A high-barrier composite film and its preparation method

Abstract

The present invention discloses a high-barrier composite film and a preparation method thereof, belonging to the technical field of composite films. The present invention uses carboxyl-modified polyvinyl alcohol resin and nanohydrotalcite as the main components, strengthens the barrier performance through a crosslinking agent, and also adds carboxyl-terminated polyethylene glycol siloxane to modify the surface of the nanohydrotalcite, shielding its surface hydroxyl groups, and using the steric hindrance effect of the polyethylene glycol macromolecular chain segments to inhibit the agglomeration of the nanosheets and strengthen the dispersibility, so that it not only meets the recyclability but also has remarkable barrier properties. In addition, in the present invention, carboxyl-modified polyethylene is introduced into the preparation raw materials of the first PE layer and the second PE layer, and after corona treatment, the surface has more carboxyl functional groups, which can interact with the carboxyl-modified polyvinyl alcohol resin, carboxyl-terminated polyethylene glycol siloxane-modified nano filler and multi-functional aziridine crosslinking agent in the high-barrier coating to enhance the barrier performance and bonding strength.

Description

Technical Field

[0001] The present invention relates to the technical field of composite films, and more specifically, to a high-barrier composite film and a preparation method thereof. Background Art

[0002] Recyclable plastic flexible packaging is a new type of environmentally friendly packaging material, which usually requires that the proportion of a single material component reaches more than 95%. When recyclable plastic flexible packaging is applied to occasions such as food, medicine, and electronic devices where high freshness preservation of the contents is required and water and oxygen barrier conditions need to be met, it often also needs to have high barrier performance. Traditional high-barrier flexible packaging films, such as aluminized films or multilayer coextruded films, cannot meet the recyclable index. Therefore, developing a plastic flexible packaging film with both high barrier performance and recyclability is an important topic.

[0003] In order to meet packaging processability, barrier properties, and recyclability, preparing a composite film by coating a high-barrier coating on a base film is an ideal solution. Polyvinylidene chloride (PVDC) emulsion is a traditional polymer coating used to prepare coated barrier films. For example, the patent with the publication number CN101654165A discloses a composite paper-plastic food packaging material using PVDC as a barrier coating. However, PVDC contains chlorine element, is toxic when incinerated, and is difficult to recycle and dispose of waste, and is also not environmentally friendly, and has gradually been phased out in food packaging. Polyvinyl alcohol (PVA) is a polymer material commonly used to prepare high-barrier coatings, and has the characteristics of wide source, stable performance, excellent barrier performance, non-toxic and harmless, etc. Another example is the patent with the publication number CN103382677A, which discloses a high-barrier polyvinyl alcohol coating for inner liner paper coating and a preparation method thereof. The coating is directly coated on the inner liner paper substrate and has good adhesion and barrier properties, but there is still room for improvement in its barrier performance.

[0004] In order to make the proportion of a single material reach more than 95% to meet recyclability, the coating thickness cannot be too large. However, existing technical solutions are difficult to meet the fresh-keeping and barrier requirements of food grade when the coating thickness is small. In addition, PVA is easy to absorb moisture, and its barrier performance drops sharply after absorbing moisture; the bonding force between PVA and conventional packaging materials (such as polyethylene (PE)) is poor. These disadvantages seriously limit the development and application of coated recyclable high-barrier composite films. Summary of the Invention

[0005] Based on this, in order to solve one of the above problems, the present invention provides a high-barrier composite film and a preparation method thereof. The specific technical solutions are as follows:

[0006] A high-barrier composite film, which comprises a first PE layer, a high-barrier coating and a second PE layer arranged in sequence, and the thicknesses of the first PE layer and the second PE layer respectively account for 20% - 79% of the total thickness of the high-barrier composite film, and the thickness of the high-barrier coating accounts for 1% - 5% of the total thickness of the high-barrier composite film;

[0007] Among them, both the first PE layer and the second PE layer comprise the following raw materials for preparation in parts by weight: 30 - 80 parts of PE resin, 20 - 70 parts of carboxyl-modified polyethylene, and 0.1 - 10 parts of auxiliary materials;

[0008] The high-barrier coating comprises the following raw materials for preparation in parts by weight: 100 parts of carboxyl-modified polyvinyl alcohol resin, 40 - 400 parts of nano-hydrotalcite, 1 - 80 parts of carboxyl-terminated polyethylene glycol siloxane, 3 - 12 parts of cross-linking agent, and 3 - 12 parts of auxiliary agent.

[0009] Further, the melt index of the PE resin under the conditions of 190°C and 2.16 kg ranges from 1 g / 10 min to 30 g / 10 min.

[0010] Further, the carboxyl-modified polyethylene is one or more of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, acrylic acid grafted polyethylene, and methacrylic acid grafted polyethylene.

[0011] Further, the auxiliary materials include one or more of antioxidant, ultraviolet absorber, plasticizer, flame retardant, nucleating agent, and inorganic filler.

[0012] Further, the carboxyl-modified polyvinyl alcohol resin has a weight-average molecular weight of 60,000 g / moL - 300,000 g / moL, a degree of alcoholysis of 80% - 99%, and a mass fraction of carboxyl of 0.2% - 5%.

[0013] Further, the nano-hydrotalcite is an inorganic nanosheet with a layered structure, the single sheet thickness is 6 nm - 20 nm, and the average aspect ratio of the single sheet is 150 - 250.

[0014] Further, the carboxyl-terminated polyethylene glycol siloxane has a weight-average molecular weight of the polyethylene glycol segment of 200 g / moL - 4000 g / moL;

[0015] The chemical structural formula of the carboxyl-terminated polyethylene glycol siloxane is as follows: .

[0016] Further, the crosslinking agent is a multi-functional aziridine crosslinking agent, and the multi-functional aziridine crosslinking agent is one or more of trimethylolpropane tris[3-(2-methylaziridinyl)]propionate, trimethylolpropane tris(3-aziridinyl)propionate, and pentaerythritol tris(3-aziridinyl)propionate.

[0017] Further, the auxiliary agents include one or more of defoamers, leveling agents, antioxidants, hydrolysis inhibitors, and UV absorbers.

[0018] In addition, the present invention provides a method for preparing a high-barrier composite film, and the preparation method includes the following steps:

[0019] Mix the raw materials for preparing the first PE layer evenly, melt-blend and extrude them into pellets through a twin-screw extruder to obtain the first PE layer mixture, and then melt-process the film into a shape. After corona treatment, obtain the first PE layer base film;

[0020] Mix the raw materials for preparing the second PE layer evenly, melt-blend and extrude them into pellets through a twin-screw extruder to obtain the second PE layer mixture, and then melt-process the film into a shape. After corona treatment, obtain the second PE layer base film;

[0021] Disperse the carboxyl-modified polyvinyl alcohol resin, crosslinking agent, and auxiliary agents in an appropriate amount of water to obtain a carboxyl-modified polyvinyl alcohol aqueous dispersion; then disperse the nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, and stir at 50°C to 80°C for 6h to 24h to obtain a carboxyl-modified nano-hydrotalcite aqueous dispersion, and cool it to room temperature; then, under stirring conditions, add the carboxyl-modified nano-hydrotalcite aqueous dispersion to the carboxyl-modified polyvinyl alcohol aqueous dispersion, and adjust the solid content to be within the range of 3% to 15% to obtain a high-barrier coating;

[0022] Coat the high-barrier coating on one side of the first PE layer base film and / or the second PE layer base film, then bond the coated side, dry it with hot air at 60°C to 105°C, and then cure it at 45°C to 80°C for 48h to 72h to obtain a high-barrier composite film.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. By optimizing the raw materials for preparing the high-barrier coating, the present invention uses carboxyl-modified polyvinyl alcohol resin and nano-hydrotalcite as the main components, which have more excellent denseness. The barrier performance is strengthened by a cross-linking agent, and carboxyl-terminated polyethylene glycol siloxane is also added to modify the surface of the nano-hydrotalcite, shielding the surface hydroxyl groups thereof. At the same time, the steric hindrance effect of the polyethylene glycol macromolecular chain segment is used to inhibit the aggregation of the nanosheets and strengthen their dispersibility. The single-sheet thickness of the nano-hydrotalcite is defined as 6 nm to 20 nm, and the average diameter-thickness ratio of the single sheet is 150 to 250, so that when the coating thickness does not exceed 5% of the thickness of the high-barrier composite film, it not only meets the recyclability but also has significant barrier properties.

[0025] 2. By introducing carboxyl-modified polyethylene into the raw materials for preparing the first PE layer and the second PE layer, and after corona treatment, the surface has more carboxyl functional groups, which can interact with the carboxyl-modified polyvinyl alcohol resin, carboxyl-terminated polyethylene glycol siloxane-modified nano-fillers and multi-functional aziridine cross-linking agent in the high-barrier coating. While ensuring the high-barrier performance, it initiates the carboxyl cross-linking reaction of each component, significantly increasing the bonding force between the first PE layer, the high-barrier coating and the second PE layer. Specifically, a multi-functional aziridine cross-linking agent is added to initiate the reaction of the first PE layer, the high-barrier coating layer and the second PE layer, so that they are combined by chemical bond action to avoid the peeling of the coating; it initiates the reaction between the carboxyl-modified polyvinyl alcohol resin, carboxyl-terminated polyethylene glycol siloxane and nano-hydrotalcite, not only strengthening the mechanical strength of the high-barrier coating but also significantly improving the barrier performance of the high-barrier coating. Overall, it solves the problem of poor bonding force between the polar high-barrier coating and the non-polar PE layer.

[0026] 3. By setting the sandwich structure of the first PE layer, the high-barrier coating and the second PE layer, the non-polar PE layer has excellent water resistance. With the synergistic effect of the high-barrier coating, it can significantly improve the moisture intrusion. And by adding a multi-functional aziridine cross-linking agent to promote the cross-linking of the carboxyl-modified polyvinyl alcohol resin, it can also significantly reduce the moisture absorption of the composite film. Description of the Drawings

[0027] Figure 1 It is a schematic structural diagram of the high-barrier composite film prepared in Example 1 of the present invention;

[0028] Figure 2 It is a schematic principle diagram of the carboxyl-terminated polyethylene glycol siloxane-modified nano-hydrotalcite in Example 1 of the present invention.

[0029] Description of the Reference Numerals:

[0030] 1 - First PE layer, 2 - High-barrier composite layer, 3 - Second PE layer. Detailed Embodiments

[0031] In order to make the objectives, technical solutions and advantages of the present invention more clear and understandable, the present invention will be further described in detail below in conjunction with its embodiments. It should be understood that the specific implementation manners described herein are only used to explain the present invention and do not limit the protection scope of the present invention.

[0032] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this invention belongs. The terms used herein in the description of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0033] A high-barrier composite film in an embodiment of the present invention, the high-barrier composite film includes a first PE layer, a high-barrier coating layer and a second PE layer arranged in sequence, and the thicknesses of the first PE layer and the second PE layer respectively account for 20% to 79% of the total thickness of the high-barrier composite film, and the thickness of the high-barrier coating layer accounts for 1% to 5% of the total thickness of the high-barrier composite film;

[0034] Wherein, both the first PE layer and the second PE layer include the following raw materials in parts by weight: 30 parts to 80 parts of PE resin, 20 parts to 70 parts of carboxyl-modified polyethylene, and 0.1 part to 10 parts of auxiliary materials;

[0035] The high-barrier coating layer includes the following raw materials in parts by weight: 100 parts of carboxyl-modified polyvinyl alcohol resin, 40 parts to 400 parts of nano-hydrotalcite, 1 part to 80 parts of carboxyl-terminated polyethylene glycol siloxane, 3 parts to 12 parts of cross-linking agent, and 3 parts to 12 parts of auxiliary agent.

[0036] In one embodiment, the melt index of the PE resin at 190°C and 2.16 kg is in the range of 1 g / 10 min to 30 g / 10 min, preferably 5 g / 10 min to 20 g / 10 min. It has better processing performance within this range.

[0037] In one embodiment, the PE resin is one or more of low-density polyethylene, high-density polyethylene, linear low-density polyethylene, metallocene polyethylene, ethylene-α-olefin copolymer, and bimodal polyethylene.

[0038] In one embodiment, the carboxyl-modified polyethylene is one or more of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, acrylic acid-grafted polyethylene, and methacrylic acid-grafted polyethylene.

[0039] In one embodiment, the melt index of the carboxyl-modified polyethylene at 190 °C and 2.16 kg is in the range of 1 g / 10 min to 30 g / 10 min, preferably 5 g / 10 min to 20 g / 10 min. It has better processing performance within this range.

[0040] In one embodiment, the mass fraction of the carboxyl functional monomer in the carboxyl-modified polyethylene ranges from 0.5% to 25%. It has good reactivity and processability within this range.

[0041] In one embodiment, the auxiliary materials include one or more of antioxidants, UV absorbers, plasticizers, flame retardants, nucleating agents, and inorganic fillers.

[0042] In one embodiment, the weight-average molecular weight of the carboxyl-modified polyvinyl alcohol resin is 60,000 g / mol to 300,000 g / mol, the degree of alcoholysis is 80% to 99%, and the mass fraction of carboxyl is 0.2% to 5%. The carboxyl-modified polyvinyl alcohol resin within this range has good water solubility, reactivity, and storage stability.

[0043] In one embodiment, the nano-hydrotalcite is an inorganic nanosheet with a layered structure, the single sheet thickness is 6 nm to 20 nm, and the average aspect ratio of the single sheet is 150 to 250. When the single sheet thickness is less than 6 nm, not only the raw material production cost is high, but also the strength of the composite film is affected; when the single sheet thickness is greater than 20 nm, the dispersibility is extremely poor, which will affect the stability of the coating; when the average aspect ratio of the single sheet is less than 150, an effective barrier channel cannot be formed, and its barrier performance will be affected; when the average aspect ratio is greater than 250, the strength of the nano-hydrotalcite sheet is low, it is easy to spontaneously break, and the processing cost is high.

[0044] In one embodiment, the nano-hydrotalcite is one or more of magnesium-aluminum hydrotalcite, aluminum-nickel hydrotalcite, magnesium-indium hydrotalcite, magnesium-gallium hydrotalcite, and zinc-aluminum hydrotalcite, preferably magnesium-aluminum hydrotalcite.

[0045] In one embodiment, the weight-average molecular weight of the polyethylene glycol segment of the carboxyl-terminated polyethylene glycol siloxane is 200 g / mol to 4,000 g / mol;

[0046] The chemical structural formula of the carboxyl-terminated polyethylene glycol siloxane is as follows: .

[0047] The carboxyl-terminated polyethylene glycol siloxane can react with the surface hydroxyl groups of the nano-hydrotalcite, shielding its surface hydroxyl groups. The high molecular weight polyethylene glycol chain segments further play a steric hindrance role, reducing the agglomeration of the nano-hydrotalcite and enhancing the water dispersibility of the nanosheets. The terminal carboxyl groups can participate in the cross-linking reaction of the coating, increasing the coating strength. If the molecular weight of the above-mentioned polyethylene glycol chain segments is too small, the steric hindrance effect is too weak and the dispersion effect is not ideal; if the molecular weight is too large, the steric hindrance effect is too strong, which will affect the reaction between the siloxane and the hydroxyl groups.

[0048] In one embodiment, the cross-linking agent is a multi-functional aziridine cross-linking agent, and the multi-functional aziridine cross-linking agent is one or more of trimethylolpropane-tris[3-(2-methylaziridinyl)]propionate, trimethylolpropane-tris(3-aziridinyl)propionate, and pentaerythritol tris(3-aziridinyl)propionate.

[0049] In one embodiment, the reaction formula of the multi-functional aziridine cross-linking agent and the carboxyl group is as follows:

[0050] 。

[0051] In one embodiment, the auxiliary agents include one or more of defoamers, leveling agents, antioxidants, anti-hydrolysis agents, and UV absorbers.

[0052] In addition, the present invention provides a method for preparing a high-barrier composite film, and the preparation method includes the following steps:

[0053] Mix the raw materials for preparing the first PE layer evenly, melt-blend and extrude granulate in a twin-screw extruder to obtain the first PE layer mixture, and then melt-process into a film and corona-treat to obtain the first PE layer base film;

[0054] Mix the raw materials for preparing the second PE layer evenly, melt-blend and extrude granulate in a twin-screw extruder to obtain the second PE layer mixture, and then melt-process into a film and corona-treat to obtain the second PE layer base film;

[0055] Disperse the carboxyl-modified polyvinyl alcohol resin, cross-linking agent, and auxiliary agents in an appropriate amount of water to obtain a carboxyl-modified polyvinyl alcohol aqueous dispersion; then disperse the nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, and stir at 50°C to 80°C for 6h to 24h to obtain a carboxyl-modified nano-hydrotalcite aqueous dispersion, and cool to room temperature; then, under stirring conditions, add the carboxyl-modified nano-hydrotalcite aqueous dispersion to the carboxyl-modified polyvinyl alcohol aqueous dispersion, and adjust the solid content to be in the range of 3% to 15% to obtain a high-barrier coating;

[0056] Coat the high-barrier coating on one side of the first PE layer base film and / or the second PE layer base film, then bond the coated sides together, dry them with hot air at 60°C to 105°C, and then cure them at 45°C to 80°C for 48h to 72h to obtain a high-barrier composite film.

[0057] In one embodiment, the melt processing film forming includes, but is not limited to, processes such as blow molding, casting, and calendering.

[0058] In the above solution, by optimizing the composition of each layer, overall, excellent bonding strength can be obtained. Even when the thickness of the coating layer is not more than 5% of the overall thickness of the composite film, it still has significant barrier properties and meets the requirements for recyclability.

[0059] The following will describe the implementation schemes of the present invention in detail with specific embodiments.

[0060] It should be noted that the CPVA resin described in this application is a carboxyl-modified polyvinyl alcohol resin.

[0061] Example 1:

[0062] A high-barrier composite film has a three-layer structure, which is sequentially arranged as a first PE layer, a high-barrier coating layer, and a second PE layer;

[0063] Both the first PE layer and the second PE layer include the preparation raw materials described in Table 1 below, and the high-barrier coating layer includes the preparation raw materials described in Table 2 below;

[0064] Table 1: Preparation raw materials of the first PE layer and the second PE layer

[0065]

[0066] Table 2: Preparation raw materials of the high-barrier coating layer

[0067]

[0068] The preparation method of the high-barrier composite film in Example 1 is as follows:

[0069] First step, dry and mix the preparation raw materials of the first PE layer and the second PE layer respectively in proportion, put them into a twin-screw extruder for melt blending and extrusion granulation to obtain a PE layer mixture; then melt-cast the PE layer mixture into a film, and after corona treatment, obtain the first PE layer base film and the second PE layer base film respectively;

[0070] Step 2: Dissolve / disperse the metered CPVA resin, crosslinking agent, and additives in an appropriate amount of water to obtain a CPVA aqueous dispersion. Disperse the metered nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, and stir at 80 °C for 6 h to prepare an aqueous dispersion of carboxyl-modified nano-hydrotalcite. After cooling to room temperature, add it to the above CPVA aqueous dispersion while stirring, and adjust the water volume to make the overall solid content of the coating 8%, obtaining a high-barrier coating;

[0071] Step 3: Uniformly coat the high-barrier coating on one side of the first PE layer base film, and then cover the second PE layer base film above the side coated with the high-barrier coating. Dry it with hot air at 95 °C, and then cure it at 80 °C for 48 h to obtain the high-barrier composite film of this example.

[0072] The total thickness of the high-barrier composite film prepared in Example 1 is 0.15 mm. The thickness of the first PE layer accounts for 48% of the total thickness of the high-barrier composite film, the thickness of the high-barrier coating accounts for 4% of the total thickness of the high-barrier composite film, and the thickness of the second PE layer accounts for 48% of the total thickness of the high-barrier composite film.

[0073] Example 2:

[0074] A high-barrier composite film has a three-layer structure, which are sequentially arranged as a first PE layer, a high-barrier coating, and a second PE layer;

[0075] The first PE layer includes the preparation raw materials as described in Table 3 below, the second PE layer includes the preparation raw materials as described in Table 4 below, and the high-barrier coating includes the preparation raw materials as described in Table 5 below;

[0076] Table 3: Preparation raw materials of the first PE layer

[0077]

[0078] Table 4: Preparation raw materials of the second PE layer

[0079]

[0080] Table 5: Preparation raw materials of the high-barrier coating

[0081]

[0082] The preparation method of the high-barrier composite film in Example 2 is as follows:

[0083] Step 1: Dry and mix the preparation raw materials of the first PE layer and the second PE layer respectively in proportion, put them into a twin-screw extruder for melt blending and extrusion granulation to obtain a PE layer mixture; then melt-cast the PE layer mixture into a film, and after corona treatment, obtain the first PE layer base film and the second PE layer base film respectively;

[0084] Step 2: Weigh the CPVA resin, crosslinking agent, and additives, dissolve / disperse them in an appropriate amount of water to obtain a CPVA aqueous dispersion. Weigh the nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane, disperse them in an appropriate amount of water, and stir at 50 °C for 16 h to prepare an aqueous dispersion of carboxyl-modified nano-hydrotalcite. After cooling to room temperature, add it to the above-mentioned CPVA aqueous dispersion while stirring, and adjust the water volume to make the overall solid content of the coating 15% to obtain a high-barrier coating;

[0085] Step 3: Uniformly coat the high-barrier coating on one side of the first PE layer base film, then cover the second PE layer base film above the side coated with the high-barrier coating, dry it with hot air at 85 °C, and then cure it at 60 °C for 72 h to obtain the high-barrier composite film of this example.

[0086] The total thickness of the high-barrier composite film prepared in Example 2 is 0.15 mm. The thickness of the first PE layer accounts for 65% of the total thickness of the high-barrier composite film, the thickness of the high-barrier coating accounts for 2% of the total thickness of the high-barrier composite film, and the thickness of the second PE layer accounts for 33% of the total thickness of the high-barrier composite film.

[0087] Example 3:

[0088] A high-barrier composite film has a three-layer structure, which is sequentially arranged as a first PE layer, a high-barrier coating, and a second PE layer;

[0089] The first PE layer includes the preparation raw materials shown in Table 6 below, the second PE layer includes the preparation raw materials shown in Table 7 below, and the high-barrier coating includes the preparation raw materials shown in Table 8 below;

[0090] Table 6: Preparation Raw Materials of the First PE Layer

[0091]

[0092] Table 7: Preparation Raw Materials of the Second PE Layer

[0093]

[0094] Table 8: Preparation Raw Materials of the High-Barrier Coating

[0095]

[0096] The preparation method of the high-barrier composite film in Example 3 is as follows:

[0097] First step: Dry and mix the preparation raw materials of the first PE layer and the second PE layer evenly according to the proportion, put them into a twin-screw extruder for melt blending and granulation to obtain a PE layer mixture; then melt-cast and form the PE layer mixture, and after corona treatment, obtain the first PE layer base film and the second PE layer base film respectively;

[0098] Second step: Dissolve / disperse the metered CPVA resin, cross-linking agent and additives in an appropriate amount of water to obtain a CPVA aqueous dispersion. Disperse the metered nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, and stir at 70 °C for 24 h to prepare an aqueous dispersion of carboxyl-modified nano-hydrotalcite. After cooling to room temperature, add it to the above CPVA aqueous dispersion while stirring, and adjust the water volume to make the overall solid content of the coating 4% to obtain a high-barrier coating;

[0099] Third step: Uniformly coat the high-barrier coating on one side of the first PE layer base film, then cover the second PE layer base film above the side coated with the high-barrier coating, dry it with hot air at 100 °C, and then cure it at 45 °C for 72 h to obtain the high-barrier composite film of this example.

[0100] The total thickness of the high-barrier composite film prepared in Example 3 is 0.15 mm. The thickness of the first PE layer accounts for 50% of the total thickness of the high-barrier composite film, the thickness of the high-barrier coating accounts for 1% of the total thickness of the high-barrier composite film, and the thickness of the second PE layer accounts for 49% of the total thickness of the high-barrier composite film.

[0101] Example 4:

[0102] A high-barrier composite film has a three-layer structure, which is sequentially arranged as a first PE layer, a high-barrier coating and a second PE layer;

[0103] The first PE layer and the second PE layer include the preparation raw materials as shown in Table 9 below, and the high-barrier coating includes the preparation raw materials as shown in Table 10 below;

[0104] Table 9: Preparation raw materials of the first PE layer and the second PE layer

[0105]

[0106] Table 10: Preparation raw materials of the high-barrier coating

[0107]

[0108] The preparation method of the high-barrier composite film in Example 4 is as follows:

[0109] First step: Dry and mix the preparation raw materials of the first PE layer and the second PE layer proportionally, then put them into a twin-screw extruder for melt blending and pelletizing to obtain a PE layer mixture. Subsequently, melt-cast the PE layer mixture into a film, and after corona treatment, obtain the first PE layer base film and the second PE layer base film respectively.

[0110] Second step: Dissolve / disperse the metered CPVA resin, crosslinking agent and additives in an appropriate amount of water to obtain a CPVA aqueous dispersion. Disperse the metered nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, and stir at 55 °C for 20 h to prepare an aqueous dispersion of carboxyl-modified nano-hydrotalcite. After cooling to room temperature, add it to the above CPVA aqueous dispersion while stirring, and adjust the water volume to make the overall solid content of the coating 10% to obtain a high-barrier coating.

[0111] Third step: Uniformly coat the high-barrier coating on one side of the first PE layer base film, then cover the second PE layer base film above the side coated with the high-barrier coating, dry it with hot air at 60 °C, and then cure it at 75 °C for 30 h to obtain the high-barrier composite film of this example.

[0112] The total thickness of the high-barrier composite film prepared in Example 4 is 0.15 mm. The thickness of the first PE layer accounts for 36% of the total thickness of the high-barrier composite film, the thickness of the high-barrier coating accounts for 4% of the total thickness of the high-barrier composite film, and the thickness of the second PE layer accounts for 60% of the total thickness of the high-barrier composite film.

[0113] Example 5:

[0114] A high-barrier composite film has a three-layer structure, which is sequentially arranged as a first PE layer, a high-barrier coating and a second PE layer;

[0115] The first PE layer and the second PE layer include the preparation raw materials shown in Table 11 below, and the high-barrier coating includes the preparation raw materials shown in Table 12 below;

[0116] Table 11: Preparation raw materials of the first PE layer and the second PE layer

[0117]

[0118] Table 12: Preparation raw materials of the high-barrier coating

[0119]

[0120] The preparation method of the high-barrier composite film in Example 5 is as follows:

[0121] First step: The raw materials for preparing the first PE layer and the second PE layer are dried and mixed evenly according to the ratio respectively, then put into a twin-screw extruder for melt blending and granulation to obtain a PE layer mixture. Subsequently, the PE layer mixture is melt cast into a film, and after corona treatment, a first PE layer base film and a second PE layer base film are obtained respectively.

[0122] Second step: The metered CPVA resin, crosslinking agent and auxiliary agent are dissolved / dispersed in an appropriate amount of water to obtain a CPVA aqueous dispersion. The metered nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane are dispersed in an appropriate amount of water, and a water dispersion of carboxyl-modified nano-hydrotalcite is prepared by stirring at 80 °C for 15 h. After cooling to room temperature, it is added to the above CPVA aqueous dispersion while stirring, and the amount of water is adjusted to make the total solid content of the coating 9.6% to obtain a high-barrier coating.

[0123] Third step: The high-barrier coating is evenly coated on one side of the first PE layer base film, and then the second PE layer base film is covered above the side coated with the high-barrier coating. After drying with hot air at 100 °C, and then curing at 80 °C for 65 h, the high-barrier composite film of this example is obtained.

[0124] The total thickness of the high-barrier composite film prepared in Example 5 is 0.15 mm. The thickness of the first PE layer accounts for 64% of the total thickness of the high-barrier composite film, the thickness of the high-barrier coating accounts for 3% of the total thickness of the high-barrier composite film, and the thickness of the second PE layer accounts for 33% of the total thickness of the high-barrier composite film.

[0125] Comparative Example 1:

[0126] Compared with Example 1, nano-hydrotalcite was not added in Comparative Example 1, and others were the same as in Example 1.

[0127] Comparative Example 2:

[0128] Compared with Example 1, carboxyl-modified polyethylene was not added to the first PE layer and the second PE layer in Comparative Example 2, and others were the same as in Example 1.

[0129] Comparative Example 3:

[0130] Compared with Example 1, the crosslinking agent was not added to the raw materials for preparing the high-barrier coating in Comparative Example 3, and others were the same as in Example 3.

[0131] Comparative Example 4:

[0132] Compared with Example 1, conventional polyvinyl alcohol resin was used to replace CPVA resin in the raw materials for preparing the high-barrier coating in Comparative Example 4, and others were the same as in Example 1.

[0133] Comparative Example 5:

[0134] Compared with Example 1, carboxyl-terminated polyethylene glycol siloxane was not added to the raw materials for preparing the high-barrier coating in Comparative Example 5, and the others were the same as in Example 1.

[0135] Comparative Example 6:

[0136] Compared with Example 1, the process in Comparative Example 6 was not subjected to corona treatment, and the others were the same as in Example 1.

[0137] Comparative Example 7:

[0138] Compared with Example 1, the single-piece thickness of the nano-hydrotalcite in Comparative Example 7 was 25 nm, and the average diameter-to-thickness ratio of the single piece was 120, and the others were the same as in Example 1.

[0139] Comparative Example 8:

[0140] Compared with Example 1, the single-piece thickness of the nano-hydrotalcite in Comparative Example 8 was 25 nm, and the average diameter-to-thickness ratio of the single piece was 300, and the others were the same as in Example 1.

[0141] The high-barrier composite film samples of Examples 1 to 5 and the high-barrier composite film comparative samples of Comparative Examples 1 to 8 were respectively subjected to performance tests according to the following methods.

[0142] Coating adhesion grade: The test was carried out by the cross-cut method according to the method of GB / T 9286 of the national standard. The adhesion grade was divided into six grades from good to bad as 0-5. For the same sample, no less than 5 regions were randomly selected for the test, and the lowest value of the adhesion grade was recorded as the test result.

[0143] Oxygen transmission rate (OTR): The test was carried out with reference to the test method of GB / T 19789-2021 of the national standard. The test temperature was 23 °C and the relative humidity was 0. Five different regions of the sample were selected for the test and their average value was taken. The lower the OTR value, the better the barrier performance.

[0144] Water vapor transmission rate (WVTR): The test was carried out with reference to the test method of GB / T 26253-2010 of the national standard. The test temperature was 23 °C and the relative humidity was 50%. Five different regions of the sample were selected for the test and their average value was taken. The lower the WVTR value, the better the barrier performance. The results are shown in Table 13 below.

[0145] Table 13: Performance test results

[0146]

[0147] It can be seen from the data analysis in Table 13 that after the optimization of the composition and process of the present application, the prepared composite film has significantly high barrier performance. Combining Figures 1 to 2 Analysis, Figure 1It is a schematic structural diagram of the high-barrier composite film prepared in Example 1 of the present invention. It is a three-layer structure, including a first PE layer 1, a high-barrier composite layer 2, and a second PE layer 3. Figure 2 It is a schematic diagram of the principle of carboxyl-terminated polyethylene glycol siloxane modified nano-hydrotalcite in Example 1 of the present invention. The surface of nano-hydrotalcite is modified with carboxyl-terminated polyethylene glycol siloxane to shield its surface hydroxyl groups. At the same time, the steric hindrance effect of the polyethylene glycol macromolecular chain segments is used to inhibit the aggregation of nanosheets and strengthen its dispersibility. Only under the condition of sufficient dispersion and single-piece peeling can the best barrier effect be ensured with the minimum dosage. Through the above method, the barrier coating still obtains a high-barrier effect when the thickness is less than 5%.

[0148] In Comparative Example 1, since the barrier coating does not contain nano-hydrotalcite and only relies on CPVA resin to provide the barrier effect, the barrier effect is limited, showing relatively high OTR and WVTR.

[0149] In Comparative Example 2, since the component does not contain carboxyl-modified polyethylene, there are no reaction sites between the barrier coating and the PE-based film, and the two cannot produce a bonding effect. The polarity difference between the barrier coating and the PE-based film is large, the coating adhesion is poor, and the OTR and WVTR also increase.

[0150] In Comparative Example 3, since there is no cross-linking agent, the barrier coating and the PE-based film are combined only by physical adsorption, and the binding force is low, and the coating adhesion is insufficient. In addition, CPVA cannot undergo a cross-linking reaction, resulting in a sharp increase in OTR and WVTR.

[0151] In Comparative Example 4, conventional polyvinyl alcohol resin is used, and the binding force and compatibility with the non-polar PE-based film are poor, so the coating adhesion is poor.

[0152] In Comparative Example 5, carboxyl-terminated polyethylene glycol siloxane is not included, and nano-hydrotalcite is prone to aggregation, resulting in uneven dispersion, and it cannot participate in the subsequent cross-linking reaction, affecting the bonding strength of the coating, and the OTR and WVTR also increase.

[0153] In Comparative Example 6, the base film has not undergone a corona process to further enhance the density of surface carboxyl functional groups, and there are fewer surface reaction sites. The coating adhesion is not as good as that of the example, and the barrier performance is also insufficient.

[0154] In Comparative Examples 7-8, the single-piece thickness and the average aspect ratio of the single piece of nano-hydrotalcite are limited. Due to the relatively large thickness of the hydrotalcite in the comparative example, the single-piece density decreases under the same mass, and in addition, the average aspect ratio of the single piece is relatively small, and the coverage is not as good as that of Example 1. If the average aspect ratio of the single piece is greater than the limited value, it is easy to break during the processing, resulting in a rapid decrease in the aspect ratio and also a decrease in the coverage. Macroscopically, its barrier performance is not as good as that of Example 1.

[0155] In summary, compared with Comparative Examples 1-8, Examples 1-5 of the present invention still have good coating adhesion when the coating thickness ratio does not exceed 5%, and at the same time have extremely low oxygen transmission rate and water vapor transmission rate, indicating that the examples have more excellent barrier properties and do not affect their recyclability.

[0156] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A high-barrier composite film, characterized in that, The high-barrier composite film includes a first PE layer, a high-barrier coating, and a second PE layer arranged in sequence. The thicknesses of the first PE layer and the second PE layer respectively account for 20% - 79% of the total thickness of the high-barrier composite film, and the thickness of the high-barrier coating accounts for 1% - 5% of the total thickness of the high-barrier composite film; Among them, both the first PE layer and the second PE layer include the following raw materials for preparation in parts by weight: 30 - 80 parts of PE resin, 20 - 70 parts of carboxyl-modified polyethylene, and 0.1 - 10 parts of auxiliary materials; The high-barrier coating includes the following raw materials for preparation in parts by weight: 100 parts of carboxyl-modified polyvinyl alcohol resin, 40 - 400 parts of nano-hydrotalcite, 1 - 80 parts of carboxyl-terminated polyethylene glycol siloxane, 3 - 12 parts of cross-linking agent, and 3 - 12 parts of auxiliary agent; Among them, the nano-hydrotalcite is an inorganic nanosheet with a layered structure, the single-piece thickness is 6nm - 20nm, and the average diameter-thickness ratio of the single piece is 150 - 250; The cross-linking agent is a multi-functional aziridine cross-linking agent, and the multi-functional aziridine cross-linking agent is one or more of trimethylolpropane-tris[3-(2-methylaziridinyl)]propionate, trimethylolpropane-tris(3-aziridinyl)propionate, and pentaerythritol-tris(3-aziridinyl)propionate; The weight-average molecular weight of the polyethylene glycol segment of the carboxyl-terminated polyethylene glycol siloxane is 200g / moL - 4000g / moL; The chemical structural formula of the carboxyl-terminated polyethylene glycol siloxane is as follows: ； The preparation method of the high-barrier composite film includes the following steps: Mix the raw materials for the preparation of the first PE layer evenly, melt and blend and extrude granulation in a twin-screw extruder to obtain the first PE layer mixture, then melt-process the film into shape, and after corona treatment, obtain the first PE layer base film; Mix the raw materials for the preparation of the second PE layer evenly, melt and blend and extrude granulation in a twin-screw extruder to obtain the second PE layer mixture, then melt-process the film into shape, and after corona treatment, obtain the second PE layer base film; Disperse the carboxyl-modified polyvinyl alcohol resin, cross-linking agent, and auxiliary agent in an appropriate amount of water to obtain a carboxyl-modified polyvinyl alcohol aqueous dispersion; then disperse the nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, stir at 50°C - 80°C for 6h - 24h to obtain a water dispersion of carboxyl-modified nano-hydrotalcite, and cool to room temperature; then, under stirring conditions, add the water dispersion of carboxyl-modified nano-hydrotalcite to the carboxyl-modified polyvinyl alcohol aqueous dispersion, and adjust the solid content to be within the range of 3% - 15% to obtain a high-barrier coating; Coat the high-barrier coating on one side of the first PE layer base film and / or the second PE layer base film, then bond the side coated with the high-barrier coating, dry it with hot air at 60°C - 105°C, and then cure it at 45°C - 80°C for 48h - 72h to obtain the high-barrier composite film.

2. The high-barrier composite film according to claim 1, characterized in that, The melt index of the PE resin under the conditions of 190°C and 2.16kg ranges from 1g / 10min to 30g / 10min.

3. The high-barrier composite film according to claim 1, characterized in that, The carboxyl-modified polyethylene is one or more of ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, acrylic acid-grafted polyethylene, and methacrylic acid-grafted polyethylene.

4. The high-barrier composite film according to claim 1, characterized in that, The auxiliary materials include one or more of antioxidant, ultraviolet absorber, plasticizer, flame retardant, nucleating agent, and inorganic filler.

5. The high-barrier composite film according to claim 1, characterized in that, The weight-average molecular weight of the carboxyl-modified polyvinyl alcohol resin is 60,000 g / moL to 300,000 g / moL, the degree of alcoholysis is 80% to 99%, and the mass fraction of carboxyl is 0.2% to 5%.

6. The high-barrier composite film according to claim 1, characterized in that, The auxiliary agents include one or more of defoamer, leveling agent, antioxidant, hydrolysis-resistant agent, and UV absorber.

7. A method for preparing a high-barrier composite film, characterized in that, The preparation method is used to prepare the high-barrier composite film as described in any one of claims 1 to 6, and the preparation method includes the following steps: Mix the raw materials for preparing the first PE layer evenly, melt-blend and extrude granulate in a twin-screw extruder to obtain the first PE layer mixture, then melt-process the film into shape, and after corona treatment, obtain the first PE layer base film; Mix the raw materials for preparing the second PE layer evenly, melt-blend and extrude granulate in a twin-screw extruder to obtain the second PE layer mixture, then melt-process the film into shape, and after corona treatment, obtain the second PE layer base film; Disperse the carboxyl-modified polyvinyl alcohol resin, cross-linking agent, and auxiliary agent in an appropriate amount of water to obtain a carboxyl-modified polyvinyl alcohol aqueous dispersion; then disperse nano-hydrotalcite and carboxyl-terminated polyethylene glycol siloxane in an appropriate amount of water, and stir at 50°C to 80°C for 6h to 24h to obtain an aqueous dispersion of carboxyl-modified nano-hydrotalcite, and cool to room temperature; then, under stirring conditions, add the aqueous dispersion of carboxyl-modified nano-hydrotalcite to the carboxyl-modified polyvinyl alcohol aqueous dispersion, and adjust the solid content to be within the range of 3% to 15% to obtain a high-barrier coating; Coat the high-barrier coating on one side of the first PE layer base film and / or the second PE layer base film, then bond the coated side, dry it with hot air at 60°C to 105°C, and then cure it at 45°C to 80°C for 48h to 72h to obtain the high-barrier composite film.

Images