as air can be used to expand the bubble formed by the extruded polymer passing through the annular die. Specifically, the blow-up ratio and film thickness can be controlled by adjusting the pressure of the gas in the bubble. The greater the pressure, the larger the bubble, the lower the film thickness, and the higher the transverse orientation of the film. In the present invention, the blow-up ratio during film blowing is preferably (1-6):1, preferably (2-5):1; wherein the blow-up ratio refers to the ratio of the diameter of the blown film bubble to the diameter of the film blowing machine die; and the draft ratio is preferably 1-5, preferably 1.5-2.

[0158] According to a preferred embodiment of the present invention, Figure 2The composite film is prepared in a multi-layer co-extrusion blown film preparation device with a uniaxial stretching device as shown. The preparation method of the barrier film includes: adding a blend containing a degradable resin as a base layer, a blend containing a multimodal molecular weight distribution polyglycolic acid as a barrier layer, and a blend containing a polyglycolic acid block copolymer as a bonding layer to the hopper 10a of a single-screw extruder 20a, the hopper 10b of a single-screw extruder 20b, and the hopper 10c of a single-screw extruder 20c, respectively, and then entering the corresponding single-screw extruder 20a, the single-screw extruder 20b, and the single-screw extruder 20c for melting. , extruded into the melt pump 30a, melt pump 30b, and melt pump 30c for pressurization, and then enters the co-extrusion distributor 40b through the feed pipe 40a for distribution. The distributed molten material enters the film blowing die 50a, is blown by gas (such as air) through the air ring 50b and pulled upward to cool to form a film bubble 01a. After cooling, the film bubble 01a is guided by the herringbone splint 60 and squeezed by the clamping roller 70a to obtain a precursor film 01b. The precursor film 01b is stretched by the unidirectional stretching device 80 to obtain a stretched film 01c. The stretched film 01c is wound and collected on the winding roller 90.

[0159] According to a preferred embodiment of the present invention, Figure 3 The composite film is prepared in a multi-layer co-extrusion cast film preparation device with a uniaxial stretching device as shown. The preparation method of the composite film includes: adding a blend containing a degradable resin as a base layer, a blend containing a multimodal molecular weight distribution polyglycolic acid as a barrier layer, and a blend containing a polyglycolic acid block copolymer as a bonding layer into the hopper 10a of the single-screw extruder 20a, the hopper 10b of the single-screw extruder 20b, and the hopper 10c of the single-screw extruder 20c, respectively, and then entering the corresponding single-screw extruder 20a, single-screw extruder 20b, and single-screw extruder 20c. The rod extruder 20b and the single-screw extruder 20c are respectively melted and extruded to the melt pump 30a, the melt pump 30b, and the melt pump 30c for pressurization, and then enter the co-extrusion distributor 40b through the feed pipe 40a for distribution. The distributed melted material enters the casting die 50c for extrusion casting and is cooled by the cooling roller 70b to obtain the precursor film 01b. Then, the precursor film 01b is stretched by the unidirectional stretching device 80 to obtain the stretched film 01c, and the stretched film 01c is wound and collected on the winding roller 90.

[0160] In the present invention Figure 2 and Figure 3 Part of the structure of the preparation device is the same, so the same part of the structure and other parts in the present invention use the same figure marks.

[0161] The film blowing, cooling, stretching, and winding in the present invention are conventional technical means in this field. There are no special requirements for the process conditions, as long as a film layer of corresponding thickness can be prepared. Therefore, the specific conditions in the present invention and the embodiments are not described in detail, and those skilled in the art can choose according to their needs.

[0162] In the present invention, multi-layer co-extrusion is used to prepare the barrier film, but it is not limited thereto. Preferably, the conditions for multi-layer co-extrusion include: the blend containing a degradable resin as the base layer, the blend containing polyglycolic acid with a multimodal molecular weight distribution as the barrier layer, and the blend containing a polyglycolic acid block copolymer as the adhesive layer are each melt-extruded at a temperature of 180°C to 260°C.

[0163] The equipment for multi-layer co-extrusion in the present invention is not particularly limited. For example, each of the materials is melted and extruded in a screw extruder (single-screw extruder or twin-screw extruder), and the screw speed of the screw extruder is preferably independently 10 to 200 rpm; the screw speed when the protective layer material is melted is preferably 40 to 60 rpm, the screw speed when the barrier layer material containing multimodal molecular weight distribution polyglycolic acid is melted is preferably 30 to 40 rpm, and the screw speed when the adhesive layer material is melted is preferably 8 to 12 rpm.

[0164] The third aspect of the present invention provides applications of the multi-layer barrier film of the present invention in food packaging bags, agricultural films, medical packaging, and electronic fields.

[0165] The multilayer barrier film of the present invention has excellent interlayer peeling strength, heat sealing strength and barrier properties, and has excellent performance when used in food packaging bags, agricultural films, medical packaging and electronic fields.

[0166] The present invention will be described in detail below through examples. In the following examples, the sources and parameters of the raw materials are shown in Table 1.

[0167] Table 1

[0168]

[0169]

[0170] Example 1

[0171] To prepare the base material, polybutylene terephthalate-co-adipate (PBAT), polylactic acid (PLA), talc, antioxidant 1010, EBS dispersant, and chain extender ADR 4370 were mixed uniformly in a mass ratio of 80:20:7:0.5:0.2:0.3 and pelletized using a KraussMaffei ZE25 UTXi parallel, co-rotating twin-screw extruder (screw diameter: 25 mm, aspect ratio: 56). The extruder had 14 sections from the feed port to the die, numbered 1-14. Section 1 served only for feeding and was not heated. The temperatures in sections 2-14 were 150°C, 200°C, 200°C, 200°C, 200°C, 220°C, 220°C, 220°C, 200°C, 200°C, and 200°C, respectively. The total feed rate was 15 kg / h, the screw speed was 150 rpm, and the residence time was 3.5 min.

[0172] Preparation of the bonding layer: Glycol, PBAT, stannous octoate, antioxidant 1010, and antioxidant 626 were mixed uniformly in a mass ratio of 100:400:0.04:0.3:0.3 and pelletized using an HK53 twin-screw extruder (screw diameter 50.6 mm, aspect ratio 56) from Nanjing Keya Chemical Complete Equipment Co., Ltd. The extruder consisted of 14 sections from the feed port to the die, numbered 1-14. Section 1 served only for feeding and was not heated. The temperatures in sections 2-14 were 50°C, 150°C, 190°C, 190°C, 190°C, 200°C, 210°C, 220°C, 230°C, 230°C, 230°C, 230°C, and 230°C, respectively. The feed rate was 20 kg / h, the screw speed was 60 rpm, and the residence time was 5.5 min.

[0173] Preparation of barrier layer material: glycolide, stannous octoate, ethylene-vinyl alcohol copolymer (EVOH), 1,4-butanediol, antioxidant 1010 and antioxidant 626 were mixed uniformly in a mass ratio of 100:0.1:0.015:0.035:0.3:0.6 and then extruded into granules using a Labtech parallel co-rotating twin-screw extruder (screw diameter: 20 mm, aspect ratio: 40) to obtain multimodal molecular weight distribution polyglycolic acid particles. The extruder has 11 sections from the feed port to the die, numbered 1 to 11, of which the first section only serves to add materials and cannot be heated. The temperatures of sections 2 to 11 of the extruder are 160°C, 200°C, 220°C, 220°C, 220°C, 220°C, 230°C, 235°C and 240°C, respectively. The raw material particles were collected and characterized by molecular weight using GPC. The GPC curve of the multimodal molecular weight distribution polyglycolic acid particles is shown in the figure. Figure 1As shown, the weight average molecular weight of the multimodal molecular weight distribution polyglycolic acid is 268200 g / mol, and the molecular weight distribution index is 2.1, wherein the weight average molecular weight of the polyglycolic acid graft copolymer is 2011500 g / mol, the molecular weight distribution index is 1.1, and the mass proportion is 7.4%; the weight average molecular weight of the polyglycolic acid homopolymer is 199200 g / mol, the molecular weight distribution index is 1.6, and the mass proportion is 92.6%; the multimodal molecular weight distribution polyglycolic acid particles are subjected to a melt flow rate test to characterize their melt flow rate at the processing temperature, which is 5.4 g / 10 min; the melt strength at 235°C is 10 cN, and the melt break draw speed is 320 mm / s.

[0174] Preparation of multilayer barrier films: Figure 3 As shown, a multilayer barrier film is prepared using a Labtech LCR-33HD multilayer co-extrusion film blowing machine. The base layer material, the adhesive layer material, and the barrier layer material are respectively added to the hopper 10a of the single screw extruder 20a, the hopper 10b of the single screw extruder 20b, and the hopper 10c of the single screw extruder 20c. The materials are then melted and extruded in the corresponding single screw extruders 20a, 20b, and 20c, and then pressurized in the melt pumps 30a, 30b, and 30c. The materials are then extruded according to the following formula: Figure 4 The structure of the multi-layer barrier film shown in FIG. The distributed molten material enters the co-extrusion distributor 40b through a feed pipe 40a for distribution. The distributed molten material then enters the blown film die 50a, where it is inflated by air through an air ring 50b and pulled upward to cool, forming a film bubble 01a. After cooling, the bubble 01a is guided by a herringbone splint 60 and squeezed by a nip roller 70a to form a precursor film 01b. The precursor film 01b is stretched by a uniaxial stretching device 80 to form a stretched film 01c. The stretched film 01c is wound and collected on a wind-up roller 90 to form a multi-layer barrier film. The screw speeds of the three single-screw extruders 20a, 20b, and 20c are 40 rpm, 30 rpm, and 10 rpm, respectively. The extruder, melt pump, and die temperatures are all set at 230°C. The speeds of the three melt pumps 30a, 30b, and 30c are 20 rpm, 15 rpm, and 5 rpm, respectively. The blow-up ratio is approximately 2.3, and the draft ratio is approximately 1.8.

[0175] The single layer thickness of the base layer, the single layer thickness of the bonding layer and the single layer thickness of the barrier layer are 45 μm, 12.5 μm and 25 μm respectively, and the total thickness of the multilayer film is about 140 μm.

[0176] Example 2

[0177] Preparation of base material: The preparation method is similar to that of Example 1, except that the ratio of polybutylene terephthalate-co-adipate (PBAT), polylactic acid (PLA), talc, antioxidant 1010, EBS dispersant and chain extender ADR 4370 is changed to: 60:40:6:0.5:0.1:0.4.

[0178] Preparation of bonding layer material: The preparation method is similar to that of Example 1, except that the chain extender ADR4370 is additionally added, and the ratio of glycolide, PBAT (weight average molecular weight 70,000 g / mol), stannous octoate, ADR 4370, antioxidant 1010 and antioxidant 626 is changed to 100:150:0.04:0.3:0.3:0.3.

[0179] Preparation of barrier layer material: The preparation method is the same as that in Example 1.

[0180] Preparation of a multilayer film: The preparation method was similar to that of Example 1, except that the screw speeds of the three single-screw extruders (20a, 20b, and 20c) were set to 50 rpm, 30 rpm, and 15 rpm, respectively, and the speeds of the three melt pumps (30a, 30b, and 30c) were set to 30 rpm, 15 rpm, and 10 rpm, respectively. The blow-up ratio was approximately 1.7, and the draw-down ratio was approximately 1.5.

[0181] The thickness of the base layer, the adhesive layer and the barrier layer are 60μm, 25μm and 30μm respectively, and the total thickness of the multilayer film is about 200μm.

[0182] Example 3

[0183] Preparation of base material: The preparation method is the same as that in Example 1.

[0184] Preparation of bonding layer material: The preparation method is similar to that of Example 1, except that the ratio of glycolide, PBAT, stannous octoate, antioxidant 1010 and antioxidant 626 is changed to 100:67:0.04:0.3:0.3.

[0185] Preparation of barrier layer material: The preparation method is the same as that in Example 1.

[0186] Preparation of multilayer film: The preparation method is similar to that of Example 1, except that the blow-up ratio is about 2.2 and the draw-down ratio is about 1.8.

[0187] The single layer thickness of the base layer, the single layer thickness of the bonding layer and the single layer thickness of the barrier layer are 45 μm, 15 μm and 30 μm respectively, and the total thickness of the multilayer film is about 150 μm.

[0188] Example 4

[0189] Preparation of base material: The preparation method is similar to that of Example 1, except that PBAT is replaced by PBST.

[0190] Preparation of bonding layer material: The preparation method is similar to that of Example 1, except that PBAT is replaced by PBST (weight average molecular weight 60,000 g / mol).

[0191] Preparation of barrier layer material: The preparation method is similar to that of Example 1, except that ethylene-vinyl alcohol copolymer (EVOH) is replaced with polyvinyl alcohol (PVA), and the ratio of glycolide, stannous octoate, polyvinyl alcohol (PVA), 1,4-butanediol, antioxidant 1010, and antioxidant 626 is set to 100:0.1:0.02:0.04:0.5:0.3, ultimately preparing multimodal molecular weight distribution polyglycolic acid particles. The collected multimodal molecular weight distribution polyglycolic acid particles were characterized by GPC. The GPC curve of the multimodal molecular weight distribution polyglycolic acid particles is shown in FIG. Figure 1 As shown, the weight average molecular weight of the multimodal molecular weight distribution polyglycolic acid is 204500 g / mol, and the molecular weight distribution index is 1.8, wherein the weight average molecular weight of the polyglycolic acid graft copolymer is 1430800 g / mol, the molecular weight distribution index is 1.1, and the mass proportion is 3.8%; the weight average molecular weight of the polyglycolic acid homopolymer is 173800 g / mol, the molecular weight distribution index is 1.6, and the mass proportion is 96.2%; the multimodal molecular weight distribution polyglycolic acid particles are subjected to a melt flow rate test to characterize that the melt flow rate at the processing temperature is 9.9 g / 10 min; and the melt strength at 235°C is 20 cN.

[0192] Preparation of multilayer film: The preparation method is similar to that of Example 1, except that the blow-up ratio is about 2.0 and the draw-down ratio is about 1.8.

[0193] The single layer thickness of the base layer, the single layer thickness of the adhesive layer and the single layer thickness of the barrier layer are 50 μm, 15 μm and 30 μm respectively, and the total thickness of the multilayer film is about 160 μm.

[0194] Example 5

[0195] Preparation of base material: The preparation method is similar to that of Example 1, except that talc and EBS dispersant are not added, and the ratio of polybutylene terephthalate-co-adipate (PBAT), polylactic acid (PLA), antioxidant 1010 and chain extender ADR4370 is changed to 40:60:0.5:0.5.

[0196] Preparation of bonding layer material: The preparation method is similar to that of Example 1, except that PBAT (weight average molecular weight 70,000 g / mol) is replaced by alcoholysis-modified PBAT (weight average molecular weight 20,000 g / mol).

[0197] The general preparation process for alcoholysis-modified PBAT is as follows: PBAT, zinc acetate, and ethylene glycol are added to a Labtech parallel, co-rotating twin-screw extruder (screw diameter: 20 mm, aspect ratio: 40) in a mass ratio of 1000:3:10. The extruder is extruded, water-cooled, crushed, and vacuum-dried to obtain the alcoholysed PBAT product. The extruder has 11 sections from the feed port to the die, numbered 1-11. Section 1 only serves to feed the material and does not heat the extruder. The temperatures in sections 2-11 are 150°C, 160°C, 190°C, 195°C, 195°C, 195°C, 195°C, 190°C, 185°C, and 180°C, respectively.

[0198] Preparation of barrier layer material: The preparation method is the same as that in Example 1.

[0199] Preparation of multilayer film: The preparation method is similar to that of Example 1, except that the blowing ratio is about 1.8 and the drawing ratio is about 1.8.

[0200] The single layer thickness of the base layer, the single layer thickness of the bonding layer and the single layer thickness of the barrier layer are 52.5 μm, 22.5 μm and 30 μm respectively, and the total thickness of the multilayer film is about 180 μm.

[0201] Example 6

[0202] Preparation of protective layer material: The preparation method is similar to that of Example 1, except that polylactic acid (PLA) is not added, and polybutylene terephthalate-co-adipate (PBAT), talc, antioxidant 1010, EBS dispersant and chain extender ADR 4370 are mixed in a ratio of 100:7:0.5:0.2:0.3.

[0203] Preparation of the adhesive layer material: The preparation method is the same as that in Example 1. Preparation of the barrier layer material: The preparation method is the same as that in Example 1.

[0204] Preparation of multilayer film: The preparation method is similar to that of Example 1, except that the blowing ratio is about 2.4 and the drawing ratio is about 2 during the preparation process.

[0205] The single layer thickness of the base layer, the single layer thickness of the bonding layer and the single layer thickness of the barrier layer are 35 μm, 10 μm and 20 μm respectively, and the total thickness of the multilayer film is about 110 μm.

[0206] Comparative Example 1

[0207] Preparation of protective layer material: the same as in Example 1.

[0208] Preparation of barrier layer material: the same as in Example 1.

[0209] Preparation of multilayer film: Similar to Example 1, except that no adhesive layer is used, the material of screw 10b is changed to protective layer material, the blowing ratio is about 1.5, and the drawing ratio is about 1.5.

[0210] The single layer thickness of the base layer, the single layer thickness of the adhesive layer and the single layer thickness of the barrier layer are approximately 60 μm, 20 μm and 40 μm respectively, and the total thickness of the multilayer film is approximately 180 μm.

[0211] Comparative Example 2

[0212] Preparation of protective layer material: The preparation method is the same as that in Example 1.

[0213] Preparation of bonding layer material: The preparation method is the same as that in Example 1.

[0214] Preparation of barrier layer material: The preparation method is similar to that of Example 1, except that no ethylene-vinyl alcohol copolymer (EVOH) is added, and the ratio of glycolide, stannous octoate, 1,4-butanediol, antioxidant 1010, and antioxidant 626 is changed to 100:0.1:0.5:0.3:0.6, ultimately producing polyglycolic acid particles. The collected polyglycolic acid particles were characterized by GPC for molecular weight. The GPC curve of the polyglycolic acid particles is shown in the figure below. Figure 1 As shown, the polyglycolic acid has only one peak, a number average molecular weight of 124,900 g / mol, a weight average molecular weight of 197,800 g / mol, and a molecular weight distribution index of 1.58; the melt flow rate test of the polyglycolic acid particles is performed to characterize its melt flow rate at the processing temperature, which is 26.2 g / 10 min; and the melt strength at 235°C is 3 cN.

[0215] Preparation of multilayer film: Same as Example 1, film blowing failed during the film blowing process.

[0216] Comparative Example 3

[0217] Preparation of protective layer material: The preparation method is the same as that in Example 1.

[0218] Preparation of bonding layer material: The preparation method is the same as that in Example 1.

[0219] Preparation of multilayer film: The preparation method is similar to that of Example 1, except that no barrier layer is used, that is, the material used for the 10c screw is changed to a protective layer material, the blowing ratio is about 1.5, and the drawing ratio is about 1.5.

[0220] The single layer thickness of the base layer, the single layer thickness of the adhesive layer and the single layer thickness of the barrier layer are approximately 60 μm, 20 μm and 40 μm respectively, and the total thickness of the multilayer film is approximately 200 μm.

[0221] Comparative Example 4

[0222] Preparation of pure PBAT hot-pressed film: Polybutylene terephthalate-co-adipate (PBAT) was tightly stacked between two stainless steel plates and hot-pressed at 180°C with a pressure of 100-200 kN for 4 minutes using a LP-S-50 hot press (maximum pressure 500 kN) from Labtech, Thailand, and then cooled to room temperature to obtain a pure PBAT hot-pressed film.

[0223] The thickness of the prepared pure PBAT hot-pressed film is 280 μm.

[0224] Comparative Example 5

[0225] Preparation of pure PLA hot-pressed film: The preparation method is similar to that of Comparative Example 4, except that polybutylene terephthalate-co-adipate (PBAT) is replaced by polylactic acid (PLA).

[0226] The thickness of the prepared pure PLA hot-pressed film is 200 μm.

[0227] Comparative Example 6

[0228] Preparation of Pure PGA Monolayer Blown Film: The barrier layer material from Example 1 was passed through a Dr. Collin E30P single-screw extruder (screw diameter 30 mm, aspect ratio 30:1) and a matching BL 180 / 600 film blowing machine from the same company. After melting, extrusion, drawing, cooling, stretching, and winding, a pure PGA monolayer blown film was obtained. The extruder screw speed was 50 rpm, and the extruder and die temperatures were set at 180°C, 230°C, 230°C, and 230°C, respectively.

[0229] The thickness of the prepared pure PGA single-layer blown film is 25 μm.

[0230] Test Example 1

[0231] Interlayer peeling force (i.e., used to characterize interlayer peeling strength) was tested on some examples and comparative example 4, with a strip width of 15 mm. The test results are listed in Table 2.

[0232] Table 2

[0233] Bonding layer material Interlayer peeling force (N / 15mm) Example 1 PGA-b-PBAT-20 / 80 2.6 Example 2 PGA-b-PBAT-40 / 60 3.1 Example 3 PGA-b-PBAT-60 / 40 3.4 Comparative Example 1 none ≤0.1

[0234] The interlayer peeling force (interlayer peeling strength) of other examples not listed in Table 2 is not significantly lower than that of Example 3.

[0235] Test Example 2

[0236] The heat sealing strength test was performed on Example 1 and Comparative Example 5, with the strip width being 15 mm. The test results are listed in Table 3.

[0237] Table 3

[0238]

[0239]

[0240] The heat sealing strength of other embodiments not listed in Table 3 is not significantly lower than that of Example 5.

[0241] Test Example 3

[0242] Barrier properties of some embodiments and comparative examples were tested. The oxygen barrier performance was tested at a temperature of 23°C and a relative humidity (RH) of 65%. The water vapor barrier performance was tested at a temperature of 38°C and a relative humidity of 90%. The pressure was 1 standard atmosphere (atm), and the test time was 24 hours. The test results are shown in Table 4.

[0243] Table 4

[0244]

[0245] The oxygen transmission rates and water vapor transmission rates of the other examples not listed in Table 4 are not significantly higher than those of Example 3.

[0246] From the results in Tables 2 to 4, it can be seen that the multilayer barrier film of the present invention has excellent barrier properties, the layers are not easily peeled off, and it also has excellent heat sealing strength.

[0247] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A multi-layer barrier film, characterized in that: The barrier film is provided with a surface layer as a base layer, an intermediate layer including at least a barrier layer and an adhesive layer, and the base layer is provided by bonding the adhesive layer to the barrier layer; wherein the barrier layer comprises polyglycolic acid with a multimodal molecular weight distribution; The tie layer contains a polyglycolic acid block copolymer.

2. The barrier film according to claim 1, wherein The multimodal molecular weight distribution polyglycolic acid is a homogeneous continuous phase; and / or, The multimodal molecular weight distribution polyglycolic acid comprises a polyglycolic acid graft copolymer and a polyglycolic acid homopolymer; preferably, The main chain of the polyglycolic acid graft copolymer comprises: A grafting structural unit represented by formula (I1); Optionally a polyvinyl alcohol structural unit represented by formula (I2); Optionally a polyethylene structural unit represented by formula (I3); Optionally, a polyvinyl acetate structural unit represented by formula (I4); The side chain of the polyglycolic acid graft copolymer contains a glycolic acid structural unit as shown in formula (I5), In formula (I1) and formula (I5), * represents a linking site.

3. The barrier film according to claim 2, wherein The sum of the number x of grafting structural units, the number y2 of polyvinyl alcohol structural units, the number z of polyethylene structural units, and the number y1 of polyvinyl acetate structural units is not less than 50, preferably 50 to 6000, more preferably 200 to 2500; and / or, The number m of glycolic acid structural units is not less than 50, preferably 50 to 1000; Preferably, the ratio of z to x+y1+y2+z is 0% to 50%; and / or, The proportion of y1 to x+y1+y2 is 0% to 32%; and / or, The polyglycolic acid homopolymer contains glycolic acid structural units and co-initiator structural units provided by a hydroxyl or amino-containing small molecule co-initiator. Preferably, the number of glycolic acid structural units in the polyglycolic acid homopolymer is 50 to 5000.

4. The barrier film according to claim 2 or 3, wherein In the multimodal molecular weight distribution polyglycolic acid, the content of the polyglycolic acid graft copolymer is 0.1% to 80% by mass, preferably 1% to 30% by mass; and / or, In the multimodal molecular weight distribution polyglycolic acid, the content of the polyglycolic acid homopolymer is 20% to 99.9% by mass, preferably 70% to 99% by mass; and / or, The multimodal molecular weight distribution polyglycolic acid contains 2 to 4 peaks; and / or, The weight average molecular weight of the polyglycolic acid graft copolymer is 500,000 to 10,000,000 g / mol, preferably 1,000,000 to 6,000,000 g / mol; and / or, The molecular weight polydispersity index of the polyglycolic acid graft copolymer is 1.01 to 3.0, preferably 1.05 to 1.5; and / or, The weight average molecular weight of the polyglycolic acid homopolymer is 50,000 to 350,000 g / mol, preferably 100,000 to 200,000 g / mol; and / or, The molecular weight polydispersity index of the polyglycolic acid homopolymer is 1 to 3, preferably 1.4 to 2.

9.

5. The barrier film according to any one of claims 1 to 4, wherein The weight average molecular weight of the multimodal molecular weight distribution polyglycolic acid is 200,000 to 1.5 million g / mol, preferably 250,000 to 500,000 g / mol; and / or, The molecular weight distribution index of the multimodal molecular weight distribution polyglycolic acid is 1.5 to 20.0, preferably 2.0 to 3.5; and / or, The multimodal molecular weight distribution polyglycolic acid has a melt flow rate of not more than 20.0 g / 10 min at 230° C. / 2.16 kg, preferably 0.5 to 10.0 g / 10 min; and / or, The multimodal molecular weight distribution polyglycolic acid has a melt strength at 235° C. of not less than 4 cN, preferably not less than 8 cN.

6. The barrier film according to any one of claims 1 to 5, wherein The polyglycolic acid block copolymer contains: polyglycolic acid structural units and polyester structural units; Preferably, the polyester structural unit includes at least one of a polybutylene terephthalate-co-adipate structural unit, a polybutylene terephthalate-co-succinate structural unit, a polybutylene succinate structural unit, a polybutylene succinate-adipate structural unit, a polylactic acid structural unit, a polypropylene carbonate structural unit, and a polyhydroxyalkanoate structural unit; More preferably, the polyglycolic acid block copolymer comprises at least one of a diblock or multiblock copolymer of polyglycolic acid and polybutylene terephthalate-co-adipate, a diblock or multiblock copolymer of polyglycolic acid and polybutylene terephthalate-co-succinate, a diblock or multiblock copolymer of polyglycolic acid and polylactic acid, and a diblock or multiblock copolymer of polyglycolic acid and polypropylene carbonate; More preferably, the polyglycolic acid block copolymer is selected from a diblock or triblock copolymer of polyglycolic acid and polybutylene terephthalate-co-adipate, and / or a diblock or triblock copolymer of polyglycolic acid and polybutylene terephthalate-co-succinate.

7. The barrier film according to any one of claims 1 to 6, wherein The base layer contains a degradable resin; and / or, The water vapor permeability coefficient of the base layer is not greater than 20000 g·μm / (m 2 ·day·atm); Preferably, The base resin providing the polyester structural unit is the same as the degradable resin in the base layer; and / or, The degradable resin is selected from degradable polyester resins. Preferably, the degradable polyester resin includes a blend of any one or more of polybutylene succinate, polybutylene adipate, polybutylene succinate-co-adipate, polybutylene terephthalate-co-adipate, polybutylene terephthalate-co-succinate, poly(ethylene terephthalate-co-adipate), poly(ethylene terephthalate-co-succinate), polylactic acid, polypropylene carbonate, polyhydroxyalkanoate and thermoplastic starch. Preferably, the degradable polyester resin includes at least polybutylene terephthalate-co-adipate and / or polybutylene terephthalate-co-succinate. More preferably, The degradable polyester resin is polybutylene terephthalate-co-adipate; and / or, The degradable polyester resin is selected from a blend of polybutylene terephthalate-co-adipate and polylactic acid; and / or, The degradable polyester resin is selected from a blend of polybutylene terephthalate-co-adipate and polypropylene carbonate; and / or, The degradable polyester resin is selected from a blend of polybutylene succinate and polylactic acid; and / or, The degradable polyester resin is selected from a blend of polybutylene terephthalate-co-adipate, polypropylene carbonate and polylactic acid.

8. The barrier film according to any one of claims 1 to 7, wherein The thickness of a single layer of the barrier layer is 1 to 50 μm, preferably 5 to 40 μm; and / or, The thickness of each single layer of the base layer is 4 to 90 μm, preferably 20 to 75 μm; and / or, The thickness of the single layer of the adhesive layer is 0.5 to 35 μm, preferably 3 to 30 μm; and / or, The total thickness of the multi-layer barrier film is 10 to 300 μm, preferably 15 to 250 μm; and / or, The heat sealing strength of the multi-layer barrier film is not less than 3.5 N / 15 mm, preferably not less than 5.0 N / 15 mm; and / or, The interlayer peel strength of the multilayer barrier film is not less than 1.5N / 15mm, preferably not less than 2.5N / 15mm; and / or, The multi-layer barrier film has an oxygen transmission rate of no more than 6 cm at 23 ± 0.5 ° C and a relative humidity of 65% ± 5%. 3 / (m 2 ·day·atm), preferably no larger than 2cm 3 / (m 2 ·day·atm); and / or, The multi-layer barrier film has an oxygen permeability coefficient of no more than 1500 cm at 23±0.5°C and a relative humidity of 65%±5%. 3 μm / (m 2 ·day·atm), preferably not more than 500cm 3 μm / (m 2 ·day·atm); and / or, The water vapor transmission rate of the multilayer barrier film is not more than 30g / (m 2 ·day·atm), preferably not more than 15g / (m 2 ·day·atm); and / or, The water vapor permeability coefficient of the multilayer barrier film is not greater than 2000 g·μm / (m 2 ·day·atm), preferably not more than 1500g·μm / (m 2 ·day·atm).

9. A method for preparing the multilayer barrier film according to any one of claims 1 to 8, characterized in that: The preparation method comprises: A blend comprising a degradable resin as a base layer, a blend comprising polyglycolic acid having a multimodal molecular weight distribution as a barrier layer, and a blend comprising a polyglycolic acid block copolymer as a tie layer are co-extruded in multiple layers or extruded separately, followed by a step comprising film formation; Preferably, the film-making method is blown film or cast film, preferably blown film.

10. Use of the multilayer barrier film according to any one of claims 1 to 8 in food packaging bags, agricultural films, medical packaging, and electronic fields.

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