A method for preparing a glue-free, repulpable, multilayer, high-barrier packaging material

Abstract

The application provides a preparation method of a glue-free and repulpable multi-layer high-barrier packaging material, which comprises the following steps: taking a first paper base and a second paper base, preparing a barrier coating, and adding a plasticizer to the barrier coating; coating the barrier coating on a first surface of the first paper base to form a first paper base barrier layer with a two-layer structure; and coating the barrier coating on a second surface of the second paper base to form a second paper base barrier layer with a two-layer structure; and folding one surface of a barrier material against the other surface and hot-pressing to obtain a high-barrier packaging material; further, the plasticizer is a bio-based plasticizer, the high-barrier packaging material formed by the design can be two-layer split, the surfaces of the two split layers are coated with the barrier material, and the same barrier material is combined by using a hot-pressing process to form a synergistic and associated effect from the addition and use of the environment-friendly material to the processing technology, so that the interlayer bonding force of the material is effectively improved, the problems of material bulging and cracking are prevented, and the comprehensive performance of water vapor, oxygen and repulpability is improved.

Description

Technical Field

[0001] This invention relates to the technical field of packaging paper preparation, specifically to a method for preparing a glue-free, repulpable, multi-layered, high-barrier packaging material. Background Technology

[0002] With the increasing demand for high barrier properties in packaging materials, traditional single-layer packaging materials have been gradually replaced by multi-layer, multi-functional composite packaging materials. Existing preparation methods for these composite packaging materials mainly include multi-layer co-extrusion, adhesive lamination, and coating. However, packaging materials prepared using these methods have the following drawbacks:

[0003] (1) Multilayer co-extrusion method: Materials with different properties are combined and co-extruded into packaging materials by a composite machine. Due to the incompatibility and viscosity difference between different materials, it is easy to generate pores and weak interlayer bonding, which affects the overall barrier performance and mechanical strength of the material.

[0004] (2) Coating and bonding method: The layers are bonded together by adhesives. A large amount of adhesives are needed to ensure the interlayer bonding strength between different materials. Not only is the production cost high, but solvent-based adhesives are also toxic, resulting in a large amount of volatile organic compound emissions. In addition, because the adhesives are tightly bonded to other materials, it increases the difficulty of re-pulping, recycling and reuse, and energy consumption.

[0005] (3) Coating method: Most existing water-based water vapor barrier coatings are highly hydrophobic polymers. Their low surface energy characteristics make it difficult for other functional coatings to spread evenly on them, which easily causes coating defects such as poor leveling and pinholes. This non-recoatability results in a single barrier function, which limits the diversity of barrier performance and makes it difficult to meet the needs of different packaging scenarios.

[0006] A high-barrier packaging paper and its processing technology are disclosed in CN114808544A. This patent improves the barrier performance of the packaging paper by pre-coating the upper and lower surfaces of the paper with water-based high-barrier coatings to form a high-barrier base coating layer 1 and a high-barrier base coating layer 2, combined with a metal layer and a transparent medium layer. However, the multi-layer structure preparation process of this technical solution is relatively complex, especially the introduction of the metal layer, which will increase the production cost and production difficulty.

[0007] The patent, CN112900148A, discloses a method for improving the water vapor barrier performance of food packaging paper under high temperature and high humidity. This patent improves the water vapor barrier performance of paper by uniformly coating a physically cross-linked polyvinyl alcohol / nanoclay / alkali lignin composite gel onto the paper surface and drying it under normal pressure to form a stable and dense layer. However, the preparation and coating process of the composite gel in the technical solution is relatively complicated, and the stability, durability and anti-aging properties of the composite gel are poor under high temperature and high humidity conditions.

[0008] The above problems indicate that existing high-barrier packaging paper, used to prepare multi-layered, multi-functional composite packaging materials, suffers from several shortcomings, including complex processing, large adhesive usage, poor interlayer adhesion, poor barrier performance under high temperature and humidity conditions, limited barrier properties, cumbersome preparation process, difficulty in recycling, and high production costs.

[0009] To address the aforementioned background technology and problems, there is a need to provide a method for preparing a glue-free, re-pulpable, multi-layer high-barrier packaging material. Summary of the Invention

[0010] This invention addresses the comprehensive shortcomings of existing multi-layered, multi-functional composite packaging materials, which suffer from various deficiencies. It provides a method for preparing a glue-free, re-pulpable multi-layered high-barrier packaging material, comprising the following steps:

[0011] S10: Take the first paper base and the second paper base;

[0012] S20: Prepare a barrier coating, wherein the barrier coating contains a plasticizer;

[0013] S30: The barrier coating is applied to the first side of the first paper base to form a two-layer first paper base barrier layer; and applied to the second side of the second paper base to form a two-layer second paper base barrier layer;

[0014] S40: The first paper-based barrier layer and the second paper-based barrier layer are stacked on one side of their barrier materials and hot-pressed to obtain the high-barrier packaging material.

[0015] Furthermore, both the first paper base and the second paper base are one of kraft paper, extensible paper, regenerated cellulose membrane, or nanocellulose membrane.

[0016] Furthermore, the barrier coating is a water vapor barrier coating.

[0017] Furthermore, the plasticizer is a bio-based plasticizer, optionally one or more of citrate, carboxymethyl cellulose, hydroxypropyl cellulose, starch, chitosan, nanocellulose, epoxidized soybean oil, epoxidized castor oil, and epoxidized linseed oil.

[0018] Furthermore, the components of the water vapor barrier coating include a thermoplastic hydrophobic polymer, a crosslinking agent, and a defoamer.

[0019] Furthermore, forming the high-barrier packaging material includes preparing an oxygen-barrier coating, and sequentially applying the oxygen-barrier coating and the barrier coating to the first surface of the first paper base to form a three-layer structure first paper base double barrier layer.

[0020] Furthermore, the components used to make the oxygen barrier coating include natural resin, modified polyvinyl alcohol, and added nano-silica and starch-grafted acrylate.

[0021] Furthermore, the nano-silica is silane coupling agent modified nano-silica.

[0022] Furthermore, the modified polyvinyl alcohol is one or more of epoxy resin modified polyvinyl alcohol, succinic acid modified polyvinyl alcohol, and butenaldehyde modified polyvinyl alcohol.

[0023] Furthermore, the first coating layer is pre-pressed.

[0024] Furthermore, the hot pressing is a double-roller hot pressing; the first roller of the double-roller hot pressing is a heating roller, and the second roller is a finishing roller.

[0025] Furthermore, after the hot pressing, infrared light curing treatment is performed.

[0026] Furthermore, the high-barrier packaging material comprises at least one of the following features (A) to (F):

[0027] (A) After standing for 21 days at 38℃ and 90%RH, the water vapor transmission rate before and after bending was 0.70 g / (m). 2 • 24h) to 1.30g / (m 2 ·24h);

[0028] (B) The oxygen permeability before and after bending is 0.50 cm. 3 / (m 2 • 24h • 0.1MPa) to 0.70cm 3 / (m 2 ·24h·0.1MPa);

[0029] (C) The test time was 60 minutes, and the Cobb water absorption value before and after bending was 0 g / m. 2 ;

[0030] (D) The oil resistance Kit value is 12 before and after bending;

[0031] (E) Heat seal strength is 2.0 N / 15 mm to 7.0 N / 15 mm;

[0032] (F) Repulpingability is 85 to 90 points, calculated out of a maximum of 100 points.

[0033] Furthermore, forming the high-barrier packaging material includes preparing a heat-sealing coating, first applying the heat-sealing coating to the second side of the first paper base, and then applying the barrier coating to the first side of the first paper base to form a three-layer structure first paper base double-sided barrier layer.

[0034] Furthermore, forming the high-barrier packaging material includes preparing a heat-sealing coating, first applying the heat-sealing coating to the second side of the first paper base, and then applying the oxygen-barrier coating and the barrier coating sequentially to the first side of the first paper base to form a four-layer structure of the first paper base three-barrier layer.

[0035] The beneficial effects of the technical solution of this invention mainly include:

[0036] (1) From a structural perspective, a novel multi-layer composite paper structure is designed to form an overall structure that can be divided into upper and lower layers from the middle for processing. The structure designed by the technical solution of this invention forms a barrier layer that is split from the middle and two functional layers are made simultaneously. Then, through the hot pressing process, the overall high barrier packaging material is formed. This forms an effective allocation of each functional layer, a structural basis that does not interfere with each other and can be processed independently, and provides a structural basis for material improvement and process improvement.

[0037] (2) Based on the structural splitting, the barrier coating is applied to the first side of the first paper base and the second side of the second paper base, and then hot-pressed. This fully utilizes the matching properties of the same material in the hot-pressing process, such as plasticity and bonding, to form an effective interlayer bond, thereby effectively improving the interlayer bonding force, overall integrity and structural reliability of the material. In other words, the multi-layer composite paper is split from the middle of the barrier layer, and after being made separately, it is hot-pressed to form a whole.

[0038] (3) Further, the water vapor barrier layer is separated, and plasticizer is added to the water vapor barrier coating to improve the plasticizing performance, which is used to support and cooperate with the subsequent hot pressing process to form an effective plasticizing bond of the same material in the hot pressing process. Furthermore, the plasticizer is a bio-based plasticizer, which has good hot pressing plasticizing characteristics and better biodegradability. It replaces the existing technology of using a large amount of adhesive for coating and bonding, effectively reducing production costs and improving environmental protection and re-sizing properties.

[0039] (4) The process of coating each functional layer with coating and then hot pressing is much better than the existing technology of multi-layer co-extrusion which is prone to pores and weak interlayer bonding. It effectively reduces the difference in tensile effect between materials and reduces the uneven internal stress caused by the difference in extrusion tensile effect, thereby reducing the possibility of cracking of thermoplastic resin layer. Compared with coating composite, hot pressing can effectively improve the bonding strength between layers, improve the integrity of multi-layer composite packaging materials, and prevent cracking, delamination and other problems.

[0040] (5) Furthermore, typically, since multi-layer composite paper needs to simultaneously possess oxygen barrier properties, an oxygen barrier layer needs to be fabricated within the multi-layer composite paper structure. Simultaneously, due to the aforementioned improvements to the composition of the water vapor barrier layer and the use of an improved hot-pressing process, and because the glass transition temperature of the oxygen barrier layer is lower than that of the water vapor barrier layer, a mismatch in the shrinkage degree between the water vapor barrier layer and the oxygen barrier layer after hot pressing results in problems such as cracks, fissures, and wrinkles. This technical solution employs the method of adding nano-silica to the oxygen barrier coating to form a reinforcing material. The addition of starch-grafted acrylate as a solubilizer helps to suppress excessive shrinkage and deformation of the oxygen barrier layer during subsequent hot pressing. This solubilizer can form effective hydrogen bonds with modified polyvinyl alcohol, thereby improving the toughness of the oxygen barrier layer and achieving a more similar performance to the water vapor barrier layer material. This reduces the difference in thermal shrinkage between the oxygen barrier layer and the water vapor barrier layer, thus significantly improving the problems of cracking, cracking, and wrinkling after hot pressing. Furthermore, both nano-silica and starch-grafted acrylate are environmentally friendly materials with good re-sizing properties.

[0041] (6) Further, after the first paper-based double barrier layer, which forms a water vapor barrier layer, an oxygen barrier layer and a first paper base laminate, is made, pre-pressing is performed. This allows the water vapor barrier layer and the oxygen barrier layer to be further bonded by pressure physical action before hot pressing, releasing some internal stress. Pre-pressing can also improve the smoothness of the surface of the water vapor barrier layer, so that each layer can be better bonded to each other during the subsequent hot pressing process. From the perspective of process processing, this further prevents the material from wrinkling, cracking, splitting, delamination and blistering. After hot pressing, infrared light is irradiated to further solidify the material inside, improving the structural integrity and barrier performance of the material in high temperature and high humidity environments. Furthermore, if the internal microstructure of the multi-layer high barrier packaging material contains gas, resulting in poor interlayer bonding, infrared light irradiation and heating can, to a certain extent, cause the hidden gas to expand, forming visually observable bubbles, delamination and other problems. This facilitates timely detection of material processing quality and timely adjustment of material composition or processing conditions.

[0042] (7) Furthermore, the material needs to have heat-sealing properties and be able to be made into packaging bags. Therefore, the structure of the technical solution of the present invention is also designed with a heat-sealing layer, which is first coated on the second side of the first paper base. During the processing, the heat-sealing layer can give the first coating layer stronger tensile strength and a certain effect of preventing the rapid loss of heat, so that the heat is retained in the multi-layer structure, promotes the plasticizing effect and hot-melt bonding effect between the layers, and ensures the flatness and uniformity during the hot pressing process.

[0043] (8) The technical solution is based on the process design of using hot pressing to replace the existing multi-layer co-extrusion and coating processing method, forming a multi-layer composite paper structure design. To further improve the interlayer bonding effect of hot pressing and ensure the repulping performance, bio-based plasticizers are added to the water vapor barrier layer, thereby forming an effective correlation between hot pressing process improvement and material improvement. Furthermore, silica and starch-grafted acrylate components are added to the oxygen barrier coating. By improving the composition of the oxygen barrier coating, the mutual processing effect of the water vapor barrier layer is improved, and the hot pressing process is improved. This prevents defects such as delamination and blistering caused by hot pressing of the multi-layer structure. The heat-sealing layer can give the first coating layer stronger tensile strength and a certain effect of preventing rapid heat loss. This forms an effective synergistic and correlation effect between the water vapor barrier layer, oxygen barrier layer, paper base layer, heat-sealing layer and hot pressing process. The pre-pressing process can further improve the processing effect and reduce defects, thus forming an overall mutual influence and effective correlation between material improvement and process improvement. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0045] Figure 1 This is a schematic diagram of the process flow of an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of the structure of the first high-barrier packaging material according to an embodiment of the present invention;

[0047] Figure 3 Tg test chart for water vapor barrier coating without added bio-based plasticizers;

[0048] Figure 4 Tg test chart of water vapor barrier coating with added bio-based plasticizer in this embodiment;

[0049] Figure 5 This is a schematic diagram of the structure of a second high-barrier packaging material according to an embodiment of the present invention;

[0050] Figure 6 This is a photograph of a second type of high-barrier packaging material according to an embodiment of the present invention.

[0051] Figure 7 SEM image of the surface of the second high-barrier packaging material according to an embodiment of the present invention;

[0052] Figure 8 The image shows a multi-layered high-barrier packaging material (stained with Herxel dye) with surface wrinkles, cracks, or fissures.

[0053] Figure 9 The image shows a real-life example of multi-layered high-barrier packaging material with bulging.

[0054] Figure 10 A schematic diagram of the process for producing the second high-barrier packaging material according to this embodiment;

[0055] Figure 11 This is a schematic diagram of the structure of the third high-barrier packaging material according to an embodiment of the present invention;

[0056] Figure 12 This is a schematic diagram of the structure of the fourth high-barrier packaging material according to an embodiment of the present invention;

[0057] Figure 13 A schematic diagram of the process for producing the fourth type of high-barrier packaging material according to this embodiment;

[0058] Figure 14 This is a photograph of the fourth high-barrier packaging material according to an embodiment of the present invention.

[0059] Figure 15 SEM image of the surface of the fourth high-barrier packaging material according to the present invention;

[0060] Figure 16 Experimental diagram for testing the water vapor barrier performance of the multilayer high-barrier packaging materials prepared in Example 1, Comparative Example 2 and Comparative Example 3 using the cup method.

[0061] Figure 17 This is a photograph of a packaging bag made using the multi-layer high-barrier packaging material obtained in Example 1.

[0062] Explanation of icon numbers:

[0063] label name label name 100 First paper base 310 First Water Vapor Barrier Coating 200 Second paper base 410 Second Water Vapor Barrier Coating 300 First barrier layer 510 Oxygen Barrier Coating 400 Second barrier layer 610 Heat-sealing coatings 500 oxygen barrier layer 710 rubber roller 600 heat seal layer 720 steel roller 700 bulge 730 Preload rollers 10A The second type of high-barrier packaging material 740 Infrared curing box 10B The fourth type of high-barrier packaging material 810 air flotation oven

[0064] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0065] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. It should be understood that these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0066] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0067] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features; thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0068] The weights of the relevant components mentioned in the embodiments of this invention can refer not only to the specific content of each component, but also to the proportional relationship between the weights of each component. Therefore, as long as the content of the relevant components is proportionally increased or decreased according to the embodiments of this invention, it is within the scope disclosed in the embodiments of this invention. Specifically, the weights mentioned in the embodiments of this invention can be well-known mass units in the chemical industry, such as μg, mg, g, kg, cm, mm, wt%, MPa, L, mL, etc.

[0069] Please see Figure 1 , Figure 1 This is a schematic diagram of the process flow according to an embodiment of the present invention.

[0070] The preparation process of the glue-free, re-pulpable, multi-layered high-barrier packaging material according to embodiments of the present invention includes using... Figure 1 The implementation of each step in the process will be described below. Figure 1 The process of each step will be explained step by step.

[0071] Please see Figure 2 , Figure 2 This is a schematic diagram of the structure of the first high-barrier packaging material according to an embodiment of the present invention.

[0072] Step S10: Take the first paper base and the second paper base. Further, the first paper base and the second paper base are one or more of kraft paper, extensible paper, regenerated cellulose membrane, and nanocellulose membrane, and are all bio-based repulping environmentally friendly substrates.

[0073] Furthermore, the paper base, as the base material in the embodiments of the present invention, needs to have certain strength, flatness and toughness; the first paper base and the second paper base are pretreated to remove impurities and dust from the paper surface to ensure the uniformity and surface flatness of the paper base and provide printability.

[0074] Please see Figure 3 and Figure 4 , Figure 3 Tg test chart for water vapor barrier coating without added bio-based plasticizers. Figure 4 Tg test chart of water vapor barrier coating with added bio-based plasticizer in this embodiment.

[0075] Step S20: Prepare a barrier coating, wherein a plasticizer is added to the barrier coating.

[0076] Furthermore, the barrier coating is a water vapor barrier coating. Optionally, the plasticizer is a bio-based plasticizer, which may be one or more mixtures of citrate, carboxymethyl cellulose, hydroxypropyl cellulose, starch, chitosan, nanocellulose, epoxidized soybean oil, epoxidized castor oil, and epoxidized linseed oil.

[0077] Since most water-based water vapor barrier coatings are made of highly hydrophobic polymers, the low surface energy of these coatings prevents other functional coatings such as waterproofing, oil-proofing, and heat-sealing from spreading evenly, easily leading to defects such as poor leveling and pinholes. This embodiment adds a bio-based plasticizer to the water vapor barrier coating, allowing the bio-based plasticizer molecules to penetrate between the molecular chains of the thermoplastic hydrophobic polymer. Through reaction with the active groups on the polymer molecular chains, chemical bonds or interaction sites are formed. This adjusts the internal structure of the polymer, enhancing the mobility and flexibility of the polymer molecular chains, thereby lowering the polymer's glass transition temperature (from...). Figure 3 and Figure 4 It can be seen that after adding bio-based plasticizers, the glass transition temperature (Tg) of the water vapor barrier coating decreased from -6.33℃ to -12.39℃. The lower glass transition temperature makes the polymer more prone to deformation during twin-roll hot pressing, and the molecular chains can better interpenetrate and entangle with each other, improving thermoplasticity. This results in a stronger fusion of the first and second paper-based water vapor barrier layers and better interlayer bonding. On the other hand, bio-based plasticizers can make the cross-linking between polymer molecular chains more efficient, ultimately forming a stable network structure with both strength and flexibility. This structure can prevent excessive decomposition or disordered movement of polymer molecular chains during heating, thus ensuring the thermal stability of the polymer within a certain temperature range. This provides the necessary basic component conditions for interlayer bonding in subsequent hot pressing processes. Furthermore, this structure can effectively disperse stress when subjected to bending, preventing stress concentration in local areas that could lead to coating cracking, thereby improving the coating's folding resistance.

[0078] In this embodiment, the combination of water vapor barrier coating and bio-based plasticizer not only provides the packaging material with good water vapor barrier performance, but also ensures that the packaging material has good mechanical strength and processing performance. Furthermore, the bio-based plasticizer is a bio-based material, which not only reduces dependence on non-renewable resources, but also reduces the environmental burden at the end of the packaging material's life cycle.

[0079] Furthermore, the components of the water vapor barrier coating include a thermoplastic hydrophobic polymer, a crosslinking agent, and a defoamer.

[0080] Further, the thermoplastic hydrophobic polymer is one or more mixtures of polyacrylate, styrene-acrylate copolymer, styrene-butadiene copolymer, ethylene-acrylic acid copolymer, polyolefin, polyurethane, and vinyl acetate-ethylene copolymer.

[0081] Furthermore, the crosslinking agent is one of diimide, epoxy, acid anhydride, silane, propane, or alkanolamine, and the crosslinking agent accounts for 0.1% to 9.5% of the total water vapor barrier coating system by mass.

[0082] Crosslinking agents can react with functional groups in hydrophobic polymers to form a three-dimensional network structure, which makes the coating denser and effectively prevents moisture penetration and diffusion. In addition, because crosslinking agents can promote chemical bonding between different components, they not only enhance the bonding force within the coating but also improve the adhesion strength between the coating and other functional layers, making the interlayer bonding stronger, reducing the risk of delamination or peeling, and improving the overall reliability and durability of the packaging material.

[0083] Furthermore, the formed three-dimensional network structure can enhance the mechanical strength and durability of the water vapor barrier coating layer, making the water vapor barrier coating layer more stable during application and less susceptible to the effects of factors such as temperature and humidity.

[0084] Step S30: Apply the barrier coating to the first side of the first paper base to form a two-layer first paper base barrier layer; and apply it to the second side of the second paper base to form a two-layer second paper base barrier layer.

[0085] In this embodiment, the same barrier coating is applied to the surfaces of the first and second paper bases, which are split into two parts, and then dried (preferably using an air-floating oven). The barrier coating forms the first barrier layer and the second barrier layer, respectively, providing the prerequisite that "the same material has better plasticizing properties, compatibility, and mutual bonding" for subsequent hot pressing.

[0086] It is worth noting that if subsequent processes such as hot pressing are directly used at this stage, the resulting layered structure of the first type of high-barrier packaging material is: first paper base 100, first barrier layer 300, second barrier layer 400, and second paper base 200 (see [link]). Figure 2 ).

[0087] Please see Figure 5 , Figure 6 and Figure 7 , Figure 5 This is a schematic diagram of the structure of a second high-barrier packaging material according to an embodiment of the present invention.

[0088] Furthermore, forming the high-barrier packaging material includes preparing an oxygen-barrier coating, and sequentially applying the oxygen-barrier coating and the barrier coating to the first surface of the first paper base to form a three-layer structure first paper base double barrier layer.

[0089] In order to enable the membrane to have good oxygen barrier properties, an oxygen barrier layer is made simultaneously in this embodiment. The oxygen barrier coating is also applied to the paper base surface by coating.

[0090] It is worth noting that, following the above manufacturing process, if subsequent processes such as hot pressing are used at this point, the resulting layered structure of the second type of high-barrier packaging material is: first paper base 100, oxygen barrier performance 500, first barrier layer 300, second barrier layer 400, and second paper base 200 (see [link to documentation]). Figure 5 ).

[0091] Please see Figure 6 and Figure 7 , Figure 6 This is a photograph of a second type of high-barrier packaging material according to an embodiment of the present invention. Figure 7 SEM image of the surface of a second type of high-barrier packaging material according to an embodiment of the present invention.

[0092] Depend on Figure 6 It can be seen that the second type of high-barrier packaging material has a smooth surface, without cracks, bulges, delamination, unevenness, or other problems; Figure 7 It can be seen that the second type of high-barrier packaging material has good density, as well as good water vapor barrier and oxygen barrier properties.

[0093] Please see Figure 8 , Figure 8 This is a photograph of a multi-layered high-barrier packaging material (Herxheimer reagent staining) with surface wrinkles, cracks, or splitting.

[0094] Furthermore, the components used to make the oxygen barrier coating include natural resin, modified polyvinyl alcohol, and added nano-silica and starch-grafted acrylate.

[0095] During the research and development process, an issue arose where an oxygen barrier coating was applied followed by a water vapor barrier coating, and then dried (preferably using an air-float oven) to form oxygen and water vapor barrier layers. Subsequent hot pressing resulted in wrinkling, cracking, and splitting of both the oxygen and water vapor barrier layers. The reason for this is that the oxygen barrier coating has a lower glass transition temperature, while the water vapor barrier layer has a higher one. During the coating and curing process, the oxygen barrier coating deforms more than the water vapor barrier layer. This difference in deformation increases dimensional instability, leading to the visible cracks, splitting, and wrinkles (see [link to relevant documentation]). Figure 8 ).

[0096] Therefore, the oxygen barrier coating in this embodiment specifically incorporates nano-silica and starch-grafted acrylate. Nano-silica has a good effect on enhancing rigidity and thermal stability. After being uniformly dispersed in the oxygen barrier coating, it promotes the support of the three-dimensional network structure, which can suppress excessive shrinkage and deformation of the oxygen barrier layer during hot pressing. It also further refines the coating structure and reduces the channels for oxygen molecule diffusion. Starch-grafted acrylate has a good compatibilizing effect. It can interact with the modified polyvinyl alcohol through hydrogen bonds of its own carboxyl groups, improve the interfacial bonding force, thereby enhancing the compatibility and bonding force between the oxygen barrier layer and the water vapor barrier layer based on polyvinyl alcohol, reducing the deformation difference during hot pressing, and thus improving the phenomena of cracking, splitting, and wrinkling.

[0097] Furthermore, the amount of nano-silica used accounts for 2% to 5% of the mass of the oxygen barrier coating system.

[0098] Furthermore, the nano-silica is silane coupling agent modified nano-silica.

[0099] The nano-silica was modified using a silane coupling agent to increase its dispersibility and further enhance its interfacial compatibility with polyvinyl alcohol and natural resins.

[0100] Furthermore, the modified polyvinyl alcohol is one or more of epoxy resin modified polyvinyl alcohol, succinic acid modified polyvinyl alcohol, and butenaldehyde modified polyvinyl alcohol.

[0101] Modifying polyvinyl alcohol with epoxy resin, succinic acid, or butylene aldehyde introduces specific functional groups, enhancing its compatibility with other components (such as nano-silica, starch-grafted acrylate, and natural resins). This helps form a denser coating structure, reduces oxygen molecule diffusion channels, and further improves oxygen barrier performance. Furthermore, good compatibility contributes to the uniform distribution of stress within the coating. This uniform stress distribution and good component bonding make the coating less prone to cracking or breakage during repeated bending, thus improving its flexural strength.

[0102] Further, the first coating layer is pre-pressed; further, the pre-pressing temperature is 22°C to 45°C, the pressure is 10kN to 15kN, and the pre-pressing roller drive speed (i.e., vehicle speed) is the same as that of the subsequent hot pressing, which is 100m / min to 300m / min.

[0103] By pre-pressing the water vapor barrier layer, oxygen barrier layer, and the initial structure formed by the first paper base, the bonding effect between the water vapor barrier layer and the oxygen barrier layer can be further improved, preventing wrinkling and cracking caused by direct hot pressing. On the other hand, the water vapor barrier layer is effectively solidified after baking in an air-floating oven. Pre-pressing makes the interface smoother, filling internal gaps and unevenness, which is more conducive to the bonding of the water vapor barrier layer and the oxygen barrier layer. It can also prevent air from seeping in during hot pressing due to rough interface, causing the multi-layer composite paper to bulge and the heat seal to be incomplete due to gas expansion after hot pressing.

[0104] Step S40: Overlap one side of the barrier material of the first paper-based barrier layer and the second paper-based barrier layer and hot press them together to obtain the high-barrier packaging material.

[0105] Furthermore, the hot pressing is a double-roller hot pressing; the first roller of the double-roller hot pressing is a heating roller, and the second roller is a finishing roller; furthermore, the heating roller is a steel roller, and the finishing roller is a rubber roller.

[0106] Please see Figure 9 , Figure 9 This is a photograph of a multi-layered, high-barrier packaging material that exhibits bulging.

[0107] If the coating method is used directly, the interlayer bonding force is weak, and there is a problem of gas being trapped in the interlayer microstructure. When the finished material is tested or used, bulging problems will occur.

[0108] This embodiment is based on the aforementioned method of structurally separating a multi-layered composite paper into two layers, then coating each layer with a water vapor barrier layer, and specifically adding a bio-based plasticizer to the water vapor barrier coating to form two opposing, identical, and plasticizable interface layers. A single-stage hot-pressing process using two rollers ensures that the water vapor barrier layers exhibit good plasticity, adhesion, and compatibility, resulting in an effective structural bond. Simultaneously, by creating an oxygen barrier layer and adding nano-silica and starch-grafted acrylate to the oxygen barrier coating, not only can the packaging paper material possess excellent oxygen barrier properties and improved mechanical strength, but the oxygen barrier layer also exhibits good compatibility and bonding strength with the water vapor barrier layer. After pre-pressing, a double-roller hot-pressing process further ensures an effective and thorough interlayer bond.

[0109] Furthermore, the temperature of the steel roller is 120°C to 200°C, the pressing pressure between the steel roller and the rubber roller is 0.5MPa to 1.5MPa, and the hot pressing time is 0.2s to 1.5s.

[0110] Furthermore, the diameters of the steel roller and the rubber roller are similar or the same, with a diameter difference of less than or equal to 10 mm.

[0111] Having similar or identical diameters makes the stress on the material layer more uniform, which is conducive to the formation of a dense water vapor barrier layer, thereby improving the material's barrier performance against water vapor, oxygen, etc., and solving the problem of poor leveling and keyholes in coatings caused by existing coating methods.

[0112] Furthermore, after the double-roll hot pressing process, the high-barrier packaging material is subjected to photocuring treatment, preferably by infrared light irradiation treatment, with an infrared light intensity of 500W / m2 to 1500W / m2.

[0113] Because the high-barrier packaging material formed by hot pressing is relatively thin, infrared light irradiation treatment has a good penetrating effect on the material. It can supplement the degree of mutual plasticization and fusion of the internal molecular structure of the material during hot pressing, promote the further curing and bonding of the water vapor barrier layer of the first coating layer and the water vapor barrier layer of the second coating layer at the molecular level, and improve the bonding effect of the oxygen barrier layer and the water vapor barrier layer at the molecular level, further preventing delamination and bubbling problems caused by microscopic voids between layers.

[0114] Furthermore, since this embodiment uses a hot-pressing process, the layers of multi-layer high-barrier packaging materials may contain gases hidden in their internal microstructures that are not directly observable by the eye, or there may be microscopic impurities or foreign objects. Hot pressing can lead to poor interlayer bonding. Heating with infrared light can, to some extent, cause the hidden gases to expand, forming visually observable bubbles and delamination. This facilitates timely detection of material processing quality, timely adjustment of material composition or processing conditions, and promotes real-time quality inspection and capability improvement during product processing.

[0115] Furthermore, the above-mentioned coating methods include blade coating, doctor blade coating, air knife coating, curtain coating, slot coating, slope coating, and micro-recessed coating; the roller drive speed of the coating is 100m / min to 300m / min.

[0116] Furthermore, after each coating, drying is required, preferably using an air-floating oven at a temperature of 80°C to 160°C.

[0117] The high-barrier packaging material prepared by the above steps contains at least one of the following characteristics (A) to (F):

[0118] (A) After standing for 21 days at 38℃ and 90%RH, the water vapor transmission rate before and after bending was 0.70 g / (m). 2 • 24h) to 1.30g / (m 2 ·24h);

[0119] (B) The oxygen permeability before and after bending is 0.50 cm. 3 / (m 2 • 24h • 0.1MPa) to 0.70cm 3 / (m 2 ·24h·0.1MPa);

[0120] (C) The test time was 60 minutes, and the Cobb water absorption value before and after bending was 0 g / m. 2 ;

[0121] (D) The oil resistance Kit value is 12 before and after bending;

[0122] (E) Heat seal strength is 2.0 N / 15 mm to 7.0 N / 15 mm;

[0123] (F) Repulpingability is 85 to 90 points, calculated out of a maximum of 100 points.

[0124] Please see Figure 10 , Figure 10 This is a schematic diagram of the process for producing the second type of high-barrier packaging material according to this embodiment.

[0125] Furthermore, the preparation process of the above-mentioned material is as follows: the first paper base 100 is placed on the conveyor roller, and the first surface of the first paper base 100 is coated with oxygen barrier coating 510 and water vapor barrier coating 310 in sequence. After being dried in the air flotation oven 810, an oxygen barrier layer 500 and a first barrier layer 300 are formed. The material is then conveyed to the pre-pressing roller 730 through the tension roller, and then transferred to the hot pressing section.

[0126] Simultaneously, the second paper base 200 is placed on the conveyor rollers, and the first side of the second paper base 200 is coated with the second water vapor barrier coating 410. It is then conveyed to the air flotation oven 810 via the conveyor rollers. After drying, the second barrier layer 400 is formed and conveyed to the hot pressing section via the tension rollers. The two layers are then hot-pressed together using a double-roller hot pressing device consisting of a rubber roller 710 and a steel roller 720. Afterward, the layers are conveyed to the infrared irradiation box 740 via the tension rollers, and then conveyed and wound up via the cooling rollers to form the second high-barrier packaging material 10A.

[0127] It is worth noting that effective and good bonding can be achieved when the water vapor barrier coating is applied to the surface of the first paper base, or the oxygen barrier coating is applied to the first paper base, or the water vapor barrier coating is applied to the surface of the second paper base, through coating, drying, and hot pressing. This will not be elaborated further.

[0128] Please see Figure 11 , Figure 11 This is a schematic diagram of the structure of the third high-barrier packaging material according to an embodiment of the present invention.

[0129] It is worth noting that, in one embodiment, the high-barrier packaging material further includes a heat-sealing layer; the preparation process is as follows: a heat-sealing coating is prepared; forming the first coating layer includes: firstly applying the heat-sealing coating to the second side of the first paper base, and then sequentially applying the oxygen barrier coating and the water vapor barrier coating to the first side of the first paper base to form a three-layer structure first paper base double-sided barrier layer.

[0130] It is worth noting that, following the above manufacturing process, if subsequent processes such as hot pressing are used at this point, the resulting multi-layered high-barrier packaging material will have the following structure: heat-sealing layer 600, first paper base 100, first barrier layer 300, second barrier layer 400, and second paper base 200 (see [link to documentation]). Figure 11 ).

[0131] Please see Figure 12 and Figure 13 , Figure 12 This is a schematic diagram of the structure of the fourth high-barrier packaging material according to an embodiment of the present invention. Figure 13 This is a schematic diagram of the process for producing the fourth type of high-barrier packaging material according to this embodiment.

[0132] Furthermore, in one embodiment, forming the high-barrier packaging material includes preparing a heat-sealing coating, first applying the heat-sealing coating to the second side of the first paper base, and then applying the oxygen-barrier coating and the barrier coating sequentially to the first side of the first paper base to form a four-layer structure of the first paper base three-barrier layer.

[0133] It is worth noting that, following the above manufacturing process, if subsequent processes such as hot pressing are used at this point, the resulting fourth type of high-barrier packaging material has the following layered structure: heat-sealing layer 600, first paper base 100, oxygen barrier layer 500, first barrier layer 300, second barrier layer 400, and second paper base 200 (see [link to documentation]). Figure 12 ).

[0134] The preparation process of the fourth type of high-barrier packaging material 10B involves placing a first paper base 100 on a conveyor roller, coating the second side of the first paper base 100 with a heat-sealing coating 610, drying it in an air-float oven 810 to form a heat-sealing layer 600, then flipping it over by a coating-side turning roller, and sequentially coating the first side of the first paper base 100 with an oxygen barrier coating 510 and a first water vapor barrier coating 310. Subsequent processing steps are the same as those for the second type of high-barrier packaging material 10A described above (see [link to documentation]). Figure 13 ).

[0135] Furthermore, the heat-sealing coating comprises a fine-particle-size thermoplastic polymer, an antistatic agent, and an anti-sticking agent; the fine particle size is 90 nm to 200 nm.

[0136] Furthermore, the antistatic agent is one or more of polyethylene glycol ester, polyethylene glycol ether, polyol fatty acid ester, fatty acid alkanolamide, and fatty amine ethoxy ether, and the antistatic agent accounts for 0.2% to 5.0% of the total heat-sealing coating system by mass.

[0137] Multi-layer high-barrier packaging materials require heat-sealing properties to be manufactured into packaging bags. Therefore, the structure of this invention also includes a heat-sealing layer. The heat seal has certain heat insulation or heat buffering properties (or cold resistance), providing good heat insulation or heat buffering for the high-barrier packaging material. At the same time, during processing, the heat-sealing layer can give the first coating layer stronger tensile strength and a certain degree of heat loss prevention, keeping the heat within the multi-layer structure, promoting interlayer plasticization and thermal bonding, and ensuring flatness and uniformity during hot pressing. It is worth noting that during hot pressing, the heat-sealing layer needs to be placed on the side that is in contact with the rubber roller to prevent the heat-sealing layer from melting due to excessive temperature.

[0138] Introducing fine-particle-size thermoplastic polymers into the heat-sealing layer not only provides excellent heat-sealing performance, but also increases the specific surface area of ​​the polymer due to the smaller particle size. Under the same mass, the polymer molecular chains are relatively short and have stronger mobility, making it easier for them to approach each other and undergo self-crosslinking. After self-crosslinking, the stacking mode of the polymer molecules changes, the surface roughness decreases, the surface energy decreases, and the contact angle of liquids on its surface increases. Water and oil are difficult to spread, wet, and penetrate on its surface. This characteristic gives the heat-sealing coating excellent waterproof and oil-proof properties.

[0139] Because heat-sealing coatings have a relatively smooth surface, they are prone to generating static electricity and attracting dust when heat-sealing powdered products, affecting the sealing of the packaging. Therefore, antistatic agents are introduced into water vapor barrier coatings. The antistatic agent is one or more of polyethylene glycol ester, polyethylene glycol ether, polyol fatty acid ester, fatty acid alkanolamide, and fatty amine ethoxy ether. The mass percentage of the antistatic agent is 0.2% to 5.0%. Through the polar groups of the antistatic agent itself, local conductive channels can be formed inside the polymer, and electrons or ions can move along this structure, thereby playing an antistatic role.

[0140] Please see Figure 14 and Figure 15 , Figure 14 This is a photograph of the fourth high-barrier packaging material according to an embodiment of the present invention. Figure 15 SEM image of the surface of the fourth high-barrier packaging material according to the present invention.

[0141] Depend on Figure 14 It can be seen that the fourth type of high-barrier packaging material has a smooth, glossy surface without cracks, bulges, delamination, or unevenness, indicating good processing results; Figure 15 It can be seen that the fourth type of high-barrier packaging material is superior to... Figure 7 Its good density and near-seamless properties indicate that it has good water vapor barrier, oxygen barrier, and heat-sealing properties.

[0142] It is worth noting that the "layers" described in the structures of the first, second, third, and fourth high-barrier packaging materials are not obvious layered structures, but rather fuzzy layered structures with microscopic interweaving and permeation. That is, the various "layers" form a fuzzy structure that partially permeates each other's materials through physical hot pressing or chemical cross-linking, grafting, and other reactions.

[0143] To illustrate the effect of the feature materials and feature preparation process of this embodiment compared with the materials and preparation processes of the prior art, high-barrier packaging materials were prepared using the examples and comparative examples in Table 1 below, and performance tests were conducted for comparison.

[0144] Table 1

[0145]

[0146] The packaging materials prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were subjected to performance tests, and the test results are shown in Table 2.

[0147] Table 2

[0148]

[0149] As can be seen from the test results of Example 1 and Comparative Examples 1, 2 and 3 above, the high-barrier packaging material prepared using the material of this embodiment, with the addition of bio-based plasticizer, nano-silica and starch-grafted acrylate, and using the preparation process of this embodiment, which specifically employs coating, drying, pre-pressing, hot pressing and infrared irradiation, has good interlayer peel strength and no bulging, cracking or splitting phenomena when the material thickness is the same. In addition, the water vapor transmission rate, oxygen transmission rate, Cobb water absorption value, oil-resistant Kit value, heat seal strength and re-sizing properties are all good.

[0150] Among them, Example 1 showed good resizing properties compared to Comparative Example 1; Example 1 also showed good resizing properties compared to Comparative Example 2, and all other test results were good.

[0151] Compared with Comparative Example 2, and based on the two comparative situations mentioned above, the barrier coating of this embodiment, with the addition of a bio-based plasticizer, and the oxygen barrier coating of this embodiment, with the addition of nano-silica and starch-grafted acrylate, and the preparation process of this embodiment, showed a significant decrease in interlayer peel strength compared to the absence of bio-based plasticizer, nano-silica, and starch-grafted acrylate. A small number of bulges, cracks, and splitting phenomena also occurred. This indicates that the added key components and the preparation process (coating, drying, pre-pressing, hot pressing, and infrared irradiation) formed a good synergistic and correlated effect.

[0152] Please see Figure 16 , Figure 16 Experimental diagram showing the water vapor barrier performance test of the multilayer high-barrier packaging materials prepared in Example 1, Comparative Example 2 and Comparative Example 3 using the cup method.

[0153] The water vapor barrier properties tested are listed in Table 2 above.

[0154] Please see Figure 17 , Figure 17 This is a photograph of a packaging bag made using the multi-layer high-barrier packaging material obtained in Example 1.

[0155] In the process of making packaging bags, the first side of the second paper base can be printed with ink (patterns, characters, etc.), and the other layers do not have any incompatibility with ink printing. The material has good heat-sealing properties, mechanical strength, stiffness and other properties, forming good processability such as being printable and being able to be processed into packaging bags. The finished packaging bags also have good heat-sealing properties, as well as good water vapor barrier and oxygen barrier properties, and can be widely used in food packaging, pharmaceutical packaging, agricultural product packaging and even fluid packaging.

[0156] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0157] The above-described embodiments are merely examples of several implementation methods of the present invention (examples) to facilitate a detailed understanding of the technical solutions of the present invention, but they should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided by the present invention through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of the present invention patent should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing a glue-free, re-pulpable, multi-layered high-barrier packaging material, characterized in that: Includes the following steps: S10: Take the first paper base and the second paper base; S20: Prepare a water vapor barrier coating, wherein the water vapor barrier coating contains a plasticizer; The plasticizer is a bio-based plasticizer, which is one or more mixtures of citrate, epoxidized soybean oil, epoxidized castor oil, and epoxidized linseed oil; The components of the water vapor barrier coating include a thermoplastic hydrophobic polymer, a crosslinking agent, and a defoamer; S30: Prepare a heat-sealing coating and an oxygen barrier coating. First, apply the heat-sealing coating to the second side of the first paper base. Then, apply the oxygen barrier coating and the water vapor barrier coating to the first side of the first paper base in sequence and pre-press to form a four-layer structure of the first paper base with three barrier layers. The oxygen barrier coating comprises natural resin, modified polyvinyl alcohol, and contains nano-silica and starch-grafted acrylate. The nano-silica is silane coupling agent modified nano-silica; The modified polyvinyl alcohol is one or more of epoxy resin modified polyvinyl alcohol, succinic acid modified polyvinyl alcohol, and butenaldehyde modified polyvinyl alcohol. The water vapor barrier coating is applied to the second side of the second paper base to form a two-layer structure of the second paper base barrier layer. S40: The first paper-based three-barrier layer and one side of the water vapor barrier coating of the second paper-based barrier layer are stacked together and hot-pressed, and then infrared light curing treatment is performed to obtain the high barrier packaging material. The hot pressing is a double-roller hot pressing; the first roller of the double-roller hot pressing is a heating roller, and the second roller is a finishing roller; The high-barrier packaging material comprises the following features (A) to (E): (A) After standing for 21 days at 38℃ and 90%RH, the water vapor transmission rate before and after bending was 0.70 g / (m). 2 • 24h) to 1.30g / (m 2 ·24h); (B) The oxygen permeability before and after bending is 0.50 cm. 3 / (m 2 • 24h • 0.1MPa) to 0.70cm 3 / (m 2 ·24h·0.1MPa); (C) The test time was 60 minutes, and the Cobb water absorption value before and after bending was 0 g / m. 2 ; (D) The oil resistance Kit value is 12 before and after bending; (E) Repulpingability is 85 to 90 points, calculated out of a maximum of 100 points.

2. The preparation method according to claim 1, characterized in that: Both the first paper base and the second paper base are one of kraft paper, extensible paper, regenerated cellulose membrane, or nanocellulose membrane.

3. The preparation method according to claim 1, characterized in that, The heat-sealing strength of the high-barrier packaging material is from 2.0 N / 15 mm to 7.0 N / 15 mm.

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