Polyethylene high-barrier film for bag-in-box

Abstract

The invention discloses a polyethylene high-barrier film for a bag in a box. The polyethylene high-barrier film comprises a polyethylene base film, an interface modification layer, a middle barrier coating and a protective layer which are arranged in sequence, the interface modification layer comprises a polyethylene homopolymer / copolymer modified by maleic anhydride or an epoxy functional monomer; the middle barrier coating is coated on the surface of one side, far away from the polyethylene film, of the interface modification layer. The high-barrier polyethylene film with good oxygen-barrier and moisture-barrier functions and high coating adhesion strength is obtained by adopting an interface engineering technology and a middle barrier coating coating mode, and compared with a polyethylene base film, the high-barrier polyethylene film has the advantages that the oxygen permeability can be as low as 0.6 cm < 3 > / (m < 2 > day), and the water vapor permeability can be as low as 2.7 g / (m < 2 > day). After the formula of the polyethylene base material film and the barrier coating is optimized, a material with better barrier performance can be obtained, and the high-barrier polyethylene film manufactured by the method meets the requirement of a single material and has great development potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible packaging materials, and particularly relates to a fully polyethylene high-barrier film realized by molecular interface engineering design. This technology is particularly suitable for the bag-in-box packaging of oxygen-sensitive products such as fruit juices, wines, and medical preparations. Background Art

[0002] In recent years, especially during the epidemic of the novel coronavirus, the bag-in-box form of packaging has grown significantly in some large-scale retail. Its obvious advantages compared with traditional glass bottle packaging include light weight, foldability, and low manufacturing cost. Currently, bag-in-box is mainly applied in the packaging fields of beverages, foods, medical chemical reagents, pesticides, etc. Rigid requirements such as long shelf life and low risk of oxidative deterioration require the inner bag of the bag-in-box to have a barrier function.

[0003] The current mainstream technical routes for the inner barrier film of bag-in-box are metallized barrier layer (such as aluminum foil) composite films, ethylene-vinyl alcohol copolymer multi-layer co-extruded films, and metal / transparent oxide coating films. These technologies have significant technical bottlenecks. Metallized composite films such as aluminum foil composite films have problems of non-thermosealability and electromagnetic shielding resulting in the failure of liquid level detection, and the recycling of the aluminum-plastic composite structure is difficult. The formula of the ethylene-vinyl alcohol copolymer multi-layer co-extruded film is complex, and its shelf life decays severely under high temperature and high humidity environments. It needs to be multi-layered with other barrier films to extend its service life, and its cost advantage is insufficient. Nano-coating films such as SiOx and AlOx prepared by vacuum coating technology have excellent barrier properties and optical transparency, but the film has poor folding resistance, and the micro-cracks of the coating have a significant impact on the barrier properties of the material, and the reliability is not high. The above related technologies can be seen in patents such as CN 110154477 A and CN118900809 A, while some solutions disclosed in CN 210392034 U and CN 214000839 U have too many composite layers and the process is slightly cumbersome. Based on this, the invention aims to provide a film for bag-in-box with low cost, simple process, and excellent barrier properties and its preparation method. Summary of the Invention

[0004] The purpose of the present invention is to realize the continuous production of a single-material high-barrier film on ordinary equipment through the synergistic effect of interface modification of the polyethylene film substrate and the intermediate barrier coating, breaking through the dependence of traditional processes on multi-layer film co-extrusion equipment.

[0005] To solve the above technical problems, the purpose of the present invention is achieved as follows: A polyethylene high-barrier film for bag-in-box according to the present invention, the polyethylene high-barrier film comprises a polyethylene base film, an interface modification layer, an intermediate barrier coating, and a protective layer arranged in sequence; The interface modification layer includes a polyethylene homopolymer / copolymer modified with maleic anhydride or an epoxy functional monomer; The intermediate barrier coating is coated on the surface of the interface modification layer away from the polyethylene film; The protective layer covers the surface of the barrier coating.

[0006] Based on the above solution and as a preferred solution of the above solution: The implementation form of the interface modification layer on the polyethylene-based film can be one of multilayer coextrusion and coating; The coating method of the intermediate barrier coating is one or more of knife coating, spin coating, roll coating, dip coating.

[0007] Based on the above solution and as a preferred solution of the above solution: The implementation form of the protective layer can be one of coating and lamination; among them, the coating method is selected from one or more of knife coating, spin coating, roll coating, dip coating; the lamination method is selected from dry lamination, extrusion lamination, wet lamination, solventless lamination, hot melt lamination, coating lamination.

[0008] Based on the above solution and as a preferred solution of the above solution: The particles used for the polyethylene-based film are selected from one or more of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, metallocene polyethylene, high-density polyethylene.

[0009] Based on the above solution and as a preferred solution of the above solution: The particles used for the interface modification layer are selected from one or more of maleic anhydride grafted polyethylene, glycidyl acrylate grafted polyethylene, glycidyl methacrylate grafted polyethylene.

[0010] Based on the above solution and as a preferred solution of the above solution: The intermediate barrier coating is selected from one or more of a modified polyvinylidene chloride aqueous dispersion, a cellulose fiber aqueous dispersion, a polyvinyl alcohol aqueous solution, a chitosan aqueous dispersion; The protective layer is a polyethylene film.

[0011] Based on the above solution and as a preferred solution of the above solution: The interface modification layer is selected from one or more of ethylene-acrylic acid copolymer, maleic anhydride grafted ethylene-vinyl acetate copolymer, maleic anhydride grafted ethylene-methyl acrylate copolymer, (meth)acrylic acid glycidyl ester grafted ethylene-vinyl acetate copolymer, (meth)acrylic acid glycidyl ester grafted ethylene-methyl acrylate copolymer.

[0012] Based on the above solution and as a preferred solution of the above solution: The intermediate barrier coating is formed by crosslinking and curing of polyvinyl alcohol and its derivatives and bio-based nanofillers through a crosslinking agent; the protective layer is constructed by doping functional inorganic fillers into a functionalized polyethylene copolymer; The functionalized polyethylene copolymer is selected from one or more of maleic anhydride grafted ethylene-vinyl acetate copolymer, maleic anhydride grafted ethylene-methyl acrylate copolymer, glycidyl (meth)acrylate grafted ethylene-vinyl acetate copolymer, and glycidyl (meth)acrylate grafted ethylene-methyl acrylate copolymer; The functional inorganic filler is selected from one or several of carbon nanotubes, halloysite nanotubes, graphene nanosheets, strip-shaped silica particles, and flaky mica.

[0013] Based on the above solution and as a preferred solution of the above solution: The bio-based nano filler is mainly one or two of carboxyl-modified cellulose fibers and carboxyl-modified cellulose nanocrystals.

[0014] Based on the above solution and as a preferred solution of the above solution: The crosslinking agent is selected from one or more of boric acid, glutaraldehyde, malic acid, glycerol triglycidyl ether, polyglycidyl methacrylate, polyacrylic acid, and polyisocyanate.

[0015] The beneficial effect of the present invention is that: A high-barrier polyethylene film for bag-in-box of the present invention uses interface engineering technology and intermediate barrier coating coating methods to obtain a high-barrier polyethylene film with good oxygen and moisture barrier functions and high coating adhesion strength. Compared with the polyethylene base film, its oxygen transmission rate can be as low as 0.5 cm 3 / (m 2 ·day), and the water vapor transmission rate can be as low as 2.7 g / (m 2 ·day). After optimizing the polyethylene base film and the barrier coating formula, materials with better barrier properties can be obtained. The high-barrier polyethylene film manufactured by this invention meets the single material requirement and has great development potential. Description of the Drawings

[0016] Figure 1 is a schematic structural diagram of the high-barrier polyethylene film involved in the present invention. The markings in the figure are explained as follows: 1 - polyethylene base film; 2 - interface modification layer; 3 - intermediate barrier coating; 4 - protective layer.

[0017] Figure 2 is an infrared spectrogram of the surface of the polyethylene base film after the composite peeling test involved in Example 1 and Comparative Example 1. Detailed Embodiments

[0018] The present invention will be further described below with reference to the drawings and specific embodiments.

[0019] A polyethylene high-barrier film for bag-in-box, the polyethylene high-barrier film comprises a polyethylene base film 1, an interface modification layer 2, an intermediate barrier coating 3 and a protective layer 4 which are arranged in sequence; the interface modification layer 2 comprises a polyethylene homopolymer / copolymer modified by maleic anhydride or an epoxy functional monomer; the intermediate barrier coating 3 is coated on one surface of the interface modification layer 2 away from the polyethylene film 1.

[0020] The present invention provides a method for preparing a polyethylene high-barrier film with excellent oxygen and moisture barrier functions, which mainly applies interface engineering technology and gradient functional coating technology in principle. The interface modification of the polyethylene film is mainly based on a polyethylene homopolymer / copolymer modified by maleic anhydride or an epoxy functional monomer. In the intermediate barrier coating, polyhydroxy / carboxyl structures such as main agent polyvinyl alcohol and carboxyl modified cellulose, and polyepoxy / isocyanate structures of crosslinking agents can form physical strong hydrogen bond interactions and chemical covalent bond crosslinks with functional groups on the polyethylene film such as maleic anhydride / glycidyl (meth)acrylate, thereby forming a molecular interpenetrating network structure at the interface between the polyethylene base film and the intermediate barrier coating. The formation of this molecular interpenetrating network structure promotes the adhesion strength of the intermediate barrier coating at the interface, and the overall consistency of the polyethylene base film and the barrier coating film is better, avoiding the risk of delamination during long-term use or high-temperature cooking of the material. The mechanism of good binding between the interface modification layer and the intermediate barrier layer, and between the intermediate barrier layer and the protective layer also stems from this. The interface modification layer 2 selects a functional group-modified vinyl copolymer to ensure the compatibility of the coating and the polyethylene base film 1 from the polar level, and functional groups such as maleic anhydride / glycidyl (meth)acrylate further realize the binding with the barrier coating. In addition, surface polyhydroxy polymers such as cellulose and halloysite nanotubes also belong to this category. Their use in the coating will also form an interface binding at the molecular scale with the functional polymer, further improving the strength and barrier performance of the coating.

[0021] Example 1 Combined with Figure 1 , a detailed description of this example is given. A polyethylene high-barrier film for bag-in-box involved in this example, the polyethylene high-barrier film comprises the following steps when being prepared: Firstly, a polyethylene base film is prepared by using a three-layer blown film machine. The formula mainly uses LLDPE, LDPE, mLLDPE and maleic anhydride grafted PE. The formula and barrel temperature of different layers are shown in Table 1, and finally a film with a thickness of 50 μm is prepared.

[0022] Table 1 Blown film process of Example 1 In this embodiment, the inner layer and the middle layer form a polyethylene film 1, and the outer layer is an interfacial modification layer 2 formed by maleic anhydride grafted PE. The thickness of the polyethylene film with the interfacial modification layer 2 formed is 10 μm - 100 μm. And the ratio of the outer layer: the middle layer: the inner layer = 1:1:1.

[0023] Take a certain amount of polyvinyl alcohol ( M w = 74.8 kDa), dissolve it to prepare an aqueous solution with a concentration of 10 wt%, and then add a small amount of boric acid to the PVA solution. The mass ratio of boric acid to polyvinyl alcohol is 1:100. The uniformly stirred solution is coated on the above-mentioned polyethylene film by means of knife coating, and the coating amount is 8 g / m 2 , and then the moisture is dried in an oven at 70 °C. The dried film is further cured in an oven at 60 °C for 3 days, and the formed is an intermediate barrier coating 3 on one side of the interfacial modification layer 2.

[0024] The coated polyethylene film is further compounded with the uncoated polyethylene film to prepare a PE / coated / PE composite film, that is, a polyethylene high-barrier film. The thickness of the polyethylene high-barrier film is about 102 μm, and the glue used for compounding is selected from two-component polyurethane solvent glue.

[0025] The oxygen barrier property and water vapor barrier property of the above-mentioned polyethylene film, coated PE film and PE / coated / PE film are tested by using MOCON OX-TRAN2 / 28 and MOCON AQUATRAN 3 / 38 respectively. The oxygen barrier property test conditions are 23 °C / 0% RH, and the water vapor barrier property test conditions are 38 °C / 90%RH. The test results are shown in Table 2. It can be seen from the data in the table that the barrier property of the polyethylene film is poor. The oxygen transmission rate of the coated PE film is reduced by 2 - 3 orders of magnitude, and the water vapor transmission rate of the PE / coated / PE composite film decreases significantly with the increase of the thickness of the PE film.

[0026] The composite film is subjected to a peel test by using a standard machine-packaged electronic tensile machine, where the width of the tensile film sample is 15 mm and the tensile speed is 100 mm / min. At the same time, the surface of the substrate film after peeling is analyzed by infrared spectroscopy using Thermo Fisher FTIR, as shown in the appendix Figure 2 . The C-O characteristic group on the polyvinyl alcohol at the wavenumber of 1000 - 1200 cm -1 indicates that there is still a coating attached to the surface of the PE film after the peel test.

[0027] Table 2 Barrier property data of each film in Example 1 Comparative Example 1 For the composite film solution prepared in this comparative example, except for the base film process formulation, the preparation methods of the remaining samples are the same as those in Example 1. The base film process solution is shown in Table 3, and the difference is that the outer layer material of the PE base film is conventional PE. The Fourier infrared curve after the peel test is shown in the appendix Figure 2 As shown. By comparing the curves in Example 1, it can be found that the coating did not remain on the PE surface after peeling, indicating that a molecular penetration network structure could not be formed between the film without functional groups on the surface and the barrier coating.

[0028] Table 3 Blown film process of Comparative Example 1 Example 2 A polyethylene high-barrier film for bags-in-box involved in this example includes the following steps during preparation: Similar to Example 1, a polyethylene base film is prepared using a three-layer blown film machine. The formulations of different layers are shown in Table S2-1, and the thickness of the prepared film is also 50 μm.

[0029] Table 4 Blown film process of Example 2 The formed polyethylene base film 1 consists of three layers, namely layer A, layer B, and layer C. Each layer is made of LLDPE, LDPE, and mLLDPE in different proportions.

[0030] An ethylene-acrylic copolymer (ESCOR TM EAA 5050) aqueous emulsion with a solid content of 20% and a maleic anhydride grafted ethylene-vinyl acetate copolymer (BYNEL TM EVA-g-MAH 39E660) aqueous emulsion with a solid content of 40% are prepared by the solution emulsification method. The prepared aqueous emulsions are blended at a ratio of EVA:EAA = 4:1 and continuously stirred evenly. Subsequently, the blended emulsion is coated on the previously prepared polyethylene base film 1 by roll coating, and the moisture on the film surface is dried in an oven at 80 °C to obtain a polyethylene base film 1 with an interfacial modification layer 2.

[0031] A certain amount of polyvinyl alcohol with a weight average molecular weight of 60 kDa is used to prepare an aqueous solution with a solid content of 10 wt%. After the solid is completely dissolved, a carboxyl-modified cellulose fiber solution is added to the solution. The mass ratio of the carboxyl-modified cellulose fiber to polyvinyl alcohol is 5:95. After mixing and stirring for 4 h, a small amount of glutaraldehyde and hydrochloric acid are added to the solution. Glutaraldehyde accounts for about 0.5% of the solid content in the mixed solution. The uniformly stirred coating solution is evenly coated on the above polyethylene base film by roll coating. The oven temperature is set in the range of 60-75 °C, and the dried film is further cured in an oven at 60 °C for 72 h for standby.

[0032] Furthermore, an aqueous emulsion (EMA-g-GMA) of glycidyl methacrylate grafted ethylene-methyl acrylate copolymer (LOTADER EMA AX8900) with a solid content of 20% was prepared by the solution emulsification method. Meanwhile, halloysite nanotubes with a length of about 1 μm and an aspect ratio of 100 were weighed and dispersed in a mixed solution of deionized water and ethanol by ultrasonic dispersion to prepare an inorganic filler dispersion of halloysite nanotubes with a solid content of 2%. Subsequently, the above EMA-g-GMA aqueous dispersion was mixed with the inorganic filler dispersion and stirred continuously at room temperature for 2 h for standby, where the proportion of halloysite nanotubes in the polymer was 10%. The uniformly mixed dispersion was further coated on the surface of the barrier coating by roll coating, dried in an oven at 80 °C, and then cured in a curing chamber at 55 °C for 48 h to obtain the required sample. The thickness of the final finished film was measured to be 55 μm.

[0033] The barrier property testing equipment and testing conditions of the materials in this example were the same as those in Example 1. The test results are shown in Table 5. The results show that compared with the polyethylene base film, the oxygen barrier property of the polyethylene high-barrier film formed after coating has been significantly improved. At the same time, the oxygen barrier property of the polyethylene high-barrier film hardly changes after boiling sterilization in water at 80 °C for 15 min.

[0034] Table 5 Comparison of barrier property data of the films in Example 2 and Comparative Example 1 The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative efforts. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention based on the concept of the present invention through logical analysis, reasoning, or limited experiments on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A polyethylene high-barrier film for bag-in-box, characterized in that, It includes a polyethylene film (1), an interfacial modification layer (2), an intermediate barrier coating (3), and a protective layer (4) arranged in sequence; The interfacial modification layer (2) includes a polyethylene homopolymer / copolymer modified with maleic anhydride or epoxy functional monomers; The intermediate barrier coating (3) is coated on the surface of the interfacial modification layer (2) away from the polyethylene film (1).

2. The protective layer (4) covers the surface of the barrier coating (3).

3. A polyethylene high-barrier film for bag-in-box according to claim 1, wherein, The implementation form of the interfacial modification layer (2) on the polyethylene film (1) can be one of multilayer coextrusion and coating; the coating method of the intermediate barrier coating (3) is one or more of knife coating, spin coating, roll coating, and dip coating.

4. A polyethylene high-barrier film for bag-in-box according to claim 1, characterized in that, The implementation form of the protective layer (4) can be one of coating and lamination; among them, the coating method is selected from one or more of knife coating, spin coating, roll coating, and dip coating; the lamination method is selected from dry lamination, extrusion lamination, wet lamination, solvent-free lamination, hot melt lamination, and coating lamination.

5. A polyethylene high-barrier film for use in bag-in-box according to claim 1, characterized in that, The particles used for the polyethylene film (1) are selected from one or more of low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, metallocene polyethylene, and high-density polyethylene.

6. A polyethylene high-barrier film for bag-in-box according to any one of claims 1-4, characterized in that, The particles used for the interfacial modification layer (2) are selected from one or more of maleic anhydride-grafted polyethylene, glycidyl acrylate-grafted polyethylene, and glycidyl methacrylate-grafted polyethylene.

7. A polyethylene high-barrier film for bag-in-box according to claim 5, characterized in that, The intermediate barrier coating (3) is selected from one or more of modified polyvinylidene chloride aqueous dispersion, cellulose fiber aqueous dispersion, polyvinyl alcohol aqueous solution, and chitosan aqueous dispersion; The protective layer (4) is a polyethylene film.

8. A polyethylene high-barrier film for bag-in-box according to any one of claims 1-4, characterized in that The interfacial modification layer (2) is selected from one or more of ethylene-acrylic acid copolymer, maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted ethylene-methyl acrylate copolymer, (meth)acrylic acid glycidyl ester-grafted ethylene-vinyl acetate copolymer, and (meth)acrylic acid glycidyl ester-grafted ethylene-methyl acrylate copolymer.

9. A polyethylene high-barrier film for pouch-in-box according to claim 7, characterized in that, The intermediate barrier coating (3) is formed by crosslinking and curing of polyvinyl alcohol and its derivatives and bio-based nanofillers through a crosslinking agent; the protective layer (4) is constructed by doping a functionalized polyethylene copolymer with functional inorganic fillers; The functionalized polyethylene copolymer is selected from one or more of maleic anhydride-grafted ethylene-vinyl acetate copolymer, maleic anhydride-grafted ethylene-methyl acrylate copolymer, (meth)acrylic acid glycidyl ester-grafted ethylene-vinyl acetate copolymer, and (meth)acrylic acid glycidyl ester-grafted ethylene-methyl acrylate copolymer; The functional inorganic fillers are selected from one or more of carbon nanotubes, halloysite nanotubes, graphene nanosheets, strip-shaped silica particles, and flaky mica.

10. A polyethylene high-barrier film for pouch-in-box according to claim 8, characterized in that, The bio-based nanofillers are mainly one or two of carboxyl-modified cellulose fibers and carboxyl-modified cellulose nanocrystals.

11. A polyethylene high-barrier film for bag-in-box according to claim 8, characterized in that, The crosslinking agent is selected from one or more of boric acid, glutaraldehyde, malic acid, glycerol triglycidyl ether, polymethyl methacrylate glycidyl ester, polyacrylic acid, and polyisocyanate.

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