High-moisture-retention aluminum-free packaging paper and preparation method thereof

Abstract

The invention relates to a preparation method of aluminum-free high-moisture-retention packaging paper, which is characterized in that liquid metal modified high-barrier two-dimensional flaky filler is introduced into a coating on the surface layer of lining paper, so that a dense barrier network structure which is free of agglomeration, horizontally oriented and lapped in filler gap is constructed, and the barrier property is improved so as to realize aroma and moisture retention functions; meanwhile, the flexibility and the bending stretchability of the paper are ensured. The technology does not need an organic solvent, the preparation steps are simple, equipment and energy consumption do not need to be increased, the bottleneck problems that traditional aluminum-free packaging paper is poor in moisture retention and poor in comprehensive performance are hopefully solved, a new packaging paper choice which is environmentally friendly and excellent in performance is provided, and the technology is suitable for improving various packaging paper.

Description

Technical Field

[0001] This invention belongs to the field of packaging paper technology, specifically relating to a high-moisture-retaining aluminum-free packaging liner paper and its preparation method. Background Technology

[0002] As the initial packaging layer of cigarettes, the inner liner paper is crucial for preserving aroma, moisture, and light, preventing mold growth and aroma loss. Traditional cigarette inner liner paper relies on an aluminum foil layer on its surface for aroma and moisture retention; the dense metallic atomic lattice structure of aluminum blocks water vapor and other small molecules. However, the use of large amounts of aluminum, its non-degradability, and the high energy consumption and pollution associated with electrolytic aluminum production and aluminizing processes significantly hinder the green and environmentally friendly development of inner liner paper and cigarette packaging. Developing aluminum foil-free inner liner paper materials is currently a key research focus, potentially accelerating carbon neutrality in the paper packaging and tobacco industries. However, aluminum foil-free inner liner paper materials exhibit poor moisture retention.

[0003] Applying one or more layers of polymer barrier coating to the back of the liner paper is considered a viable strategy. Patent 202010200554.1 discloses a technology that, by applying one or more layers of a dense polymer coating to the back of the liner paper, can enhance barrier properties and improve the paper's moisture retention without affecting the glossy decorative coating on the surface. While the back coating can improve moisture retention, this multi-coating process introduces a significant amount of additional equipment, processes, and energy consumption, which is not conducive to the green and environmentally friendly development of the liner paper. More importantly, a simple polymer coating can only reduce water vapor transmission rate to about 40% of that of the original white paper (approximately 400 g / m³). 2 24h), barrier properties of ordinary aluminum-layered inner lining paper (<200g / m²) 2 There is still a distance (24 hours).

[0004] Two-dimensional materials possess highly refined crystal lattices within a plane, theoretically offering atomic-level barrier capabilities against small oxygen and water vapor molecules. Introducing two-dimensional materials into materials can effectively enhance their barrier and moisture retention properties. However, the efficiency and cost of growing or transferring an additional layer of two-dimensional material onto the paper surface are unacceptable. Incorporating two-dimensional materials into the glossy coating on the front side of the liner paper to create a composite coating is a potential strategy. However, due to the strong interlayer forces of two-dimensional materials, adding large amounts of them to the coating can lead to aggregation and interface defects, resulting in decreased barrier and moisture retention properties of both the coating and the paper. Furthermore, the addition of large amounts of filler significantly increases the paper's elastic modulus, causing the packaging paper to lose its original bending and stretching properties, making it difficult to form and apply in practice. Existing reports almost exclusively show aluminum foil-free packaging papers that simultaneously possess low water vapor transmission rate, low elastic modulus, and stretchability. This invention proposes to use liquid metal to modify the surface of two-dimensional materials. The modified two-dimensional materials are doped into the glossy coating on the surface of the inner lining paper. On the one hand, the liquid metal solves the problem of water permeability caused by the aggregation and non-overlapping of the two-dimensional materials, thus improving the barrier performance. On the other hand, it solves the problem of the high modulus of the two-dimensional material coating being difficult to bend and stretch. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a packaging paper with high water vapor barrier properties, soft and stretchable, and aluminum-free layer, as well as a method for preparing the same, so as to ensure the paper's fragrance and moisture retention properties, bending and stretchability, and meet the requirements of green and sustainable development in the packaging industry.

[0006] The present invention achieves the above objectives through the following technical solutions:

[0007] The first technical problem to be solved by this invention is to provide a paper coating liquid doped with two-dimensional materials. The raw materials of the two-dimensional filler coating doping liquid include: 0.1 to 40.0 parts by weight of liquid metal modified two-dimensional material, 60.0 to 99.9 parts by weight of polyvinyl alcohol, 0.1 to 10.0 parts by weight of gloss-enhancing agent, and 0.1 to 5.0 parts by weight of color paste additive; wherein, polyvinyl alcohol is used as the matrix phase, liquid metal modified two-dimensional material is used as the main filler, and gloss-enhancing additive and color paste are used as additives. The special feature is that the liquid metal two-dimensional material constructs a dense barrier network with horizontal orientation inside the coating, that is, the two-dimensional materials are all horizontally oriented, and liquid metal exists in the gaps between the two-dimensional materials, which overlaps the two-dimensional materials, and there are no defects at the interface between the two-dimensional materials and no agglomeration of the two-dimensional materials.

[0008] Furthermore, the liquid metal-modified two-dimensional material is prepared by the following method: a two-dimensional layered material with a d50 size of 0.1 μm to 50.0 μm is mixed and compounded with a liquid metal-containing substance in a high-pressure reactor at 2–8 MPa and 40–180 °C under high shear conditions, wherein the shear mixing rate is 1000–4000 rpm. Here, d50 refers to the particle size corresponding to 50% of the particle size distribution. The adsorption and binding of the liquid metal to the two-dimensional material are achieved through the dipole-dipole coordination interaction between the liquid metal oxide layer (metal oxide bonds) and the polar groups (oxygen-containing and nitrogen-containing groups) of the two-dimensional material.

[0009] Furthermore, in the above-mentioned method for preparing liquid metal modified fillers, the weight ratio of the two-dimensional sheet material to the liquid metal-containing material is 60.000~99.999:0.001~40.000.

[0010] Furthermore, the d50 size of the two-dimensional sheet material is 0.01 μm to 30.00 μm.

[0011] Furthermore, the two-dimensional sheet material includes one or more of montmorillonite, hexagonal boron nitride, molybdenum disulfide, graphene, graphene oxide, and Mxene.

[0012] Preferably, the two-dimensional sheet material includes montmorillonite, hexagonal boron nitride, and graphene oxide, and has the characteristics of intrinsic lattice integrity and high aspect ratio.

[0013] Furthermore, the liquid metal-containing substance is selected from at least one liquid metal chosen from: mercury, bismuth, gallium, tin, indium, rubidium, or cesium; and mixtures or alloys of the above liquid metals and non-liquid metals. It can also be a mixture of the above metals. Preferably, selecting a mercury-free liquid metal improves environmental friendliness.

[0014] Furthermore, the solvent for the polyvinyl alcohol is water, which is safe and environmentally friendly; the dissolution temperature is 30–110°C.

[0015] Furthermore, the polyvinyl alcohol is one or more of PVA-0488, PVA-0588, PVA-1388, PVA-1588, PVA-1788, PVA-0599, PVA-1399, PVA-1599, PVA-1799 and PVA-2199.

[0016] Furthermore, the polyvinyl alcohol has been dissolved in an aqueous solvent before use and is in an aqueous solution state in subsequent use. The dissolution method is one or a combination of cold dissolution or hot dissolution. The concentration of polyvinyl alcohol in water is 5 wt% to 40 wt% by weight.

[0017] Furthermore, the gloss-enhancing additive is one or more of gold particles, silver particles, iron particles, cobalt particles, nickel particles, zinc particles, copper particles, aluminum particles, and various pearlescent powders, and has the characteristic of high gloss. The d50 size of the additive is 0.01μm to 500.00μm.

[0018] Furthermore, the color paste is an aqueous monochromatic color paste, and the color paste composition contains aqueous polyacrylic acid, aqueous polyurethane, water solvent, ethanol solvent, and one or more components of red dye, yellow dye, white dye, silver dye, or various color dyes.

[0019] Furthermore, the microstructure of the liquid metal modified two-dimensional sheet material exhibits the following characteristics: the introduction of liquid metal avoids the aggregation between two-dimensional materials, while the two-dimensional materials work together with the liquid metal to form a horizontally oriented, densely nested structure, and the liquid metal is embedded in the gaps and boundaries of the two-dimensional materials to perform bridging and wrapping, thereby eliminating the interfacial voids between the two-dimensional materials.

[0020] The second technical problem to be solved by the present invention is to provide a method for preparing a two-dimensional material doping coating liquid, wherein the preparation method is as follows: the two-dimensional material doping liquid is prepared by mixing liquid metal modified two-dimensional material, polyvinyl alcohol solution and gloss additive through solution blending.

[0021] Furthermore, in the above preparation method, the blending temperature is room temperature, the blending time is 10 to 180 min, and the blending speed is 100 rpm to 10000 rpm. Under appropriate ratio and blending speed, it can not only eliminate the aggregation of fillers, but also form a two-dimensional material orientation network of liquid metal overlap by means of the bridging effect of liquid metal, thereby improving the barrier performance.

[0022] Furthermore, in the above preparation method, during the blending of the coating liquid, one or more of the following measures are used to remove air bubbles from the coating liquid: defoamer, centrifugation equipment, and high-vacuum pump.

[0023] Furthermore, in the above preparation method, after solution mixing, high-power water bath ultrasound is used to achieve uniform dispersion of the two-dimensional material. The ultrasound time is 3-8 hours and the ultrasound power is 100-1600W.

[0024] Furthermore, in the above preparation method, solution blending is carried out in multiple steps. The first step is to mix the polyvinyl alcohol solution with the liquid metal modified two-dimensional material. The second step is to mix the polyvinyl alcohol solution with the gloss-enhancing agent and the color paste agent. The third step is to mix the solutions obtained in the first two steps. The three-step mixing can ensure the uniform dispersion and high performance of all solid components in the coating liquid of the inner lining paper to the greatest extent.

[0025] The third technical problem to be solved by the present invention is to provide a method for preparing high-moisture aluminum-free packaging paper, wherein the preparation method is as follows: using a roll-to-roll automatic coating machine to uniformly coat the two-dimensional material-doped coating liquid onto the paper, and finally passing it through a smoothing roller or a patterned roller to make the coating thickness uniform.

[0026] Furthermore, the composite liquid coating can be used for paper coating by surface coating, spraying, or dip coating.

[0027] Furthermore, the coating thickness of the coating machine is 1μm to 300μm.

[0028] A further option is to dry the paper after coating by passing it through a far-infrared channel, a drying oven, or a high-temperature drying tunnel, with the drying temperature ranging from room temperature to 200°C.

[0029] The beneficial effects of this invention are:

[0030] This invention introduces liquid metal-modified, high-barrier two-dimensional sheet fillers into the coating of the inner liner paper, constructing a dense barrier network structure with no agglomeration, horizontal orientation, and inter-filler overlap. This fully leverages the excellent barrier properties of the two-dimensional material lattice and the advantages of liquid metal in removing agglomerates and constructing dynamic overlapping interfaces, significantly improving the water vapor barrier performance of the inner liner paper surface and achieving its aroma and moisture retention functions. Simultaneously, the introduction of soft and stretchable liquid metal alleviates the high stress at the rigid two-dimensional material interface, reduces the elastic modulus of the inner liner paper surface, improves stretchability, and eliminates the negative impact of large-scale doping of two-dimensional materials on the bending and stretching properties of the inner liner paper during molding. The raw materials selected in this invention are inexpensive and readily available, contain no organic solvents, and do not pollute the environment. The preparation process is simple and suitable for large-scale industrial production. The packaging paper of this invention possesses comprehensive properties of high moisture retention, low modulus, and stretchability, and is expected to solve the bottleneck problems of poor moisture retention and overall performance of traditional aluminum-free packaging paper, making it suitable for improving various types of packaging paper. Attached Figure Description

[0031] Figure 1 The cross-sectional microstructure of (a) Example 1 (inner liner paper with liquid metal modified two-dimensional material doped coating) and (b) Comparative Example 1 (ordinary unfilled coated inner liner paper) were observed using scanning electron microscopy (SEM).

[0032] Figure 2 The following are scanning electron microscope (SEM) images of the surface microstructure of Example 3 at (a) low magnification and (c) high magnification, and of Comparative Example 1 at (c) low magnification and (d) high magnification.

[0033] Figure 3 The water vapor transmission rate of the inner lining paper coated with two-dimensional materials with different coating thicknesses in this invention is given. Detailed Implementation

[0034] This invention is the first to utilize liquid metal-modified two-dimensional sheet materials as high-barrier fillers. The two-dimensional sheet materials and liquid metal form a dense nested network structure with no agglomeration, horizontal orientation, and overlapping filler gaps, achieving optimal barrier performance and best aroma and moisture retention. In addition, the ultra-low modulus deformable liquid metal can reduce the elastic modulus of the inner liner paper coating, solving the defects of high modulus, easy rebound, and poor folding resistance that have always existed in other technical routes, such as traditional filler composite aluminum-free inner liner paper and back-coated aluminum-free inner liner paper, enabling better molding and practical application. In the preparation process, this process does not require organic solvents or additional chemical synthesis steps. The steps are simple, and the blended doping coating liquid can directly follow the one-step coating process of the original packaging paper without increasing equipment and energy consumption, reducing costs. It is a new generation of green and low-carbon cigarette packaging material that is significantly different from traditional aluminum-free inner liner paper solutions.

[0035] The present invention will be further described in detail below through specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention.

[0036] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0037] Example 1

[0038] Step 1: Preparation of liquid metal-modified two-dimensional materials

[0039] 0.06 g of liquid gallium metal and 5.94 g of two-dimensional montmorillonite were sheared and mixed in a high-pressure reactor (pressure 6.0 MPa) at 90 °C with a shear rate of 2000 rpm. The high temperature, high pressure and high shear force were used to induce adsorption between the liquid metal and montmorillonite, thereby reducing the aggregation of montmorillonite.

[0040] Step 2: Preparation of two-dimensional material doping coating solution

[0041] First, 6.00g of the liquid metal-modified two-dimensional filler obtained in the previous step was added to 54.00g of polyvinyl alcohol aqueous solution (30wt% polyvinyl alcohol solution), and stirred at 2000rpm for 150min at room temperature using a reactor and a stainless steel stirrer to obtain a dispersion of the two-dimensional filler. Next, 3.00g of zinc particle gloss enhancer and 1.00g of yellow aqueous pigment enhancer were added to 6.00g of polyvinyl alcohol aqueous solution (30wt% polyvinyl alcohol solution), and stirred at 2000rpm for 150min at room temperature to obtain a dispersion of the enhancer. Finally, 60.00g of the two-dimensional filler dispersion and 10.00g of the enhancer dispersion were stirred slowly at 100rpm for 120min under a vacuum of 100Pa in a reactor with a vacuum pump to ensure uniform mixing of the components and remove air bubbles from the dispersion, resulting in the final two-dimensional material doped coating solution.

[0042] Step 3: Preparation of high-moisture-retaining aluminum-free packaging paper

[0043] The two-dimensional material-doped coating solution is evenly coated onto the front surface of the paper using an automatic coating machine. A doctor blade is used for coating, and the coating amount is 10 g / m². 2 The coating thickness was 40 μm, and the coating thickness was then uniformly applied using a smoothing roller. Drying was then carried out at different temperatures ranging from room temperature to 200°C to obtain a novel aluminum-free inner liner paper. The water vapor transmission rate, elastic modulus, and elongation at break of the obtained inner liner paper are shown in Table 1. The water vapor transmission rate was measured using a Labthink C360M differential pressure permeability analyzer, with a sample area of ​​approximately 15 cm². 2 The elastic modulus and elongation at break were tested using an INSTRON 68TM-10 universal tensile impact tester to assess the mechanical properties of the samples at room temperature.

[0044] Example 2

[0045] A novel aluminum-free inner liner paper differs from Example 1 in that the amount of liquid metal added is increased from 0.06g to 0.60g, and the amount of montmorillonite added is decreased from 5.94g to 5.40g, while the other conditions and process parameters remain unchanged.

[0046] Example 3

[0047] A novel aluminum-free inner liner paper differs from Example 1 in that the amount of liquid metal added is increased from 0.06g to 1.20g, and the amount of montmorillonite added is decreased from 5.94g to 4.80g, while the other conditions and process parameters remain unchanged.

[0048] Example 4

[0049] A novel aluminum-free inner liner paper differs from Example 1 in that the two-dimensional barrier material is changed from montmorillonite to boron nitride, while the other conditions and process parameters remain unchanged.

[0050] Example 5

[0051] A novel aluminum-free inner liner paper differs from Example 1 in that the coating thickness of the coating machine is increased from 40μm to 80μm, while the other conditions and process parameters remain unchanged.

[0052] Comparative Example 1

[0053] The difference from Example 1 is that no two-dimensional material is added, and no dispersion of liquid metal modified two-dimensional material is prepared. Instead, the dispersion of the additive formed by mixing gloss-enhancing agent, color paste and polyvinyl alcohol solution is directly coated on the paper. All other conditions and parameters remain unchanged, representing ordinary coated inner lining paper without special formula improvement.

[0054] Comparative Example 2

[0055] The difference from Example 1 is that the two-dimensional filler is not modified with liquid metal, that is, the two-dimensional material montmorillonite dispersion does not contain liquid metal. The other conditions and parameters remain unchanged, representing ordinary unmodified two-dimensional material coating liquid coating of inner lining paper.

[0056] Comparative Example 3

[0057] The difference from Comparative Example 1 is that an additional coating step is added at the end, in which a water-based polyurethane coating is applied to the back of the coated inner liner paper. After drying, a coated inner liner paper with a back coating is obtained. The surface coating of this inner liner paper does not contain two-dimensional materials or liquid metals. Its feature is that there is a barrier-enhancing coating on the back, representing a coated inner liner paper of the ordinary back coating technology route.

[0058] The results of water vapor transmission rate, elastic modulus and elongation at break of the aluminum-free inner lining paper obtained in Examples 1-5 and Comparative Examples 1-3 are shown in Table 1.

[0059] Table 1 shows the results of water vapor transmission rate, elastic modulus, and elongation at break of the lining paper obtained in Examples 1-5 and Comparative Examples 1-3.

[0060]

[0061] The performance comparison between Examples 1-3 and Comparative Example 1 shows that, compared with the inner liner paper without added two-dimensional filler (Comparative Example 1), the water vapor transmission rate of the aluminum-free inner liner paper with two-dimensional filler doping (Examples 1-3) is significantly improved, from 1400 g m -2 d -1 Optimal reduction to 240g m -2 d -1This improves the barrier properties. Simultaneously, the introduction of liquid metal significantly enhances the elastic modulus and elongation at break of the inner liner paper, decreasing the modulus from 4749 MPa to an optimal 2934 MPa, and increasing the elongation at break from 2.28% to an optimal 7.45%. The increased liquid metal content leads to a marked improvement in the inner liner paper's performance, demonstrating the synergistic effect of the two-dimensional material and the liquid metal in constructing a densely nested, internally doped structure that improves the material's barrier properties.

[0062] Microstructure diagrams of the cross-section of the inner lining paper coating in Example 1 and Comparative Example 1 are shown below. Figure 1 As shown, in the cross-section of a typical coated inner liner paper (Comparative Example 1), the coating contains no two-dimensional filler, only irregularly shaped solid particulate additives. These particles are not horizontally oriented and are not tightly connected. Furthermore, there are numerous air pores at the interface between the particulate filler and the coating matrix. These defective structures allow water vapor molecules to easily penetrate rapidly through the defects, resulting in a decrease in the barrier and moisture retention performance. Figure 1 As shown on the right, in the cross-section of the coating of the modified two-dimensional material doped with aluminum-free inner lining paper, the two-dimensional material is horizontally oriented, and there are no gaps or agglomerations between the two-dimensional materials, forming a perfect barrier and shielding network, which prolongs the diffusion path of water vapor molecules and results in better water retention and barrier performance.

[0063] The performance comparison between Example 1 and Comparative Example 2 shows that the liquid metal-modified two-dimensional material doped coating can more effectively reduce water vapor transmission rate from 684 g / m² compared to ordinary two-dimensional material doped coatings. -2 d -1 Decreased to 548g m -2 d -1 The modulus decreased from 4939 MPa to 3504 MPa, and the elongation at break increased from 1.98% to 4.63%. As can be seen from the comparison between Examples 1-3, a higher content of liquid metal can better reduce water vapor transmission rate, decrease the elastic modulus of the material, and increase the elongation at break. The principle is that directly adding two-dimensional materials will cause agglomeration due to the interlayer interaction of the two-dimensional materials, resulting in insufficient overlap between the two-dimensional materials, thereby reducing the material's barrier properties, increasing the paper's elastic modulus, and decreasing the elongation. Liquid metal can alleviate agglomeration and strengthen the overlap and orientation between two-dimensional materials, while also relieving interfacial stress and strain, and improving the paper's softness and tensile strength. A comparison of the water vapor transmission rates of Examples 1 and 5, and the effect of different coating thicknesses on the water vapor transmission rate of the liner paper, are shown below. Figure 3 As shown, it can be observed that as the coating thickness of the coating machine increases, the water vapor permeability of the inner lining paper gradually decreases, indicating that the thicker the coating, the better the barrier performance.

[0064] Furthermore, the microstructure of the inner liner paper surface in Example 3 and Comparative Example 1 also shows that the surface structure of the coated inner liner paper doped with liquid metal-modified two-dimensional materials is more complete, such as... Figure 2As shown in the figure, the surface of Comparative Example 1 has more pores and through holes, which reflects poor data in terms of barrier performance; In Example 3, the coating surface is smooth and without defects. Even if a small amount of filler is added, the filler will accumulate, but the surface is dense and without gaps, which proves the improvement of the barrier performance of the new inner lining paper at the microscopic level.

[0065] A performance comparison of Example 1 with Comparative Examples 1 and 3 shows that while the aluminum-free inner liner paper in Comparative Example 3, produced using a conventional back-coating process, achieves acceptable barrier properties, the multi-layer coating process increases the paper's elastic modulus from 3504 MPa to 4929 MPa, significantly increasing rigidity and reducing folding resistance, which is detrimental to subsequent paper packaging processing. In contrast, Example 1, with its uncoated liquid metal-modified two-dimensional material doped coating, balances both folding resistance and barrier properties.

Claims

1. A two-dimensional material-doped base paper coating liquid characterized by comprising: The raw materials of the two-dimensional filler coating doping liquid include: 0.1-40.0 parts by weight of liquid metal modified two-dimensional material, 60.0-99.9 parts by weight of polyvinyl alcohol, 0.1-10.0 parts by weight of luster aid, and 0.1-5.0 parts by weight of color paste aid.

2. The two-dimensional material-doped base paper coating liquid according to claim 1, characterized by, The modification method of the liquid metal modified two-dimensional material is: mixing and compounding the two-dimensional layered material and the substance containing liquid metal under high shear at high temperature and high pressure in a high-pressure reaction kettle to obtain the corresponding modified material; wherein the weight ratio of the two-dimensional sheet material to the substance containing liquid metal in the liquid metal modified two-dimensional material is: 60.000-99.999 parts by weight of two-dimensional sheet material and 0.001-40.000 parts by weight of liquid metal.

3. The two-dimensional material doped base paper coating liquid according to claim 1 or 2, characterized in that: The two-dimensional sheet material includes one or more of montmorillonite, hexagonal boron nitride, molybdenum disulfide, graphene, graphene oxide, and Mxene; The substance containing liquid metal is selected from at least one of the following: liquid metal of mercury, bismuth, gallium, tin, indium, rubidium, and cesium; and a mixture or alloy of the above liquid metal and non-liquid metal; and a mixture of the above metal and the above metal; The polyvinyl alcohol is one or more of PVA-0488, PVA-0588, PVA-1388, PVA-1588, PVA-1788, PVA-0599, PVA-1399, PVA-1599, PVA-1799, and PVA-2199; The luster additive is one or more of gold particles, silver particles, iron particles, cobalt particles, nickel particles, zinc particles, copper particles, aluminum particles, and various pearl powders; The color paste is a water-based single-color color paste, and the color paste composition contains one or more components of water-based polyacrylic acid, water-based polyurethane, water solvent, ethanol solvent, and one or more of red dye, yellow dye, white dye, silver dye, or various color dyes; Preferably, the substance containing liquid metal is selected to be mercury-free liquid metal to improve environmental protection; and the two-dimensional sheet material includes one or more of montmorillonite, hexagonal boron nitride, and graphene oxide.

4. A method for preparing a two-dimensional material doping coating liquid, characterized by comprising: The method is: mixing the liquid metal modified two-dimensional material, the polyvinyl alcohol solution, and the luster additive by solution blending to obtain the two-dimensional material doping liquid.

5. The method for preparing a two-dimensional material doped coating liquid according to claim 4, characterized in that, During the solution blending, one or more of a defoaming agent, a centrifugal device, and a high-vacuum vacuum pump is used to remove air bubbles in the coating liquid; further, high-power water bath ultrasonic is used to realize uniform dispersion of the two-dimensional material after solution blending.

6. The method for preparing a two-dimensional material doped coating liquid according to claim 4, characterized in that, The solution blending is divided into three steps: the first step is to mix the polyvinyl alcohol solution and the liquid metal modified two-dimensional material, the second step is to mix the polyvinyl alcohol solution with the luster aid and the color paste aid, and the third step is to mix the solutions obtained in the first two steps, which can maximize the uniform dispersion of all solid components in the base paper coating liquid and ensure high performance.

7. A method of making a high-moisture-preservation aluminum-free wrapping paper, characterized by, The preparation method is: using a roll-to-roll automatic coating machine to uniformly coat a two-dimensional material doping coating solution on paper, and finally passing through a smoothing roller or a pattern roller to make the coating thickness uniform, wherein the coating machine coating thickness is 1-300 mu m.

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